MXPA01005909A - An absorbent structure including a thin, calendered airlaid composite and a process for making the composite - Google Patents

Abstract

The present invention pertains to an airlaid composite which is made of pulp fibers, at least about 2%by weight bicomponent fiber, and moisture. This airlaid composite is unique in that a uniformly even composite is made which upon calendering, becomes a thin structure which maintains significant absorbency when saturated. The bicomponent fibers of the present invention include a first polymer component and a second polymer component, and the first polymer component melts at a temperature lower than the melting temperature of the second polymer component. Mixing of the pulp fibers with the bicomponent fibers is done in such a way that the fibers are evenly dispersed in the airlaid composite. This airlaid composite is then heated such that at least a portion of the first polymer component of the bicomponent fiber is melted, which bond the bicomponent fibers to many of the pulp and bicomponent fibers when cooled. Moisture is added on to the composite to further facilitate bonding when the composite is subsequently subjected to calendering. Optionally, a sheet layer may be attached to the airlaid composite to form a multi-layered absorbent structure. Such composites and absorbent structures are characterized by a drape stiffness of at least about 5 cm, an absorbency of at least about 12 g/g, and a dry tensile strength of at least about 1300.

Description

AN ABSORBENT STRUCTURE THAT INCLUDES A COMPOUND PLACED BY CALENDERED AND THIN AIR AND A PROCESS TO MAKE THE COMPOUND Field of the Invention This invention relates to a composite placed by calendered and thin air which may or may not include three additional sheet layers to form a multi-layer absorbent structure. The air-laid compound is useful as an absorbent article (eg, absorbent pad), particularly in the meat and poultry industry to absorb exudates from a package. The invention also includes a process for making such a compound placed by air.

Background of the Invention This invention relates to air-laid composites and absorbent structures for use as absorbent articles which may be particularly useful in the meat and chicken packaging industry to absorb exudates. To absorb this exudate, the absorbent pads are usually placed inside the package along with the meat or chicken.

Most absorbent pads of the prior art which are used to absorb the exudates of food products consist of absorbent layers which are generally multilayer layers of tissue, paper towel and / or wood fluff. Prior art pads tend to limit absorbency and tend to break when saturated with exudate. To overcome the tearing tendency the prior art pads can be wrapped (sealed around and around the peripheral edges) between fluid impervious and fluid permeable layers, which are both expensive and difficult to process.

The present invention is distinguished from the absorbent pads of the prior art in that the pads of the prior art are generally loose, bulky and fluffy materials. As a matter of fact, this fluffy appearance of many prior art pads is required to achieve absorbency. In the case of absorbent pads formed of tissue or wood fluff, it has been a common belief that liquids are absorbed and retained mainly within the voids which are formed in the cellulose fiber network rather than the individual fibers absorbed. In such cases, the amount of liquid absorbed by an absorbent body of cellulose fibers is therefore greater than the lowest density, which is of greater volume. Consequently, it has been previously thought that anything that affects the density and can cause the absorbent material to fold will contribute to a reduction in its absorption capacity. Some pads still include rigid particles to prevent folding (eg, nodules, pyramids).

Some pads of the prior art have attempted to combine the binder fibers together with absorbent fibers (eg, pulp). It should be noted that pads of the prior art employing ah + i binder fibers have generally employed such fibers for the purpose of maintaining or establishing a high foaming of the pad, while providing mechanical integrity to the block. Additionally, the pads of the prior art have generally used very short binder fibers (having an average length of about 1 millimeter) with the intention that the fibers are completely melted and therefore act as a glue which binds the absorbent fibers together. Such pads may have good strength and an ability to absorb liquids, but will generally have a fairly low total capacity.

Even with the various incorporations of the prior art pads, most will lose their elasticity and the pad will be folded when wetted and subjected to pressure, regardless of the fact that the pulp fibers are interconnected to form a frame. Products such as tissue will tend to break when wet. Such materials also readily release their absorbed fluids when placed under a compressive load such as the loading of the meat product onto the pad and the loads such as when the packages are stacked one on top of the other as in the shipping boxes and store displays. .

Yet another problem with prior art pads is the variability in thickness by as much as +/- 15%. Such thickness variation results in a variation of absorbency as well. Variable thicknesses also affect the issues of convertibility. Since these materials are usually fed through the machines with the pressure point rollers or bands, the wide variation in the thicknesses results in a slippage and clogging in the machines which decreases the production rates resulting in higher costs.

In the development of such products, an absorbent structure is required which provides a broad absorbency, which has a uniform thickness and which will not be broken during handling or use.

As for the process of making such absorbent structures, particularly those including binder fibers, the typical air-laid materials with binder fibers are mechanically compacted several times during processing to provide strength so that the material placed by air can be handled during the process. prosecution. Usually, the material placed by air and compressed by a compaction roller immediately after leaving the air former. The air-laid compound of the present invention is not compacted in any way before heating since the air-laid compound must remain in a swelling arrangement so that adequate and complete bonding can occur. Additionally, unlike conventional air-laying processes, the air-laid compound of the present invention is cooled before calendering and the calenders are not heated. By cooling the air-laid compound in this manner, the structure is not seen in a compacted state until after the bicomponent fibers have been cooled and re-solidified. The calendered and thin air-laid compounds of the present invention thus exhibit an unexpected good absorbency in both the ability to absorb and the ability to retain the liquid while presenting in a form which is easy to handle and has sufficient strength to avoid the tendency to break.

Synthesis of the Invention The present invention relates to a compound placed by air which is made of pulp fibers, at least about 2% by weight of bicomponent fibers and moisture. The compound placed by air is unique in the sense that a uniformly even compound is made which with calendering becomes a thin structure which maintains a significant absorbency when saturated. The bicomponent fibers of the present invention include a first polymer component and a second polymer component, and the first polymer component is melted at a temperature lower than the melt temperature of the second polymer component. The mixing of the pulp fibers with the bicomponent fibers is done in such a way that the fibers are evenly dispersed in the compound placed by air. The air-laid compound is then heated so that at least a portion of the first polymer component of the bicomponent fibers melts, which binds the bicomponent fibers to many of the bicomponent and pulp fibers when cooled. Moisture is added over the compound to further facilitate bonding when the compound is subsequently subjected to calendering. Optionally, a sheet cap can be attached to the composite placed thereon to form a multi-layer absorbent structure. Such compounds and the absorbent structures are characterized by a drop stiffness of at least about 5 centimeters, an absorbency of at least about 12 g / g and a dry tensile strength of at least about 1,300 g.

Brief Description of the Drawings Figure 1 is a perspective view of an apparatus and a process for making the air-placed compound of the present invention.

Figure 2 is a perspective view of an apparatus and a process for making the multi-layer absorbent structure of the present invention.

Figure 3 is a perspective view of a compound placed by air plus two layers of sheet, in this case film layers, involving the features of the present invention.

Figure 4 is a perspective view of the compound placed by air plus a layer of sheet in this case a layer sprayed with melt.

Figure 5 is a photograph at a 200x magnification of an electron scanning microscope (SEM) of a compound placed by uncalendered air of 520 grams per square meter of total weight composed of 455 grams per square meter of pulp fiber, 8.7 % by weight of bicomponent fiber, and 4% by weight of moisture where the bicomponent fiber has been melted to bind the pulp fibers.

Figure 6 is a photograph of electron microscope analysis of a 200x amplification of an air-entrained and calendered (2,000-ply) composite of a total weight of 466 grams per square meter composed of 400 grams per square meter of pulp fiber , 3.4% by weight of bicomponent fiber, and 10.7% by weight of moisture.

Figure 7 is a 60x magnification of an electron scanning electron microscope photograph of cross-sectional side view of a composite placed by calendered air (2,000 pli) of 349 grams per square meter of total weight composed of 300 grams per square meter of pulp fiber, 3.4% by weight of bicomponent fiber and 10.7% by weight of moisture.

Figure 8 is an electron scanning electron microscope photograph of a 300x magnification of a compound placed by uncalendered air with a total weight of 520 grams per square meter composed of 481 grams per square meter of pulp fiber, 3.6% by weight of bicomponent fiber, and 3.8% by weight of moisture where the bicomponent fiber has been melted to bind the pulp fiber.

Figure 9 is an electron scanning electron microscope photograph of a 200x magnification of a compound placed by uncalendered air of 520 grams per square meter of total weight composed of 455 grams per square meter of pulp fiber, 8.7% by weight of mixed biconstituent fiber of polyethylene / polypropylene, and 4% by weight of moisture wherein the binder fiber has melted but does not agglutinate the pulp fibers.

Detailed description of the invention Compound Placed by Air; The present invention is directed to a multi-layered structure of composite placed by thin calendered air and absorbent articles formed therefrom. The present invention is a calendered and thin structure which has an advantage of ease of handling due to its thinness, rigidity and strength, while still achieving an unexpectedly good absorbency.

As used herein, the term "absorbency" refers to the absorbent capacity of the absorbent material as measured by the "Free Swollen Absorbency Test" which is discussed in more detail below in relation to the examples. The absorbency of the material is measured as liquid absorbed, in grams, over a period of time measured, per gram of absorbent material being tested. The average absorbency of the absorbent structure of the present invention is determined by the average of three (3) or more individual absorbance determinations for a given sample.

The thin calendered air-laid compound of the present invention is made of pulp fibers, bicomponent fibers, and aggregate moisture, and is formed according to the inventive process which is discussed further below. This air-laid compound is characterized by its ability to exhibit an unexpectedly good absorbency even when it has been calendared and is unusually thin.

How it was used here, the term "pulp fibers" will mean pulp fibers which have been derived from wood and which retain a substantial part of the lignin present in the wood not reduced to pulp but from which enough lignin has been removed in order to make pulp fibers somewhat hydrophilic. The pulp fibers should have an average fiber length of at least about 2 millimeters, preferably 2-3 millimeters, for ease of mixing with the bicomponent fibers. For the air-laid compound of the present invention, it has been found that the pulp fiber should be present in the compound in the range of about 70/98% by weight of the compound, preferably 90/98% by weight and more preferably 96/98% by weight. Since pulp fibers are a major factor for absorbency in the laid compound of the present invention, compounds having less than 70% pulp fibers will have a high tensile strength (assuming that the rest was made of bicomponent fibers), but they will not have sufficient absorbency because the bicomponent fibers are hydrophobic. Similarly, more than about 98% of the pulp fiber will result in a structure which will separate when saturated. The pulp fibers used may or may not be branched (designated "B" for example BCTMP). Suitable pulp fibers include thermomechanical pulp fibers, quimotermomechanical pulp fibers, quimomechanical pulp fibers, mechanical refiner pulp (RMP) fibers, stone pulp fibers (SG), fibers of mechanical peroxide pulp (PMP).

Thermo-mechanical pulp fibers (TMP) are produced by steaming wood chips at an elevated temperature and pressure to soften the lignin in wood chips. The vaporization of the wood softens the lignin so that the separation of fiber occurs preferably in the middle lamellar of high lignin between the fibers, facilitating the production of less damaged and longer fibers.

The preferred type of pulp fiber to be used in the present invention is quimotermomecánic pulp fiber (CTMP), also sometimes referred to as chemically modified thermomechanical pulp fibers. In quimotermomechanical pulp processes, wood chips, which may be made of soft wood, hardwood or a mixture of softwood and hardwood, preferably softwood, are given a mild chemical treatment in addition to a step of vaporization before mechanical defibration and then refined. Chemical treatment is limited to minimize the removal of lignin while increasing the ionic bonding potential of the fibers unlike the conventional chemical pulping process (which removes a major part of the lignin). This chemical treatment used in the quimotermomechanical pulp processes has the benefit of obtaining a high yield (generally> 90%) of the process, unlike the chemical processes which generally yield 50%. This has the additional benefit of removing some lignin while not going to the extension and the cost of a complete chemical treatment, while minimizing the environmental impact since the typical chemical processes are not friendly to the environment. The quimotermomecánica pulp which can be additionally bleached, is commercially available as "SPHINX FLUFF" of Metsa-Serla Group (of Tampere, Finland) and the standard class of pulp 550-78 of Millar; Western, Ltd., (from Edmonton, Alberta, Canada).

A variant of the quimotermomechanical pulp for which an analogous chemical treatment has been applied is known as quimotermomechanical pulp, which omits the step of vaporization practiced in the manufacture of the thermomechanical pulp and the quimotermomechanical pulp. It is also known to chemically treat the pulp after the start or complete the fibrization. Such treatment can be applied to the pulp which has not been chemically treated in advance, or to the pulp which has been chemically treated in advance. Other types of pulp fibers may be useful in the present invention as long as the fibers exhibit the combination of hydrogen bonding and wet elasticity as described more fully below. Examples of these additional types include mechanical refiner pulp (RMP), stone pulp (SGW), and mechanical peroxide pulp (PMP).

The laid compound of the present invention also includes bicomponent fibers. How it was used here, the term "bicomponent fibers" refers to fibers which have been formed from at least two thermoplastic polymers which are excluded from separate extruders but spun together to form a fiber and which have a side-by-side arrangement, a pod / core arrangement. In a sheath / core bicomponent fiber, a first polymer component is surrounded by a second polymer component. The polymers of the bicomponent fibers are arranged in different zones placed essentially constant across the cross section of the bicomponent fiber and extend continuously along the length of the fibers. Various combinations of the polymers for the bicomponent fiber may be useful in the present invention, but it is important that the first polymer component melts at a temperature lower than the melt temperature of the second polymer component. The fusion of the first polymer component of the bicomponent fiber is necessary to allow the bicomponent fibers to form a sticky skeletal structure, which when cooled, captures and agglutinates many of the pulp fibers. Typically, the polymers of the bicomponent fibers are made of different thermoplastic materials, such as, for example, of polyolefin / polyester bicomponent fibers (sheath / core) whereby the polyolefin, for example the polyethylene sheath, melts at a lower temperature than the core, for example polyester.

Typical thermoplastic polymers include polyolefins, for example, polyethylene, polypropylene, polybutylene, and copolymers thereof, polytetrafluoroethylene, polyesters, for example polyethylene terephthalate, polyvinyl acetate, polyvinyl chloride acetate, polyvinyl butyral, acrylic resins, example, polyacrylate and polymethylacrylate, polymethylmethacrylate, polyamides, namely nylon, polyvinyl chloride, polyvinylidene chloride, polystyrene, polyvinyl alcohol, polyurethanes, cellulosic resins, namely cellulose nitrate, cellulose acetate, cellulose acetate butyrate, ethyl cellulose, etc., copolymers of any of the above-mentioned materials, for example ethylene-vinyl acetate copolymers, acrylic acid-ethylene copolymers, butadiene-styrene block copolymers, Kraton and the like.

In a bicomponent sheath / core fiber, the core can also be made of a heat-resistant resin such as phenol-formaldehyde, phenol furfural, urea-formaldehyde, melamine-formaldehyde, silicone rubber and the like. Particularly preferred in the present invention is a bicomponent fiber known as Celbond type 255 available from Trevira GmbH & Co from Frankfurt, Germany, which is a polyethylene sheath fiber / polyester core.

The bicomponent fiber will be present in the composite placed by air in at least about 2% by weight of the compound, with the substantial remainder being composed of pulp fibers. It has been found that no more than 10% by weight is necessary to achieve adequate bonding and that the use of more than 10% by weight is usually prohibitively expensive. In addition, the more pulp fiber is present in the composite, the greater the absorbency. Air-laid compounds having less than about 2% by weight of bicomponent fibers do not have adequate wet integrity when saturated with fluid (eg, polar fluids such as water or water-based solutions such as exudate). Preferably, the compounds placed by air will contain about 4% by weight of bicomponent fibers. As used herein, the term "wet integrity" refers to the ability of the compounds to maintain their structure even when wet, as discussed in more detail in the examples that follow. In other words, a wet compound of the invention will not break, will flake or otherwise crumble when taken or handled.

The bicomponent fiber should have a fiber length that does not exceed about 1.5 inches (38.1 millimeters) since the fibers which are too long tend to become entangled with themselves rather than to disperse evenly to the pulp fibers. Preferably, the fiber length will be in the range of about 3-15 millimeters, more preferably around 4-8 millimeters, and will have a denier of about 1.5 to 4. Both versions the food class and the non-food grade. of bicomponent fiber can be used, depending on the intended use of the compound.

The addition of sufficient moisture is also required in the air-laid compound of the present invention to facilitate the binding of the compound to the calendering. (as defined below). It is the Applicant's theory that such aggregate of moisture facilitates bonding by creating hydrogen bonds between the pulp fibers and the calender. Once the moisture has been added and the compound has been calendared to form a compound placed by calendered and thin air as if at least about 5% by weight of the compound is moisture, then sufficient moisture has been added during the process to facilitate the union. The addition of sufficient moisture during processing has been found to be in the range of about 5 to about 20% by weight of the compound. For example, a sample of the compound placed by air weighing 400 grams per square meter (gsm) with 4% by weight of bicomponent fiber, 10% by weight of moisture will contain 2,344 grams per square meter pulp + 16 grams per square meter of bicomponent fibers + 40 grams per square meter of water.

It should be clear to one of ordinary skill in the art that the moisture absorbed, for example from a humid environment, after the formation of the air-laid compound of the present invention is not sufficiently moist to facilitate bonding without subjecting the composite to an additional calender. In other words, if the compound absorbs moisture from the atmosphere, the compound will have calendared for the benefits of the present invention. The added moisture of the present invention must be added before calendering to facilitate bonding.

As used herein, the term "thin" refers to the ratio of thickness to basis weight (where the basis weight is that of the pulp of only the bicomponent fibers) of the composite placed by air and / or of the absorbent structure resulting. For the purposes of the present invention, a thickness to basis weight ratio of about 3.0 x 10"3 millimeters / 1 gram per square meter to 1.0 x 10" 3 millimeters / 1 gram per square meter has a distinct advantage of a handling of improved roll. The calendering of the compound also provides an important feature in that it reduces the overall fraying associated with the absorbent articles which improves the overall appearance and reduces the tendency to contaminate the meat product of an unwanted lint material. The compounds of the present invention will instead have a uniformly smooth and even surface. The thickness of these compounds does not vary by more than a minor amount on the cross section of the compound placed by air. For many of these compounds there is a relatively uniform basis weight for a given area.

The air-laid compound of the present invention which is both thin and compressed exhibits a drop stiffness of at least about 5 centimeters, preferably of 6-10 centimeters which is important to facilitate processing in some equipment, such as for example such as the automated classification of the absorbent pads in meat trays.

The compound placed by air will have a basis weight of 50-500 grams per square meter and is calendered with an initial thickness of approximately 1.27 centimeters - 1.91 centimeters and a density of around 0.02 - 0.05 grams per cubic centimeter. As used herein, the term "calendering" means that the compound placed by air has been compressed at a pressure of about 800 to 4,000 pounds per linear inch (pli) (143-715 kilograms / linear centimeter) preferably from 1,500 -3,000. pounds per linear inch (268 - 536 kilograms per linear centimeter), more preferably 2,000 - 3,000 pounds per linear inch (358-536 kilograms per linear centimeter) to form a compound placed by thin calendered air having a thickness ratio of base weight of 3.0 x 10"3 millimeters / l gram per square meter to 1.0 x 10" 3 millimeters / 1 grams per square meter, a thickness of 0.025 - 0.15 centimeters and a density of 0.5 grams per cubic centimeter. Such calendering is not the same as compaction and compression usually used in the air laying industry. Instead, it is closer to what is used in the paper industry (known as "supercalendered") in the sense that much higher pressures are carried out. It is the applicant's task that such calendering is critical in the formation of the air-laid compound of the present invention because this creates an energy stored in the compound placed by air due to hydrogen bonding, to the three-dimensional orientation of the fibers of pulp and the elastic nature of the pulp fibers. Subsequent contact with polar fluids (eg, absorbing water or water-based solutions such as exudate) allows the pulp fibers to separate and return to a more relaxed configuration resulting in an open porous structure suitable for absorbency. Figure 6 shows a 200x magnification of an SEM photograph of a compound placed by air (466 grams per square meter of total weight) having 400 grams per square meter of pulp fiber with 3.4% by weight of bicomponent fiber and 10.7% by weight of humidity, where the compound placed by air has been calendared to 2,000 pounds per linear inch. Figure 7 shows an electron scanning electron microscope photograph of cross-sectional side view of a 60x amplification of an air-laid and calendered compound (2,000 pounds per linear inch (349 grams per square meter total weight) of 300 grams per square meter of pulp fiber, 3.4% by weight of bicomponent fiber and 10.7% by weight of moisture These figures show a dense absorbent structure that has bicomponent fibers attached to many of the pulp fibers so that the calendered structure and thin exhibits unexpectedly good absorbent properties while in a thin and dense form.

Properties such as absorbency, tensile strength, thinness (ratio of thinness to basis weight), absorbency that regain, density, rigidity, wet integrity and overall appearance are all properties important for the structures of the present invention. When these air-laid compounds are made according to the invention, the following benefits are exhibited in the compounds placed by air. By one, a higher density, hence a reduced thickness, result in overall improvements for roll handling, storage and transportation because more of the compound placed to hear air can be placed on a roll. When more material is on the roll, production is improved because less time is needed to change the roll and less space is needed for storage and transportation. Also the improvements in stiffness together with the tensile strength exhibited by the air placed composites of the present invention allows for improved processing since there will be fewer breaks when the rolls are converted into pads. Probably more importantly, the air-laid compounds made according to the present invention have a uniform thickness and absorbency. The air-laid compounds of the present invention will exhibit an absorbency of at least about 12 g / g, preferably about 16 g / g. In use, the calendered and thin air-laid compounds have the ability to regain 70-90% of the precalendered absorbency with saturation, even under compressive loads such as the placement of the meat on the pad, which is important for the absorbency of the structure. Such a compound placed by calendered and thin air with a good absorbency has unexpectedly been unknown up to this point.

Although not required, the compound placed by air may additionally include various combinations of sheet layers bonded to one or both sides of the composite. Such sheet layers can be added to the air-laid composite for several reasons including: 1) to provide additional dry surface integrity such as to reduce or cover the loose and short potential fibers (eg lint) that may be present in the compound placed by air, 2) to serve as a barrier layer of separation between the food product and the compound placed by air, and 3) to increase the appearance of the compound placed by air when it has absorbed the exudate since the exudate absorbed It is usually ugly. Examples of suitable sheet layers include film layers, tissue layers, melt and spray layers and nonwoven layers. The sheet layer is attached to the composite placed by air by any suitable method including corona treatment, calendering, adhesive, sonic bonding or combinations thereof.

A layer of film that has a thickness of 0.4 to 1 thousandth of an inch, for example, can be used. The film layer can be useful for maintaining the multi-layer structure together, particularly when freezing since the pad can be peeled from the meat without breaking the pad. The polymeric film layer can be either liquid permeable or liquid impervious. Additionally, for food packaging applications, the film layer must be compatible with food products. Such films may include polypropylene, high density polyethylene, low density polyethylene, linear low density polyethylene, cellophane, polyvinyl acetate, polyvinyl alcohol, polycaprolactane, polyester, polytetrafluoroethylene, or mixtures thereof. extrusions of one or more of these materials. Polyethylene, polypropylene, and polyester polymer film layers are generally preferred, more preferably a layer of polyethylene film having a thickness of 0.4 mils.

A preferred method for attaching the sheet layer to the composite placed by air is by corona treatment, followed by calendering. The corona treatment involves the application of a voltage across the surface of the sheet layer. The resulting treated surface is very reactive and allows the sheet layer to form chemical as well as mechanical bonds with the surface of the composite placed by air. This provides a firm hold of the sheet layer to the composite placed by air.

The tissue layer may be a composite of cellulosic fibers having a basis weight of 10-30 pounds / ream (4.5 - 13.6 kilograms / ream). The tissue layer can also be a layer of multiple layers. Applications where the absorbent pad is embedded within a food tray as in United States of America No. 4,702,377 issued to Grone will be a particularly useful application for an air-laid compound of the present invention including a tissue layer. . The tissue layer will then provide a non-contact separation layer between the compound placed by air and the food.

A melt sprayed layer is a polymer layer or coating, such as for example a polyolefin polymer, which has been forced through, for example, a die tip and sprayed onto the surface of the air-laid compound. . A rough molten polyolefin spray at 1.5 to 10 grams per square meter will be acceptable for use as a sheet layer of the compound placed by air. The melt sprayed layer can be made of polypropylene, polyethylene, polyester, or nylon. Generally, polypropylene is preferred.

The non-woven layer can also be added to the air-laid compound of the present invention. As used herein the term "non-woven layer" means a sheet layer having a structure of individual fibers or threads which are in between, but not in an identifiable manner as in a knitted fabric. The non-woven layers have been formed from many processes such as, for example, meltblowing processes, spinning processes and carded and bonded tissue processes.

In order to provide an absorbent food pad that will kill or inhibit the growth and spreading of pathogens that arise in food, the air-laid compound can be impregnated with an antimicrobial composition which consists of a water soluble carboxylic acid and a surfactant as described in commonly assigned U.S. Patent No. 4,865,855 to Hansen et al. Also, superabsorbents such as carboxymethyl cellulose are not necessary for the present invention but can be added if desired. Other materials may be added to the compound placed by air for the desired effects, including fluid thickeners and activated carbon granules or fibers, perfumes, optical brighteners, photostability promoters, salts, surfactants and the like. It will be understood by one of ordinary skill in the art that such additives are useful only in such amounts which will not adversely affect the properties of the air-laid compounds of the present invention.

For the purposes of the present invention, the air placed composite can be used as an absorbent article, with or without additional sheet layers. Returning to Figure 4, there is shown a multi-layer absorbent structure 10 encompassing the present invention. The multi-layer absorbent structure 10 is rectangular in shape so as to conveniently fit into a food product packaging tray. The multi-layer absorbent structure 10 consists of a composite placed by air 12 fastened to a sprayed and melted layer 20.

In Figure 3, another embodiment shows a multi-layer absorbent structure 10A having three layers: a layer of melt-impermeable polymeric film 16, a compound placed by air 12 and a layer of fluid permeable film 17. The fluid permeable layer 17 is shown here with rows of slits 24 sufficient to pass fluids having a viscosity as high as 24 centipoise under a flow of severity over a 24-hour period (eg blood or chicken exudate). Similarly, the fluid-permeable layer 17 can be perforated with holes. The holes or slits in the fluid-permeable layer 17 allow the exudate which has been drained out of the meat to be absorbed by the transmission action through the fluid-permeable layer 17 to the compound placed by air 12. As can be seen in FIG. It showed, it is not necessary to enclose (seal around the peripheral edges) the film layers since the fastening has been achieved as described above. In addition, by not sealing the peripheral edges, an additional conduit for the absorption of the fluid remains by leaving the compound placed by air 12 exposed around the edges.

In use a multi-layer absorbent structure 10A of Figure 3 is placed between the food product and the tray or other packaging material, with the film layers 16 or 17 in contact with the food product. When the juices or liquids of the food product are released, these additionally drain to the edge of the absorbent structure of multiple layers and are absorbed by the compound placed by underlying air 12. Unlike the previously known absorbent pads, the compound placed by air calendered and thin has a sufficient capacity to recover the thickness, even under a compressive load, such as for example the weight of the meat product, by the couple transmission to absorb the exudate. In addition, the compound placed by air 12 is less feasible to release its fluids under such loads.

Process to make the Compound Placed by Air The preparation of the compound placed by air begins with the fibrization of the pulp. Fiberisation is the process of breaking up the pulp packed or rolled into fine pulp fibers. Since the pulp is compared in either a bale form or rolled form and the pulp is therefore in a hard and dense form, fiberization is required to render the pulp in an unusable form. There are many known methods for fibrizing the pulp. See for example the patents of the United States of America number 3,825,194 granted to Buell, 4,100,324 granted to Anderson and 3,793,678 granted to Appel.

Once the pulp is fibrized, it is ready to be mixed with the bicomponent fibers. The mixing of the fibers begins with the dosing of the pulp fibers and the bicomponent fibers at the desired weight ratio in a mixer. As will be generally understood by one with ordinary skill in the art, the dosage can be variable as much as by ± 1 - 2% by weight of each component due to the capacity of the machine. Various methods for dosing the fibers are known including using a bag chamber or a drop supply. The pulp fibers and the bicomponent fibers are then mixed integrally in a mixing step, which is important because good dispersion of the bicomponent fibers in the pulp fibers is necessary to effect the bonding which will be discussed in more detail. detail below. Mixing methods include mixing in an air stream or other mechanical mixing device (e.g. a mill) and the like.

The integrally blended pulp fibers and the bicomponent fibers are then formed into a composite placed by air by transporting the fibers by means of air through a forming nozzle or head and feeding the fibers continuously onto an endless forming surface, such as a wire grid. Vacuum media can also be included to pull the fibers against the grid. Unlike most air laying processes and only this process, the compression or compaction of the compound placed by air thus formed is not required, as will be illustrated in the examples given below.

As used in the prior art, the compaction used a set of rollers up and down the material placed by air to compact it in order to increase its self-adherence and therefore its mechanical integrity for further processing. The compaction rollers carried out this function very well but were considered as having a number of disadvantages including a decrease in volume or foaming in the final product which was considered undesirable.

It is important for the present invention that the air-laid compound remain in its foamed arrangement until the compound has been subjected to heating and cooling means so that a proper and complete bonding between many of the pulp fibers can occur. and of the bicomponent fibers and / or between the bicomponent fibers while still in a fluffed arrangement. The compound placed by air does not have, therefore, a high mechanical integrity at this point of the process. It is also important to note that wet laying processes will not work in the present invention because it would not be possible to achieve the foamed arrangement required for bonding if the compound were wet laid before the bonding step.

The compound placed by air can be formed into a continuous sheet as described above or alternatively it can be formed into individual pads or applicators on equipment such as for example a forming drum. A forming drum has discontinuous pockets on the circumferential surface, each bag having a permeable surface at the bottom of the bag. A vacuum is pulled over the inside of the drum through the permeable surface, thereby allowing air to flow into the bag making pulp fibers, bicomponent fibers and any dust or granular products carried in the air. stay in the bag. The remaining circumferential surface of the drum is impermeable to air so that the fibers are not formed on this flat surface. When the drum is rotated, the vacuum is blocked and the fibrous material trapped in the bag is transferred by means of vacuum, pressure and / or other mechanical means to a forming surface, resulting in the placement of individual applicators on the forming surface which are discreetly spaced and separated one from the other. These applicators can subsequently be carried through the rest of the process by a carrier sheet layer such as a pulp tissue or a non-woven layer. Alternatively, the individual applicators can be transferred through the process through a series of vacuum bands and mechanical means.

In one embodiment of the present invention, a roll of a sheet layer such as a tissue or a nonwoven can be unrolled and carried on the forming surface and the pulp / bicomponent fiber mixture can be placed by air on the surface of the sheet layer. A layer of film sheet will not be suitable in this phase since the composite placed by air will be carried through a heating means where the film layer will block the flow of heated air through the structure, (and which will melt the film), and also because the vacuum necessary to retain the fibers placed by air can not be transmitted through the film layer. For that matter, it is important that any layer of sheet held in this phase should be able to withstand the heating means without adversely affecting its properties.

The compound placed by air is then subjected to a bonding step in which the compound passes through a heating means to activate the bicomponent fibers to bond the compound placed by air (for example to melt the sheath of a fiber of bicomponent sheath / core). The heating allows the bicomponent fibers to form a sticky skeletal structure, which upon cooling, captures and agglutinates many of the pulp fibers, which are shown more clearly in Figures 5 and 8. Figure 8 is a photograph electron microscope of a 300x amplification of a compound placed by uncalendered air (total weight of 520 grams per square meter) including 500 grams per square meter of pulp fiber which has been fiberized with 3.8% by weight of bicomponent fiber and 3.6% by weight of moisture where the sheath of the bicomponent fiber has been melted to bind the fibers together. In this figure, the molten polyethylene sheath has clearly fused out of the polyester core and is bonded to the pulp fiber. This figure also shows the additional advantage of the bicomponent sheath / core fiber in the sense that the core does not curl or otherwise wrinkle, but instead maintains a column configuration that provides additional strength to the core. compound. Figure 5 is an electron scanning microscope photograph at a 200x magnification of a compound placed by uncalendered air. In this figure, the compound (total weight of 520 grams per square meter) included 500 grams per square meter) included 500 grams per square meter of fiberized pulp, 8.7% by weight of bicomponent fiber, and 4% by weight of moisture where the bicomponent fiber has been melted to bind the pulp fibers. The fibers which appear to have a rough texture and small holes are the pulp fibers while the fibers that have a smoother surface are the bicomponent fibers. The discrete joining points can be seen where indicated by the arrows.

The heating of the compound placed by air can be achieved, for example, by dry heat, such as by passing hot air through the compound or by heating in an electric furnace. It is important that the heating conditions be controlled at a temperature and at an air flow rate sufficient to melt only the first polymer component of the bicomponent fiber, while not melting the second polymer component (e.g. pod and not the nucleus). As will be understood by one of ordinary skill in the art, suitable temperatures and air flow rates are dependent on the type of polymers used in bicomponent fibers. Of course, the proper heating condition will also be a function of the heating rate of the air flow. As the air flow rate is increased, a lower temperature can be used, while a decreased flow rate will require an increased temperature to achieve melting within the same time interval. Whatever the conditions used, it is important that the air flow rate is not set at a rate which will result in the compression of the compound placed by air since the uniform fading will not occur. It will also be understood that the heating can be achieved by other means such as the exposure of the compound placed by air to the radiation, for example to an infrared radiation of a suitable intensity and duration.

It will be understood by one of ordinary skill in the art that subjecting the composite placed by air to such heating means will remove any surface moisture that may have been present in the composite up to that point. It is a requirement of the present invention that the compound placed by air is then rewetted. The wetting and heating step can occur simultaneously if for example wet heat is used such as by the use of moist hot air or a superheated steam, provided that the proper amounts (as described above) of moisture are imparted and therefore it is reached in sufficient temperatures to melt the sheath of the bicomponent fiber. In a similar way, these steps can be independent steps. In this case, one such method of wetting the compound placed by air may be by exposing the compound to a spray of atomized water. Whatever the method used, it is important that the moisture is distributed evenly through the compound placed by air. Thus, for example, a vacuum box can be placed below the air-placed compound to pull moisture through the compound, thus imparting the moisture distribution of the z-direction (thickness direction) of the composite placed by air .

Alternatively, a humidity chamber may be used as a high pressure steam to add moisture to the air placed composite. Typical placements of the humidity chamber can be placed at a distance of 90% relative humidity and 70 ° F. Both the high pressure steam and humidity chamber methods will very likely not require a vacuum, while the application of Humidity using a spray atomizer will very likely require a vacuum.

Once the air-laid compound has been heated it must be used before calendering to resolidify the bicomponent fibers, thereby joining the bicomponent fibers to the pulp fibers and / or joining the bicomponent fibers together. If the wetting step occurs, simultaneously with the heating step, separate cooling is advantageous. If, on the other hand, the wetting and heating steps are independent steps, cooling can also be effected during the wetting step by varying the temperature of the humidity applied to the compound placed by air. In addition, an independent cooling step which occurs between the heating and wetting steps can be useful. For the purposes of the present invention it has been found that sufficient cooling occurs when the humidity is applied at room temperature. Other means of cooling will be recognized by those with ordinary skill in the art.

After forming the air-laid compound, a sheet layer can be fastened to one or both sides of the composite whether or not a sheet layer has been previously secured in the process. Such a sheet layer can be formed by spraying a meltblown polymer layer onto the surface of the compound placed by air, either before or after the wetting means. The sheet layers can also be held by unwinding a sheet layer previously made and attached to either side of the composite. The sheet layers will preferably be corona treated prior to attachment to the composite which will facilitate adequate adhesion so that a multi-layered structure thus formed will not be easily delaminated. Additional adhesion will occur through calendering as discussed in more detail below. Examples of multi-layer structures include, but are not limited to: film / composite; pe 1 í cul a / compue s t o / pe 1 í cu 1 a; film / composite / blown with fusion; nonwoven / composite / blown with fusion; tissue / composite / film; tissue / compound / tissue; and tissue / compound / blown with fusion. The film layer may be either permeable or impermeable to the fluid as necessary to achieve the desired properties in the final structure.

The compound placed by air, including the additional sheet layers if present, will then be calendered as defined above. Such calendering can occur, for example, using two preferably steel rolls or a series of rolls in such a spatial relationship and pressure, to calenuate the air-laid compound or the multilayer structure therebetween. Other examples of roller combinations may also include a steel roller and a rubber (or rubber coated) roller; and a steel roller and a paper coated roller. Alternatively, a press for calendering the compound may also be used, requiring the material or press to be indexed and stopped on the wire and then pressed. Such an arrangement may also incorporate cutting the compound into pads thereby combining calendering and cutting in one step. The compound placed by calendered air gains resistance to dry stress and a reduction in volume (thickness) of calendering. It is important that the calendering is carried out at room temperature or only slightly elevated temperatures (for example the rollers are not generally heated) because the higher temperatures would damage the compound placed by air.

The composite placed by thin calendered air or the multi-layer absorbent structure thus formed has sufficient strength so that it can be rolled or handled as a sheet for storage, transport or unwinding purposes, and sufficient to prevent de-scaling. or otherwise breaking when saturated. The tensile strength (both wet and dry) has been measured for the air-laid compounds of the present invention as discussed more fully below in the examples. It has been found that these compounds exhibit a dry tensile strength in the machine direction (MD) in the range of about 1,500-10,500 grams and a dry tension resistance in the cross machine direction (CD ) in the range of about 1,300-6,900 grams.

Figure 1 diagrammatically illustrates one forms of a suitable apparatus for forming the air-placed compound 12 of the present invention. The pulp fibers 30 are fiberized in a fiberizer 40 and the metering means 42 combine the established amounts of pulp fibers 30 with the bicomponent fibers 32. The pulp fibers 30 and the bicomponent fibers 32 are then mixed integrally in a mixer 44. A separate mixing step will not always be required. For example, when the density of the pulp fiber is about 1 gram per cubic centimeter and the density of the bicomponent fiber is about 0.9 grams / cubic centimeter, the two fibers will easily mix together in the turbulent air flow the which is typical in a process of placement by air. The fibers are thus formed into an air-laid compound 12 by transporting the fibers by air through a forming head 46 and supplying the fibers continuously on an endless forming surface 48, while sufficient vacuum means 50 is provided. they assure the compound without diminishing its spongy state. The air-laid compound 12 is then carried through a heater 52 which can also use the vacuum means with heater 51 to secure the compound and pull the hot air. The heater 52 melts the first polymer component of the bicomponent fibers 32 without melting the second polymer component. As shown, the air-laid compound 12 is then carried through a humidifier 54, which can also use a humidifying vacuum means 53, where the humidifier 54 both cools the composite causing the bicomponent fibers 32 to come together. to pulp fibers 30 and add moisture to the compound. The air-laid compound thus formed 12 is then compressed using the calendering means 58 to form a compound placed by thin calendered air 1.

Fig. 2 illustrates diagrammatically a form of a suitable apparatus for forming the multi-layer absorbent structure 10 of the present invention, which is essentially the same as that described in Fig. 1 above except that the additional sheet layers may be added to the air-laid compound 12. As discussed above, a sheet layer such as a layer of tissue 18 can optionally be added to the forming surface 48 so that the air-laid compound 12 is formed directly on the tissue layer. 18. Also, several layers can be added to one or both sides of the composite by means such as for example blowing a sprayed and melted layer 20 directly onto the air-laid compound 12 using the melt spray means 56 or by unwinding the sheet layers such as the fluid impermeable film layer 16 and a fluid permeable film layer 17. The composite placed by air co n the additional sheet layers, it is then calendered to form a calendered and thin multiple layer absorbent structure 2.

The multi-layer or composite absorbent structure can then be cut into several shapes depending on the final application. Such compounds and structures will be particularly useful in applications where high absorbency and exceptional thinness will be a value. Examples of such absorbent applications include, but are not limited to, absorbent pads in meat and poultry packaging, in other food packages where the food product tends to sweat or expel fluid (eg, salad packs), in sachets of shipping or packages in which the products shipped have a potential to release the fluid and / or an accumulation (eg blood / medical applications) in personal care products and the like.

Alternate uses for the air-laid compound of the present invention include packings, dams, or dikes that can be made to seal the boundary or edge of a product when the liquid comes into contact with such a boundary. The material expands in contact with liquids such as water and can expand up to several times its original compressed thickness. This action, when in a direction perpendicular to the fluid flow and in a constrained environment, will act as a seal, slowing down or preventing additional discharges of liquid, preventing them from passing through this area. This aspect of the present invention may be a particular use in a waistband or leg cuff of desirable absorbent garments such as baby diapers or incontinent garments. The sealing action acts as a prey to prevent fluids from passing into the waist leg opening and provides additional time for the absorbent core of the garment to transmit the fluids out of the openings.

The following examples illustrate the preparation of the air-laid composite and the multi-layer absorbent structures according to the present invention.

Examples The samples of the present invention and the comparative examples were prepared as described below. The samples were then subjected to the following tests. When layers of additional fabric were added to the air-laid compound to form a multi-layer absorbent structure such layers are noticed.

Weight of the Compound; The weight of the samples used for the examples given below was determined by cutting a piece of a compound placed by air and weighing it on a conventional scale. The weight was recorded in grams. The basis weight was determined by dividing the weight by the area of the cut sample.

Thickness; The thickness was measured using a manually raised Starrett volume tester held in the hand which has an anvil 7 centimeters in diameter and weighing 80 grams and which was recorded in inches.

Density; The density of the compound placed by air and calendering is calculated by dividing the weight of the sample of compound by the volume of the sample and recorded in grams / cubic centimeter.

Wet Integrity; As described above, a sample which has been saturated with fluid (e.g. water or exudate) was considered to have a wet integrity if it is not separated, scaled or otherwise broken when taken or handled. The examples indicated below say that the sample either had wet integrity or not.

Fall stiffness; "Drop stiffness" is a test that measures the drop stiffness or the bend resistance of the compound. The length of bending is a measure of the interaction between the weight of the compound and the stiffness as shown by the way in which the compound bends under its own weight, in other words, by employing the principle of cantilever bending of the compound under its own weight. In general, the sample was slid at 12 centimeters per minute in a direction parallel to its long dimension, so that its front edge was projected from the edge of the horizontal surface. The length of the hanging was measured when the tip of the sample was depressed under its own weight at the point where it joined the tip to the edge of the platform made at an angle of 48.5 degrees with the horizontal. The longer the hanging, the slower the sample in bending; therefore, higher numbers indicate more rigid compounds. This method conforms to the specifications of the ASTM D 1388 standard test.

The test samples were prepared as follows. The samples were cut into rectangular strips measuring 2.54 centimeters wide and 15.24 centimeters long, unless otherwise indicated. Three samples in each direction of the machine and cross machine to each sample were tested. A suitable Drape-Flex stiffness tester, such as a FRL cantilever bending tester, model 79-10, available from Testing Machine Inc., located in Amityville, New York, was used to conduct the test.

The drop stiffness, measured in inches, is one-half of the length of the sample hung when it reached the 41.5 ° tilt. The drop stiffness reported below the sample was the arithmetic average of the results obtained from the samples tested in each of the directions of the machine and cross machine, reported separately. The drop rigidity of the sample was reported to the nearest 0.254 millimeters.

Free Bloated Absorbency; The free swell absorbency test is a test designed to measure absorbency-the ability of the absorbent material to absorb and retain a liquid and was designed to mimic the absorbent material in use, for example as an absorbent pad to absorb the exudate in a package of a bird tray. The absorbent capacity was reported as the weight of the liquid absorbed over a period of time measured, expressed in grams of liquid per gram of absorbent material. The free swell absorbency test was carried out as follows. The test procedure for absorbency was one in which each sample (sized as noted below in the examples) was taped, using a double-sided tape, to a chicken meat tray (for example "3P"), the which was 16.51 centimeters wide, 22.23 centimeters long and 3.175 centimeters deep. The tray was then filled with liquid (500 milliliters) thereby submerging the sample in the liquid. The sample was allowed to absorb the liquid for a certain amount of time (soaking time) which was generally 24 hours unless otherwise noted. The tray with the sample was then drained (by tilting the tray to drain the liquid outside) for a certain amount of time (draining time) which was generally 1 minute unless otherwise noted, and any water in excess was cleaned from the tray. The absorbent capacity was determined as follows: Absorbent Capacity (g) = wet weight of the tray and sample-dry weight of the tray and sample.

The liquid absorbed by the sample was then used to calculate the absorbance of the sample according to the following equation: Absorbency (g / g) = absorbent capacity (9) / [(weight of the sample-weight of the film) x (percentage of the pulp fiber in the sample)].

Gag Absorbency; The ability of the sample to regain the absorbency after the sample has been calendared and saturated has been measured. This regained absorbency is the same as described above for free swelling absorbency except that the absorbance of the saturated sample was measured both before the sample had been calendered and after calendering. The rebound absorbency is expressed as the percent absorbency of the calendered compound based on the absorbency of the same compound before calendering and indicates the calendering absorbency.

Absorbency returned to gain (%) = [Absorbency of the calendered compound (g) / Absorbency of the compound not calendered (g / g)] * 100 Resistance to Tension; The cut strip test method measured the tensile strength (break) of the composites when they were subjected to a continuously increasing load in a single direction at a constant extension rate. The method used conforms to the standard test ASTM D 5034-95, as well as to the standard federal test methods number 191A method 5102-78, with the following exceptions: sample size 5.08 x 15.24 centimeters, load cell 4.56 kilograms , cross head speed 25 centimeters / minute (a constant rate of extension) and a measurement length of 10.16 centimeters. The results were expressed in units of weight (at break).

The samples were tested in both the machine direction and the cross machine direction and the results are expressed in grams at break. Higher numbers indicate a stronger structure. The specimen was tested, for example, on an Instron 1130 apparatus, available from Instron Corporation, or a Thwing-Albert model INTELLECT II apparatus available from Thwing Albert Instrument Company, 10960 Dutton Road, Philadelphia, Pennsylvania 19154. Additionally, unless noted otherwise, the samples were tested under dry conditions, which include only the added moisture which was necessary to form the compound placed by air. Where noted, some samples were also tested under wet conditions, which added fluid or exudate to the sample to test the performance of resistance under conditions that more closely resemble actual use. In such cases, 10 milliliters of fluid were applied and instantaneously tested to the center of the sample before being subjected to the test as described above.

Examples 1-1 to 1-3; Several composite samples placed by air were made according to the following process. Using Example 1-1 to write the process, in Example 1-1 the pulp fiber (in this case BCTMP) was provided with "SPHINX FLUFF" available from Metsa Serla Group (Tampere, Finland)) and fiberized into a usable fiber shape. The pulp fibers were combined with 5.4% by weight of bicomponent fibers known as Celbond type 255, non-food grade, non-dyed fibers which are bicomponent fibers of polyester core / polyethylene sheath, with a length of 6 millimeters and a 3 mm denier, available from Trevira GmbH & Co from Frankfurt, Germany, the Hoeschst polyester business and were transported through an air stream to a mixing point where they were mixed with and integrally combined with the bicomponent fibers according to the air placement process conventionally described generally in U.S. Patent No. 4,640,810 issued to Laursen et al., assigned to Sean Web of North America, Inc. An air-laid compound of 400 grams per square meter of pulp fiber and 26 grams per square meter of bicomponent fiber which was 0.75 inches (1.90 centimeters) thick was then formed.

There was no compression of the compound placed by air by a compaction roller or a compression roller before heating or cooling the compound.

The bicomponent fibers were then melted by transporting the composite placed by non-compacted air through a conventional forced air binding furnace at a temperature of 335 degrees F (168.3 degrees Celsius), thereby melting the polyethylene sheath. (The desired melt temperature of this particular bicomponent fiber is in the range of 132.2-168.3 degrees C)). When leaving the furnace, the compound placed by air was cooled by the addition of moisture. The cooling solidified the polyethylene sheath, thereby joining the bicomponent fibers to many of the pulp fibers and joining many of the bicomponent fibers together.

Additional cooling and wetting was carried out using a spray atomizer which added an amount of water as noted in the table given below at a rate of 1.019 gallons per minute (3,857.3 liters per minute) to the air-laid compound. A vacuum box under the forming wire applied a vacuum of 1.08 pounds per square inch (7,472 Pa) to pull the water evenly through the compound placed by air. The composite was then rolled onto a roll of 30 inches (76.2 centimeters) wide when cut into narrower widths of about 22.9 centimeters. The rolled composite was then placed in an air-proof bag to maintain the moisture content for a sufficient period for uniform moisture distribution throughout the composite.

The compound placed by moistened air was then removed from the bag and unrolled for calendering. A 0.4 mil sheet layer of fluid impervious polyethylene film (available as SF 181 from Huntsman Corporation of Salt Lake City, UT) was unwound with the compound placed by air and calendered together at a pressure of 2,000 pounds per inch. linear inch (357.2 kilograms per linear centimeter). Five repetitions of the calendered and thin multi-layer absorbent structure thus formed were tested as described above and had the properties as shown in Table 1 below.

Table 1 also includes the data for examples 1-2 and 1-3, which were made as described above except that they had 6.9% and 8.7% respectively of the bicomponent fibers. Absorbency was tested as described above using a sample size of 10.16 x 15.24 centimeters, a soaking time of 24 hours and a draining time of 1 minute.

Table Comparative Examples 1-1 to 1-3; Three repetitions of several air-laid compound samples were created as described above in Example 1, this time using soft wood kraft pulp fibers instead of BCTMP fibers and wetting using a humidity chamber rather than a spray atomizer . The compounds were placed in the humidity chamber set at 21.1 ° C and 70% relative humidity for at least 2 hours. The kraft pulp is a pulp which has been chemically induced in an effort to remove a main part of the pulp lignin. The "kraft or sulphate pulp" is one that has been cooked with strong NaOH plus Na2S to essentially remove the lignin. The average values of the various samples weighed with the variable amounts of the bicomponent fibers are shown below in Table 2. The air placed composite made according to the present invention, (examples 1-1 to 1-3 given above) , exhibited absorbencies which were from 6.7 to 10.2 grams / gram greater than the absorbencies of the comparative examples Cl-1 through Cl-3. In addition, the kraft air-laid compound made according to the process of the present invention did not have a return spring; it will not gain its volume or thickness again, thus affecting its ability to absorb. The ability to regain the volume or thickness when saturated is exhibited only by the air-laid compound of the present invention and is the reason for the improvement in the absorbency of the compound. Once it is moistened it expands, thereby gaining its thickness and returning and absorbing the liquid.

Table Comparative Examples 2; A comparative sample placed by air was made, as described above in Example 1 except that the compound placed by air was compacted directly after forming the compound on the forming wire as is done in a conventional air-laying process, and in addition that the calendering pressure was 660 kilograms per linear centimeter. The air-laid compound was made of BCTMP pulp fiber and a bicomponent fiber of a polyethylene sheath and of a polypropylene core known as Chisso HR6 bicomponent fiber available from Chisso Corporation of Osaka, Japan. The bicomponent fiber having a length of 3.81 centimeters and a denier of 3 was difficult to open in the process (for example separating the compressed masses of fibers in loose strands) because the length of the fiber said bicomponent fiber became entangled with s + i same because the length was very long. The absorbency was tested by a soaking time of 1 minute and a draining time of 3 seconds for a sample size of 10.16 by 17.78 centimeters. The absorbance was measured at 12.23 g / g.

Comparative Examples 3 and 4 A composite sample placed by air was made as described in comparative example 2 except that the compound was further compressed at a pressure of about 35.7 kilograms per linear centimeter directly after heating in the oven (so that the compound placed by air it was not cooled before compression, no film was added and calendering was not carried out (3,700 pounds per linear inch) BCTMP pulp fiber was used to make the compound but this time using comparative example 3 Trevira bicomponent and for comparative example 4 a polyolefin fiber known as T-410 of 2.2 denier per filament (dpf) polyethylene fiber, available from Hercules Incorporated of Wilmington, Delaware, which is not a bicomponent fiber, but is a biconstituent mixture of 85/15 polyethylene / polypropylene, with 1 denier of 3. The polyolefin fiber is a fiber formed of two polymers and it was extruded from the same extruder as a mixture in a monofibre. This sample did not have wet integrity when it was prepared as an air-laid compound according to the present invention because the polyolefin fibers tended to melt together rather than melt and agglutinate with the pulp fibers as can be seen in Figure 9. Figure 9 is an electron scanning electron microscope photograph of a 200x magnification of a composite placed by uncalendered air of 520 grams per square meter of total weight composed of 500 grams per square meter of pulp fiber, 8.7 % by weight of the mixed biconstituent fiber of polyethylene / polypropylene, and 4% by weight of moisture. Even at higher melting temperatures, the biconstituent fibers tended to melt in a balloon rather than melt and cook with the pulp fibers. The tensile strength was tested for two repetitions as shown below in tables 3 and 4 which were the first indication that the bicomponent fiber provides significantly improved tensile strength to the compound placed by air over the biconstituent fiber. .

Table Table Example 2 and Comparative Example 5; The following data shows that the absorbency of the compound placed by air is increased when the compression / compaction is removed from the "conventional" air placement process. Both examples were made using a Trevira bicomponent fiber and example 2 was made as described above for example 1 in which the compound placed by air was not contacted after the formation. Comparative example 5 was made as described above for example 1 except that there was not a compaction roller used to compact the compound placed by air directly after it was formed. The absorbance was tested and reported below in Table 5 along with the standard deviation. Example 2 represents the average of 5 repetitions, while comparative example 5 represents the average of 20 repetitions. An increase of 3.84 grams / gram (24.4% increase) in absorbency was found when the compaction roller was removed.

Table Examples 3-1 to 3-17; A composite sample placed by air was made as described above in Example 1 of 400 grams per square meter of pulp fiber and 32 grams per square meter (8% by weight of pulp fiber) bicomponent fiber, except that the moisture It was added using a spray humidifier held in the hand and the compound was calendered at a pressure of 2,000 pounds per linear inch with several aggregate percentages of moisture, as shown in Table 6. The samples were prepared having an area of 130.64 centimeters squares. Of the resulting materials, calendered material with moisture between 11.2% and 18.1% achieved the desired balance of weight, thickness and density properties, while also having a non-lint and uniform appearance.

Table Examples 4-1 and 4-2; The compounds were made as described above in Example 1 and the gain again of the absorbency was tested as shown in Table 7. The uncalendered absorbency is the absorbance of a sample which was tested after the sample was It had warmed up, but before the addition of water and the calendering. The sample was tested with a soaking time of 1 minute, a draining time of 1 minute and 1,500 milliliters of water. The calendered absorbance was as described above for a sample of the present invention.

Table Examples 5 and Comparative Example 6; In Table 8 the density was measured for Example 5 which was done as in Example 1 except that no film was applied and Comparative Example 6 which was done as in Comparative Example 3 given above. A density range of 0.5 and 1 gram per cubic centimeter is desired because the calendered and thin air-laid compounds within their density range exhibit an improvement in properties as described above.

Table 8 Comparative Example 7 and Comparative Example 8; Table 9 shows an improvement in absorbency when the compaction step of the compound placed by air directly after the heating is removed and the compound placed by air is cooled before calendering. Comparative example 7 and comparative example 8 were made as described above for example 1 except that both samples were compacted directly after compounding on the forming wire and no film was added. The comparative example 8 was further compressed at a pressure of about 35.7 kilograms per linear centimeter directly directly after heating in the oven. The comparative example 7 represents the average of two repetitions while the comparative example 8 was a repetition and the absorbance was tested for one minute of soaking time, a draining time of 3 seconds, and the sample size was 10.16 x 17.78 centimeters.

Table 9 Example 6 and Comparative Examples 9-11; It has been hypothesized that prior art chicken absorbent pads made of multi-layer tissue actually pull chicken liquid (desorption) when the pad (tissue) expands when it is moistened (beyond the film layer) and the tissue gets in contact with the chicken. The fluid lost by a piece of chicken breast without bone and without skin when in contact with the various pads was tested and the results are summarized in Table 10 shown below. Comparative example 9 was of an absorbent pad available from Sealed Air Company which was a multi-layered layer structure having a perforated film layer on the upper surface of a 17-layer tissue layer, wherein the tissue layer was expanded in the x and y directions when it got wet. In the test, the film layer was placed in contact with the chicken breast. Comparative example 10 was the absorbent pad of comparative example 9 except that the tissue layer was in contact with the chicken instead of the film layer. Example 6 was an air placed composite made according to the present invention as described in example 1 given above (493 grams per square meter of basis weight, 5.3% bicomponent fiber, 11.4% moisture) having a layer of fluid permeable film having grooves, wherein the compound expanded in the z direction when it was wetted. Comparative Example 11 was only one layer of film, having a thickness of 0.4 mils, made of polyethylene as available from Huntsman Company. Comparative example 11 indicates that an absorption did not occur due to the film layer. The original weight of the chicken and the system ("the system") was a closed container which included the absorbent pad) without the chicken was determined before the test. The test involves placing the chicken in contact with each material within a closed system for 24 hours. The chicken is removed and the weight of the system is determined. The weight added to the system is the fluid lost by the chicken.

Percent by weight lost by chicken (%) = [System after test - System before test (g / g)] / original weight of chicken (g) x 100.

Using fresh ranch chicken, the test showed that the chicken in contact with the tissue pad (comparative example 9) and the film / tissue absorbent pad (comparative example 10) was desorbed by these pads.

For the air-laid compound of the present invention (example 6), less fluid was lost which indicates that the compound placed by air does not cause as much desorption of the chicken products as do the known prior pads. The film only (comparative example 11) is the control sample in which the fluids were not desorbed.

Table 10 Example 7-1 to 7-3 and Comparative Examples 12-1 to 12-3; Table 11 below shows the composition for the samples made as described in Example 1 except that the comparative examples were not calendered and the film was not added to any of these samples.

Table 11 Table 12 shows the data for compounds made without calendering, while Table 13 shows the data for compounds which are calendered and made according to the present invention. Improvements in tensile strength and stiffness can be seen in the examples of the invention, without significantly compromising absorbency (see Table 15 given below).

Table 12 N.D. = No e ecc n Examples 8-1 to 8-3; Table 14 shows the composition for samples made as described in example 7 except as indicated above that a 0.4 mil polyethylene film layer was inherited to examples 8-1 to 8-3. Table 15 shows the absorbency and wet integrity results for examples 8 (the example made according to the present invention including calendering) and comparative examples 12 (compositions as shown above in table 11 and were made without calendering). These results indicate that the absorbance is not compromised when the examples were made according to the present invention.

Table 14 Comparative Example 13; As a comparative example, a sample was made according to the composition and process described in commonly assigned United States of America patent number 4,100,324 issued to Anderson et al.

The BCTMP was used as described above and instead of the bicomponent fiber, 10% by weight of binder fibers blown with polypropylene melt was added to the compound as described in the patent of the United States of America number 4, 00.324. The compound known as "coform" was formed as described in another way above in example 1. Table 16 shows the absorbency of the coform compound which was considerably lower than the air-laid compounds made according to the present invention.

Table 16 Having described the various embodiments of the present invention with reference to the accompanying figures, it will be appreciated that various changes and modifications may be made without departing from the scope or spirit of the invention.

Claims (34)

R E I V I N D I C A C I O N S

1. A compound placed by calendered and thin air comprising: a) pulp fibers; Y b) at least about 2% by weight of bicomponent fiber comprising a first polymer component and a second polymer component, wherein said first polymer component is melted at a temperature lower than the melt temperature of said polymer component. second polymer component, and further wherein said bicomponent fibers are integrally mixed and are evenly dispersed with said pulp fibers and said first polymer component is bonded to many of said pulp fibers and bicomponent fibers; wherein the percent by weight is based on the total weight of a) and b), and also wherein said air-laid composite has a drop stiffness of at least about 5 centimeters, an absorbency of at least about of 12 g / g, and a dry tensile strength of at least about 1,300.

2. The compound, placed by air, calendered and thin as claimed in clause 1 characterized in that the compound expands in contact with polar fluids.

3. The compound, placed by air, calendered and thin, as claimed in clause 2, characterized in that the polar fluid is water or water-based solutions.

4. The compound, placed by air, calendered and thin as claimed in clause 4, characterized in that said expansion is of the compressed thickness of said compound.

5. The compound, placed by air, calendered and thin as claimed in clause 1 characterized in that said bicomponent fiber is a bicomponent sheath / core fiber wherein said sheath is said first polymer component and said core is said second polymer component of said bicomponent fiber.

6. The compound, placed by air, calendered and thin as claimed in clause 5 further characterized because it has a density of at least about 0.5 g / cc.

7. The compound, placed by air, calendered and thin as claimed in clause 6 further characterized because it has a return to gain absorbency of at least about 70%.

8. The compound, placed by air, calendered and thin as claimed in clause 7 further characterized because it comprises at least about 2-10% by weight of said bicomponent fiber.

9. The compound, placed by air, calendered and thin as claimed in clause 8 characterized in that said bicomponent fiber is a thermoplastic fiber.

10. The compound, placed by air, calendered and thin as claimed in clause 9, characterized in that said thermoplastic bicomponent fiber further comprises a polyethylene sheath and a polyester core.

11. The compound, placed by air, calendered and thin as claimed in clause 10, characterized in that said bicomponent fiber is a fiber of basic length.

12. The compound, placed by air, calendered and thin as claimed in clause 11, characterized in that said bicomponent fiber is a fiber of basic length having a length that does not exceed about 3.81 centimeters.

13. The compound, placed by air, calendered and thin as claimed in clause 12, characterized in that said pulp fibers are at least one of the thermomechanical pulp fiber, a quimotermomechanical pulp fiber or a quimomechanical pulp fiber.

14. The compound, placed by air, calendered and thin as claimed in clause 13, characterized in that the pulp fibers are quimotermomechanical pulp fibers.

15. The compound, placed by air, calendered and thin as claimed in clause 14 further characterized because it comprises at least about 5% by weight to about 20% by weight of moisture.

16. The compound, placed by air, calendered and thin as claimed in clause 15 further characterized in that it comprises at least one antimicrobial agent, one superabsorbent, one fluid thickener, one activated carbon fiber or granule, one perfume, one optical brightener, a photostability promoter such as a salt or surfactant.

17. A calendered and thin multi-layer absorbent structure comprising: a) a compound placed by thin calendered air further comprising: i) pulp fibers; Y ii) at least about 2% by weight of bicomponent fiber having a first polymer component and a second polymer component, wherein said first polymer component is melted at a temperature lower than the melting temperature of said polymer component. second polymer component, and further wherein said bicomponent fibers are integrally mixed and evenly dispersed with said pulp fibers and said first polymer component is bonded to many of said pulp fibers and bicomponent fibers; wherein the percent by weight is based on the total weight of i) and ii); Y b) at least one sheet layer; wherein said multi-layer absorbent structure has a drop rigidity of at least about 5 centimeters, an absorbency of at least about 12 g / g, and a dry tensile strength of at least around 1,300.

18. The calendered and thin multi-layer absorbent structure as claimed in clause 17 characterized in that said sheet layer is a film layer, a tissue layer, a melt spray layer or a non-woven layer.

19. The calendered and thin multi-layer absorbent structure as claimed in clause 18 characterized in that said sheet layer is a fluid impervious film layer.

20. The calendered and thin multi-layer absorbent structure as claimed in clause 17 characterized in that the sheet layer is a layer of fluid-permeable film.

21. The calendered and thin multi-layer absorbent structure as claimed in clause 19 characterized in that said layer of fluid impervious film is on one side of said calendered and thin multi-layer absorbent structure and further includes a film layer permeable to the film. fluid on the opposite side of said calendered and thin multi-layer absorbent structure ..

22. A process for preparing a compound placed by calendered and thin air comprising: a) provide pulp fibers; b) mixing integrally and evenly dispersing at least about 2% by weight of bicomponent fiber with said pulp fibers, wherein said bicomponent fiber has a first polymer component and a second polymer component and said first polymer component melts at a temperature lower than the melting temperature of said second polymer component; c) forming a composite placed by air with said pulp fibers and said bicomponent fiber without compressing said air-laid compound; d) heating said air-placed compound by melting a part of said first component of said bicomponent fibers; e) cooling said air-laid compound thereby binding many of said bicomponent fibers to said pulp fibers and bicomponent fibers; f) moistening said air-laid compound so that said air-placed compound further comprises an aggregate of sufficient moisture to facilitate further bonding; g) then calendering said compound placed by air to form a compound placed by calendered and thin air having a drop stiffness of at least 5 centimeters, an absorbency of at least about 12 9/9 / Y a resistance to the dry stress of at least about 1,300, and wherein the percent by weight is based on the total weight of said pulp fibers and bicomponent fibers.

23. The process as claimed in clause 22 further characterized because the cooling steps (step e) and wetting (step f) are carried out simultaneously.

24. The process as claimed in clause 22 further characterized in that the heating steps (step d) and wetting steps (step f) are carried out simultaneously.

25. The process as claimed in clause 23 further characterized in that it comprises the step of clamping at least one layer of sheet to said compound placed by air to form a multi-layer absorbent structure.

26. The process as claimed in clause 25 characterized in that said sheet layer is attached to said compound placed by air by a corona treatment combined with said calendering.

27. The process as claimed in clause 26 characterized in that said wetting is provided by a spray atomizer.

28. The process as claimed in clause 27 characterized in that said calendering is carried out in the range of 143-715 kilograms per linear centimeter at room temperature.

29. An absorbent article made of a compound placed by calendered and thin air as claimed in clause 1.

30. An absorbent article made of a calendered and thin multi-layer absorbent structure as claimed in clause 17.

31. An absorbent pad for use in sending envelopes or packages for handling fluids, said absorbent pad is made of the calendered and thin multi-layer absorbent structure as claimed in clause 17.

32. An absorbent pad for use in food packaging made of the calendered and thin multi-layer absorbent structure as claimed in clause 17.

33. A personal care product made of air-laid, calendered and thin compound as claimed in clause 1.

34. A personal care product made of the calendered and thin multi-layer absorbent structure as claimed in clause 17. SUMMARY The present invention relates to a compound placed by air which is made of pulp fibers of at least about 2% by weight of bicomponent fiber and moisture. The compound placed by air is unique in that the uniformly even compound is made which with calendering, becomes a thin structure which maintains a significant absorbency when saturated. The bicomponent fibers of the present invention include a first polymer component and a second polymer component and the first polymer component is melted at a lower temperature than the melting temperature of the second polymer component. The mixing of the pulp fibers with the bicomponent fibers is done in such a way that the fibers are evenly dispersed in the compound placed by air. This air-laid compound is then heated so that at least a portion of the first polymer component of the bicomponent fiber is melted, which binds the bicomponent fibers to many of the bicomponent pulp fibers when cooled. Moisture is added to the compound to further facilitate bonding when the compound is subsequently subjected to calendering. Optionally, a sheet layer can be attached to the composite placed by air to form a multi-layer absorbent structure. Such compounds and absorbent structures are characterized by a drop stiffness of at least about 5 centimeters, an absorbency of at least about 12 g / g, and a dry tensile strength of at least about of 1,300.