Cooking-resistant metal flat plate prime coat-free printing method

Abstract

A cooking-resistant metal flat plate prime coat-free printing method comprises the following steps that S1, a metal flat plate is subjected to corona discharge treatment, an oil film on the surface of the metal flat plate is removed, and the corona discharge treatment is used for removing an oil film formed by DOS oil on the surface of the metal flat plate; s2, printing ink on the metal flat plate in a waterless offset printing manner to form a waterless offset printing layer, and curing the ink; s3, the surface of the printing ink is coated with protective paint in a rubber roller coating mode, and the protective paint is baked and cured through a rear-end drying room; the printing ink is printed on the metal flat plate in a waterless offset printing mode, coating bottoming does not need to be conducted on the surface of the metal flat plate, waste fountain solution is not generated in the printing process, meanwhile, volatilization of pungent volatile organic compounds on the printing site is reduced, and the printing mode has the good environment-friendly performance.

Description

Technical Field

[0001] The invention belongs to the technical field of printing methods, and in particular relates to a method for printing a boiling-resistant metal flat plate without primer. Background Art

[0002] The offset lithography process is the most widely used printing process for metal plates used for food packaging. The offset lithography process currently available on the market includes the following steps: first, a primer is formed on the surface of the metal plate by roller coating, then the image is printed by offset lithography, and then a glossy oil layer is applied to the surface of the metal plate after the printed image by roller coating, and the glazing process is used to achieve the effect of protecting the surface of the printed product. This type of offset lithography process applies a primer at the beginning of printing, and the primer increases the printing cost and increases the emission of volatile organic compounds. However, if the primer is not used, printing directly on the surface of plain iron will cause the ink layer to have unstable adhesion and there is a risk of whitening of the coating after the finished product is sterilized at high temperature. Summary of the invention

[0003] In view of the above shortcomings, the technical problem to be solved by the present invention is to provide a boiling-resistant metal flat plate primer-free printing method for realizing direct printing on plain iron, reducing printing costs and reducing volatile organic compound emissions.

[0004] In order to solve the above technical problems, the technical solution adopted by the present invention is: A method for printing a boiling-resistant metal flat plate without primer, comprising the following steps: S1, performing corona discharge treatment on the metal plate to remove the oil film on the surface of the metal plate; S2, printing ink on the metal plate by waterless offset printing to form a waterless offset printing layer, and solidifying the ink; S3, apply protective paint on the ink surface by roller coating, and then cure it in the back-end drying room.

[0005] As a preferred solution of the present invention, step S1 further includes the following steps: S1.1, the metal plate is placed under the electrode, and the distance between the electrode and the metal plate is 3~5cm, S1.2, a voltage of 10-15 kV is applied to the electrode, and the electrode treats the oil film on the surface of the metal plate; S1.3, when the electrode is discharging, the metal plate is translated relative to the electrode at a speed of 3600~5000m / h.

[0006] As a preferred solution of the present invention, the printing temperature in step S2 is 22°C to 30°C, and the ambient temperature of metal flat plate printing is 15°C to 30°C.

[0007] As a preferred embodiment of the present invention, step 2 comprises the following steps: S2.1, printing an ink-repellent layer and an ink-receptive layer on the surface of the metal plate according to the pattern; S2.2, the ink is transported to the metal plate through a printing press, and the ink is printed on the metal plate through the ink-receptive layer.

[0008] As a preferred embodiment of the present invention, the ink in step S2 uses VT-LED waterless offset printing ink produced by Zhaoqing Yingke Chemical Co., Ltd., and 2% (w / w) of detackifier is added to the VT-LED waterless offset printing ink, and the detackifier includes 90% (w / w) propoxylated glyceryl triacrylate and 10% (w / w) silica.

[0009] As a preferred embodiment of the present invention, the ink in step S2 has a tinting strength of 100%-110%, a viscosity of 6-10S, a fineness of ≤5µm, and a fluidity of 27-37mm.

[0010] As a preferred embodiment of the present invention, in step S2, the ink is cured by LED illumination, the LED light source intensity is ≥8W / cm2, and the printed surface absorption energy value is ≥300mj / cm2 As a preferred embodiment of the present invention, the protective paint in step S3 adopts golden paint of model 3NX220507 produced by Suzhou Sanxin Material Technology Co., Ltd., and 3-6% diluent is added to the golden paint, and the diluent includes 40-70% (w / w) of xylene, 20-30% (w / w) of n-butanol, and 25-35% (w / w) of cyclohexanone.

[0011] As a preferred embodiment of the present invention, the viscosity of the protective paint is 110-150S.

[0012] As a preferred embodiment of the present invention, the coating amount of the protective paint is 6 g / ㎡~9 g / ㎡.

[0013] The beneficial effect of the present invention is that the ink is printed on the metal plate in the form of waterless offset printing, and there is no need to coat the surface of the metal plate with a primer. No fountain solution waste is generated during the printing process, and the pungent volatile organic matter volatilization at the printing site is reduced, so that the printing method has better environmental protection performance. DETAILED DESCRIPTION

[0014] The present invention is further described below.

[0015] A method for printing a boiling-resistant metal flat plate without primer, comprising the following steps: S1, corona discharge treatment is performed on the metal plate to remove the oil film on the metal plate surface. This corona discharge treatment is used to remove the oil film formed by DOS oil on the metal plate surface (DOS oil is dioctyl sebacate, molecular formula C 26 H 50 O4).

[0016] S2, printing ink on the metal plate by waterless offset printing to form a waterless offset printing layer, and solidifying the ink; S3, apply protective paint on the ink surface by roller coating, and then cure it in the back-end drying room.

[0017] The ink is printed on the metal plate in the form of waterless offset printing. There is no need to coat the surface of the metal plate with a primer. No fountain solution waste is generated during the printing process. At the same time, the pungent volatile organic matter volatilization at the printing site is reduced, making this printing method have better environmental performance.

[0018] Step S1 also includes the following steps, S1.1, place the metal plate under the electrode, ensuring that the distance between the electrode and the metal plate is 3~5cm; S1.2, a voltage of 10-15 kV is applied to the electrode, and the electrode treats the oil film on the surface of the metal plate; S1.3, when the electrode is discharging, the metal plate is translated relative to the electrode at a speed of 3600~5000m / h.

[0019] When high voltage is applied to the electrode, a large amount of plasma gas and ozone will be generated at the end of the electrode to interact with the molecules of the DOS oil film on the surface of the metal plate, so that polar groups such as carbonyl and nitrogen-containing groups are generated on the molecular chain of the DOS oil film on the surface of the metal plate. The surface tension of the DOS oil film is significantly increased, and the strong impact of plasma gas will coarsen the surface of the high metal plate, remove oil, water vapor and dirt, etc., so that the adhesion firmness of the metal plate surface to the ink, ink-repellent layer and ink-receptive layer in the subsequent process is significantly improved.

[0020] In step S1, the metal plate is MR type tin-plated tinplate or chrome-plated iron that meets the requirements of GB / T2520, with a thickness of 0.19-0.23 mm, a hardness range of T3.5-T4, and an annealing method of BA grade bright annealing or CA grade bright annealing. When the metal plate is MR type tin-plated tinplate, the tinning amount of the tin-plated tinplate is ≤5.6 g / ㎡, the surface state is R1 surface, and the DOS oil spraying amount on the inner and outer surfaces is controlled at 1.5-3.5 mg / ㎡.

[0021] Step 2 includes the following steps, S2.1, customizing a printing plate according to the pattern, setting an ink-repelling area and an ink-receptive area on the printing plate, the ink-repelling area is used to print an ink-repelling layer, and the ink-receptive area is used to print an ink-receptive layer, and the ink-repelling layer and the ink-receptive layer are formed by printing on the surface of a metal flat plate through the printing plate, the ink-repelling layer is made of ink-repelling silicone rubber material, and is used to form a blank part of the printed pattern, and the ink-receptive layer is made of ink-receptive photosensitive material, and is used to form the graphic part of the printed pattern; S2.2, the ink is transported to the metal plate through the printing press, and due to the effect of the ink-repellent layer and the ink-receptive layer, the ink is printed on the ink-receptive layer, so that the ink is printed on the metal plate; S2.3, curing the ink by light.

[0022] The printing process of step S2 does not use fountain solution, which can prevent water vapor in the fountain solution from remaining on the surface of the iron sheet, thereby ensuring that the ink-repellent layer and the ink-receptive layer are wrapped between the iron sheet and the protective paint, reducing the problem of water mist and whitening in the finished product during the high-temperature sterilization process.

[0023] The ink in step S2 uses VT-LED waterless offset printing ink produced by Zhaoqing Yingke Chemical Co., Ltd., and 2% (w / w) of detackifier is added to the VT-LED waterless offset printing ink. The detackifier includes 90% (w / w) propoxylated glycerol triacrylate and 10% (w / w) silicon dioxide. The detackifier can reduce the viscosity and wire drawing of the ink, which is beneficial to ink transfer and printing clarity. Using VT-LED waterless offset printing ink can reduce VOCs emissions, and can be matched with lithographic waterless offset printing plates to achieve ink transfer.

[0024] The ink in step S2 has a tinting strength of 100%-110%, a viscosity of 6-10S, a fineness of ≤5µm, and a fluidity of 27-37mm.

[0025] The printing temperature of the printing plate used for printing the ink-repellent layer and the ink-receptive layer and the ink roller used for printing ink in steps S2.1 and S2.2 is 22°C~30°C, and the ambient temperature for metal plate printing is 15°C~30°C. At this temperature, better adhesion between the ink-repellent layer, the ink-receptive layer and the metal plate can be ensured.

[0026] In step S2.3, the curing is performed by UV light curing, and the light source intensity is ≥8W / cm 2 , the printed surface absorbed energy value ≥ 300mj / cm 2 The intensity of the light source and the energy absorbed by the printing surface combined with the ink in step 2 can ensure better adhesion between the metal plate and the ink layer.

[0027] In step S3, the protective paint includes ethylene glycol butyl ether, ethylene glycol butyl ether, xylene, n-butanol, and S-100 aromatic solvent, with a solid content of 33-37 wt %, and a coating amount of the protective paint of 6 g / ㎡-9 g / ㎡.

[0028] In order to adapt the protective paint to different appearance color effects, the protective paint uses golden paint model 3NX220507 produced by Suzhou Sanxin Material Technology Co., Ltd., and adds 3~6% diluent to the golden paint. The diluent includes 40~70% (w / w) of xylene, 20~30% (w / w) of n-butanol, and 25~35% (w / w) of cyclohexanone, with a viscosity of 110~150S, to ensure that the protective paint has better construction performance.

[0029] The construction viscosity of the protective paint is 110~150S, the baking temperature of the metal plate is 200~205℃, and the baking time is maintained for 10~12 minutes. After the construction is completed, the surface hardness of the protective paint is the hardness of a 2H pencil.

[0030] The scratch resistance of the protective paint coating on the surface is ≥1000g, which ensures the adhesion and strength of the metal plate, ink and protective paint, and avoids damage to the coating caused by subsequent processing. The high temperature sterilization ability meets the requirements of 121℃×60min boiling. The coating turns white or changes color after surface sterilization.

[0031] After the metal plate printing is completed, the following tests are performed.

[0032] (1) Surface hardness test: The surface hardness test is carried out using a Zhonghua brand pencil in accordance with GB / T6739, and the hardness test value is ≥2H.

[0033] (2) Adhesion test: 3M #610 tape was used in accordance with GB1720-1979. The adhesion grade of the printed layer was Grade I.

[0034] (3) Surface scratch resistance test method: Use the British brand SHEEN hardness tester, place a 150mm×100mm sheet sample with the coating facing upward on the flat plate of the instrument, add weights, and move the flat plate from left to right at a constant speed. The weight of the weight without exposing the bottom is used as the standard for the hardness of the coating. The scratch resistance refers to ≥1000g.

[0035] (4) Solvent resistance (MEK) test method: refer to the industry standard QB / T 2763-2006 for coating tin (or chromium) thin steel plates, use the instrument RJCS solvent resistance tester, wipe the contact surface diameter 14mm±0.5mm, wipe the stroke 12cm±0.5cm, wipe the frequency (60±5) times / minute, and record the number of wipes when the metal plate is exposed to the substrate. The test result is ≥50 times.

[0036] (5) Impact resistance test method: Take a 120mm×120mm sheet sample, put it into the instrument slot with the dry film surface of the tested surface facing down, and use a 1kg hammer to impact the iron sheet from a height of 100cm to form a semi-convex circle. The steel substrate should not be damaged during the impact process. The front and back of the same test piece should be impacted twice. Immerse the sample cover in a 20% copper sulfate solution (containing 10% hydrochloric acid) for 2 minutes, then take it out, wash and dry it, and observe the corrosion condition of the impact stretching area with the help of a 16x magnifying glass. There is no continuous corrosion, and the number of corrosion points is ≤15 (corrosion with a diameter of φ≤0.5mm is referred to as corrosion points).

[0037] (6) High temperature sterilization test method: refer to the industry standard QB / T 2763-2006 for coating tin (or chromium) thin steel plates, fold the sample repeatedly into squares with a spacing of 3 cm, immerse two samples in an inert container filled with distilled water, and place the other two samples in an inert container without water. Place the test container in a vertical pressure steam sterilizer, heat to 121°C and keep it for 60 minutes (higher than the industry standard requirement of 30 minutes), naturally reduce the pressure and cool, take out the sample, and observe the coating condition. After the test, the coating of the product with outer wall has no bubbles, no shedding, no discoloration, and no whitening.

[0038] The above description of the disclosed embodiments enables one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention; therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

[0039] Although more terms are used in this article, the possibility of using other terms is not excluded; these terms are used only to more conveniently describe and explain the essence of the present invention; interpreting them as any additional limitations is contrary to the spirit of the present invention.

Claims

1. A method for printing a boiling-resistant metal flat plate without primer, characterized in that: The following steps are included: S1, performing corona discharge treatment on the metal plate to remove the oil film on the surface of the metal plate; S2, printing ink on the metal plate by waterless offset printing to form a waterless offset printing layer, and solidifying the ink; S3, apply protective paint on the ink surface by roller coating, and then cure it in the back-end drying room.

2. A method for printing a boiling-resistant metal flat plate without primer according to claim 1, characterized in that: The step S1 also includes the following steps: S1.1, the metal plate is placed under the electrode, and the distance between the electrode and the metal plate is 3~5cm, S1.2, a voltage of 10~15kV is applied to the electrode, and the electrode processes the oil film on the surface of the metal plate. When the electrode discharges, the metal plate moves relative to the electrode at a speed of 3600~5000m / h.

3. The method for printing a boiling-resistant metal flat plate without primer according to claim 1, characterized in that: The printing temperature in step S2 is 22° C. to 30° C., and the ambient temperature for metal plate printing is 15° C. to 30° C.

4. The method for printing a boiling-resistant metal flat plate without primer according to claim 1, characterized in that: The step 2 comprises the following steps, S2.1, printing an ink-repellent layer and an ink-receptive layer on the surface of the metal plate according to the pattern; S2.2, the ink is transported to the metal plate through a printing press, and the ink is printed on the metal plate through the ink-receptive layer.

5. The method for printing a boiling-resistant metal flat plate without primer according to claim 1, characterized in that: The ink in step S2 is VT-LED waterless offset ink, and 2% (w / w) of a detackifier is added to the VT-LED waterless offset ink. The detackifier includes 90% (w / w) propoxylated glyceryl triacrylate and 10% (w / w) silicon dioxide.

6. The method for printing a boiling-resistant metal flat plate without primer according to claim 1, characterized in that: The ink in step S2 has a tinting strength of 100%-110%, a viscosity of 6-10S, a fineness of ≤5µm, and a fluidity of 27-37mm.

7. The method for printing a boiling-resistant metal flat plate without primer according to claim 1, characterized in that: In step S2, the ink is cured by LED light, and the LED light source intensity is ≥8W / cm 2 , the printed surface absorbed energy value ≥ 300mj / cm 2 .

8. The method for printing a boiling-resistant metal flat plate without primer according to claim 1, characterized in that: In step S3, the protective paint is golden paint, and 3-6% of a diluent is added to the golden paint. The diluent includes 40-70% (w / w) xylene, 20-30% (w / w) n-butanol, and 25-35% (w / w) cyclohexanone.

9. A method for printing a boiling-resistant metal flat plate without primer according to claim 8, characterized in that: The viscosity of the protective paint is 110-150S.

10. The method for printing a boiling-resistant metal flat plate without primer according to claim 1, characterized in that: The coating amount of the protective paint is 6g / ㎡~9g / ㎡.