JP2001001664A - Doctor blade - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a doctor blade which causes no plate fog even in the case where printing is performed at a practical printing speed and for a practical printing length (number of sheets to be printed) in gravure printing which uses water-base ink, while providing long service life for the doctor blade for scraping excess ink with its forward end pushed against a gravure printing roller. SOLUTION: This doctor blade is composed of a core metal 3a made of carbon steel or stainless steel, a primer coating 3b harder than the hardness of the core metal 3a, which is coated on one face or both faces of the core metal 3a, and a diamond-like carbon coating 3c further overcoated thereon. The diamond-like carbon coating has high smoothness and high hardness and is extremely small in its Young's modulus. The coating has flexibility and makes the doctor blade easily slidable on the surface of printing plate, whereby the doctor blade is made accessible to water-base ink existing in sandpaper marks formed in a non-image area on the surface of the printing plate and ink which passes through the underside of the doctor blade is controlled to an extremely small quantity. Accordingly, the doctor blade has excellent wear resistance and can favorably maitain the shapes of ink for a long time. Thus, plate fog can effectively be avoided, and no plate fog is caused even in the case where printing is performed at a practical printing speed and for a practical printing length.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is applied to gravure printing using a water-based ink, in which a doctor blade is protruded from a gravure printing roll to extend the life of a doctor blade for applying ink to cells and scraping off excess ink. The present invention also relates to a doctor blade that does not easily cause plate fogging even at a printing speed equivalent to that of gravure printing using oil-based ink, and can achieve gravure printing using water-based ink to a practical level.

[0002]

2. Description of the Related Art FIG. 2 shows a doctor device in a conventional gravure printing machine. In FIG. 2, reference numeral 1 denotes a gravure printing roll, and reference numeral 2 denotes a doctor blade of a doctor device. The doctor device is a device that supports the doctor blade 2 and pushes its tip against the gravure printing roll 1 to scrape off excess ink. The tip of the doctor blade 2 has a knife-edge shape. The doctor blade 2 performs a slow horizontal slide indicated by an arrow A during printing so that one point of the knife edge of the doctor blade 2 contacts only one fixed point in the roll surface length direction of the gravure printing roll 1. By avoiding this, uniform wear of the tip shape is achieved. If the doctor blade 2 does not perform the horizontal slide indicated by the arrow A during printing, the wear of the tip of the doctor blade 2 will not be uniform, and some of the tips of the doctor blade 2 will be heavily worn at an early stage, and the ink will be scraped there. Printing is performed in a state in which the taking function is lost and straight lines which are not present in the plate image and are continuous in the circumferential direction of the plate surface, that is, doctor streaks are generated in a large number of unexpected places. Prior art documents relating to doctor blades include JP-A-61-12396, JP-A-62-227645, and JP-A-62-238743.
JP, JP-A-62-503085, JP-A-63
-25038, JP-A-63-116852, JP-A-63-246249, JP-A-3-00
No. 7,394, JP-A-4-012853, JP-A-4-070341, JP-A-4-070342, JP-A-4-296556, JP-A-6-039
No. 991, JP-A-7-276601, JP-A-8-164598, JP-A-9-254356, JP-A-10-278222, JP-A-10-3
No. 37840, Japanese Utility Model Laid-Open No. 62-005959,
There is Japanese Utility Model Laid-Open No. 63-094576. Most of these documents relate to improving durability. JP Hei 10
JP-A-337840 aims to eliminate plate fog, but is not effective in gravure printing using aqueous ink. USP # 5,638,751, USP # 4,8
There are 95,071 improvements, all of which are improvements regarding the shape and holding structure of the doctor blade.

[0003] In gravure printing using oil-based inks, technical improvements have been achieved for plate fog. On the other hand, in gravure printing using water-based ink, no technical improvement has been achieved with respect to plate fogging, and practical use has not progressed at all. So far, gravure printing using an oil-based ink has been performed for gravure photo printing folded into a flexible packaging film, a calendar, or a magazine for packaging.

[0004]

As can be seen from the above-mentioned prior art documents, the improvement / improvement regarding the doctor blade has so far been improved in abrasion resistance and durability.
It has been proposed exclusively from the viewpoint of prolonging life, eliminating doctor muscles, and eliminating the occurrence of whiskers. For example, when the ink contains titanium white or the like, the wear rate becomes relatively high.How to reduce the running cost of the consumable doctor blade, how can it have abrasion resistance and improve the service life? Had been a problem.

Conventionally, there is no example in which the doctor blade is improved from the viewpoint of achieving practical use by eliminating plate fogging in gravure printing using aqueous ink. In gravure printing using oil-based ink, more than 50% of the organic solvent contained in the oil-based ink is volatilized and contributes to the contamination of the atmosphere. Switching is attracting attention. However, gravure printing using water-based ink tends to cause remarkable plate fog, and high-precision printing cannot be realized at all.

In gravure printing, a doctor blade is pushed against a gravure printing roll to fill the cells with ink and scrape off excess ink. In theory, no ink remains in the non-image area. In this case, the ink flies under the doctor blade and remains in the non-image area, so that plate fogging occurs. In the case of plate fogging, the ink is left on the non-image area of the plate surface under the doctor blade, and the ink does not reach a necessary degree of drying before printing, so that the ink is transferred to a printing material and an image is stained. This is a phenomenon that occurs when the printing speed is too high or the number of prints increases and wear of the doctor blade progresses. Plate fogging is a problem that occurs remarkably especially when using water-based ink and is difficult to avoid at present, but is a phenomenon that occurs even when oil-based ink is used.

The mechanism by which plate fogging occurs will be described. Suppose now that the roll surface is buff-polished to an extremely high precision mirror surface, then chromium plating is performed to form the cells and the printing durability is applied, the plating burrs are removed, and an extremely high accuracy mirror surface is used and oil-based ink is used. Gravure printing shall be performed,
Further, the doctor blade has a blade edge capable of performing an ink scraping function extremely well. in this case,
The doctor blade can scrape off the non-image area of the plate surface for a short time so that no oil-based ink remains. However, scraping of the ink in this process results in the absence of lubricant between the doctor blade and the plate surface. Therefore, the relative coefficient of friction between the doctor blade and the non-image portion of the printing plate becomes large, the doctor blade and the printing plate are easily worn, the ink scraping function of the doctor blade is reduced, and the printing plate is quickly roughened. . Then, the oil-based ink passes through the doctor blade and remains in the non-image area, and this becomes a plate fog. Further, if there is no lubricant between the doctor blade and the printing plate, the frictional force generated in correlation with the doctor blade and the non-image area of the printing plate is constantly changed due to the eccentricity of the printing roll, and vibration occurs. As a result, the oil-based ink passes through the doctor blade and remains in the non-image area, resulting in large fogging of the plate. Therefore, the roll surface of the surface roughness is buff-polished to an extremely high precision mirror surface with a grinding stone of about 2000-3000, then the cells are formed and chrome plating is applied to give the printing durability, deburring and sufficiently uniform When performing hand finish polishing in which sandpaper marks remain, self-lubrication occurs on the plate surface. As a result, printing that does not cause plate fogging in gravure printing using oil-based ink is performed. The self-lubricating property of the printing plate can be explained as follows. When chrome plating, which gives the printing durability to the plate surface, is rubbed with sandpaper, sandpaper marks are left on the non-image area. The doctor blade is pushed against the gravure printing roll to fill the cells with ink and scrape off excess ink. Then, a very small amount of oil-based ink in the sandpaper mark goes under the doctor blade. The oil-based ink that remains on the sandpaper marks that have passed through the doctor blade has a small amount of pigment and a large amount of resin and solvent. The oil-based ink remaining on the sandpaper trace has a resin component and a solvent interposed as a lubricant between the doctor blade and the plate surface when it dives under the doctor blade.
For this reason, the relative coefficient of friction between the doctor blade and the non-image area of the plate surface is reduced, and wear of the blade edge of the doctor blade and wear of the plate surface are reduced. Since the trace amount of the oil-based ink remaining in the sandpaper mark is extremely thin, the area ratio exposed to dry air is dramatically increased. Therefore, the solvent content in the oil-based ink is 110 to 130 m / m.
It evaporates within a very short period of time before shifting to the printing position at a printing speed of in. As a result, the pigment and the resin component are drawn to the bottom of the sandpaper mark, become a lightly dried state, and do not transfer to the print substrate. Then, when the pigment and resin are attracted to the bottom of the sandpaper mark and lightly dried, when they are combined with the oil-based ink to be applied again, the solvent is impregnated and becomes wet. do not do. For this reason, plate fogging does not occur even after the printing time has elapsed. However, when the printing speed is increased, a very small amount of oil-based ink remaining in the sandpaper marks formed in the non-image area under the doctor blade does not evaporate within the time elapsed until the printing position is reached. Happens. The above is the reason why plate fogging does not occur in gravure printing using an oil-based ink if the plate surface is provided with self-lubricating properties. On the other hand, in gravure printing using water-based ink, the causal relationship between imparting self-lubricating properties to the plate surface and preventing plate fogging cannot be discussed in the same way. Another situation in which plate fogging occurs in gravure printing with aqueous inks. First, the roll surface is buff-polished to a very high precision mirror surface, then chromium plating is performed to form the cells and the printing durability is given, and deburring is performed. In the case, as in the case of performing the gravure printing using the oil-based ink described above, the doctor blade can scrape off the non-image area of the plate surface such that no oil-based ink remains at all for a very short time in the first place. Due to the large relative coefficient of friction between the blade and the non-image area of the plate, the abrasion is large and the surface is quickly roughened, and the water-based ink passes through the doctor blade and remains on the non-image area, resulting in large fog on the plate. Will happen. Therefore, as in the case of gravure printing using oil-based ink, the roll surface with a surface roughness is buff-polished to an extremely high precision mirror surface with a grinding wheel of number 2000 to 3000, then the cells are formed and chromium plating that gives the printing durability When the printing roll is manufactured by removing the burrs and hand finishing polishing that leaves sandpaper marks evenly enough, self-lubrication occurs on the plate surface,
In gravure printing using water-based ink, plate fogging remarkably occurs, and high-precision printing cannot be realized at all. There are several complex reasons for this. Aqueous ink has a pigment component concentration about 30% higher than oil-based ink.Therefore, water-based ink that exists in the sandpaper marks and scrapes the doctor blade has a high pigment concentration. Since the drying load is much larger than the drying of the volatile pigment of the organic solvent and the drying is considerably delayed, the water-based ink that has passed through the doctor blade does not dry sufficiently within a very short time before moving to the printing position. In particular, the bound water bound to the pigment and resin does not evaporate easily, and the lightly dried pigment and resin that is drawn to the bottom of the sandpaper mark has an affinity for water with an affinity for solvent. It is small in comparison with the water-based property, and even when combined with the aqueous ink applied again by the furnisher roll, the affinity of the ink component with water or alcohol is delayed and it is deposited on the bottom of the sandpaper mark. In addition, since doctor blades made of carbon steel were used in the past, when printing 20,000 m, the wear was large and the cutting edge was retreated greatly, and the thickness of the cutting edge was reduced from 55 μm to 100 μm from the initial thickness, and the ink scraping function Is remarkably reduced, and the amount of the water-based ink that passes through the scraping of the doctor blade is considered to increase. Thus, in gravure printing using water-based ink, the formation of sandpaper marks in the non-image area provides self-lubrication to the plate surface, but does not eliminate plate fog, but rather causes plate fog. Would. Therefore, in gravure printing using aqueous ink, it is necessary to increase the relative lubricity between the doctor blade and the plate surface and prevent plate fogging by other means without forming sandpaper marks on the non-image area of the plate surface. There is.

The present invention has been devised in view of the above points, and has a long life of a doctor blade of a doctor device in which a doctor blade is protruded from a gravure printing roll to apply ink to cells and scrape excess ink. The object of the present invention is to provide a doctor blade which can be applied to gravure printing using water-based ink, and hardly causes plate fogging even at the same printing speed as gravure printing using oil-based ink, and can make gravure printing using water-based ink to a practical level. And

[0009]

According to the present invention, there is provided a doctor blade in which the tip of a doctor blade is protruded from a gravure printing roll, ink is applied to cells, and excess ink is scraped off. A core metal made of a carbon steel sheet or a stainless steel sheet, a base coat coated on the core metal, harder than the core metal, softer than the diamond-like carbon coating, and reinforcing the hardness of the core metal; And a diamond-like carbon coating for coating at least the knife edge.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a doctor blade according to the present invention will be described with reference to FIG. The doctor blade 3 varies depending on the size of the gravure printing roll and the machine. Specifically, the length is 220 to 1,050 mm × the width, 60 to 80 mm.
× Thickness of 120 to 180 mm × μm, and on one or both sides, has a cutting edge whose thickness at the tip is about 50 to 70 μm, the position is adjusted according to the diameter of the gravure printing roll The edge of the gravure printing roll is protruded in an inclined state with respect to the gravure printing roll to scrape off excess ink and fill the cells of the gravure printing roll with ink.

[0011] The doctor blade 3 of the present invention comprises a metal core 3
a, a base coat 3b for coating the core metal 3a, and a diamond-like carbon coat 3c for overcoating the base coat 3b.

The core metal 3a is formed of a thin steel plate or stainless steel having a strong stiffness and flexibility, and has a knife edge at the tip. The core metal 3a made of a steel plate has a Vickers hardness of about 60 by quenching.
It consists of carbon steel which is 0. As used herein, the knife edge includes a wedge-shaped cross section in which the thickness gradually decreases toward the tip, and a stepped cross section in which the tip is reduced in thickness by one step or several steps.

The undercoat 3b is coated on one side or both sides of the metal core 3a with a thickness of about 5 to 10 μm on the surface on the ink scraping side. The undercoat 3b is provided to increase the wear strength of the core 3a, and is therefore made of a plating material or a ceramic material that is harder than the core 3a. On the other hand, the base coat 3b needs to be softer than the diamond-like carbon coat 3c. If the undercoat 3b is harder than the diamond-like carbon coating 3c, the reinforcement of the abrasion strength of the core metal 3a is too large, and the diamond-like carbon coating 3c is worn away first, and is exposed and scraped with respect to the plate surface. In this case, the abrasion of the plate surface is increased due to the large sliding friction coefficient of the undercoat 3b, and the undercoat 3b is hard and has a large Young's modulus, which is remarkable in the gravure printing using the water-based ink. No special effect is exerted on plate fogging that occurs in The hardness of the plate surface is Vickers hardness of 1000 ~ in case of hard chrome plating
1100, and the undercoat 3b is preferably softer than the plate surface. The reason is that the undercoating 3b also rubs the plate surface, and therefore, in order to suppress the abrasion of the plate surface, it is necessary to select a material that is hard but has a small friction coefficient, or a material that is softer than the plate surface, as the undercoating 3b. Because there is. From such a viewpoint, a material suitable for the undercoat 3b is ceramic composite nickel plating. This plating is performed in an electroless nickel bath or an electric nickel bath.
One kind or a plurality of kinds of ceramic fine powder appropriately selected from various ceramic fine powders such as silicon carbide and boron nitride are added in an appropriate amount, and plating is performed with stirring, so that nickel plating is performed at the same time. The fine powder is deposited in the plating film and is subjected to a baking treatment as required. In addition, the base film 3b may be formed by forming hard nickel plating or soft chromium plating, or may be formed by forming silicon nitride ceramic, zirconia, or the like, or may be sprayed with alumina. The base coat 3b may be coated on at least one or both sides of the cutting edge of the cored bar 3a. Undercoat 3b
Is formed in a thickness of about 5 to 10 [mu] m, depending on the type. In the case of spraying alumina, it can be formed only on one surface of the cutting edge of the metal core 3a on the ink scraping side.

The diamond-like carbon coating 3c is
An amorphous carbon compound film formed on both surfaces of the core metal 3a coated with the base film 3b to a thickness of 0.1 to 5 [mu] m by a thin film forming technique of processing under vacuum. The diamond-like carbon coating 3c is harder and more abrasion-resistant than ceramic which is said to be hard, yet does not have the brittleness of ceramic, has a very small Young's modulus, is flexible as a coating, and has a smooth surface. It has excellent properties such that the coefficient of friction is as small as μ = 0.12 and it is easy to slip, the surface energy is extremely small, the generation of frictional heat is small, and there is no risk of seizure. The diamond-like carbon coating 3c may be formed by a vapor deposition method, a sputtering method, an ion plating method, or a vapor deposition method. The surface roughness of the diamond-like carbon film is Ra = 7.3 angstroms, and the surface roughness of the hard TiN film is Ra = 113 angstroms. Diamond-like carbon coating 3c
Has much higher surface smoothness, hardness and wear resistance than quenched carbon steel or stainless steel. Further, the friction coefficient of the diamond-like carbon film is extremely small, about 1/4 of the friction coefficient of a TiN film, a CrN film, a TiCN film or a cemented carbide which is a hard film, and is much smaller than that of quenched carbon steel. The hardness of a diamond-like carbon coating differs depending on the material to be coated, and is said to be about Vickers hardness 500 when formed on silicon rubber and 2000-3000 when formed on titanium steel. . When the diamond-like carbon coating 3c formed on the carbon steel was rubbed with a file having a Vickers hardness of 950, no mark was formed. It was harder than a ceramic doctor as measured by an ultra-micro hardness tester. In the present invention, the formation of the diamond-like carbon coating 3c covering both sides of the blade edge of the doctor blade 3 can improve the wear resistance of the doctor blade,
This is because plate fogging that occurs remarkably in gravure printing using water-based ink can be avoided, and abrasion of the plate surface can be suppressed.

The practical use of gravure printing using water-based ink is as follows.
Switching the number of screen lines from 175 lines / inch meter to 300 lines / inch meter to increase the resolution of the plate image and shorten the time of water evaporation, reduce doctor blade wear and plate surface wear, It is necessary to improve the use of water-based inks that are unlikely to cause fogging, and this problem is solved especially on the assumption that the plate is mirror-finished so that the surface roughness of the plate after chrome plating is reduced as much as possible. There is a need. However, mirror-finishing the plate surface makes it possible to reduce the amount of ink that penetrates the doctor blade to almost nothing, and keeps the self-lubricating property of the plate surface low, increasing the coefficient of friction between the doctor blade and the plate surface. It is expected that the wear on both the plate and the plate surface will increase. However, the doctor blade according to the present invention is not limited to the undercoat 3b in which the hardness of the metal core 3a is reinforced.
Is further covered with a diamond-like carbon coating 3c, which has extremely high wear resistance and a friction coefficient of TiN.
Coefficient of friction of film, CrN film, TiCN film and cemented carbide
A very small diamond-like carbon coating of / 4 carries most of the frictional force, and the sharing of the frictional force on the end faces of the cutting edge of the core metal and the base coating having a large frictional coefficient can be suppressed to a small value. Can be kept small. The pressing force of the doctor against the plate surface has a pressure distribution that is large on the ink scraping side and becomes smaller toward the back side. The end faces of the cutting edges of the metal core 3a and the undercoat 3b have a large abrasion coefficient but a much larger contact area with the plate surface than the diamond-like carbon coating 3c, so that the pressure per unit area is smaller than that of the diamond-like carbon coating 3c. , So that the contribution of the plate surface to abrasion is reduced.
Therefore, the diamond-like carbon coating 3c having a large pressure per unit area greatly contributes to the abrasion of the plate surface, and in particular, the diamond-like carbon coating 3c on the ink scraping side plays a significant role. However, the diamond-like carbon coating 3c has extremely high hardness and abrasion resistance, has an extremely smooth surface, and has a friction coefficient μ = 0.
It has excellent characteristics that it is small and easy to slip, has a very small surface energy, generates little friction heat, and does not cause seizure, so the abrasion of the plate is sufficiently smaller than before. Will be involved. Diamond-like carbon coating 3a on ink scraping side
Has extremely high abrasion resistance and does not easily wear away,
The end faces of the cutting edges of the cored bar 3a and the undercoat 3b are not easily worn away. The end surfaces of the cutting edges of the metal core 3a and the undercoat 3b are
Since the diamond-like carbon coating 3c is softer and has less wear resistance than the diamond-like carbon coating 3c, the wear is reduced as the diamond-like carbon coating 3a on the ink scraping side is reduced. Even if the diamond-like carbon coating 3a is worn, the end faces of the cutting edges of the core metal 3a and the base coating 3b do not remain and are not exposed. The diamond-like carbon coating 3c on the back side effectively suppresses abrasion of the end surfaces of the cutting edges of the core metal 3a and the base coating 3b. The diamond-like carbon coating 3c overcoated on the base coating 3b
When the undercoat 3b is made of a hard and brittle ceramic, cracks in the ceramic can be avoided. Therefore, the doctor blade of the present invention can avoid an increase in the coefficient of friction between the mirror-finished plate surface and the diamond-like carbon coating, which has extremely high abrasion resistance. Even when printing is performed, it is possible to satisfactorily maintain the ink at the blade edge of the doctor blade forever.

In the doctor blade 3 of the present invention, the diamond-like carbon coating 3c slides on the plate surface to add ink to cells and scrape off excess ink.
Since the diamond-like carbon coating 3c has a high surface smoothness and an extremely small Young's modulus, the ink can be kept satisfactorily forever. The diamond-like carbon coating 3c has a very small Young's modulus, has elasticity different from ceramics, TiN, CrN, TiCN, etc., and has a small frictional coefficient in contact with the plate surface, but has a friction coefficient. μ is as extremely small as 0.12, and the abrasion of the plate surface can be kept small. Further, since the diamond-like carbon coating 3c has a small surface energy, heat generation due to friction is small and there is no fear that seizure may occur. When using a diamond-like carbon coated doctor blade, the smoothness and linearity of the cutting edge are high, the wettability is large, the hardness is large, but the Young's modulus is extremely small and the film is flexible, so it is easy to slide on the plate surface, especially elasticity Because it is, it is easy to approach the water-based ink in the sandpaper marks formed on the non-image area of the plate surface, and the amount of ink that dives under the doctor blade is extremely small, so the abrasion resistance is large and the ink at the blade edge of the doctor blade is cut off Can be effectively maintained forever, plate fogging can be effectively avoided, and printing at a practical printing speed and printing length does not cause plate fogging. On the other hand, to suppress the wear of the plate surface to a small extent is an effective means of preventing plate fogging since the surface of the non-image area can be prevented from being roughened after the printing time has elapsed. On the other hand, a doctor blade made of ceramic has a large coefficient of friction, so that abrasion of the plate surface is increased to cause fogging of the plate.

The doctor blade 3 of the present application covers both surfaces of a quenched edge of carbon steel or a stainless steel edge with a diamond-like carbon coating, is superior in wear resistance to ceramics, has a long life, and has a chipped edge. There is no fear that doctor muscles will occur due to no occurrence of doctor, and the reliability as a doctor is high. Ceramic doctor blades have low wear and long life, but may cause doctor streaks due to chipping.

[0018]

EXAMPLES (1) Gravure printing using water-based ink was performed, and an appropriate printing speed at which occurrence of plate fogging was not observed was examined.
In the doctor blade of the present invention, a 10 μm thick base coat made of ceramic composite nickel plating is coated on both sides of a 150 μm thick metal core quenched with carbon steel, and a diamond-like carbon coat is overcoated to a thickness of 4 μm. Same as gravure printing using oil-based ink
No fogging was observed at a practical printing speed of 110 to 130 m / min. Also, even if printing reaches 100,000m,
No doctor muscle or whiskers were found. On the other hand, a conventional doctor blade made of ultra-thin strip steel plate
Plate fogging was observed at a printing speed of / min. or,
With the ceramic doctor blade, plate fogging was observed at substantially the same printing speed, and doctor streaks were observed when the printing time was prolonged. (2) Attach the doctor blade of the present invention of the above (1),
After performing gravure printing using water-based ink (water-based ink is Aquapia White (trade name / containing titanium white) manufactured by Toyo Ink Co., Ltd.) and printing 28,000m, the wear amount of the blade edge was measured. there were. This was the rate at which abrasion of 30 μm occurred per 10,000 m of printing length. On the other hand, gravure printing using water-based ink was performed with a doctor blade made of a conventional ultra-thin strip steel plate, and 20,000 m
After printing, the wear amount of the blade edge was measured, and as a result, it was found to be 660 μm. This is equivalent to 330 m per 10,000 m of printing length.
It was the rate at which wear of μm occurred. In the gravure printing using the water-based ink, it was also found that when the blade edge of the doctor blade had the same wear and retreat as that in the gravure printing using the oil-based ink, the plate fogging became remarkable. (3) Attach the doctor blade of the present invention of the above (1),
After performing gravure printing using water-based ink (water-based ink is Akwa Ecole (trade name) manufactured by Toyo Ink Co., Ltd.) and printing 50,000 m, the amount of wear on the plate was measured. 2 μm, 0 to 1 in non-image area
There was a wear of μm. On the other hand, gravure printing using water-based ink was performed with a conventional doctor blade made of ultra-thin strip steel sheet, and the amount of wear on the plate after printing 50,000 m was measured. 2 μm at the line
There was abrasion. (4) With respect to the doctor blade of the present invention, a diamond-like carbon film was formed by a plasma CVD method, and the annealing hardness was measured. The temperature during the formation of the diamond-like carbon film by the thermo label was 210 ° C. on the inner surface and 200 ° C. on the outer surface. On the other hand, the quenching temperature of the blade core 3a made of carbon steel is 30
Since the temperature exceeds 0 ° C., the blade core 3a is not annealed by heating during film formation, the hardness of Vickers hardness 600 is maintained, and the hardness of the blade core 3a as a support of the diamond-like carbon coating is improved. Is never too small. (5) As a result of examining the relationship between the plate surface roughness of the printing roll, the plate surface wettability and the plate fogging, the larger the plate surface roughness, the smaller the apparent wettability and the contact angle of the dripping liquid. And the plate fog appears greatly. As is evident from the above, it was confirmed that the diamond-like carbon coating had an extremely smooth surface and had a smaller contact angle and higher wettability than any of carbon steel, nickel and ceramic.

[0019]

As described above, according to the doctor blade of the present invention, a core metal 3a made of carbon steel or stainless steel is coated on one or both sides with a base coat 3b harder than the core metal 3a. Furthermore, since the diamond-like carbon coating 3c is overcoated, the self-lubricating function and abrasion resistance of the doctor blade that protrudes the tip of the gravure printing roll to scrape off excess ink can be ensured to extend the life, There is no fear of gently damaging the plate. According to the doctor blade of the present invention, plate fogging does not occur even when printing at a practical printing speed and a practical printing length (number of prints) in gravure printing using aqueous ink. The use of a diamond-like carbon coated doctor blade increases the smoothness and linearity of the cutting edge, increases wettability, and has a flexible surface, so the water-based ink on the sandpaper marks formed on the non-image area of the plate surface , And the amount of ink that dives through the doctor blade can be kept very small, so that plate fogging can be effectively avoided. In conventional gravure printing using water-based ink, plate fogging occurred at a practical printing speed.However, using the doctor blade of the present invention reduces the surface roughness of the plate surface and makes the plate image highly precise. Commercial use of gravure printing using water-based inks can be realized for the first time in combination with the use of gravure printing. According to the doctor blade of the present invention, since the wear of the cutting edge that guarantees the ink scraping function is about 1/10 of that of the conventional product, the life of the doctor blade can be extended 10 times as compared with the conventional product. As a result, generation of plate fogging can be avoided for a long time. Also, there is no need to replace the doctor blade every short time, which makes maintenance easier. According to the doctor blade of the present invention, the wear of the printing plate can be suppressed to a small value, so that the number of printings on the printing plate can be substantially doubled or more, and the number of times of re-chrome plating can be reduced by half.

[Brief description of the drawings]

FIG. 1 is a sectional view of a main part showing an embodiment of a doctor device of the present invention.

FIG. 2 is a schematic perspective view showing a conventional doctor device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Gravure printing roll 2 ... Doctor blade 3 ... Doctor blade 3a ... Core metal 3b ... Undercoat film 3c ... Diamond-like carbon film

Claims (1)

[Claims] 1. A doctor blade in which a tip of a doctor blade is protruded from a gravure printing roll and ink is applied to cells and excess ink is scraped. The doctor blade is made of a thin carbon steel sheet having a knife edge at the tip or made of stainless steel. A steel core, a base coat coated on the core, harder than the core and softer than the diamond-like carbon coating to reinforce the hardness of the core, and diamond coated on at least a knife edge of the core. A doctor blade comprising a like carbon coating.