WO2017204799A1

WO2017204799A1 - Polyester sheet modified with hydrous aluminum silicate having improved snapability

Info

Publication number: WO2017204799A1
Application number: PCT/US2016/034165
Authority: WO
Inventors: Zheng TIAN
Original assignee: Bemis Company, Inc.
Priority date: 2016-05-25
Filing date: 2016-05-25
Publication date: 2017-11-30

Abstract

The present invention is directed to a fracturable thermoformable packaging sheet comprising at least one thermoplastic layer having a thickness of between 10 mil and 50 mil which is composed of a polymer matrix of between 50% (wt.) to 95% (wt.) relative to the total weight of the thermoplastic layer of substantially amorphous aromatic polyester. Incorporated into this polymer matrix is an inorganic filler comprising hydrous aluminum silicate which is present in an amount of between 5% (wt.) to 50% (wt.) relative to the total weight of the thermoplastic layer. The fracturable thermoformable packaging sheet of the present invention may be used to form thermoformed packages having a single product cavity with a snap-open tab or covering and multi-pack type packages having multiple single-serve product cavities where each individual cavities can be easily separated from each other by simply breaking the flange connecting two or more cavities.

Description

POLYESTER SHEET MODIFIED WITH HYDROUS

ALUMINUM SILICATE HAVING IMPROVED SNAP ABILITY

BACKGROUND OF THE INVENTION

[01] The present invention relates generally to primary packaging and more particularly, to thermoformable packaging sheets which may be molded into various rigid or semi-rigid container shapes.

[02] Packaging sheets are used for many purposes. One of these many purposes includes thermoforming the sheet into articles, such as trays, cups, etc., which may then be used to package food, medical and industrial products. Use of single serve plastic containers is well known in the food product industry. These single serve containers are sometimes manufactured and sold in a multiple portion packaging tray comprising an array of separable containers. The containers are generally connected to one another along their flanges and may be broken apart by breaking the connection at the flanges. These containers work well when made of a relatively brittle plastic. Use of less brittle or more pliable polymers makes the containers more difficult to break apart. For some foods, brittle plastics, such as polystyrene, cannot provide the necessary protection and high moisture and/or oxygen barrier polymer is needed.

[03] One high moisture barrier packaging sheet that is currently used for thermoforming into packaging articles comprises a fully coextruded sheet with polyvinylidene chloride (PVdC) sandwiched between high impact polystyrene (HIPS), with ethylene vinyl acetate copolymer (EVA) used to laminate the central PVdC layer to the outer HIPS layers. This PVdC sheet generally has no significant sticking, forming, cutting, filling or sealing issues when used for thermoforming into articles. However, it is well known that PVdC has many environmental health concerns, with chlorine as the source of many of these concerns. Both the manufacture and the disposal of PVdC produce dioxin, a highly carcinogenic chemical; and many localities do not permit a converter or packager to reprocess or landfill-dispose of packaging materials containing PVdC.

[04] Another high moisture and oxygen barrier thermoformable packaging sheet that is currently used comprises a fully coextruded sheet with ethylene vinyl alcohol copolymer (EVOH) sandwiched between HIPS, with high density polyethylene (HDPE) between the central EVOH layer and the outer HIPS layers as described in U.S. Pat. No. 5,972,447. Such a sheet may have a layer structure of HIPS/HDPE/EVOH/HDPE/HIPS or HIPS/tie/HDPE/tie/EVOH/tie/HDPE/tie/HIPS (where 7" is used to indicate the layer boundary). However, both structures are known to have significant forming and cutting issues when used for thermoformed articles and styrene-containing materials present challenging recycling concerns.

[05] What is needed is an environmental-friendly thermoformable sheet which is relatively brittle to provide a snap-apart package which allows a first section of the packaging to be readily snapped away from the second section of the packaging. Accordingly, a solution to this long-felt but hitherto unresolved problem is desired which is simple and economical yet reliable, and durable.

SUMMARY OF THE INVENTION

[06] The present invention is directed to a fracturable thermoformable packaging sheet comprising at least one thermoplastic layer having a thickness of between 10 mil and 50 mil which is composed of a polymer matrix of between 50% (wt.) and 95% (wt.) relative to the total weight of the thermoplastic layer of a substantially amorphous aromatic polyester. Incorporated into this polymer matrix of the at least one thermoplastic layer is an inorganic filler of hydrous aluminum silicate which is present in an amount of between 5% (wt.) and 50% (wt.), between 10% (wt.) and 40% (wt.), or between 15% (wt.) and 30% (wt.), relative to the total weight of the thermoplastic layer. The fracturable thermoformable packaging sheet of the present invention may be used to form thermoformed packages having a single product cavity with a snap-open tab or covering and multi-pack type packages having multiple single-serve product cavities where each individual cavities can be easily separated from each other by simply breaking the flange connecting two or more cavities. Each of these packages may optionally include a partial cut and/or crease line extending across a portion of the package to facilitate the snapping apart of the two sections of the package.

It should be understood that the present invention may include any number of additional layers depending upon the packaging requirements for a particular product. For example, the present invention may include only one thermoplastic layer having a polymer matrix composed of a substantially amorphous aromatic polyester and inorganic filler of hydrous aluminum silicate. Alternatively, the present invention may include the thermoplastic layer having a polymer matrix composed of a substantially amorphous aromatic polyester, inorganic filler of hydrous aluminum silicate, and a multilayer film adhesively laminated to the amorphous aromatic polyester thermoplastic layer. The multilayer film may in include any number of layers having any layer composition arranged in any sequence as desired. In a preferred embodiment, the present invention includes the amorphous aromatic polyester thermoplastic layer adhesively laminated to a sealant layer comprising a heat sealable material. Heat sealable materials include, but are not limited to polyethylene such as low density polyethylene, ultra-low density polyethylene, linear low density polyethylene, ethylene alpha- olefin copolymers, ethylene vinyl acetate, ionomer or blends thereof. In another preferred embodiment, the present invention includes the amorphous aromatic polyester thermoplastic layer adhesively laminated to multilayer oxygen barrier sealant film having an oxygen barrier layer comprising ethylene vinyl alcohol copolymer and a sealant layer. In still another preferred embodiment, the sheet may be adhesively attached to the first surface and the opposing second surface of a multilayer barrier film to serve as rigid components in the following packaging laminate structure: first rigid component//multilayer barrier film//second rigid component. This type of packaging laminate structure is described more completely in U.S. Application Ser. No. 12/611,880, filed November 3, 2009, entitled "Chlorine-Free Packaging Sheet With Tear-Resistance Properties", Ser. No. 13/100,250, filed May 3, 2011 , entitled "High Density Polyethylene Blends", and U.S. Patent No. 8,574,694 issued on November 5, 2013, entitled "Packaging Sheet With Improved Cutting Properties."

[08] In one preferred embodiment, the sheet of the present invention is non-oriented.

[09] In another embodiment, the sheet of the present invention is thermoformed.

[10] In one important aspect of the present invention, the sheet of the present invention is formed from a polymer matrix composed of substantially amorphous aromatic polyester which may be any amorphous aromatic polyester known in the art. Non-limiting examples of suitable polymer matrix materials include substantially amorphous polyethylene terephthalate, polyethylene isophthalate, glycol-modified polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, a blend of amorphous polyethylene terephthalate and crystalline polyethylene terephthalate, a blend of amorphous polyethylene terephthalate and glycol-modified polyethylene terephthalate or blends thereof. It is also within the scope of the present invention that post-recycled amorphous polyethylene terephthalate also known as "RPET" can be used as suitable amorphous aromatic polyester. In one preferred embodiment, the amorphous aromatic polyester is substantially amorphous polyethylene terephthalate, polybutylene terephthalate or polyethylene naphthalate. Those skilled in the art will recognize that some crystalline aromatic polyester can be made substantially amorphous by rapidly cooling the molten crystalline polymer below its T_g or glass transition temperature. [11] Another important aspect of the present invention is inclusion of an inorganic filler of hydrous aluminum silicate in the polymer matrix such that the resulting sheet has enough brittleness to allow two sections of the sheet to cleanly break apart in a snap-like manner. This breaking or snapping apart of the filled matrix sheet can be measured as its "Peak Snapping Energy" or the total energy (in Joules) at maximum force to break the sheet into two separate sections. A more detailed description of this test is provided below. The inventor has discovered that for optimal snapping performance, a peak snapping energy at a rate of 5 in/min of less than 1 mJ/mil (millijoule per a thousandth of an inch), preferably, less than 0.7 mJ/mil, less than 0.6 mJ/mil, and more preferably, between 0.21 mJ/mil and 0.65 mJ/mil is highly desirable. This result can be achieved by blending between 5% (wt.) to 50% (wt.) relative to the total weight of the thermoplastic layer of an inorganic filler of hydrous aluminum silicate into the polymer matrix of amorphous aromatic polyester. The inventor has also discovered that the particle size of the inorganic filler may affect the desired snapping performance. For example, in some preferred embodiments, the hydrous aluminum silicate has an average particle size of between 1.5 μιτι (micron) and 12 μm.

[12] It is also contemplated that processing aids such as anti-oxidants, anti-static and anti-block agents, cross-linking agents, colorants, dispersions agents and impact modifiers may be included in the polymer matrix at concentrations typically known in the art to minimize or eliminate processing problems.

DETAILED DESCRIPTION OF THE INVENTION

[13] As used throughout this application, the term "sheet" refers to a plastic web having a thickness of at least about 0.254 mm (10 mil). The term "film" means a plastic web of any thickness and is not limited to a plastic web having a thickness of less than about 0.254 mm (10 mil). In one preferred embodiment, the sheet of the present invention has a thickness of between 0.254 mm and 1.27 mm (10 mil and 50 mil). In other preferred embodiments, the sheet of the present invention has a thickness of between 0.381 mm and 1.143 mm (15 mil and 45 mil) or between 0.508 mm and 0.762 mm (20 mil and 30 mil).

[14] As used throughout this application, the terms "thermoformable" and "thermoformed" refer to monolayer or multilayer thermoplastic polymer sheets, films or webs having sufficient rigidity or stiffness to be formed into a desired shape by the application of a differential pressure between the film or sheet and a mold, by the application of heat, by the combination of heat and the application of a differential pressure between the film or sheet and a mold, or by any thermoforming technique known to those skilled in the art. For purposes of this application, the term "thermoformable" also refers to non-oriented monolayer or multilayer thermoplastic polymer sheets, films or webs having a thickness of at least 10 mil. In the simplest form, thermoforming is the draping of a softened sheet over a shaped mold. In the more advanced form, thermoforming is the automatic high speed positioning of a sheet having an accurately controlled temperature into a pneumatically actuated forming station whereby the article's shape is defined by the mold, followed by trimming and regrind collection as is well known in the art. Still other alternative arrangements include the use of drape, vacuum, pressure, free blowing, matched die, billow drape, vacuum snap- back, billow vacuum, plug assist vacuum, reverse draw with plug assist, pressure bubble immersion, trapped sheet, slip, diaphragm, twin-sheet cut sheet, twin- sheet roll-fed forming or any suitable combinations of the above.

[15] As used throughout this application, the term "aromatic polyester" refers to any polyester having at least one phenyl (or benzene) moiety within one or both monomer repeating units used to form the material. Specific non-limiting examples of aromatic polyesters include a homopolymer or copolymer of alkyl- aromatic esters including but not limited to polyethylene terephthalate (PET), amorphous polyethylene terephthalate (APET), glycol-modified polyethylene terephthalate (PETG), polyethylene naphthalate (PEN) and polybutylene terephthalate (PBT); polyethylene isophthalate (PEI), polycycloterephthalate (PCT), polytriethylene terephthalate (PTT), a copolymer of terephthalate and isophthalate including but not limited to polyethylene terephthalate/isophthalate copolymer; and blends of any of these materials. A non-limiting example of APET is Eastman™ PET 9921 , which is available from Eastman Chemical Company (Kingsport, TN, USA). A non-limiting example of PETG is Eastar™ Copolyester 6763, which is also available from Eastman Chemical Company (Kingsport, TN, USA). A non-limiting example of APET include ParaStar™ 2400 and PET 9921 polyethylene terephthalate both available from Eastman Chemical Company (Kingsport, TN, USA); Performance™ PET 1708 available from StarPet, Inc. (Asheboro, N.C., USA); and CLEARTUF® 8006 polyester resin available from Gruppo Mossi & Ghisolfi (Wilmington, N.C., USA). Exemplary of another suitable amorphous polyethylene terephthalate (APET) includes, but are not limited to DAK Laser+® C9921 (F65A) supplied by DAK Americas (Chadds Ford, PA, USA).

As used throughout this application, the term "hydrous aluminum silicate" refers to a phyllosilicate mineral composed of aluminum silicate hydroxide having the chemical formula: AI₂(Si₄O₁₀)(OH)2. Another common name for hydrous aluminum silicate is pyrophyllite. In the present invention, the inventor has discovered that the use of hydrous aluminum silicate substantially uniformly disperses in the above-mentioned amorphous aromatic polyesters. It should be understood that hydrous aluminum silicate is a specific type of clay mineral chemically different from other phyllosilicate-like clays such as talc. Specifically, talc has magnesium ions instead of aluminum ions in its crystal lattice giving it the chemical formula: Mg₃(Si₄O₁₀)(OH)2. One can readily distinguish hydrous aluminum silicate from talc by a simple chemical test for aluminum. In some preferred embodiments, the hydrous aluminum silicate to be used has a nano- sized particle of between 1 pm and 20 pm, and preferably between 1.5 pm and 15 pm. In some preferred embodiments, the hydrous aluminum silicate to be used has an aspect (length to thickness ratio) of at least 5:1 , at least 10:1 , at least 15:1 and more preferably of between 15 to 20:1. In some preferred embodiments, the hydrous aluminum silicate has a bulk density of between 100 g/L (grams per liter) and 500 g/L, and more preferably between 200 g/l and 300 g/l. In the present invention, the hydrous aluminum silicate is used in hydrated form, i.e. the hydrate water which is present in natural form is not removed by heating or calcining before use. Examples of commercially available hydrous aluminum silicate are sold under the trademark Profylite® byToyota Tsusho America, Inc., New York, NY.

SHEET EXAMPLES

Examples 1-15 are monolayer packaging sheets exemplifying the present invention. The hydrous aluminum silicate was initially compounded as a masterbatch (55 wt.% in APET), then diluted with APET during the extrusion process. Each of these sheets was produced, by flat die or slot cast extrusion and the composition are shown in TABLE 1. Also shown in TABLE 1 are Comparative Examples 1-2 which are also monolayer sheets. The Comparative Examples were produced in a similar manner as Examples 1-15 of the present invention. Examples 1-10 varied in the amount of hydrous aluminum silicate from approximately 5 wt.% and 50 wt.% present in the sheet and each had an average thickness of approximately 0.762 mm (30 mil). Examples 11-15 had a constant amount of hydrous aluminum silicate of approximately 20 wt.% present in the sheet and varied in thickness from approximately 0.508 mm and 1.27 mm (20 mil and 50 mil). The Comparative Examples each had a constant thickness of approximately 0.762 mm (30 mil) and did not include any hydrous aluminum silicate. All percentages of hydrous aluminum silicate (approximate values) are based relative to the total weight of the monolayer sheet. The breaking or snapping of the sheets of the present invention and comparative examples were also measured as its "Peak Snapping Energy" or the total energy (in Joules) at maximum force to break the sheet into two separate sections. Test specimens were fabricated having the dimensions of 25.4 mm width x 127 mm length (1 in width x 5 inch length) having an inverted triangular shaped score-line or groove cut across the width of each specimen at 254. mm (one inch) from the end of the specimen to a depth of 0.254 mm and a width of 0.254 mm (10 mil and a width of 10 mil). The specimen was then mounted to a test fixture such that the score- line was aligned with the end of the fixture leaving about 0.254 mm (one inch) of the specimen exposed. A steel probe was then lowered onto the specimen approximately 0.02 mm (0.75 in) from the score-line or end of the fixture at a rate of 5 inch/min to test the snapping resistance. The compression force and energy consumption were recorded and calculated, respectively. The snapping energy is the integrated area under the force/bending extension curve (Load [N] vs. Bending Extension [mm]) starting from zero to the peak extension value (a maximum load) and normalized for thickness. The snapping energy is considered to represent the snapability of each sheet and is also reported in TABLE 1.

[18] APET¹ was an amorphous polyethylene terephthalate (APET) sold under the trademark M&G CLEARTUF^® 8006C and supplied by Gruppo Mossi & Ghisolfi (Wilmington, N.C.). It should be noted that a dispersion agent was included in all these examples with hydrous aluminum silicate at a maximum concentration of about 0.2 wt.% relative to the total weight of the sheet.

[19] HIPS was a high impact polystyrene sold under the trademark Total™ E825 and supplied by Total Petrochemicals & Refining USA, Inc. (Houston, TX, USA). [20] Another desirable parameter which may be used to identify optimal snapping performance of suitable blends of materials is the shape of the curve generated when measuring the snapping strength verses bending extension curve (Load [N] vs. Bending Extension [mm]). In Figure 1 , there is shown the snapping force in the machine direction (MD) as a function of bending extension for various Comparative Examples and Examples of the present invention. The inventor has discovered that when sheet compositions exhibit a relatively steep descending curve, for example, as in the case of Examples 3, 4 and 5 compared to a more gradual descent as shown for Comparative Examples 1 and 2, the material snaps cleanly apart leaving no webbing or strands of material within the fracture line.

[21] The present invention also offers advantages in improving the thermal stability of thermoformable sheets over conventional thermoformable sheets which do not include hydrous aluminum silicate. For examples, a sheet comprising 2 wt.% titanium dioxide, 15 wt.% hydrous aluminum silicate and 83 wt.% amorphous aromatic polyethylene terephthalate exhibited no change in white color after heating in an oven at 288° C (550° F) for 10 min. In contrast, a sheet comprising 2 wt.% titanium dioxide and 98 wt.% amorphous polyethylene terephthalate which was heated in an oven at 288° C (550° F) for 10 min changed its color from white to brownish-grey. The absence of any color change for the hydrous containing samples should be interpreted as improving the thermal oxidation/degradation resistance of the material. This skilled in the art will appreciate that thermoformable sheets having improved thermal oxidation/degradation resistance are desirable for cook-in or ovenable applications.

[22] The above description and examples illustrate certain embodiments of the present invention and are not to be interpreted as limiting. Selection of particular embodiments, combinations thereof, modifications, and adaptations of the various embodiments, conditions and parameters normally encountered in the art will be apparent to those skilled in the art and are deemed to be within the spirit and scope of the present invention.

Claims

What is claimed:

1. A fracturable thermoformable packaging sheet comprising:

at least one thermoplastic layer having a thickness of between 0.254 mm and 1.27 mm (10 mil and 50 mil) and comprising a polymer matrix formed from a substantially amorphous aromatic polyester which is present in an amount of between 50% (wt.) to 95 % (wt.) relative to the total weight of the thermoplastic layer; and

an inorganic filler comprising hydrous aluminum silicate incorporated into the polymer matrix which is present in an amount of between 5% (wt.) to 50% (wt.) relative to the total weight of the thermoplastic layer.

2. A fracturable thermoformable packaging sheet according to claim 1 , wherein the sheet has a peak snapping energy at a rate of 5 in/min of between 8.27 mJ/mm and 26.38 mJ/mm (0.21 mJ/mil and 0.67 mJ/mil).

3. A fracturable thermoformable packaging sheet according to any of claims 1-2, wherein the sheet has a peak snapping energy at a rate of 127 mm/min (5 in/min) of between 8.27 mJ/mm and 15.75 mJ/mm (0.21 mJ/mil 0.40 mJ/mil).

4. A fracturable thermoformable packaging sheet according to any of claims 1-3, wherein the substantially amorphous aromatic polyester is polyethylene terephthalate, glycol-modified polyethylene terephthalate, polybutylene terephthalate, polyethylene isophthalate or polyethylene naphthalate.

5. A fracturable thermoformable packaging sheet according to any of claims 1-4, wherein the substantially amorphous aromatic polyester is polyethylene terephthalate.

6. A fracturable thermoformable packaging sheet according to any of claims 1-5, wherein the hydrous aluminum silicate has a chemical formula of AI₂(Si₄O₁₀)(OH)₂.

7. A fracturable thermoformable packaging sheet according to any of claims 1-6, wherein the hydrous aluminum silicate has an aspect ratio of 15-20:1.

8. A fracturable thermoformable packaging sheet according to any of claims 1-7, wherein the hydrous aluminum silicate has a particle size between 1.5 and 12 μιτι.

9. A fracturable thermoformable packaging sheet according to any of claims 1-8, wherein the hydrous aluminum silicate is present in an amount of between 10% (wt.) and 25% (wt.) relative to the total weight of the thermoplastic layer.

10. A fracturable thermoformable packaging sheet according to any of claims 1-9, wherein the hydrous aluminum silicate is present in an amount of between 15% (wt.) and 20% (wt.) relative to the total weight of the thermoplastic layer.

11. A fracturable thermoformable packaging sheet according to any of claims 1-10, wherein the thermoplastic layer has a thickness of between 0.381 mm and 1.14 mm (15 mil and 45 mil).

12. A fracturable thermoformable packaging sheet according to any of claims 1-11 , wherein the thermoplastic layer has a thickness of between 0.508 mm and 0.762 mm (20 mil and 30 mil).

13. A fracturable thermoformable packaging sheet according to any of claims 1-12, wherein the sheet is non-oriented.

14. A fracturable thermoformable packaging sheet according to any of claims 1-13, wherein the sheet is thermoformed.

15. A fracturable thermoformable packaging sheet according to any of claims 1-14, wherein the sheet is adhesively laminated to a sealant layer comprising a heat sealable material.

16. A fracturable thermoformable packaging sheet according to any of claims 1-15, wherein the sheet is adhesively laminated to a multilayer oxygen barrier sealant film having an oxygen barrier layer comprising ethylene vinyl alcohol copolymer and a sealant layer.

17. A fracturable thermoformable packaging sheet according to any of claims 1-16, wherein the sheet is adhesively attached to the first surface and the opposing second surface of a multilayer barrier film to serve as rigid components in a packaging laminate.

18. A fracturable thermoformable packaging sheet according to any of claims 1 -17, wherein the sheet further comprises a dispersion agent.

19. A fracturable thermoformable packaging sheet according to any of claims 1-18, wherein the sheet further comprises a maximum concentration of a dispersion agent of 0.2 wt.% relative to the total weight of the sheet. A fracturable thermoformable packaging sheet according to any of claims 1-19, wherein the sheet does not exhibit any visible color change after 10 minutes at 288° C (550° F).