Chemistry: natural resins or derivatives; peptides or proteins; – Natural resins or derivatives – Rosin or derivative used as starting material in process – or...
Patent
1995-05-16
1996-09-03
Nutter, Nathan M.
Chemistry: natural resins or derivatives; peptides or proteins;
Natural resins or derivatives
Rosin or derivative used as starting material in process, or...
530210, 530215, 530218, 156327, 156332, 526911, 526931, 526932, B01F 1734, B01F 1752, C08L 9304, C09J 900
Patent
active
055525199
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a new surfactant, to a process for the production thereof and to the use of the surfactant as a dispersing agent for tackifiers. The invention also relates to aqueous tackifier dispersions including the new surfactant and to the use of the aqueous tackifier dispersions in pressure sensitive adhesives.
Pressure sensitive adhesives based on e.g. aqueous acrylic and carboxylated styrene butadiene polymers are usually formulated to include a tackifier. The tackifier facilitates the coating process for the adhesive and improves the adhesive properties such as tackiness, peel-resistance and ease of surface wetting. The tack of an adhesive enables it to form an immediate bond between contacted surfaces when they are brought together.
Tackifier resins consist mainly of rosin and derivatives thereof or hydrocarbon resins. In aqueous based adhesives it is common to include the tackifier resin in the form of an aqueous dispersion. The aqueous dispersion is made by first melting the rosin or resin and then adding a surfactant and water to form a dispersion in which the rosin/resin is the dispersed phase and water the continuous phase. A to of different surfactants are known. As typical surfactants there can be mentioned alkyl sulphonates, fatty alcohol sulphates, phosphate esters. GB 2 155 942 relates to a surfactant comprising a salt of a sulphosuccinate half ester of an alkoxylated, fortified rosin. The drawback with known tackifier dispersions is that they reduce the cohesive strength (internal strength) of the adhesive dramatically. This is due to a combined effect of the lower molecular weight of the tackifier, compared with polymer resin, and the kind of surfactant used in the tackifier dispersion.
It is accordingly an object of the present invention to obtain a surfactant for the preparation of tackifier dispersion with reduced loss in cohesive strength when formulated compared to known tackifier dispersions. It is further an object of the present invention to obtain a tackifier dispersion which is stable at room temperature and which has a good mechanical stability and low foaming characteristics.
The objects of the invention are achieved by a surfactant as claimed in the claims. The surfactant is obtainable by anhydride, the mole ratio carboxylic acid or anhydride/rosin (calculated as each rosin associated with a rosin ester) being from 0.05:1-1.5:1, Mw of 1000-20000, the mole ratio glycol/free carboxylic acid group being from 0.2:1-1:1 to an acid value of less than 30, alternatively polyethylene glycol with a Mw of 1000-20000, the mole ratio glycol/free carboxylic acid group or anhydride being from 0.2:1-1:1 to an acid value less than 30, being from 0.05:1-1.5:1.
Similar surfactants are known from U.S. Pat. No. 4,260,550 but for quite different purposes. These surfactants are used in cream and lotion and hair care formulations.
It was surprisingly found that with the new surfactants according to the invention stable tackifier dispersions could be prepared which resulted in adhesives with improved cohesive strength compared with known tackifier systems but without detrimentally affecting the adhesive performance. With some polymer binders the tackifier dispersion according to the invention even maintains the same cohesive strength as with the neat polymer.
The surfactant according to the invention is prepared from a rosin. Rosin is a natural product consisting of mixed unsaturated acids. The rosin acids are mainly monobasic carboxylic acids containing the phenanthrene skeleton with 20 carbon atoms in the molecule. The difference between the acids is the number and position of the double bonds. Natural rosin may be classified due to its origin namely as gum rosin, wood rosin or tall oil rosin. The surfactant according to the invention can be prepared from any of these rosins or from mixtures thereof.
It is also possible to start with a disproportionated rosin. Disproportionation is a method of stabilizing the rosin. It involves transferring hydrogen atoms from one molecule of a
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Chemical Abstract 108: 9669x 1987.
Hemmings Paul N.
Wang Long
Eka Nobel AB
Mancini Ralph J.
Morris Louis A.
Nutter Nathan M.
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