Pressure sensitive .. Why Is It Called That?
It's called “pressure sensitive” (PS) because all it takes is pressure to effect instant, allover bonding. Unlike other types of labeling, PS requires no glue, no water, and no heat. To apply a pressure sensitive label, just pull away the backing (the liner) from the PS material (the facestock) .. and press it directly onto the item you are labeling. The result is instant adhesion with only slight pressure.
Before the introduction of pressure sensitive, all that was available to the printer and the end-user was sticky paper. . . commonly known as Gum (gummed) paper. Gum paper, both dry and wet, is no longer as popular for many applications for several reasons:
• The water on the printing press must be controlled to an optimal level for good printability and press performance. If not controlled correctly, the excessive water activates the adhesive on the dry-gummed material… resulting in the paper and its adhesive literally gumming up the press and causing down time.
• The adhesive on pressure sensitive covers the entire surface efficiently, so adhesion is 100% corner-to-corner. No water is ever needed. The adhesive on dry-gummed material must be activated by the application of water. Often the water does not cover the entire adhesive surface, allowing dry areas that do not adhere to the item being labeled.
• Storage is often a problem for dry-gummed material. If too much moisture is present, the sheets may stick to themselves and cannot be used for printing.
For these reasons, many commercial, in-plant and instant print shops show a strong preference for pressure sensitive products. Dry gum products are still used and available in a variety of face stocks.
The Construction of Pressure Sensitive Media
The typical pressure sensitive construction consists of Top Coating, Facestock, Primer, Release Coating, Liner, and ABC Coating.
Top coating, or off-machine coatings, are sometimes applied to improve the performance of the paper or film products. This process can improve the smoothness, opacity, water resistance, ink hold out or gloss level.
The facestock is the surface that is to be printed. It may be a paper stock, film, foil, or a fabric cloth material that has been designated to be printed and converted into PS stock. Pressure sensitive manufacturers offer a wide variety of facestocks from which to chose, according to the type and quality of the printing as well as the labels intended end use.
Primers can be added to facestocks to increase facestock opacity or improve the anchorage of the adhesive to the facestock. The primer is applied to the adhesive side of the facestock and can also help prevent the adhesive from “bleeding through” the facestock.
The middle component is the adhesive. The adhesive is what makes the pressure sensitive facestock adhere to a wide variety of dissimilar surfaces upon contact papers, corrugated cartons, plastics, glass, steel, cardboard and a multitude of surfaces. Adhesives have different qualities and are designed to satisfy specific end user purposes and conditions.
This coating is applied to the liner. Usually silicone is used as the release coating and is applied uniformly on the liner. This coating must be formulated to work with the adhesive being used and the liner.
The “back” component of the PS is the liner. It is designed to protect and maintain the freshness and adhesive quality of the adhesive, before, during, and after the printing. The liner can also provide support for the facestock providing stability during printing and finishing stages.
Each manufacturer will either have a printed or unprinted liner. There are three different types of liners offered in the industry.
The liner is not altered in any way for removal. Since it is plain backed “it is ideal for kiss die cutting.”
Back – cuts are made through the liner allowing for different strips to be removed separately. This is generally done on a custom basis to meet a customers specific requirement.
• SCORED BACK
The liner is mechanically altered, but not
cut all the way through (generally it is scored. This is the most popular liner removal system available today. The two widely accepted styles are diagonal crackline liner, and vertical scored liner. The diagonal crackline liner is available exclusively on Fasson’s CRACK N PEEL products. Both of these liners must be “cracked” by the user to remove the liner. These designs are the easiest and most trouble free liners for printers and end users to work with.
Anti-Block Coating (ABC), is applied to some pressure sensitive constructions to prevent migration of the adhesive to the back side of the liner. This is sometimes used for “soft” adhesives and is not generally used if the liner itself is to be printed. Nearly all sheet pressure sensitive products are designed for back printing.
Facts About Facestocks
Normally the end use of the printed piece (labels application) will determine the choice of pressure sensitive facestock.
The two primary considerations in the selection of the facestock are the printing process and result desired, and the end use requirements.
Desired Printing Process/Results
It is important to consider the printing process to be used when making a material selection. Most standard paper facestocks are suitable for letterpress, offset and flexographic printing as long as the proper ink and drying conditions are used.
The film products with their non-absorbent facestocks present different considerations, particularly with normal letterpress and offset ink. Most film products (polyesters and top coated vinyls) will require the use of special oxidizing inks because the ink must dry on the surface of the film.
Desired End-Use Performance Characteristics
Another important consideration is to select a facestock with the proper performance characteristics. If the label is going to be exposed to any degree of moisture, a moisture resistant facestock, such as latex-impregnated, top coated vinyl. Teslin or PolyArt, should be selected.
If a label is to be written upon with pen, pencil, or other marker, an uncoated stock, such as an uncoated offset. in white or colors, is the best choice.
If a customer is looking for a name badge label, offer a Name Badge, Convention Badge, or Satin Cloth stock – depending on the customers desired finished appearance and budget. A name badge is typically used for short term applications and the adhesive must be clean and remove from a lapel or cloth material without leaving an adhesive residue. For this reason a “badge” product is not recommended for silk. leather, vinyl. suede or fur.
Always consider moisture and temperature factors when selecting a face stock. Will the label he subjected to ultra violet rays, hot or cold conditions or even rain?
The three general types of facestocks include:
White coated and uncoated paper make up most of the market for pressure sensitive papers. Coated facestocks print like conventional coated printing papers.
Typical coated paper facestocks:
High-Gloss – a cast coated paper.
Semi-Gloss – a gloss enamel coated paper.
Matte/Satin Litho – a matte clay coated paper.
Yellow Litho – a yellow coated paper.
Fluorescents – a fluorescent blade coated paper.
Typical coated paper facestocks:
Uncoated Offset – available in smooth or vellum finish.
Pastel Colors – soft colors.
Bright Colors – bright and vibrant colors.
And also text papers:
Text Papers – Designer grades of text paper. (i.e. Strathmore Label. Classic Crest Label, etc.)
A latex-impregnated paper is used when a label needs to be more flexible (such as one going around a cylinder or bottle) or moisture resistant (such as a bumper sticker or food product label that will be refrigerated) Latex impregnated paper is made by either mixing latex into the fibers during the paper making process or by saturating the absorbent fibers with a compounded latex. This added strength offers more resilience and durability. A label for outdoor use or constant handling would require such added strength.
Use Coated Tag stock when extra stiffness is required. Generally available in 8 point. tag is also available in 10 point and 14 point. Point-of-purchase displays often require tag stocks as well as some packaging applications.
Acetate is defined as crushed cellulose fiber, bleached until clear. Acetate products should be used indoors. Two mil clear acetate is generally used as an indoor window decal. Other calipers are available on a custom basis. Acetate is inherently weak, but rigid. It will tear so it is not recommended for labels that will be scuffed or put under rigorous use.
Laminated Foils (available in gold and silver) have a very thin layer of foil laminated to a paper stock. They are used when design plays a part of a desired end use, but should be used indoors only. This product has some moisture resistance but extreme elements could cause delamination. Laminated foils generally have a nitrocellulose top coating so they may be offset printed.
Satin Cloth is a rayon acetate facestock. Satin Cloth is generally used for name badges or fabric labels. Badge labels are not designed for long term use because a “permanent” bond is not desired (* Note that any fabric labels for long-term use – more than 12 hours – will require special adhesive designed for the specific application).
There are two different kinds of vinyl facestocks available. The first kind is cast vinyl. This type of vinyl is actually “cast” on the liner sheet. Cast vinyl is silk screen printable, not offset printable, and generally has an outdoor life of 2 to 5 years. It is typically used in marking of trucks, cars, or other surfaces that are exposed to the outdoors long- term.
The second kind of vinyl is calendered vinyl. This type of vinyl is run through a set of “calendering” rollers (usually at the vinyl manufacturing plant) which is where the name calendered vinyl is derived from – to stretch the film. Calendered vinyl may be top coated for offset printability. Generally the outdoor life of calendered vinyls is 1 to 2 years because the product will begin to break down from the exposure to ultra violet rays and heat and cold variations. Calendered vinyls are used for bumper stickers, bus marking, and other promotional stickers.
Polyester is a synthetic (Duponts polyester is known as Mylar) film that has excellent tear strength and heat resistance. Polyesters generally have 23 years outdoor durability. Polyester products are a good choice for outdoor window decals and for product labels where durability is required. Parking lot permits for car windows, store window decals that indicate at entrance ways, “push” or “pull” and store window decals that advertise the credit cards they accept are a few of the suggested applications.
Reflective films will reflect back light for improved visibility of a label. This is the type of material used in street signs and license tags.
Facts About Adhesives
Always test the label product on the substrate before printing or converting. The adhesive is the component that makes pressure sensitive facestocks adhere to a wide variety of dissimilar surfaces upon contact Adhesives can have different qualities and are designed to satisfy specific end use purposes and conditions.
Adhesives are manufactured by three different processes in two formulations. The two adhesive formulations are called Both of these adhesive formulations can be processed by the manufacturer as a:
Adhesive compounds are dissolved with petrochemicals HOT MELT: adhesive compounds are dissolved with heat EMULSION: adhesive compounds are dissolved with water For our purposes, we refer to the adhesive formulations most often (Rubber or Acrylic, rather than how they are manufactured. Once you understand the different properties between rubber based and acrylic based adhesives, you will see why some adhesives work better than others under certain circumstances. Always test the label product on the substrate before printing or converting.
Rubber Based adhesives
• Have what we call good “cold flow”, which means that the adhesive can penetrate the pores of the surface it comes in contact with rather quickly. This quality usually indicates that the adhesive is “soft” or more fluid than an acrylic based adhesive.
• Have a high initial tack, which means that the adhesive seems to bond to the surface of the substrate quickly. This does not mean, however, that the adhesive will always bond better than an acrylic, just more quickly.
• And the service temperature ranges up to 200 degrees. This means that once applied to a substrate the adhesive will not break down until the temperature reaches approximately 200 degrees.
• Have poor resistance to ultra violet rays, which means the adhesive can break down when exposed to sunlight.
Acrylic Based adhesives
• Have good “solvent resistance” which means that the adhesive can be exposed to a variety of chemicals without breaking down.
• Have ‘service temperature” ranges up to 300 degrees, which gives the acrylic based adhesive a distinct advantage in industrial applications.
• Have “moderate initial tack”, which means i lakes some time before the adhesive seems to bond to the substrate. The ultimate adhesive bond may be better than an adhesive that has a high initial tack.
• Have good resistance to ultra violet rays, which makes it a good choice for many outdoor applications.
Rubber based and acrylic based adhesives are available in both a permanent and removable formulation. The formulations are altered to change the degree to which the adhesive will bond with a substrate. It is, believe it or not, more difficult and costly to produce a removable adhesive. Here is a brief definition of both:
Bonds tightly to the surface or substrate and remains bonded over a period or time. Removal requires destruction of the facestock or substrate. Generally this adhesive is identified by red imprinting on the liner (but not always).
Can be removed without damage to the facestock or substrate. Removability will vary with time, the surface applied to, and ambient conditions. generally, this adhesive is identified by green or blue imprinting of the liner. Note that removable adhesives will become permanent over time, depending upon the surface adhered to and ambient conditions.
An adhesive can also be formulated for a SPECIAL application. A SPECIAL adhesive is designed for a specific need or surface This requires a great deal of testing. There are. however. SPECIAL adhesives available as stocked products from some manufacturers like Cold Temperature Adhesives (to be applied to a frozen surface), Block-out or Opaque Adhesives (for covering up printed material) and Badge Adhesives (for short term applications to clothing at a convention or reunion). Please note that a Badge Adhesive is not recommended for fur, suede, leather silk or vinyl.
Repositionable vs. Short Term Removal
Some applications require an adhesive that will be removable for a short period of time before becoming permanent. This feature is desirable if the label is misapplied and must be removed and then reapplied correctly other labels are designed for removal after being used, like a bumper sucker, but are not intended to be reused. This is typical of the standard removables available.
A true repositionable adhesive is similar to a 3M brand “post-it” note and is available from a select number of manufacturers. This type of adhesive has many applications with children’s stickers and in advertising where the label, or sticker is taken off one substrate and reapplied to another, multiple times.
Facts About Liners
The liner is one of the Most distinguishable aspects of Ps material. The removal system not only makes the label more useful for the end user, but can also impact all aspects of the printing and finishing stages. The liner must also provide sufficient support to the facestock, and must lay flat to eliminate the possibility of curl and wave .. in storage and. In particular, in the production and finishing phases.
Types of liners:
The Image Producing, Polycoated and Plastic liners are used for specific product applications and product constructions. They are usually available in roll label products, not sheet products.
Moisture and humidity changes should be gradual in order to minimize potential curl.
For our purposes, the Supercalendered and Machine Finished liners are used for most sheet products of pressure sensitive. They have good stay-flat properties and are good for kiss die-cutting.
A Supercalendered liner is a highly refined Kraft paper which is smooth and dense. This hard and smooth paper is ideal for a uniform release coating using a minimum amount of silicone. It is excellent for kiss die-cutting but is not always a choice for sheet products because it is sometimes sensitive to humidity changes. The manufacturer must maintain the proper moisture content in the liner for stay-flat properties.
A Machine Finished Liner is less refined but is much more stable as a lay-flat product when sheeted. Usually it is clay coated paper for a smoother surface and less absorbency.
The pressure sensitive product does not become a functional product until it is first printed or converted. The four things printers and/or converters look for and expect from pressure sensitive materials are:
The need to have trouble and hassle free cutting of pressure sensitive products. Most manufacturers recommend cutting their products in the face down position to avoid adhesive build up on the cutting blade. It is also recommended to minimize the clamp pressure when cutting: However, many products on the market today have little adhesive buildup compared to a decade ago. The technology advancements have nearly eliminated many such problems.
The need to be able to cleanly feed through the press. If sheets are rippled, curled, or lifting it will result in frequent misfeeds. If adhesive has oozed, causing blocking of the sheets or adhesive build up on grippers and blankets, it could be costly to the printer. Also, there should be no premature breaking of the liner going through the press.
The printer requires the same quality facestock on which to print that they normally would expect from a conventional paper stock.
A satisfied customer, who appreciates the print quality as well as the functionality of the label will become a repeat customer of these specialty products.
Easy removal of liner from the face stock. Adhesive performance on substrate. Quality print reproduction (a function of choosing the right face stock).
Storage & Processing
There are some general guidelines one should know about storing processing and finishing most pressure sensitive materials.
• Best kept at 70 degrees and 50% relative humidity.
• Avoid direct sunlight.
• Store in original wrapper.
• Stack no more than 5 cartons high (Extreme weight on the bottom sheets can cause the adhesive to ooze.)
• Do not double stack skids.
• Avoid storing near any heat sources.
• Bring stock into printing area 24 hours prior to use.
• Equalize paper temperature and press roorn temperature.
• Do not remove protective wrapper until ready to use.
• Cut face down.
• Powder edges to eliminate ooze.
• Minimize clamp pressure.
• Use chip board to reduce adhesive build up on blades.
• Preconditioning of blades (usually with a silicone spray).
To decide which PS product to recommend you must first know how the label will be used. There are several variables and factors which will affect which facestock should be chosen, as well as how well a permanent or removable label will adhere to a substrate.
Some of the questions you should ask are:
What is the end use?
What is the texture of the substrate surface?
Smooth surfaces, such as stainless steel or glass, provide 100% adhesive contact, resulting in very high adhesion, even when using a removable adhesive. Rough surfaces, such as corrugated boards or textured plastics, provide much less adhesive contact to their surface and the label must have stronger bonding adhesive to achieve acceptable adhesion.
What is the shape and size of the surface?
Highly curved and cylindrical surfaces will require a highly aggressive adhesive is one that adheres quickly and will not lift at the edges. The surface size- or label size - is an important consideration with removable labels. Small removable" labels of stiff facestock materials may not adhere well to curved or irregular surfaces unless the adhesive is aggressive enough. In order to help adhesive bonding, a more pliable facestock, such as a latex impregnated, may be recommended.
What Is the application or exposure conditions that the label must withstand (temperature, weather, and substance)? .
It is important to check the temperature of the substrate that the label will be applied to at the time of application. In the pressure sensitive industry, two temperatures are important:
• Application temperature: the temperature of the substrate at time of application.
• Service temperature range: the temperature range an adhesive will withstand once it has bonded to a substrate (generally 12-24 hours). .
Many standard permanent adhesives should be applied above 40 degrees Fahrenheit (the minimum application temperature) and have a service temperature range of -40 degrees Fahrenheit to 175 degrees Fahrenheit.
For temperatures outside this range, a special cold temperature adhesive or adhesive that withstands high temperatures may be required. It is also important to consider: .
• Exposure to moisture - will the label be exposed to rain or water?
• Exposure to sunlight (ultra violet rays) will the label be outdoors or in a window?
• Exposure to food (may require special FDA adhesive) will the label be applied directly to a food product, like a banana, or to the outside Ctn/Pkg of a food product?
• Childrens labels (may require low chemical content) Will the label need to be approved for the application with certification from the manufacturer?
• Labels for Underwriters Laboratory listed components will the label meet UL approval if required for the application?
• Will the label be exposed to chemicals or solvents?
• Will the label need to be strong and/or chemically resistant because the end user is applying it to a product containing chemicals or abrasives?
REMEMBER...IT IS ALWAYS RECOMMENDED THAT YOU OR YOUR CUSTOMER TEST THE PRODUCT AT THE END USE!
Laser printers have become a part of nearly every office. The price of a laser printer has become more affordable, but more importantly, the cost effectiveness has become more evident to office managers. Additionally, the different types of stocks that can now be run through a laser printer has grown tremendously.
The growth of laser printers is continuing and we at Steadfast Paper see more and more products being developed for this market.
Pressure sensitive products, and related specialty products, are very popular with the small environment because the software capabilities have brought the “desk top” publishing to home. This means more applications for the small user. The important thing to remember about pressure sensitive laser labels is that they must be able to withstand the high temperature of the laser printer. Please take note:
Things to consider:
• Laser labels are designed to be flexible enough to go through and around the laser printer path. This is a full 180 degrees without curling.
• Laser labels are designed to withstand the heat of a laser printer without curling up and jamming. They must withstand temperatures upwards of 375 degrees.
• The heat from the laser printer must not “melt” the adhesive causing to ooze from the edges; damaging your valuable printer.
• The pre diecut labels cannot delaminate (peel off) while running through the printer.
• The thickness of the pressure sensitive label stock must not exceed the recommended caliper of the laser printer. The feeding mechanism will not pick up a stock that is too heavy or it may jam when it begins to go around the drum cylinder.
• Will the heat affect the adhesive properties? Once subjected to a high heat, the adhesive can lose its ability to bond well to the surface you intend to stick it on.
For these reasons, we suggest you use only laser compatible products when choosing a pressure sensitive product. In addition, please follow the suggestions of your laser printer manual and use only label products that meet their guidelines. Each brand of laser printer has different requirements. Though there are standard" laser label products, they do not work the same in the various types of printers available. Always test first.