WO2009152114A1

WO2009152114A1 - Methods and products for improving the recyclability of oxygen scavenging containers

Info

Publication number: WO2009152114A1
Application number: PCT/US2009/046670
Authority: WO
Inventors: Richard Leonard Hoch; Matthew James Dauzvardis
Original assignee: Constar International LLC
Current assignee: Constar International LLC
Priority date: 2008-06-09
Filing date: 2009-06-09
Publication date: 2009-12-17
Anticipated expiration: 2010-12-09

Abstract

Containers comprise a base polymer and a color-correcting material The color of a polymer-based container is corrected by adding a effective amount of a color correcting matenal to a container compnsing a base polymer Other methods of correcting the color of a polymer-based container include mixing a base polymer with an effective amount of a color-correcting material to form a mixture, forming the mixture into a preform, and forming the preform into a container An effective amount of a color-correcting matenal can be injected at the trailing edge of a preform, and the preform can be formed into a container.

Description

METHODS AND PRODUCTS FOR IMPROVING THE RECYCLABILITY OF OXYGEN SCAVENGING CONTAINERS

CROSS REFERENCE TO RELATED APPLICATIONS This application claims the benefit of U.S. Provisional Application 61/059,833, filed

June 9, 2008, which provisional application is incorporated herein by reference in its entirety.

FIELD OF THE INVENTION

The present invention relates to articles and methods that change the color of recyclable, polymer-based containers.

BACKGROUND OF THE INVENTION

Polymer-based containers, such as those comprised of polyethylene terephthalate (PET), polyolefms, for example, polypropylene, polystyrene, polylactic acid (PLA), and the like, provide a cost-effective, lightweight, shatter-resistant packaging method. These containers frequently include additives such as, for example, UV-inhibitors, and/or residual polymerization catalysts. While these containers are generally recyclable, one undesirable attribute is that they have a tendency to undergo a color change upon degradation of the base polymer or oxidation of the additives, for example.

Oxygen scavenging compositions, such as those described in, for example, U.S. 6,544,611 (assigned to Arteva North American S.A.R.L.); U.S. 6,410,156 (assigned to Honeywell Int'l, Inc.); U.S. 6,083,585 (assigned to B.P. Amoco Corp.); U.S. 5,641,825

(assigned to Chevron Chem. Co.); U.S. 5,952,066 (assigned to Continental PET Tech., Inc.); U.S. 6,365,247 (assigned to BP Corp. North America, Inc.); U.S. 5,492,742 (assigned to W.R. Grace & Co.); U.S. 6,406,766 (assigned to BP Corp. North America, Inc.); and U.S. 5,021,515 (assigned to Constar Int'l, Inc.), have provided manufacturers of oxygen-sensitive products, such as ketchup, fruit juice, wine, and beer, the opportunity to package their products in lightweight, recyclable, unbreakable, PET. Prior to the advent of these oxygen scavenging materials, packaging of oxygen-sensitive products in PET resulted in their rapid spoliation and/or discoloration. Since these materials are comprised primarily of PET, they are generally recyclable, however, they also have a tendency to experience a color change upon degradation and/or exposure to oxygen. Presently, most types of commercially available polymer-based containers can be recycled. A conventional recycling process often begins with the collection of the polymer- based containers and separation of the containers based on resin type as identified by the Society of the Plastics Industry, Inc. (SPI) resin identification coding system. The containers are then sorted from other household waste and sorted by color - e.g., uncolored, blue, green, amber, and mixed color. The sorted containers are then crushed and pressed into bales for sale to recyclers, with the uncolored lots being the most valuable and the mixed color lots being of lesser value. The recycler then processes the containers into "flakes," pellets, or chips. This processed material can then be sold and used for the manufacture of new containers and other products.

While polymer-based containers are generally recyclable, they have a tendency to change color during the recycling process, where these containers are exposed to, for example, atmospheric oxygen, heat, moisture, processing chemicals, and light. This tendency is undesirable because the once valuable "uncolored" material, or blue, green, or amber lot, must now be sorted into the lesser-valued "mixed color" lot.

In order to increase the value of these off-color lots, recyclers use techniques from the color space field to correct the undesirable color and generate a more desirably-colored material. "Lab" color space is a color-opponent space where "L" is for "lightness" (0 is black and 100 is diffuse white); -a is green, +a is magenta, -b is blue and +b is yellow. Richard S. Hunter and Richard W. Harold, The Measurement of Appearance, 2d., John Wiley & Sons, Inc., New York (1987). By mixing yellow (+b) with blue (-b), for example, a more colorless composition can be obtained. When confronted with, for example, a yellow lot, recyclers will mix in a proportion of blue lot in an attempt to produce the more valuable, uncolored lot. A similar mixing process can be performed with other colored lots.

This color mixing is a "trial and error" process because the recycler can never be certain how much of the blue lot must to added to the yellow lot, for example, to produce the desired result. Sometimes this color mixing is successful and the recycler can sell the previously undesirably colored lot for a higher price. Oftentimes, the color mixing is unsuccessful and the recycler either sells the material as a mixed color lot or simply discards the lot. Hence, even though the polymer-based containers are technically recyclable, their tendency to change color results in them not being a valuable component to the recycling stream.

As such, what are needed are methods and products that reduce the likelihood that polymer-based containers will change color during the recycling process. Product and methods for correcting the color of polymer-based containers that have experienced a color changes are also needed.

SUMMARY OF THE INVENTION

The present invention is directed to containers comprising a base polymer and a color- correcting amount of a color-correcting material. Also described are methods of correcting the color of a polymer-based container comprising adding a color-correcting amount of a color- correcting material to a container comprising a base polymer. Other methods of correcting the color of a polymer-based container of the present invention include mixing a base polymer with a color-correcting amount of a color-correcting material to form a mixture, forming the mixture into a preform, and forming the preform into a container. Still other embodiments are directed to injecting a color-correcting amount of a color-correcting material at the trailing edge of a preform and forming the preform into a container.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 Hunter color space depiction (prior art)

FIG. 2 Depicts a preferred embodiment of a container of the present invention

FIG. 3 Depicts a preferred embodiment of a container of the present invention

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS The present invention is directed to methods and products to improve the post-consumer recyclability of polymer-based containers that exhibit color change upon exposure to oxygen, heat, moisture, processing chemicals, and light. In certain embodiments of the present invention, the base polymer of the present invention comprise polyethylene terethphalate (PET), polyolefms such as polypropylene, polyethylene, polystryene, polylactic acid (PLA), combinations thereof, and the like. In exemplary embodiments, the containers comprise an oxygen-scavenger polymer. PET-based oxygen scavenging compositions and containers are known in the art and are described in, for example, U.S. Patent Nos. 6,544,611; 6,410,156; 6,083,585; 5,641,825; 5,952,066; 6,365,247; 5,492,742; 6,406,766; and 5,021,515. Containers of the present invention may also comprise additives typically used in the polymer industry, for example, UV- inhibitors. Containers of the present invention may also comprise residual amounts of polymerization catalysts. Certain preferred containers of the present invention are oxygen scavenging containers.

Oxygen-scavenging containers of the present invention are primarily comprised of polyethylene terephthalate, with the addition of an oxygen scavenging composition, for example, MXD6, polybutadiene, and derivatives and copolymers thereof. In typical applications, the oxygen scavenging composition comprises about 1% to 10 wt.% of the container, depending on the composition and its application. These containers typically also include a transition metal catalyst. Cobalt and zinc salts are especially preferred and are typically present in an amount ranging from about 50 to 200 ppm. These containers and their manufacture are well known in the art.

Containers for use with the present invention will be manufactured according to a manufacturer's, or customer's, specifications. These specifications generally include a color specification. The containers of the present invention, while manufactured having a particular color specification, will exhibit a change from that color specification upon exposure to, for example, oxygen, heat, moisture, processing chemicals, and light. According to the present invention, color-correcting material, for example, toners, pigments, dyes, and the like, are added to the container such that upon the container's exposure to the container's color-shifting conditions, the color-correcting material results in a color-corrected polymer composition having a color specification that is within or near the scope of the original color specification or that is within the scope of different color specification.

The science and technology of color space is well understood in the art. See, e.g., Richard S. Hunter and Richard W. Harold, The Measurement of Appearance, 2d., John Wiley & Sons, Inc., New York (1987); see also, FIG. 1. Upon identification of the color specification of the color-changed material, one of skill in the art can identify what color-correcting material is appropriate to convert the color-changed material into a material having a different color specification. Once a suitable color-correcting material is identified, routine experimentation can be performed to determine the amount of color-correcting material, i.e., the "color-correcting amount," that should be used to produce the desired color specification.

Once a container for use with the present invention is identified, color-correcting material can be added to the container. The color-correcting material can be applied to the container using any method known in the art for applying color-correcting material to a polymer-based container. For example, the color-correcting material may be applied using ink jet technology. Alternatively, the color-correcting material may be applied by spraying, roll coating, or dip- coating of the container. The present invention also encompasses adding the color-correcting material in the mix delivered to an injection molding machine such that color-correcting material is either distributed throughout the preform or concentrated in one or more portions of the preform. In such embodiments, after the preform is blown into a container using conditions known in the art, the resulting container will have the color-correcting material distributed throughout or concentrated in one or more portions of the container. For example, an appropriate mass of color-correcting material may be injected at the trailing edge of the preform such that the bottom center of the preform, and hence, the bottom center of the container, has the colored color-correcting material.

In other embodiments, color-correcting material may be directly affixed to the preform after injection molding. For example, the color-correcting toner can be formulated into a polymer-based medium, and manufactured into a shaped piece, herein referred to as a "coupon," that is applied to the container using any adhesive suitable for use with polymer-based containers, such as a food grade adhesive. The coupon carrying the color-correcting material can be any size or shape, for example, circle, square, triangle, rectangle, and the like. The color- correcting material can be incorporated into the coupon or can be applied to the surface of the coupon using any known techniques. The color-correcting materials of the present invention include food-grade toners, pigments, dyes, and the like. Such materials are well known to those of skill in the art and are readily available from manufacturers such as, for example, Ciba Corp. Newport, DE; Americhem, Inc., Cuyahoga Falls, OH; ColorMatrix, Berea, OH, and the like. Preferred color- correcting materials are those that, when used in accordance with the present invention, in accordance with the principles of color space, result in a less-colored, differently colored, or uncolored material. "Uncolored," as that term is used in the present application, encompasses those materials that, while colored as measured with a spectrophotometer, appear to have little to no color as perceived by the human eye. This is a concept well understood in the art.

Color-correcting materials of the present invention may be supplied further comprising a carrier. For example, certain color-correcting materials are provided in a resin-based carrier, for example, a polymer such as, for example, PET. Other color-correcting materials for use with the present invention may include a paraffin-based carrier. Other color-correcting materials of the present invention may further comprise solvent carriers, for example, hydrocarbon-based solvents. During the recycling process, the color-correcting material, either as a coupon, as applied to the container or preform, or as distributed in or through the container or preform, gets incorporated into the recycling stream along with the oxygen scavenging container and provides color correcting properties to the container material during the recycling process. The amount of color-correcting material used in the present invention will vary depending on the color correction desired. The amount of color-correcting material will also vary depending on the type of color-correcting material used and whether the color-correcting material further comprises a carrier. In preferred embodiments, the containers of the present invention will comprise less than 20%, by weight of the container, of color-correcting material. In other embodiments, the containers will comprise less than about 10%, by weight of the container, of color-correcting material. Still other embodiments will comprise less than about 5%, by weight of the container, of color-correcting material.. Exemplary embodiments will comprise less than about 2.5% of color-correcting material, based on the weight of the container. Especially preferred are those embodiments comprising about 1%, or less, by weight of the container, of color-correcting material.

The amount of color-correcting material required to correct the color of container of the present invention can be determined using routine experimentation according to parameters understood in the art and in light of the examples set forth herein.

The following examples are illustrative of the products and methods of the present invention. It should be understood that these examples, while indicating preferred embodiments of the invention, are given by way of illustration only. From the above discussion and these examples, one skilled in the art can ascertain the essential characteristics of this invention, and without departing from the spirit and scope thereof, can make various changes and modifications of the invention to adapt it to various usages and conditions.

EXPERIMENTAL SECTION

General procedure

Eastman Vitiva PC715 PET resin (Eastman Chemical Co., Kingsport, TN) was dried under normal drying conditions for PET, i.e., at least 4 hours at 170 ⁰C in a PET desiccant dryer. PC715 resin is typical of a PET resin used for oxygen scavenging applications.

Dried PC715 was mixed with MXD6 (about 1.5 wt.%) and cobalt masterbatch (about 2 wt.%) (CoMB; cobalt-containing polyester containing 4000 ppm cobalt). Various pigment systems (color-correcting materials) were added. These blends, along with a control, were injection molded using a Boy 22S injection molding machine. The process used was typical for PET injection molding with a barrel temperature of 265 ⁰C. The blends were injected into a mold with a 3-step color chip and ASTM plaque. The plaques were 3" x 2" with a 3mm thickness (maximum).

The plaques were then "aged" under accelerated conditions selected to replicate conditions experienced during the recycling process. The plaques were placed in an oven at 140 ⁰F for 2 weeks and 180 ⁰F for 1 week. The aged plaques were ground using a laboratory mill (Thomas-Wiley Model 4) into pieces of about 2 to 4 mm.

The ground materials were then blended into CT MAX PET resin (M&G Polymers) at 10%, by weight. CT MAX is a resin typically used in manufacturing PET containers that require recycled content, for example, carbonated soft drink (CSD) containers, and was added to even further replicate recycling conditions. Recycled materials typically contain about 10% of a CSD- suitable resin. The resulting compositions are set forth in Table 1.

The resulting blends were then dried and injection molded in the same manner as described above and then measured for color (L*, a*, and b*) using a HunterLab Spectrophotometer (UltraScan Pro Model VS P40). The color of the controls and test samples were then compared. The results are shown below in Table 2.

Table 1

Americhem, Inc., Cuyahoga falls, OH 2 Ciba Corp., Newport, DE Table 2

As seen from the data in Table 2, the introduction of color correcting material to polymer-based composition can color-correct the color change incurred when the material is exposed to oxygen, light, and heat. The reduction in b* yellowing ranged from 25% to 81%, depending of the type and amount of color-correcting material used. It is expected that similar results would be achieved in color-correcting color changes associated with exposure to moisture and processing chemicals, as well.

As those skilled in the art will appreciate, numerous modifications and variations of the present invention are possible in light of the above teachings. It is therefore understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described herein, and the scope of the invention is intended to encompass all such variations. Further, the present invention may be applied to the prior art technology that is referred to herein, such as that reflected in the patents in the Background and Preferred Embodiment.

Claims

What is Claimed:

1. A container comprising a base polymer and a color-correcting amount of a color- correcting material.

2. The container of claim 1 , wherein the base polymer is polyethylene terephthalate, polypropylene, polystyrene, polylactic acid, or a combination thereof.

3. The container of claim 1 wherein the base polymer is polyethylene terephthalate.

4. The container of claim 3, further comprising an oxygen scavenging polymer.

5. The container of claim 1, wherein the color correcting material is a toner, pigment, dye, or combination thereof.

6. The container of claim 1, wherein the color-correcting material further comprises a carrier.

7. The container of claim 6, wherein the carrier is a polymer or a solvent.

8. The container of claim 1, wherein the color-correcting material is distributed throughout the container.

9. The container of claim 1, wherein the color-correcting material is concentrated in one or more portions of the container.

10. The container of claim 1, wherein the toner is applied to the container by ink jet coating, spray coating, dip coating, or brush coating.

11. The container of claim 1 , wherein the color-correcting material is applied to the container as a coupon.

12. The container of claim 11, wherein the coupon is applied with food-grade adhesive.

13. The container of claim 1, wherein the container is a bottle or jar.

14. A method of correcting the color of a polymer based container comprising: providing a container comprising a base polymer; and adding a color correcting amount of a color-correcting material to the container.

15. The method of claim 14, wherein the base polymer is polyethylene terephthalate, polypropylene, polystyrene, polylactic acid, or a combination thereof.

16. The method of claim 14, wherein the container further comprises an oxygen scavenging polymer.

17. The method of claim 14, wherein the color correcting material is a toner, pigment, dye, or combination thereof.

18. The method of claim 14, wherein the color correcting material is added as a coupon.

19. The method of claim 14, wherein the color correcting material is added by ink jet coating, spray coating, dip coating, or brush coating.

20. A method of correcting the color of a polymer-based container comprising: mixing a base polymer with a color-correcting amount of a color-correcting material to form a mixture; forming the mixture into a preform; and forming the preform into a container.

21. A method of correcting the color of a polymer-based container comprising: injecting a color-correcting amount of a color-correcting material at the trailing edge of a preform; and forming the preform into a container.