Printing method for gravure pearlescent ink on black high-brightness PET (Polyethylene Terephthalate) composite paper

Abstract

The invention discloses a printing method for gravure pearlescent ink on black high-brightness PET (Polyethylene Terephthalate) composite paper, which comprises the following steps of: carrying out plate making on image-text contents needing to be printed by using pearlescent ink by adopting a laser electronic engraving process; hoisting the single gravure and adjusting the position of the single gravure to be aligned with the front, back, left and right registration gauge lines of the printed matter; mounting a UV rubber blanket on the single gravure cylinder, locking the position of the plate clamp, and adjusting the distance between the UV rubber blanket and the printing plate; coating a layer of transparent varnish on the surface of the gravure plate; the equipment is pressed, the manual trolley is turned for one cycle, and then the pressing is released, so that the print on the gravure plate is transferred to the rubber blanket; manually and carefully digging off a rubber blanket surface adhesive layer at a blank position along the outline of the print to obtain a rubber blanket letterpress printing plate with a corresponding pattern; gravure pearlescent ink is poured into an ink cylinder to be stirred and pumped into a gravure ink groove through an air pump; and printing operation is carried out after the single-sheet gravure press is pressed. The production efficiency is improved, the printing ink cost is saved, and the color and quality are stable during mass production of products.

Description

Technical Field

[0001] The present invention relates to the technical field of gravure printing pearlescent ink on black high-gloss PET composite paper, and specifically relates to a printing method for gravure printing pearlescent ink on black high-gloss PET composite paper. Background Art

[0002] High-transparency PET composite film is a new type of packaging material with excellent physical and chemical properties, dimensional stability and transparency, and is widely used in fields such as magnetic recording, photosensitive materials, electronics, electrical insulation, industrial films, packaging and decoration, screen protection, and optical-grade mirror surface protection. High-transparency PET composite film is relatively common in daily life, such as automotive explosion-proof films, mobile phone and tablet computer films, etc., but its application in small paper packaging prints is less, mainly because the composite process with paper is complex and the production cost is relatively high.

[0003] In the prior art, such as Chinese Patent Application (application number 2020104724313) has disclosed a gravure in-line printing structure and its printing method for black high-gloss composite paper. The printing structure includes a back coating, a white card bottom layer, a calendering coating layer, a composite glue layer, an aluminized layer, a black layer, a PET high-gloss film layer, and a printing layer from bottom to top. However, due to the special properties of the high-gloss PET film, it is very difficult to perform pearlescent ink printing and decoration processing on its surface. The commonly used process in the industry is to use screen printing technology to process.

[0004] Screen printing technology is the oldest printing technology, which is claimed to be able to perform printing processing on all printing substrates except water and air, and has great adaptability. However, the production speed is relatively slow, the registration accuracy is worse than that of offset printing, gravure printing, flexographic printing and other process methods, and the production appearance effect changes with the thickness of the ink layer, with poor stability. And the ink consumption is extremely large, and the production process is relatively backward. If the conventional gravure printing process is used to print pearlescent ink, the difficulty is very high, and there are mainly the following problems:

[0005] 1) The product has both large-area full-color patterns and fine small lines, and the registration requirements are relatively high;

[0006] 2) The main components of pearlescent ink are metal particles with different particle sizes, generally between several um and 20 um. The finer particles cannot be completely scraped clean by the gravure doctor blade on the gravure plate, and the leaked particles will remain in the blank position of the printing plate and be transferred to the product surface to form oily imprints, affecting the appearance of the product;

[0007] 3) The metal solid powder of pearlescent ink has extremely poor solubility in the ink vehicle, and the product has poor leveling during printing, and phenomena such as trailing will appear at the edge of the imprint;

[0008] 4) The most crucial point is that in this case, pearlescent ink needs to be printed on the surface of the high-gloss black PET aluminized composite film. The mirror-like appearance effect of the paper itself will magnify the ink dirt marks on its surface. Oil stains that are hardly visible on the surface of other raw materials are very obvious on the appearance of the high-gloss black PET aluminized composite film. Summary of the Invention

[0009] The technical problem to be solved by the present invention is to provide a gravure printing method for pearlescent ink on black high-gloss PET composite paper, realizing the finishing process of printing pearlescent ink on the surface of black PET paper, improving production efficiency, saving ink costs, and ensuring stable color and quality during mass production of products.

[0010] The technical solution adopted by the present invention is: a gravure printing method for pearlescent ink on black high-gloss PET composite paper, which includes the following steps:

[0011] Step 1, plate making: The graphic content to be printed with pearlescent ink is made into a plate by using laser electronic engraving technology. The plate-making parameters are 40um - 50um, 65 - 75L. The specifications of the gravure plate cylinder are 840mm in length and 943.5mm in circumference. The printed pattern is centered left and right, and a knife protection line is engraved at the blank position of the bite to ensure uniform ink application.

[0012] Step 2, plate installation: Lift a single gravure plate onto a single-sheet gravure printing machine, and adjust the relative position of the single gravure plate and the gravure cylinder of the single-sheet gravure printing machine to align with the front, back, left, and right registration lines of the printed matter, with an error ≤ 0.5 - 1.0mm.

[0013] Step 3, rubber cloth installation: Install a clean and brand-new UV rubber cloth on the single-sheet gravure cylinder, lock the plate clamp position to ensure it will not slide, and adjust the distance between the UV rubber cloth and the printing plate to ensure normal production pressure. Since the thickness parameter of the paper to be printed later is 0.335mm, the adjusted plate distance here is ≤ 0.25mm, and the printing pressure is 2 - 3kg to ensure normal production in the later stage.

[0014] Step 4, pre-coated coating positioning: Apply a layer of transparent varnish on the surface of the gravure plate. The single-sheet gravure printing machine is closed and pressed, and the machine is manually turned for one cycle and then released. The imprint on the gravure plate is transferred to the rubber cloth.

[0015] Step 5, manual plate engraving: The operator holds a carving knife and carefully digs out the surface glue layer of the rubber cloth at the blank position along the imprint contour under clear light irradiation, ensuring that other functional layers are not damaged. Finally, only the surface glue layer at the graphic position of the rubber cloth is retained to obtain a rubber cloth relief printing plate corresponding to the pattern.

[0016] Step 6: Ink Loading: Pour the customized gravure pearlescent ink into the ink tank. After being stirred evenly by the ink agitator, it is input into the gravure ink trough through the air pump suction pipe. The ink exceeding the rated height flows back into the ink tank through the conduit. During the production process, continuous stirring is required, and under the operation of the air pump, the ink in the ink tank and the ink trough keeps circulating continuously.

[0017] Step 7: Printing: After the single-sheet gravure press is closed, printing operations are carried out. When producing for the first time, it is necessary to carry out fine carving on the positions of individual graphics and texts multiple times, adjust the backing paper for the positions where the ink amount of the printed graphics and texts is insufficient, and synchronously adjust the pressure and position of the paper feeding and pressing wheels to adjust the paper feeding progress. Tighten the pull rule to adjust the paper feeding position of the paper. Other operation requirements are the same as those of conventional gravure production.

[0018] Further, the process parameters of the UV blanket in Step 3 above: Specification 780mm * 200mm, thickness 1.95mm, surface roughness 0.8 - 1.2μm, hardness range 78 - 82 Shore A.

[0019] Advantages of the present invention: Compared with the prior art, the effects of the present invention are as follows:

[0020] 1) In production, engraving is carried out after the pre-coated varnish ink is aligned, and then the blanket is finely carved according to actual production. Therefore, the alignment between the gravure plate and the blanket backing is very accurate, and the registration accuracy deviation is improved to ≤0.3mm (lower than the standard of the traditional screen printing registration deviation value of 0.5mm).

[0021] 2) Solve the problem of plate surface contamination during the production of single-sheet gravure pearlescent ink printing. The products produced by the printing method of the present invention have a clean and tidy surface: Since the oleophilic surface glue layer of the blank position of the blanket has been engraved and removed before printing, the remaining plate surface, except for the oleophilic graphics and texts, is a non-oleophilic plastic textile layer. And since one-fourth of the thickness of the printing plate is removed, there is almost no contact between the blank position of the blanket and the gravure plate, and there is no pressure between the two, and there is no ink transfer effect. Therefore, the plate surface contamination rate is reduced by more than 90%.

[0022] 3) The main materials of the pearlescent ink are metal particles such as aluminum powder, with poor solubility and easy precipitation, and it often becomes thick and viscous during production; in the whole production process of the present invention, the ink is continuously stirred to keep it in a dynamic cycle all the time, avoiding the precipitation of coarse metal particles and circumventing the problem that the pearlescent effect becomes coarser with printing.

[0023] 4) The laser-engraved gravure steel plate has extremely high strength and hardly deforms during the production process. Therefore, the thickness of the transferred pearlescent ink layer is stable, and there is no color difference problem caused by the change of thickness.

[0024] 5) Since the raw materials of pearlescent ink are finely ground metal materials and the processing technology is relatively complex, the purchase unit price is 2-3 times higher than that of ordinary UV ink. The amount of pearlescent ink used in gravure printing is 40% less than that of screen printing ink, greatly reducing the cost. Brief Description of the Drawings

[0025] Figure 1 It is a process flow chart of a printing method for gravure printing pearlescent ink on a black high-gloss PET composite paper;

[0026] Figure 2 It is a file diagram of the gravure printing pattern for the strip box;

[0027] Figure 3 It is a file diagram of the gravure printing pattern for the small box. Detailed Embodiments

[0028] The present invention will be further introduced below in conjunction with specific embodiments.

[0029] Embodiment 1: As Figure 1 shown, a printing method for gravure printing pearlescent ink on a black high-gloss PET composite paper, the method comprising the following steps:

[0030] Step 1, plate making: The graphic content to be printed with pearlescent ink (such as Figures 2 - 3 the colored positions shown) is plate made by laser electronic engraving technology, the plate making parameters are 40um - 50um, 65 - 75L, the gravure plate cylinder specifications are 840mm in length and 943.5mm in circumferential length, the printing pattern is centered left and right, and a knife protection line is engraved at the blank position of the bite to ensure uniform ink application;

[0031] Step 2, plate installation: The single gravure plate is hoisted onto the single-sheet gravure printing machine according to the conventional operation process, and the relative position of the single gravure plate and the gravure cylinder of the single-sheet gravure printing machine is adjusted to align with the front, back, left, and right registration lines of the printed matter, with an error ≤ 0.5 - 1.0mm;

[0032] Step 3, rubber blanket installation: A clean and brand-new UV rubber blanket is installed on the single-sheet gravure cylinder, the clamping plate position is locked to ensure no sliding, and the distance between the UV rubber blanket and the printing plate is adjusted to ensure normal production pressure. Since the thickness of the printed paper is 0.335mm, the plate distance is set ≤ 0.25mm;

[0033] Process parameters of the UV rubber blanket: specification 780mm * 200mm, thickness 1.95mm, surface roughness 0.8 - 1.2μm, hardness range 78 - 82 Shore A;

[0034] Step 4. Pre-coated coating positioning: Apply a layer of transparent varnish on the surface of the gravure plate. The single-sheet gravure press is closed for manual jogging for one cycle and then opened. Transfer the imprint on the gravure plate to the blanket;

[0035] Step 5. Manual engraving: The operator holds a cutter and carefully digs out the surface glue layer of the blanket at the blank position along the imprint contour under clear lighting, ensuring that other functional layers are not damaged. Finally, only the surface glue layer at the graphic position remains on the blanket, obtaining a relief printing plate of the blanket corresponding to the pattern;

[0036] Step 6. Ink loading: Pour the customized gravure pearlescent ink into the ink tank. After being stirred evenly by the ink agitator, it is input into the gravure ink fountain through the air pump suction pipe. The ink exceeding the rated height flows back to the ink tank through the conduit. During the production process, continuous stirring is required, and the ink in the ink tank and the ink fountain is kept in continuous circulation under the operation of the air pump;

[0037] Step 7. Printing: After the single-sheet gravure press is closed, printing operations are carried out. During the first production, it is necessary to perform fine carving on the positions of individual graphics multiple times, and adjust the backing paper for the positions where the ink amount of the printed graphics is insufficient. The other operation requirements are the same as those of conventional gravure production.

[0038] The advantages of the present invention are as follows:

[0039] 1) In production, engraving is carried out after the pre-coated varnish ink registration position is determined, and then the blanket is finely carved according to actual production. Therefore, the alignment between the gravure plate and the blanket backing is very accurate, and the registration accuracy deviation is improved to ≤0.3 mm (lower than the standard of the traditional screen printing registration deviation value of 0.5 mm);

[0040] 2) Solve the problem of plate surface contamination during the production of single-sheet gravure pearlescent ink printing. The products produced by the printing method of the present invention have a clean and tidy surface: Since the oil-loving surface glue layer of the blanket at the blank position has been engraved and removed before printing, the remaining plate surface, except for the oil-loving graphics, is a non-oil-loving plastic textile layer. And since a quarter of the thickness of the printing plate has been removed, there is almost no contact between the blank position of the blanket and the gravure plate, and there is no pressure between the two, so there is no ink transfer effect. Therefore, the plate surface contamination rate is reduced by more than 90%;

[0041] 3) The main materials of pearlescent ink are metal particles such as aluminum powder, with poor solubility and easy precipitation, and it often becomes thick and viscous during production; in the whole production process of the present invention, the ink is continuously stirred to keep it in a dynamic circulation state, avoiding the precipitation of coarse metal particles and circumventing the problem of the pearlescent effect becoming coarser with each printing;

[0042] 4) The gravure steel plate engraved by laser has extremely high strength and hardly deforms during the production process. Therefore, the thickness of the pearlescent ink layer transferred by printing is stable, and there is no color difference problem caused by the change of thickness.

[0043] 5) Since the raw material of the pearlescent ink is finely ground metal and the processing technology is relatively complex, the purchase unit price of the pearlescent ink is 2-3 times more expensive than that of the ordinary UV ink. The consumption of the pearlescent ink used in the gravure process is 40% less than that of the screen printing ink, which greatly reduces the cost.

[0044] As mentioned above, it is only the specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention can easily think of changes or substitutions, which should be covered within the protection scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the claims.

Claims

1. A method for gravure printing pearlescent ink on black high-gloss PET composite paper, characterized in that: The method comprises the following steps: Step 1: Plate making: The graphic content to be printed with pearlescent ink is made by laser electronic engraving process. The plate making parameters are 40um-50um, 65-75L, the gravure plate roller specifications are 840mm long and 943.5mm circumference, the printing pattern is centered on the left and right, and the knife guard line is engraved on the blank position of the bite; Step 2: Plate loading: hoist the single gravure plate onto the single-sheet gravure printing press, and adjust the relative position of the single gravure plate and the gravure cylinder of the single-sheet gravure printing press, aligning them with the front, back, left, and right registration lines of the printed matter, with an error of ≤0.5-1.0mm; Step 3: Install the rubber blanket: Install a clean, brand new UV rubber blanket on a single gravure cylinder, lock the plate clamp position, and adjust the distance between the UV rubber blanket and the printing plate. The adjusted plate distance is ≤0.25mm, and the printing pressure is 2-3kg; Step 4: Pre-coating positioning: manually apply a layer of transparent varnish on the surface of the gravure plate, manually turn the single-sheet gravure press for one cycle and then release the press to transfer the imprint on the gravure plate to the rubber blanket; Step 5: Manual engraving: The operator uses a carving knife to carefully dig out the rubber layer on the blank area along the outline of the imprint under clear light. The final rubber only retains the rubber layer on the image area to obtain a rubber plate with the corresponding pattern. Step 6: Fill ink: Pour the customized gravure pearlescent ink into the ink cylinder, stir it evenly in the ink agitator, and then input it into the gravure ink tank through the air pump ink suction tube. The ink exceeding the rated height will flow back to the ink cylinder through the conduit. During the production process, it is necessary to keep stirring and keep the ink in the ink cylinder and the ink tank circulating under the operation of the air pump. Step 7, Printing: After the single-sheet gravure printing machine is pressed, the printing operation will be carried out. During the first production, it is necessary to perform fine carving on the positions of individual images and texts for many times, and adjust the bottom lining paper for the positions where the printed images and texts have insufficient ink. At the same time, the pressure and position of the paper feeding pinch wheel are adjusted to adjust the paper feeding progress, and the tension gauge is used to adjust the paper feeding position.

2. The method for gravure printing pearlescent ink on black high-gloss PET composite paper according to claim 1, characterized in that: Process parameters of UV blanket in step 3: Specification 780mm 1200mm, thickness 1.95mm, surface roughness 0.8-1.2μm, hardness range 78-82 Shore A.

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