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...
Reexamination Certificate
1998-07-27
2003-05-13
Szekely, Peter (Department: 1714)
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...
C106S031410, C106S031730, C106S218000, C106S230000, C106S241000, C524S270000, C524S271000, C524S272000, C530S212000, C530S215000, C530S218000
Reexamination Certificate
active
06562888
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to rosin esters, and adhesives containing the rosin esters.
BACKGROUND OF THE INVENTION
Esters of rosin and polyhydric alcohols (polyols), which are generally called rosin esters, have been known for over 70 years. See, e.g., U.S. Pat. No. 1,696,337 to Symmes. They are typically prepared by the reaction of rosin (a mixture of isomeric C
20
tricyclic mono-carboxylic acids) with polyhydric alcohols (hereinafter “polyols”) such as pentaerythritol. Rosin esters currently find widespread commercial use in many applications, including as tackifiers for packaging and pressure-sensitive adhesives, and in cosmetic formulations.
For many applications, the color of a rosin ester is a property which determines its commercial viability. Rosin ester coloration is typically measured on the Gardner color scale, with a Gardner color of zero being colorless, and a color of fifteen being red-brown. The marketplace places a premium on rosin esters that are light in color, and will not accept very darkly colored esters. However, light-colored rosin esters are difficult and/or expensive to prepare and maintain. A considerable amount of research has been directed at producing rosin esters that are both initially light-colored, and will maintain this light coloration upon prolonged storage and/or during a heating process to which the ester may be subjected during its formulation into a specific final product. See, e.g., U.S. Pat. Nos. 2,409,173 to Webb; 3,423,389 to Glenn and 5,395,920 to Maeda et al., which are representative only. The '920 patent to Maeda et al. discloses that it is possible (although, in practice, probably cost-prohibitive) to make a rosin ester having a Gardner color of not more than one, through extensive purification, disproportionation and dehydrogenation of the starting rosin and/or final rosin ester.
Despite a significant amount of research, there remains a need in the art for cost-effective methods to achieve light-colored rosin esters. The present invention fulfills this need and provides related advantages as described herein.
SUMMARY OF THE INVENTION
In one aspect, the present invention provides a light-colored esterification product of rosin and an aromatic or aliphatic hydrocarbon moiety containing at least two hydroxyl groups, with the proviso that the hydroxyl groups are separated in the moiety by at least four carbon atoms. In preferred embodiments, the product has undergone disproportionation, has not undergone dehydrogenation, has a color of Gardner value of less than 2.5, includes a stabilizer such as an antioxidant or UV stabilizer, and/or is prepared from a starting rosin having a color of Gardner value of at least 3.
Another aspect of the present invention provides an adhesive composition that includes polymer and, as a modifier thereof, the light-colored esterification product of rosin and an aromatic or aliphatic hydrocarbon moiety containing at least two hydroxyl groups, as described above.
These and other aspects of this invention will become apparent upon reference to the following detailed description. To this end, certain references are cited herein for purpose of clarity and completeness. Such references are incorporated herein by reference in their entirety.
DETAILED DESCRIPTION OF THE INVENTION
The present invention is directed to the esterification products of rosin and aromatic or aliphatic hydrocarbon moieties containing at least two hydroxyl groups. The invention is also directed to adhesive compositions containing these rosin esters. It has been surprisingly discovered that when rosin esters have ester groups separated by at least four carbon atoms, the esters have remarkably light color, and remarkably good performance properties as tackifiers in adhesive formulations.
Rosin is mainly a mixture of C
20
, tricyclic fused-ring, monocarboxylic acids, typified by pimaric and abietic acids, which are commonly referred to as “resin acids.” Rosin which is suitable for use in the present invention can be obtained from many sources, and can have a wide range of purities. For example, wood rosin may be employed in the present invention, where wood rosin is obtained from Pinus stumps after harvesting the stumps, chipping the stumps into small chips, extracting the chips with hexane or higher-boiling paraffins, and distilling the hexane or paraffin to yield wood rosin. Gum rosin, which is the name given to rosin that is obtained after scoring a pine tree, collecting the exudate sap, and then distilling away the volatile components, may also be employed in the invention.
The rosin may be tall oil rosin, which is a by-product of the kraft (i.e., sulfate) pulping process for making paper. According to this process, pinewood is digested with alkali and sulfide, producing tall oil soap and crude sulfate turpentine as by-products. Acidification of this soap followed by fractionation of the crude tall oil yields tall oil rosin and fatty acids. Any one or more of the C
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cyclic carboxylic acid-containing isomers present in rosin may be used in the invention.
Regardless of its source, rosin is typically characterized by its acid number, and rosins having acid numbers ranging from about 160 to about 195 are preferred according to the invention. Rosin may also be characterized by its Gardner color, where lower Gardner color numbers indicate lighter-colored rosin. Light-colored rosin is preferred for preparation of tackifiers. However, in order for the present invention to have commercial viability, the rosin is preferably not subjected to extensive purifying or modifying processes, which will necessarily add cost to the process for making the rosin ester. Thus, in a preferred embodiment, the rosin is “standard” grade rosin as is readily available from many commercial distillers of naval stores. This standard grade rosin has not be subjected to disproportionation or dehydrogenation processes prior to its use in the esterification reaction of the present invention. Furthermore, the standard grade of rosin has also not undergone any special purification procedures such as redistillation (i.e., further distillation of rosin after it has already been isolated by distillation from crude tall oil), recrystallization or extraction procedures to remove impurities. Instead, the preferred rosin of the present invention is the standard grade of rosin that is produced upon distillation of crude tall oil, and is available from many sources. Such “standard grade” rosin has a color of Gardner value of at least 3, more typically of at least 4, and still more typically of at least 5. In one embodiment, the present invention provides rosin esters having a color that is at least as light as the color of the rosin charged to the esterification reaction vessel, and typically provides rosin esters which are lighter in color than the starting rosin by at least one, at least one and a half, or at least two Gardner value units.
A significant advantage of the present invention is that it provides light-colored and low odor rosin esters from standard grade rosin. Of course, if desired, a purified rosin could also be employed in the present invention. If dehydrogenated rosin would be used in the invention, and the rosin is from crude tall oil, then the tall oil rosin will require substantially higher catalyst levels to achieve dehydrogenation (compared to, e.g., a gum or wood rosin) in order for all of the catalyst not to be deactivated by the sulfur bodies that are present in tall oil rosin.
A preferred standard grade of rosin is available commercially from Union Camp Corporation (Wayne, N.J.) under the UNI-TOL® trademark. Gum rosin, including Indonesian and Chinese gum rosins, is another suitable rosin for preparing rosin esters of the invention, where gum rosin may afford higher melting point rosin esters than can be obtained from using an equivalent amount of tall oil rosin, although may not provide the lightness in color that may be obtained from tall oil rosin.
The esterification product of the invention is prepared from rosin as descr
Frihart Charles R.
Lawson Nelson E.
Neumann Brett A.
Arizona Chemical Company
Seed Intellectual Property Law Group PLLC
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