Printing & Marketing
The Process
All printing begins with an idea. A customer works with a graphic artist to create the design on the package. Once the design is complete, the art can be transferred to a package layout, scaling items up or down to get a balanced appearance.
Before a sack is manufactured, its outer ply is usually printed on rotary printing presses of various types. In general, the process involves photographic film of the artwork being transferred to plates which are mounted on a printing cylinder. The plate then transfers the image to the paper surface.
Historically, (many years ago) the press most often used for printing sacks has been the letterpress. The letterpress uses a plate with raised type to carry the image into direct contact with the paper being printed. Letterpress inks are viscous, tacky pastes which usually are cured by oxidation.
Current Trends
Today, most paper shipping sacks are printed with a much more efficient printing process called flexography. A flexographic press uses photopolymer plates, either digital or conventional, mounted on a printing cylinder.
This process uses very fluid, fast drying solvent or water-based inks. It is especially adaptable to high speed, low cost, in-line printing. Today’s flexographic printing process is a worthy competitor to other major printing processes.
Multiwall sack with four-color graphics.
The speed of a new, eight-color flexographic press can range from 1200 feet per minute for a single color to 500-800 feet per minute for process color and can be operated by two people: a pressman and an assistant.
Newer photopolymer plates provide longer plate life, excellent print fidelity and added uniformity in durometer and thickness.
Also, commonly used are water-based printing inks that can be printed at high speed in top-quality process printing while greatly reducing pollution.
Flexographic-Stack or Central Impression (CI) Press
A. Image Carrier (Relief Plates)
The relief plate is made from photopolymer sheets or formed and etched from a liquid photopolymer resin.
B. Method of Printing
The flexible plate is mounted on a cylinder. The plate picks up ink from the anilox roll which receives ink from the ink chamber or a rubber roll. The plate cylinder turns and applies ink directly to the sheet as it presses against the impression roll.
Offset Printing
A. Image Carrier (Plano Plates)
Colors are separated onto film negatives. An exposure light then penetrates the clear area of the negatives and burns the image on a light-sensitive, flat aluminum plate for each color. Today, plates are usually exposed with a digital image setter.
B. Method of Printing
The plate is attached to the cylinder with special locking devices. As the plate cylinder turns, the plate is first coated with water. Since water will not stick to the image on the plate and ink will not adhere to water on the plate, ink is therefore only accepted on the image area of the plate. As the plate cylinder continues to turn, ink from the plate is transferred to a rubber blanket cylinder and then to the paper.
C. Inks
Inks used for offset printing are of a pasty consistency, oil-based and more expensive than other inks commonly used for multiwall sacks.
D. Advantages of Offset Printing
- Very high quality
- Inexpensive plates
- Quick and easy plate changes
- Fine line or process printing can be accomplished on rougher substrates than with gravure or flexography due to the use of the rubber blanket and the ink hold-out
E. Disadvantages of Offset Printing
- Higher ink costs
- Plates are not as durable as relief plates
- When water is used, presence of the fountain solution can create problems in creasing, seaming, drying and discoloration of non-printed areas
Rotogravure Printing (Gravure)
A. Image Carrier (Engraved Cylinder)
The image carrier is normally a copper-coated, metal cylinder which is chemically or electronically engraved, then chrome-plated to resist doctor blade wear. The printing image consists of many thousands of tiny recessed cells per square inch which vary in depth and width so they can accurately meter the proper amount of ink.
B. Method of Printing
The gravure cylinder picks up ink from the ink fountain. A conventional angle doctor blade wipes off all excess ink and allows it to return to the ink fountain. The ink remaining in the cylinder’s cells is transferred to the substrate when the substrate passes between the engraved cylinder and the impression roll.
C. Inks
The inks used are very thin and can be adjusted to operating viscosity at the press.
D. Advantages of Rotogravure Printing
- Relatively simple mechanical features
- Excellent process and line printing quality
- A very high degree of consistency throughout the run
- Prints a number of substrates such as paper, film, foil, etc.
- Excellent for long runs and repeated runs of medium quantities
E. Disadvantages of Rotogravure Printing
- Extremely high engraving costs
- Very high plate costs for short runs unless the job will be repeated many times
Flexographic Printing
A. Image Carrier (Relief Plates)
Flexible photopolymer plates are produced and then mounted on a cylinder of the desired size and repeat length. The ink is pumped into a fountain or directly on the anilox roll.
B. Methods of Printing
1. Three-roll system – The ink is transferred from the fountain directly to the anilox roll by the fountain roll. The fountain roll also serves as a metering device to allow all excess ink to return to the fountain.
2. Two-roll system (reverse angle doctor blade) – The ink is pumped directly to the anilox roll above the doctor blade assembly. The doctor blade wipes off all excess ink and allows it to return to the ink fountain. In both systems the anilox roll applies a uniform film of ink to the printing plate which is mounted on the plate cylinder. The plates transfer the ink to the substrate by pressing against the impression roll.
C. Inks
The inks for flexographic printing are liquid and can be adjusted to the press for proper viscosity.
D. Advantages of Flexographic Printing
- Good quality process and line printing
- Fast press changeover with easy clean-up
- Less expensive plate costs than rotogravure
- Can print on different substrates
- No fire hazard with water-based inks
- Excellent registration
E. Disadvantages of Flexographic Printing
- Replacement of anilox rolls due to wear
- High drying costs
- Rotogravure cannot be matched for consistency throughout a run
Marketing Applications Of Multiwall Sacks
Paper shipping sack users have begun to realize the value of shipping sacks as a marketing tool to help sell the product inside the sack. Historically, shipping sacks were constructed of plain brown kraft paper, with either minimal or no graphics. Now, rather than just being a way to transport goods to market, shipping sacks can also carry a product’s image – right to the point of sale and beyond.
At the Point of Sale
Marketers spend millions of dollars every year for point-of-sale (POS) or point-of-purchase (POP) materials such as store banners, posters, shelf-toppers and mobiles to influence consumers who are about to make a purchase. But with improvements in four-color offset and flexographic printing producing high-quality art and graphics, the paper shipping sack itself can function as a POS item.
Because of the fierce competition among brands for shelf space in retail outlets such as supermarkets and discount and hardware stores, store managers often stock shipping sacks on their faces due to stacking ease or, to save space, on their ends with one side facing the store aisle. With this in mind, package designers try to devise shipping sack graphics which include the side of the sack.
The Traveling Billboard
Image-conscious marketers use paper shipping sacks to carry their advertising message as the product travels from the POS in the store into the home. When consumers see related advertisements on television or in magazines, they are constantly reminded of their purchase, thus reinforcing buyer loyalty.
Paper Shipping Sacks as a Communications Medium
Many marketers also use paper shipping sacks to carry coupons, rebate offers and direct response materials, either by inclusion inside the sack or attached to the sack’s face. For example, a pet food manufacturer might insert a coupon good for a discount on future purchases. Stapled or “tipped-on” coupons (coupons that are affixed by an adhesive allowing easy removal) appearing on the outside of shipping sacks visually attract consumers, thus serving as an excellent POS persuader.
Marketing Plans Built with the Sack
The role of the shipping sack in purchasing decisions can be an influential one. In the design and construction stages it is important to consider the marketing usages of the package. For example, a seasonal promotion such as a Christmas offer might be particularly effective if the graphics had a holiday theme. This theme used on shipping sacks in conjunction with television and print ads, could serve as a successful marketing and communications tool.