Surfactant for forming stable dispersions of rosin esters

Details Surfactant for forming stable dispersions of rosin esters Surfactant for forming stable dispersions of rosin esters

1994-01-27

2001-08-14

Mulcahy, Peter D. (Department: 1713)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

At least one aryl ring which is part of a fused or bridged...

C524S271000, C524S272000, C524S273000, C524S274000, C530S218000

Reexamination Certificate

active

06274657

ABSTRACT:

The present invention relates to compounds which may be used as surfactants to disperse rosin esters. The present invention also relates to methods for the preparation of such compounds.
Water dispersed adhesives are used extensively to adhere various substrates together. These adhesives typically comprise a high molecular weight elastomeric latex (such as an acrylic or styrene-butadiene rubber [SBR]latex) and a dispersed tackifier resin. The preparation of water-dispersed elastomeric latexes is well known in the art of adhesive preparation as is the preparation of tackifier resins. It is more difficult to produce a stable dispersion of a tackifier resin which is compatible with the latexes. The stabilization of rosin ester tackifier resins is particularly difficult.
Usually, rosin esters must be dispersed at relatively high pressures using rapid stirring. This increases the cost of preparation and therefore decreases the ease of use of such dispersions. In addition, most current commercial dispersions do not provide an adequate level of shear strength or stability.
With these problems in mind, it is an object of the present invention to provide a surfactant for forming stable dispersions of rosin esters compatible with elastomeric latexes.
It is an additional object of the present invention to provide a surfactant which is preferably capable of forming stable dispersions, at atmospheric pressure, of rosin esters having a variety of softening points.
It is another object of the present invention to provide a surfactant which is preferably capable of forming dispersions having an average particle size of less than about 2.0 micron.
The present inventors have discovered that esterifying rosins, rosin dimers or a mixture of rosins and rosin dimers with polyethylene glycol (PEG) produces a surfactant which will form a stable dispersion of rosin ester which is compatible with acrylic latexes. The term “rosin” is used herein and in the claims, unless otherwise noted, to refer to rosin, rosin dimer or a mixture of rosin and rosin dimer. Rosin chiefly comprises resin acids of the abietic and pimaric types having acid numbers greater than 100. The esterification involves the direct treatment of a rosin with polyethylene glycol. The reaction is complete after about 5 hours when the resulting product has an acid number of about 2.
One method of preparation of the surfactant of the present invention comprises the reaction of the rosin and polyethylene glycol in the presence of a catalytic amount of hypophosphorous acid with a reaction temperature of between about 260° C. and about 290° C. under a nitrogen atmosphere. Typically, the reaction requires about 5 hours to go to substantial completion. The stoichiometry of the rosin to polyethylene glycol determines the hydrophobe to lipophobe balance and structure of the final surfactant. The rosin-to-rosin dimer ratio on the surfactant also affects the structure of the final surfactant.
As used in the present invention, the rosin is either rosin monomers, rosin dimers or a mixture of monomers and dimers. The rosin generally has an acid number of between about 140 and about 185. The equivalent weight of the rosin typically falls between about 302 and about 400.
The PEG, as used in the present invention, has a molecular weight of between about 1,000 and about 20,000.
More specifically, treating 15 g of SYLVATAC 140 (Arizona Chemical), equivalent weight 400, a rosin-rosin dimer mixture containing about 60-70% of dimerized rosin, with 200 g of PEG (molecular weight of 8000) results in the formation of a surfactant with the structure of rosin-PEG/rosin-PEG-rosin. Treating 10 g of SYLVATAC 140 with 200 g of PEG in a similar manner yields a surfactant with polymeric structures such as PEG-rosin-PEG, rosin-PEG-rosin-PEG, etc. Treating 13.5 g of SYLVATAC 295 (Arizona Chemical), equivalent weight 359, a rosin-rosin dimer mixture containing about 30% of dimerized rosin, with 200 g of PEG in a similar manner also gives a surfactant with polymeric structures. Each of these surfactants will function effectively to disperse rosin ester tackifier resins in water.
In making a dispersion of a tackifier, the tackifier resin is heated to above its melting point (generally, below 98° C.). A mixture of surfactant, as prepared above, and water is then added with stirring to the melted tackifier resin. The stirring can be, but need not be, carried out at atmospheric pressure with good results. Generally, the mixture of tackifier, surfactant and water is stirred for one hour at a moderate speed. After the inversion point is reached (i.e., after the water just becomes the continuous phase) additional hot water is slowly added until the dispersion is at the desired solids content (usually about 60%). The dispersion is then cooled to room temperature slowly. The final dispersion has a particle size of about 2.0 micron or less and is stable.
The dispersion is compatible with elastomeric latexes and is used to prepare appropriate adhesives. In preferred embodiments of the invention, the elastomer latexes are selected from the group consisting of acrylic or styrene-butadiene rubber.
In order to provide a further understanding of the present invention, the following examples are given by way of illustration and not by way of limitation.


REFERENCES:
patent: 4057527 (1977-11-01), Columbus
patent: 4769406 (1988-09-01), Keithley
patent: 4792582 (1988-12-01), Hoefer et al.
patent: 4822526 (1989-04-01), Tsuchida et al.
patent: 5306762 (1994-04-01), Hutter

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