Reviewing the hot foiling process

The early hot stamp foiling process still had a number of limitations. The use of real gold made the foils very expensive, while bronze powder foils were easily tarnished. In addition, the coloring dyes used with the metallic powders were not light stable and tended to fade. This meant that other alternatives for metallic image printing continued to be considered.

It was not until the 1950s that vacuum or vapour metallised foils using aluminium were developed and hot foil stamping products and technology that were to Rev metallic image printing throughout the whole graphic arts industry were introduced – and are still used today, particularly in the label and package printing sectors.

In the modern hot foil stamping process, a pigmented or metalised coated foil is transferred from a carrier, more usually today a polyester film, and fused to a substrate by heated die in a platen flatbed or rotary hot stamping machine or a hot stamping unit in a roll-label press. This means that the pigmented or metalised coating has to be compatible with the material to be stamped. For this reason, hot stamping foils are manufactured in various formulations designed to give quality prints on a specific material. Also incorporated in the foils are qualities such as abrasion resistance, oil and grease resistance, and chemical resistance.

Before looking at hot foil dies and tooling it is as well to understand a little more about the nature of hot stamping foils as these can have an impact on the hot foiling process and die manufacture.

HOT STAMPING FOILS

In principle, the structure of all stamping foils is as shown in Figure 6.2 although, depending upon the type of product involved, the release and adhesive layers are not always separate entities. As can be seen the foil is made up of a series of coatings that need to be transferred. The carrier layer is made from polyester film that can range from just under 0.0005” to about 0.0015” (12.7 microns to 38.1 microns). The thinner the carrier, the faster the foil can be expected to transfer. 

Hot foiling units, whether flatbed or rotary, comprise principally of a number of key components:

• a heating system in which temperature can be set and controlled

• the flat, segmented or rotary foiling die

• the impression platen or anvil impression cylinder, with a means of adjusting pressure.

Manufacturers of foiling units have differing approaches to the their design, operation and control, but broadly speaking it is the need to adjust and control pressure and temperature evenly across the full width of the die, and the ease with which this can be achieved, that are critical factors which will have some impact on the quality of the final product and the efficiency with which this can be achieved in production.

Hot foiling units must therefore have a means of, firstly, adjusting pressure and then maintaining this pressure at an even depth of impression throughout the foiling run. To be able to achieve high foiling speeds the latest rotary foiling units (Figure 6.4) have steel bearers added to the rotary die so that the die and anvil are sandwiched between a lower anvil roller and an assist roll which can be set and monitored. The heated die must also be able to be taken off impression when the press is stationary.

Hot foiling units, whether flatbed or rotary, comprise principally of a number of key components:

• a heating system in which temperature can be set and controlled

• the flat, segmented or rotary foiling die

• the impression platen or anvil impression cylinder, with a means of adjusting pressure.

Manufacturers of foiling units have differing approaches to the their design, operation and control, but broadly speaking it is the need to adjust and control pressure and temperature evenly across the full width of the die, and the ease with which this can be achieved, that are critical factors which will have some impact on the quality of the final product and the efficiency with which this can be achieved in production.

Hot foiling units must therefore have a means of, firstly, adjusting pressure and then maintaining this pressure at an even depth of impression throughout the foiling run. To be able to achieve high foiling speeds the latest rotary foiling units (Figure 6.4) have steel bearers added to the rotary die so that the die and anvil are sandwiched between a lower anvil roller and an assist roll which can be set and monitored. The heated die must also be able to be taken off impression when the press is stationary.

Whichever type of die carrier base is used, the sheet and the foil are brought together in position between the die and the lower counter plate. The press then brings the upper and lower elements together to deliver uniform pressure across the entire sheet or web.

In semi-rotary hot foil stamping the flat counterplate is replaced by a rotating cylinder, with the die moving horizontally in synchronization with the cylinder rotation to deliver a narrow linear zone of pressure where the die, foil, adhesive, and cylinder all meet.

Rotary hot foiling is undertaken in a similar way to rotary printing. The dies are mounted on a cylinder that rotates in synchronization with a counter cylinder. The substrate and foil are brought together between the two in the narrow nip point.

Standard self-adhesive production widths and rotary foiling cylinders and dies are used where a combination of printing processes include foil blocking. Some hot foiling may be carried out off-line on dedicated finishing lines, such as with the majority of HP Indigo presses. Larger sheet-feed presses are mainly used for foil blocking on large sheets of glue-applied or in-mould labels, as well as in the carton printing sector.

The hot-foil process can print on a wide range of substrates and surfaces and is used to produce bright metallic effects, or to print high opacity pigmented foil colors using relatively simple equipment. The process is particularly well used to provide a luxury (metallic) look on many cosmetics, toiletries, health and beauty labels, on wines and spirit labels (Figure 6.7) and in other higher added-value label applications. The process may also be combined with embossing.

HOT FOILING DIES

Hot foiling dies are engraved metal plates, segments or cylinders where the printing image areas are in relief and raised above the non-printing areas. Whether sheet- or web-fed, sophisticated handling systems are needed to position the substrate and foil between the plate or cylinder that holds the dies and the platen or anvil that supplies the counter pressure. To produce good quality foiling dies there are a number of critical elements that are required to ensure that they perform correctly. These factors are:

• The material used for the die must be a good conductor of heat (have a high coefficient of thermal conductivity).

• The die material must be durable and have physical properties compatible with its usage and length of life.

• The die material must be suitable for the required machine engraving or chemical etching processes.

• The image on the die must be ‘dispro'd’ and positioned correctly across and around the die and must be perfectly aligned to the axis.

• The die should have a high surface finish. The smoother the surface the higher the gloss of the printed foil.

HOT FOILING DIE MATERIAL OPTIONS

As already mentioned, hot foil stamping dies must be good conductors of heat and must be durable. They must be suitable for engraving and/or etching and provide for a high surface finish quality. Suitable die materials commonly used for foiling dies, depending on length of life and performance, include steel, brass, copper, magnesium and photopolymer. Each of these materials can be summarised as follows:

Steel tool material is machined, engraved, hardened and ground and is particularly suitable for long running applications and, although it is the most expensive of the die materials, can pay for itself with reduced downtime. It can be engraved to fit contoured parts.

Brass tool materials are widely used and have similar properties to steel, except that they are around a quarter less expensive than steel. They also have a better heat transfer than steel, although they are not nearly as durable. They are suitable for machine engraving and are 100 per cent recyclable. CNC-engraved brass dies are the more traditional choice for hot stamp label decoration. They are also the best choice when stamping a thick substrate or carton board stock, as the manufacturing process can accommodate such substrates.

Brass cylinders make the most efficient use of heat conductivity when compared with other current hot foil tooling options. Segmented brass hot foil dies are available that are divided into segments and/or rings. The rings are cut from brass in a similar fashion as that for solid cylinders, but each ring is limited in size specific to the image. The rings are then slid onto a mandrel, which typically is aluminum. The ring system can accommodate both electrical and oil thermal heating units.

Copper tool material is generally photoetched from artwork and has a similar durability and heat transfer to brass. Copper is claimed to be good material for ornate graphics, with the etching process being faster than mechanical engraving. A limiting factor is that coper dies can only be etched .004” deep, although open areas can be machined deeper.

For narrow-web converting there are chemically etched flexible copper dies or sleeves that are produced with a thin steel backing that is securely held to a heated magnetic cylinder. Such dies offer fast, easy and reliable changeovers, which make them a suitable choice for short- to medium-run hot foiling jobs. Copper faced steel sleeves provide a cost-effective alternative to engraved brass dies and they can be run on low cost aluminium mandrels.

Another die option enables flexible copper dies to be mounted around a mandrel using an existing OEM mechanical fastening system. This can also be an economical option for short- to medium-run applications.

Magnesium tool materials are able to transfer heat as well as copper or brass, and can be photoetched like copper. Plates are etched using two chemical baths and are available in different gauges. Magnesium is the least expensive foiling die material, but is also the least durable. Different thicknesses are available.

Photopolymer dies mounted onto steel anvils are available from some suppliers, but are typically more limited to flat embossing rather than foiling due to the poor heat conducting properties of the polymer when compared to solid brass cylinders or flexible copper dies. The photopolymer, being softer than metal, will also limit the lifespan of the die.

PRODUCTION OF HOT FOILING DIES

Having selected the most appropriate foiling die material and received the required artwork specifications, the dies need to be etched or engraved (milled) as required. There are two main methods of producing the hot foiling dies: photoengraving and Computed Numerically Controlled (CNC) engraving.

Photoengraving has long been a traditional method of producing both printing plates and foiling dies. With this process the image is transferred to the surface of a plate or die that has been coated with a photosensitive substance using a photographic negative. The background areas are then dissolved or etched away in an acid bath using a strong acid to leave a relief printing or foiling surface. Photoengraving is a relatively high overhead process, but has proved to be excellent for more complex images.

Magnesium is the softest of the materials used for flatbed metal dies and is the least expensive. The imaging of a magnesium plate is done using a chemical etching process. A photo sensitive coating is applied to the magnesium plate to be imaged and a film negative of the image to be produced is then placed in contact with the plate surface and exposed to a light source before being photographically developed to produce the image. The plate is then chemically etched to remove the ‘non-image’ area leaving the ‘image’ area in relief.

Copper dies are imaged using an etching process similar to magnesium die etching. The copper die is harder than magnesium and therefore more suitable for longer production runs and multiple image work. Good image etching characteristics will give excellent foiling results.

While magnesium and copper dies are chemically etched, flatbed brass dies are imaged using a CNC (computer numerical control) digitally driven engraving system. This method of imaging applies to both flatbed and rotary dies. Flatbed dies are engraved in the flat. The quick separation of the foiling material from the substrate surface enables very fine detail to be achieved.

In general, it can be expected that the transfer results will change as the web speed is raised. A slight increase in pressure will normally correct this.

While rotary foil blocking has gained ground for long-run labeling applications where other (combination press) print units may print the detail by, say, flexo or offset, the majority of hot-foiling for label printing is still short-run text and solid color, produced on small flat-bed machines.

Units designed for the hot-foil printing or decoration of labels or packaging come in a variety of configurations and widths. Stand-alone hot-foil blocking machines are generally narrow-web and operate on similar principles to those of flat-bed die-cutters. In flatbed foiling the foiling dies are either attached to a flat honeycomb chase allowing for variable positioning, or in fixed positions on a flat metal plate for repeat jobs.

Whichever type of die carrier base is used, the sheet and the foil are brought together in position between the die and the lower counter plate. The press then brings the upper and lower elements together to deliver uniform pressure across the entire sheet or web.

In semi-rotary hot foil stamping the flat counterplate is replaced by a rotating cylinder, with the die moving horizontally in synchronization with the cylinder rotation to deliver a narrow linear zone of pressure where the die, foil, adhesive, and cylinder all meet.

Rotary hot foiling is undertaken in a similar way to rotary printing. The dies are mounted on a cylinder that rotates in synchronization with a counter cylinder. The substrate and foil are brought together between the two in the narrow nip point.

Standard self-adhesive production widths and rotary foiling cylinders and dies are used where a combination of printing processes include foil blocking. Some hot foiling may be carried out off-line on dedicated finishing lines, such as with the majority of HP Indigo presses. Larger sheet-feed presses are mainly used for foil blocking on large sheets of glue-applied or in-mould labels, as well as in the carton printing sector.

The hot-foil process can print on a wide range of substrates and surfaces and is used to produce bright metallic effects, or to print high opacity pigmented foil colors using relatively simple equipment. The process is particularly well used to provide a luxury (metallic) look on many cosmetics, toiletries, health and beauty labels, on wines and spirit labels (Figure 6.7) and in other higher added-value label applications. The process may also be combined with embossing.

HOT FOILING DIES

Hot foiling dies are engraved metal plates, segments or cylinders where the printing image areas are in relief and raised above the non-printing areas. Whether sheet- or web-fed, sophisticated handling systems are needed to position the substrate and foil between the plate or cylinder that holds the dies and the platen or anvil that supplies the counter pressure. To produce good quality foiling dies there are a number of critical elements that are required to ensure that they perform correctly. These factors are:

• The material used for the die must be a good conductor of heat (have a high coefficient of thermal conductivity).

• The die material must be durable and have physical properties compatible with its usage and length of life.

• The die material must be suitable for the required machine engraving or chemical etching processes.

• The image on the die must be ‘dispro'd’ and positioned correctly across and around the die and must be perfectly aligned to the axis.

• The die should have a high surface finish. The smoother the surface the higher the gloss of the printed foil.

HOT FOILING DIE MATERIAL OPTIONS

As already mentioned, hot foil stamping dies must be good conductors of heat and must be durable. They must be suitable for engraving and/or etching and provide for a high surface finish quality. Suitable die materials commonly used for foiling dies, depending on length of life and performance, include steel, brass, copper, magnesium and photopolymer. Each of these materials can be summarised as follows:

Steel tool material is machined, engraved, hardened and ground and is particularly suitable for long running applications and, although it is the most expensive of the die materials, can pay for itself with reduced downtime. It can be engraved to fit contoured parts.

Brass tool materials are widely used and have similar properties to steel, except that they are around a quarter less expensive than steel. They also have a better heat transfer than steel, although they are not nearly as durable. They are suitable for machine engraving and are 100 per cent recyclable. CNC-engraved brass dies are the more traditional choice for hot stamp label decoration. They are also the best choice when stamping a thick substrate or carton board stock, as the manufacturing process can accommodate such substrates.

Brass cylinders make the most efficient use of heat conductivity when compared with other current hot foil tooling options. Segmented brass hot foil dies are available that are divided into segments and/or rings. The rings are cut from brass in a similar fashion as that for solid cylinders, but each ring is limited in size specific to the image. The rings are then slid onto a mandrel, which typically is aluminum. The ring system can accommodate both electrical and oil thermal heating units.

Copper tool material is generally photoetched from artwork and has a similar durability and heat transfer to brass. Copper is claimed to be good material for ornate graphics, with the etching process being faster than mechanical engraving. A limiting factor is that coper dies can only be etched .004” deep, although open areas can be machined deeper.

For narrow-web converting there are chemically etched flexible copper dies or sleeves that are produced with a thin steel backing that is securely held to a heated magnetic cylinder. Such dies offer fast, easy and reliable changeovers, which make them a suitable choice for short- to medium-run hot foiling jobs. Copper faced steel sleeves provide a cost-effective alternative to engraved brass dies and they can be run on low cost aluminium mandrels.

Another die option enables flexible copper dies to be mounted around a mandrel using an existing OEM mechanical fastening system. This can also be an economical option for short- to medium-run applications.

Magnesium tool materials are able to transfer heat as well as copper or brass, and can be photoetched like copper. Plates are etched using two chemical baths and are available in different gauges. Magnesium is the least expensive foiling die material, but is also the least durable. Different thicknesses are available.

Photopolymer dies mounted onto steel anvils are available from some suppliers, but are typically more limited to flat embossing rather than foiling due to the poor heat conducting properties of the polymer when compared to solid brass cylinders or flexible copper dies. The photopolymer, being softer than metal, will also limit the lifespan of the die.

PRODUCTION OF HOT FOILING DIES

Having selected the most appropriate foiling die material and received the required artwork specifications, the dies need to be etched or engraved (milled) as required. There are two main methods of producing the hot foiling dies: photoengraving and Computed Numerically Controlled (CNC) engraving.

Photoengraving has long been a traditional method of producing both printing plates and foiling dies. With this process the image is transferred to the surface of a plate or die that has been coated with a photosensitive substance using a photographic negative. The background areas are then dissolved or etched away in an acid bath using a strong acid to leave a relief printing or foiling surface. Photoengraving is a relatively high overhead process, but has proved to be excellent for more complex images.

CNC engraving is a more recent method of engraving both flatbed and rotary hot foiling dies using a computer to control a machine that does the engraving process. The image is created using specialised CAD/CAM computer programs to produce the required computer file, in turn gets fed into a particular CNC engraving machine for production. The computer software file drives the tooling heads to remove the unwanted material, enabling cylinders and dies to be produced very efficiently, particularly for less complex images.

CNC engraving machines are used to produce highly accurate engravings. CNC engraving is also great for reproducing the same, consistent results for mass production and use a wide variety of different tools . such as different drills or saws . to create a variety of products and engravings. The latest CNC engraving machines often combine many tools into a single ‘cell’. In other cases a human or robotic external controller may change the parts on a machine required for engraving.

HOT-FOILING FLATBED DIES

The hot foiling dies used for flatbed hot-foiling need to be of a hard material and have a raised image similar to that used by the letterpress process. The fact that image transfer relies upon both heat and pressure restricts plate materials to either a very hard thermoformed plastic plate for very short runs or plates produced from magnesium, brass, steel, or copper, for the longer runs.

Magnesium is the softest of the materials used for flatbed metal dies and is the least expensive. The imaging of a magnesium plate is done using a chemical etching process. A photo sensitive coating is applied to the magnesium plate to be imaged and a film negative of the image to be produced is then placed in contact with the plate surface and exposed to a light source before being photographically developed to produce the image. The plate is then chemically etched to remove the ‘non-image’ area leaving the ‘image’ area in relief.

Copper dies are imaged using an etching process similar to magnesium die etching. The copper die is harder than magnesium and therefore more suitable for longer production runs and multiple image work. Good image etching characteristics will give excellent foiling results.

While magnesium and copper dies are chemically etched, flatbed brass dies are imaged using a CNC (computer numerical control) digitally driven engraving system. This method of imaging applies to both flatbed and rotary dies. Flatbed dies are engraved in the flat. The quick separation of the foiling material from the substrate surface enables very fine detail to be achieved.

The metal dies used in the flatbed foiling process are not as sophisticated as those used in the full rotary foiling system. The flatbed die does not have any curvature issues and can be etched or engraved in the flat. Once the image has been engraved or etched the die is ready for mounting in the press.

In flatbed foiling the foiling dies are either mechanically or magnetically attached to a flat magnetic or honeycomb base allowing for variable positioning, or in fixed positions on a flat metal plate for repeat jobs. Figure 6.10 shows an example of a magnetic flat base.

SEGMENTED DIES

Segmented dies provide a means of mounting individual brass dies onto a full rotary honeycomb cylinder without the need to use an expensive solid brass die. The curved segment dies are placed in position on a honeycomb cylinder configuration and held in position using clips located along the edges of each individual die.

Once they have been located and placed in their correct positions, each individual curved segment die is securely fixed to the honeycomb base using a special tensioning key to fully tighten the securing clips. For multi versions or variations of labels it is easy to remove and replace one or more die segments as required, which can be particularly cost-effective.

COLD-FOILING

A more recent development of hot-foil blocking is the cold foil process, in which a print unit is used to print a special adhesive on the label web where the metallic effect is required. When the metallic foil is brought into contact with the adhesive it adheres to it to produce the printed foil design on the label. Cold foiling provides another option for product decoration, offering higher running speeds when compared to hot foiling.

Cold foiling will normally give the best results on smooth and high gloss substrates. Semi-gloss papers will require a coating to be applied if the best results are to be achieved.

The idea behind cold foiling is quite simple: using a photopolymer plate, an image is printed onto the label substrate with the use of special UV-curable cold foil adhesive. UV light from a UV curing unit then activates the adhesive. The foil material is brought into contact with and bonded to the adhesive and substrate, with the non-bonded waste being removed. The extracted foil that is affixed to the printed adhesive is what creates the cold foiled image. See Figures 6.15 and 6.16.

While there is a place in product decoration for cold foiling, the overall quality and consistency is still regarded by many as not quite as high as that of hot stamping. For high-end label applications, which is largely the case in the health, beauty, wine and spirits sectors, hot foil remains the preferred process.

Another benefit of the hot foiling process is that it smooths the fibers of the substrate, so providing an ideal base for ensuring the highest sheen and brilliance the foil has to offer. In cold foiling, the foil is laid on top of the adhesive and fibers of the paper, which can cause the resulting foil image to be less brilliant/shiny in appearance when compared to hot stamped images.

Cold foiling also has an added expensive component – the adhesive. This additional cost needs to be balanced against the desired effect when choosing the type of foiling that is best for any particular end-use application.

MAKING FOIL STAMPING WORK

The use of hot, and cold, foil decoration has become an increasing part of the label converter’s business as brand owners seek to distinguish their products from competitors. Rotary hot foil stamping in particular has continued to be a popular choice for all types of foil-decorated labels, and if all the necessary foiling parameters are correct, then the result is a clean, crisp and consistent foil transfer, making foiling an important production process amongst competitive label printers. However, it is key that the converter ensures good quality foil transfer at maximum production running speeds. Attention therefore needs to be paid to the following:

Foil selection. Foil manufacturers today have an array of foil selections to maximize the performance of the job being produced. Foils are available for porous stocks, plastic stocks, fine details, large solids and over-printable foils, so confer with the foil supplier to make the correct selection. Keep the foil rolls properly labeled as it is virtually impossible to identify the foil products without a label, especially when they are in similar color shades.  

Testing of label stock. Most label stocks today are able to accept hot foil stamped images. However, there are some that may require a topcoat or primer in order to overcome porosity and to give the stock a better base for adhesion of the foil. It is therefore recommended that the stock to be used is tested with the selected foil to see if a coating or primer is required. With clear plastic substrates being a popular choice for adding decorated foil there will be a requirement to select a low temperature foil to keep the material from wrinkling or melting.

Choice of foiling anvil. While most hot foiling jobs can be run successfully with a 90 durometer Shore compound, a harder 100 durometer anvil may be a better choice for use with textured stock so that the tool can compress the substrate texture without embedding into the anvil. Compounds must be able to withstand 400 degrees F and be resilient.

Use of magnetic cylinders. Magnetic cylinders can be used with a flexible foiling die or with engraved brass dies. Engraved brass dies are still recommended for very long runs and/or jobs that continuously will repeat. However, for shorter runs, a flexible die with a metal back can be extremely effective and much less costly for the customer. 

Getting started. Ensure that proper training is included with any new installation. Inline hot foil stamping adds a completely new capability to a label press and will require on-press training time to fully master for the best results. However, with the proper pre-planning, acquired technical knowledge and the proper training, converters can be up and running quality foil stamped labels in a matter of days.

SLEEVED ROTARY FOILING DIES

Another option for creating a rotary foiling die involves a sleeve system. This type of cost effective rotary hot foiling system reduces the metal content of engraved rotary dies by chemically etching a sleeve that is manufactured to fit the width of the specific image area required. This can be seen in Figure 6.13 in which, in this case, a chemically etched copper faced steel sleeve is produced that can be mounted onto a low cost aluminium mandrel.

The sleeve is slid onto the mandrel and can be positioned both laterally and circumferentially to give the correct registration position. The mandrels are considerably lighter than brass or magnetic foiling dies and are easier to handle and set up. End adaptors in mandrels for oil heated foiling units remain in place at all times reducing set up time for press operators.

Foiling sleeves are lightweight, easy to handle and very economic to transport with customers befitting from reduced freight costs.

MAGNETIC FLEXIBLE FOILING DIES

Magnetic foiling dies work on the same basic principle as wraparound flexible cutting dies used for the profile die-cutting of the label shape. The foiling die is a chemically etched flexible plate or ‘shim’ which has a steel backing and a copper surface layer which carries the foiling image. Copper is used because of its good heat conductivity. The imaged shim is positioned onto a heated magnetic cylinder (see Figure 6.14) and the cylinder and die are mounted in the foiling unit in the same way as a solid rotary die. 

While there is a place in product decoration for cold foiling, the overall quality and consistency is still regarded by many as not quite as high as that of hot stamping. For high-end label applications, which is largely the case in the health, beauty, wine and spirits sectors, hot foil remains the preferred process.

Another benefit of the hot foiling process is that it smooths the fibers of the substrate, so providing an ideal base for ensuring the highest sheen and brilliance the foil has to offer. In cold foiling, the foil is laid on top of the adhesive and fibers of the paper, which can cause the resulting foil image to be less brilliant/shiny in appearance when compared to hot stamped images.

Cold foiling also has an added expensive component – the adhesive. This additional cost needs to be balanced against the desired effect when choosing the type of foiling that is best for any particular end-use application.

MAKING FOIL STAMPING WORK

The use of hot, and cold, foil decoration has become an increasing part of the label converter’s business as brand owners seek to distinguish their products from competitors. Rotary hot foil stamping in particular has continued to be a popular choice for all types of foil-decorated labels, and if all the necessary foiling parameters are correct, then the result is a clean, crisp and consistent foil transfer, making foiling an important production process amongst competitive label printers. However, it is key that the converter ensures good quality foil transfer at maximum production running speeds. Attention therefore needs to be paid to the following:

Foil selection. Foil manufacturers today have an array of foil selections to maximize the performance of the job being produced. Foils are available for porous stocks, plastic stocks, fine details, large solids and over-printable foils, so confer with the foil supplier to make the correct selection. Keep the foil rolls properly labeled as it is virtually impossible to identify the foil products without a label, especially when they are in similar color shades.  

Testing of label stock. Most label stocks today are able to accept hot foil stamped images. However, there are some that may require a topcoat or primer in order to overcome porosity and to give the stock a better base for adhesion of the foil. It is therefore recommended that the stock to be used is tested with the selected foil to see if a coating or primer is required. With clear plastic substrates being a popular choice for adding decorated foil there will be a requirement to select a low temperature foil to keep the material from wrinkling or melting.

Choice of foiling anvil. While most hot foiling jobs can be run successfully with a 90 durometer Shore compound, a harder 100 durometer anvil may be a better choice for use with textured stock so that the tool can compress the substrate texture without embedding into the anvil. Compounds must be able to withstand 400 degrees F and be resilient.

Use of magnetic cylinders. Magnetic cylinders can be used with a flexible foiling die or with engraved brass dies. Engraved brass dies are still recommended for very long runs and/or jobs that continuously will repeat. However, for shorter runs, a flexible die with a metal back can be extremely effective and much less costly for the customer. 

Getting started. Ensure that proper training is included with any new installation. Inline hot foil stamping adds a completely new capability to a label press and will require on-press training time to fully master for the best results. However, with the proper pre-planning, acquired technical knowledge and the proper training, converters can be up and running quality foil stamped labels in a matter of days.

COLD-FOILING

A more recent development of hot-foil blocking is the cold foil process, in which a print unit is used to print a special adhesive on the label web where the metallic effect is required. When the metallic foil is brought into contact with the adhesive it adheres to it to produce the printed foil design on the label. Cold foiling provides another option for product decoration, offering higher running speeds when compared to hot foiling.

Cold foiling will normally give the best results on smooth and high gloss substrates. Semi-gloss papers will require a coating to be applied if the best results are to be achieved.

The idea behind cold foiling is quite simple: using a photopolymer plate, an image is printed onto the label substrate with the use of special UV-curable cold foil adhesive. UV light from a UV curing unit then activates the adhesive. The foil material is brought into contact with and bonded to the adhesive and substrate, with the non-bonded waste being removed. The extracted foil that is affixed to the printed adhesive is what creates the cold foiled image. See Figures 6.15 and 6.16.

While there is a place in product decoration for cold foiling, the overall quality and consistency is still regarded by many as not quite as high as that of hot stamping. For high-end label applications, which is largely the case in the health, beauty, wine and spirits sectors, hot foil remains the preferred process.

Another benefit of the hot foiling process is that it smooths the fibers of the substrate, so providing an ideal base for ensuring the highest sheen and brilliance the foil has to offer. In cold foiling, the foil is laid on top of the adhesive and fibers of the paper, which can cause the resulting foil image to be less brilliant/shiny in appearance when compared to hot stamped images.

Cold foiling also has an added expensive component – the adhesive. This additional cost needs to be balanced against the desired effect when choosing the type of foiling that is best for any particular end-use application.

MAKING FOIL STAMPING WORK

The use of hot, and cold, foil decoration has become an increasing part of the label converter’s business as brand owners seek to distinguish their products from competitors. Rotary hot foil stamping in particular has continued to be a popular choice for all types of foil-decorated labels, and if all the necessary foiling parameters are correct, then the result is a clean, crisp and consistent foil transfer, making foiling an important production process amongst competitive label printers. However, it is key that the converter ensures good quality foil transfer at maximum production running speeds. Attention therefore needs to be paid to the following:

Foil selection. Foil manufacturers today have an array of foil selections to maximize the performance of the job being produced. Foils are available for porous stocks, plastic stocks, fine details, large solids and over-printable foils, so confer with the foil supplier to make the correct selection. Keep the foil rolls properly labeled as it is virtually impossible to identify the foil products without a label, especially when they are in similar color shades.  

Testing of label stock. Most label stocks today are able to accept hot foil stamped images. However, there are some that may require a topcoat or primer in order to overcome porosity and to give the stock a better base for adhesion of the foil. It is therefore recommended that the stock to be used is tested with the selected foil to see if a coating or primer is required. With clear plastic substrates being a popular choice for adding decorated foil there will be a requirement to select a low temperature foil to keep the material from wrinkling or melting.

Choice of foiling anvil. While most hot foiling jobs can be run successfully with a 90 durometer Shore compound, a harder 100 durometer anvil may be a better choice for use with textured stock so that the tool can compress the substrate texture without embedding into the anvil. Compounds must be able to withstand 400 degrees F and be resilient.

Use of magnetic cylinders. Magnetic cylinders can be used with a flexible foiling die or with engraved brass dies. Engraved brass dies are still recommended for very long runs and/or jobs that continuously will repeat. However, for shorter runs, a flexible die with a metal back can be extremely effective and much less costly for the customer. 

Getting started. Ensure that proper training is included with any new installation. Inline hot foil stamping adds a completely new capability to a label press and will require on-press training time to fully master for the best results. However, with the proper pre-planning, acquired technical knowledge and the proper training, converters can be up and running quality foil stamped labels in a matter of days.