Stock material or miscellaneous articles – Composite – Of polyester
Reexamination Certificate
1998-09-29
2001-11-06
Chen, Vivian (Department: 1773)
Stock material or miscellaneous articles
Composite
Of polyester
C428S481000, C264S555000, C264S563000, C264S564000, C264S572000, C264S173110, C264S173120, C264S173150, C156S244110, C156S244240
Reexamination Certificate
active
06312823
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to compostable multilayer structures, methods for the manufacture of compostable multilayer structures, and articles prepared from compostable multilayer structures. More particularly, the compostable multilayer structures are films having desirable properties of flexibility and tear resistance and can be used to provide disposable bags or wrappers.
BACKGROUND OF THE INVENTION
Plastic trash bags and wrappers are primarily made of hydrocarbon polymers such as polyethylene, polypropylene, or polyvinyl polymers. While hydrocarbon polymers can be useful for commercially manufacturing trash bags and wrappers having adequate flexibility and puncture and tear resistance, they are resistant to degradation and mineralization and have a tendency to build up in land fills. Under most conditions, hydrocarbon polymers take a long time to decompose. In addition, hydrocarbon polymers are not manufactured from renewable resources.
Hydrocarbons have been combined with starch in attempts at increasing degradability. Trash bags which incorporate starch can be physically degradable, which means that they become broken into many small parts as the starch biodegrades. The hydrocarbon component, however, remains resistant to degradation and mineralization. In certain circumstances, it is believed that the hydrocarbon component has a tendency to encapsulate the starch thereby preventing further biodegradation of the starch. Furthermore, materials incorporating large amounts of starch can be very sensitive to moisture and can have mechanical properties which vary considerably with humidity.
Attempts have been made at developing thermoplastic films having degradable properties. For example, U.S. Pat. No. 4,133,784 to Otey et al. describes degradable mulch films with improved moisture resistance prepared from starch and ethylene/acrylic acid copolymers. U.S. Pat. No. 5,091,262 to Knott et al. describes a multilayer polyethylene film containing a starch filled inner layer, and prodegradant filled outer layers. U.S. Pat. No. 5,108,807 to Tucker describes a multilayer thermoplastic film having a core layer made of polyvinyl alcohol, and outer layers made of polyethylene and prodegradant. U.S. Pat. No. 5,391,423 to Wnuk et al. describes multilayer films prepared from various biodegradable polymers for use in disposable absorbent products, such as diapers, incontinent pads, sanitary napkins, and pantyliners.
Many biodegradable polymers have been found to possess the desirable characteristics of biodegradability and compostability. At room temperature, however, many biodegradable polymers are either too brittle to provide the desired puncture and tear resistance necessary for commercially acceptable trash bags, or they do not have adequate stability for storage and transport. In addition, many biodegradable polymers are difficult to process into films using commercial manufacturing lines.
SUMMARY OF THE INVENTION
Compostable multilayer structures with desired properties of flexibility and tear resistance are provided by the present invention. The compostable multilayer structures are preferably in the form of films, sheets, laminates and the like. The compostable multilayer structures can be manufactured into disposable consumer products such as bags, wrappers, cups, and the like, which can degrade when subjected to composting conditions. Preferably, the multilayer structure is in the form of a film.
The compostable multilayer structures can be provided in various layered arrangements. A preferred compostable multilayer structure includes a core layer having a first surface and a second surface, a first blocking reducing layer covering the first surface of the core layer, and a second blocking reducing layer covering the second surface of the core layer. Preferably, the core layer has a glass transition temperature (T
g
) below about 20° C., and at least one of the first and second blocking reducing layers includes a semicrystalline polymer composition and/or has a glass transition temperature above about 50° C.
Applicants discovered that certain desirable properties of compostable polymer compositions, such as flexibility, tear resistance, and puncture resistance, can be adjusted by controlling the glass transition temperature thereof. For example, for many compostable polymer compositions, such as hydrolyzable polymer compositions, reducing the (T
g
) provides a layer having increased flexibility, tear resistance, and puncture resistance to commercially acceptable levels for bags and wrappers. In addition, Applicants discovered that certain polymers compositions can be used to provide blocking reducing layers when applied over the compostable polymer compositions having increased flexibility, tear resistance, and puncture resistance. As used in the context of the present invention, blocking occurs when polymer composition layers fuse or stick together. The extent of blocking is evaluated relative to the degree of fusion between the layers or tackiness of the layers. Many polymer compositions having low glass transition temperature have been found to possess increased incidence of blocking. Applicants discovered, however, that resistance to blocking can be adjusted by controlling the glass transition temperatures. For many compostable polymer compositions such as certain hydrolyzable polymer compositions, an increased glass transition temperature tends to reduce blocking. In addition, Applicants additionally discovered that controlling the crystallinity of a polymer composition can provide reduced blocking.
The layers of the compostable multilayer structures are preferably made of materials which are compostable, such as polymer compositions which include, for example, hydrolyzable polymers. Exemplary hydrolyzable polymers include copolymers and polymer blends of poly(trimethylene carbonate) and polyesters such as poly(lactic acid), poly(lactide), poly(glycolide), poly(hydroxy butyrate), poly(hydroxy butyrate-co-hydroxy valerate), poly(caprolactone), poly(ethylene-oxylate), poly(1,5-dioxepan 2-one), poly(1,4-dioxepan 2-one), poly(p-dioxanone), poly(delta-valerolactone), polyethylene(oxylate), polyethylene(succinate), polybutylene(oxalate), polybutylene(succinate), polypentamethyl(succinate), polyhexamethyl(succinate), polyheptamethyl(succinate), polyoctamethyl(succinate), polyethylene(succinate-co-adipate), polybutylene(succinate-co-adipate), polybutylene(oxylate-co-succinate), polybutylene(oxylate-co-adipate). Aliphatic polyesters which are preferred because of their ability to hydrolyze to generally biodegradable units. It should be appreciated that lactic acid residue containing polymers such as poly(lactide) and poly(lactic acid) are preferred hydrolyzable polymers because of their composting and biodegradable properties. Even more preferred are copolymers prepared from lactide or lactic acid and epoxidized multifunctional oil, such as soybean oil or linseed oil.
The polymers which can be used to provide the layers of the multilayer structure should have a molecular weight which is sufficient to provide a polymer composition having film or sheet forming properties. This means that the molecular weight should be sufficiently high so that the polymer composition can form a sheet or film having integrity, and that the molecular weight should not be too high that the polymer composition is too viscous and has problems forming a sheet or film using commercial film or sheet forming equipment. Moreover, it should be appreciated that the molecular weights of the polymers used to provide the various layers can be different, reflecting the desired properties of the individual layers. For example, the molecular weight of the polymer used to prepare the core layer should be sufficiently high to provide sufficient tear strength and puncture resistance, and the molecular weight of the polymers used to prepare the blocking reducing layers should be sufficient to provide the desired glass transition temperature.
Practically, it is believed that this generally corresp
Brosch Andrea Lee
Buehler Nancy Uzelac
El-Afandi Ali Zakareya
Gruber Patrick Richard
Hartmann Mark
Cargrill Incorporated
Chen Vivian
Merchant & Gould P.C.
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