7/27/2019 Best Practices for Front Seal Gumming Lt-5662[1]

http://slidepdf.com/reader/full/best-practices-for-front-seal-gumming-lt-56621 1/2

1. Gum FormulationThe majority of envelope seal gums in use today are

blends of synthetic resin and dextrin (modified corn

or potato starch). This type of formulation provides

an excellent balance of properties needed for

high speed automatic inserting. Different adhesive

manufacturers offer formulations of varying resin-to-

dextrin ratios. Higher resin content translates into

better lay-flat, better adhesion, higher mileage and

faster drying speed, but it also tends to dry faster

on the rollers during machine shutdowns and is

more difficult to clean up.

Certain jobs may require the use of a resin seal or“tropical gum” formulation. This type of seal gum

has better adhesion and resistance to humidity

blocking than resin-dextrin blends. However, resin

seals are lower in solids content and, therefore,

require more drying on the machine. They also

do not remoisten as easily as resin-dextrin blends

and lack the high remoistening tack desirable for

automatic inserting.

2. Gum Viscosity 

The viscosity (flow property) of the gum is an

important factor in determining how much isbeing carried on the rollers, and ultimately how

much gum is being applied to the envelope. It is

important to note that viscosity of the gum varies

with the gum temperature. If the seal gum is cold,

the viscosity will increase dramatically, and its flowwill be sluggish. At high temperatures, the opposite

occurs. Viscosity changes can significantly impact

application amount, so care should be taken to

maintain a consistent gum temperature in the gum

box. Seal gum that is allowed to dry out in the

gum box will skin over and thicken as moisture is

lost. The seal gum can be diluted, but a gum liquor

should be used. If a machine is going to be down

for more than a few minutes, the gum rollers may

need to be kept moist with a wet cloth or with a

spritz of water from a spray bottle.

3. Application Amount

Assuring the proper application amount of front

seal adhesive is critical to producing envelopes

of good quality. Refer to National Adhesives’

 Adjuster’s Gum Guide for proper amounts. An

insufficient application of seal gum can dramatically

diminish its adhesion, speed of set, and tack in an

automatic inserter. Assuring a sufficient application

amount is especially critical on difficult papers,

such as rag bond, kraft or coated stocks. Excessive

application of front seal gum can lead to problems

with insufficient drying on the machine which canlead to blocking of the seal flap. It can also result in

excessive curl of the seal flap.

For Front Seal Gumming

Proper application of the front seal is one of themost critical factors in producing envelopes of good quality. The

factors listed below are believed to be some of the key variables

affecting quality and consistency in front seal gumming. Provided

are some suggestions and the current industry best practices

for each.

7/27/2019 Best Practices for Front Seal Gumming Lt-5662[1]

http://slidepdf.com/reader/full/best-practices-for-front-seal-gumming-lt-56621 2/2

® and ™ designate trademarks o Henkel Corporation or its afliates. ® = registered in the U.S. Patent and Trademark Ofce. © Henkel Corporation, 2009. All rights reserved. 6012/LT-5662 (7/09).

Henkel Corporation

10 Finderne Avenue, Bridgewater, NJ 08807

1-866-4-HENKEL (866-443-6535)

www.henkelna.com/envelopes

For Front Seal Gumming

4. Weight of Transfer Roll

Most envelope folding machines use a floating

transfer roll. Choosing the proper floating roll for the

viscosity of the seal gum being used is important

to ensure good metering. Brass and aluminum are

the two types of floating rolls most commonly used. Aluminum with brass inserts can also be used.

Since brass is heavier than aluminum, it is typically

used for seal gums of higher viscosity. Aluminum is

lighter and is better for lower viscosity seal gums.

5. Drying

There are several types of drying that can be used

to dry seal gum, including radiant heat, blown

hot air, infrared lamps and even radio frequency

drying. Most machines use forced hot air drying

or radiant heat lamps, but some newer equipment

uses a combination of IR lamps and forced hot air.

Infrared is an efficient method of drying that does

not produce as much radiant heat as other types of

drying. Radio frequency (RF) drying is used where

there is a need for maximum drying in a short

amount of time. This type of drying may require that

the seal gum contain a conductive salt to facilitate

the drying.

6. Supply to the Gum Box

A bottle feed system is still the most commonly

used method for maintaining a steady supply

of seal gum in the gum box. Recirculation is

sometimes used to prevent the seal gum from

skinning over and to reduce the need for gum bottle

changes. The preferred method for delivering a

consistent supply of seal gum to the gum box with

little or no intervention from the adjuster is with the

use of an on-demand level sensing device.