Stock material or miscellaneous articles – Coated or structually defined flake – particle – cell – strand,... – Particulate matter
Reexamination Certificate
2000-08-29
2004-03-16
Short, Patricia A. (Department: 1712)
Stock material or miscellaneous articles
Coated or structually defined flake, particle, cell, strand,...
Particulate matter
C525S425000, C525S439000, C525S444000, C525S462000
Reexamination Certificate
active
06706399
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to polyester articles. More specifically, the present invention is directed to non-blocking polyester articles.
BACKGROUND OF THE INVENTION
Polyesters are synthesized from a variety of reactant combinations and process conditions. In most cases, a generic repeating unit is obtained having a main-chain structure of:
H—[—O—R—O—C—R′—]
x
—OH
wherein R and R′ may or may not be different and are generally straight, branched, and cyclic aliphatic and aromatic groups. Typical industrial processes are based on the reaction of at least one diol with at least one diacid or diester to yield the linear polymer structure shown supra. It is well known that alcohols, acids (esters) or both alcohols and acids having more than 2 functional groups may be used to produce branched polyesters. The chemical structure of the monomers will determine the physical properties of the resulting polymer.
One key property relating to the present invention is the glass transition (T
g
) temperature, which is sometimes referred to as the softening point. At temperatures below the T
g
a polymer is hard and glassy, while temperatures above the T
g
result in a change to a soft and rubbery or sticky material. In the absence of crystallinity, the polymer may be considered a solid below the T
g
and as a liquid above the T
g
. Therefore, when the T
g
of an amorphous polymer is at or below ambient temperature the polymer behaves as a liquid that will undergo viscous flow. When separate quantities of a “liquid” polymer are placed next to each other they will tend to stick together and eventually the viscous flow may result in the formation of a single mass. Convenient product forms, such as pellets or pastilles, are normally encountered for substantially amorphous polymers only when the T
g
is not significantly lower than the ambient temperature. From a product-packaging viewpoint, ambient temperature can be defined as a nominal room temperature of 25° C. to a more climatic extreme of 50° C.
Polyesters having low molecular weights, i.e., less than about 5,000, are used extensively in the coatings (alkyds) and thermosetting moulding (unsaturated polyesters) industries. Both of these application areas involve curing or crosslinking of the resin to form a non-tacky film or object. Before curing, the product containing the polyester is most conveniently handled in the bulk form or in a liquid vehicle. Therefore, a low T
g
polyester of this type normally does not need to be packaged in the neat form as discrete partides in order to provide an easily handled product.
Polyesters having high molecular weights, i.e., greater than about 10,000 are used in film, fiber, packaging, and moulding or engineering materials applications. Most common are poly(ethylene terephthalate) (PET), poly(butylene terephthalate) (PBT), terephthalate copolyesters containing 1,4-cyclohexanedimethanol (CHDM), and polyester thermoplastic elastomers. These products have appreciable amounts of crystallinity and/or glass transition temperatures above the ambient range, which allows them to be packaged as free-flowing pellets. Some specialty polyesters containing at least some of the monomers listed above and other acids and diols, such as isophthalic acid and diethylene glycol, are commercially available, but also have the T
g
and/or melting point (T
m
) characteristics that allow for a pelletizable product.
The commercial exploitation of low T
g
, substantially amorphous polyesters has been hindered in part by the difficulty in providing a suitable package form to the end-user. Some of the polyester raw materials encountered in the adhesives industry are illustrative of this situation. For example, a line of low T
g
, amorphous, water-dispersible sulfopolyesters is available from Eastman Chemical Company, Kingsport, TN, under the AQ™ mark. These products (e.g., Eastman AQ 1350) are currently packaged as 50-pound blocks in release-lined cartons. Another example is found within the Mor-Ester product line of polyesters available from Morton Chemical Company. Mor-Ester 49001 is a soft, tacky, high molecular weight polyester that is supplied in the neat form as 6-pound blocks contained in a 36-pound box equipped with dividers. In both of these examples it is inconvenient, labor intensive, and costly to produce suitable package forms. Furthermore, the large unit mass of a 50-lb block is problematic to manufacturing operations as it may damage mixer blades and has less desirable heat transfer characteristics due to its low surface to volume ratio.
Packaging options, other than blocks of various sizes, also suffer from limitations and are not preferred. If the polyester is equilibrated at a temperature significantly lower than the T
g
, it is possible to grind the product into a free-flowing granular form. Storing packages of the granules at a temperature less than the T
g
in a refrigerated environment can prevent blocking. Unfortunately, maintaining the temperature significantly below the T
g
is typically too burdensome to have practical value.
It is also known to treat the granules with a surface-adhereing agent (i.e., an antiblock agent), such as a talc, wax, or polymer powder that will inhibit blocking. (See, for example, U.S. Pat. No. 5,257,491). However, the granules must be treated with such large quantities of antiblock to achieve non-blocking that contamination of the product occurs resulting in deterioration of the polyester properties.
Amorphous polyolefins (APO) are another class of polymers used in the adhesives industry that suffer from the packaging limitations described supra. Reduced particle size product forms of APO's are manufactured by a method known as “slatting”. (See, for example, U.S. Pat. Nos. 5,733,645 and 5,942,304). Slats may be obtained by coating a thin layer of a non-blocking polyolefin, such as low-density polyethylene (LDPE) around a ribbon of APO. LDPE has sufficient crystallinity to prevent blocking and during subsequent melt processing operations forms a compatible or miscible blend with the core material (APO). Polyolefins are nonpolar, addition polymers and there is no reaction that occurs between the APO and the exterior coating. The success of this packaging technology hinges on the ability of a exterior coating to be selected that may be used in small amounts and does not deleteriously contaminate the APO. Chain-growth polymerization techniques allow for control of monomer sequence distribution and polymer architecture, which results in a of variety products (i.e., physical properties) that may be obtained from a specific monomer or combination of monomers. This attribute of addition polymers facilitates the advantageous selection of the core and external coating materials for a slatted product form, since materials with high degrees of chemical identity may have different physical properties.
Unlike polyolefins, polyesters are step-growth polymers and it is typically not possible to control the sequence distribution of a chosen set of monomers during melt phase manufacturing processes. A specific composition has a given set of physical properties and selection of a shell material for an amorphous polyester core would require a chemically dissimilar polyester. The core and shell materials are not likely to have good compatibility, which may result in a non-viable product form.
In view of the above discussion, it is evident that there is a need for a substantially non-blocking low T
g
polyester article that does not block when contacted with other low T
g
polyesters. It is further apparent that there is a need for a low T
g
polyester that does not block and is not contaminated by an outer layer of non-blocking material.
SUMMARY OF THE INVENTION
The present invention provides an article of manufacture having a coating or is otherwise surrounded or wrapped in large measure by a second polymer which has non-blocking characteristics. In a preferred embodiment, the article possesses a core polymer which has a T
g
of less than 25° C. which is
Bowers David T.
Fleenor Coralie McKenna
George Scott Ellery
Miller Richard Anthony
Thompson Ricky
Eastman Chemical Company
Graves, Jr. Bernard J.
Owen Polly C.
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