terborne Adhesive Tackifiers Development of Viscous Liquid Resin

Is Based on Replenishable Tall Oil Rosin

PANAMA CITY. FLORIDA s.-. . b L ,

and water, accompanied by sufficient agitation to emulsify the system. These tackifiers can then be used with latex elastomers in largely aqueous formula-

many Of which

ber af problems fer nnr instantaneously While solvent-assisted emulsion sys- tems have met with a degree of success in formulating pressure sensitive adhe- sives, they have several disadvantages. The solvent content of these systems precludes totally solvent-free adhesives. Also. there is reported evidence that surfactants used to stabilize the emul- sion can adversely affect tack properties of the final adhesive (1).

.c neither immediately developed for, nor A lack of stability can alsobe a trou- instantaneously applied to a specific blesome problem in storage and han-

cost and problem area. Rather, it 'is an evolu- 4lhg'e.f these .products., Emulsion sta- facing a tionary process of continual product bility can be destroyed irreversibly existing and performance improvements. when subjected to temperatures below

The development of aqueous resin/ freezing or to mechanical shear. Such rubber pressure sensitive adhesives is emulsion resins are usually produced at progressing through a similar evolu- 50-60 percent solids content, which can

sol- * tionary process. The basic concept re- be a limitation in formulating solids, the volvca around the use of a latex elas- water-based adhesives.

tomer for cohesive strength, tackified A second approach to waterborne by a waterborne resin. One of the ear- tackifying resins is the solvent-free dis-

con- liest and easiest approaches to prepar- persion. Using more sophisticated dis- onal ing this kind of tackifying resin is that persing or homogenizing technique@,

of solvent-assisted emulsions. Such along with the a emulsions are prepared by dissolving level of emulsifier,

relied upon sol- Often, technological innovation is neither

The industry, immediately developed tions.

apprrea to, a specific problem area. Rather,

it is an evolutionary process of continual

product improvements

Figure 1. Performance properties of compounded latex adhesive system based on 27°C softening point rssinlSBR Latex A (Amsco 6140, Union Oil Co. of California - solid line) and Latex B (Polysar 222, Polysar Latex - dashed line).

tunity to produce solvent-free adhesives when used in concert with the appro- priate latex elastomer.

They, nevertheless, also possess some of the same drawbacks as the solvent emulsion systems. Mechanical and freezelthaw instability, surfactant con- tent, and low solids can all be limita- tions of resin dispersions.

The manufacturing process for sol- vent-free dispersions can also be more complicated than the process used to produce solvent emulsions. Forming a dispersion of a high softening point resin with the aid of a solvent places greater demands on the equipment used. Solvent removal from resin emul- sions would also require additional equipment and processing steps. In many cases, the adhesive compounder lacks the capability to produce solvent- free dispersions and must depend upon resin suppliers for these products.

A Recent Development Recently a technology has been de-

veloped that simplifies the conversion

to water-based adhesives and over- comes the aforementioned problems. This technology is an emulsifier-free, high solids, completely freeze/thaw sta- ble tackifying resin. It is developed spe- cifically for water-based adhesive com- pounding with latex elastomers. The new products are viscous liquid resins based on replenishable tall oil rosin. Their proprietary composition allows spontaneous dispersibility in water without added surfactants or solvents.

Adhesive formulating simplicity and versatility are advantages of these wa- ter-dispersible resins. Their design pro- vides a broad range of formulating lat- itude; the adhesive formulator can achieve high solids, develop desired vis- cosity, and formulate a wide range of resin-to-rubber ratios with a variety of latex elastomers.

Complicated processing equipment is not required, only mild heat and agi- tation in three steps:

(1) Charge the desired amount of wa- ter-dispersible resin to a blending vessel equipped with an agitator and heat.

sion. (3) Stop the heat and

latex to the stirred resin itation is usually contin

To date, three water- ins have been developed

mulations. These products, wh modified rosin esters, have soft, points of 5"C, 27OC and 4loC*; average molecular weights are 550, 670, and 750, respective1

The lowest softening (5OC) improves the tack per many latex formulations. however, has greater potential modifying resin used in c with other tackifiers. It has useful in aqueous polymer ap other than pressure sensitive a

The resin with a softenin 27°C (Table I) has been f an excellent balance of properties when used as t fier in pressure sensitive ad mulations. Such two- tems using the 27OC resin and several latex been evaluated over a rubber ratios. Elastomers dude carboxylated styr rubber (SBR), natural prene, and acrylic. Table I1 test conditions used in the Note that shear data was using two conditions.

The performance data of softening point resin in carb

'Aquatac 8005, 9027, tied waterdispersible Panama City, Florida.

Figure 1. Performance properties of compounded latex adhesive system based on 27°C softening point resinlSBR Latex A (Amsco 6140, Union Oil Co. of California - solid line) and Latex B (Polysar 222, Polysar Latex - dashed line).

tunity to produce solvent-free adhesives to water-based adhesives and over- when used in concert with the appro- comes the aforementioned problems. priate latex elastomer. This technology is an emulsifier-free,

They, nevertheless, also possess some high solids, completely freeze/thaw sta- of the same drawbacks as the solvent ble tackifying resin. It is developed spe- emulsion systems. Mechanical and cifically for water-based adhesive com- freezelthaw instability, surfactant con- pounding with latex elastomers. The 27OC tent, and low solids can all be limita- new products are viscous liquid resins an e tions of resin dispersions. based on replenishable tall oil rosin.

The manufacturing process for sol- Their proprietary composition allows vent-free dispersions can also be more spontaneous dispersibility in water complicated than the process used to without added surfactants or solvents. produce solvent emulsions. Forming a Adhesive formulating simplicity and dispersion of a high softening point versatility are advantages of these wa- resin with the aid of a solvent places ter-dispersible resins. Their design pro- greater demands on the equipment vides a broad range of formulating lat- used. Solvent removal from resin emul- itude; the adhesive formulator can

550, 670,

rubbe clude rubbe

sions would also require additional equipment and processing steps. In many cases, the adhesive compounder lacks the capability to produce solvent- free dispersions and must depend upon resin suppliers for these products.

A Recent Development Recently a technology has been de-

veloped that simplifies the conversion

achieve high solids, develop desired vis- cosity, and formulate a wide range of resin-to-rubber ratios with a variety of latex elastomers.

Complicated processin not required, only mild tation in three steps:

(1) Charge the desired amoun ter-dispersible resin to a blending equipped with an agitator and he

shown in Figure 1. of SBR latex signif-

performance propcr-

27°C softening point resin I natural rubber (Hartex 103, Firestone Synthetic Rubber and Latex - solid line) and natural rubberlSBR Latex B (1:l blend - dashed line).

ive has excel- ingly in adhesives composed of blends hich rapidly ferences include bound styrene content, of natural rubber and SBR latices. A 40:60 resin/ 5O:SO blend of natural rubber and SBR formulation was evaluated and it, too, is shown in

two SBR latex adhesives. Potential dif-

molecular weight, molecular weight dis- tribution, surfactant level and type, and

containing from about 35-45 percent ilar formulation based on natural rub- ce of both Latex bound styrene and having glass transi- ves show contin- tion temperatures (Tg) in the region of However, a significant decrease in

ber alone.

pear in Figure 2. As shown, both peel and tack are improved as the residrub- ber ratio increases. As expected, the

ginning at a rcsin/rubber ratio of about 3070 in the 'A )) x %", 500 gm test and at 5050 in the 1 It x 1 " , 1 .OOO gram test.

Adhesive formulations based on the 27°C softening point resin and neo- prene" rubber display a good baladce of

batwten the ob- shear performance decreases rapidly be- tack, p l , and shear properth. The peel strength increased in direct pro- portion to the tackifier concentration as shown in Figure 3. Both Polykca probe

may account

b

ottulox 103, M-W rubbor, Piroatono SynMotb R u b "Wp" 111, ohlorooram cooofvnm, El. du (w

figure 3. Performance properties of compounded latex adhesive system based on 27'C softening point resin I Neoprene (Neoprene 115, chloroprene copolymer, Du Pont - solid line) and acrylic (Ucar 173, Union Carbide - dashed line).

tack and the quick stick properties of to the lack of cohesive strength of the the adhesives show similar increases acrylic elastomer. with increasing resinlrubber ratios. The In addition to the aforementioned cohesive strength of the water-dispersi- performance properties, rolling ball ble resinlneoprene formulations is out- tack has also been used to evaluate standing up to a resinlrubber ratio of resinlelastomer adhesives (Table 111). approximately 45% using a 95'' x%", Because each of the commonly used 500 gram test. When the 1" x 1". 1,OOO tack determinations measure different gram test is used, the cohesive strength phenomena, the rolling ball tack often remains high at a 55:45 resinlrubber does not correlate with probe tack or blend. As shown, this level of tackifier quick stick. The natural rubber-based also gives good tack and peel proper- adhesive has the most aggressive roliing ties. ball tack despite its relatively poor

When compounded with an acrylicn Polyken probe tack and quick stick. A latex (Figure 3), the 27'C softening formulation using a blend of natural point resin provides increasing peel rubber and SBR Latex B also shows adhesion with increasing resin concen- good rolling ball tack. The SBR Latex tration until a maximum is achieved at A adhesive has the poorest rolling ball about a 60:40 blend. The tack proper- tack performance. ties of the formulation are slowly im- The performance properties of the proved as the resin concentration is in- two-component adhesive formulation, creased. The shear decreases rapidly (27OC softening resin/SBR Latex B in a when compared with the previous elas- one-to-one ratio), are the following: tomer systems. This is probably related Rolling ball tack - 3.3 in.

180" peel - 4.9 lb/in. 178' shear (E" x %", 500 gm) -

Wcar 173, acrylic. Union Carblde Corp.. Danbury, Connecticut. 59 min.

Polyken - 864 gm. Quick stick - 2.7 Ib/in.

This formulation s

The 27OC softening point Latex A formulation in has excellent shear with a of tack and peel perfo properties of this formulation

Rolling ball tack - 7.2 in. 180" peel - 2.5 Ib/in 178' shear (1" x l", 1,000gm

Polyken - 743 gm. Quick stick - 1.6 Iblin.

This combination of perfo properties is typical of some pre sensitive tape adhesives.

Properties of the Aged Films In addition to determining the

sive performance propert freshly prepared adhesives, ties of the aged adhesives w amined. The adhesive test subjected to an accelerated aging 140'F for 14 days. In this no antioxidants were added hesive formulations.

The results of aging the ening point resin/SBR Latex 140'F for 14 days indicated Polyken probe tack and qu were virtually unaffected by he The rolling ball tack exhibite cant degradation in p flecting a lack of correl

adhesion increased somewhat ov range of resin concentrations while the shear properties The appropriate antioxidant vide satisfactory performance s ties. Studies to verify this ass were not complete at the tim writing.

9,600 min.

Properties other than tack, pee

POlyken - 864 gm. Quick stick - 2.7 Ib/in.

This formulation shows a ance of high peel and high approximates the adhesion ments of some label applications

The 27°C softening point re Latex A formulation in a has excellent shear with a g of tack and peel performan properties of this formulation ar

Rolling ball tack - 7.2 in. 180" peel - 2.5 lb/in 178" shear (1" x l", 1,OOO gm

Polyken - 743 gm. Quick stick - 1.6 Ib/in,

This combination of perfor properties is typical Of Some press sensitive tape adhesives.

I

I

9,600 min.

Figure 3. Performance properties of compounded latex adhesive s y s t e m based on 27°C softening point resin/ Neoprene (Neoprene 115, chloroprene copolymer, Du Pont - solid line) and acrylic (Ucar 173, Union Carbide - dashed line).

tack and the quick stick properties of the adhesives show similar increases with increasing residrubber ratios. The cohesive strength of the water-dispersi- ble resinheoprene formulations is out- standing up to a resinhubber ratio of approximately 4555 using a 1/" x1/", 500 gram test. When the 1" x l", 1,OOO gram test is used, the cohesive strength remains high at a 5 5 ~ 4 5 resinhbber blend. As shown, this level of tackifier also gives good tack and peel proper- ties.

When compounded with an acrylicY latex (Figure 3), the 27°C softening point resin provides increasing peel adhesion with increasing resin concen- tration until a maximum is achieved at about a 60:40 blend. The tack proper- ties of the formulation are slowly im- proved as the resin concentration is in- creased. The shear decreases rapidly when compared with the previous elas- tomer systems. This is probably related

lUcar 173, acrylic, Union Carblde Corp.. Danbury. Connecticut.

to the lack of cohesive strength of the acrylic elastomer.

In addition to the aforementioned performance properties, rolling ball tack has also been used to evaluate resinlelastomer adhesives (Table 111). Because each of the commonly used tack determinations measure different phenomena, the rolling ball tack often does not correlate with probe tack or quick stick. The natural rubber-based e adhesive has the most aggressive rolling ball tack despite its relatively poor Polyken probe tack and quick stick. A formulation using a blend of natural rubber and SBR Latex B also shows good rolling ball tack. The SBR Latex A adhesive has the poorest rolling ball tack performance.

The performance properties of the two-component adhesive formulation, (27°C softening resin/SBR Latex B in a one-to-one ratio), are the following:

Rolling ball tack - 3.3 in. 180" peel - 4.9 Ib/in. 178" shear (Vi" x Vi", 500 gm) -

59 min.

Properties of the Aged Films In addition to determining the a

sive performance properties on freshly prepared adhesives, ties of the aged adhesives w amined. The adhesive test subjected to an accelerated 140°F for 14 days. In this no antioxidants were added hesive formulations.

ening point r e s ids 140°F for 14 days Polyken probe tac were virtually unaf The rolling ball tack exhibited cant degradation in p flecting a lack of correl tack measurements. adhesion increased somewhat ov range of resin concentrations while the shear properties The appropriate antioxidant may vide satisfactory performan ties. Studies to verify this were not complete at the t writing.

The results of aging the 27

Properties other than tack, pee

Figure 3. Performance properties of compounded latex adhesive system based on 27°C softening point resin/ Neoprene (Neoprene 115, chloroprene copolymer, Du Pont - solid line) and acrylic (Ucar 173, Union Carbide - dashed line).

tack and the quick stick properties of the adhesives show similar increases with increasing residrubber ratios. The cohesive strength of the water-dispersi- ble resinlneoprene formulations is out- standing up to a residrubber ratio of approximately 45:55 using a % '' x%", 500 gram test. When the 1" x l", 1,OOO gram test is used, the cohesive strength remains high at a 55:45 residrubber blend. As shown, this level of tackifier also gives good tack and peel proper- ties.

When compounded with an acrylicY latex (Figure 3), the 27°C softening point resin provides increasing peel adhesion with increasing resin concen- tration until a maximum is achieved at about a 60:40 blend. The tack proper- ties of the formulation are slowly im- proved as the resin concentration is in- creased. The shear decreases rapidly when compared with the previous elas- tomer systems. This is probably related

lUcar 173. acrylic, Unlon Carblde Corp., Danbury, Connecticut.

to the lack of cohesive strength of the acrylic elastomer.

In addition to the aforementioned performance properties, rolling ball tack has also been used to evaluate resin/elastomer adhesives (Table 111). Because each of the commonly used tack determinations measure different phenomena, the rolling ball tack often does not correlate with probe tack or quick stick. The natural rubber-based adhesive has the most aggressive rolling ball tack despite its relatively poor Polyken probe tack and quick stick. A formulation using a blend of natural rubber and SBR Latex B also shows good rolling ball tack. The SBR Latex A adhesive has the poorest rolling ball tack performance.

The performance properties of the two-component adhesive formulation, (27°C softening resin/SBR Latex B in a one-to-one ratio), are the following:

Rolling ball tack - 3.3 in.

178" shear (%" x %", 500 gm) - 180" peel - 4.9 Ib/in.

59 min.

Polyken - 864 gm. Quick stick - 2.7 Ib/in.

This formulation shows a ance of high peel and high approximates the adhesion ments of some label application

The 27OC softening point re Latex A formulation in a 60: has excellent shear with a good of tack and peel performance properties of this formulation are:

Rolling ball tack - 7.2 in. 180" peel - 2.5 Ib/in 178" shear (1" x l", 1,OOO g

Polyken - 743 gm. Quick stick - 1.6 Ib/in.

This combination of perform properties is typical of some pre sensitive tape adhesives.

Properties of the Aged Films In addition to determining the

sive performance properties freshly prepared adhesives, the ties of the aged adhesives were amined. The adhesive test film subjected to an accelerated aging test 140°F for 14 days. In this evaluatio no antioxidants were added to the hesive formulations.

The results of aging the 27 ening point resin/SBR Latex A 140OF for 14 days indicated Polyken probe tack and qui were virtually unaffec The rolling ball tack cant degradation in flecting a lack of cor tack measurements. The 1 adhesion increased somewhat ov range of resin concentrations exa while the shear properties decrew The appropriate antioxidant may #I vide satisfactory performance stab ties. Studies to verify this assu were not complete writing.

Properties other

9,600 min.

&thaw stability;

/thaw shear main-

Figure 4. Properties of compounded latex adhesive system based on 41 'C softening point resin (the most recently developed waterborne tackifying resin with highest softenlng point and molecular weight in the series)/Latex A.

solids level sup- at low tackifying resin levels, the prop- erties of the elastomer dominate; as the

advantages of this new product are its ease of handling and excellent range of

resin concentration increases, its influ- ence ,becomes more noticeable, as do the differences between these two res- ins. The 178' shear is somewhat better at using the 41OC softening point resin as one would expect from a higher soft- ening point resin. Excellent shear (%" 6 %", 5 0 0 grams) is maintained up to

about 45 percent resin; at 1" x l", 1,OOO grams, the shear is about 125 hours

waterborne highest soft- weight in the

41OC soft- ie shown in

quick stick, the 41°C adhashres conditions uscd.

even at 60 percent resin. The Williams plasticity indicates an increase in tensile moduli or flow properties at low resin concentrations, while the plasticities are similar at 70 percent resin. One expla- nation for this unexpected behavior is that at high resin levels, the formula- tion is so soft that differences in plas- ticity cannot be differentiated under the

8 b n0c Concluslon to-hfqh

ihrd that A novel water-based tackifier resin

tochnolonv has boen develod . and tho

performance properties. Stable aqueous adhesives based upon a variety of latex elastomers have been produced using an easy three-step blending process. The performance properties tested for the new two-component adhesives compare well to the performance properties of conlmonly used pressure sensitive pr,od- ucts. In addition, continued laboratory work has resulted in the development of water-based resins that have soften- ing points higher than these current water-reducible resins.

References

advantages of this new product are its ease of handling and excellent range of performance properties. Stable aqueous adhesives based upon a variety of latex elastomers have been produced using an easy three-step blending process. The performance properties tested for the new two-component adhesives compare well to the performance properties of commonly used pressure sensitive pr,od- ucts. In addition, continued laboratory work has resulted in the development of water-based resins that have soften- ing points higher than these current water-reducible resins.

References (1) Parry, S. A. and Ritchie, P.F. 1966.

New methods for measuring tack in emulsion adhesives. Adhesives Age. 9(11):28-33.