Co-processable multi-layer laminates for forming high...

Stock material or miscellaneous articles – Liquid crystal optical display having layer of specified... – With substrate layer of specified composition

Reexamination Certificate

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C428S001100, C428S035700, C428S036600, C428S036700, C428S212000, C428S213000, C428S332000, C428S412000, C428S480000, C428S483000, C428S542800

Reexamination Certificate

active

06426128

ABSTRACT:

BACKGROUND OF THE INVENTION
Billions of containers and packaging products are manufactured each year for packaging food and beverage products and other household items. Various materials are used to manufacture these containers, depending on the particular use or application. Container manufacturers and food and beverage marketers must balance the design requirements for a packaging application against the economics of producing a given container. Design requirements may often include visually perceptible container properties such as surface gloss and reflectiveness, the clarity of the container wall, and the transparency and haze level of the container wall material. These visual properties have importance in the selection of a cost-effective packaging material for both functional and aesthetic reasons. The aesthetic elements of a packaging material choice may also be driven by consumer preference, because ultimately the consumer's decision to purchase a packaged product, for example a food or beverage, can be influenced by the appearance of the container. The functional aspects of these visual properties generally relate to container and/or product inspection, especially inspection of filled containers.
Glass containers are widely used and have properties of transparency and clarity, with little or no haze. These visual properties of glass will generally satisfy the functional and aesthetic requirements for a given container use. Glass containers also have gas barrier properties as well as heat resistance, making them suitable for packaging carbonated soft drinks and beer, as well as perishable products that are sensitive to oxygen and products which must be sterilized or hot-filled into containers at temperatures of 85° C. or more. The initial cost of glass containers is low, however, the efforts to recycle used glass containers have been hampered by the transportation expense involved in transporting the heavy glass containers to a recycle facility. These transportation expenses are also a cost factor when the glass containers are shipped to the user or when they are filled with new products and shipped to their point of sale. Moreover, glass containers are susceptible to breakage and inconvenient to handle.
On the other hand, containers made from plastic are often chosen by consumers and packagers due to their combination of light weight, durability and shatter resistance. Plastic containers may be formed from a variety of different polymers. Depending on the polymeric material selected, certain properties of the container may be achieved such as gas or water vapor barrier properties, impact strength, transparency and heat resistance.
Polyolefins such as polyethylene and polypropylene have barrier properties against water vapor, yet they are generally unsatisfactory from the standpoint of transparency and gloss. Polyvinyl chloride has gas barrier properties and is satisfactory in terms of transparency, but has inferior heat resistance. Polycarbonate has good transparency and sufficient heat resistance to withstand steam sterilization but does not have good gas and water vapor barrier properties.
Polyethylene terephthalate (PET) is widely used in the manufacture of containers for its excellent transparency and impact strength. In certain applications, polyethylene terephthalate also has satisfactory barrier properties against water vapor and gasses.
Polyethylene terephthalate is a crystallizable polymeric material which may exist in either an amorphous state or a crystallized state, or in a combination of both the amorphous and crystalline states. When heated to a temperature above its glass transition temperature and below its melting point, polyethylene terephthalate undergoes a transition from its amorphous state to its crystalline state, although this transition does not occur instantaneously. Similarly, when cooled slowly from its melting point to its glass transition point, polyethylene terephthalate undergoes crystallization, a transition from the amorphous phase to the crystalline phase. This transition does not occur instantaneously either, and substantially amorphous polyethylene terephthalate may be obtained by rapidly quenching from the melt, as is disclosed in U.S. Pat. No. 4,414,266 to Archer, et al.
Crystallization upon heating of a crystallizable polyester may be due to the further growth of existing crystals in the polymer or to the formation of new crystals, or both. Many physical and chemical properties of the polyester material change as the level of crystallinity increases and a variety of techniques are used to characterize the amount of crystallinity in a polymer. The crystallinity may be observed directly, for example by optical or electron microscopy techniques, or can be inferred by refraction techniques.
The crystallization behavior of polyesters such as polyethylene terephthalate is often determined by either a specific heat vs. temperature curve or a differential scanning calorimeter (DSC) curve, or both, for a sample of the polymer. At a temperature higher than the glass transition temperature (T
g
), crystallization takes place, which is demonstrated both by a sharp drop in the specific heat curve and also by a sharp upward peak in the differential scanning calorimeter curve. The crystallization onset temperature of a polyester determined by differential scanning calorimetry is that temperature at which the exothermic crystallization reaction begins, or the beginning of the rise toward the peak of the exothermic crystallization reaction curve. The peak crystallization temperature of a polyester determined by differential scanning calorimetry is that temperature at which the exothermic crystallization reaction peaks. The crystallization onset temperature and the peak crystallization temperature determined by differential scanning calorimetry are both located in the range between the glass transition temperature and the melting temperature (T
m
) of the material and they are both dependent upon polymer chain length and composition, and the heating rate.
Amorphous phase polymer chains may be axially or bi-axially oriented by applying force, in either one or two directions, respectively, to the polymeric material while it is above its glass transition temperature. Products such as biaxially oriented flat film and shaped objects such as cups thermoformed from flat sheet exhibit improved mechanical properties including dimensional stability, heat resistance and strength resulting from stretching and/or shaping at temperatures above T
g
.
Characterization of the uniaxial drawing properties of PET sheet at processing temperatures above T
g
illustrates that the material yields in a controlled and uniform manner at such temperatures. At higher strain levels, i.e. draw ratios, the stress increases sharply and strain hardening occurs prior to rupture. Developing strength and rigidity via strain hardening is important in applications such as manufacturing containers for carbonated soft drinks and PET processing temperatures on the order of 85-100° C. are often used in such processes. If the resin temperature in such a process is increased to above 110° C., the polymer flows more and a much higher stretch is required to achieve a given degree of strain hardening. The amount of orientation attained at this higher stretch is less than that obtained at the same stretch ratio at lower temperatures. This results in lower strength in the hot stretched polymer, although shrinkage is reduced, presumably because of the lower degree of orientation.
Another process variable affecting properties in the stretched polymer is the strain rate. At high strain rates there is considerable molecular resistance to chain disentanglement and movement. Strain hardening will occur at lower stretch ratios as the strain rate is increased. Also, at high strain rates a higher degree of crystallinity is achieved in the product. Increased crystallinity results in product rigidity but at higher levels can result in brittleness and a resistance to molecular movement which may adver

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