Understanding Gravure Ink for Gravure Printing

Gravure ink is a type of ink specifically formulated for use in the gravure printing process. Gravure printing, also known as intaglio printing, is a high-quality printing method that utilizes engraved cylinders or plates to transfer ink onto the printing surface. Gravure inks are designed to meet the unique requirements and characteristics of this printing process.

Gravure Ink Classifications

According to the model of plate making:

• Photogravure ink
• Intaglio ink

According to ink property:

• Wate-based gravure ink
• Alcohol gravure ink
• Benzene gravure ink
• Gasoline gravure ink
• Benzoyl gravure ink for plastic film
• Gravure composite plastic (cold composite, hot composite) ink
• Paper gravure ink
• Film gravure ink

According to the printing machine type:

• Platform gravure ink
• Rotary gravure ink

According to bonding materials:

• Polyamide (PA) ink for graphics print
• Parlon (PPA) ink for inside print OPP
• Polyurethane (PU) ink for inside print PET, NY retort
• Cellulose nitrate ink for paper printing

Grauvre Ink Properties

Gravure inks possess several important properties that contribute to their suitability for the gravure printing process and the quality of the printed results. Some key properties of gravure inks include:

Hue

Hue is the fundamental characteristic of color and represents the body or essence of color. It refers to the specific wavelength of light that is perceived by the human eye and is associated with different colors. Hue is what distinguishes one color from another on the color spectrum.

Brightness

Brightness refers to the perceived intensity or luminance of a color. It represents the level of lightness or darkness of a color and is influenced by factors such as the spectral radiance of the light source, the relative reflectivity of the colored object, and the level of stimulation or excitement in the visual system.

Saturability

Saturability, also known as chroma or intensity, refers to the purity or vividness of a color. It is a measure of how much the color deviates from a neutral gray of the same brightness. Saturability is independent of brightness and hue, focusing solely on the strength or concentration of the color itself.

In advanced terms, saturability is a property that describes the level of dominance of a specific hue in a color. A highly saturated color appears vibrant and pure, while a desaturated color appears more muted or washed out.

Gravure Ink Compositions

Gravure ink compositions can vary depending on the specific application and printing requirements.

Pigments or Dyes

These provide the color and visual appearance of the printed image. Pigments are solid particles that are dispersed in the ink most of them insoluble in ink, while dyes are soluble substances that dissolve in the ink. The choice of pigments or dyes depends on the desired color intensity, lightfastness, and other color properties. The pigments contain:

• Organic Pigment: Bright in color, good transparency and high tinting strength
• Inorganic Pigment: Good weather ability, strong heat resistance and hiding power
• Color Lake

Binders or Resins

Binders are polymers or resins that help hold the pigments together and adhere them to the printed surface. They provide film-forming properties, durability, and adhesion. Common binders used in gravure inks include nitrocellulose, polyamide resins, polyurethanes, and acrylic resins. The choice of binder depends on factors such as drying speed, substrate compatibility, and ink properties.

Solvents

Solvents act as carriers for the pigments and binders, providing fluidity and facilitating ink transfer during the printing process. The selection of solvents depends on factors such as drying speed, substrate compatibility, and environmental considerations. Common solvents used in gravure inks include alcohols, ketones, esters, and aromatic hydrocarbons.

Additives

Various additives may be included in gravure inks to enhance specific properties or address specific requirements. Examples of additives in gravure inks include driers to promote quick drying, anti-foaming agents to prevent foam formation, wetting agents to improve ink spreading, tone modifiers to render intent and rheology modifiers to control ink viscosity and flow.

An Idealized Model of Ink

In an idealized model of ink, the ink consists of finely ground solid particles that are hard and coated with a soft shell made of surface solvent. These particles are stably suspended in a viscous binder. When adding solvent to the ink, it is important to do so slowly while stirring. Rapidly injecting the solvent can cause the evenly dispersed pigment particles in the ink to become bare, resulting in a loss of the desired gloss and transparency.

To maintain the desired properties of the ink, a gradual addition of solvent is recommended. This allows for proper interaction between the solvent and the surface shell of the pigment particles, ensuring that the particles remain coated and dispersed evenly. Stirring the ink during the solvent addition helps to facilitate the proper mixing and distribution of the solvent throughout the ink mixture.

By adding the solvent slowly and stirring continuously, the ink formulation can be maintained in a stable state, preserving the gloss and transparency of the printed result. This careful approach helps to prevent any negative impact on the ink’s performance and ensures consistent and desirable printing outcomes.

Gravure Ink for plastic film

Gravure inks for plastic film are specifically formulated inks designed for printing on various types of plastic films using the gravure printing process. These inks are tailored to meet the unique requirements of plastic films, such as adhesion, flexibility, durability, and compatibility.

The Elements for Plastic Film Gravure Printing

Plastic film gravure inks primarily consist of binding agents, polyamide resins, pigments, and additives.

• These ingredients are processed through grinding and filtering to achieve the desired ink formulation. It is crucial to control the softening point of the polyamide resin at 121°C to prevent print adhesion issues during the rainy season when the resin softening point is low. Conversely, in winter, when the resin’s softening point is high, it can freeze, necessitating heating and mixing to facilitate dissolution.
• Plastic film gravure printing ink thinners typically include toluene, isopropyl alcohol, xylene, butanol, and other ester solvents. These thinners are used to adjust the viscosity of the ink. Toluene and isopropyl alcohol are fast-drying solvents, while xylene and butanol are slower-drying solvents.
  When using butanol as a thinner, it is important to note that if the ink dries too quickly, it can lead to loss of graphics and dot reproduction. Adding an appropriate amount of butanol can improve ink reproducibility, ensuring clear and accurate small prints and dots.
  However, adding too much butanol can cause the ink to dry slowly, especially during the rainy season, which may result in print adhesion or sticking issues.
• The bonding material used in plastic gravure ink is primarily chlorinated polypropylene resin. This resin exhibits high adhesion to films such as OPP, PET, and NY.
  When used in composite inks, the black ink is typically sandwiched in the inner layer, making it suitable for printing high-grade plastic soft bags.
  The main solvents used for diluting this type of ink include toluene, ethyl ketone, butyl ketone, and ethyl acetate. Methyl ethyl ketone, toluene, and ethyl acetate are classified as fast-drying solvents, while butyl ketone is considered a slow-drying solvent.
  It is important to avoid adding alcohol solvents to this type of ink as it can lead to ink deterioration. Therefore, alcohol solvents should be excluded from the ink formulation to maintain its stability and desired properties.

The Application of Plastic Film Gravure Ink

Plastic film gravure ink is commonly used for printing on plastic films such as PE, PP, OPP, and NY. It is also suitable for printing on composite flexible packaging materials. However, when printing composite flexible packaging, it is important to ensure that the printing area does not contain large color blocks.

Plastic Film Gravure Ink Selection

It is crucial to carefully select and use plastic gravure compound inks, as ink manufacturers design different inks for high-speed and low-speed drying machines. When printing, the speed of the gravure printing machine should be taken into account to determine the appropriate ink choice. If a slow-speed machine is used with high-speed drying ink, the ink may not dry properly within the gravure dot pits. Similarly, if a high-speed machine is used with slow-drying ink, the ink may not dry adequately.

For applications such as plastic flexible packaging or printing on retort aluminum foil, it is necessary to select specialized two-component gravure inks that are resistant to cooking and suitable for aluminum foil. Failure to use the appropriate ink may result in ink dilution, discoloration, and unclear images and text after cooking. It is also important to choose high-temperature resistant materials and retort two-component adhesives for the production of retort packaging bags.

The surface tension of plastic gravure inks is typically around 36 dynes, while PE and OPP films have surface tensions of about 32 dynes. To ensure proper adhesion between the ink and the film during gravure printing, it is necessary to treat the film surface using corona treatment. This treatment disrupts the molecular structure of the plastic surface, improving the film’s surface tension to over 38 dynes. This allows for strong adhesion between the ink and the film, ensuring that the ink cannot be easily removed by hand or adhesive tape, meeting the quality requirements for printing.

Careful consideration and adherence to these factors are essential to achieve optimal printing quality and performance when using plastic gravure compound inks.

Printing Outside and Printing Inside

When it comes to printing on packaging materials, such as flexible packaging, there is a distinction between printing on the outside and printing on the inside.

Printing on the Outside

Printing on the outside refers to the surface of the packaging material that is visible to the consumer or end-user. This is typically where the brand logos, product information, graphics, and designs are printed. The goal is to create an attractive and informative package that catches the consumer’s attention and communicates the desired message.

The ink used for printing on the outside of packaging materials should have good adhesion to the substrate and provide excellent color vibrancy and print quality. It should also have resistance to scratching, rubbing, and other external factors that may affect the appearance and durability of the printed design. Additionally, considerations such as lightfastness (resistance to fading due to exposure to light) and weather resistance may be important, depending on the intended use and storage conditions of the packaging.

The ink sequence for printing outside is generally from light to dark like white to yellow to red to blue to black.

Printing on the Inside

Printing on the inside of packaging materials refers to the surface that comes into direct contact with the product or contents of the package. This can include printing on the inner layer of a flexible packaging laminate or printing directly on the inner surface of a carton or box.

The ink used for printing on the inside of packaging materials should be safe from contact with food or other sensitive products. It should comply with relevant regulations and standards for food-grade or product-safe printing. The ink should also exhibit good adhesion to the substrate, as well as resistance to moisture, grease, and other factors that may affect the integrity of the printed design.

The ink sequence for printing inside is generally from dark to light like black to blue to red to yellow to white.

Functions and characteristics of ink

Different types of inks serve various functions and possess distinct characteristics based on their intended applications. Here are some common types of inks and their functions:

Solvent Propetries

A solvent is a substance that has the ability to dissolve, disperse, or extract other substances without undergoing a chemical reaction with them. In the context of ink, the solvent refers to the liquid component that has the ability to dissolve or disperse the resin or grease present in the ink formulation. The solvent plays a crucial role in maintaining the ink’s fluidity and facilitating its application onto the desired surface.

• Ture Solvent: The solvent that has the ability to dissolve the ink resin is commonly referred to as a “true solvent.” True solvents are specifically selected based on their compatibility with the ink resin and their ability to dissolve or solvate it effectively.
• Co-solvent: In ink formulation, a solvent that cannot dissolve the ink resin is commonly referred to as a “co-solvent.” Unlike the true solvent, the primary function of a co-solvent is not to dissolve the ink resin but rather to fulfill other specific roles in the ink formulation.

Indeed, the classification of a solvent as either a true solvent or a co-solvent is relative to the specific resin used in the ink formulation. The solubility of a resin in a particular solvent depends on the chemical composition and compatibility between the two.

In the case of polyamide resins, solvents like xylene and ethanol have the ability to dissolve them effectively. These solvents are considered true solvents for polyamide resins because they can completely solvate and disperse the resin, resulting in a homogeneous ink formulation.

On the other hand, when it comes to nitrocellulose (nitrofiber) resins, solvents like xylene and ethanol may not have the same ability to dissolve them completely. Instead, they may act as co-solvents in this scenario. Co-solvents for nitrocellulose resins are used to adjust the viscosity, dilute the ink, or modify the volatility of the ink formulation, rather than fully dissolving the resin.

The choice of a true solvent or a co-solvent depends on the solubility characteristics of the specific resin being used. Different resins have different chemical properties, such as polarity, molecular weight, and functional groups, which determine their solubility in various solvents.

In ink formulation, ink manufacturers carefully select solvents, whether true solvents or co-solvents, based on their compatibility with the specific resin and their ability to achieve the desired ink properties and performance. The goal is to create a stable and homogeneous ink formulation that provides optimal printing results for the chosen resin system.

The Function of Solvent

The solvent in ink serves several important functions in the ink formulation and printing process. These functions include:

• Dissolving and dispersing ink components: The primary function of the solvent is to dissolve or disperse the solid components present in the ink formulation. This includes resins, binders, pigments, dyes, and additives. By dissolving or dispersing these components, the solvent ensures that they are evenly distributed and can be applied smoothly onto the printing surface.
• Controlling viscosity: The solvent plays a crucial role in controlling the viscosity or thickness of the ink. By adjusting the amount and type of solvent used, ink manufacturers can achieve the desired flow characteristics for different printing processes, such as offset printing, flexography, or screen printing. The solvent helps in achieving the optimal balance between fluidity and stability of the ink.
• Facilitating ink transfer: The solvent helps in the transfer of ink from the printing plate or cylinder to the substrate. It reduces the surface tension of the ink, allowing it to spread evenly and adhere to the printing surface. This enables the ink to create sharp and accurate printed images or text.
• Regulating drying time: The solvent influences the drying characteristics of the ink. It affects the rate of evaporation, which determines how quickly the ink dries on the substrate. By selecting solvents with specific evaporation rates, ink manufacturers can control the drying time, ensuring proper ink penetration and adhesion while preventing smudging or smearing.
• Adjusting color intensity: In some cases, the solvent can affect the color intensity or transparency of the ink. By carefully choosing solvents with specific properties, ink manufacturers can adjust the color strength, allowing for vibrant or subdued hues as required.
• Compatibility with substrates: The solvent must be compatible with the printing substrate. It should not react or interact adversely with the surface, ensuring good adhesion and preventing damage. Different types of solvents are selected based on the substrate being printed, such as paper, plastic, fabric, or metal.

Overall, the solvent in ink formulation plays a critical role in achieving the desired ink properties, such as viscosity, color intensity, drying time, and print quality. Its proper selection and balance are crucial for ensuring optimal ink performance during the printing process.

The Classification of Solvent

Classify according to chemical construction:

• Aromatic: Such as toluene, xylene est with strong solubility
• Esters: Such as ethyl acetate, butyl acetate etc with strong solubility, can dissolve nitro fibers and artificial resins
• Ketone: Widely used for dissolved nitrocellulose
• Alcohols: It can miscible with water
• Ethers: Ethylene glycol methyl ether, fibrinolytic agent, butyl fibrinolytic agent

The Properties of Solvent

Solvents possess several properties that are important for their various applications. Some of the key properties of solvents include:

Solubility

Refers to the capacity of a solvent to dissolve a solute and form a homogeneous solution. It is a measure of how much solute can be dissolved in a given amount of solvent under specific conditions, such as temperature and pressure.

When solvents have similar solubility parameters and cohesive forces, they tend to exhibit miscibility, meaning they can be mixed together in all proportions to form a homogenous solution. Miscibility is often observed when the difference in solubility parameter values between the solvents is not greater than 1.

The solubility parameter is a concept used to quantify the solvency characteristics of a solvent or the compatibility between solvents and solutes. It takes into account factors such as polarity, intermolecular forces, and molecular size. Solvents with similar solubility parameter values are more likely to dissolve each other and form a single phase.

Similarly, when it comes to dissolving polymers, it is desirable to use solvents with similar or matching solubility parameter values. Polymers have different solubility characteristics depending on their chemical composition and structure. Solvents with solubility parameters close to those of the polymer can effectively interact with and dissolve the polymer chains.

Volatility

The evaporation rate of a solvent is indeed influenced by its boiling point. Solvents with lower boiling points tend to evaporate more quickly compared to solvents with higher boiling points. In the context of gravure printing, solvents with boiling points ranging from 60 to 150 °C are commonly used.

• Low boiling point solvent: Solvents with boiling points below 100℃ are indeed considered low boiling point solvents. These solvents have a tendency to evaporate quickly, leading to faster drying of the ink. They also tend to have strong solvating power, effectively dissolving ink components.
• Medium boiling point solvent: Solvents with boiling points between 100-150℃ are indeed considered medium boiling point solvents. These solvents offer certain advantages when used in ink formulations, although they may also affect the drying time of the ink.
• High boiling point solvent: Solvents with boiling points above 150°C are indeed considered high boiling point solvents. These solvents possess certain advantages when used in ink formulations, such as strong solubility and viscosity reduction. However, they also have some drawbacks, including slow drying time and potentially higher cost. Such as hexanone, benzyl alcohol, dibutyl ester.
• Plasticizer: Solvents with boiling points in the range of 150-250°C are categorized as high boiling point solvents. On the other hand, solvents with boiling points above 250°C are often referred to as plasticizers.