Method for manufacturing biodegradable packaging material, biodegradable packaging material and a package or a container made thereof

Abstract

A biodegradable packaging material, a method of manufacturing the same, as well as products made of the material wherein the manufacture comprises extrusion onto a fibrous substrate one or more polymer coating layers including at least one layer of a polymer blend consisting of (i) 20-95 wt-% of polylactide having a high melt index of more than 35 g/10 min (210° C.; 2.16 kg), (ii) 5-80 wt-% of polybutylene succinate (PBS) or a biodegradable derivate thereof, and (iii) 0-5 wt-% of one or more polymeric additives. The components of the blend are melted and blended in connection with the extrusion step. The goal is to improve extrudability, increase machine speed in extrusion and maintaining good adhesiveness to the substrate and good heat-sealability of the coating. The products include disposable drinking cups and board trays, as well as sealed carton packages for solids and liquids.

Claims

1. A biodegradable packaging material, comprising: a multilayer coating extruded on a fibrous substrate, said extruded multilayer coating having a non-aromatic innermost layer, an outermost layer, and a middle intermediate layer between said non-aromatic innermost and outermost layers, said non-aromatic innermost layer consisting of (i) 30-60 wt-% of polylactide having a high melt index of 50-100 g/10 min (210° C.; 2.16 kg), (ii) 40-70 wt-% of polybutylene succinate or a derivate thereof, and (iii) greater than 0 wt-% up to 5 wt-% of said ethylene butyl acrylate glycidyl methacrylate terpolymer, and said middle intermediate layer consisting of polylactide having a low melt index of 5-35 g/10 min (210° C.; 2.16 kg).

2. The biodegradable packaging material of claim 1 in the form of a drinking cup having an inner liquid-contact side, said non-aromatic innermost layer located on the inner liquid-contact side of the cup.

3. The biodegradable packaging material of claim 1 in the form of a sealed liquid package having an inner liquid-contact side, said non-aromatic innermost layer located on the inner liquid-contact side of the sealed liquid package.

4. The biodegradable packaging material of claim 1 in the form of a sealed carton package having an outside, said non-aromatic innermost layer located on the outside of the sealed carton package.

5. The biodegradable packaging material of claim 1 in the form of a tray package for ready-made food having at least one food contact side, said non-aromatic innermost layer located on said at least one food contact side of the tray package.

6. The biodegradable packaging material of claim 1, wherein said outermost layer being non-aromatic, said non-aromatic outermost layer consisting of (i) 30-60 wt-% of polylactide having a high melt index of 50-100 g/10 min (210° C.; 2.16 kg), (ii) 40-70 wt-% of polybutylene succinate or a derivate thereof, and (iii) greater than 0 wt-% up to 5 wt-% of said ethylene butyl acrylate glycidyl methacrylate terpolymer.

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) The invention can be completely understood in consideration of the following detailed description of various aspects and embodiments of the present invention in connection with the accompanying drawings, in which:

(2) FIG. 1 is a schematic presentation of coating machine speeds (runnability) obtained in various comparative materials and embodiments according to the present invention.

(3) FIG. 2 is a schematic presentation of adhesion properties obtained in various comparative materials and embodiments according to the present invention.

(4) FIG. 3 is a schematic presentation of heat-sealing properties obtained in various comparative materials and embodiments according to the present invention.

(5) FIG. 4 is a schematic summary of properties of three-layered structures according to the present invention.

(6) FIG. 5 compares schematically the properties of comparative monolayered structures and three layered structures according to the present invention.

(7) FIGS. 6a-6e show as examples structural embodiments of the packaging material according to the present invention.

DETAILED DESCRIPTION OF THE PRESENT INVENTION

(8) The present invention is based on a surprising finding that extrudability of a PLA-based polymer blend at an extrusion coating machine producing the packaging material can be improved while running speed of the machine, as well as, heat sealability of the polymer-coated material may be preserved by using PLA having a high melt index of more than 35 g/10 min (210° C.; 2.16 kg) as a polymer blend with polybutylene succinate (PBS) or its biodegradable derivate, e.g. poly(butylene succinate adipate) (PBSA).

(9) As an overall rule, the melt index and the molecular weight (MW) of PLA are in reverse ratio to each other, i.e. as the melt index increases the MW decreases. In general, the high melt index PLA as used in the present invention has a MW of less than 160 000, preferably about 100 000. The low melt index PLA as used in multilayer embodiments of the present invention has a MW of at least 160 000, and preferably about 200 000.

(10) A multilayer coating may be produced by extruding onto a fibrous substrate inner, middle and outer coating layers. The inner and outer layers contain a blend comprising polylactide having a melt index >35 g/10 min (210° C.; 2.16 kg) and PBS or its derivate. Optionally the blend may comprise even other components, for instance acrylic copolymers, which shall not destroy the overall biodegradability of the coating layer, however.

(11) The fibrous substrate in the packaging material may be paper or board, paper-board as well as cardboard.

(12) Amount of said polylactide having a melt index >35 g/10 min in said blend is 20-95 wt-%, preferably 30-60 wt-%.

(13) Melt index of said polylactide is >35 g/10 min, preferably >40 g/10 min, and more preferably 50-100 g/10 min, still more preferably 60-90 g/10 min, and most preferably even 70-85 g/10 min (210° C.; 2.16 kg). The inventors have demonstrated that PLA having high melt index allows blending of a higher share of another biodegradable polymer such as polyester to the coating and allows using higher machine speeds in the extrusion process.

(14) Up to now, the PLA used for coating fibrous substrates has in most cases had a molecular weight of about 200 000 g/mol and a melt index at most about 25 g/10 min (210° C.; 2.16 kg). Within the meaning of the present invention, the phrase “high melt index PLA” refers to PLA with a melting index, which is more than 35 g/10 min (210° C.; 2.16 kg), and a molecular weight reduced, preferably by at least about 40%, compared to traditionally used low melt index PLA.

(15) Further, PLA can be produced by using renewable starting material. It is also biodegradable e.g. in composting and can be burned.

(16) Within the meaning of the present invention, the term “biodegradable” means polymers that will decompose in natural aerobic (composting) and anaerobic (landfill) environments. Biodegradation of polymers occurs when microorganisms metabolize the polymer to either assimilable compounds or to humus-like materials that are less harmful to the environment. They may be derived from renewable raw materials, or petroleum-based plastics which contain additives. Aromatic polyesters are almost totally resistant to microbial attack, most aliphatic polyesters are biodegradable due to their potentially hydrolysable ester bonds. Polybutylene succinate (PBS) is an examples of such biodegradable polyesters.

(17) Especially PLA used in the present invention may be of natural origin, i.e. manufactured from renewable natural resources such as corn, potato, tapioca, cellulose, soy protein, lactic acid etc., or can be naturally produced (e.g. by microbial fermentation), and is biodegradable or compostable. Also, PBS and its derivates, such as PBSA, are biodegradable or compostable, but may even be of fossil (petroleum) origin.

(18) Amount of PBS or its derivate in the blend is 5-80 wt-%, preferably 40-70 wt-% and most preferably 45-65 wt-%. Preferably the polymer is PBS, which improves the adhesion properties of the coating layer as well as heat-sealablility.

(19) Within the meaning of the present invention, term “adhesion” means adhesion to any surface including fibrous material and polymer coated surface but particularly it means adhesion to raw fibrous material (paper or board) constituting the fibrous substrate. The aim is to achieve complete adhesion, which means that an attempt to detach the coating results in breaking within the fibrous substrate layer, instead of the coating peeling off as a whole.

(20) Within the meaning of the present invention, the term “heat-sealability” means that the polymer coating in softened or melted condition may be attached to an opposite surface of material, which may be the same or another polymer, raw fibrous material etc. A firm seal between the surfaces is formed as the heated polymer cools down and solidifies. When a polymer blend is used in accordance with the invention an acceptable heat-sealing can be achieved within a broader temperature range than in case PLA alone is used.

(21) A major advantage of the method according to the present invention is improved runnability of the coating machinery, i.e. sufficient extrusion and adhesion properties allow using a high machine speed in spite of use of the high melt index PLA.

(22) In the method, the machine speed in extrusion is at least 100 m/min. Preferably the machine speed is at least 150 m/min, more preferably at least 200 m/min, still more preferably at least 250 m/min and most preferably at least 300 m/min. The high machine speed improves the economy of the manufacturing process.

(23) As a preferable third component, the blend may comprise a minor amount, at most about 5% by weight, an acrylate copolymer, such as ethylene butyl acrylate glycidyl methacrylate terpolymer (EBAGMA). The packaging material of the present invention may thus comprise a coating layer consisting of a blend of (i) 30 to 60 weight-% of high melt index PLA, (ii) 40 to 70 weight-%, of PBS or its derivate, and (iii) 0 to 5 weight-% of an acrylate copolymer.

(24) The acrylate polymer is added to further improve the adhesion of the extruded polymer coating layer to the fibrous substrate. Acrylate polymers, including EBAGMA, are as such non-biodegradable, but when used in small amounts of 5 weight-% at most do not prevent disintegration of the coating layer as a whole.

(25) According to the present invention, the preferred biodegradable polymer blended with PLA is polybutylene succinate (PBS). The specific advantage of PBS is superior blendability with high melt index PLA in the extruder, into which PBS and PLA granules may be fed separately.

(26) PBS, or its derivate, blended with PLA improves adhesion of a coating layer consisting of the blend in extrusion onto a fibrous board substrate. At the same time, raw edge penetration of liquid in drinking cups made of the coated packaging material according to the present invention is significantly reduced in comparison with PLA alone, which in case of hot coffee is seen as markedly less, if any, brown colouring along the vertical heat-seal lines in the cup jacket. The improved adhesion is also supposed to increase the ability of the coating to withstand the vapour pressure generated within the fibrous substrate by the hot drink, thus preventing the coating from loosening from the substrate layer and opening pathways to liquid penetration.

(27) In addition to good adhesion and heat-sealing properties and extrudability as PLA blends, PBS and derivates such as PBSA are biodegradable and the blend can be manufactured predominantly from raw materials obtained from renewable natural sources.

(28) A biodegradable polymer blend as discussed above may advantageously be extruded as the uppermost surface layer of the coated packaging material. In this case, PBS or its derivate serves to improve the heat-sealability of the polymer coated packaging material. Addition of a minor amount of acrylate copolymer, such as EBAGMA, further improves heat-sealability of the coating layer.

(29) A biodegradable polymer blend as discussed above may advantageously be extruded into a direct contact with the fibrous substrate of the packaging material. Due to good adhesion properties there is no need to use separate adhesion layers between the fibrous substrate and the coating of the present invention. This simplifies the manufacturing process and reduces raw material costs. PBS or its derivate serves to improve adhesion of the coating layer to the underlying fibrous substrate. In the multilayer coating, said coating layer is the lowermost layer.

(30) In the coextruded multilayer coating, each layer should substantially consist of biodegradable polymers, which preferably are based on renewable raw materials. The material may have a polymer coating on one side or on both sides thereof. The coatings on the opposite sides of the fibrous substrate may be similar or differ from each other, for instance a multilayer coating on one side and a monolayer coating on the opposite side.

(31) According to the present invention, the components of the blend are melted and blended in connection with the extrusion step, more specifically the components of the polymer blend are mixed as granules and melted at a single step, immediately followed by extrusion of the melt onto a paper or board substrate. This works especially well with PLA and PBS or its derivate. Mixing of the components first in the extruder allows easy adjustment of the respective shares of the components being mixed, an advantage over use of premade compounded blends. Availability of granulate PLA and polyesters is good and typically also the price is lower compared to pre-mixed blends.

(32) The total amount of polymer coating on one side of the fibrous substrate may be in the range of 10-60 g/m.sup.2, typically about 25 g/m.sup.2. In a multilayer coating the amount of polymer per layer may be 4-20 g/m.sup.2, preferably 6-15 g/m.sup.2. A representative example could be a triple layer coating with a middle layer of solely low melt index PLA and coating layer weights of 7, 11 and 7 g/m.sup.2, respectively.

(33) A useful embodiment of the present invention is a packaging material comprising a fibrous substrate and one or more extruded polymer coating layers including at least one layer of a polymer blend consisting of (i) 20-95 wt-% of polylactide having a high melt index of more than 35 g/10 min (210° C.; 2.16 kg), (ii) 5-80 wt-% of polybutylene succinate (PBS) or a biodegradable derivate thereof, and (iii) 0-5 wt-% of one or more polymeric additives.

(34) A preferred embodiment of the present invention is a fibrous paper or board-based packaging material comprising coextruded inner, middle and outer coating layers, the inner and outer layer comprising a blend of 20-95 wt-% of PLA having a melt index of above 35 g/10 min (210° C.; 2.16 kg), 5-80 wt-% of PBS or its biodegradable derivate and, optionally, 0-5 wt-% of an acrylic copolymer such as EBAGMA, and the middle layer comprising polylactide having a melt index of 5-35 g/10 min (210° C.; 2.16 kg). The inner layer would provide superior adhesion in extrusion to the fibrous substrate and the outer layer would provide superior heat-sealability to an uncoated fibrous surface or to a polymer layer, similar or dissimilar to said outer heat-seal layer itself. Middle layer containing PLA with low melting index supports the polymer layers during extrusion process. PLA is also renewable and useful material having e.g. good moisture barrier properties as well as low cost. Multilayered structure allows optimizing the raw material without compromising the extrudability or properties of the resulting coating.

(35) In a more preferred embodiment, said packaging material comprises a fibrous substrate and an extruded multilayer coating including innermost and outermost layers of a blend of 30-60 wt-% of polylactide having a melt index of 50-100 g/10 min (210° C.; 2.16 kg), 40-70 wt-% of PBS or derivate, and 0-5 wt-% of an acrylic copolymer, and a middle layer of polylactide having a melt index of 5-35 g/10 min (210° C.; 2.16 kg). The same blend is advantageously used for the innermost and outermost layers.

(36) The present invention further provides improved containers made of the packaging material as described above. Disposable drinking cups for hot drinks, especially hot coffee, are a prime example of such containers.

(37) According to the present invention, a drinking cup made of a packaging material manufactured by the method of the present invention, or of a packaging material of the present invention, has the polymer coating lying on the inner liquid-contact side of the cup.

(38) According to the present invention, a sealed liquid package of a packaging material manufactured by the method of the present invention, or of a packaging material of the present invention, has the polymer coating lying on the inner liquid-contact side of the package. However, a similar package may even be used as a carton package for dry products.

(39) According to the present invention, a sealed carton package of a packaging material manufactured by the method of the present invention, or of a packaging material of the present invention, may have the polymer coating lying on the outside of the package.

(40) According to the present invention, a tray package for ready-made food, the tray being made of a packaging material manufactured by the method of the present invention, or of a packaging material of the present invention, has the polymer coating lying on the food-contacting upper side of the tray.

(41) The product packages according to the present invention are preferably completely made of the packaging material as described above. In each case even the reverse side of the packaging material may be polymer-coated, e.g. for improving heat-sealability or for gas or aroma barrier purposes.

EXAMPLES

(42) FIGS. 6a-6e show as examples five structural embodiments of packaging materials according to the present invention. “PLA1” means low melt index PLA; “PLA2” means high melt index PLA; “PBS” means polybutylene succinate and “board” indicates the fibrous substrate layer, which is paper, paperboard or cardboard. Instead of PBS, even biodegradable derivates of PBS may be used.

(43) There are extruded or coextruded monolayer or multilayer coatings of a blend of PLA2 and PBS and mere PLA1 on one side or on both sides of a fibrous paper or board substrate (“board”). The share of PLA2 in the blend is 20 to 95 weight-%, preferably 30 to 60 weight-%, and the share of PBS may vary from 5 to 80 weight-%, preferably being 40 to 70 weight-%. As an optional third component at most 5 weight-% of an acrylate copolymer such as ethylene butyl acrylate glycidyl methacrylate terpolymer (EBAGMA) may be included in the blend. The substrate may be paper, paperboard or cardboard of a weight of 40 to 350 g/m.sup.2, preferably a cupboard or a liquid package board of 170 to 350 g/m.sup.2.

(44) It is understood by a skilled reader that if the packaging material has extruded polymer coatings on both sides, the coatings on the opposite sides need not be identical. There may be a mono-layer coating on one side and a multilayer coating on the other side of the fibrous substrate. It is also possible to include in multilayer coatings layers of other biodegradable polymers suitable for extrusion coating, preferably in blends with high melt index polylactide.

(45) Usefully PBS is available as a commercial product under trade name GsPLA FZ91PD by Mitsubishi, and EBAGMA is commercially available under trade name Biomax Strong 120 by DuPont.

(46) More particularly, FIG. 6a shows the substrate 1 with a single extruded coating layer 2 of the blend of PLA2 and PBS. The weight of this monolayer 2 may be from 10 to 30 g/m.sup.2. In FIG. 6b there is such a PLA2+PBS blend layer 2 on both sides of the substrate 1.

(47) FIG. 6c shows a coextruded multilayer coating with an innermost PLA2+PBS blend layer 2, a middle layer 3 of PLA1, and an outermost PLA2+PBS blend layer 4. The weight of each of the three layers 2, 3, 4 may be from 4 to 13 g/m.sup.2. The total weight of the multilayer coating is thus 12-39 g/m.sup.2. Including a middle layer 3 of PLA1 serves to add to the total thickness of the coating while improving its extrudability. FIG. 6d shows similar multilayer coatings 2, 3, 4 on both sides of the substrate 1.

(48) FIG. 6e shows a packaging material comprising a board substrate 1 and coextruded innermost, middle and outermost coating layers 2, 3, 5. Only the innermost layer 2 consists of a PLA2+PBS blend as described above. The middle layer 3 consists of mere PLA1. The outermost heat-sealing layer 5 comprises a blend of about 45 weight-% of PLA2 and 55 weight-% of polybutylene adipate terephtalate (PBAT). The weights of the three coating layers 2, 3, 5 may correspond to the respective layers 2, 3, 4 in the embodiment of FIG. 6c.

(49) If the packaging material has extruded polymer coatings on both sides, the coatings on the opposite sides need not be identical. There may be a monolayer coating on one side and a multilayer coating on the other side of the fibrous substrate. It is also possible to include in multilayer coatings layers of other biodegradable polymers suitable for extrusion coating, preferably in blends with PLA2. FIG. 6e is an example of such embodiments. In addition to PBAT, other examples of useful polymers are PHA (polyhydroxy alkanoate), PHB (polyhydroxy butyrate), PHBV (polyhydroxybutyrate hydroxyvalerate), PGA (polyglycolic acid), PEG (polyethylene glycol), PCL (polycaprolactane), and starch based biopolymers. The innermost layer of the multilayer structure shall be of the blend containing PLA and PBS or its derivate, however.

Tests

(50) In the following, the present invention is illustrated by means of laboratory tests. Extrusion grade polylactides having “low” or “high” melt indexes (see Table 1 below) and polybutylene succinate (PBS) were used as coating polymers as such or blended as shown in Table 2. The blends as well as pure PLA (used also as a reference) were then extruded as monolayers or as three layered structures onto one side of a board substrate having a weight of 280 g/m.sup.2. True coating weights in both monolayer and three layer structures were measured. Due to the coating techniques they varied slightly, between 24.9 and 27.6 g/m.sup.2 (about 25 g/m.sup.2).

(51) TABLE-US-00001 TABLE 1 Characteristics of the polymers used in experimental part. Polymer melting index temperature PLA1 25 g/10 min; 210° C. “low” PLA2 75 g/10 min; 210° C. “high” PBS 4.5 g/10 min 190° C.

(52) For each coated test material the runnability of the coating machine and adhesion and heat-sealing properties of the resulting coating were measured.

(53) Adhesion to the board substrate was determined on a scale from 0 to 5, the highest figure representing the best adhesion. The polymeric coatings were thus introduced onto the substrate by extrusion, and their adhesion to the board surface was defined on said scale, whereby the classification was as follows:

(54) 1=no adhesion, the polymeric layer peels off;

(55) 2=poor adhesion, some fibres are stuck to the polymeric layer that peels off;

(56) 3=poor adhesion, when detaching the polymeric layer, less than 50% of the paper board breaks in the area of coating;

(57) 4=moderate adhesion, when detaching the polymeric layer, over 50% of the paper board breaks in the area of coating;

(58) 5=perfect adhesion, when detaching the polymeric layer, the paper board breaks throughout the area of coating.

(59) Heat-sealability is given as the lowest sealing temperature providing successful sealing between the heat-seal layer and a countersurface, in the tests the heat-seal layer itself. The criterium is that an attempt to tear open the seal results in a break in the fibrous board substrate instead of opening of the seal.

(60) Runnability is given as the lowest operable machine speed in extrusion or coextrusion.

(61) TABLE-US-00002 TABLE 2 The adhesion, heat-sealablity and runnability (coating machine speed) results of monolayer and three layer coatings applied on board substrate. PLA1 is conventionally used PLA having melt index (about 25 g/10 min) and PLA2 has high melt index (about 75 g/10 min). Column at right, when appropriate, refers to the general structure as shown in FIG. 6. Heat- sealability Runnability Adhesion (° C.) (m/min) FIG. Board/10% PBS + PLA1 4 440 290 Board/15% PBS + PLA1 — — — Board/20% PBS + PLA1 — — — Board/20% PBS + PLA2.sup.(1)   4.5 380 100 6a Board/40% PBS + PLA2.sup.(1)   4.5 400 240 6a Board/60% PBS + PLA2.sup.(1) 4 410 100 6a Board/20% PBS + PLA1/PLA1/20% PBS + PLA1 5 460 250 Board/40% PBS + PLA1/PLA1/40% PBS + PLA1 — — — Board/60% PBS + PLA1/PLA1/60% PBS + PLA1 — — — Board/80% PBS + PLA1/PLA1/80% PBS + PLA1 — — — Board/20% PBS + PLA2/PLA1/20% PBS + PLA2.sup.(1) 5 410 270 6c Board/40% PBS + PLA2/PLA1/40% PBS + PLA2.sup.(1) 5 410 320 6c Board/60% PBS + PLA2/PLA1/60% PBS + PLA2.sup.(1) 5 380 300htd 6c Board/80% PBS + PLA2/PLA1/80% PBS + PLA2.sup.(1) 4 360 300 6c Board/PLA2/PLA1/PLA2 4 390 220 Board/PBS/PLA1/PBS 4 350 200 Board/PBS 4 350 180 Board/PLA2 3 390 poor .sup.(1)signifies examples according to the invention, the other examples are comparative.

(62) Lack of result implies failure in testing and thus unworkability.

(63) The runnability results (coating machine speed) are shown in FIG. 1. It was proved that the machinery was unable to handle high (>40%) PBS concentrations by using conventional PLA (PLA1) whereas replacing conventional PLA (PLA1) with high melt index PLA (PLA2) and/or 3-layer structure (PLA1 layer in the middle and PLA2+PBS in inner and outer layer) resulted in superior runnability. Also monolayered structure using PLA2, especially when blended with 40% of PBS, had good runnability. Coating could not be successfully done solely with PLA2.

(64) The adhesion results are shown in FIG. 2. In each case use of high melt index PLA in combination with PBS improved the adhesion value. No improvement was detected after 20% PBS concentrations.

(65) Heat-sealability results are shown in FIG. 3 and show that using high melt index PLA the heat-sealability is significantly improved, c.f. the lower heat-sealing temperatures. In addition it was found that a blend comprising high melt index PLA and PBS can be heat-sealed in a broad temperature range thereby providing flexibility to process (data not shown).

(66) The three layered coating structures (FIG. 6c), where PLA1 is used in the middle layer and PLA2 is blended with PBS in the innermost and outermost layers, were found to be especially beneficial by enabling the highest coating machine speed (runnability) and excellent heat-sealing and adhesion properties. It is believed that PLA1 in the middle layer gives rigidity to film.

(67) Although specific examples have been illustrated and described herein, it will be appreciated by those of ordinary skill in the art that any arrangement calculated to achieve the same purpose could be substituted for the specific examples shown. This application is intended to cover adaptations or variations of the present subject matter. Therefore, it is intended that the present invention be defined by the attached claims and their legal equivalents, as well as the following illustrative embodiments.