JP2008183888A - Letterpress for offset can printing - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a letterpress for offset can printing which can raise the quality of printing by reducing the fat of dots. <P>SOLUTION: A letterpress 1A is equipped with many projections 2 as a streak section. Moreover, about a projection 2 corresponding to a dot the dot area ratio of which is below a predetermined value, the height h of a projection 2 falls off following the reduction of a dot area ratio. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a relief printing plate for offset printing for printing on the outer surface of a can such as a metal can, for example, and a can offset printing apparatus provided with the relief printing plate.

  For example, the following method is known as a method for manufacturing a relief plate for printing on a printing medium by offset printing.

  That is, a plate material having a photosensitive resin layer that can be cured by irradiation with, for example, ultraviolet rays as an actinic ray is prepared. Then, the original film is placed in close contact with the photosensitive resin layer, and the photosensitive resin is cured by irradiation with ultraviolet rays in accordance with the printing pattern of the original film. Next, the uncured photosensitive resin is removed by brush cleaning. Thereafter, the plate material is dried. Thereby, a desired relief printing plate is manufactured.

  Moreover, as a method of performing printing by offset printing using a relief plate on the outer surface of a can as a substrate to be printed, for example, a method described in JP-A-2006-181727 is known (see Patent Document 1). In this method, a laser exposure resin relief plate having a screen line number of 120 to 200 Lpi and a Shore A hardness of 60 ° to 90 ° is used as the relief plate. The manufacturing method of this laser exposure resin letterpress is as follows.

  That is, a carbon coating layer is formed on a photosensitive resin layer that can be cured by ultraviolet irradiation. And this carbon coating film layer is removed by laser irradiation according to a printing pattern. Subsequently, the photosensitive resin of the site | part from which the carbon coating film layer was removed is hardened by ultraviolet irradiation. Thereafter, the remaining carbon coating film and the uncured photosensitive resin are washed away with water. Thereby, the desired laser exposure resin relief printing plate is manufactured.

In addition, although it is not the printing method by offset printing using a relief printing plate, the printing method by offset printing using a waterless lithographic plate is also known as another method of printing on the outer surface of a can (refer patent document 2).
JP 2006-181727 A (see paragraphs [0007] and [0018], FIG. 4) JP 2002-36710 A

  Thus, the above conventional method has the following problems.

  In other words, the relief printing plate used in the above conventional method is suitable for halftone dots of various sizes, such as convex portions corresponding to halftone dots having a small halftone dot area ratio and convex portions corresponding to halftone dots having a large halftone dot area ratio. A number of corresponding convex portions are provided as the image line portions, and the heights of these convex portions are set to be equal to each other. Therefore, when the ink adhering to these convex portions is transferred to the blanket, the amount of convex portions corresponding to halftone dots having a small halftone dot area ratio bites into the blanket and corresponding to halftone dots having a large halftone dot area ratio. The amount by which the convex part bites into the blanket is substantially the same. Therefore, regardless of the size of the convex portion, the ink is transferred to the blanket in a state where it spreads outside the convex portion. Then, the ink transferred to the bracket in this spread state is transferred from the bracket to the outer surface of the can. As a result, the halftone dots are thickened regardless of the size of the halftone dots on the outer surface of the printed can. As a result, the halftone image is crushed and the print quality is degraded.

  The present invention has been made in view of the above-described technical background, and an object of the present invention is to provide a relief printing plate for offset printing capable of improving printing quality by reducing the thickness of halftone dots, and the relief printing plate. An object of the present invention is to provide a can offset printing apparatus, a can printed using the relief printing plate, and a can outer surface printing method using the relief printing plate.

  The present invention provides the following means.

[1] In the relief printing for offset printing of a can for printing on the outer surface of the can by offset printing,
A relief printing plate for offset printing of a can, characterized in that the height of the convex portion decreases as the halftone dot area rate decreases for the convex portion corresponding to the halftone dot whose halftone dot area ratio is a predetermined value or less. .

[2] For printing with a screen line number of 80 to 200 Lpi,
2. The relief printing plate for offset printing of cans according to item 1, wherein the predetermined value is 10%.

  [3] The height of the convex portion according to the above item 2, wherein the height of the convex portion is lowered at a ratio of 0.005 to 0.02 mm in the amount of reduction in the height of the convex portion per 1% of the reduction amount of the halftone dot area ratio. Letterpress for offset printing of cans.

  [4] The relief printing plate for offset printing of the can according to the item 3, wherein the maximum reduction in the height of the convex portion is set to 0.1 mm or less.

  [5] Any of the preceding items 1 to 4, wherein the convex portion includes a base portion and a cylindrical tip portion formed at a central portion of the upper surface of the base portion and having a diameter smaller than the diameter of the upper surface. A letterpress for offset printing of the crab.

  [6] The offset of the can according to item 5 above, wherein the height of the upper surface of the base portion of the convex portion is constant and the length of the tip portion of the convex portion is shortened as the halftone dot area ratio decreases. Letterpress for printing.

  [7] The relief printing plate for offset printing of the can according to any one of items 1 to 6 above, wherein a convex portion is formed by a direct laser engraving method.

[8] It has a photosensitive resin cured layer cured by irradiating the photosensitive resin with actinic rays,
The relief printing plate for offset printing of cans according to 7 above, wherein a convex portion is formed on the surface of the cured resin layer.

[9] In a can offset printing apparatus for printing on the outer surface of a can by offset printing using a relief plate,
A can offset printing apparatus comprising the relief plate according to any one of items 1 to 8 as the relief plate.

[10] In the can printed on the outer surface by offset printing using a relief printing plate,
A can having a screen line number of 80 to 200 Lpi and having a halftone dot area ratio of 4% or less and a dot thickness of 5% or less.

  [11] The can according to the item 10, wherein printing is performed in a printing state in which no halftone dots having a halftone dot area ratio of 4% or less are printed.

  [12] The can according to the above item 10 or 11, wherein the relief plate is printed by offset printing using the relief plate according to any one of items 1 to 8.

[13] In a method for manufacturing a can whose outer surface is printed,
A method for producing a can, wherein printing is performed by offset printing using the relief printing plate according to any one of items 1 to 8.

  [14] A method for printing an outer surface of a can, comprising printing on the outer surface of the can by offset printing using the relief printing plate according to any one of items 1 to 8.

  The present invention has the following effects.

  In the invention of [1], with respect to the convex portions of the relief printing plate corresponding to the halftone dots having a halftone dot area ratio of a predetermined value or less, the height of the convex portions decreases as the halftone dot area ratio decreases. Therefore, when the ink adhering to the convex portion of the relief printing plate is transferred to the blanket, the amount of the convex portion corresponding to the halftone dot having a small dot area ratio bites into the blanket is reduced. Thereby, the spread of the ink adhering to this convex part is suppressed. Then, the ink is transferred from the blanket to the outer surface of the can in a state where the spread of the ink is suppressed in this way. Therefore, the fatness of a small halftone dot can be reduced. Thereby, the quality of printing can be improved.

  In the invention of [2], when printing on the outer surface of the can with a screen line number of 80 to 200 Lpi, it is possible to reduce the thickness of halftone dots with a dot area ratio of 10% or less.

  In the invention of [3], it is possible to reliably reduce the thickness of halftone dots having a halftone dot area ratio of 10% or less.

  In the invention of [4], it is possible to more reliably reduce the thickness of halftone dots having a halftone dot area ratio of 10% or less.

  In the invention of [5], the convex part of the relief plate has a base part and a cylindrical tip part formed at the center part of the upper surface of the base part and having a smaller diameter than the diameter of the upper surface. . As a result, when the convex part to which the ink is attached is pressed by the blanket and the ink spreads outside the convex part, the protruding part of the ink is between the upper surface of the base part of the convex part and the peripheral surface of the tip part. Captured in the corners. Thereby, the fatness of a halftone dot can be reduced further reliably.

  In the invention [6], the strength of the tip of the convex portion can be ensured.

  In the invention of [7], the convex portion of the relief plate can be easily formed, and the relief plate can be produced in a short time by shortening the production process of the relief plate.

  In the invention of [8], the shavings generated during laser engraving can be removed by washing with water. Therefore, a relief printing can be manufactured easily.

  According to the invention [9], an offset printing apparatus for cans that exhibits the same effect as the effect of any of the inventions [1] to [8] can be provided.

  In the invention of [10], a can having a high-quality print on its outer surface can be provided.

  In the invention of [11], a can having a higher quality printed on the outer surface can be provided.

  In the invention of [12], a can having high-quality printing on the outer surface can be provided reliably.

  In the invention of [13], high-quality printing can be performed on the outer surface of the can.

  In the invention [14], high-quality printing can be performed on the outer surface of the can.

  Next, several embodiments of the present invention will be described below with reference to the drawings.

  In FIG. 1, (20) is the offset printing apparatus of the can which concerns on one Embodiment of this invention. This printing device (20) performs printing by offset printing (more specifically, dry offset printing) on the outer surface of the cylindrical can body (31) of the can (30) shown in FIG.

  This can (30) is a seamless can, and the material thereof is a metal. More specifically, the can (30) is, for example, aluminum (including an alloy thereof; the same applies hereinafter). Moreover, this can (30) is a DI can (Draw and Ironing can), and the can body part (31) and the can bottom part (32) are integrally formed. In addition, the can lid part of this can (30) is not illustrated. Beverages (eg, beer) and foods are accommodated in the can (30).

  As shown in FIG. 1, the printing apparatus (20) sends the blanket cylinder (23), the plurality of plate cylinders (22), the plurality of inking means (21), and the can (30) to the blanket cylinder (23) side. A can feed means (24), a can feed means (25) for feeding the can (30) to the can feed means (24), and the like are provided.

  A relief plate (1A) according to an embodiment of the present invention is attached to a plate cylinder (22) of a printing apparatus (20), and cans (offset printing) using the printing apparatus (20) can ( 30) used for halftone dot printing on the outer surface of the can body (31).

  As shown in FIG. 2, this relief printing plate (1A) is made of a cured photosensitive resin that is cured by irradiating ultraviolet rays (U) onto a photosensitive resin that can be cured by irradiation with ultraviolet rays (U) as active rays. It has a layer (7) (see FIGS. 3 and 4). In this specification, this layer (7) is referred to as a “photosensitive resin cured layer”. The cured resin layer (7) is formed on a base material (9) made of steel or the like via an adhesive layer (8).

  Furthermore, on the surface of the cured resin layer (7) (that is, the plate surface of the relief plate (1A)), a large number of projections (2) are formed as image line portions (image portions). These convex portions (2) correspond to the halftone dots of dot printing applied to the outer surface of the can (30), and the printing ink adheres to the top surfaces of these convex portions (2). It is.

  In this relief printing (1A), the height h of the convex portion (2) is increased as the halftone dot area ratio decreases for the convex portion (2) corresponding to the halftone dot having a halftone dot area ratio of a predetermined value or less. Gradually decreasing. In this embodiment, the number of screen lines is 80 to 200 Lpi (i.e., 31.5 to 78.7 lines / cm), and the projection corresponding to halftone dots having a dot area ratio of 10% or less (i.e., in the range of 0 to 10%). As for the portion (2), the height h of the convex portion (2) gradually decreases in a stepwise manner as the halftone dot area ratio decreases. On the other hand, the height h of the convex portion (2) corresponding to the halftone dots exceeding the halftone dot area ratio of 10% is not lowered, that is, is constant.

  Furthermore, the height h of the convex portion (2) is decreased at a ratio in which the amount of decrease in the height h of the convex portion (2) per 1% reduction in the halftone dot area ratio is in the range of 0.005 to 0.02 mm. is doing. In FIG. 2, −Δh indicates a decrease amount of the height h of the convex portion (2).

  Furthermore, the maximum reduction amount of the height h of the convex portion (2) with respect to the reference height of the convex portion (2) is set to 0.1 mm or less. Note that the reference height of the convex portion (2) is the height of the convex portion (2) among the large number of convex portions (2) that is not lowered. The height of the convex portion (2) corresponding to a halftone dot exceeding 10% is set to the reference height of the convex portion (2). Specifically, for example, a halftone dot having a halftone dot area ratio of 20% The height of the convex portion (2) corresponding to is set to the reference height of the convex portion (2). In FIG. 2, (2z) is the bottom of the convex portion (2). The height h of the convex part (2) with respect to the bottom part (2z) is set, for example, in a range of 0.3 to 0.5 mm, specifically, for example, 0.4 mm.

  Furthermore, each convex part (2) is coaxial with the axis | shaft of the base part (3) in the center part of the base part (3) of longitudinal cross-section trapezoid shape, and the upper surface (3a) of this base part (3). A cylindrical tip portion (4) formed integrally and having a diameter smaller than the diameter a of the upper surface (3a). Thereby, the front-end | tip part (4) of a convex part (2) is formed in top hat shape. In this embodiment, the base part (3) is specifically formed in a truncated cone shape. The top surface of the tip (4) of the convex portion (2) corresponds to the top surface of the convex portion (2).

  The ratio a / b between the diameter a of the upper surface (3a) of the base part (3) of the convex part (2) and the diameter b of the tip part (4) is set in the range of 1.2 to 3, for example. Is desirable.

  Further, as the halftone dot area ratio decreases, the height h1 of the upper surface (3a) of the base portion (3) of the convex portion (2) is constant, but the tip portion (4) of the convex portion (2). The length t is gradually shortened step by step. By doing so, the strength of the tip (4) of the convex portion (2) can be ensured, and the height h of the convex portion (2) can be set by the direct laser engraving method described later. It can be done easily. In addition, height h1 of the upper surface (3a) of the base part (3) with respect to the bottom part (2z) of a convex part (2) is set to the range of 0.2-0.4 mm, for example.

  Further, the relief angle θ of the base portion (3) of the convex portion (2) is set in a range of 30 to 90 °, for example.

  However, in the present invention, h, a / b, t, h1, and θ are not limited to being within the above ranges, respectively.

  Next, the manufacturing method of this letterpress (1A) is demonstrated below.

  The convex portion (2) of the relief plate (1A) is formed by a known direct laser engraving method.

  That is, as shown in FIG. 3, a photosensitive resin that can be cured by irradiation with ultraviolet rays (U) as active rays on the base material (9) through the adhesive layer (8) as the plate material of the relief plate (1 A). A plate material on which the layer (6) is formed is prepared. Then, the surface of the photosensitive resin layer (6) is irradiated with ultraviolet rays (U) from the light source (S), whereby the photosensitive resin layer (6) is cured to a depth of about 0.4 mm, for example, to cure the photosensitive resin. Layer (7) is formed. As the photosensitive resin, for example, a polyvinyl alcohol-based, vinyl ester-based or polyamide-based resin is used, and those having a Shore D hardness of, for example, 20 to 80 are preferably used.

Next, as shown in FIG. 4, by irradiating the surface of the resin cured layer (7) with laser light (L), a large number of convex portions (2) are directly engraved on the surface of the resin cured layer (7). To do. The laser engraving depth at this time is, for example, 0.3 to 0.5 mm. The laser beam (L) to be used is, for example, a CO ₂ gas laser beam (wavelength 10640 nm), and its output is, for example, 500 W.

  Next, the shavings adhering to the surface of the cured resin layer (7) are removed by washing with water, and then the surface of the cured resin layer (7) is dried.

  Next, the uncured portion remaining in the resin cured layer (7) is cured by irradiating the surface of the resin cured layer (7) with ultraviolet rays again.

  The desired relief (1A) shown in FIG. 2 is manufactured by the above process.

  Next, the structure of the printing apparatus (20) of this embodiment is demonstrated below with reference to FIG.1 and FIG.5.

  This printing apparatus (20) has a known configuration except for the letterpress (1A). That is, the relief plate (1A) of this embodiment is attached to each plate cylinder (22) of the printing apparatus (20). Each relief plate (1A) is supplied with printing ink (K) by, for example, a multi-stage roll type inking means (21), and the ink (K) adheres to a large number of projections (2) of each relief plate (1A). Is done. In the present embodiment, the printing apparatus (20) includes three sets of inking means (21) and a plate cylinder (22). These inking means (21) are, for example, three colors (indigo, grass, Yellow) printing ink (K) can be supplied. A plurality of blankets (10) are attached to the blanket cylinder (23). This blanket (10) is the same as the conventional one, and is made of rubber, for example.

  In the printing method using this printing apparatus (20), as shown in FIGS. 1 and 5, the blanket (23) is moved to the convex part (2) of the relief plate (1A) as the blanket cylinder (23) rotates. The adhered ink (K) is transferred. At this time, the convex portion (2) is pressed against the blanket (10) so that the convex portion (2) whose height h is not lowered bites into the blanket (10), for example, to a depth of 0.15 mm. On the other hand, the can (30) delivered to the can feeding means (24) by the can feeding means (25) is rotatably held by the mandrel (24a) of the can feeding means (24). 24), the can (30) is rotated while the outer surface of the can body (31) of the can (30) is in contact with the blanket (10). At this time, the ink (K) adhering to the blanket (10) is transferred from the blanket (10) to the outer surface of the can body (31) of the can (30). As a result, printing is performed on the outer surface of the can body portion (31), and thus the can (30) printed on the outer surface is manufactured.

  Thus, the offset printing relief plate (1A) of the present embodiment has the following advantages.

  That is, for the convex portion (2) of the relief printing plate (1A) corresponding to a halftone dot having a halftone dot area ratio of a predetermined value or less, the height of the convex portion (2) decreases as the halftone dot area ratio decreases. is doing. Therefore, as shown in FIG. 5, when the ink (K) adhering to the convex portion (2) of the relief plate (1A) is transferred to the blanket (10), the convex corresponding to the halftone dot having a small halftone dot area ratio. The amount that the part (2) bites into the blanket (10) decreases. Thereby, the spread of the ink (K) adhering to this convex part (2) is suppressed. Then, the ink (K) is transferred from the blanket (10) to the outer surface of the can body (31) of the can (30) in a state where the spread of the ink (K) is suppressed in this way. Therefore, the fatness of a small halftone dot can be reduced. Thereby, the quality of printing can be improved.

  Furthermore, this letterpress (1A) is for printing with 80 to 200 Lpi of screen lines, and since the predetermined value is 10%, the dot area ratio is 10% or less. Can be reduced. Particularly for printing with a screen line number of 100 to 200 Lpi, and when the predetermined value is 10%, it is possible to reduce the thickness of halftone dots with a dot area ratio of 10% or less.

  In addition, the height h of the convex portion (2) is reduced at a ratio in which the amount of decrease in the height h of the convex portion (2) per 1% reduction amount of the halftone dot area ratio is 0.005 to 0.02 mm. By doing so, it is possible to reliably reduce the thickness of the halftone dots having a halftone dot area ratio of 10% or less.

  In addition, by setting the maximum decrease in the height h of the convex portion (2) to 0.1 mm or less, it is possible to more reliably reduce the thickness of the halftone dots with a dot area ratio of 10% or less. it can.

  Furthermore, the convex part (2) is formed in the center part of the base part (3) having a trapezoidal cross section and the upper surface (3a) of the base part (3), and is larger than the diameter a of the upper surface (3a). A small-diameter columnar tip (2). Thereby, as shown in FIG. 5, when the convex part (2) to which the ink (K) is adhered is pressed by the blanket (10) and the ink (K) spreads outside the convex part (2), the ink The protruding part of (K) is captured by the corner part (5) between the upper surface (3a) of the base part (3) of the convex part (2) and the peripheral surface of the tip part (4). Thereby, the fatness of a halftone dot can be reduced further reliably.

  Furthermore, as shown in FIG. 2, the height h1 of the upper surface (3a) of the base portion (3) of the convex portion (2) is constant as the halftone dot area ratio decreases, but the convex portion (2 The length t of the tip (4) of) is shortened. Thereby, the intensity | strength of the front-end | tip part (4) of a convex part (2) is securable.

  Furthermore, since the convex portion (2) is formed by the direct laser engraving method, the convex portion (2) of the relief plate (1A) can be easily formed, and the production process of the relief plate (1A) can be shortened. The letterpress (1A) can be produced in a short time.

  Further, the relief plate (1A) has a photosensitive resin cured layer (7) cured by irradiating the photosensitive resin with ultraviolet rays (U), and a convex portion is formed on the surface of the cured resin layer (7). Since (2) is formed, the shavings generated during laser engraving can be removed by washing with water. Therefore, a letterpress (1A) can be manufactured easily.

  Moreover, since the printing apparatus (20) of this embodiment is provided with the relief printing plate (1A) of this embodiment, there is an advantage similar to the above-described advantage.

  Further, by printing on the outer surface of the can (30) by offset printing using the relief printing plate (1A) of the present embodiment, for example, as shown in Examples 1 to 5 described later, the screen line number is 80 to 200 Lpi. In addition, the can (30) can be provided which is printed on the outer surface in a high quality printing state in which the thickness of the halftone dots having a halftone dot area ratio of 4% or less is 5% or less. In addition, for example, the can (30) printed on the outer surface can be provided in a higher quality printing state in which there is no missing dot with a dot area ratio of 4% or less.

  Moreover, both the manufacturing method of the can of this embodiment and the outer surface printing method of a can print by offset printing using the relief printing plate (1A) of this embodiment. Therefore, high quality printing can be performed on the outer surface of the can (30).

  Although one embodiment of the present invention has been described above, the present invention is not limited to that shown in the above embodiment, and various modifications can be made.

  For example, in the above embodiment, as shown in FIG. 2, the convex portion (2) of the relief plate (1A) includes a base portion (3) having a trapezoidal cross section and an upper surface (3a) of the base portion (3). ) And a cylindrical tip portion (4) having a diameter smaller than the diameter a of the upper surface (3a). However, in this invention, the convex part (2) of a letterpress (1A) is not limited to the thing of the shape shown in FIG. That is, in the present invention, the convex portion (2) may not have a cylindrical tip portion, for example, as in the relief plate (1B) shown in FIG.

  Moreover, in the said embodiment, although the photosensitive resin hardened | cured material is used as a material of a letterpress (1A) at the point which can manufacture a letterpress (1A) easily, in this invention, the material of a letterpress (1A) is It is not limited to being a photosensitive resin cured product, but may be ordinary resin, carbon, rubber or the like.

  Moreover, in the said embodiment, about the convex part (2) corresponding to the halftone dot of the dot area ratio 10% or less (namely, the range of 0-10%), as the halftone dot area ratio decreases, the convex part (2 However, in the present invention, for example, the halftone dot area ratio is reduced for the convex part (2) corresponding to the halftone dot area ratio of 8, 6 or 4% or less. As it does, the height of the convex portion (2) may be lowered. Further, in the present invention, the minimum convex portion among the convex portions (2) whose height is lowered is not particularly limited. For example, the convex portion corresponding to a halftone dot having a halftone dot area ratio of 0.5%. May be a convex portion corresponding to a halftone dot having a halftone dot area ratio of 1%, or may be a convex portion corresponding to a halftone dot having another halftone dot area ratio.

  Moreover, in this invention, a can (30) is not limited to the thing of the shape shown in FIG. 6, In addition, for example, a bottle can may be sufficient. In the present invention, the material of the can (30) is not limited to aluminum, but may be steel, for example.

  Next, specific examples and comparative examples of the present invention are shown below.

<Examples 1-5>
According to the method for producing the relief plate (1A) shown in the above embodiment, the convex portion (2) of the relief plate (1A) having the following constitution was formed by a direct laser engraving method.

  That is, this relief printing plate (1A) has the structure shown in FIG. 2, and the surface of this relief printing plate (1A) (that is, the printing plate surface) has a large number of projections corresponding to a range of 1 to 30% of dot area ratio. Part (2) is formed. Further, for the convex portion (2) corresponding to a halftone dot with a halftone dot area ratio of 10% or less, the reduction amount of the height h of the convex portion (2) per 1% reduction amount of the halftone dot area ratio is 0.01 mm. In proportion, the height h of the convex portion (2) decreases. On the other hand, the height h of the convex portion (2) corresponding to the halftone dots exceeding the halftone dot area ratio of 10% is not lowered, that is, is constant. Further, the maximum reduction amount of the height h of the convex portion (2) with respect to the reference height of the convex portion (2), that is, the convex corresponding to a halftone dot having a halftone dot area ratio of 1% with respect to the reference height of the convex portion (2). The amount of decrease in the height h of the part (2) is 0.1 mm. In addition, the reference | standard height of a convex part (2) is the height of the convex part (2) corresponding to the halftone dot exceeding a dot area rate of 10%.

  The ratio a / b between the diameter a of the upper surface (3a) of the base portion (3) of the convex portion (2) and the diameter b of the tip portion (4) is set to 1.5. Moreover, the height h1 of the upper surface (3a) of the base part (3) of the convex part (2) with respect to the bottom part (2z) of the convex part (2) is set to 0.3 mm. Further, the relief angle θ of the base portion (3) of the convex portion (2) is set to 50 °.

The laser engraving depth is 0.4 mm, and the used laser light (L) is CO ₂ gas laser light, and its output is, for example, 500 W.

  Using the relief plate (1A) having the above-described configuration, dot printing with a screen line number of 80 to 200 Lpi was performed on the outer surface of the can body (31) of the can (30) according to the printing method described in the above embodiment. Then, the dot thickness (dot gain) was examined for the printing. The results are shown in Table 1. The thickness of the halftone dot was calculated by the following formula (a).

Thickness of halftone dot (%) = [(actual value of halftone dot area−theoretical value of halftone dot area) / theoretical value of halftone dot area] × 100 (a)
<Comparative Examples 1-5>
The relief printing plate (50) shown in FIG. 8 was produced by the conventional method shown below.

  A plate material having a photosensitive resin layer (53) was prepared. The original film was placed in close contact with the photosensitive resin layer (53), and the photosensitive resin was cured by irradiation with ultraviolet rays in accordance with the printing pattern of the original film. Next, the uncured photosensitive resin was removed by brush cleaning. Next, the plate material was dried.

  The height h of the convex portion (52) of the relief printing plate (50) manufactured through the above steps is set to be constant regardless of the size of the halftone dot area ratio. In FIG. 8, (55) is a base material, and (54) is an adhesive layer.

  Using this letterpress (50), halftone dot printing with a screen line number of 80 to 200 Lpi was performed on the outer surface of the can body (31) of the can (30) under the same printing conditions as in Examples 1 to 5. And the thickness of the halftone dot was investigated about the printing. The results are shown in Table 1.

  As shown in Table 1, in Examples 1 to 5, the thickness of halftone dots having a halftone dot area ratio of 10% or less was very small as compared with Comparative Examples 1 to 5. In addition, in Examples 1 to 5, printing is performed on the outer surface of the can body (31) of the can (30) in a high-quality printing state in which the dot area ratio is 4% or less and the thickness of the dot is 5% or less. I was able to. Therefore, smooth gradation reproduction is possible by printing using the relief printing plate (1A) according to the present invention.

  On the other hand, in Comparative Examples 1 to 3, some of the halftone dots with a halftone dot area ratio of 2% or less were missing. Further, in Comparative Examples 4 and 5, all of the halftone dots having a halftone dot area ratio of 8% or less were missing. The reason for this is that the convex portions (52) corresponding to the halftone dots having a dot area ratio of 2% or less or 8% or less were broken and lost during brush cleaning when producing the relief plate (50).

  INDUSTRIAL APPLICABILITY The present invention is applicable to, for example, a relief printing relief plate for printing on the outer surface of a can such as a metal can, and a can offset printing apparatus provided with the relief printing plate.

FIG. 1 is a schematic configuration diagram of an offset printing apparatus according to an embodiment of the present invention. FIG. 2 is a schematic sectional view of a relief printing relief plate according to an embodiment of the present invention. FIG. 3: is a schematic sectional drawing of the process of irradiating a photosensitive resin layer with an ultraviolet-ray among the manufacturing processes of the same relief printing plate. FIG. 4 is a schematic cross-sectional view of a step of forming a convex portion on the surface of the cured resin layer by a direct laser engraving method in the production process of the relief printing plate. FIG. 5 is a schematic enlarged cross-sectional view showing a state where the convex portion of the relief plate is pressed against the blanket in order to transfer the printing ink attached to the convex portion of the relief plate to the blanket. FIG. 6 is a partially cutaway perspective view of a can printed by the printing apparatus. FIG. 7 is a schematic sectional view of a relief printing relief plate according to another embodiment of the present invention. FIG. 8 is a schematic cross-sectional view of the relief printing plate used in Comparative Examples 1-5.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1A, 1B ... Letterpress 2 ... Convex part 3 ... Base part 3a ... Upper surface 4 ... Tip part 5 ... Corner part 6 ... Photosensitive resin layer 7 ... Photosensitive resin cured layer 8 ... Adhesive layer 9 ... Base material 10 ... Blanket 20 ... Printing device 21 ... Inking means 22 ... Plate cylinder 23 ... Blanket cylinder 24 ... Can feeding means 25 ... Can feeding means 30 ... Can 31 ... Can barrel part K ... Printing ink L ... Laser light U ... Ultraviolet light (active light)

Claims (14)

In the relief printing for offset printing of cans for printing on the outer surface of the cans by offset printing,
A relief printing plate for offset printing of a can, characterized in that the height of the convex portion decreases as the halftone dot area rate decreases for the convex portion corresponding to the halftone dot whose halftone dot area ratio is a predetermined value or less. . For printing screen lines of 80-200 Lpi,
The relief printing plate for offset printing of cans according to claim 1, wherein the predetermined value is 10%.   3. The can according to claim 2, wherein the height of the convex portion is reduced at a ratio of the amount of reduction in the height of the convex portion per 1% of the decrease in the halftone dot area ratio in the range of 0.005 to 0.02 mm. Letterpress for offset printing.   The relief printing plate for offset printing of a can according to claim 3, wherein the maximum reduction in the height of the convex portion is set to 0.1 mm or less.   The convex part has a base part and a cylindrical tip part formed in the center part of the upper surface of the base part and having a smaller diameter than the diameter of the upper surface. The letterpress for offset printing of the described can.   6. The offset printing of a can according to claim 5, wherein the height of the upper surface of the base portion of the convex portion is constant and the length of the tip portion of the convex portion is shortened as the halftone dot area ratio decreases. Letterpress.   The relief printing plate for offset printing of cans according to any one of claims 1 to 6, wherein the convex portions are formed by a direct laser engraving method. It has a photosensitive resin cured layer cured by irradiating the photosensitive resin with actinic rays,
The relief printing plate for offset printing of a can according to claim 7, wherein a convex portion is formed on a surface of the cured resin layer. In the can offset printing device that prints on the outer surface of the can by offset printing using a relief printing plate,
A can offset printing apparatus comprising the relief plate according to claim 1 as the relief plate. In the can printed on the outer surface by offset printing using relief printing,
A can having a screen line number of 80 to 200 Lpi and having a halftone dot area ratio of 4% or less and a dot thickness of 5% or less.   11. The can according to claim 10, wherein printing is performed in a printing state in which a halftone dot area rate of 4% or less is not lost.   The can of Claim 10 or 11 currently printed by the offset printing using the relief plate in any one of Claims 1-8 as the said relief plate. In the manufacturing method of the can printed on the outer surface,
A can manufacturing method, wherein printing is performed by offset printing using the relief printing plate according to claim 1.   A method for printing an outer surface of a can, comprising printing on the outer surface of the can by offset printing using the relief printing plate according to claim 1.

Images