MXPA01006251A - Reduced die lip buildup extrusion of polymer compositions - Google Patents

Abstract

Process for die extrusion of melted polymers that reduces die lip buildup and its deleterious effects. Direct extrusion of mixed polymer pellets and filler concentrate pellets in one embodiment avoids a precompounding step and reduces the tendency of polymer and filler particles to adhere to the exit portion of the die. In other embodiments a reduced die lip radius and lower melt processing temperatures further enhance the benefits obtained. For co-extruded multilayer film embodiments elimination of fillers and antiblock additives in skin layers (18, 20) add to the levels of die lip buildup reduction obtained. Hours of continuous operation without excessive die lip buildup in one arrangement have been increased from a level of 4 to 6 hours, for example, to in excess of 20 hours. Reduced product defect levels have also been attained.

Description

EXTRUSION OF REDUCED MATRIX LIP ACCUMULATION OF POLYMER COMPOSITIONS This application claims the priority of the provisional patent application of the United States of America No. 60 / 112,804 filed on December 18, 1998.

Field of the invention The present invention is directed to the processes for matrix extrusion of polymers and resulting in extruded products. The process of the invention allows extended running times without quenching the extrusion line for cleaning due to the build-up of matrix lip and improves the resulting products.

BACKGROUND OF THE INVENTION Many products today require highly fabricated components and yet, at the same time, they must be produced at a cost consistent with disposable or limited use. By disposable or limited use, it means that the product and / or component is used only a small number of times or possibly only once before being discarded. Examples of such products include, but are not limited to, health-related and surgical products such as gowns and surgical covers, disposable workwear such as covers and lab coats and products. personal care absorbers such as diapers, training pants, incontinence garments, sanitary napkins, bandages, wipes and the like. All these products can and use as components, films and fibrous non-woven fabrics. While both materials are often used interchangeably, the films extend to have superior barrier properties, especially to liquids, while fibrous non-woven fabrics have, among other things, better tactility, comfort and aesthetic properties. When these materials are used in limited use and / or disposable products, the impetus. to maximize the construction properties while reducing the cost is extremely high. For this purpose, it is often desirable to use either a film or a nonwoven to achieve the desired results because the combination often becomes expensive. In the area of films, there have been previous attempts to make multi-layer films with reduced thicknesses. An advantage in the formation of multilayer films is that specific properties can be designed in the film, and, when making multi-layer films, the most expensive ingredients can be relegated to the outer layers where they are most likely to be needed.

Additionally, in the production of a film filled with capacidabd. for breathing is like employing a significant percentage (by weight) of filler such as, for example, calcium carbonate. As is known in the art, the narrowing of the filled film creates a fine pore network which allows the film to continue to act as a barrier to liquids and particulate matter yet still allows air and water vapor to pause through it. In order to obtain a more uniform barrier and vapor transmission properties through the film, it is desirable to have a filler equally distributed throughout the film. Therefore, although such barriers - with the ability to breathe can act as a barrier to liquids and particle matter - they themselves can be a source of unwanted particles (for example the filler :) which can be a source of contamination of matrix lip and accumulation. This accumulation of filler and / or separation can also be an undesirable cause of defects in the various applications or articles used by l_? barrier fabric. A filled film which retains good ability to breathe and low defects levels producing them without the accumulation of matrix lip is therefore desirable. In this regard, there is a continuing need for a multilayer film having outer layers with little or no filler, however, this does not significantly reduce the breathing capacity of the multilayer film. Moreover, many filled films fail to provide a good addition to additional layers, such as, for example, non-woven fabrics. Multilayered films, the ctxales are able to provide good adhesion to a support fabric without loss of ability to breathe are in the same way necessary.

As mentioned, the production of such films and non-wovens has, however, been accompanied by more persistent problems of accumulation of the composition which is extruded at the tip of the die causing loss of machine work for cleaning, often after only a few hours of operation. Various mechanisms are known to facilitate cleaning and maintenance of the dies used for the extrusion of polymer materials, while minimizing the period of loss of work. The molten polymers are extruded through the matrices to form films, yarns, non-woven fabrics, and other forms of finished polymer. Particularly with the polymer compositions containing fillers, while the polymer leaves the matrix, some of the polymer composition clings to the openings of the matrix or "lips", which accumulates on the outer surface of the matrix. This accumulation of the matrix lip gradually increases until it accumulates to a point where it breaks, possibly causing a defect in the product, which can be, for example, in the form of thin spots or tears or otherwise pernicious effects on the texture or other aesthetic properties of the product. Significant engineering goes down in the design of the matrices and selection of extrusion compositions to minimize: that is accumulation. Angled, radiated, convergent and divergent matrix lip geometries are all examples of methods developed to minimize this accumulation. However, no matrix design does not completely eliminate. It is common practice to temporarily stop the extrusion operation, to perform maintenance on the matrix and remove this accumulation.

In U.S. Patent No. 5,435,708 issued thereto, it discloses a meltblown die head with opposing die lips mounted on the lip guides pivotally connected to the respective stop bars. To facilitate cleaning and maintenance of the die, the lips can be swiveled away from the spinning organ in the respective lip guides. This allows to reduce the period of loss of work during maintenance of the matrix, but does not allow maintenance during the operation of the line.

In U.S. Patent No. 5,720,986 issued to Gohlisch et al., It describes an extrusion head having a fixed stationary part in an extrusion installation. The installation includes a plurality of extrusion cylinders. The stationary part has flow channels, each in communication with a respective extrusion cylinder and a common extrusion die. Two external pivoted parts hinged in the stationary part are selectively swingable individually between the closed and open positions. The external parts define an extrusion hole for the die in its closed position. When the external parts are open, maintenance can be carried out in the matrix.

In the patent of the United States of America No. 4,413,973, issued to Peters, describes a matrix which has a removable extrusion plate that covers the die head. The plate can be removed and replaced to minimize the period of lost work required for maintenance. The requested patent application of the States United States serial number 09 / 075,510 registered on May 8, 1998 to Cook entitled "Extruded Matrix System with Removable Insert" describes an insert to clean the tips of the matrix "in the fly".

Also, the selection of the polymer compositions and the extruded structures have varied in an effort to minimize buildup of the matrix lip. For example, the coveted United States patent application serial number granted to McCormack and others entitled "Lower Calibrated Film and Non-Woven Film Laminates" recorded on July 25, 1997 and incorporated herein in its entirety by reference describes the film structures that have thin outer skins that reduce the accumulation of the matrix lip.

A common feature of prior art devices and processes is that a routine cleaning and maintenance requires at least some period of loss of work. While efforts have been made to reduce maintenance and the period of loss of work, it remains a goal to also increase the operating times required between cleanings.

Synthesis of the invention The present invention is directed to the extrusion of matrix products such as films and nonwovens. The films can be: made by conventional film-forming techniques? such as the processes of forming blown and melted coextruded film and those not woven by conventional processes such as spinning and meltblowing. The films in a particular embodiment are created with a core layer made of an extrudable thermoplastic polymer with the core layer defining a first outer surface and a second outer surface. In the basic embodiments of the present invention, the core layer may have a first skin layer attached to the first outer surface of the core layer and a second skin layer attached to the second outer surface of the core layer. In such situations the first skin layer and the second skin layer may have a combined thickness which does not exceed about 15 percent of the total thickness and more desirably for applications that require breathing ability, or the first skin thickness and the second skin thickness exceeds by more than about 7.5 percent of the total thickness of the multilayer film. If desired, one or more of the layers may contain other additives such as, for example, a particulate filler. More typically, such fillers may be mainly used in the core layer at, for example, a weight percentage of at least about 40 percent, based on the total weight of that particular layer, more preferably about 40 percent up to around 70 percent by weight. Typically such multi-capacity films with breathability may have water vapor transmission rates of at least 300 grams per square yard per 24 hours (g / rrr / day) and frequently higher depending on the application.

Such films, nonwovens and laminates have a wide variety of uses including, but not limited to, applications in absorbent articles for personal care including diapers, training underpants, sanitary napkins, devices for incontinence, bandages and the like. These same films and laminates can also be used in articles such as gowns and surgical covers as well as various articles of clothing either as the entire article or simply as a component thereof.

According to the invention the extrusion is of a mixture of pellets which avoids the precomposition steps of the prior art, and in certain embodiments a particular die lip radius and unfilled skin layer in a co-extruded structure are employed. The reduced melting temperatures also increase the benefits of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a schematic illustration of a multilayer film extrusion process.

Figure 2 is a schematic cross section of a film extrusion die tip of the prior art.

Figure 3 is a schematic cross section of a film extrusion die tip useful in the present invention.

Figure 4 is a cross-sectional side view of a multilayer film according to the present invention.

Detailed description of the invention The present invention is directed to matrix extruded products such as fibrous non-woven fabrics and multilayer films, that is, for example, films "having two or more layers.

While it will be exemplified in terms of the extrusion of multilayer film. those with skill in the art will be able to recognize that the invention also applies to the extrusion "of other products that are extruded through a matrix, such as non-wovens blown with fusion.

The figure. 1 schematically illustrates a multilayer film extrusion process. The pellets (not shown) of polymer and filler concentrate are mixed and fed to the extruders 41 at feed locations 101. The extruders 41 further mix and melt the polymer composition and pellets of the filler concentrate and supply them to the former. of casting film 40 which co-extrudes the multilayer film composition 10 directed to cool the roll 42.

Figure 2 schematically illustrates a matrix lip typical of prior art devices. In this case, the composition of said polymer (which can be in the combined form of multiple layers) moves in the direction of the arrow to the exit point 102 formed by sliders 103 of matrix 104. The matrix lip is formed by the ends 105 which have xsxi radius of curvature R ,, in the range of, for example, 8 to 12 mils and made of carbon steel lining with a deformation resistant material such as chromium.

Figure 3 is a similar view like that of Figure 2 except that in this case the matrix 105 has a radius of curvature, R2, in the range of, for example, about 0.5 to 3 mils. In this case, the matrix 105 can be formed of, for example, with a less d_trable stainless steel but resistant to corrosion.

Refer to Figure 4, there is shown, not to scale, a multilayer film 10 which, for purposes of illustration, has been divided on the right side of the drawing. The multilayer film 10 includes a core layer 12 made of an extrudable thermoplastic polymer such as a polyolefin, which includes copolymers and / or mixtures thereof. The core layer 12 has a first outer surface 14 and a second outer surface 16. The core layer also has a core thickness 22. Attached to the first outer surface 14 of the core layer 12 is a first skin layer 22 »Fastened the first outer surface 14 of the core layer 12 is still a first skin layer 18 which has a first skin thickness 24. Fastened the second outer surface 16 of the core layer 12 is a second layer of skin optionally 20 which has a second skin thickness 26. Additionally, the multilayer film 10 has a total thickness 28. Ta? is multi-layer films 10 can be formed by a wide variety of processes well known to those with an ordinary skill in the film-making industry. Two particularly advantageous processes are the processes of coextrusion of molten film and the processes of coextrusion of blown film. In such processes, two or three layers are formed simultaneously and leave the matrix in a multi-layer form. Due to the extremely thin nature of the multilayer films according to the present invention such coextrusion processes will most likely prove to be the most advantageous although it may also be possible to form multilayer films that exhibit separate extrusion processes . For more information regarding such processes, but, for example, the patents of the United States of America Nos. 4,522,203; a polyolefin, which includes copolymers and / or mixtures thereof. The core layer 12 has a first outer surface 14 and a second outer surface 16. The core layer also has a core thickness 22. Attached to the first outer surface 14 of the core layer 12 is a first layer of core. Skin 22. Attached to the first outer surface 14 of the core layer 12 is still a first skin layer 18 which has a first: skin thickness 24. Attached to the second outer surface 16 of the core layer 12 is a second layer optional leather 20 which has a second skin thickness 26. Additionally, the multilayer film 10 has a total thickness of 28. Such multilayer films 10 can be formed by a wide variety of processes well known to those of ordinary skill in the film forming industry. Two particularly advantageous processes are the processes of coextrusion of molten film and the processes of coextrusion of blown film. In such processes, two or three layers are formed simultaneously and leave the matrix in a multi-layered form. Due to the extremely thin nature of the multilayer films according to the present invention such coextrusion processes will most likely prove to be the most advantageous although it may also be possible to form multilayer films using separate extrusion processes. For more information regarding such processes, but, for example, the patents of the United States of America Nos. 4,522,203; 4,494,629 and 4,734,324, each of which is incorporated herein by reference in its entirety.

To additionally reduce the cost of the core layer 12 and / or for the ability to breathe one or more types of fillers can be added, in many cases, to the core layer polymer extrusion mixture. Both inorganic and organic fillers can be used. The fillers should be selected so as not to interfere chemically with and adversely affect the extruded film. These fillers can be used to reduce the amount of polymer that is used for the core layer 12 and / or to impart particular properties such as the ability to breathe and / or the reduction of odor. Examples of fillers may include, but are not limited to, calcium carbonate (CaC03), various types of clay, silica (Si02), alumina, barium sulfate, sodium carbonate, talc, magnesium sulfate, titanium dioxide , zeolites, aluminum sulfate, cellulose-type powders, diatomaceous earth, magnesium sulfate, magnesium carbonate, barium carbonate, kaolin, mica, carbon, calcium oxide, magnesium oxide, aluminum hydroxide, baking soda, pulp powder, wood dust, cellulose derivatives, polymer particles, chitin and chitin derivatives.

The amount of filler that can be used resides within the discretion of the end user, however, addition of from 0 to 80 by weight based on the total weight of core layer 12 are possible. According to one aspect of the invention, the filling is formed as pellets concentrated in a polymer concentration. The filler in such pellets of concentrate and can be even greater, for example, up to 90 percent, or, in some cases, 95 percent while the filler can be diluted in the final extruder. Generally the fillers may be in the form of a particle and usually may have something of an irregular shape with average particle sizes in the range of about 0.1 to about 7 microns. The term "" particle size "as used herein refers to the longest single dimension of the particle.In addition, if enough finders used in combination with a sufficient narrowness in the multilayer film 10, then voids can be created around the particles contained within the core layer 12 in what makes the core layer breathable.The charges of about 40 to about 70 percent by weight of the core layer 12 when combined with narrowness proportion to films which have good ability to breathe.

Such films with the ability to breathe can generally "may have water vapor transmission rates (WVTR) as measured by the normal ASTM E9680, in excess of 300 grams per square meter per 24 hours (g / m2 / day) and more desirably water vapor transmission rates in excess of 800 grams per square meter for 24 hours, 2000 grams per square meter for 24 hours, 3000 grams per square meter for 24 hours, and even 4000 grams per square meter for 24 hours.

The skin caps 18 and 20 may typically include extrudable thermoplastic polymers and / or additives which provide specialized properties to the multilayer film 10. Therefore, the first skin layer 18 and / or the second skin layer 20 and the second skin layer 18 and / or the second skin layer 20. they can be made of polymers which give such properties as antimicrobial activity, water vapor transmission, adhesion properties and / or antiblocking. Therefore, the particular polymers or polymer chosen for skin layer 18 and 20 may depend on the particular attributes desired. Examples of possible polymers that can be used alone or in combination include homopolymers, copolymers and blends of polyolefin as well as ethylene vinyl acetate (EVA), ethylene ethyl acrylate (EEA), acid ethylene acrylic (EAA), ethylene methyl acrylate (EMA), ethylene butyl acrylate (EBA), polyester (PET), nylon (PA), ethylene vinyl alcohol (EVOH), polystyrene (PS) ), polyurethane (PU) and olefinic thermoplastic elastomers which are multi-step reaction products in which a random copolymer of amorphous ethylene propylene is molecularly dispersed in a predominantly binder continued from lower ethylene monomer / higher polypropylene monomer semicrystalline In applications where a good ability to breathe (for example, or a high rate of water vapor transmission) is desired, the foot layers preferably comprise, at least a part, an extrudable water vapor transmitting polymer; examples include, but are not limited to, ethylene vinyl acetate, methyl ethylene acrylate, polystyrene, polyurethane, polyamide, and mixtures thereof. The copolymers of ethylene vinyl acetate and ethylene methyl acrylate preferably contain no more than about 80 percent ethylene by weight of the copolymer. Desirably the skin layer (s) comprise from about 30 percent to about 100 percent water vapor transmitting polymer and from about 0 to about 70 percent by weight of a polyolefin-based polymer, and even more desirable The vapor-transmitting polymer can comprise from about 40 percent to about 60 percent by weight of the skin layer. Additionally, the skin layer may comprise two or more water vapor transmitting polymers such as, for example, 30 percent to 70 percent by weight of ethylene wine acetate or ethylene methyl acrylate with 30 percent to 70 percent by weight. weight polystyrene.

Additionally, it may be desirable to add antiblock material to improve the process and / or prevent unwanted adhesion or a sticky skin layer to other surfactants; As an example, some layers of skin may adhere to the multi-layered film itself when unrolled in a roll. Therefore, it may often be desirable to add from 0 to 10 percent of anti-blocking material to the skin layers, and even more desirable from about 0.5 to about 5 percent by weight. Particulate matter such as diatomaceous earth may be added to the skin layers, although other antiblocking materials may be used that include, but are not limited to, silica earth. Desirably the antiblock particles comprise particles having an average particle size of about 6 to 10 microns. In cases where winding on a roll is not necessary anti-blocking additives may be omitted, and it is a feature of the present invention that the results of accumulation of reduced matrix lip are further increased in such cases. See in this regard, for example, in the online training process described in the provisional United States patent application of Arraérica No. 60 / 101,306 granted to Bradley et al entitled "Processes to be a Laminate of a Film. Without Aging and a Nonwoven Fabric without Aging and Products Produced from Same ™ registered on September 22, 1998, incorporated herein in its entirety.

It may often be desirable to laminate the multilayer film 10 to one or more substrates or capable of support such as a non-woven fabric. The core layer may not have sufficient clamping or adhesive properties to make bonding easier to the backing layer. As a result, the first film layer 18 may comprise a polymer or polymers which exhibit superior adhesion properties and / or a lower bond point than the core layer 12.

A particularly desirable result for personal care applications is to achieve a lower total film thickness and, important, the film layers which are only a small percentage of the total thickness of the multilayer film 10. In the three layer film constructions in such cases the combined thickness of the first skin layer 18 and the second layer of skin 20 often will not exceed 15 percent of the total thickness and, generally, the first layer of skin 18 will frequently not exceed more than 7.5 percent and even more desirably each foot layer in does not exceed more than 5 percent of the total thickness of the film 28. The same is also true with respect to the second skin layer 20. In a further aspect, the skin layer or the layers may each have an individual thickness of 24, 26 or less than about 2 microns , desirably less about 1.0 microns and still more desirably less than about 0.5 microns. As a result, the thickness of the core 22 comprises at least 85 percent of the total thickness 28 and the first skin layer 18 and the second skin layer 20 each will generally be able to comprise no more than 7.5 percent of the total thickness 28. Generally , it has been possible to create thin films with total thickness, around 30 microns are less and in certain applications with layers of skin that do not extend 2 microns. Desirably, the total thickness twenty-eight is less than about 25 microns and even more desirable in less than about 20 microns. This possible disposal by first forming a multilayer film 10 and then narrowing or orienting the film in the machine direction, as explained in more detail below, such that the resulting multilayer film 10 has the increased strength properties in the machine direction or "MD", for example, the direction which is parallel to the direction of the film while it is taken out of the film extrusion equipment.

The resulting film can be laminated to one or more support layers such as fibrous non-woven fabrics. The manufacture of such fibrous non-woven fabrics is well known to those of ordinary skill in the art of non-woven manufacturing. Such fibrous non-woven fabrics can add additional properties to the multilayer film 10, such as a softer, fabric-like feel. This is particularly advantageous when the multilayer film 10 is being used as a barrier layer for liquids in such applications as outer covers for absorbent articles for personal care and as barrier materials for room cleaning applications, surgical and hospital such as, for example, surgical covers, robes and other forms of clothing.

The attachment of the support layers to the first skin layer 18 and the second skin layer 20 obey by the use of a separate adhesive such as hot melt and solvent based adhesives or through the use of heat and / or pressure as in the heated bonding rolls. With a result, it may be desirable to design either or both sides the first skin layer 1 = 8 and the second skin layer 20 so that they have inherent adhesive properties to facilitate the rolling process.

A particularly advantageous support layer is a fibrous non-woven fabric. Such fabrics can be formed from a number of processes including, but not limited to, processes linked by spinning, melt blown, hydroentanglement, air laid and bonded carded fabric. The meltblown fibers are formed by extruding molten thermoplastic material through a plurality of capillaries, usually circular, thin as fused wires or filaments in a gas stream usually hot at high speed such as air, which attenuates the filaments of molten thermoplastic material to reduce their diameters.

Then, the meltblown fibers are transported by the gas stream usually hot at high speed and are deposited on a collection surface to form a randomly dispersed, scattered, confused blown fabric. The process of blowing confusion in a known and is described in several patents and publications, including the NRL report, "Manufacture of Superfine Organic Fibers" by B.A. Wendt, E.L. Boone and C.D. Fluhartyr report NRL 5265, "An Improved Device for the Formation of Superfine Thermoplastic Fibers" by K.D. Lawrence, R.T, Likas, J.A. Young; U.S. Patent No. 3,676,242, issued July 11, 1972, to Prentice; and U.S. Patent No. 3,849,241, issued November 19, 1974, to Butin et al. The aforementioned references are incorporated herein by reference in their entirety.

Spunbonded fibers are formed by extruding a molten thermoplastic material as filaments from a capillary capillary, usually circular, fine in a. spinner organ with the diameter of the extrudate filaments being then rapidly reduced, for example, by no-passing or ejection of fluid pull or other well-known spinning linkage mechanisms. The production of spun-bonded woven fabrics are illustrated in the patents such as U.S. Patent No. 4,340,563 issued to Appel et al .; U.S. Patent No. 3,802,817 issued to Matsuki et al .; the patent of the United States of America No. 3,692,618 issued to Dorschner and others; to patent of the United States America No. 3,338,992 granted to Kinney; U.S. Patent No. 3,276,944 issued to Levy; U.S. Patent No. 3,502,538 issued to Peterson; the patent of the United States of America No. 3,502,763 granted to Hartman; the patent of the United States of America No. 3, and 542,615 granted to Dobo and others; U.S. Patent No. 5,382,400 issued to Pike et al .; and Canadian Patent No. 803,714 issued to Harmon. All of the aforementioned references are incorporated herein by reference in their entirety. A yarn-bonded fabric of 20 or 70 grams per square meter (gsm) such as, for example, polypropylene fibers is an example of a support fabric.

Multilayer security layers can also be used. Examples of such materials may include, for example, spunbonded / meltblown laminates and spunbond / meltblown / spunbonded laminates as taught in U.S. Patent No. 4,041,203 granted to Brock and others which is incorporated herein by reference in its entirety.

The carded and bound fabrics are made of basic fibers which are usually acquired in bales. The bales are placed in a collector which separates the fibers. Then the fibers are sent through a carding or combination unit which also breaks and aligns the basic fibers in the machine direction so as to form a fibrous nonwoven fabric oriented towards the machine direction. Once the tissue has been formed, and is then joined by one or more of several joining methods. A bonding method is the bonding of powder wherein a powder adhesive is distributed through the tissue and then activated, usually by heating the fabric and the adhesive with hot air. Another joining method is pattern bonding where heated calendering rolls or ultrasonic bonding equipment is used to join the fibers together, usually in a localized bonding pattern although the bond can be attached across its entire surface if so it is desired. When using bicomponent basic fibers, air-binding equipment is, for many applications, especially advantageous.

A process for forming the multilayer film 10 is shown in Figure 1 of the drawings. Referring to the figure, the multilayer film 10 is formed of a coextrusion film apparatus 40 such as a blow or blow unit as previously described above. Typically the apparatus 40 may include two or more polymer extruders 41. In accordance with one aspect of the present invention, the reduced melting temperatures are used initiates found to contribute in reducing the build-up of matrix lip. While it is not intended to limit the invention to a particular theory, it is believed that the effects of lower shearing results in reduced thermal degradation of the polymers and the tendency of the extrudate to accumulate in the matrix lip is also reduced. These benefits have been obtained, for example, by operating within a range of up to about 135 ° C above the lowermost casting component. As may be apparent to those with a skill in the art, compositions and equipment configurations can be selected to maximize operation at these lower temperatures. The multi-stage film is extruded in a cooling roll 42 which may have a pattern to impart a pattern to the freshly formed film. This is particularly advantageous to reduce the brightness of the film and give it a matte finish. Using a three layer film construction as shown in Figure 4, typically in the multilayer film 10, as initially formed, it may have a total thickness of 28 of about 40 micraaies or more with the first layer of skin 18 and each skin layer 20 has an initial thickness of 3 microns or more which collectively may be approximately 15 percent of total initial thickness in a construction as in Figure 4.

From the coextrusion film apparatus 40 the film 10 can be directed to a film shrinkage unit (not shown) such as a machine direction finder or "MD" Or which is a device commercially available from vendors such as the Marshall and Williams Company of Providende, Rhode Island. The apparatus has a plurality of nip rolls which narrow and thin the multilayer film 10 in the machine direction of the film which is the path direction of the film 10 through the process. After leaving the film narrowing unit, the film 10 for applications of disposable personal care products can stop a maximum thickness of approximately thirty microns and each of the skin layers can have a maximum thickness of no more than about 2 microns which in turn collectively less; about 15 percent of the total film and more desirably less than 10 percent of the total film thickness.

As previously mentioned, the multilayer film 10 and the laminates that include it can be used in a wide variety of applications in the least of which include absorbent articles for personal care such as diapers, underpants for training , devices for incontinence and products for feminine hygiene such as sanitary napkins.

Other uses for the multilayer film and the laminates of multilayer film backing layers according to the present invention include, but are not limited to, gowns and surgical covers, wipes, barrier materials and clothing items or parts thereof that includes such items as work clothes and lab coats.

Examples All the films of the examples were cast films of three layers, with two skin layers or external layers in each example being the same although these varied in some cases from example to example.

Example 1 (comparative) In Example 1 the core layer was formed of pellets previously composed of a simple composition that includes, in a percentage of basis weight a based on the total weight of the layer, 50 percent calcium carbonate and FL 2029® with a size of average particle of 1 micron and a superior cut of 7 microns. The calcium carbonate obtained from the English China Clay and has a coating of 1.2 percent of behenic acid. The core layer also included 45 percent low density linear polyethylene (LLDPE) NG 3310 from the Dow Chemical Company, 4.8 percent low density polyethylene 40 from 12 from Dow Chemical Company and 0.2 percent from antioxidant B900 from Ciba a Specialties Company of Tarrytown, New York.

The two skin layers or outer layers on the opposite sides of the core layer comprise 45.1 percent Himont KS357P Catalloy® polymer from Himont U.S.A. , 4 percent antiblocking of diplomacy soil, 0.5 of antioxidant to B900, and 50.4 percent of Exxon 768.36 (28 percent of ethylene vinyl acetate copolymer). The Himont Catalloy® polymer is an olefinic thermoplastic elastomer or TPO multi-step reaction product wherein a random amorphous ethylene propylene copolymer is molecularly dispersed in a predominantly continuous binder of ethylene monomer of semicrystalline higher polypropylene lower monomer. The antiblock composed of Superfloss® ditomacea earth. The Superfloss® ditomacea soil antiblock is available from the Celite Corporation. The Exxon 768.36 is available from the Exxon Chemical Company of Housfton, Texas.

The die lip radius was around 8 to 12 mils and the equipment was as described in the previously described application to Bradley et al. The three layer film extruded using a melt extrusion equipment of the type described above. The outlet melting temperature for the skin layers was measured as being 450 ° F and for the core was 430 ° F. This process typifies the previous multilayer film extrusion processes which have historically had excessive extruded matrix lip buildup after about 4 to 6 hours of running time. The excess of matrix lip accumulation is determined lowered in the product specifications that are related to, for example, the hole and other defect levels in terms of size and / or frequency. While the economy of the process may dictate particular values, the present invention may differentiate through improved results without the importance of the specific numbers involved in substantially all cases. The same standards were used in each of the examples.

Example ÍA Example 1 was repeated except that the radius of the matrix lip the curvature was reduced to about 1 thousand. Based on two runs, the accumulation time of excessive matrix lip was in the range of 3 to 4 hours and 6 to 8 hours.

Example 2 Example IA was repeated except that in no antiblocking it was included in the skin layers that then constituted 50.4 percent Exxon 768.36, 0.5 percent antioxidant, and 49.1 percent Cattaloy KP 357P. The average accumulation time of excessive matrix lip was around 12 hours.

Example 3 In Example 3 the core layer was, in a percentage of basis weight based on the total weight of the layer, 67 percent of a pellet containing 75 percent ECC Supercoat® calcium carbonate »20 percent Dow 2517 polyethylene low linear density, 4.8 percent Dow 4012 low density polyethylene and 0.2 percent Ciba B900. In these pellets were mixed with 33 percent 100 percent pellets of Dow 2047 AC linear low density polyethylene, and the pellet mixture was fed directly to the extruder. The precomposite step was avoided from the earlier mixes.

The two skin layers or outer layers on opposite sides of the core layer comprised the compositions of Example IA included in the Superfloss® antiblock.

The three layer film can be taught using cast extrusion equipment of the type described above. In this case the extrusion casting temperature for the skin layers was 410 ° F and the melting temperature for the coreless layer was 400 ° F. In this case the extrusion continued for 5 hours without significant evidence of matrix lip accumulation. This run was continuous as described in the following example.

Example 4 The run of Example 3 was continued except that the anti-block supply of the skin layers was discontinued, and the skin layers then had the composition of Example 2. The 5 hour run of Example 3 continued for an additional 15 hours sim no build-up of significant matrix lip when it was discontinued because the extrudable supply was exhausted.

Therefore, it has been determined that according to the invention it is possible to run the matrix extrusion process for a period understood without any accumulation of excessive matrix lip which needs the cleaning of the die tip and an interruption of the process. As is evident, this represents a substantial cost savings and is highly advantageous. Moreover, according to the invention these results can be obtained with extruded ones that are cheap and that represent additional opportunities for cost savings. While the invention is not to be limited by any particular theory, it is believed producible that avoiding the prior composition of the extrudates before being added to the extruder results in reduced thermal degradation and a molecular weight distribution that provides viscosity and other attributes that facilitate extrusion and allow for additional steel benefits obtained from the reduced radii of curvature of the die-lip configurations, reduced melt temperatures, -and in the filler-free skin layer compositions, for example.

While the invention has been described in detail with respect to the specific embodiments thereof, and particularly and by the examples described herein, it may be apparent to those with skill in the art and various alterations, modifications and other changes may be made. without departing from the spirit and scope of the present invention. It is therefore the intention that all such alterations, modifications and other changes may be encompassed by the claims.

Claims (17)

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

1. A process for melt extrusion of thermoplastic articles with an accumulation of reduced matrix lip comprising the steps of: to. providing at least two sources of compositions containing a molten thermoplastic polymer; b. combining said compositions into a layered matrix wherein one of said layers is exposed and comprises no more than 15% of the total thickness of said layers; Y c. Extrude said combined layers through the matrix lips which form the outlet of said matrix.

2. The process as claimed in clause 1, characterized in that the temperature of said combined layers at the moment of extrusion is not higher than 135 ° C above the lowest filtration point of the melting component of said composition.

3. The process as claimed in clause 1, characterized in that said exposed layer composition is devoid of antiblock additives.

4. The process as claimed in clause 1, characterized in that the total thickness of said extruded combined layers is at least about 40 microns and said exposed layer has u_? thickness of about 3 microns or less.

5. The process as claimed in clause 4, characterized in that said exposed layer has a thickness of about 2 microns or less.

6. The process as claimed in clause 5, characterized in that said exposed layer contains an additive selected from the group consisting of EMA and EVA.

7. The process as claimed in clause 6, characterized pcexque said exposed layer has a thickness of about 1 miera or less.

8. The process as claimed in clause 1, characterized in that the extruded article is a multilayer film.

9. The process as claimed in clause 1, characterized in that said extruded article is a multi-layer fiber.

10. The process as claimed in clause 1, characterized in that said matrix lips have a radius of curvature in the range of from about 0.5 mils to about 3 mils.

11. The process as claimed in clause 1, characterized in that at least one of said layers contains a filler in an amount in the range of up to about 80% by weight.

12. The process as claimed in clause 11, characterized in that said extruded article is a multi-layer film and includes the additional step of stretching said film to impart a moisture vapor transmission rate of at least about 300 grams per square meter per 24 hours.

13. Such process and eat is claimed in clause 12, characterized in that said imparted steam transmission rate is at least about 2,000 grams per square meter per 24 hours.

14. The process as claimed in clause 13, characterized in that it includes the additional step of forming a laminate by combining said film with a non-woven layer.

15. The process as claimed in clause 1, characterized in that said exposed layer composition contains an antiblocking agent.

16. The process as claimed in clause 15, characterized in that said antiblock is contained in an amount within the range of from about 0.5 to about 5% by weight.

17. The process as claimed in clause 16, characterized in that said antiblock is selected from the group consisting of diatomaceous earth and ground silica.