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Removable Pressure Sensitive Adhesive Products

Pressure-Sensitive Adhesive products ,

are usually bonded , firmly to applied

surface.

The PSA product peel -of or

delamination is not desired or Intended.

However, there are adhesive tapes where

in the , adhesive clean and easy removal

from substrates after use is desired.

A repositionable adhesive allows a label

to be repositioned without damage , to

either the label or the substrate. Many

applications require that the adhesive

holds the label firmly in place, yet does

not leave residue behind when the label

is removed.

This material holds items firmly, yet lets

you remove or reposition your artwork or

matting as many times as you want to,

even months later. Use on your

computerized mat cutters so your mats

won't slip. Also used to hold articles in

place that requiring stitching. It resists

bleeding, staining, or wrinkling. Should

only be used for temporary bonding. This

pressure sensitive material can be

removed from paper without lifting fibers

or delaminating it.

a range of removable adhesive tapes,

clean peel and perm/peel products. Both

single and double coated, controlled peel

products, designed for clean, residue free

removal, even after extended periods

History

In 1968, Dr. Spencer Silver, a scientist at

3M in the United States, was attempting

to develop a super-strong adhesive. But

he created a "low-tack", adhesive by

accident. It was found to be

reusable, pressure-sensitive adhesive

. For five years, Silver promoted his

invention within 3M, both informally and

through seminars, but without much

success.

In 1974, a colleague of his, Art Fry, who

had attended one of Silver's seminars,

came up with the idea of using the

adhesive to anchor his bookmarks.

A year later, in 1978, 3M issued free

samples to residents of Boise, Idaho, and

94 % of the people who tried them said

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that they would buy the product. On

April 6, 1980, the product debuted in US

stores as "Post-It Notes". In 1981, Post-

its were launched in Canada and Europe.

In 2003, the company came out with

Post-it Brand Super Sticky notes, with a

stronger glue that adheres better to

vertical and non-smooth surfaces.

Standard Post-it Brand notes have only

partial adhesive coating on the back,

along one edge. Similar products are

used for specialized purposes with full

adhesive coating; the US Post Office

uses such yellow address labels to

forward mail.

The yellow color was chosen by

accident; a lab next-door to the Post-it

team only had scrap yellow paper, which

the team initially used.

Introduction

Often we require a pressure sensitive

adhesive (PSA) bond that is not

permanent, and the substrates need to be

purposely "detached" at a certain time.

Uses for such adhesives include

nonstructural applications such as

removable labels, masking tape, surface

protection films, easily replaceable and

removable note paper, and bonding credit

cards to mailers. Applications can even

include structural applications such as

tooling placement, prototyping, and the

assembly of parts for eventual reuse or

recycling.

There are various types of removable

pressure sensitive adhesives available to

the end-user depending on the degree of

bond strength required. PSAs that are

filled with microspheres are claimed to

be the most repositionable of these

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systems. Here "repositionable" is defined

as the ability of the substrates to be

detached and then rebonded repeatedly.

This feature is desired when the bond is

meant to be repeatedly detached and

rebonded or when substrates are

commonly misapplied and need to be

repositioned.

Thus, repositionable adhesives differ

from what is referred to as "removable"

adhesives. Removable adhesives are

generally those providing an adhesive

bond that can withstand the rigors of

service but in which the substrates can be

purposefully detached leaving little or no

adhesive residue. The substrates

generally cannot be rebonded once they

are detached.

Mechanism

The concept of a repositionable PSA

made by incorporating microspheres into

a polymeric binder has been around for

several decades. For example, 3M

Company's famous Post-It™ Notes

product, commercialized in the 1980s,

consists of tacky, crosslinked acrylic

microspheres, which make "point

contact" with the paper substrate4.

These repositionable adhesives have a

unique composite-like structure in which

micro-sized spheres are held together by

a polymeric binder. The binder also

serves as the base polymer in the

adhesive formulation. Due to the

presence of the microspheres and the

discontinuous morphology , the adhesive

does not completely wet the substrate to

which it is applied. As a result, the

adhesive strength is less and does not

develop with time as in the case of

conventional pressure sensitive

adhesives.

Microspheres are tiny particles

measuring between 10 and 250 microns

in diameter. Although they are

microscopic in size, these spheres are

still much larger than the emulsion

particles found in conventional

adhesives. The size difference has a

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dramatic impact on adhesive tack. By

forming a discontinuous film,

microsphere adhesives limit physical

contact, resulting in low peel,

removability and stable tack over time.

Emulsion adhesives, on the other hand,

use smaller particles, which coalesce into

a continuous film and do not allow for

easy removal or repositioning.

A repositionable adhesive allows a label

to be repositioned without damage to

either the label or the substrate. Many

applications require that the adhesive

hold the label firmly in place, yet does

not leave residue behind when the label

is removed.

Repositionable adhesives have relatively

good coat ability but a low degree of tack

and peel strength. If the microspheres are

resilient and there is sufficient binder

concentration, the adhesive bond results

in an even peel strength during

separation with little adhesive transfer.

Table 1 shows the tack and peel strength

of representative permanent, removable,

and repositionable (microsphere)

adhesive system. Shear strength of a

microsphere PSA is very low and

generally not measured.

PSA Type Peel

Strength

gm/25

mm

Loop

Tack

gm/25

mm

Shear

Permanent >2000 1400 High

Removable 250-275 400 Med

Repositionable 90-100 250 Low

The Performance Challenges

To ensure perfect placement

should offer highest degree of

repositionability

To protect fragile substrate

clean removal from varies surfaces like ,

newsprint, paper, drywall and glass, with

no adhesive residue, transfer or ghosting.

Durability

Reusability

like paper tab markers to be used again

and again.

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Materials, Handling, and Application

Most repositionable microsphere PSAs

are made from acrylic emulsion base

polymers that serve as the "binder" as

well as the microspheres. It is important

that the microspheres (measuring 10-250

microns) are significantly larger than the

emulsion binder particles. The binder

concentration must be optimized to the

particle size of the microspheres in order

to provide the surface morphology that

will achieve the best adhesive

performance.

Microsphere adhesives can be produced

via one of two processes. Typically they

are formed by a water based free radical

suspension polymerization using two

acrylic monomers. In this case, the

microspheres are acrylic and form

together with the base polymer emulsion

particles. Another method of production

can be to form the base polymer and the

microspheres separately and then mix

them together in the formulating process.

This technique is used in specialized

applications as it provides somewhat

more control of the end-properties due to

the variety of microspheres that can be

produced.

The adhesive properties of microsphere

PSAs are controlled by a number of

factors. Most significant are coating

weight, particle size, concentration of

binder, and monomer characteristics such

as glass transition temperature (Tg) and

molecular weight. Table 2 provides

information on how these factors can be

used to control adhesive performance.

These factors must be balanced by the

formulator and / or converter to provide

adhesive properties that are optimized for

the specific application.

Factor Performance Contribution

Adhesive coating

weight

Peel adhesion strength is increased

by increasing coating weight. This

is not unlike other PSAs.

However, with microsphere

adhesives too much adhesive on a

smooth facestock can cause

layering of spheres on top of each

other leading to poor cohesive

strength.

Microsphere

particle size and

amount of binder

Large particle size microspheres

and low binder levels provide

rough coatings (lowest adhesion

level). High levels of binder and

small particle size will lead to

smoother coatings and better

wetting of the adhesive on the

substrate. Smoothest coatings give

the highest peel strength and peel

values that build over time. The

roughest surface will provide the

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lowest and most stable peel values.

Glass transition

temperature, Tg

Monomers that form low Tg

polymers (e.g., 2-ethylhexyl

acrylate provide good tack and

flexibility). Comonomers with

higher Tg (e.g., methyl or ethyl

acrylate) provide higher cohesion

and shear strength. This is not

unlike other PSAs.

Molecular weight Lower molecular weight

microspheres adhesive offer higher

tack, while higher molecular

weights provide better shear

strength. Very low molecular

weights can produce cohesive

strength problems.

In addition to lowering the tack and peel

strength, repositionable adhesives must

also provide a mechanism that

counteracts the peel strength

development with time noticed with all

PSAs. To tackle this, formulators have

replaced petrochemical based acrylate

esters with esters made from alcohols

found in vegetable oils.

In general, microsphere PSAs can be

used much like conventional PSAs.

However, certain Precautions should be

observed due to the composite nature of

the product.

General

Avoid high shear forces.

Small pumps operating at slow speed and

gentle mixing are preferred.

Microspheres rise to the top of their

container.

Gently stir before each use or transfer.

Microsphere adhesives are pH sensitive.

A pH of 7.9 to 9.5 is recommended.

pH can be adjusted with 21% aqueous

ammonia.

Once microspheres are coagulated, the

adhesive is unrecoverable.

Storage

Shelf life is six months.

Store between 10°- 30° C do not freeze.

Use partial drums quickly.

Pumping and Filtration

Be sure to eliminate air from adhesive

lines as this will create foam.

Do not use felt filter bags.

Fine filtration removes spheres;

Do not use filters finer than 60 mesh or

250 microns.

Change filter bags when pressure

exceeds 30 psi.

Handling

Add all formulating ingredients slowly

under gentle agitation.

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Defoamer can be added to minimize

foam (typically 0.1-0.2% if oil based and

0.1% if silicone based).

Premix defoamer at a ratio of 1:1 with

water.

Coating

Certain microsphere products are capable

of being coated by rod, roll, or slot-die

coated.

Avoid free-fall of the adhesive during the

recirculation process.

Polymeric microspheres are now helping

deliver enhanced performance in many of

these areas. Larger than particles found

in conventional emulsion adhesives,

these spheres have a big impact on

adhesive tack. They create a

discontinuous adhesive surface that

limits physical contact with a substrate,

making removability easier. The

microsphere adhesive holds labels firmly

in place on most substrates yet is

permanently repositionable.

Typically microsphere adhesives are

formed directly from raw materials by a

water-based free-radical suspension

polymerization using two acrylic

monomers. However, for specialized

applications the microspheres are

sometimes formed by dispersion

polymerization in an organic solvent,

and then added to a separately-formed

adhesive.

Component Amount

(g)

Total

proportion

Deionized water 242.3 60.57%

Crosslinked acrylic acid 8.4 2.10%

Sulfocarboxylic acid

anionic surfactant 4 1.00%

Ethoxylated oleil alcohol non-

ionic surfactant 3.2 0.80%

Ethyl acrylate/2-ethylhexyl

acrylate 141.6 35.39%

Dibenzoyl peroxide initiator 0.56 0.14%

Suspension polymerizations are heated

until the initiators thermally decompose

to generate a sufficient number of free

radicals to begin the reaction, with

nitrogen bubbled through the reaction

mixture to deoxygenate it. Monomers are

typically already present when the

reaction is initiated. Stirring time and

speed parameters can be used to control

monomer droplet size, with average

particle size tending to decrease with

increased and prolonged agitation of the

reaction mixture.

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This process yields a process that stable

aqueous suspension of microspheres can

be used immediately as an adhesive.

Alternatively it can be compounded with

tackifiers, plasticizers, rheology

modidiers, colourants, latex binders and

other additives.

Controlling microsphere adhesive

performance

The adhesive properties of microsphere

PSAs are most often modified by varying

glass transition temperature (Tg) using

different types and amounts of co-

monomers. Monomers that form low Tg

polymers like 2-ethylhexyl acrylate

provide adhesive tack and flexibility. Co-

monomers giving higher Tg polymers

like methyl or ethyl acrylate enhance the

adhesive's cohesion and shear strength.

Varying polymer molecular weight is

another way in which microsphere PSA

properties can be controlled, especially

tack and shear strengths. This can be

done through process control, for

example by changing polymerization

temperature, or by chemical control, by

changing initiator concentration or

adding chain transfer agents. Lower

molecular weight microsphere adhesives

show higher tack strength, while higher

polymer molecular weights provide

better shear strength. Low polymer

molecular weights can produce major

microsphere cohesivity problems when

larger amounts of chain transfer agents

are used.

The Ethyl Acrylate % ( Increase Ethyl

Acrylate and Decrease 2 Ethyl hexyl

Acrylate ) is useful in altering the

Adhesive Properties .

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While microsphere pressure sensitive

adhesives have proven to be

repositionable, the strength of their bonds

increases over time. To tackle this,

scientists have replaced the

petrochemical-based acrylate esters with

esters made from alcohols found in

vegetable oils. These are produced by

reacting acrylic acid with heptanol,

octanol or decacnol from sources like

coconut oil and palm kernel oil, or

animal fats such as tallow and lard.

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Suitable Applications

Carpet tape for Aero Plane.

The carpet tape is a double-sided,

differentially coated adhesive tape with

one clean peel removable side and one

very high adhering side. The modified

acrylic adhesive on the carpet side

provides very high levels of initial tack

and adhesion. The unique, clean peel

removable acrylic on the floor side

provides very secure adhesion to

composite floor panels and easy,

controlled peel removal with the carpet.

Masking of parts during powder

coating

Masking for Abrasive or Sand Blasting

During preparation, items are abrasive

blasted to remove oils, dirt, rust and mill

scale. Threaded portions of parts are

masked to prevent damage. Because of

the extreme pressure applied during

blasting, duct tape is used to mask for

this step. Duct tape is sticky and thick

enough to stand up to the heat caused by

the friction of blasting parts.

Masking for Curing Oven

Parts can then be masked to prepare for

baking in the curing oven using a high-

temperature tape. Temperature-resistant

tape comes in many sizes and

formulations. These tapes are made from

polyester or fiberglass with special

silicone-based adhesives able to

withstand extended periods at high

temperatures.

Protection of bright parts

Mounting of protection pads

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as an application tape for auto badges

Mounting of shop front and window

graphics

Temporary fixing in print finishing and

direct mail companies

Mounting of smart cards

Adhesive tape technology is seen as the

most flexible, clean and easy solution for

the smart card market’s manufacturing

process. Adhesive use for module

embedding guarantees both card quality

and long term resistance, which in turn

reinforce the Smart Card security.

More Applications

Ultra Removable Stickers and Labels