What is Gravure Printing? Its Process, Advantages, Challenges

What is Printing?

Printing is replicating the visual and textual content through direct or indirect means.

Printing Classifications

Printing can be classified into several categories based on different criteria. Here are some common classifications of printing:

Normal Printing

• Normal printing
• Gravure printing
• Letterpress printing
• Planographic printing
• Porous printing

Special Printing

• Electrostatic printing
• Magnetic printing

What is Gravure Printing?

Gravure printing is a direct printing method that involves filling the entire printing plate with ink, removing excess ink using a specialized scraping mechanism, and retaining ink only within the ink cells corresponding to the image and text. The ink is then transferred onto the printing substrate under substantial pressure to achieve the desired print. In gravure printing, the image and text elements are recessed or concave, with the depth of the recess varying based on the image hierarchy. The non-image areas of the print surface remain raised and are in the same plane.

There are four main printing methods, and gravure printing is one of them. Gravure printing is a direct printing process where ink is directly transferred from the ink cells to the printing substrate. The gradation of colors in gravure printing is determined by the size and depth of the ink cells. Deeper cells hold more ink, resulting in thicker ink layers on the printing substrate. Conversely, shallow cells hold less ink, resulting in thinner ink layers on the substrate.

The printing cylinder used in gravure printing consists of cells that correspond to the image and text, as well as a surface area. Ink is filled into the cells, excess ink on the surface is scraped off by a doctor blade, and under a certain pressure between the printing cylinder and the printing substrate, the ink is transferred from the cells to the substrate. This completes the gravure printing process.

Gravure printing holds a significant position in the printing, packaging, and graphic publishing industries due to its advantages, including thick ink layers, vibrant colors, high color saturation, excellent cylinder durability, stable print quality, and fast printing speed. Gravure printing is widely used in flexible packaging, and with advancements in gravure technology, it has also found applications in paper packaging, wood decoration, leather materials, and pharmaceutical packaging.

However, gravure printing does have limitations. It requires complex prepress plate-making techniques, has a lengthy production process, involves high costs for printing cylinders, and can pose health risks to workers if volatile solvents are used, which can release harmful gases. Additionally, gravure printing can cause significant environmental pollution.

Gravure Printing Classifications

Gravure printing can be classified into two types based on the plate-making method: engraved gravure printing and etching gravure printing.

• Engraved gravure printing involves the use of a mechanical engraving process to create the image and text on the printing cylinder. The desired design is physically engraved onto the cylinder surface using a diamond stylus or laser engraving technology. This process creates the recessed cells that hold the ink for printing.
• Etching gravure printing, on the other hand, utilizes a chemical etching process to create the image and text on the printing cylinder. The cylinder surface is coated with a photosensitive resist, and the design is transferred onto the resist using photographic techniques. The cylinder is then exposed to chemicals that selectively etch away the unexposed areas, forming the ink cells.

Both engraved and etching gravure printing methods have their advantages and are suitable for different applications. Engraved gravure printing is known for its precision and ability to reproduce fine details, making it ideal for high-quality and high-resolution prints. Etching gravure printing, on the other hand, offers greater flexibility and is well-suited for printing large areas of solid colors or gradients.

5 factors for printing

There are several factors that can impact the quality and effectiveness of the printing.

Original Pattern

Original pattern refers to the printed object that encompasses various elements such as text, illustrations, photographs, and even compact discs.

Printing Cylinder

Printing cylinder is the medium through which the image-text is transferred during the gravure printing process. It is a cylindrical object composed of a material that can accurately reproduce the details of the original pattern. In gravure printing, the original pattern is often referred to as continuous tone due to its ability to reproduce smooth gradients and intricate details with high precision.

Ink

Ink is the primary material used to create the printed image-text. In gravure printing, the ink is formulated with several components, including solid resin, volatile solvent, pigment, filling materials, and additives. It is important to note that vegetable oil is not commonly used in gravure printing inks, and most drying methods rely on volatile substances.

Substrate

Substrate is the material that supports the ink transferred from the cylinder, resulting in the formation of the image-text. What distinguishes gravure printing significantly from other printing methods is that the image-text is composed of cells that are lower in height compared to the non-image areas.
In gravure printing, the cylinder is typically made of metal materials, such as steel or copper. The outer surface of the cylinder is often treated with chrome plating or copper plating to enhance its durability and ensure consistent ink transfer during the printing process.

Printing Machine

The printing machine is the equipment used for the printing process. It typically consists of 8 main components, which are as follows:

• Unrewind Unit: This part is responsible for unwinding the substrate from a roll and feeding it into the printing machine.
• Guide Roller: The guide roller helps to guide and maintain the proper alignment of the printing stock as it moves through the machine.
• Compression Roller: The compression roller applies pressure to ensure proper contact between the printing stock and the printing cylinder, facilitating the transfer of ink.
• Printing Roller: The printing roller, also known as the printing cylinder, carries the image text and transfers the ink onto the printing stock during the printing process.
• Inking Part: The inking part is responsible for applying ink to the printing cylinder, ensuring a consistent and controlled ink supply for the printing process.
• Doctor Blade: The doctor blade is used to scrape off excess ink from the surface of the printing cylinder, ensuring that only the ink within the cells is transferred to the printing stock.
• Dryer: The dryer helps to rapidly dry the printed ink on the substrate, allowing for efficient and timely processing of the printed materials.
• Winding Unit: The winding part collects and winds the printed materials onto a roll or spool, ready for further processing or distribution.

Additionally, some printing machines may include additional systems, such as a dynamical system for controlling machine movements, a calibration system for maintaining precise printing parameters, and an electrical system for powering and controlling the machine’s various components.

Gravure Printing Manufacturing Technique

Thanks to the high level of automation in printing machines and the superior quality of the cylinders, the technological operation in gravure printing is generally considered easier compared to planographic printing methods. The gravure printing process can be divided into three main stages: preparation before printing, actual printing, and post-printing tasks.

Preparation before Printing

This stage involves various tasks to ensure the printing process runs smoothly. It includes tasks such as preparing the printing stock and ensuring it is properly aligned and tensioned, installing the printing cylinder onto the machine, adjusting the doctor blade position and pressure, and setting up the ink supply system. Additionally, any necessary color calibration or registration adjustments are made during this stage.

Subtrate

The primary substrate used in gravure printing is plastic film, which commonly includes materials such as polyethylene (PE), polypropylene (PP), and polyvinyl chloride (PVC), among others. Plastic films usually have a glossy surface that poses challenges for ink adhesion. To overcome this, a corona treatment is performed on the film prior to printing.

During the corona treatment process, the plastic film is passed between two electrodes, and high-frequency oscillation pulses are applied to create an ionization discharge phenomenon. This discharge generates free oxygen atoms that combine with oxygen molecules in the air, producing ozone. The ozone reacts with the surface of the film, creating strong chemical groups and microscopically roughening the surface, creating invisible “burrs.”

This corona treatment increases the surface tension and roughness of the plastic film, enhancing its wettability and promoting better adhesion of ink and adhesives. The modified surface allows the ink to spread evenly and adhere more effectively, resulting in improved print quality and durability.

The corona treatment process is crucial for ensuring successful printing on plastic films, as it helps to overcome the inherent low surface energy of these materials and facilitates proper ink adhesion, thus achieving reliable and high-quality print results.

Ink

Gravure printing utilizes solvent-based inks that are volatile, and have low viscosity, good flowability, and strong adhesion properties. Commonly used solvents in gravure printing include methylbenzene, xylene, gasoline, and alcohol, among others.

Before printing, it is common practice to add a suitable diluent solvent to the ink to achieve the desired viscosity and flow characteristics. This helps in achieving optimal ink transfer and consistent printing results. It is advisable to filter the ink before use to remove any impurities or particles that may affect the print quality.

By using solvent-based inks with the appropriate solvent composition and viscosity, gravure printing can achieve excellent ink transfer, allowing for vibrant and durable prints on various substrates. The solvent properties ensure efficient drying and fast evaporation, contributing to high-speed printing and production processes.

Doctor Blade

The doctor blade in a gravure printing machine is a crucial component made of special steel. Its primary function is to scrape off excess ink from the surface of the printing cylinder. The doctor blade plays a vital role in maintaining precise ink application and preventing unwanted ink buildup.

Typically, the doctor blade has a width ranging from 60mm to 80mm and a length between 1000mm and 1500mm, depending on the size of the cylinder. It is important for the blade to be straight and free from any deformities or irregularities. A crescent-shaped scar or defect on the blade can result in the formation of wide-slanted stripes on the printing stock, leading to an undesirable phenomenon known as the “empty bar.”

To achieve optimal print quality, it is crucial to ensure the doctor blade is in excellent condition and properly aligned. Regular inspection and maintenance of the doctor blade, including replacement when necessary, help to avoid printing issues caused by improper ink control.

By maintaining a straight and defect-free doctor blade, gravure printing machines can effectively control ink application, resulting in consistent and high-quality prints without the presence of unwanted stripes or empty bars on the printing stock.

Cylinder

The cylinder is the foundation of the printing process, and it directly influences the printing quality. Therefore, it is essential to thoroughly inspect the cylinder before making any adjustments. Several key factors should be checked to ensure optimal performance.

• Firstly, it is crucial to examine the dots on the cylinder and ensure they are in the correct order and complete. Any irregularities or missing dots can significantly impact the printed image and overall quality.
• Secondly, the cylinder’s surface must be inspected for any signs of chromium removal. The chromium layer plays a vital role in maintaining the durability and smoothness of the cylinder. If there is any indication of chromium loss or damage, it can affect the cylinder’s performance and compromise the quality of the printed text and lines.
• Lastly, the text cylinder and line on the cylinder should be examined for intactness. Any damage or inconsistencies in the text or lines can result in distorted or incomplete prints.

Before installing the cylinder onto the printing machine, it is crucial to recheck all these factors to ensure the cylinder’s integrity and suitability for the printing process. By conducting a thorough inspection, any issues or defects can be identified and addressed, leading to improved printing quality and consistent results.

Special precautions should be taken to ensure the protection of the cylinder during installation. The following steps should be followed:

• Aligning the jaws: Carefully align the jaws of the printing machine with the cylinder. This alignment is crucial to ensure proper engagement and prevent any damage to the cylinder during installation.
• Push and pull: Use appropriate techniques to push or pull the cylinder into place. Apply gentle and controlled force to avoid any excessive pressure or mishandling that may cause damage.
• Fastening the cylinder: Once the cylinder is properly positioned, securely fasten it to the printing machine. Use the designated fastening mechanisms, such as bolts or clamps, to ensure a tight and stable connection. This helps prevent the cylinder from loosening during the actual printing process.
• Preventing loosening: Take measures to ensure the cylinder remains securely in place throughout the printing job. Regularly inspect the fastening mechanisms and tighten them if necessary. This helps maintain stability and prevents any unwanted movement or vibrations that could lead to cylinder loosening.

By following these precautions, the cylinder can be installed safely and securely onto the printing machine, reducing the risk of damage and ensuring stable and reliable printing operations.

Printing

Once the preparation is complete, the printing machine is set in motion. The printing stock is fed into the machine, guided by rollers, and comes into contact with the inked printing cylinder. The ink is transferred from the cylinder onto the printing stock, and the desired image-text is formed as the substrate passes through the machine. The process is highly automated, with the machine handling the precise movements and pressure required for consistent and accurate printing.

During the printing process, it is important to frequently check the samples to ensure the quality of the prints. The following aspects should be examined:

Dot Completeness

Regularly inspect the printed samples to ensure that the dots are complete and accurately reproduced. Any missing or distorted dots may indicate issues with the plate, cylinder, or ink application.

Overprint accuracy

Check the overprint alignment of the colors or layers in the printed samples. Accurate overprinting ensures the correct registration and alignment of different elements, such as text, images, or colors.

Ink Brightness

Assess the brightness and vibrancy of the ink on the printed samples. The ink should exhibit the desired color intensity and should not appear dull or faded.

Ink Viscosity and Drying

Monitor whether the viscosity and drying characteristics of the ink match the printing speed. Inks with incorrect viscosity may lead to issues such as improper ink transfer or ink buildup, while inadequate drying can result in smudging or poor print quality.

Printing Paper Issues

Examine the printed samples for any traces, blade lines, or broken edges that may be caused by uneven scraping of the doctor blade. Uneven scraping can lead to inconsistencies in ink application, resulting in undesirable artifacts on the printed material.

By frequently checking these aspects during the printing process, any deviations or problems can be identified promptly. This allows for timely adjustments, ensuring consistent print quality and addressing any issues that may arise during production.

Settle after Printing

After the printing process is complete, there are several tasks to be carried out. These may include drying the printed materials using the dryer, inspecting the printed output for quality control purposes, and conducting any necessary post-printing finishing or packaging operations. Proper maintenance and cleaning of the machine and printing cylinders are also important in this stage to ensure their longevity and optimal performance.

Property of Gravure Printing

In gravure printing, the ink carrier is comprised of cells that are engraved onto the cylinder. These cells possess distinct properties that set them apart from other printing methods.
The unique characteristics of the ink carrier cells in gravure printing contribute to its ability to produce high-quality prints with exceptional image fidelity and consistency. The precise control over ink application and transfer ensures reliable and visually appealing results across various substrates.

Anti-fake

The ink carrier in gravure printing consists of cells that are engraved on the cylinder based on the original image or text. One of the key advantages of gravure printing is the ability to control the thickness of lines and ink gradations with great precision. This level of control makes it difficult to imitate or forge prints, especially due to the intricate depth of the ink cells.

The depth of the ink cells can be adjusted to achieve specific printing effects, such as fine lines or smooth gradients. This level of detail and complexity makes it extremely challenging to replicate the engraved patterns accurately. As a result, gravure printing is widely used for printing banknotes, stamps, stocks, and other marketable securities, offering a high level of anti-counterfeiting protection.

In fact, some enterprises recognize the security benefits of gravure printing and choose to print their brand or valuable documents using this method. The inherent anti-counterfeiting properties of gravure printing make it a robust choice for creating secure prints.

Gravure printing is a powerful anti-counterfeiting printing method due to its ability to control ink thickness and gradation, as well as the intricate depth of the ink cells. This technique provides enhanced security for various applications, ensuring that printed materials are difficult to forge or replicate accurately.

High Printing Quality

Gravure printing is known for its ink consumption as it requires a significant amount of ink to achieve its characteristic features. It is particularly suitable for printing images and text with a raised, convex appearance, rich gradations, clear lines, and high printing quality. This makes gravure printing a popular choice for various applications, including books and magazines, packaging, and decorative printing.

Mass Printing

The process of cylinder making in gravure printing is known for its lengthy duration, inefficiency, and high cost. However, once the cylinder is made, it offers exceptional durability, making it well-suited for mass printing. The more significant the quantity of prints needed, the higher the potential benefits of gravure printing. As a result, gravure printing is not the most suitable choice for small-batch printing.

Due to the time and cost involved in creating the cylinders, gravure printing becomes economically viable and efficient when producing large quantities of prints. The durability of the cylinders allows for long print runs without compromising print quality, making it advantageous for high-volume production.

Conversely, when it comes to small batch printing, gravure printing may not be the most cost-effective option. The expenses associated with cylinder production and setup outweigh the benefits of smaller print quantities. Other printing methods, such as digital or offset printing, are often more suitable for smaller batches as they offer quicker setup times and lower costs per unit.

It’s important to consider the volume and cost-efficiency when choosing a printing method. Gravure printing shines in large-scale production scenarios where the benefits of durability and mass printing outweigh the initial setup costs and time investment. For smaller batches, alternative printing methods are typically more suitable due to their flexibility, cost-effectiveness, and faster setup times.

Extensive Range of Applications

Gravure printing is well-suited for a wide range of soft materials, including but not limited to plastic film, paper, and aluminum foil. It excels in printing on materials that are prone to stretching and deformation, such as textiles, thanks to its adaptability and precision. The distinctive characteristics of gravure printing set it apart from letterpress printing and planographic printing.

Challenges for Gravure Printing

There are certain challenges associated with gravure printing that need to be addressed.
Gravure printing can be susceptible to various faults or issues arising from the cylinder, ink, printing stock, and doctor blade.

Uneven Ink Graduation

Uneven ink graduation is a common issue that can occur in gravure printing. This refers to inconsistencies in the smooth transition of ink density or color across the printed image.

To address the issue of uneven ink graduation in gravure printing, several methods of exclusion can be applied:

• Correcting Cylinder Roundness
• Adjusting Doctor Blade Angle and Pressure
• Replacing the Doctor Blade

These exclusion methods aim to improve the ink transfer process and enhance the consistency of ink graduation in gravure printing. Correcting cylinder roundness, adjusting the doctor blade angle and pressure, or replacing the doctor blade when necessary can significantly contribute to resolving the issue of uneven ink graduation, resulting in higher print quality and visual appeal.

Fuzzier Marks

Fuzeeire marks typically refer to the presence of fuzzy edges or blurred details in the printed image.

To exclude the occurrence of fuzzy marks in gravure printing, several methods can be employed:

• Removing Static Electricity
• Adding Polar Solvent to Ink
• Increasing Printing Pressure Appropriately
• Adjusting the Position of the Doctor Blade

By employing these exclusion methods, it is possible to minimize or eliminate fuzzy marks in gravure printing. Removing static electricity, incorporating polar solvents into the ink, adjusting printing pressure, and optimizing the doctor blade’s position can greatly contribute to improving print quality, reducing fuzzy marks, and achieving sharper and more defined prints.

Clogging

Clogging in gravure printing refers to the blockage or obstruction of the engraved cells on the printing cylinder.

To address clogging in gravure printing, the following exclusion methods can be employed:

• Increasing Solvent Quantity in Ink
• Reducing the Drying Speed of Ink
• Using Paper with High Surface Strength

These exclusion methods aim to prevent or alleviate clogging issues in gravure printing. Increasing solvent quantity in the ink formulation, reducing ink drying speed, and choosing paper with high surface strength contribute to smoother ink flow, reduced clogging, and improved print quality. However, it is important to carefully evaluate and test these adjustments to ensure they align with specific printing requirements and to maintain the overall print performance.

Ink Overflow

Ink overflow refers to the excessive or uncontrolled flow of ink during the printing process, which can result in unwanted ink spreading beyond the intended areas and causing smudges or blotches.

To exclude the occurrence of ink overflow in printing, several methods can be employed:

• Adding Hard Mixing Ink
• Increasing Ink Viscosity
• Adjusting the Angle of the Doctor Blade
• Increasing Printing Speed
• Replacing Deep-Mesh Cylinder with Shallow-Mesh Cylinder

These exclusion methods aim to minimize or eliminate ink overflow in printing. Adding hard mixing ink, increasing ink viscosity, adjusting the doctor blade angle, increasing printing speed, and using a shallow-mesh cylinder contribute to better ink control, reduced overflow, and improved print quality. However, it is important to carefully evaluate and test these methods to ensure they align with specific printing requirements and to maintain overall printing performance.

Scratching

Scratching in gravure printing refers to the presence of unwanted lines or scratches on the printed material, which can result in compromised print quality.

To exclude the occurrence of scratching in gravure printing, several methods can be employed:

• Use Clean Ink
• Adjust Ink Viscosity, Dryness, and Adhesion
• Use High-Quality Doctor Blade
• Adjust the Angle between Doctor Blade and Cylinder

By implementing these exclusion methods, it is possible to minimize or eliminate scratching in gravure printing. Using clean ink, adjusting ink viscosity, dryness, and adhesion, utilizing a high-quality doctor blade, and adjusting the angle between the doctor blade and cylinder contribute to improved print quality, reduced scratching, and enhanced overall performance. It is essential to carefully evaluate and test these methods to ensure they align with specific printing requirements and to maintain the integrity of the printed output.

Precipitated Pigment

That is color lightening in printing. To mitigate color lightening in print, several methods can be employed:

• Use ink with excellent dispersity and stable performance
• Incorporate anti-coagulation and anti-precipitation additives
• Ensure proper ink rolling and stirring

It’s important to note that achieving desired color results in print involves a combination of factors, including ink formulation, substrate characteristics, printing process parameters, and environmental conditions. Proper ink management, including selecting suitable inks, incorporating additives, and maintaining proper ink handling practices, can contribute to minimizing color lightening and ensuring consistent and vibrant printing results.

Dirty

Dirt or debris in gravure printing, here are some methods to address dirt or debris in gravure printing:

• Use Ink with Fast Evaporation Speed
• Increase Drying Temperature
• Reduce Printing Speed

These exclusion methods aim to minimize or eliminate ink contamination on printed materials. Using ink with a fast evaporation speed, increasing the drying temperature, or reducing the printing speed contributes to improved ink drying, reduced contamination, and enhanced print quality. However, it is crucial to carefully evaluate and test these methods to ensure they align with specific printing requirements and to maintain overall printing performance.

Ink Shedding

Ink shedding in gravure printing refers to a phenomenon where the ink does not adhere properly to the printing substrate and tends to peel off or shed from the surface.
To address poor adhesion of ink on plastic film and prevent rubbing off by hand or mechanical force, several exclusion methods can be employed:

• Protect the Plastic Film from Moisture
• Use Ink with Good Affinity to Plastic Film
• Refinish the Plastic Film
• Increase Surface Tension

By implementing these exclusion methods, it is possible to improve ink adhesion on plastic film and prevent rubbing off. Protecting the film from moisture, using ink with good affinity to plastic, refinishing the film, and increasing surface tension contribute to enhanced adhesion and better print quality. However, it is important to carefully evaluate and test these methods to ensure they align with the specific plastic film characteristics and printing requirements.

Development Tendency

The development tendencies for gravure printing can be summarized as follows:

• Large and medium-sized packaging gravure printing enterprises will dominate the market, with cigarette packaging companies serving as a significant driver of this trend. These enterprises prioritize scale efficiency, high quality, and the integration of advanced technological capabilities to meet the demands of their clients and maintain a competitive edge in the industry.
• The food, medicine, and wine industries, among others, are increasingly focusing on the environmental aspects of packaging materials and printing processes. Gravure printing enterprises are placing greater emphasis on creating eco-friendly printing workshops to align with these industry demands.
• The independent drive technology in gravure printing machines, particularly the electronic shaft drive, is poised to bring about a comprehensive upgrade in the field. Electronic shaft drive serves as a pivotal technology platform that enables significant advancements in gravure printing machines, enhancing their performance and versatility.
• The market share of wide-format gravure and paper gravure printing machines is expected to rise in the coming years. This growth can be attributed to two main factors. Firstly, the decorative printing sector, particularly wood grain paper printing and carton gravure printing, is projected to experience rapid expansion. Secondly, the demand for flexible packaging gravure printing machines is anticipated to increase, leading to a surge in the number of large-format gravure printing machines.
• The processing capabilities of gravure production lines are expected to become more diverse and feature stronger functional configurations. Additional processes such as clustering, die cutting, crosscutting, and soft standard cutting will be integrated into the production line. As a result, the management systems of gravure printing machines, as well as remote technical support systems, will be increasingly utilized to ensure efficient operations.