Coating processes – With post-treatment of coating or coating material – Solid treating member or material contacts coating
Reexamination Certificate
1999-04-06
2001-03-06
Talbot, Brian K. (Department: 1762)
Coating processes
With post-treatment of coating or coating material
Solid treating member or material contacts coating
C427S365000, C427S366000, C427S391000, C427S395000
Reexamination Certificate
active
06197380
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a paper product having a melt-stable, biodegradable lactide polymer composition coated thereon and a process for manufacturing paper products coated with such melt-stable, biodegradable lactide polymers.
2. Description of the Prior Art
The need for coated paper is well established. Paper is coated with either polymeric or wax coatings for various reasons. These reasons include increasing the strength of the paper stock, imparting water resistance, enhancing gloss, improving barrier properties and the like.
In light of depleting sources of cellulosic fiber over the last decade, repulping of paper and the reuse of the cellulosic fiber recovered in the repulping process has accelerated. A typical repulping process involves mechanical agitation of the paper. Often the repulping environment involves water, heat or other harsh conditions such as an acidic or alkaline solution.
A problem that occurs with repulping coated paper is the disposal or recycling of the coating which is liberated during the repulp process. Currently, coatings such as polyethylene are popular for-their superior coating properties. However, in repulping processes, papers coated with polyethylene are not easily repulped since polyethylene is typically not broken down by the conditions of the repulping process.
Coatings have been developed which are represented to be “repulpable.” These are materials which purportedly have adequate properties as paper coatings, and when exposed to conditions of repulping, either dissolve or disperse. In a solution or dispersion, it is claimed that these materials will pass through screens and other filtering steps and pass out with the waste water before the repulping step.
Although these coatings have been extensively used, many problems have been encountered with their use often the coatings are not clear or glossy. Some coatings may also be unduly sensitive to water.
Disposal is a major problem associated with both repulpable and non-repulpable coating. For coatings which are recovered during the repulp process, there is no value in the recovered material and therefore these coatings represent waste generally disposed of in a landfill. For the coatings which pass through the filters and screens of the process, these materials end up in the waste water and may pose a problem for the waste water treatment plants.
Although not believed to be known as a paper coating material, the use of lactic acid and lactide to manufacture a biodegradable polymer is well-known in the medical industry. As disclosed by Nieuwenhuis et al. (U.S. Pat. No. 5,053,485), such polymers have been used for making biodegradable sutures, clamps, bone plates and biologically active controlled release devices. Processes developed for the manufacture of polymers to be utilized in the medical industry have incorporated techniques which respond to the need for high purity and biocompatability in the final product. These processes were designed to produce small volumes of high dollar-value products, with less emphasis on manufacturing cost and yield.
In order to meet projected needs for biodegradable packaging materials, others have endeavored to optimize lactide polymer processing systems. Gruber et al. (U.S. Pat. No. 5,142,023) disclose a continuous process for the manufacture of lactide polymers with controlled optical purity from lactic acid having physical properties suitable for replacing present petrochemical-based polymers.
Generally, manufacturers of polymers utilizing processes such as those disclosed by Gruber et al. will convert raw material monomers into polymer beads, resins or other pelletized or powdered products. The polymer in this form is then sold to end users who convert, i.e., extrude, blow-mold, cast films, blow films, thermoform, injection-mold or fiber-spin the polymer at elevated temperatures to form useful articles. The above processes are collectively referred to as melt-processing. Polymers produced by processes such as those disclosed by Gruber et al., which are to be sold commercially as beads, resins, powders or other non-finished solid forms are generally referred to collectively as polymer resins.
Prior to the present invention, it is believed that there has been no disclosure of a combination of composition control and melt stability requirements which will lead to the production of commercially viable lactide polymer coatings for cellulosic paper.
It is generally known that lactide polymers or poly(lactide) are unstable. The concept of instability has both negative and positive aspects. A positive aspect is the biodegradation or other forms of degradation which occur when lactide polymers or articles manufactured from lactide polymers are discarded or composted after completing their useful life. A negative aspect of such instability is the degradation of lactide polymers during processing at elevated temperatures as, for example, during melt-processing by end-user purchasers of polymer resins. Thus, the same properties that make lactide polymers desirable as replacements for non-degradable petrochemical polymers also creates undesirable effects during processing which must be overcome.
Lactide polymer degradation at elevated temperature has been the subject of several studies, including; I. C. McNeill and H. A. Leiper,
Polymer Degradation and Stability,
vol. 11, pp. 267-285 (1985); I. C. McNeill and H. A. Leiper,
Polymer Degradation and Stability,
vol. 11, pp. 309-326 (1985); M. C. Gupta and V. G. Deshmukh,
Colloid
&
Polymer Science,
vol. 260, pp. 308-311 (1982); M. C. Gupta and V. G. Deshmukh,
Colloid
&
Polymer Science,
vol. 260, pp. 514-517 (1982); Ingo Luderwald,
Dev. Polymer Degradation,
vol. 2, pp. 77-98 (1979); Domenico Garozzo, Mario Giuffrida, and Giorgio Montaudo,
Macromolecules,
vol. 19, pp. 1643-1649 (1986); and, K. Jamshidi, S. H. Hyon and Y. Ikada,
Polymer,
vol. 29, pp. 2229-2234 (1988).
It is known that lactide polymers exhibit an equilibrium relationship with lactide as represented by the reaction below:
No consensus has been reached as to what the primary degradation pathways are at elevated processing temperatures. One of the proposed reaction pathways includes the reaction of a hydroxyl end group in a “back-biting” reaction to form lactide. This equilibrium reaction is illustrated above. Other proposed reaction pathways include: reaction of the hydroxyl end group in a “back-biting” reaction to form cyclic oligomers, chain scission through hydrolysis of the ester bonds, an intramolecular beta-elimination reaction producing a new acid end group and an unsaturated carbon-carbon bond, and radical chain decomposition reactions. Regardless of the mechanism or mechanisms involved, the fact that substantial degradation occurs at elevated temperatures, such as those used by melt-processors, creates an obstacle to use of lactide polymers as a replacement for petrochemical-based polymers. It is apparent that degradation of the polymer during melt-processing must be reduced to a commercially acceptable rate while the polymer maintains the qualities of biodegradation or compostability which make it so desirable. It is believed this problem has not been addressed prior to the developments disclosed herein.
As indicated above, poly(lactide)s have been produced in the past, but primarily for use in medical devices. These polymers exhibit biodegradability, but also a more stringent requirement of being bioresorbable or biocompatible. As disclosed by M. Vert,
Die Ingwandte Makromolekulare Chemie,
vol. 166-167, pp. 155-168 (1989), “The use of additives is precluded because they can leach out easily in body fluids and then be recognized as toxic, or, at least, they can be the source of fast aging with loss of the properties which motivated their use. Therefore, it is much more suitable to achieve property adjustment through chemical or physical structure factors, even if aging is still a problem.” Thus, work aimed at the bioresorbable or biocompatible market focused on po
Eichen Conn Robin Sue
Gruber Patrick Richard
Hall Eric Stanley
Kolstad Jeffrey John
Ryan Christopher M.
Cargill Incorporated
Merchant & Gould
Talbot Brian K.
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