Patent Description:
This section also provides a general summary of the disclosure, and is not a comprehensive disclosure of its full scope or all of its features.

Plastic is a popular building material of modern human culture, which is used in a wide variety of applications and products. Because of its ubiquitous nature, plastic was typically used and discarded into landfills. Unfortunately, because of its material structure, it is believed to require centuries to fully decompose. Therefore, for many decades, there has been both social desire and government regulation regarding recycling of plastic material.

Generally, because of its material longevity, plastic can be recycled and reused in new products, thereby reducing the need and space associated with disposal. Recycling became more feasible in the <NUM> and <NUM> with the development and use of Polyethylene Terephthalate (PET) and other plastic materials.

Generally, plastic recycling requires sorting the plastic by the type of resin that is in their structure (seven basic types) and, in some cases, by color. The plastic is then chopped into small pieces, cleaned to remove debris and residue typically using a strong caustic (hydroxide) solution, melted down, and sometimes re-extruded into pellets. These small pellets are then transported to plastic processing plants where they are introduced and, sometimes, combined with virgin plastic material during the manufacturing process.

Unfortunately, the caustic wash solution can only remove impurities or additives that are soluble or dispersible in (alkaline) aqueous solution. Many modern plastics are combined with dyes, fillers, oxygen scavengers, colorants, passive barrier materials, and the like (collectively referred to as additives) that are often added to plastic during the manufacturing process for consumer and/or product considerations. In many cases, these additives are not easily recyclable and may complicate and/or prohibit proper recycling of the plastic material.

From <CIT> there is known a multilayer plastic container having at least one oxygen-absorbing layer and at least one oxygen-blocking layer, wherein.

From <CIT> there is known a multilayer film comprising: at least one gas barrier layer comprising a blend of a noise-damping polymer resin from about <NUM> to <NUM> percent by weight of a polyglycolic acid resin, the film having an oxygen transmission rate of less than <NUM> cc/m<NUM>*day. atm at <NUM>°F and at <NUM>% relative humidity, wherein the noise-damping polymer resin comprises a modified ethylene vinyl acetate layer disposed between the exterior layers and an interior gas barrier layer disposed between the exterior layers, the gas barrier layer comprising from about <NUM> to <NUM> percent by weight of a polyglycolic acid resin and a noise-damping polymer resin.

From <CIT> there is known an oxygen absorptive resin composition containing a polyamide compound and a transition metal catalyst wherein <NUM>-<NUM> mass parts of the transition metal catalyst are included as an amount of transition metals with respect to <NUM> mass parts of the polyamide compounds, and a multilayered material which has at least <NUM> layers of the first resin layer which contains a thermoplastic resin at least, the oxygen absorption layer consisting of an oxygen absorptive resin composition and the second resin layer containg a thermoplastic resin at least in this order.

From <CIT> there is known a package for an aqueous liquid wherein the package has a wall comprising an oxygen-scavenging polymeric composition, a thickness of the wall being adapted to achieve oxygen removal from the liquid, wherein the oxygen-scavenging polymeric composition comprises a polyamide and cobalt present in an amount of <NUM> to <NUM> ppm in the polyamide.

In view of the above it is an object of the invention to disclose an improved multilayer thermoplastic article providing an improved plastic recycling compatibility. Preferably, also improved plastic material compositions shall be provided that aid in plastic recycling. Preferably, also the addition of additives for improved consumer and/or product consideration shall be provided without negatively affecting compatibility of the plastic material for recycling.

This object is achieved by a multilayer thermoplastic article according to claim <NUM>. Further embodiments are subject of the dependent claims.

According to the principles of the present teachings, plastic products, such as multilayer containers, are provided having improved recyclability. In particular, in some embodiments, the plastic products and method of manufacturing the same have barrier and/or colorant additives blended with hydrolytically unstable gas barrier polymers for improved recyclability. Although the present teachings are described in connection with the manufacturing of plastic container products, it should be understood that the principles of the present teachings are not limited to such and are equally applicable to a wide variety of plastic products, goods, and materials.

Traditionally, in the food container industry, additives, such as oxygen scavengers, colorants, and the like, are blended directly with the base thermoplastic material (e.g. PET) which may result in unwanted contamination of the recycle stream. That is, many of these additives, which are used for improved performance of the container, are difficult to separate from the base thermoplastic material (e.g. PET) and thus require complex and/or expensive recycling procedures.

However, in order to permit the use of such additives with base thermoplastic material but without adversely affecting the recycle processing of the discarded plastic, the present teachings employ plastics having hydrolytically unstable high barrier polyester incorporated into the initial container material blend. The hydrolytically unstable high barrier according to the present teachings includes materials synthesized from glycolic acid (e.g. Polyglycolic Acid (PGA)), and other polymers, including materials synthesized from lactic acid or αHydroxy acids. According to these compositions, the resultant polymer chain reacts with water in strong alkaline solution and readily breaks down during the recycling process without unnecessarily complex and expensive materials or processes. More particularly, hydrolytic instability results in biodegradability and/or elimination during plastic recycling processes.

In some embodiments, PGA rapidly hydrolyzes in alkali wash water conditions ensuring that-unlike other barrier polymer alternatives-it can be chemically separated during the washing of PET flake, which will be further discussed in connection with the data set forth herein. PGA has been proven compatible with industrial PET recycling processes. In fact, PGA is easily dissolved in the alkaline wash water stages of rPET processing, assuring a simple and complete chemical separation of PGA from the valued rPET flake.

Hydrolytically unstable high barrier polyester, such as PGA, can be readily extruded and molded in combination with PET, polypropylene (PP), polyethylene (PE), Polylactic Acid (PLA), and other common polymers into multilayer structures on conventional processing equipment. However, for multilayer extrusion and injection, one must ensure that melt-stream properties of PGA or PGA/scavenger or PGA/colorant are compatible with the preferred process (melt viscosities, etc.). Additionally, further well-known material selection criteria for obtaining mechanically stable multilayer structures must be considered, for example adhesion of the PGA layer or PGA/scavenger blend layer to the structural layer(s) in the quenched article during service life. Without being bound by a particular theory, virgin PGA of relatively high polarity is expected to adhere well to polyester PET but poorly to nonpolar polyolefins and PGA/scavenger or PGA/colorant blends will have altered adhesion characteristics to consider.

It has been found that incorporating additives (e.g. oxygen scavengers, colorants) within the hydrolytically unstable polymer of the present teachings enables most, or all, of the additive to be removed with the hydrolytically unstable polymer during recycling or material washing. These additives, including scavengers, passive barrier materials, and colorants, would otherwise contaminate the recycle stream if incorporated directly into the PET material.

Exemplary additives that are easily removed in accordance with these teachings include O<NUM> scavengers or oxidizable organic polymers in the presence of a transition metal catalyst (e.g. cobalt stearate). Such oxidizable organic polymers may include polybutadiene; oxidzable polyamide materials such as MXD6; or poly(alkylene ether); PTMEG; unsaturated hydrocarbons; MXB_class including MXBT or m-xylylene-bis-(tetrahydrophthalimide). Other scavenging additive materials include Iron, Ascorbic Acid, oxidizable polymers, potassium sulfite. Other additives, such as colorants, can also be combined with the hydrolytically unstable high barrier polyester of the present teachings.

Exemplary hydrolytically unstable polymers that can be used in connection with the principles of the present teachings are illustrated in <FIG>, PGA polymer is strongly preferred because of its very high gas barrier to CO<NUM> and O<NUM>.

With particular reference to <FIG>, the present teachings can be used in connection with the production of food and beverage containers. Traditionally, plastic containers are manufactured using a preform <NUM> that is blow molded in a conventional manner and that is constructed in accordance with the principles of the present teachings. Although the present teachings will be discussed in connection with preform <NUM>, it should be understood that the principles of the present teachings are applicable to a wide variety of thermoplastic products and is not merely limited to food or beverage containers or products, but is equally applicable to any multilayer thermoplastic article.

In some embodiments, preform <NUM> comprises a conventional preform shape being made of a multilayer assembly. The multilayer assembly can comprise an inner layer <NUM>, an outer layer <NUM>, and an intermediate layer <NUM> disposed between the inner layer <NUM> and the outer layer <NUM>. In some embodiments, as illustrated in <FIG>, intermediate layer <NUM> can be substantially or fully encapsulated or contained between inner layer <NUM> and outer layer <NUM>. Although preform <NUM> can comprise any one of a number of suitable shapes, in some embodiments, preform <NUM> can comprise a proximal end <NUM>, having a threaded portion <NUM>, a neck portion <NUM>, a body portion <NUM>, and an enclosed distal end portion <NUM>.

In some embodiments, preform <NUM> can be arranged such that inner layer <NUM> and outer layer <NUM> are constructed of a similar or identical material, or in some embodiments inner layer <NUM> and outer layer <NUM> can be different materials. However, in some embodiments, inner layer <NUM> and outer layer <NUM> are made of PET. In some embodiments, intermediate layer <NUM>, labelled B layer in <FIG>, is made of a hydrolytically unstable polymer, such as PGA. In some embodiments, intermediate layer <NUM> defines a cross-sectional thickness relative to inner layer <NUM> and outer layer <NUM>, when viewed along a plane as illustrated in <FIG> or viewed orthogonal to a longitudinal axis of preform <NUM>. In some embodiments, the cross-sectional thickness of intermediate layer <NUM> relative to an entire thickness of inner layer <NUM>, outer layer <NUM>, and intermediate layer <NUM> is in the range of <NUM> to <NUM>%. In more preferred embodiments, it has been found that a thickness percentage of intermediate layer <NUM> in the range of <NUM>-<NUM>% is effective.

In some embodiments, intermediate layer <NUM> is a blend of the hydrolytically unstable polymer and an additive, such as, but not limited to, a scavenger, a barrier, a colorant, and the like.

In some embodiments, the blend of materials in intermediate layer <NUM> can comprise a <NUM>-<NUM> wt. % of hydrolytically unstable polymer and <NUM>-<NUM> wt. % of additive. In some embodiments, the blend of materials in intermediate layer <NUM> can comprise a <NUM>-<NUM> wt. % of hydrolytically unstable polymer and <NUM>-<NUM> wt. % of additive.

It has been found that a synergism exists when blending moisture-sensitive additives (e.g. scavenger materials) with PGA. Because PGA is hygroscopic, the PGA attracts moisture to the intermediate layer <NUM>. Thus, the concept is usable to initiate O<NUM> scavenging by moisture in polymers having Tg near room temperature - the added moisture lowers Tg, making the polymer segments more mobile, and thus launches scavenging.

Moreover, there exists additional synergism with the use of a PGA/O2 scavenger in a removable layer. That is, there is a lower wt. % required for equivalent performance of the PGA/scavenger layer structure to that of a monolayer blend. The removal of non-PET material in the recycling process is potentially much greater compared with a monolayer blend.

With reference to <FIG>, comparative calculations of candidate structures (monolayer blend O2 scavenger vs. multilayer PGA blends) with specific layer loadings is provided showing projected barrier performance and end-of-life (EOL) residuals of non-PET material in the PET stream assuming various wash efficiencies. As can be seen, in each configuration tested, a multilayer configuration, as taught herein that uses inner layer <NUM> and outer layer <NUM>, denoted by Layer A in the tables, with intermediate layer <NUM>, denoted by Layer B in the tables, being made of hydrolytically unstable polymer provides unique benefits in recyclability not found in the prior art. Particularly, configurations where the intermediate layer <NUM> (Layer B) comprises a <NUM>-<NUM> wt. % scavenger and <NUM>-<NUM> wt. % PGA will provide substantially reduced ingress O<NUM> compared to monolayer or conventional multilayer configurations. Moreover, in each configuration, the residual of PGA and scavenger is shown to be substantially reduced (down to <NUM>-<NUM>% following a wash processing step).

The use of a dye (or colorant, more generally) in the intermediate layer <NUM> may or may not be advantageous versus a monolayer dispersed colorant. The colorant system may comprise a UV blocker (to retain visually clear package or sheet material) or a colorant to tone, tint, color, or decorate the package or sheet, or a Near Infrared (NIR) absorber that is adjustable by layer placement and concentration. Unlike O<NUM> scavengers, the colorant is generally nonreactive and intended to be unchanged over time of article use. So its light-blocking (visible or UV or NIR) effectiveness is strictly proportional to Beer's Law control [A(lambda) = a(lambda) x b x C], where A is absorbance at a particular wavelength lambda, a is molar absorptivity of the colorant, b is the path length (layer thickness) and C the colorant concentration in the layer.

The colorant may be chosen according to its preferential solubility/compatibility with PGA "carrier" vs. any solubility in PET. A colorant that is a near-IR (reheat) absorber that is dispersed or dissolved in the PGA may be engineered via layer placement and absorber concentration to provide preferential heating during blow molding nearer to the middle or to the inside of a preform. A colorant may be used as a dye tracer for indicating removal of PGA at EOL during the recycle wash process. The removal of PGA will be indicated by the same Beer's Law relationship for a given flake thickness after recycle wash, where A(lambda) will be minimized for efficient wash process.

Finally, the following compatibilizers can be used to resist phase separation in two-component polymer blends: maleic anhydride (MAH), MAH-grafted functional polymers, glycidyl methacrylate group (GMA), GMA-grafted functional polymers, diblock copolymers, and nonreactive polar polymers.

Claim 1:
A multilayer thermoplastic article comprising:
an inner layer being made of a thermoplastic material;
an outer layer being made of a thermoplastic material; and
an intermediate layer disposed between the inner layer and the outer layer, the intermediate layer being made of a blended material comprising <NUM> to <NUM> wt. % of a hydrolytically unstable polymer, and <NUM> to <NUM> wt. % of a material which is selected from the group consisting of oxygen scavengers, passive barrier materials, Iron, Ascorbic Acid, oxidizable polymers, and potassium sulfite;
wherein the oxidizable polymers are selected from the group consisting of polybutadiene, oxidzable polyamide materials, or poly(alkylene ether), PTMEG; unsaturated hydrocarbons, MXBT, and m-xylylene-bis-(tetrahydrophthalimide);
wherein the hydrolytically unstable polymer is Polyglycolic Acid (PGA), or is selected from the group consisting of L-polylactide (LPLA), DL-polylactide (DLPLA), polycaprolactone (PCL), polydioxanone (PDO), polyglycolide trimethylene carbonate (PGA TMC), DL-polylactide-co-glycolide (DLPLG);
characterized in that the intermediate layer further comprises a compatibilizer which is selected from the group consisting of maleic anhydride (MAH), MAH-grafted functional polymers, glycidyl methacrylate group (GMA), GMA-grafted functional polymers, diblock copolymers, and nonreactive polar polymers.