Aluminum Paper Offset Printing Process

Composite paper is a popular packaging and decorating material at present. As a printing material, composite paper mainly includes aluminum foil composite paper (gold.silver cardboard), aluminized paper and the like. Among them, aluminum foil composite paper can not be recovered as aluminum products and can not be recycled as paper, and is gradually being replaced by environmentally friendly aluminum-plated paper. At present, aluminum-plated paper has been widely used in the packaging and labeling of products such as cold drinks, foods, alcoholic drinks, and soft drinks.

Aluminized paper is different from ordinary paper. In the printing process has its uniqueness, the printing methods that can be used include gravure printing, offset printing, screen printing and flexo printing. Offset printing is widely used because it has the advantages of easy plate making, clear dots, fast printing speed, and low cost. Aluminizing paper offset printing is different from paper offset printing. The following issues must be noted in print production.

Reasonable choice of aluminized paper
Aluminizing paper for printing must have the following characteristics: bright surface, no impurities and air bubbles, good uniformity of the same batch of products: high surface strength, strong bonding of aluminum film and base paper, good peeling resistance: the surface tension must reach 3 8× 10 -2 N/m or more. Due to the different application areas of printed materials, aluminum-plated paper should also meet certain special requirements.

(1) Liquor labels
Labels for printing recyclable liquor and beverage products. Alkaline-resistant, bottled, aluminum-plated papers with good bottle-washing properties and high wet strength should be selected.

(2) Food Packaging
Aluminum-plated paper used for fast food, dairy products and pharmaceutical packaging should be odorless, non-toxic and conform to FDA standards; aluminum-plated paper used for candy packaging should also have good fastness of aluminum layer, and it should not be dealuminated during kinking. The base paper does not contain the characteristics of fluorescent brighteners.

(3) Tobacco and wine packaging
Aluminized paper for cigarette hard packs and alcoholic beverages should have high gloss, good smoothness, and be suitable for embossing, die-cutting, embossing and embossing processing. It is odorless, non-toxic, and conforms to the US FDA standards.

In addition, since the white ink will be yellow after printing on aluminized paper, silver composite paper should be used when printing white ink.

Determination of design plate and printing process
For the self-designed prints, in order to improve the visual impact, the use of aluminized paper printing in the form of a combination of color blocks, lines, text, patterns, highlighting the characteristics of the metal color. And according to the design intent to put forward the specific requirements of printing and copying, such as which ink should be transparent, which color should be translucent or opaque, which is to highlight and so on.

(1) Printing on the metal surface
When printing lines, white or transparent text on the metal surface, in order to increase the contrast and color saturation. Design should use black. White and other colors are matched properly, for example, the theme text and adjacent background are all made of transparent ink, inlaid with black, white or dark borders. Make the text more noticeable.

(2) Avoid large areas on the ground
To avoid large-area on-site color registration, it is advisable to use the stencil printing process. To prevent the junction metal color exposure. The text and pattern should be scaled in advance, depending on the accuracy of the text pattern overlay.

(3) Handle complicated and small text patterns
Miscellaneous and small text patterns overprinting each other can easily result in difficulties in overprinting. It should be changed to a spot-colored version of Yangyu or Yinyin, and boldly typefaces should be used to prevent the disconnection of Yang characters and negative characters.

(4) Smooth surface printing
Aluminized paper has a smooth surface, less ink absorption, dark-adjustable dots and easy-to-paste printing, small dots are not easy to ink, and plate-making should use coarse mesh of 150 lines/inch or less.

(5) Label Printing
When printing wine labels, in order to make the post-process labeling not roll, the layout of the aluminized paper should be perpendicular to the bottle (container).

(6) Background printing
Due to the color of the metal surface of the aluminized paper, in order to ensure the correct reduction of the hue of the ink, the background color (white) must be printed first. On the one hand, the metal color can be covered, and on the other hand, the polar groups of the white ink can be used to increase the surface. Adsorption capacity. If printing a white ink can not cover the metal color, you can use the original version of the second overprint white ink.

(7) Printing color sequence
In the arrangement of printing color sequence, the field printing should be shallow and deep. The more appropriate printing color sequence is generally white (or opaque light color) and black (or other dark color, overlaid text with a high requirement for overprinting, line color blocks). A large area of ​​the main tone background (cyan, magenta, Yellow, transparent color, etc.)

Offset press selection
Because the surface of the aluminized paper is dense and has strong barrier properties, the aluminum-plated paper cannot effectively eliminate air when a large area is printed on the ground. In order to avoid the failure of the imprinting, the circular press-type line contact printing press should be used.

When printing color patterns. It is best to use a four-color or five-color machine to complete overprinting once and finally spray the powder. If there are no multi-color printing equipment, when using multi-color printing with a single-color or two-color printing machine, attention should be paid to the amount of powder to be sprayed, and the amount of powder to be sprayed should be minimized under the condition of non-stick back, so as not to affect the next color printing.

Selection of ink
Since aluminum-plated paper is a non-absorbent material, it should be used oxide-conjunct dry-type offset ink, or uV ink. And require high color density, vividness, good gloss: water resistance, good drying: good transferability and on-board stability; high color fastness, good rub resistance and light resistance; ink viscosity should be better than ordinary paper printing The ink is slightly lower.

Aluminium paper offset printing inks of choice for domestic brands include: Baolong POP composite paper ink of Shenzhen Shenri Dlc Ink Co., Ltd.; Tiens TsP composite paper ink of Tianjin Toyo Ink Co., Ltd.: Meining of Guangdong Meining Ink Group Co., Ltd. AG type offset composite paper ink; Hangzhou Hanghua Ink Co., Ltd. Hanghua JP aluminum foil offset printing ink.

When selecting the ink, the printing effect and the printing cost must also be taken into consideration. The primary ink or the prepared spot ink should be used for printing.

When printing gold graphic on the silver composite paper surface, transparent yellow and j lighter can be used instead of gold ink for direct printing.

Silver white aluminized paper is printed white, if adding O.05% purple or sky blue ink to white ink, can greatly improve the visual whiteness. Try to use the same manufacturer to use the same series of inks to mix spot colors, and try to use a primary ink that is closest to the spot color as the main color, and then add a secondary color to match it. The fewer the matching types, the better the color performance.

For the alp coated paper printing of wine labels, some printing manufacturers use ordinary light fast solid offset printing ink and white dry oil printing, but the drying speed is slow, easy to stick flowers, etc., there should be enough printing experience to consider the choice. After a reasonable selection of printed materials and printing processes, it is necessary to adjust the printing materials and accessories in accordance with the printability requirements of aluminum-coated paper.

(1) Reasonable control of fountain solution

Aluminized paper is a non-absorbent material. It is recommended to use a mixture of alcohol and water (15% to 25% alcohol) to minimize the amount of water on the premises. And to prevent its acidity is too large, resulting in ink drying is too slow, it is recommended to adjust the pH of the fountain solution to 5 ~ 6 is appropriate.

(2) Packing and pressure selection

According to the characteristics of aluminum-plated paper, it is possible to use stiffer liners, flexible air-cushioned blankets, and the use of the same thickness of whiteboard paper, in order to achieve a slightly greater printing pressure, to a certain extent, to make up for the hard surface of the aluminized paper, Poor adsorption, printing grade easy to appear the phenomenon of sticky dirt, so that the blanket and paper more closely. In order to facilitate the reduction of the network and ink absorption, transfer.

(3) Temperature and humidity control
The drying speed of the ink, the paper feeding process, and the ambient temperature are closely related. the experiment shows. For each 10°C increase in temperature or a 10% drop in relative humidity, the ink drying time is reduced by approximately half. In order to fully contact the vegetable oil in the ink layer with oxygen, accelerate the speed of oxidation, polymerization, and drying of the ink layer; at the same time, in order to avoid static electricity during the paper feeding process, the ambient temperature is 22 to 28°C and the relative humidity is 50% to 60%. It is advisable that offset printing plants equipped with air-conditioning devices generally meet these requirements.

(4) Reasonable printing speed
According to the ink transfer rate and the actual condition of the sample inspection, change paper holder, etc., the initial printing speed should be 3000--4000 sheets/hour.

(5) to adjust the ink adhesion of the ink viscosity <br> <br> Metallized paper is generally low. If the ink is too thick, an appropriate amount of special adjustment ink must be added. Otherwise, the ink may not be printed on or insufficient due to the adsorption force of the ink and the blanket being much larger than the adsorption force of the ink and the aluminized paper. In addition, when performing wet overprinting, in order to prevent overprinting or cross-coloring, a small amount of retreating agent should be added to the ink of the latter color to adjust the viscosity of the latter color ink to be slightly lower than that of the previous color ink.

(6) Adjustment of ink dryness
Ink manufacturers have designed a strong drying property for inks, but due to different ink layer thickness, printing conditions, or when using a new brand of ink, the dryness of the original ink must be sampled and tested according to actual production conditions before printing. Make appropriate adjustments. Under normal circumstances, you can add appropriate amount of red oil or white dry oil adjustment, in order to ensure that the ink roller does not dry knot, the print is not sticky under the premise of the drying time is controlled at 6-8 hours is more appropriate.

(7) Sample inspection
The surface reflectivity of the aluminized paper is extremely high. The difference in light intensity, light source, and observation angle will directly affect the judgment of the ink color. It is best to perform color correction, printing, and careful sample inspection in daylight.

(8) Appropriate amount of dusting, reasonably stacking prints

Aluminized paper prints are very prone to stickiness. Appropriate amount of dusting and proper stacking of the prints help the oxygen to enter between the papers and promote the solidification of the ink layers to avoid sticking faults. Therefore, the printing should be based on the actual printing area and paper specifications, under the premise of guaranteeing no stickiness, to minimize the amount of dusting, flexible control of stacking height, such as printing area of ​​70% 350g/