Patent Application
20050136155
The present invention relates to a porous infusion beverage package, which holds an infusion beverage precursor material.
Infusion beverage packages are known in the art and typically contain a beverage precursor material, such as tea or coffee. To produce a beverage, the package containing the beverage precursor is typically infused into hot water, by placing the package into hot water, pouring hot water onto or through the package, or heating water to desired temperature while the package is immersed in the water. Alternatively, the beverage infusion package may be placed in cold water to form the beverage.
These packages are generally in the form of a pouch, a bag or a sachet and are generally prepared from a very thin and light weight paper product. Typically, these packages are translucent when wet, and the contents of the package can only be seen after the package has been infused or while the package is infused in water.
Recently, tea bags have been produced form biodegradable thermoplastic polymers such as polylactic acids. See, for example, Japan published patent applications 2001-063757 A2 and 2002-101506 A2. In addition, polylactic acid binder fibers have been added to the paper making process to produce beverage infusion package, as is taught in WO 02/02871 A1.
Over the last couple of years, the infusion beverage industry has gone to more specialty products, such as long leaf tea leaves. However, with the current infusion beverage packages, the customer is unable to see the specialty beverage precursor due to the translucent nature of the current packages available and is unable to appreciate the nature and quality of the product. The customer is often unsure whether or not they are receiving a premium product. One method of preparing infusion type beverage with the premium precursors is to place the precursor directly in the beverage container. However, this method runs the risk that the beverage precursor will be ingested by the user.
With this in mind, there is a need in the art to have an infusion beverage package that will enable the user of the package to see the quality of the infusion beverage precursor, wherein the package also has sufficient strength, a quick infusion time and is biodegradable after use.
The present invention provides an infusion beverage package having a good balance of properties including, being biodegradable, good tensile strength and a short sink times, while being transparent enough so as to enable a user of the package to see the contained infusion beverage precursor within the package before infusing the package into water. The infusion beverage package of the present invention is prepared from a porous web derived from a biodegradable thermoplastic polymer, wherein the package has a transparency of at least about 30%, a tensile strength of at least about 2N/15 mm, and an infusion time of less than about 20 seconds. In addition, the seal strength of the package is at least 2N/15 mm.
The infusion beverage package of the present invention may be made hydrophilic by treating the package material with a hydrophilic treatment. Rendering the infusion beverage package hydrophilic reduces the sink time of the package and contents in water. Examples of hydrophilic treatments which can be used in this invention include, a corona treatment, coating with package material with a durable hydrophilic polymeric coating and treating the package material with a plant-based extract.
As used herein, the term “comprising” is inclusive or open-ended and does not exclude additional unrecited elements, compositional components, or method steps.
As used herein, “biodegradable” is meant to represent that a material degrades from the action of naturally occurring microorganisms such as bacteria, fungi, algae and the like. “Biodegradable” also includes a material which degrades in the presence of oxygen over an extended period of time.
As used herein, the term “polymer” generally includes, but is not limited to, homopolymers, copolymers, such as for example, block, graft, random and alternating copolymers, terpolymers, etc. and blends and modifications thereof. Furthermore, unless otherwise specifically limited, the term “polymer” shall include all possible geometrical configurations of the molecule. These configurations include, but are not limited to isotactic, syndiotactic and random symmetries.
As used herein, the term “fiber” includes both staple fibers, i.e., fibers which have a defined length between about 19 mm and about 60 mm, fibers longer than staple fiber but are not continuous, and continuous fibers, which are sometimes called “substantially continuous filaments” or-simply “filaments”. The method in which the fiber is prepared will determine if the fiber is a staple fiber or a continuous filament.
As used herein, the term “nonwoven web” means a web having a structure of individual fibers or threads which are interlaid, but not in an identifiable manner as in a knitted web. Nonwoven webs have been formed from many processes, such as, for example, meltblowing processes, spunbonding processes, air-laying processes, coforming processes and bonded carded web processes. The basis weight of nonwoven webs is usually expressed in ounces of material per square yard (osy) or grams per square meter (gsm) and the fiber diameters useful are usually expressed in microns, or in the case of staple fibers, denier. It is noted that to convert from osy to gsm, multiply osy by 33.91.
As used herein the term “spunbond fibers” refers to small diameter fibers of a drawn polymeric material. Spunbond fibers may be formed by extruding molten thermoplastic material as filaments from a plurality of fine, usually circular capillaries of a spinneret with the diameter of the extruded filaments then being rapidly reduced as in, for example, U.S. Pat. No.4,340,563 to Appel et al., and U.S. Pat. No. 3,692,618 to Dorschner et al., U.S. Pat. No. 3,802,817 to Matsuki et al., U.S. Pat. Nos. 3,338,992 and 3,341,394 to Kinney, U.S. Pat. No. 3,502,763 to Hartman, U.S. Pat. No. 3,542,615 to Dobo et al, and U.S. Pat. No. 5,382,400 to Pike et al., each herein incorporated by reference. Spunbond fibers are generally not tacky when they are deposited onto a collecting surface and are generally continuous. Spunbond fibers are often about 10 microns or greater in diameter. However, fine fiber spunbond webs (having an average fiber diameter less than about 10 microns) may be achieved by various methods including, but not limited to, those described in commonly assigned U.S. Pat. No. 6,200,669 to Marmon et al. and U.S. Pat. No. 5,759,926 to Pike et al., each is hereby incorporated by reference in its entirety.
As used herein, the term “meltblown fibers” means fibers formed by extruding a molten thermoplastic material through a plurality of fine, usually circular, die capillaries as molten threads or filaments into converging high velocity, usually hot, gas (e.g. air) streams which attenuate the filaments of molten thermoplastic material to reduce their diameter, which may be to microfiber diameter. Thereafter, the meltblown fibers are carried by the high velocity gas stream and are deposited on a collecting surface to form a web of randomly dispersed meltblown fibers. Such a process is disclosed, for example, in U.S. Pat. No. 3,849,241 to Butin, which is hereby incorporated by reference in its entirety. Meltblown fibers are microfibers, which may be continuous or discontinuous, and are generally smaller than 10 microns in average diameter The term “meltblown” is also intended to cover other processes in which a high velocity gas, (usually air) is used to aid in the formation of the filaments, such as melt spraying or centrifugal spinning.
“Bonded carded web” refers to webs that are made from staple fibers which are sent through a combing or carding unit, which separates or breaks apart and aligns the staple fibers in the machine direction to form a generally machine direction-oriented fibrous nonwoven web. Such fibers are usually purchased in bales which are placed in an opener/blender or picker which separates the fibers prior to the carding unit. Once the web is formed, it then is bonded by one or more of several known bonding methods. One such bonding method is powder bonding, wherein a powdered adhesive is distributed through the web and then activated, usually by heating the web and adhesive with hot air. Another suitable bonding method is pattern bonding, wherein heated calender rolls or ultrasonic bonding equipment are used to bond the fibers together, usually in a localized bond pattern, though the web can be bonded across its entire surface if so desired. Another suitable and well-known bonding method, particularly when using bicomponent staple fibers, is through-air bonding.
“Airlaying” or “airlaid” is a well known process by which a fibrous nonwoven layer can be formed. In the airlaying process, bundles of small fibers having typical lengths ranging from about 3 to about 19 millimeters (mm) are separated and entrained in an air supply and then deposited onto a forming screen, usually with the assistance of a vacuum supply. The randomly deposited fibers then are bonded to one another using, for example, hot air or a spray adhesive.
As used herein, the term “multicomponent fibers” refers to fibers or filaments which have been formed from at least two polymers extruded from separate extruders but spun together to form one fiber. Multicomponent fibers are also sometimes referred to as “conjugate” or “bicomponent” fibers or filaments. The term “bicomponenr” means that there are two polymeric components making up the fibers. The polymers are usually different from each other, although conjugate fibers may be prepared from the same polymer, if the polymer in each component is different from one another in some physical property, such as, for example, melting point or the softening point. In all cases, the polymers are arranged in substantially constantly positioned distinct zones across the cross-section of the multicomponent fibers or filaments and extend continuously along the length of the multicomponent fibers or filaments. The configuration of such a multicomponent fiber may be, for example, a sheath/core arrangement, wherein one polymer is surrounded by another, a side-by-side arrangement, a pie arrangement or an “islands-in-the-sea” arrangement. Multicomponent fibers are taught in U.S. Pat. No. 5,108,820 to Kaneko et al.; U.S. Pat. No. 5,336,552 to Strack et al.; and U.S. Pat. No. 5,382,400 to Pike et al.; the entire content of each is incorporated herein by reference. For two component fibers or filaments, the polymers may be present in ratios of 75/25, 50/50, 25/75 or any other desired ratios.
As used herein, the term “multiconstituent fibers” refers to fibers which have been formed from at least two polymers extruded from the same extruder as a blend or mixture. Multiconstituent fibers do not have the various polymer components arranged in relatively constantly positioned distinct zones across the cross-sectional area of the fiber and the various polymers are usually not continuous along the entire length of the fiber, instead usually forming fibrils or protofibrils which start and end at random. Fibers of this general type are discussed in, for example, U.S. Pat. Nos. 5,108,827 and 5,294,482 to Gessner.
As used herein, the term “pattern bonded” refers to a process of bonding a nonwoven web in a pattern by the application of heat and pressure or other methods, such as ultrasonic bonding. Thermal pattern bonding typically is carried out at a temperature in a range of from about 80° C. to about 180° C. and a pressure in a range of from about 150 to about 1,000 pounds per linear inch (59-178 kg/cm). The pattern employed typically will have from about 10 to about 250 bonds/inch2 (1-40 bonds/cm2) covering from about 5 to about 30 percent of the surface area. Such pattern bonding is accomplished in accordance with known procedures. See, for example, U.S. Pat. No. 239,566 to Vogt, U.S. Pat. No. 264,512 to Rogers, U.S. Pat. No. 3,855,046 to Hansen et al., and U.S. Pat. No. 4,493,868, supra, for illustrations of bonding patterns and a discussion of bonding procedures, which patents are incorporated herein by reference. Ultrasonic bonding is performed, for example, by passing the multilayer nonwoven web laminate between a sonic horn and anvil roll as illustrated in U.S. Pat. No. 4,374,888 to Bornslaeger, which is hereby incorporated by reference in its entirety.
As used herein the term “denier” refers to a commonly used expression of fiber thickness which is defined as grams per 9000 meters. A lower denier indicates a finer fiber and a higher denier indicates a thicker or heavier fiber. Denier can be converted to the international measurement “dtex”, which is defined as grams per 10,000 meters, by dividing denier by 0.9.
Description of the Test Methods
Sink time is measured by a test where a 5 gram sample of material is placed in a 8 cm high, 5 cm in diameter wire cage cylinder prepared from a wire of suitable gauge so that the cylinder weighs 3 grams. The cage and the material are dropped into room temperature water and the time of the basket to sink is measured. The full test procedure is outlined in ISO-9073, which is incorporated by reference.
Transparency is measure using a spectrophotometer, a light source and a filter holder. Any spectrophotometer may be used. For a better understanding of the set-up used attention is directed to
Tensile strength is measured in accordance with ASTM-ISO-1924-2. The material to be tested is cut into strips 25 mm in width. The clamps, which are 15 mm in width, of the tensile tester were set at 180 mm apart and the clamps are separated at a rate of 20 mm/min±5 mm/min. The force at failure is reported.
The following process measures heat seal strength. Ten sample of 100 mm×100 mm are cleanly cut. Two pieces of the samples are placed in face to face contact with one another. About a 2 mm wide seam is formed by sealing the pieces with a bar at a pressure of 70-100 N/cm2, at a temperature of 230° (110° C.)-300+ (149° C.) for 0.5 to 2.0 seconds depending on the polymers used. The seam is formed approximately ⅔ from one of the edges of the material. Next the samples are cut into strips 25 mm wide such that the cuts are perpendicular to the seam formed across the sample. In addition, the samples were cut into 100 mm long strips such that the seam is in the middle of the strips. The samples are allowed to stand at standard conditions (23° C. and 50% Relative humidity) for 5. minutes before testing. The samples are placed in the tensile tester and the seam placed in the middle of the upper and lower gripping jaws. The upper and lower jaws are set at 100 mm apart. The samples were tested at a rate of 100 mm/min. After testing, the value at failure is recorded and it is noted if the seam failed or if the material failed.
Sift out test is completed to determine the ability of the material being tested to retain the infusion beverage. In this test, seven grades of sand are used to determine the ability of the material to retain particles. The seven grades, referred to as grade 1, grade 2, grade 3, grade 4, grade 5, grade 6 and grade 7 have diameters of 75-106 μm, 106-150 μm, 150-250 μm, 250-355 μm, 355-500 μm, 500-710 μm and 710-1000 μm, respectively. A sample is cut to the shape and size of the particular horizontal shaker and/or Kilner jar used in the test. 10 g of each grade of sand are placed in three different Kilner jars. The ring of the Kilner jar is place on the jar with an appropriate size and shaped material sample being tested. A container, which is weighed before testing, is place over the Kilner jar. Each assembly of the jar, sand, ring, container and sample is inverted and placed on the shaker. Any type of shaker can be used. The shaker is operated at 3.55 Hz with a stroke of 37 mm for 14 minutes. After the shaker stops, the Kilner jar and sample are remove from the container. The weight of the sand in each of the three containers is measured and the weight percentage of sand which penetrated the sample is calculated, using the following equation:
Detailed Description of the Invention
The present invention provides an infusion beverage package having a good balance of properties including, being biodegradable, having good tensile strength and short infusion times, while being transparent enough so as to enable a user of the package to see the contained infusion beverage precursor within the package before infusion. The infusion beverage package of the present invention is prepared from a porous web comprising a biodegradable thermoplastic polymer, wherein the package has a transparency of at least about 30%, a tensile strength of at least about 2N/15 mm, and an infusion time of less than about 20 seconds. In addition, it is desirable that the package has a heat seal strength of at least 2N/15 mm. The package needs to also have the ability to contain the infusion beverage precursor.
The package material may be prepared from a porous substrate which has a sheet-like structure, such as a web or a film. The sheet-like material also may be a fibrous web, such as a woven or nonwoven fabric or web. The substrate also may include polymer fibers, per se, or polymer fibers which have been formed into a fibrous web. The fibrous web desirably will be a nonwoven web, such as, but not limited to, a meltblown web, a spunbond web, a bonded carded web, or an air-laid web. The substrate also may be a laminate of two or more layers of a sheet-like material. For example, the layers may be independently selected from the group consisting of meltblown webs, spunbond webs, bonded carded webs, and air-laid webs. However, other sheet-like materials may be used in addition to, or instead of, meltblown webs, spunbond webs, bonded carded webs, or air-laid webs. Other porous sheet like materials include, for example, a perforated film or a fiberated film. In addition, the layers of a laminate may be prepared from the same biodegradable polymer or different biodegradable polymers.
In the present invention, any biodegradable polymers may be used provided that they do not lose their strength when immersed in water under conditions of use. The biodegradable polymers used to produce the porous web include biodegradable aliphatic polyester polymers. Examples of biodegradable aliphatic polyesters usable in the present invention include, but are not limited to polyhydroxy butyrate (PHP), polyhydroxy butyrate-co-valerate (PHBV), polycaprolactane, polybutylene succinate, polybutylene succinate-co-adipate, polyglycolic acid (PGA), polylactide or polylactic acid (PLA), polybutylene oxalate, polyethylene adipate, polyparadioxanone, polymorpholineviones, and polydioxipane-2-one. Of these aliphatic polyesters, polyglycolic acid and polylactide (polylactic acid) are desirable due to the availability and recent manufacturing advances. Due to current cost considerations, polylactide (polylactic acid) is most desired.
Polylactides are sometimes referred to as polylactic acid. As used herein, the term polylactide is intended to cover both polylactides and polylactic acid. Polylactides are often abbreviated “PLA”. Polylactide polymers are commercially available from Cargill-Dow LLC, Minnetonka, Minn., for example, 6200 D grade as described by EP 1 312 702 A1, from PURAC America, Lincolnshire, Ill. and from Biomer, Krailling Germany. Polylactides are also described in U.S. Pat. No. 5,338,822 to Gruber et al.; U.S. Pat. No. 6,111,060 to Gruber et al.; U.S. Pat. No. 5,556,895 to Lipinsky et al.; U.S. Pat. No. 5,801,223 to Lipinsky et al.; U.S. Pat. No. 6,353,086 to Kolstad et al.; and U.S. Pat. No. 6,506,873 to Ryan et al., each hereby incorporated by reference in its entirety.
The material used to produce the infusion beverage package must have sufficient tensile strength so as not to tear or rip during handing or use. In addition, the material must be able to be sealed desirably with heat with a sufficient strength so that the seam formed to contain the infusion beverage precursor will be retained in the package during handling and use. The material of the package should have a tensile strength of at least 2N/15 mm, as measured by the method described above, and the heat seal strength should also be at least 2N/15 mm as measured by the test described above. Generally, the tear strength is in the range of about 2 N/15 mm and about 10 N/15 mm and usually in the range of about 2 N/15 mm to about 5 N/15 mm. Similarly, the heat seal strength should be between about 2 N/15 mm and about 10 N/15 mm and usually in the range of about 2 N/15 mm to about 5 N/15 mm.
The material used for the infusion beverage package also has a transparency of at least 30%. Transparency is measured by the test describe above. The transparency is generally in the range of about 30 to about 70%. Transparency results from using lightweight materials to form the web. For example, the material used to produce the infusion beverage package should have a basis weight less than about 68 gsm, desirably less than about 51 gsm, most desirably between about 10 to 20 gsm. Higher basis weight materials may be used; however, the transparency tends to be reduced as the basis weight increases.
When the substrate is a nonwoven web, the fibers of the nonwoven web layer may be monocomponent fibers, multiconstituent fibers, or multicomponent fibers. The multicomponent fibers may, for example, have either of an A/B or ANB/A side-by-side cross-sectional configuration, a sheath-core cross-sectional configuration, wherein one polymer component surrounds another polymer component, a pie cross-sectional arrangement or an island-in sea arrangement. Each of the polymers of the multicomponent fibers may be biodegradable, or one may be biodegradable and the other may not be biodegradable. More than two components may be used as well. Desirably, the fiber configuration of the multicomponent fiber is a sheath-core configuration.
When the polymer fibers are sheath/core fibers, it is desirable that the sheath component have a lower melting point than the core component. It is also desirable that the sheath component of the multicomponent fiber comprise a biodegradable polymer described above. The fiber may be continuous fiber or staple fibers. From a standpoint of production, it is preferable that the fibers are continuous and that the fibers are spunbond fibers.
When the material used to make the infusion beverage package is fibrous, it is desirable that the fibers have a small fiber diameter. In the present invention, it is preferable that the fibers have a fiber denier less than about 6 dpf (6.66 dtex), preferable below 5 dpf (5.55 dtex) and generally in the range of about 0.5 dpf (0.55 dtex) to about 4 dpf (4.44 dtex). Typically, the desirable denier of the fibers is about 1.5 dpf to about 3 dpf. As the fiber diameter increases, the transparency of the material tends to decrease.
A second polymer may be blended with the biodegradable polymer, in particular the aliphatic polyester polymer prior to film, fiber and/or nonwoven web formation to improve the tensile strength and heat seal strength of the package material. The second polymer may be added to the biodegradable in an amount up to about 35% by weight based on the weight of the biodegradable polymer. The amount added depends on a number of factors, such as the percentage of D isomer units in the biodegradable polymer.
The selection of the second polymer is such that the second polymer is thermoplastic and it has a lower melting point and/or a lower molecular weight than the biodegradable aliphatic polyester polymer. The second polymer is generally an amorphous polymer. Addition of the second polymer would favorably influence the melt rheology of the blend and improve bonding under the process conditions used. Further, the second polymer is desirably compatible with the first polymer. Examples of such polymers include hydrogenated hydrocarbon resins, such as REGALREZ® series tackifiers and ARKON® P series tackifiers. REGALREZ® tackifiers are available from Hercules, Incorporated of Wilmington, Del. REGALREZ® tackifiers are highly stable, light-colored, low molecular weight, nonpolar resins. Grade 3102 is said to have a softening point of 102 R&B° C., a specific gravity at 21° C. of 1.04, a melt viscosity of 100 poise at 149° C. and a glass transition temperature, Tg, of 51° C. REGALREZ® 1094 tackifier is said to have a softening point of 94° C., a specific gravity at 21° C. of 0.99, a melt viscosity of 100 poise at 126° C. and a glass transition temperature, Tg, of 33° C. Grade 1126 is said to have a softening point of 126° C., a specific gravity at 21° C. of 0.97, a melt viscosity of 100 poise at 159° C. and a glass transition temperature, Tg, of 65“C. ARKON®P series resins are synthetic tackifying resins made by Arakawa Chemical (U.S.A.), Incorporated of Chicago, Ill. from petroleum hydrocarbon resins. Grade P-70, for example, has a softening point of 70° C., while grade P-100 has a softening point of 100° C. and Grade P125 has a softening point of 125° C. ZONATEC® 501 lite resin is another tackifier which is a terpene hydrocarbon with a softening point of 105° C. made by Arizona Chemical Company of Panama City, Fla. EASTMAN® 1023PL resin is an amorphous polypropylene tackifying agent with a softening point of 150-155° C. available from Eastman Chemical Company Longview, Tex.
Generally, other examples the second polymer include, but are not limited to, polyamides, ethylene copolymers derived from ethylene and a non-hydrocarbon monomer such as ethylene vinyl acetate (EVA), ethylene ethyl acrylate (EEA), ethylene acrylic acid (EM), ethylene methyl acrylate (EMA) and ethylene normal-butyl acrylate (ENBA), wood rosin and its derivatives, hydrocarbon resins, polyterpene resins, atactic polypropylene and amorphous polypropylene. Also included are predominately amorphous ethylene propylene copolymers commonly known as ethylene-propylene rubber (EPR) and a class of materials referred to as toughened polypropylene (TPP) and olefinic thermoplastic polymers where EPR is mechanically dispersed or molecularly dispersed via in-reactor multistage polymerization in polypropylene or polypropylene/polyethylene blends. Other polymers useable as the second polymer component hetrophasic polyproplyene available under the trade designation Catalloy KS 357 P available from Montell.
In addition, polyalphaolefin resins can also be used as the second polymer. Polyalphaolefins usable in the present invention desirably have a melt viscosity of 100,000 mPa sec or greater. Commercially available amorphous polyalphaolefins, such as those used in hot melt adhesives, are suitable for use with the present invention and include, but are not limited to, REXTAC® ethylene-propylene APAOE-4 and E-5 and butylene-propylene BM-4 and BH-5, and REXTAC® 2301 from Rexene Corporation of Odessa, Tex., and VESTOPLAST® 792, VESTOPLAST® 520, or VESTOPLAST® 608 from Huls AG of Marl, Germany. These amorphous polyolefins are commonly synthesized on a Ziegler-Natta supported catalyst and an alkyl aluminum co-catalyst, and the olefin, such as propylene, is polymerized in combination with varied amounts of ethylene, 1-butene, 1-hexane or other materials to produce a predominantly atactic hydrocarbon chain.
Other biodegradable polymers having a molecular weight less than the first biodegradable polymer may also be used. Blending of the second biodegradable polymer should result in a polymer blend with improved polymer melt rheology and provide an improvement in bonding under the process conditions used. It has been discovered that the tear strength of a nonwoven fabric produced from a mixture of a crystalline polylactide and a second polylactide which has a lower melting point as compared to the crystalline polylactide is vastly improved over the tear strength of a nonwoven from the crystalline polylactide alone.
Although other aliphatic polyesters may be used in the present invention, as is noted above, polylactides are the desired biodegradable polymer due to cost and availability. However, in order to form a nonwoven web from polylactides several considerations must be taken into account. For example, many polylactides are known to have poor melt stability and tend to rapidly degrade at elevated temperatures, typically in excess of 210° C. and may generate by-products in sufficient quantity to foul or coat processing equipment. Desirably, the polylactide should be sufficiently melt-processable in melt-processing equipment such as that available commercially. Further, the polylactide should desirably retain adequate molecular weight and viscosity. The polymer should have a sufficiently low viscosity at the temperature of melt-processing so that the extrusion equipment may create an acceptable nonwoven fabric. The temperature at which this viscosity is sufficiently low will preferably also be below a temperature at which substantial degradation occurs.
In the practice of the present invention in producing a nonwoven web, the polylactides, as described by U.S. Pat. No. 6,506,873 to Ryan et al. desirably has a number average molecular weight from about 10,000 to about 300,000, depending on the type of nonwoven web being formed. For example, in a composition for a meltblown nonwoven, a polylactide having a number average molecular weight ranges from about 15,000 to about 100,000 should be used. Desirably, the number average molecular weight should be in the range from about 20,000 to about 80,000 for a meltblown web. In contrast, for a spunbond nonwoven fabric, the desired number average molecular weight range is from about 50,000 to about 250,000, and more desirably, the number average molecular weight range is from about 75,000 to about 200,000.
The lower limit of molecular weight of the polymer compositions of the present invention is set at a point above the threshold of which a fiber has sufficient diameter and density. In other words, the molecular weight cannot be lower than is necessary to achieve a targeted fiber diameter and density. The practical upper limit on molecular weight is based on increased viscosity with increased molecular weight. In order to melt-process a high molecular weight polylactide, the melt-processing temperature must be increased to reduce the viscosity of the polymer. The exact upper limit on molecular weight can be determined for each melt-processing application in that required viscosities vary and residence time within the melt-processing equipment will also vary. Thus, the degree of degradation in each type of processing system will also vary. One skilled in the art could determine the suitable molecular weight upper limit for meeting the viscosity and degradation requirements in any application and the equipment being used.
The polylactides used as the biodegradable aliphatic polyester are desirably crystalline. Polylactides with a predominate L-lactide configuration are more crystalline than polylactides having a portion of D-lactide configuration. The D-lactide configuration isomer is an impurity which is naturally formed during the production of the poly(l-lactide). The larger the percentage of the D-isomer present in the polylactide, the slower the rate of crystallization. Ideally, in the present invention it is desirable the polylactide have less than about 4.5% by weight of the D-isomer. Desirably, the D-isomer should make-up less than about 3.0% by weight and more desirable less than about 2.0% by weight of the poly(L-lactide).
Lactide polymers may also be in either an essentially amorphous form or in a semi-crystalline form. Generally, the desired range of compositions for semi-crystalline poly(lactide) is less than about 6% by weight D-isomer lactide and the remaining percent by weight either L-lactide or D-lactide, with L-lactide being more readily available. A more preferred composition contains less than about 4.5% by weight D-lactide with the remainder being substantially all L-lactide.
In polylactides which are amorphous polymers, the preferred composition of the reaction mixture is above 4.5% by weight D-lactide and a more desirably above 6.0% by weight D-lactide with the remaining lactide being substantially all L-lactide mixture. Stated another way, the more D-lactide present in a given polylactide, the less crystalline the polylactide. The D-lactide isomer can be used to control the crystallinity in a predominantly L-lactide polylactide polymer.
Even small amounts of D-lactide in a polymer will be slower to crystallize than polymerization mixtures having lesser amounts of D-lactide. Beyond about 6.0% by weight of the D-lactide content, the polymer remains essentially amorphous following a typical annealing procedure.
The polydispersity index (PDI) of the polylactide polymer is generally a function of branching or crosslinking and is a measure of the breadth of the molecular weight distribution. In most applications where crystalline polylactide is desired, the PDI of the polylactide polymer should be between about. 1.5 and about 3.5, and preferably between about 2.0 and about 3.0. Of course, increased bridging or crosslinking may increase the PDI Furthermore, the melt flow index of the polylactide polymer should be in the ranges measured at 210° C. with a 2.16 Kg weight. For meltblown fibers the melt flow index should be between about 50 and 5000, and preferably between about 100 and 2000. For spunbond fibers the melt flow index should be between about 10 and 100, and more preferably between about 25 and about 75.
The biodegradable polymeric porous web may be rendered hydrophilic with a durable hydrophilic treatment by one of two methods. In a first method of the present invention, the biodegradable polymeric substrate is rendered hydrophilic by subjecting the substrate to a corona glow discharge. In this method, the biodegradable polymeric substrate having a surface is subjected to a corona glow discharge to render the surface hydrophilic.
Corona glow discharge treatments of polymeric films are known in the art and result in a chemical modification of the polymers in the surface of the polymeric material. See for example U.S. Pat. No. 3,880,966 to Zimmerman et al., U.S. Pat. No. 3,471,597 to Schirmer Corona discharge treatment of films is also old in the art and it is known that corona discharge treatment of a polymer film in the presence of air entails substantial morphological and chemical modifications in the polymer film's surface region. See Catoire et al, “Physicochemical modifications of superficial regions of low-density polyethylene (LDPE) film under corona discharge,” Polymer, vol. 25, p. 766, et. seq, June, 1984.
Generally speaking, corona treatment has been utilized to either (1) improve the print fastness on the film, or (2) to perforate the film. For example, U.S. Pat. No. 4,283,291 to Lowther describes an apparatus for providing a corona discharge, and U.S. Pat. No. 3,880,966 to Zimmerman et al discloses a method of using a corona discharge to perforate a crystalline elastic polymer film and thus increase its permeability. U.S. Pat. No. 3,471,597 to Schirmer also discloses a method for perforating a film by corona discharge. U.S. Pat. No. 3,754,117 to Walter discloses an apparatus and method for corona discharge treatment for modifying the surface properties of thin layers or fibers which improve the adhesion of subsequently applied inks or paints or of subsequent bonding.
In the present invention, the biodegradable polymeric substrate is exposed to a corona field. As used herein, the term “corona field” means a corona field of ionized gas. In general, the generation of a corona field and exposure of the fibers are accomplished in accordance with procedures which are well known to those having ordinary skill in the art. The dose or energy density to which the fibers are exposed can range from about 1 to about 500 watt-minute per square foot (w-min/ft2), which is approximately equivalent to a range of from about 0.6 to about 323 kilojoules per square meter (kJ/m2). Desirably, such dose will be in a range of from about 15 to about 350 w-min/ft2 (from about 10 to about 226 kJ/m2). Most desirably, the dose will be in a range of from about 20 to about 80 W-min/ftmin/ft2 (from about 13 to about 52 kJ/m2). Desirably, the corona glow discharge treatment is applied to the substrate under ambient temperature and pressure; however, higher or lower temperature and pressures may be used.
In a second method of the present invention, the biodegradable polymeric substrate is rendered hydrophilic with a durable hydrophilic treatment by coating onto the substrate, a hydrophilic polymeric material which is durable to an aqueous medium at a temperature in a range of from about 10° C. to about 90° C. and does not significantly suppress the surface tension of an aqueous medium with which the fibrous web may come in contact. For example, the surface tension of the aqueous medium may not be suppressed or lowered more than about 10 percent.
By way of illustration only, the hydrophilic polymeric material may be a polysaccharide. The polysaccharide may have a plurality of hydrophobic groups and a plurality of hydrophilic groups. The hydrophobic groups may be ═CH— and —CH2— groups in the polysaccharide backbone. The hydrophobic groups may be adapted to provide an affinity of the polymeric coating material for biodegradable polymeric substrate and the hydrophilic groups may be adapted to render the polymeric material hydrophilic. Examples of polysaccharides include, for example, natural gums, such as agar, agarose, carrageenans, furcelleran, aiginates, locust bean gum, gum arabic, guar gum, gum konjac, and gum karaya; microbial fermentation products, such as gellan gum, xanthan gum, and dextran gum; cellulose, such as microcrystalline cellulose; and animal products, such as hyaluronic acid, heparin, chitin, and chitosan.
Again by way of illustration only, the hydrophilic polymeric material may be a modified polysaccharide. A modified polysaccharide also may have a plurality of hydrophobic groups and a plurality of hydrophilic groups. The hydrophobic groups may be ═CH— and —CH2— groups in the polysaccharide backbone, or pendant groups. The hydrophilic groups also may be pendant groups. Again, the hydrophobic groups may be adapted to provide an affinity of the biodegradable polymeric substrate and the hydrophilic groups may be adapted to render the polymeric material hydrophilic. By way of illustration only, examples of modified polysaccharides include modified celluloses or cellulose derivatives, such as hydroxyethyl cellulose, hydroxypropyl cellulose, methyl cellulose, ethyl cellulose, methyl hydroxypropyl cellulose, ethyl hydroxyethyl cellulose, and carboxymethyl cellulose; starch and pectin derivatives, such as carboxymethyl starch, starch aldehyde, and pectates; and animal product derivatives, such as carboxymethyl chitin and carboxymethyl chitosan.
Particularly useful types of polysaccharides and modified polysaccharides include, by way of illustration, agar; alginates; and modified celluloses, such as ethyl hydroxyethyl cellulose. In modified polysaccharides, particularly in the useful type of modified polysaccharides just noted, the hydrophobic groups may be pendant monovalent alkyl groups. For example, such hydrophobic groups may be methyl or ethyl groups. As a further example, the hydrophilic groups may be pendant monovalent hydroxyalkyl groups. As yet another example, such hydrophilic groups may be hydroxyethyl groups.
Turning now to the method for preparing a coated substrate, the method involves providing a biodegradable polymeric substrate and optionally exposing at least a portion or all of the substrate to a field of reactive species. At least a portion of the substrate, including any portion exposed to the field of reactive species, then is treated with a mixture which includes water and a hydrophilic polymeric material as described above under conditions sufficient to substantially uniformly coat the surfaces of the substrate with the hydrophilic polymeric material. Any conventional treating method, for example, spraying, applying a foam, printing, dipping and the like, may be used to coat the substrate. The coating of the hydrophilic polymeric material is durable to an aqueous medium at a temperature in a range of from about 10° C. to about 90° C. and the coating does not significantly depress the surface tension of an aqueous medium with which the coated substrate may come in contact. For example, the surface tension depression of such an aqueous medium may be less than about 10 percent. In some instances, it may be either helpful or necessary to crosslink the coating on the substrate to impart a desired level of durability.
The field of reactive species serves to increase the affinity of the hydrophilic polymeric material for the biodegradable polymeric substrate. The field of reactive species may be, by way of example, a corona field. As another example, the field of reactive species may be a plasma field.
As an alternative method, the coating may first be applied to the substrate and then the substrate may be subjected to a reactive species field.
Without wishing to be bound by theory, it is believed that exposure of the biodegradable polymer substrate to a field of reactive species results in alterations of the surfaces of the substrate, thereby temporarily raising the surface energy of the substrate. This, in turn, allows the penetration of the treating solution into the substrate; that is, the substrate may be saturated with the treating solution. It is also believed that the durability of the treatment is due to surface oxidation and enhanced secondary bonding of a hydrophilic coating which may be applied to the substrate.
Although exposure of the substrate to a field of reactive species is a desired method of temporarily raising the surface energy of the substrate, other procedures may be employed. For example, the substrate may be treated with ozone or passed through an oxidizing solution, such as an aqueous medium containing chromium trioxide and sulfuric acid. Care should be taken with such other procedures, however, to either prevent or minimize degradation of the substrate.
The strength of the field of reactive species may be varied in a controlled manner across at least one dimension of the fibrous web. Upon coating the substrate with the hydrophilic polymeric material, the extent or degree of hydrophilicity of the coating is directly proportional to the strength of the field. Thus, the hydrophilicity of the coating of polymeric material will vary in a controlled manner across at least one dimension of the fibrous web.
The strength of the field of reactive species is readily varied in a controlled manner by known means. For example, a corona apparatus having a segmented electrode may be employed, in which the distance of each segment from the sample to be treated may be varied independently. As another example, a corona apparatus having a gap-gradient electrode system may be utilized; in this case, one electrode may be rotated about an axis which is normal to the length of the electrode. Other methods also may be employed; see, for example, “Fabrication of a Continuous Wettability Gradient by Radio Frequency Plasma Discharge”, W. G. Pitt, J. Colloid Interface Sci., 133, No. 1, 223 (1989); and “Wettability Gradient Surfaces Prepared by Corona Discharge Treatment”, J. H. Lee, et al., Transactions of the 17th Annual Meeting of the Society for Biomaterials, May 1-5, 1991, page 133, Scottsdale, Ariz.
If desired, at least a portion of the biodegradable polymeric substrate may be exposed to a field of reactive species subsequent to treating at least a portion of the substrate with a mixture comprising water and a polymeric material. Such post-exposure typically increases the hydrophilicity of the coated substrate. Moreover, the strength of the field of reactive species in such post-exposure also may vary in a controlled manner across at least one dimension of the fibrous web as already described. Such post-exposure may even enhance the durability of the coating through crosslinking.
Typically, the add-on amount of the hydrophilic polymer in the coating applied to the substrate is generally in the range of about 0.01 wt % to about 2.0 wt %, and desirably between 0.05 wt % and 1.0 wt %, most desirably between about 0.1 wt % and about 0.5 wt %, each based on the dry weight of the substrate and hydrophilic polymer in the coating.
The hydrophilic treatment renders the package material wettable. As the degree of wettability increases, the sink time for the package material tends to decrease. In the present invention, it is desirable that the sink time for the package material is less than 20 seconds, and preferably as quick as possible so that the user of the package can infuse the infusion beverage package in water in a very short period of time. Typically, the package will sink in under 10 seconds, in many cases under 5 seconds, and desirably immediately.
The fiber or filaments of the nonwoven web may be generally bonded in some manner as they are produced in order to give them sufficient structural integrity to withstand the rigors of further processing into a finished product. Bonding can be accomplished in a number of ways such as ultrasonic bonding, adhesive bonding and thermal bonding. Ultrasonic bonding is performed, for example, by passing the nonwoven web between a sonic horn and anvil roll as illustrated in U.S. Pat. No. 4,374,888 to Bornslaeger, which is hereby incorporated by reference in its entirety.
Thermal bonding of a nonwoven web may be accomplished by passing the web between the rolls of a calendering machine. At least one of the rollers of the calender is heated and at least one of the rollers, not necessarily the same one as the heated one, has a pattern which is imprinted upon the nonwoven web as it passes between the rollers. As the material passes between the rollers, the nonwoven web is subjected to pressure as well as heat. The combination of heat and pressure applied in a particular pattern results in the creation of fused bond areas in the nonwoven web where the bonds thereon correspond to the pattern of bond points on the calender roll.
Various patterns for calender rolls have been developed. One example is the Hansen-Pennings pattern with between about 10 to 25% bond area with about 100 to 500 bonds/square inch as taught in U.S. Pat. No. 3,855,046 to Hansen and Pennings. Another common pattern is a diamond pattern with repeating and slightly offset diamonds. The particular bond pattern can be selected from widely varying patterns known to those skilled in the art. The bond pattern is not critical for imparting the properties to the present invention.
The exact calender temperature and pressure for bonding the nonwoven web depend on the polymers from which the nonwoven webs are formed. Generally for nonwoven web formed from polylactides, the preferred temperatures are between 250° and 350° F. (121° and 177° C.) and the pressure between 100 and 1000 pounds per linear inch. More particularly, for polylactic acid, the preferred temperatures are between 270° and 320° F. (132° and 160° C.) and the pressure between 150 and 500 pounds per linear inch. However, the actual temperature and pressures need are highly dependent of the particular polymers used. The actual temperature and pressure used to bond the fibers of the nonwoven together will be readily determined by those skilled in the art. Of the available methods for bonding the layer of the nonwoven web usable in the present invention, thermal and ultrasonic bonding are preferred due to factors such as materials cost and ease of processing.
The methods described above may be used to render the biodegradable polymer hydrophilic. In addition to being hydrophilic, the methods may provide a coating which is food safe and can be used in food storage products as well as in medical devices which are used on and in the human body, although this has not been confirmed. The treatments of the present invention impart fast wettability, durability during storage, durability during use which allows for rewetting of the surface after a first insult, have efficacy at elevated temperatures, are tasteless, are non-foaming and are food safe, such as in the case for ethyl hydroxyl cellulose coatings. Surprisingly, it has been discovered that the corona treatment of the biodegradable polymeric substrate results in a substrate which retains its imparted hydrophilic properties even after storage for an extended period of time.
Other methods of making the material hydrophilic which may be used to produce the infusion beverage bag include preparing an extract of a plant based material. Examples of extracts include, but are not limited to, tea, coffee and other plant based materials. The extracts are formed into solutions which generally contain from about 0.01% to about 50% of the plant material extract. Typically, the amount of the extract in the solution used to treat the infusion beverage is between about 0.1 and 1.0% by weight of the solution.
Advantages of using the extracts include, they tend to be naturally food safe, in the case of edible or digestible materials. Further, extracts from similar materials as the infusion beverage will not change the taste of the infusion beverage, since the extract flavor will be similar to that of the infusion beverage.
Typically, the add-on amount of the plant based extract in the coating applied to the material used for the infusion beverage package is generally in the range of about 0.01 wt % to about 2.0 wt %, and desirably between 0.05 wt % and 1.0 wt %, most desirably between about 0.1 wt % and about 0.5 wt %, each based on the dry weight of the substrate and extract in the coating.
In the present invention, it is desirable that the material for the infusion beverage package is a nonwoven material prepared from multicomponent fibers. The nonwoven is generally preferred to be a spunbond nonwoven web or a bonded carded web.
Once formed, the nonwoven material can be formed into an infusion beverage package using known techniques. The infusion beverage precursor is placed into the material and the material is sealed using the bonding techniques described herein such that the infusion beverage is contained within.
The present invention is further described by the examples which follow. Such examples, however, are not to be construed as limiting in any way either the spirit or the scope of the present invention.
Bicomponent spunbond samples were prepared using the process described in U.S. Pat. No. 5,382,400 which is hereby incorporated. The bicomponent spunbond has a sheath/core configuration and contains as the sheath component, a polyactide available from Cargill Dow, LLC under the designation Ingeo™ 6350 D. The core component is a polyactide available from Cargill Dow, LLC under the designation Ingeo™ 6250 D. The ratio of the sheath component to the core component is 1:1 in each of the Examples below.
The fibers were prepared by extruding about 0.7 grams per hole/min of the total polymer at a temperature of about 410°-430° F. (210°-221° C.) and the resulting fibers were quenched with air. The fibers were drawn at a FDU pressure of 12 psi. The fibers were laid down on a forming wire moving at about 135 feet per minute (41.2 meters per minute). The fibers had a denier of about 3 dpf (3.3 dtex). The fibers deposited on the forming wire were preliminarily bonded with a hot air knife at a temperature of 250° F. (121° C.). Next the fibers were bonded using HDD pattern bond roll, which has point bonds having about 460 pins/in.2 for a bond area of about 15% to about 23%, heated to a temperature of about 250° F. (121° C.) with an anvil having a temperature of 240° F. (115° C.). The material had a basis weight of about 25.3 gsm) and is referred to as Example 1 material. The process conditions are also summarized in Table 1.
Additional samples were prepared in the same manner except using the conditions in Table 1.
Each sample was dipped into an aqueous solutions containing 0.2 wt % of ethyl hydroxyethyl cellulose (Bermocol E481, Akzo Nobel). After complete saturation of the fabric, indicated by a change in color from white to translucent, the fabric was nipped between two rubber rollers in an Atlas laboratory wringer at 10 lbs (about 4.5 kg) nip pressure. The coated fabric then was dried in an oven at 60° C. for about 30 minutes. The results of each of the above described test are show in Table 2.
As can be seen in Table 2, the material of the present invention has a good balance of properties which makes it acceptable as an infusion beverage.
While the specification has been described in detail with respect to specific embodiments thereof, it will be appreciated that those skilled in the art, upon attaining an understanding of the foregoing, may readily conceive of alterations to, variations of, and equivalents to these embodiments.
