Article comprising several layers of polylactic acid with D-Lactide

The invention concerns an article in a material comprising polylactic acid. The material has L-Lactide units and D-Lactide units.

Polylactic Acid (PLA) is a thermoplastic polymer made from renewable resources. It has a significant biodegradability. PLA plastic sheets are used to make thermoformed containers, such as cups, for example yogurt cups.

Thermoforming is performed by applying a plug to force a heated material into a mold cavity. During thermoforming the material is stretched and the initial thickness of the material is reduced. Higher form factors (deepness dimension / section dimension) of thermoformed articles are obtained with higher stretch ratios. Mechanical properties of the stretched zone decrease as the thickness decreases. Stretching inhomogeneity can also be a source of mechanical properties degradations by generating local defaults.

There is a need in improved articles made with PLA that can allow or present good mechanical properties, for example due to good thickness profiles and/or due to good homogeneity after stretching, and/or that can allow or present well-formed shapes, for example without retraction after mold removal.

Thermoforming PLA materials comprising L-Lactide units and D-Lactide units has been described. For example "Processing technologies for poly(lactic acid)", L.-T. Lim, Progress in Polymer Science 33 (2008) 820-852, discloses that PLA resins of higher D- isomer contents (4-8%) are more suitable for thermoforming (page 822). Meanwhile the same article discloses on figure 8 the effect on crystallinity, at concentrations of D-Lactide units of from 1 .8% to 7.2%, when drawing a biaxially stretched PLA at 80°C to draw ratios up-to 4 in an experimental setting that does not correspond to thermoforming. There is a need for thermoformed articles and thermoforming process with higher stretching and/or with higher form factors, and/or with well-formed shapes, for example without retraction after mold removal.

Document EP1577346B1 discloses blends of PLA polymers having various D- Lactide units amounts, properties of the blends, and thermoforming. Paragraphs [0103] and [0104] disclose thermoforming a bi-oriented sheet of 300 μηι in a mold having a diameter of 100 mm and being 30 mm deep. This corresponds to a cylinder with a total stretch ratio of 2.2. There is a need for articles that can be thermoformed and for thermoforming processes with higher stretching and/or with higher form factors. There is also a need for articles having a thermoformed part that can be made, with higher productivity processes and/or with higher processability windows. There is also a need for articles, such as sheets, that can allow this. The is also a need for articles and/or processes thereto with better formed shapes, for example without retraction after mold removal.

The invention addresses at least one of the problems or needs above with an article comprising a multilayer plastic material comprising at least:

A) one layer A of a material A comprising polylactic acid having D-Lactide units and L- Lactide units, as a copolymer and/or blend, with a ratio A between D-Lactide units and L-

Lactide units,

B) one layer B of a material B comprising polylactic acid having D-Lactide units and L- Lactide units, as a copolymer and/or blend, with a ratio B between D-Lactide units and L- Lactide units,

wherein:

- 4.0/96.0 < ratio A < 20.0/80.0, preferably 5.0/95.0 < ratio A < 10.0/90.0, and

- 0.1/99.9 < ratio B < 4.0/96.0, preferably 1 .0/99.0 < ratio B < 3.7/96.3.

The article of the invention can be a plastic sheet or a container comprising a thermoformed part typically obtained from the plastic sheet.

The invention also concerns a process of making a plastic sheet article, comprising a step of co-extruding the layers.

The invention also concerns process of making an article comprising a thermoformed part, comprising the steps of:

a) providing a plastic sheet article, and

b) thermoforming at least a part of the plastic sheet.

It has been surprisingly found that the articles and/or the processes of the invention allow or present good mechanical properties such as compression resistance and/or good thickness profiles, and/or good homogeneity and/or control of thickness profiles and/or lack of retraction in the mold and/or good other properties such as banderoles adhesion. It has been surprisingly found that it was possible to achieve an improved control and/or homogeneity while avoiding retraction in the thermoforming mold. Definitions

In the present application a non-foamed polylactic acid (PLA) material refers to polylactic acid substantially depleted of gas inclusions, either directly in the PLA or in microspheres embedded in the PLA. Non-foamed PLA has typically a density of higher than 1 .2. Non-foamed PLA is also referred to as "compact PLA".

In the present application a foamed polylactic acid (PLA) material refers to polylactic acid comprising gas inclusions, preferably directly in the PLA, typically as opposed to gas inclusions in microspheres embedded in the PLA. Foamed PLA has typically a density of up to 1 .2, preferably of at less than 1 .2, preferably of up to 1 .1 .

In the present application "additives" refer to products that can be added to polylactic acid or other thermoplastic materials.

In the present application the "total stretch ratio" refers to the ratio between the surface of the article opening, corresponding to the thermoforming area of a sheet, and the surface of the developed thermoformed part, corresponding to the surface of the plastic in contact with a mold.

In the present application the "local stretch ratio" or "local draw ratio" refers to the stretch ratio at a local zone of the thermoformed part. The local stretch ratio can be estimated by dividing the local thickness in the thermoformed part by the initial thickness before thermoforming. Non thermoformed parts, such as flanges, typically have this initial thickness.

In the present application a "stereocomplex" refers to a complex organized structure of a L-Lactide homopolymer and a D-Lactide homopolymer having a crystalline structure that the melting temperature is of more than 210°C. PLA materials that are different from a stereocomplex typically have a melting temperature of 150°C-180°C.

Articles structure

The article has a multilayer structure, for example a bi-layer structure or a three- layer structure. Thus the article comprises a multilayer plastic material comprising at least: A) one layer A of a material A comprising polylactic acid having D-Lactide units and L- Lactide units, as a copolymer and/or blend, with a ratio A between D-Lactide units and L- Lactide units, B) one layer B of a material B comprising polylactic acid having D-Lactide units and L- Lactide units, as a copolymer and/or blend, with a ratio B between D-Lactide units and L- Lactide units,

wherein:

- 4.0/96.0 < ratio A < 20.0/80.0, preferably 5.0/95.0 < ratio A < 10.0/90.0, and

- 0.1/99.9 < ratio B < 4.0/96.0, preferably 1 .0/99.0 < ratio B < 3.7/96.3.

The article can comprise further layers, for example at least one layer C, for example between layer A and layer B. Layer C can be of a material C comprising polylactic acid, comprising polylactic acid having D-Lactide units and L-Lactide units, as a copolymer and/or blend, with a ratio C between D-Lactide units and L-Lactide units. Preferably ratio B < ratio C < ratio A.

In a preferred embodiment [ratio A - ratio B] > 0.3, preferably [ratio A - ratio B] > 1 .0, preferably [ratio A - ratio B] > 2.0.

The amounts of the layers by distance along the article thickness can correspond to the following profile:

- layer A: from 10 to 90%,

- layer B: from 10 to 90%,

the total of all layers being 100% of the thickness.

For example the amount of layer A can be of from 15% to 85%, for example from 15% to 50%. For example the amount of layer B can be of from 15% to 85%, for example from 15% to 50%. In some particular embodiments, the amounts by distance along the article thickness are as follows:

- layer A: from 10% to 40%,

- layer C: from 10% to 80%, and

- layer B: form 10% to 40%,

the total of all layers being 100% of the thickness.

The materials of the layers can be a foamed polylactic acid material or a non-foamed polylactic acid material. In a particular embodiment all the materials are non-foamed polylactic acid materials. In a particular embodiment at least one layer is in a foamed polylactic acid material. For example layer C can be of a foamed polylactic acid material, while layers A and B are of a non-foamed polylactic acid material.

In one embodiment the article is a plastic sheet. It has typically a thickness e. It has typically two other dimensions such as a length I and a broadness b. Typically both other dimensions I and b are at least 10 times, preferably 100 times the thickness e. The plastic sheet can typically have a thickness 0.5 mm to 2.0 mm, preferably from 0.6 mm to 1 .0 mm. Examples of thicknesses are 0.5 mm, or 0.7 mm, or 0.8 mm, or 0.9 mm, or 1 .0 mm. The broadness can be typically of from 20 cm to 200 cm. The length can be of at least 200 cm. The plastic sheets can be presented as rolls.

In one embodiment the article comprises a thermoformed part. Such an article can be a container. The container can be a thermoformed article, preferably obtained from the plastic sheet. It can be for example a thermoformed cup, preferably in a multipack form or in an individual cup form. The container typically comprises at least a part corresponding to the multilayer structure. It can comprise a stretched part and a non-stretched part. The non-stretched part can typically correspond to the plastic sheet, with the plastic sheet thickness. The non-stretched part can be for example a flange at the periphery of a stretched part. For example the article can be a thermoformed cup, having a body corresponding to a stretched, typically thermoformed, part of a sheet, and flanges at the periphery of the body, corresponding to a non-stretched part of a sheet. Further details about containers are given below.

Preferably layer A is the internal layer of the thermoformed part. Preferably layer B is the external layer of the thermoformed part, optionally at least partially covered by a banderole. Despite a ratio B toward less amorphous behavior, it has been surprising found that layer B allows a better adhesion of banderoles.

Material A

Material A comprises polylactic acid having D-Lactide units and L-Lactide units, as a copolymer and/or blend, with a ratio A between D-Lactide units and L-Lactide units of from 4.0/96.0 to 20.0/80.0, preferably from 5.0/95.0 to 10.0/90.0. As the D-Lactide units or monomers and the L-Lactide units or monomers have the same molecular weight, the ratios by weight and the ratios by number are considered herein as identical.

For example ratio A can be of from 4.0/96.0 to 5.0/95.0, or from 5.0/95.0 to 6.0/94.0, or from 6.0/96.0 to 7.0/93.0, or from 7.0/93.0 to 8.0/92.0, or from 8.0/92.0 to 9.0/91 .0, or from 9.0/91 .0 to 10.0/90.0, or from 10.0/90.0 to 1 1 .0/89.0, or 1 1 .0/89.0 to 12.0/88.0, or from 12.0/88.0 to 13.0/87.0, or from 13.0/87.0 to 14.0/86.0, or from 14.0/86.0 to 15.0/85.0, or from 15.0/85.0 to 16.0/84.0, or from 16.0/84.0 to 17.0/83.0, or from 17.0/83.0 to 18.0/82.0, or from 18.0/82.0 to 19.0/81 .0, or from 19.0/81 .0 to 20.0/80.

It is mentioned that the polylactic acid is preferably different from a stereocomplex.

Polylactic Acid (PLA) polymers are known by the one skilled in the art. These are typically obtained by polymerization of lactic acid monomers, in an L-Lactide form and/or in a D-Lactide form. The lactic acid monomers are typically obtained by a microbiological process, involving micro-organisms such as bacteria. Polylactic Acid (PLA) polymers with various ratios between D-Lactide units and L-Lactide units are commercially available. Examples of PLA polymers that can be used, typically in blends, to obtain layer A include for example Ingeo® 2003D and Ingeo® 4060D, both marketed by NatureWorks.

In one embodiment the polylactic acid of Material A is a copolymer having D- Lactide units and L-Lactide units in the ratios mentioned above. Such copolymers are typically obtained by copolymerizing D-Lactide monomers and L-Lactide monomers in the ratios mentioned above. Preferably the copolymers do not comprise more than 10% by weight, preferably 7.5%, preferably 5%, preferably 2.5%, preferably 1 %, preferably 0.5%, preferably 0.1 %, of units different from L-Lactide and D-Lactide units.

In one embodiment the polylactic acid of Material A is a blend of at least a first polylactic acid polymer and at least a second polylactic acid polymer. The first polylactic acid polymer comprises L-Lactide and optionally D-Lactide units. The second polylactic acid comprises D-Lactide units and L-Lactide units. The blend is such that the ratios between D-Lactide units comprised in all the polylactic acid polymers of the blend and the L-Lactide units comprised in all the polylactic acid polymers of the blend are in the ranges mentioned above. Typically the at least first polylactic acid polymer and the at least second polylactic acid polymer are mixed in amounts appropriate to obtain the ratios mentioned above. The blend can be obtained by mixing and melting the polymers, typically upon extruding a sheet. The ratios by weight between the first and second polymers can be from example of from 1 /99 to 99/1 , preferably from 10/90 to 90/10, preferably from 20/80 to 90/10, preferably from 34/66 to 80/20.

In one embodiment one implements for Material A a blend of a first polylactic acid polymer having less than 4.2% units of D-Lactide and more than 95.8% units of L-Lactide, and a second polylactic acid polymer having from 4.3% to 80.0%, preferably 4.3% to 50.0%, preferably 4.3% to 20.0%, preferably 8.0% to 15.0%, units of D-Lactide and from 20.0% to 96.0%, preferably 50.0% to 96.0%, preferably 80.0% to 96.0%, preferably 85.0% to 92.0%, units of L-Lactide. In one embodiment the second polylactic acid polymer is present in an amount of less than 50% of the first polylactic acid polymer.

It is mentioned that material A can comprise a non polylactic acid masterbatch polymer, preferably polyethylene, or Ethylene-Vinyl Acetate. The material can comprise further additives.

Material B

Material B comprises polylactic acid having D-Lactide units and L-Lactide units, as a copolymer and/or blend, with a ratio B between D-Lactide units and L-Lactide units of from 0.1/99.1 to lower than 4.0/96.0, preferably from 1 .0/99.0 to 3.7./96.3. As the D- Lactide units or monomers and the L-Lactide units or monomers have the same molecular weight, the ratios by weight and the ratios by number are considered herein as identical.

For example ratio B can be of from 0.1/99.9 to 0.5/99.5, or from 0.5/99.5 to 1 .0/99.0, or from 1 .0/99.0 to 1 .5/98.5, or from 1 .5/98.5 to 2.0.0/98.0, or from 2.0/98.0 to 2.5/97.5, or from 2.5/97.5 to 3.0/97.0, or from 3.0/97.0 to 3.5.0/96.5, or 3.5/96.5.0 to 3.7/96.3.

It is mentioned that the polylactic acid is preferably different from a stereocomplex.

Polylactic Acid (PLA) polymers are known by the one skilled in the art. These are typically obtained by polymerization of lactic acid monomers, in an L-Lactide form and/or in a D-Lactide form. The lactic acid monomers are typically obtained by a microbiological process, involving micro-organisms such as bacteria. Polylactic Acid (PLA) polymers with various ratios between D-Lactide units and L-Lactide units are commercially available. Examples of PLA polymers that can be used, typically in blends, to obtain layer B include for example Ingeo® 2003D and Ingeo® 4032D, both marketed by NatureWorks. In one embodiment the polylactic acid of Material B is a copolymer having D- Lactide units and L-Lactide units in the ratios mentioned above. Such copolymers are typically obtained by copolymerizing D-Lactide monomers and L-Lactide monomers in the ratios mentioned above. Preferably the copolymers do not comprise more than 10% by weight, preferably 7.5%, preferably 5%, preferably 2.5%, preferably 1 %, preferably 0.5%, preferably 0.1 %, of units different from L-Lactide and D-Lactide units.

In one embodiment the polylactic acid of Material B is a blend of at least a first polylactic acid polymer and at least a second polylactic acid polymer. The first polylactic acid polymer comprises L-Lactide and optionally D-Lactide units. The second polylactic acid comprises D-Lactide units and L-Lactide units. The blend is such that the ratios between D-Lactide units comprised in all the polylactic acid polymers of the blend and the L-Lactide units comprised in all the polylactic acid polymers of the blend are in the ranges mentioned above. Typically the at least first polylactic acid polymer and the at least second polylactic acid polymer are mixed in amounts appropriate to obtain the ratios mentioned above. The blend can be obtained by mixing and melting the polymers, typically upon extruding a sheet. The ratios by weight between the first and second polymers can be from example of from 1 /99 to 99/1 , preferably from 10/90 to 90/10, preferably from 20/80 to 90/10, preferably from 34/66 to 80/20.

In one embodiment one implements for Material B a blend of a first polylactic acid polymer having from 3.7 to 4.1 % units of D-Lactide and more than 95.9% to 96.3% units of L-Lactide, and a second polylactic acid polymer having less than 3.7% units of D- Lactide and more than 96.3% units of L-Lactide.

It is mentioned that material B can comprise a non polylactic acid masterbatch polymer, preferably polyethylene, or Ethylene-Vinyl Acetate. The material can comprise further additives.

Further additives

The materials of the layers can comprise further additives, for example an impact and/or snapability modifier. Other additives that can be used include for example:

- mineral fillers,

- aspect modifiers, such as pigments or colorants,

- stabilizers,

- lubricants, - mixtures or associations thereof.

Pigments can be for example Ti0 ₂ pigments, for example described in document WO 201 1 1 19639.

Mineral fillers can be for example calcium carbonates of natural or synthetic origin, magnesium carbonate, zinc carbonate, mixed salts of magnesium and calcium such as dolomites, limestone, magnesia, barium sulfate, calcium sulfates, magnesium and aluminum hydroxides, silica, wollastonite, clays and other silica-alumina compounds such as kaolins, silico-magnesia compounds such as talc, mica, solid or hollow glass beads, metallic oxides such as zinc oxide, iron oxides, titanium oxide and, more particularly, those selected from natural or precipitated calcium carbonates such as chalk, calcite.

The further additives can be added in the form of masterbatches, wherein the additive is dispersed in a polymer matrix, for example PLA or a polymer of ethylenically unsaturated monomers, such as an ethylene vinyl acetate copolymer.

Further additives, if present, in the material can be typically present in an amount of 0.1 % to 15% by weight, for example in an amount of 1 % to 10% by weight.

Impact and/or snapabilitv modifiers

Impact and/or snapability modifiers compounds are known by the one skilled in the art, and available on the market as such. They typically modify the mechanical properties of thermoplastics by increasing the tensile stress of said thermoplastics. Various mechanisms can be involved, such as cavitation upon impact or diffused energy released upon impact. Compounds that have such properties are typically appropriate. Examples of impact modifiers include alkyl sulfonates, aromatic-aliphatic polyesters, poly(butylene adipate-co-terephthalate), for example those described in document EP 2065435, ethylene copolymers, for example described in document WO 201 1 1 19639, Acetyl TriButyl citrate, Triethyl citrate, Polybutylene Succinate, Polyvinyl Alcohol (PVA), ethylene vinyl acetate, hydrogenated soil oil.

In a preferred embodiment the impact and/or snapability modifier is a core/shell polymeric compound or an alkyl sulfonate compound.

In a preferred embodiment the material comprises from 0.01 % to 20% by weight of impact and/or snapability modifier, preferably from 0.1 % to 10%, preferably from 0.2 to 5%. In a preferred embodiment material A comprises from 0.01 % to 20% by weight of impact and/or snapability modifier, preferably from 0.1 % to 10%, preferably from 0.2 to 5%. In a preferred embodiment material B comprises from 0.01 % to 20% by weight of impact and/or snapability modifier, preferably from 0.1 % to 10%, preferably from 0.2 to 5%. Material C can either comprise or not comprise impact and/or snapability modifier. In an embodiment material C comprises from 0.01 % to 20% by weight of impact and/or snapability modifier, preferably from 0.1 % to 10%, preferably from 0.2 to 5%.

Impact and/or snapability modifiers can be added in the form of masterbatches, wherein the impact modifier is dispersed in a polymer matrix, for example PLA or a polymer of ethylenically unsaturated monomers, such as an ethylene vinyl acetate copolymer.

The core-shell polymeric compound, also referred to as core-shell copolymer, is typically in the form of fine particles having an elastomer core and at least one thermoplastic shell, the particle size being generally less than 1 micron and advantageously between 150 and 500 nm, and preferably from 200 nm to 450 nm. The core-shell copolymers may be monodisperse or polydisperse.

By way of example of the core, mention may be made of isoprene homopolymers or butadiene homopolymers, copolymers of isoprene with at most 3 mol % of a vinyl monomer and copolymers of butadiene with at most 35 mol % of a vinyl monomer, and preferably 30 mol % or less. The vinyl monomer may be styrene, an alkylstyrene, acrylonitrile or an alkyl(meth)acrylate. Another core family consists of the homopolymers of an alkyl (meth)acrylate and the copolymers of an alkyl(meth)acrylate with at most 35 mol % of a vinyl monomer, and preferably 30 mol % or less. The alkyl(meth)acrylate is advantageously butyl acrylate. Another alternative consists in an all acrylic copolymer of 2-octylacrylate with a lower alkyl acrylate such as n-butyl-, ethyl-, isobutyl- or 2-ethylhexyl- acrylate. The alkyl acrylate is advantageously butyl acrylate or 2-ethylhexyl- acrylate or mixtures thereof. According to a more preferred embodiment, the comonomer of 2- octylacrylate is chosen among butyl acrylate and 2-ethylhexyl acrylate. The vinyl monomer may be styrene, an alkylstyrene, acrylonitrile, butadiene or isoprene. The core of the copolymer may be completely or partly crosslinked. All that is required is to add at least difunctional monomers during the preparation of the core; these monomers may be chosen from poly(meth)acrylic esters of polyols, such as butylene di(meth)acrylate and trimethylolpropane trimethacrylate. Other difunctional monomers are, for example, divinylbenzene, trivinylbenzene, vinyl acrylate and vinyl methacrylate. The core can also be crosslinked by introducing into it, by grafting, or as a comonomer during the polymerization, unsaturated functional monomers such as anhydrides of unsaturated carboxylic acids, unsaturated carboxylic acids and unsaturated epoxides. Mention may be made, by way of example, of maleic anhydride, (meth)acrylic acid and glycidyl methacrylate.

The shells are typically styrene homopolymers, alkylstyrene homopolymers or methyl methacrylate homopolymers, or copolymers comprising at least 70 mol % of one of the above monomers and at least one comonomer chosen from the other above monomers, vinyl acetate and acrylonitrile. The shell may be functionalized by introducing into it, by grafting or as a comonomer during the polymerization, unsaturated functional monomers such as anhydrides of unsaturated carboxylic acids, unsaturated carboxylic acids and unsaturated epoxides. Mention may be made, for example, of maleic anhydride, (meth)acrylic acid and glycidyl methacrylate. By way of example, mention may be made of core-shell copolymers (A) having a polystyrene shell and core-shell copolymers (A) having a PMMA shell. The shell could also contain functional or hydrophilic groups to aid in dispersion and compatibility with different polymer phases. There are also core-shell copolymers (A) having two shells, one made of polystyrene and the other, on the outside, made of PMMA. Examples of copolymers (A) and their method of preparation are described in the following U.S. Pat. No. 4,180,494, U.S. Pat. No. 3,808,180, U.S. Pat. No. 4,096,202, U.S. Pat. No. 4,260,693, U.S. Pat. No. 3,287,443, U.S. Pat. No. 3,657,391 , U.S. Pat. No. 4,299,928 and U.S. Pat. No. 3,985,704.

The core / shell ratio can be for example in a range between 10/90 and 90/10, more preferably 40/60 and 90/10 advantageously 60/40 to 90/10 and most advantageously between 70/30 and 95/15.

Examples of appropriate core/shell impact and/or snapability modifiers include Biostrength ranges, for example Biostrength 150, marketed by Arkema. Impact and/or snapability modifier can be comprised is one or several layer of the article, for example in layer A and/or layer B.

Thermoforminq - thermoformed articles

The article of the invention can comprise a thermoformed part. The thermoformed part can comprise at least one zone wherein the local stretch ratio is of at least 4.2, preferably 4.3, preferably at least 4.5, preferably at least 5 (5.0), preferably at least 6 (6.0), preferably at least 7 (7.0). The thermoformed part can have a total stretch ratio of at least 2.5, preferably at least 3 (3.0), preferably at least 4 (4.0), preferably at least 5 (5.0).

The article can comprise a part that has not undergone any stretch, said part being considered herein as a non-thermoformed part. The article can be typically obtained by thermoforming a plastic sheet in the material.

The thermoforming is a process known by the one skilled in the art. It typically comprises stretching under heating a plastic material such as a sheet, typically by applying in a mold cavity mechanical means such as plugs and/or by aspiration. The mechanical means can optionally be enhanced by applying a gas under pressure. The stretching results in local stretch ratios in zones forming the thermoformed part. If the stretching is uniform the local stretch ratios are equal everywhere. As the stretching is typically non uniform, the thermoformed part typically presents various zones having different local stretch ratios.

The thermoformed part of the article can have a thickness varying in a range of from 60 μηι to 750 μηι, preferably from 70 μηι to 500 μηι.

The material and process finds particular interest in articles presenting at least one or several of the following features:

- the article is a container having a hollow body and optionally at least one flange, the hollow body defining said thermoformed part, the hollow body being provided with an opening);

- in this embodiment the hollow body is at least partially covered by a banderole;

- the hollow body comprises:

- a bottom at the opposite from the opening,

- a side wall presenting at least a portion that is not covered by a banderole;

- the opening is a generally circular opening and the bottom has a generally circular outer edge;

- the side wall has a generally cylindrical upper portion having a height h2 and a lower portion having a height hi , tapering from the upper portion toward the bottom in a curved manner, the upper portion and the lower portion intersecting and interconnecting at a peripheral intersection line;

- the bottom is a planar bottom, and wherein the peripheral intersection line is spaced at a substantially constant distance from the planar bottom, the lower portion having a height hi corresponding to a minoritary fraction of the height H of the container;

- the height h2 of said upper portion is constant, the ratio h2/H being comprised between 3:5 and 6:7, and preferably between 2:3 and 4:5;

- the ratio h2/H is inferior or equal to 3:4;

- the side wall has a thickness profile such that the average thickness of the lower portion is superior to the average thickness of the upper portion; and/or

- the opening has an inner diameter which is inferior to the height H of the container and superior to the height hi of the lower portion.

It is mentioned that articles having a lower portion that is not covered by a banderole and are particularly challenging articles as to manufacture, homogeneity and/or mechanical properties, where the use of the mineral filler find a particular interest.

The article can be thermoformed from a sheet having for example a thickness of higher than 300 μηι, preferably at least 500 μηι, preferably at least 750 μηι, preferably from 750 to 1500 μηι. The flange, if present in the article, typically has such a thickness. Containers

The article can be a container, for example a container used as a dairy product container, like a yogurt cup. The invention also concerns the container filled with a food or non-food product, preferably a dairy product, preferably a milk-based (milk being an animal milk or a vegetal milk substitute such as soy milk or rice milk etc ..) product, preferably a fermented dairy product, for example a yogurt. The container can have a yogurt cup shape, for example with a square cross section or a square with rounded corners cross section, or round cross section. The container can have a tapered bottom, preferably a tapered rounded bottom. The container has walls (perpendicular to the cross section), typically a tubular side wall, that can be provided with elements such as stickers or banderoles. Elements such as banderoles can contribute to re-enforcing the mechanical resistance of the container.

The container filled with a food or non-food product may comprise a closure element to seal the opening. A flange defines a support surface for attachment of the closure element to the containing part of the container. The closure element remains above and at a distance from the side wall. A membrane seal or thin foil, optionally suitable for food contact, may form the closure element. When the container is provided with a flange, the closure element may have the same general cut as the flange.

The container can be for example a container of 50 ml (or 50 g), to 1 L (or 1 kg), for example a container of 50 ml (or 50 g) to 80 ml (or 80 g), or 80 ml (or 80 g) to 100 ml (or 10Og), or 100 ml (or 100 g) to 125 ml (or 125 g), or 125 ml (or 125 g) to 150 ml (or 150 g), or 150 ml (or 150 g) to 200 ml (or 200 g), or 200 ml (or 200 g) to 250 ml (or 250 g), or 250 ml (or 250 g) to 300 ml (or 300 g), or 300 ml (or 300 g) to 500 ml (or 500 g), or 500 ml (or 500 g) to 750 ml (or 750 g), or 750 ml (or 750 g) to 1 L (or 1 kg).

Process

The article can be prepared by any appropriate process. Material A and/or material B can be prepared before forming the article or during the formation of the article. Thermoplastic materials, such as PLA, can be introduced in the form of powder, pellets or granules.

Materials A and B can be mixture of several ingredients: a blend of PLAs and optionally further additives such as an impact and/or snapability modifier. These ingredients can be mixed upon forming the article, typically in an extruder. One can implement masterbatches of impact and/or snapability modifiers and optionally of further additives to be mixed with the thermoplastic material. In another embodiment one can use pre-mixed compounds typically in the form of powder, pellets or granules.

In a preferred embodiment layer A and layer B, and optional further layers, are co- extruded, typically from flows of material A and material B, and optional further layer material, in a molten form. Co-extrusion processes are known from the one skilled in the art. These typically involve extruding separates flows through separates side by side dies. Beyond the dies the flows merge and form at least one interface. There is one interface for two-layer articles and two interfaces for three-layer articles. The materials are then cooled to form a solid article. One can implement appropriate treatments after the co- extrusion in order to obtain the desired product, for example a sheet or a film. Treatment steps are for example press treatments, calendering, stretching etc... Parameters of these treatment steps such as temperatures, pressure, speed, number of treatments can be adapted to obtain the desired product, for example a sheet. In one embodiment the article is a sheet prepared by a process involving co-extruding and calendering. The article can be obtained by thermoforming a plastic sheet. A typical process of making the article comprises the steps of:

a) providing a plastic sheet in the multilayer material,

b) thermoforming at least a part of the plastic sheet, preferably such that the thermoformed part comprises at least one zone wherein the local stretch ratio is of at least 4.2, preferably at least 4.5, preferably at least 5 (5.0), preferably at least 6 (6.0), preferably at least 7 (7.0) and/or such that the total stretch ratio of at least 2.5, preferably at least 3 (3.0), preferably at least 4 (4.0), preferably at least 5 (5.0).

In preferred embodiments the sheet has a thickness of higher than 300 μηι, preferably at least 500 μηι, preferably at least 750 μηι, preferably from 750 μηι to 1500 μηι.

The material can be prepared before forming the sheet or during the formation of the sheet. Thermoplastic materials, such as PLA, can be introduced in the form of powder, pellets or granules.

Typically the process comprises a step of providing the polylactic acid, for example by mixing a first polylactic acid polymer and a second polylactic acid polymer and optionally further additives. These can be mixed upon forming the sheet, typically in an extruder.

Thermoforming is a known operation. One can thermoform the sheet so as to obtain the final product of the desired shape. It is mentioned that some stretching occurs upon thermoforming. Local stretching ratios of at least 4.2, preferably at least 4.5, preferably at least 5 (5.0), preferably at least 6 (6.0), preferably at least 7 (7.0) are considered as quite high ratios, corresponding to deep thermoforming. Total stretching ratios of at least 2.5, preferably at least 3 (3.0), preferably at least 4 (4.0) preferably at least 5 (5.0) are considered as quite high ratios, corresponding to deep thermoforming. The higher the ratio is, the deeper the thermoforming is, the more difficult the control is. The total stretching ratio can be for example of from 2.5 to 8.0, preferably between 3.0 to 7.0, preferably between 4.0 to 6.5. The article can present some local stretching ratios of from 2.5 to 10.0, for example of from 2.5 to 4 and/or from 4 to 6 and/or from 6 to 8 and/or from 8 to 10. Thermoforming may be for example performed thanks to a Form Fill Seal thermoforming line. The thermoforming can present the following steps:

- sheet introduction on guide chains (i.e. spike or jaws);

- sheet heating, by heating contact plates;

- forming thanks to a negative mold, assisted by forming plugs and air pressure. The mold may comprise or not a label for example a banderole. The banderol can be a partial banderole positioned only in the top of the mold, to obtain an article that is covered by the banderole on the upper portion of the body or similar upper area of the thermoformed part, and not covered by the banderole in a lower portion. In a Form Fill Seal thermoforming line, one typically performs the following steps after the thermoforming:

- the resulting forms are filled with a product, and then, thermosealed with a lid film,

- finally, they are cut and optionally precut by one or several mechanical trimming tool(s).

Further details or advantages might appear in view of the following non limiting examples.

Examples

The examples are implemented with using the following materials:

- PLA1 : Ingeo® 2003D marketed by NatureWorks

- PLA2: Ingeo® 4060D marketed by NatureWorks

- PLA3: Ingeo® 4032D marketed by NatureWorks

- Modifier (M): Masterbatch of an impact and/or snapability modifier in PLA.

Example 1 - Plastic sheets

A multilayer (layer A)-(layer C)-(layer B) PLA plastic sheet is prepared by co-extrusion according to the procedure below. All the layers are compact layers.

The materials (PLA1 , PLA2, PLA3, M) of the different layers are separately extruded with extruders. The temperature along the screws is between 170°C and 200°C. Behind the extruders, the different material flows are fed into feedblock channels through different passages separated by two thin planes (die). At the end of the separation planes, the three flows merge and form two interfaces, and the sheet is extruded through a die with a temperature of about 160°C. The sheet is then calendered on 3 rolls having a temperature of about 35 °C to control the thickness.

The thickness of the sheet is 0.75 mm.

Table 1 below presents the arrangement and the compositions of the various layers.

Table 1

Example 2 - Yogurt cups

The plastic sheet of example 1 is thermoformed into yogurt cups according to the procedure below.

Procedure:

The sheet is introduced into a F.F.S. thermoforming line and is then thermoformed in 4 oz cups with the following parameters:

- Heating plates temperatures: 100°C;

- The sheet is gradually heated thanks to six heating steps, each of the heating boxes having a closing time of 1 .2 s.

- The thermoforming step is performed with conventional felt forming plug, applied on layer A, such that layer A is the container internal layer and layer B is the container external layer. Mold temperature is fixed at 55°C to activate the label hot melt and to cool down the PLA material;

Forming air pressure: 4.0 bars;

Blowing time: 250 ms

Machine speed: 30 strokes per minute.

Distance between bottom of mold and plug at lowest point: 2 mm

Shape: As shown on Figure 1 and Figure 2, wherein distances as indicated as mm and the cross section is a square with rounded corners.

Banderole: a full banderole, as shown on figure 1 , made of paper or a paper/plastic based complex applied in the mold.

Evaluations

The cups present both a good homogeneity resulting from and/or allowing a good processability, while being well formed, showing no substantial retraction after mold removal, with good or regular adhesion of the banderoles.