Patent Application
20200139612
Articles with one or more structured surfaces are useful in a variety of applications (e.g., abrasive discs, assembly of automobile parts, and disposable absorbent articles). The articles may be provided as films that exhibit, for example, increased surface area, mechanical fastening structures, or optical properties.
Mechanical fasteners, which are also called hook and loop fasteners, typically include a plurality of closely spaced upstanding projections with loop-engaging heads useful as hook members, and loop members typically include a plurality of woven, nonwoven, or knitted loops. Mechanical fasteners are useful for providing releasable attachment in numerous applications. For example, mechanical fasteners are widely used in wearable disposable absorbent articles to fasten such articles around the body of a person. In typical configurations, a hook strip or patch on a fastening tab attached to the rear waist portion of a diaper or incontinence garment, for example, can fasten to a landing zone of loop material on the front waist region, or the hook strip or patch can fasten to the backsheet (e.g., nonwoven backsheet) of the diaper or incontinence garment in the front waist region. Mechanical fasteners are also useful for disposable articles such as sanitary napkins. A sanitary napkin typically includes a backsheet that is intended to be placed adjacent to the wearer's undergarment. The backsheet may comprise hook fastener elements to securely attach the sanitary napkin to the undergarment, which mechanically engages with the hook fastener elements.
Structured surfaces can be joined to a fabric to provide a laminate with higher strength, softness, and/or function in comparison to the structured surface itself. For example, U.S. Pat. No. 5,260,015 (Kennedy) discloses providing a hook and loop fastener with a surface opposite the surface containing upstanding hooks that is suitable for adhering to other materials or that provides loops for a back-to-back hook and loop fastener. U.S. Pat. No. 6,582,642 (Buzzell et al.) and U.S. Pat. No. 7,897,078 (Petersen et al.) disclose laminates formed from stretched thermoplastic layers having upstanding male fastening elements. U.S. Pat. No. 7,373,698 (Erdman et al.) and U.S. Pat. Appl. Pub. No. 2013/0289514 (Cheng) disclose bonding a hook material to a tab material with a pattern of bonding sites. Mechanical fasteners are reported to be joinable to a second material using adhesives, extrusion lamination, thermal bonding, ultrasonic welding, and sewing.
The manufacture of products such as disposable absorbent articles involves the use of narrow webs of mechanical fastening materials. Due to their narrow widths and flexibility, these materials can present handling difficulties. For example, web materials are sometimes processed in the form of planetary wound rolls, often called “pancake rolls” where the web material is wound directly upon itself. Narrow planetary wound rolls can be unstable and tend to warp or fall apart when lifted. Support members can be used to protect the roll from distortion or damage, but that introduces a new structure and increases the processing cost of the web material and the cost to change rolls. Moreover, individual planetary wound rolls can have a relatively short run time, which undesirably leads to frequent roll changes.
To circumvent these difficulties, narrow web materials can be level wound. By oscillating the narrow web material back and forth across the roll during winding, the level winding process yields a stable roll form that resists damage. Again, however, the level winding process can add significant expense to the web material.
For ease of handling, mechanical fastener webs are often used in wide formats. These wide webs often can include strips web material separated by splitting channels or perforations. Processing of such wide webs often requires simultaneously separating the strips of web material using specialized equipment such as splitting combs or slitting blades. Not only is such specialized equipment expensive to obtain and operate, but its use is practical only for converting operations that can accommodate simultaneous processing of multiple strips.
The present disclosure provides a method of making a laminate in which a thermoplastic layer is stretched and laminated to a substrate in-line.
In one aspect, the present disclosure provides a method of making a laminate. The method includes stretching a thermoplastic layer in a machine direction so that it plastically deforms and decreases in width by at least 25 percent and subsequently laminating the thermoplastic layer to a substrate to form the laminate. The stretching and laminating are completed in-line. After stretching, the thermoplastic layer has a width of up to 60 millimeters. The thermoplastic layer has a first surface and a second surface opposite the first surface, with the first surface of the thermoplastic layer bearing a plurality of male fastening elements. The second surface of the thermoplastic layer is laminated to the substrate.
In another aspect, the present disclosure provides a method of making a laminate. The method includes stretching a thermoplastic layer in a machine direction using first and second rolls of different speeds so that it plastically deforms and decreases in width and subsequently laminating the thermoplastic layer to a substrate to form the laminate. The stretching and laminating are completed in-line. After stretching, the thermoplastic layer has a width of up to 60 millimeters. The thermoplastic layer has a first surface and a second surface opposite the first surface, with the first surface of the thermoplastic layer bearing a plurality of male fastening elements. The second surface of the thermoplastic layer is laminated to the substrate. The second roll has a faster speed than the first roll, and wherein the thermoplastic layer is not directed onto a third roll having a slower speed than the second roll before the laminating.
Stretching narrow thermoplastic layers and laminating, for example, in-line can be useful for obtaining a thermoplastic layer having male fastening element having a desired width without having to maintain multiple rolls of inventory. For example, a single roll of a narrow thermoplastic layer can be stretched to different extents for different products made on the same manufacturing line. The single roll can have a width that is wide enough for maintaining a stable roll but narrow enough for achieving a variety of desirable widths in a final product.
In this application, terms such as “a”, “an” and “the” are not intended to refer to only a singular entity, but include the general class of which a specific example may be used for illustration. The terms “a”, “an”, and “the” are used interchangeably with the term “at least one”. The phrases “at least one of” and “comprises at least one of” followed by a list refers to any one of the items in the list and any combination of two or more items in the list. All numerical ranges are inclusive of their endpoints and non-integral values between the endpoints unless otherwise stated (e.g., 1 to 5 includes 1, 1.5, 2, 2.75, 3, 3.80, 4, 5, etc.).
The terms “first” and “second” are used in this disclosure. It will be understood that, unless otherwise noted, those terms are used in their relative sense only. The designation of “first” and “second” may be applied to the major surfaces of the thermoplastic backing merely as a matter of convenience in the description of one or more of the embodiments.
The terms “multiple” and “a plurality” refer to more than one.
The term “machine direction” (MD) as used herein denotes the direction of a running web of material during a manufacturing process. When a strip is cut from a continuous web, the dimension in the machine direction corresponds to the length “L” of the strip. The terms “machine direction” and “longitudinal direction” may be used interchangeably. The term “cross-machine direction” (CD) as used herein denotes the direction which is essentially perpendicular to the machine direction. When a strip is cut from a continuous web, the dimension in the cross-machine direction corresponds to the width “W” of the strip. Accordingly, the term “width” typically refers to the shorter dimension in the plane of the first surface of thermoplastic layer, which is the surface bearing the male fastening elements. As used herein the term “thickness” usually refers to the smallest dimension of the thermoplastic layer, which is the dimension perpendicular to the first surface of the thermoplastic layer.
The term “in-line,” as used herein, means that the steps are completed without the thermoplastic layer being rolled up on itself. The steps may be completed sequentially with or without additional steps in-between. For clarification, the thermoplastic layer may be supplied in rolled form and the finished laminate may be rolled up on itself. However, the thermoplastic layer is not rolled up on itself after the stretching step.
The term “edge effect,” as used herein, refers to an appreciable drop in retardance near the edge of a layer, for example, in a range from 10 micrometers to 50 micrometers from the edge.
Percent elongation and percent tensile strain are used interchangeably. It is calculated from the following formula: (final length−initial length/initial length)×100.
Percent necking and percent decrease in width are used interchangeably. It is calculated from the following formula: (1−final width/initial width)×100.
Draw ratio refers to the linear draw ratio: final length divided by initial length.
The above summary of the present disclosure is not intended to describe each disclosed embodiment or every implementation of the present disclosure. The description that follows more particularly exemplifies illustrative embodiments. It is to be understood, therefore, that the drawings and following description are for illustration purposes only and should not be read in a manner that would unduly limit the scope of this disclosure.
The disclosure may be more completely understood in consideration of the following detailed description of various embodiments of the disclosure in connection with the accompanying drawings, in which:
Reference will now be made in detail to embodiments of the disclosure, one or more examples of which are illustrated in the drawings. Features illustrated or described as part of one embodiment can be used with other embodiments to yield still a third embodiment. It is intended that the present disclosure include these and other modifications and variations.
In the method according to the present disclosure, the distance between the different speed rolls may affect the decrease in width (in other words, the amount of necking). In some embodiments, long air gaps between the rolls (in other words, long draw instead of short draw) may be desired to increase necking. Stretching the thermoplastic layers incrementally between rollers of progressively faster speeds may be useful, for example, for controlling necking, allowing faster line speeds, providing more consistent stretch, and allowing for higher stretch ratios in the method of making laminate.
Referring again to
In some embodiments, before stretching, the thermoplastic layer 2 has a width of 10 millimeters (mm) to 50 mm (in some embodiments, 10 mm to 40 mm or 10 mm to 30 mm). Stretching a narrow thermoplastic layer (e.g., having a width of 10 mm to 50 mm, 10 mm to 40 mm, or 10 mm to 30 mm), can be advantageous over stretching a wider web (e.g., having a width of at least 100 mm, 200 mm, 250 mm, 500 mm, or 750 mm). For example, when webs are stretched, cross-web caliper variations can be observed, with more stretching occurring in the center of the web than at the edges. Because of this, the edges are generally trimmed off to not cause hardbands when the web is rolled up in a jumbo. Such differences in caliper are minimized when a narrow web is stretched. Also, when a thermoplastic layer is stretched, it becomes thinner Difficulties in handling thinner webs can be more pronounced in wider webs than in narrower webs.
Stretching narrow thermoplastic layers and laminating, for example, in-line can be useful for obtaining a thermoplastic layer having male fastening element having a desired width without having to maintain multiple rolls of inventory. For example, a single roll of a narrow thermoplastic layer can be stretched to different extents for different products made on the same manufacturing line. The single roll can have a width that is wide enough for maintaining a stable roll but narrow enough for achieving a variety of desirable widths in a final product.
In any of the embodiments of the method described herein, the rolls used for stretching and laminating the thermoplastic layer may be made from various materials. At least some of the rolls may be smooth metal (e.g., aluminum or steel) rolls. Also, at least some of rolls may be provided with a coating. The coating type on the rolls may influence how the thermoplastic layer is grabbed by the rolls and therefore also have an influence on how the thermoplastic layer stretches. A high-friction coating may be useful, for example. The high-friction coating can be, for example, a plasma coating known to provide a high-friction surface. Suitable plasma coatings include those available, for example, from Plasma Coating, Middlebury, Conn., under product family designations “10000” and “10015”. The high-friction coating may also be a coating or layer of a rubbery material.
Stretching the thermoplastic layer is carried out to an extent that it plastically deforms. Depending on the thermoplastic from which the thermoplastic layer is made, the draw ratio sufficient to plastically deform the thermoplastic layer can be at least 1.20, 1.25, 1.30, 1.5, or more. In some embodiments, the draw ratio used for stretching the thermoplastic layer is about 2.0, 2.25, 2.5, 2.75, or 3. The maximum draw ratio is limited by the tensile strength of the selected material. In some embodiments, the thermoplastic layer is stretched with a draw ratio of 1.25 to 5 in the machine direction. In some embodiments, the thermoplastic layer is stretched with a draw ratio of 1.5 to 4 in the machine direction. Draw ratios of up to 5, 7.5, or 10 may be useful, depending on material selection and the temperature of the thermoplastic backing when it is stretched. The draw ratios can result an elongation of, for example, 20%, 25%, 30%, 50%, 100%, 125%, 150%, 175%, 200%, or more in the thermoplastic layer.
As described above, stretching the thermoplastic layer in the machine direction can be performed by propelling the web over rolls of increasing speed, with the downweb roll speed faster than the upweb roll speed. In some embodiments, it is useful to stretch in the machine direction at a speed of up to 350 meters per minute, 300 meters per minute, 250 meters per minute, 200 meters per minute, 100 meters per minute, 75 meters per minute, 50 meters per minute, 25 meters per minute, 10 meters per minute, or 5 meters per minute.
The second roll has a faster speed than the first roll. The ratio of the speed of the second roll to the speed of the first roll is the draw ratio and can be any of those described above. In some embodiments, he thermoplastic layer is not directed onto a third roll having a slower speed than the second roll before laminating.
In some embodiments, the method according to the present disclosure further comprises heating the thermoplastic layer. Heating may be useful, for example, before or during the stretching or a combination thereof. This may allow the thermoplastic layer to be more flexible for stretching and improve the uniformity of stretching. Also, heat applied during the stretching process can reduce curl in lamination caused by differential stresses that may be present in the thermoplastic layer and the substrate. In some embodiments in which the thermoplastic layer is a polypropylene backing, stretching is carried out in a temperature range from 35° C. to 110° C., 50° C. to 100° C., or 60° C. to 75° C. In some embodiments, the thermoplastic layer can be heated after stretching and before lamiation. Heating at such a time may be useful for annealing the thermoplastic layer.
For any of these purposes, heating can be provided, for example, by IR irradiation, hot air treatment or by performing the stretching in a heat chamber. Rollers that may be used for stretching the thermoplastic backing in the machine direction may be heated. Heated rollers may also be useful, for example, for annealing the stretched thermoplastic layer. For annealing, the heated thermoplastic layer can also be directed onto a chilled roller for rapid cooling. In some embodiments, heating is only applied to the second surface of the thermoplastic layer (i.e., the surface opposite the first surface from which the discrete elements protrude) to minimize any damage to the male fastening elements that may result from heating. For example, in these embodiments, only rollers that are in contact with the second surface of the thermoplastic backing are heated. Heating is typically only carried out below the melting temperature of the thermoplastic layer.
The thermoplastic layer useful for practicing the method disclosed herein may be made from a variety of suitable materials. Examples of suitable thermoplastic materials include polyolefin homopolymers such as polyethylene and polypropylene, copolymers of ethylene, propylene and/or butylene; copolymers containing ethylene such as ethylene vinyl acetate and ethylene acrylic acid; polyesters such as poly(ethylene terephthalate), polyethylene butyrate, and polyethylene napthalate; polyamides such as poly(hexamethylene adipamide); polyurethanes; polycarbonates; poly(vinyl alcohol); ketones such as polyetheretherketone; polyphenylene sulfide; and mixtures thereof. In some embodiments, the thermoplastic layer comprises at least one of a polyolefin, a polyamide, or a polyester. In some embodiments, the thermoplastic is a polyolefin (e.g., polyethylene, polypropylene, polybutylene, ethylene copolymers, propylene copolymers, butylene copolymers, and copolymers and blends of these materials).
For any of the embodiments in which the thermoplastic layer includes polypropylene, the polypropylene may be an impact-modified polypropylene. In some embodiments, the polypropylene can include an impact modifier. Suitable impact modifiers include an ethylene propylene elastomer, an ethylene octene elastomer, an ethylene propylene diene elastomer, an ethylene propylene octene elastomer, polybutadiene, a butadiene copolymer, polybutene, or a combination thereof. Other suitable impact modifiers include styrene/butadiene rubber (SBR) and block copolymers such as styrene-isoprene-styrene, styrene-butadiene-styrene, styrene-ethylene-butylene-styrene triblock or styrene-isoprene, styrene-butadiene, styrene-ethylene-butylene starblock polymers. In some embodiments, the impact modifier is an ethylene octene elastomer. Some suitable impact modifiers can be obtained, for example, from Dow Chemical Company, Midland, Mich., under the trade designation “ENGAGE”.
For any of the embodiments in which the thermoplastic layer includes polypropylene, the polypropylene may include alpha and/or beta phase polypropylene. In some cases, a thermoplastic layer 2 as described above that includes beta-phase polypropylene before stretching may include alpha-phase polypropylene after stretching to form the stretched thermoplastic layer 10. Semi-crystalline polyolefins can have more than one kind of crystal structure. For example, isotactic polypropylene is known to crystallize into at least three different forms: alpha (monoclinic), beta (pseudohexangonal), and gamma (triclinic) forms. In melt-crystallized material the predominant form is the alpha or monoclinic form. The beta form generally occurs at levels of only a few percent unless certain heterogeneous nuclei are present or the crystallization has occurred in a temperature gradient or in the presence of shearing forces. The heterogeneous nuclei are typically known as beta-nucleating agents, which act as foreign bodies in a crystallizable polymer melt. When the polymer cools below its crystallization temperature (e.g., a temperature in a range from 60° C. to 120° C. or 90° C. to 120° C.), the loose coiled polymer chains orient themselves around the beta-nucleating agent to form beta-phase regions. The beta form of polypropylene is a meta-stable form, which can be converted to the more stable alpha form by thermal treatment and/or applying stress. In some embodiments, the thermoplastic layer comprises a beta-nucleating agent. Micropores can be formed in various amounts when the beta-form of polypropylene is stretched under certain conditions; see, e.g., Chu et al., “Microvoid formation process during the plastic deformation of β-form polypropylene”, Polymer, Vol. 35, No. 16, pp. 3442-3448, 1994, and Chu et al., “Crystal transformation and micropore formation during uniaxial drawing of β-form polypropylene film”, Polymer, Vol. 36, No. 13, pp. 2523-2530, 1995. Pore sizes achieved from this method can range from about 0.05 micrometer to about 1 micrometer, in some embodiments, about 0.1 micrometer to about 0.5 micrometer. In some embodiments, at least a portion of the thermoplastic layer is microporous after stretching.
Generally, when the thermoplastic layer comprises polypropylene, it should be understood that the thermoplastic layer may comprise a polypropylene homopolymer or a copolymer containing propylene repeating units. The copolymer may be a copolymer of propylene and at least one other olefin (e.g., ethylene or an alpha-olefin having from 4 to 12 or 4 to 8 carbon atoms). Copolymers of ethylene, propylene and/or butylene may be useful. In some embodiments, the copolymer contains up to 90, 80, 70, 60, or 50 percent by weight of polypropylene. In some embodiments, the copolymer contains up to 50, 40, 30, 20, or 10 percent by weight of at least one of polyethylene or an alpha-olefin. The thermoplastic layer may also comprise a blend of thermoplastic polymers that includes polypropylene. Suitable thermoplastic polymers include crystallizable polymers that are typically melt processable under conventional processing conditions. That is, on heating, they will typically soften and/or melt to permit processing in conventional equipment, such as an extruder, to form a sheet. Crystallizable polymers, upon cooling their melt under controlled conditions, spontaneously form geometrically regular and ordered chemical structures. Examples of suitable crystallizable thermoplastic polymers include addition polymers, such as polyolefins. Useful polyolefins include polymers of ethylene (e.g., high density polyethylene, low density polyethylene, or linear low density polyethylene), an alpha-olefin (e.g, 1-butene, 1-hexene, or 1-octene), styrene, and copolymers of two or more such olefins. A blend of thermoplastic polymers may comprise mixtures of stereo-isomers of such polymers, e.g., mixtures of isotactic polypropylene and atactic polypropylene or of isotactic polystyrene and atactic polystyrene. In some embodiments, a blend that includes polypropylene contains up to 90, 80, 70, 60, or 50 percent by weight of polypropylene. In some embodiments, the blend contains up to 50, 40, 30, 20, or 10 percent by weight of at least one of polyethylene or an alpha-olefin.
In embodiments of the method according to the present disclosure in which the thermoplastic layer comprises a beta-nucleating agent, the beta-nucleating agent may be any inorganic or organic nucleating agent that can produce beta-spherulites in a melt-formed sheet comprising polyolefin. Useful beta-nucleating agents include gamma quinacridone, an aluminum salt of quinizarin sulphonic acid, dihydroquinoacridin-dione and quinacridin-tetrone, triphenenol ditriazine, calcium silicate, dicarboxylic acids (e.g., suberic, pimelic, ortho-phthalic, isophthalic, and terephthalic acid), sodium salts of these dicarboxylic acids, salts of these dicarboxylic acids and the metals of Group IIA of the periodic table (e.g., calcium, magnesium, or barium), delta-quinacridone, diamides of adipic or suberic acids, different types of indigosol and cibantine organic pigments, quiancridone quinone, N′,N′-dicyclohexil-2,6-naphthalene dicarboxamide (available, for example, under the trade designation “NJ-Star NU-100” from New Japan Chemical Co. Ltd.), antraquinone red, and bis-azo yellow pigments. The properties of the extruded film are dependent on the selection of the beta nucleating agent and the concentration of the beta-nucleating agent. In some embodiments, the beta-nucleating agent is selected from the group consisting of gamma-quinacridone, a calcium salt of suberic acid, a calcium salt of pimelic acid and calcium and barium salts of polycarboxylic acids. In some embodiments, the beta-nucleating agent is quinacridone colorant Permanent Red E3B, which is also referred to as Q-dye. In some embodiments, the beta-nucleating agent is formed by mixing an organic dicarboxylic acid (e.g., pimelic acid, azelaic acid, o-phthalic acid, terephthalic acid, and isophthalic acid) and an oxide, hydroxide, or acid salt of a Group II metal (e.g., magnesium, calcium, strontium, and barium). So-called two component initiators include calcium carbonate combined with any of the organic dicarboxylic acids listed above and calcium stearate combined with pimelic acid. In some embodiments, the beta-nucleating agent is aromatic tri-carboxamide as described in U.S. Pat. No. 7,423,088 (Mader et al.).
A convenient way of incorporating beta-nucleating agents into a semi-crystalline polyolefin useful for making a thermoplastic layer for the method disclosed herein is through the use of a concentrate. A concentrate is typically a highly loaded, pelletized polypropylene resin containing a higher concentration of nucleating agent than is desired in the final thermoplastic layer. The nucleating agent is present in the concentrate in a range of 0.01% to 2.0% by weight (100 to 20,000 ppm), in some embodiments in a range of 0.02% to 1% by weight (200 to 10,000 ppm). Typical concentrates are blended with non-nucleated polyolefin in the range of 0.5% to 50% (in some embodiments, in the range of 1% to 10%) by weight of the total polyolefin content of the thermoplastic layer. The concentration range of the beta-nucleating agent in the final thermoplastic layer may be 0.0001% to 1% by weight (1 ppm to 10,000 ppm), in some embodiments, 0.0002% to 0.1% by weight (2 ppm to 1000 ppm). A concentrate can also contain other additives such as stabilizers, pigments, and processing agents.
The level of beta-spherulites in the thermoplastic layer can be determined, for example, using X-ray crystallography and Differential Scanning calorimetry (DSC). By DSC, melting points and heats of fusion of both the alpha phase and the beta phase can be determined in a thermoplastic layer useful for practicing the present disclosure. For semi-crystalline polypropylene, the melting point of the beta phase is lower than the melting point of the alpha phase (e.g., by about 10 to 15 degrees Celsius). The ratio of the heat of fusion of the beta phase to the total heat of fusion provides a percentage of the beta-spherulites in a sample. The level of beta-spherulites can be at least 10, 20, 25, 30, 40, or 50 percent, based on the total amount of alpha and beta phase crystals in the film. These levels of beta-spherulites may be found in the thermoplastic layer before it is stretched.
Since the thermoplastic layer stretched according to the present disclosure is plastically deformed, it should be understood that the thermoplastic backing is generally non-elastic. The term “non-elastic” refers to any material (such as a film that is 0.002 mm to 0.5 mm thick) that does not exhibit recovery from stretching or deformation to a large extent. For example, a non-elastic material that is stretched to a length that is at least about 50 percent greater than its initial length will recover less than about 40, 25, 20, 10, or 5 percent of its elongation upon release of its stretching force. In some embodiments, a non-elastic material may be considered to be a flexible plastic that is capable of undergoing permanent plastic deformation if it is stretched past its reversible stretching region.
In some embodiments, the thermoplastic layer with male fastening elements can be made from a multilayer or multi-component melt stream of thermoplastic materials. This can result in male fastening elements formed at least partially from a different thermoplastic material than the one predominately forming the backing. Various configurations of upstanding posts made from a multilayer melt stream are shown in U.S. Pat. No. 6,106,922 (Cejka et al.), for example. A multilayer or multi-component melt stream can be formed by any conventional method. A multilayer melt stream can be formed by a multilayer feedblock, such as that shown in U.S. Pat. No. 4,839,131 (Cloeren). A multicomponent melt stream having domains or regions with different components could also be used. Useful multicomponent melt streams could be formed by use of inclusion co-extrusion die or other known methods (e.g., that shown in U.S. Pat. No. 6,767,492 (Norquist et al.).
In some embodiments, the thermoplastic layer can be biaxially stretched or stretched in the cross-direction before it is stretched in the machine direction to decrease its width. Stretching in a cross-machine direction can be carried out on a continuous web using, for example, diverging rails or diverging disks. A versatile stretching method that allows for monoaxial and sequential biaxial stretching of the thermoplastic layer employs a flat film tenter apparatus. Such an apparatus grasps the thermoplastic layer using a plurality of clips, grippers, or other film edge-grasping means along opposing edges of the thermoplastic web in such a way that monoaxial and biaxial stretching in the desired direction is obtained by propelling the grasping means at varying speeds along divergent rails. Increasing clip speed in the machine direction generally results in machine-direction stretching. Stretching at angles to the machine direction and cross-direction are also possible with a flat film tenter apparatus. Monoaxial and biaxial stretching can also be accomplished, for example, by the methods and apparatus disclosed in U.S. Pat. No. 7,897,078 (Petersen et al.) and the references cited therein. Flat film tenter stretching apparatuses are commercially available, for example, from Brückner Maschinenbau GmbH, Siegsdorf, Germany.
In the method according to the present disclosure, the thermoplastic layer and the male fastening elements are integral (that is, generally formed at the same time as a unit, unitary). Male fastening elements such as upstanding posts on a thermoplastic layer can be made, for example, by feeding a thermoplastic material onto a continuously moving mold surface with cavities having the inverse shape of the male fastening elements. The thermoplastic material can be passed between a nip formed by two rolls or a nip between a die face and roll surface, with at least one of the rolls having the cavities. Pressure provided by the nip forces the resin into the cavities. In some embodiments, a vacuum can be used to evacuate the cavities for easier filling of the cavities. The nip has a large enough gap such that a coherent thermoplastic layer is formed over the cavities. The mold surface and cavities can optionally be air or water cooled before stripping the integrally formed thermoplastic layer and upstanding posts from the mold surface such as by a stripper roll. In some embodiments, the male fastening elements can be made by a modification of the mold surface described above, in which the cavity includes a main cavity with multiple smaller cavities within the main cavity.
Suitable mold surfaces for forming upstanding posts include tool rolls such as those formed from a series of plates defining a plurality of cavities about its periphery including those described, for example, in U.S. Pat. No. 4,775,310 (Fischer). Cavities may be formed in the plates by drilling or photoresist technology, for example. Other suitable tool rolls may include wire-wrapped rolls, which are disclosed along with their method of manufacturing, for example, in U.S. Pat. No. 6,190,594 (Gorman et al.). Another example of a method for forming a thermoplastic layer with upstanding posts includes using a flexible mold belt defining an array of upstanding post-shaped cavities as described in U.S. Pat. No. 7,214,334 (Jens et al.). Yet other useful methods for forming a thermoplastic layer with upstanding posts can be found in U.S. Pat. No. 6,287,665 (Hammer), U.S. Pat. No. 7,198,743 (Tuma), and U.S. Pat. No. 6,627,133 (Tuma).
In any of the mold surfaces mentioned above, the cavities and the resultant male fastening elements may have a variety of cross-sectional shapes. For example, the cross-sectional shape of the cavity and male fastening element or post may be a polygon (e.g., square, rectangle, rhombus, hexagon, pentagon, or dodecagon), which may be a regular polygon or not, or the cross-sectional shape of the post may be curved (e.g., round or elliptical). The male fastening element may taper from its base to its distal tip, for example, for easier removal from the cavity, but this is not a requirement. The cavity may have the inverse shape of a post having a loop-engaging head or may have the inverse shape of an upstanding post without loop-engaging heads that can be formed into loop-engaging heads, if desired.
If upstanding posts formed upon exiting the cavities do not have loop-engaging heads, loop-engaging heads could be subsequently formed by a capping method as described in U.S. Pat. No. 5,077,870 (Melbye et al.). Typically, the capping method includes deforming the tip portions of the upstanding posts using heat and/or pressure. The heat and pressure, if both are used, could be applied sequentially or simultaneously. The formation of male fastening elements can also include a step in which the shape of the cap is changed, for example, as described in U.S. Pat. No. 6,132,660 (Kampfer). Such capping and cap modification steps can be carried out before or after stretching in the method of making a laminate disclosed herein.
Another useful method for forming male fastening elements on a thermoplastic layer is profile extrusion described, for example, in U.S. Pat. No. 4,894,060 (Nestegard), which is incorporated herein by reference in its entirety. Typically, in this method a thermoplastic flow stream is passed through a patterned die lip (e.g., cut by electron discharge machining) to form a web having downweb ridges, slicing the ridges, and stretching the web to form separated projections. The ridges may form hook precursors and exhibit the cross-sectional shape of male fastening elements (e.g., with loop-engaging heads) to be formed. The ridges are transversely sliced at spaced locations along the extension of the ridges to form discrete portions of the ridges having lengths in the direction of the ridges essentially corresponding to the length of the male fastening elements to be formed. Providing a thermoplastic layer having a first surface bearing a plurality of male fastening elements can be carried out by transversely slicing such ridges, and stretching the thermoplastic layer so that it plastically deforms results in the separation of the male fastening elements.
For any of the embodiments described above in which the male fastening elements are upstanding posts with loop-engaging overhangs, the term “loop-engaging” relates to the ability of a male fastening element to be mechanically attached to a loop material. Generally, male fastening elements with loop-engaging heads have a head shape that is different from the shape of the post. For example, the male fastening element may be in the shape of a mushroom (e.g., with a circular or oval head enlarged with respect to the stem), a hook, a palm-tree, a nail, a T, or a J. In some embodiments, each male fastening element includes an upstanding post and a cap with loop engaging overhangs extending in multiple (i.e., at least two) directions, in some embodiments, at least two orthogonal directions. For example, the male fastening element may be in the shape of a mushroom, a nail, a palm tree, or a T. In some embodiments, the male fastening elements are provided with a mushroom head (e.g., with an oval or round cap distal from the thermoplastic layer). The loop-engageability of male fastening elements may be determined and defined by using standard woven, nonwoven, or knit materials. A region of male fastening elements with loop-engaging heads generally will provide, in combination with a loop material, at least one of a higher peel strength, higher dynamic shear strength, or higher dynamic friction than a region of posts without loop-engaging heads. Male fastening elements that have “loop-engaging overhangs” or “loop-engaging heads” do not include ridges described above that are precursors to fastening elements (e.g., elongate ridges that are profile extruded and subsequently cut to form male fastening elements upon stretching in the direction of the ridges). Such ridges would not be able to engage loops before they are cut and stretched. Such ridges would also not be considered male fastening elements. Typically, male fastening elements that have loop-engaging heads have a maximum width dimension (in either dimension normal to the height) of up to about 1 (in some embodiments, 0.9, 0.8, 0.7, 0.6, 0.5, or 0.45) millimeter (mm). In some embodiments, the male fastening elements have a maximum height (above the backing) of up to 3 mm, 1.5 mm, 1 mm, or 0.5 mm and, in some embodiments a minimum height of at least 0.03 mm, 0.05 mm, 0.1 mm, or 0.2 mm. In some embodiments, the male fastening elements have aspect ratio (that is, a ratio of height to width at the base at the thermoplastic layer) of at least about 0.25:1, 1:1, 2:1, 3:1, or 4:1.
The method according to the present disclosure can be useful with thermoplastic layers having a variety of thicknesses. In some embodiments, the thickness of the thermoplastic layer suitable for the method disclosed herein may be up to about 400 micrometers (μm), 300 micrometers, or 250 micrometers and at least about 30 micrometers or 50 micrometers before stretching. This thickness does not include the height of the male fastening elements protruding from the first major surface of the thermoplastic layer. In some embodiments, the thickness of the thermoplastic layer is in a range from 30 to about 225 micrometers, from about 50 to about 200 micrometers, or from about 50 to about 150 micrometers before stretching. In some embodiments, the thermoplastic layer, excluding the discrete elements, is substantially uniform in thickness. For a thermoplastic layer that is substantially uniform in thickness, a difference in thickness between any two points in the thermoplastic layer may be up to 5, 2.5, or 1 percent. In some embodiments, after stretching, the thermoplastic layer has an average thickness of up to 80 μm, 75 μm, 70 μm, 65 μm, 60 μm, 55 μm, or 50 μm. In some embodiments, the average thickness of the thermoplastic layer after stretching is in a range from 20 μm to 80 μm, 30 μm to 75 μm, 40 μm to 75 μm, 20 μm to 70 μm, 30 μm to 70 μm, or 20 μm to 50 μm. In general, the thermoplastic layer has no through-holes before or after stretching. In some embodiments, the thermoplastic layer, excluding the discrete elements, is substantially planar. A substantially “planar” thermoplastic layer refers to portions of thermoplastic layer occupying substantially the same plane when placed on a flat surface. The term “substantially” in this regard can mean that a portion of the thermoplastic layer may be out of plane by up to 15, 10, or 5 degrees. A thermoplastic layer that is substantially planar is not corrugated and not profile-extruded to have multiple peaks and valleys.
Male fastening elements on the first surface of the thermoplastic layer may have an initial density (i.e., before stretching) of at least 10 per square centimeter (cm2) (63 per square inch in2). For example, the initial density of the male fastening elements may be at least 100/cm2 (635/in2), 248/cm2 (1600/in2), 394/cm2 (2500/in2), or 550/cm2 (3500/in2). In some embodiments, the initial density of the male fastening elements may be up to 1575/cm2 (10000/in2), up to about 1182/cm2 (7500/in2), or up to about 787/cm2 (5000/in2). Initial densities in a range from 10/cm2 (63/in2) to 1575/cm2 (10000/in2) or 100/cm2 (635/in2) to 1182/cm2 (7500/in2) may be useful, for example. The spacing of the male fastening elements need not be uniform. In some embodiments, the density of the male fastening elements after stretching may be up to about 1182/cm2 (7500/in2) or up to about 787/cm2 (5000/in2). Densities after stretching in a range from 2/cm2 (13/int) to 1182/cm2 (7500/in2), 124/cm2 (800/in2) to 787/cm2 (5000/in2), 248/cm2 (1600/in2) to 550/cm2 (3500/in2), or 248/cm2 (1600/in2) to 394/cm2 (2500/in2) may be useful, for example. Again, the spacing of the male fastening elements need not be uniform.
In some embodiments, stretching the thermoplastic layer comprises adjusting a density of the male fastening elements to achieve a pre-determined density. The pre-determined density may be selected, based on a desired performance of the male fastening elements on the thermoplastic film. The desired performance can be a desired shear or peel strength to a fibrous substrate. The fibrous substrate can be a standard woven, nonwoven, or knit material or can be any fibrous substrate useful, for example, in an absorbent article.
As described above, when the thermoplastic layer includes a beta-nucleating agent, stretching the film provides micropores in at least a portion of the film. Without wanting to be bound by theory, it is believed that when the film is stretched in at least one direction, for example, the semi-crystalline polypropylene converts from the beta-crystalline structure to the alpha-crystalline structure in the film, and micropores are formed in the film. Male fastening elements are affected differently from the rest of the film. For example, male fastening elements (e.g., posts and caps) on a backing are typically not affected by the stretching or are affected to a much lesser extent than the backing and therefore retain beta-crystalline structure and generally have lower levels of microporosity than the backing. The resulting stretched thermoplastic layers can have several unique properties. For example, the micropores formed in the thermoplastic layer along with stress-whitening can provide an opaque, white film with transparent male fastening elements. When micropores are formed in the thermoplastic layer disclosed herein, the density of the film decreases. The resulting low-density thermoplastic layer feels softer to the touch than films having comparable thicknesses but higher densities. The density of the film can be measured using conventional methods, for example, using helium in a pycnometer. The softness of the film can be measured, for example, using Gurley stiffness. In some embodiments, stretching a thermoplastic layer with a first surface bearing male fastening elements that includes a beta-nucleating agent is carried out at temperature range from 50° C. to 110° C., 50° C. to 90° C., or 50° C. to 80° C. In some embodiments, stretching at lower temperatures may be possible, for example, in a range from 25° C. to 50° C. A thermoplastic layer with a first surface bearing male fastening elements that includes a beta-nucleating agent can typically be stretched at a temperature of up to 70° C. (e.g., in a range from 50° C. to 70° C. or 60° C. to 70° C.) and still successfully achieve microporosity.
After stretching to the point of plastic deformation in the method disclosed herein, the thermoplastic layer will have stretch-induced molecular orientation. Stretch-induced molecular orientation in the thermoplastic layer can be detected by standard spectrographic analysis of the birefringent properties of the thermoplastic layer.
The thermoplastic layer may be laminated to the substrate using a variety of methods, for example, thermal bonding, adhesive bonding (e.g., with pressure sensitive adhesives), ultrasonic welding, laser welding, compression bonding, surface bonding, or combinations thereof. The thermoplastic layer may be joined to the substrate in a nip, or the laminate can be nipped downweb from where the thermoplastic layer is joined to the substrate.
Typically, the second surface of the thermoplastic layer (i.e., the surface opposite the first surface having the male fastening elements) is joined to the substrate. The substrate may be continuous (i.e., without any through-penetrating holes) or discontinuous (e.g. comprising through-penetrating perforations or pores). The substrate may comprise a variety of suitable materials including woven webs, non-woven webs, textiles, plastic films (e.g., single- or multilayered films, coextruded films, laterally laminated films, or films comprising foam layers), and combinations thereof. The term “non-woven” refers to a material having a structure of individual fibers or threads that are interlaid but not in an identifiable manner such as in a knitted fabric. Examples of non-woven webs include spunbond webs, spunlaced webs, airlaid webs, meltblown web, and bonded carded webs. In some embodiments, the substrate is a fibrous material (e.g., a woven, nonwoven, or knit material). Useful fibrous materials may be made of natural fibers (e.g., wood or cotton fibers), synthetic fibers (e.g., thermoplastic fibers), or a combination of natural and synthetic fibers. Examples of suitable materials for forming thermoplastic fibers include polyolefins (e.g., polyethylene, polypropylene, polybutylene, ethylene copolymers, propylene copolymers, butylene copolymers, and copolymers and blends of these polymers), polyesters, and polyamides. The fibers may also be multi-component fibers, for example, having a core of one thermoplastic material and a sheath of another thermoplastic material. In some embodiments, the substrate comprises multiple layers of nonwoven materials with, for example, at least one layer of a meltblown nonwoven and at least one layer of a spunbonded nonwoven, or any other suitable combination of nonwoven materials. For example, the substrate may be a spunbond-meltbond-spunbond, spunbond-spunbond, or spunbond-spunbond-spunbond multilayer material. Or, the substrate may be a composite web comprising a nonwoven layer and a dense film layer. A variety of combinations of film and nonwoven layers may be useful. Useful substrates may have any suitable basis weight or thickness that is desired for a particular application. For a fibrous substrate, the basis weight may range, e.g., from at least about 5, 8, 10, 20, 30, or 40 grams per square meter, up to about 400, 200, or 100 grams per square meter. The substrate may be up to about 5 mm, about 2 mm, or about 1 mm in thickness and/or at least about 0.1, about 0.2, or about 0.5 mm in thickness.
In a laminate made by the method of the present disclosure, the thermoplastic layer and the substrate may be substantially continuously bonded or intermittently bonded. “Substantially continuously bonded” refers to being bonded without interruption in space or pattern. Substantially continuously bonded laminates can be formed by passing the thermoplastic layer and the substrate between a heated smooth surfaced roll nip if at least one of them is thermally bondable or applying a substantially continuous adhesive coating or spray to one of the thermoplastic layer or substrate before bringing it in contact with the other of the thermoplastic layer or substrate. “Intermittently bonded” can mean not continuously bonded and refers to the thermoplastic layer and substrate being bonded to one another at discrete spaced apart points or being substantially unbonded to one another in discrete, spaced apart areas. Intermittently bonded laminates can be formed, for example, by ultrasonic point bonding, by passing the thermoplastic layer and the substrate through a heated patterned embossing roll nip if at least one of them is thermally bondable, or by applying discrete, spaced apart areas of adhesive to one of the thermoplastic layer or substrate before bringing it into contact with the other of the thermoplastic layer or substrate. An intermittently bonded laminate can also be made by feeding an adhesively coated apertured ply or scrim between the thermoplastic layer and the substrate.
When the thermoplastic layer includes microporosity that provides opacity in the thermoplastic layer, bonding the thermoplastic layer and the substrate using at least one of heat or pressure can collapse the microporous structure in the bond sites. The bond sites may be see-through regions of lower porosity that contrast with the surrounding opaque, microporous region. The term “see-through” refers to either transparent (that is, allowing passage of light and permitting a clear view of objects beyond) or translucent (that is, allowing passage of light and not permitting a clear view of objects beyond). The see-through region may be colored or colorless. It should be understood that a “see-through” region is large enough to be seen by the naked eye. The substrate may have a contrasting color from the thermoplastic layer that may be visible in the bond sites once the microporous structure is collapsed. Contrasting colors in the thermoplastic layer and the substrate may be provided by including a dye or a pigment in at least one of the thermoplastic layer or substrate. Bond sites made by at least one of heat or pressure can have a wide variety of geometric shapes, numbers, pictures, symbols, alphabetical letters, bar codes, or combinations thereof. The bond sites can also include a company name, brand name, or logo that may be readily identified by a customer. It is also possible that the microporous structure in a thermoplastic layer can be collapsed with at least one of heat or pressure before lamination. In this way the thermoplastic layer can be customized with a wide variety of geometric shapes, numbers, pictures, symbols, alphabetical letters, bar codes, or combinations thereof regardless of how it is laminated to the substrate.
In some embodiments of the method according to the present disclosure, the thermoplastic layer can be joined to a fibrous substrate using surface bonding or loft-retaining bonding techniques. The term “surface-bonded” when referring to the bonding of fibrous materials means that parts of fiber surfaces of at least portions of fibers are melt-bonded to the second surface of the thermoplastic layer, in such a manner as to substantially preserve the original (pre-bonded) shape of the second surface of the thermoplastic layer, and to substantially preserve at least some portions of the second surface of the thermoplastic layer in an exposed condition, in the surface-bonded area. Quantitatively, surface-bonded fibers may be distinguished from embedded fibers in that at least about 65% of the surface area of the surface-bonded fiber is visible above the second surface of the thermoplastic layer in the bonded portion of the fiber. Inspection from more than one angle may be necessary to visualize the entirety of the surface area of the fiber. The term “loft-retaining bond” when referring to the bonding of fibrous materials means a bonded fibrous material comprises a loft that is at least 80% of the loft exhibited by the material prior to, or in the absence of, the bonding process. The loft of a fibrous material as used herein is the ratio of the total volume occupied by the web (including fibers as well as interstitial spaces of the material that are not occupied by fibers) to the volume occupied by the material of the fibers alone. If only a portion of a fibrous substrate has the second surface of the thermoplastic layer bonded thereto, the retained loft can be easily ascertained by comparing the loft of the fibrous substrate in the bonded area to that of the web in an unbonded area. It may be convenient in some circumstances to compare the loft of the bonded substrate to that of a sample of the same substrate before being bonded, for example, if the entirety of fibrous substrate has the second surface of the thermoplastic layer bonded thereto. In some of these embodiments, the joining comprises impinging heated gaseous fluid (e.g., ambient air, dehumidified air, nitrogen, an inert gas, or other gas mixture) onto a first surface of the fibrous substrate web while it is moving; impinging heated fluid onto the second surface of the thermoplastic layer while the continuous web is moving, wherein the second surface is opposite the male fastening elements on the thermoplastic layer; and contacting the first surface of the fibrous substrate web with the second surface of the thermoplastic layer so that the first surface of the fibrous substrate web is melt-bonded (e.g., surface-bonded or bonded with a loft-retaining bond) to the second surface of the thermoplastic layer. Impinging heated gaseous fluid onto the first surface of the fibrous substrate web and impinging heated gaseous fluid on the second surface of the thermoplastic layer may be carried out sequentially or simultaneously. Further methods and apparatus for joining a continuous thermoplastic web to a fibrous substrate web using heated gaseous fluid may be found in U.S. Pat. Appl. Pub. No. 2011/0151171 (Biegler et al.) and U.S. Pat. No. 9,096,960 (Biegler et al.).
In some embodiments, at least the portion of the substrate joined to the thermoplastic layer is generally not extensible. In some of these embodiments, the portion of substrate joined to the thermoplastic layer will have up to a 10 (in some embodiments, up to 9, 8, 7, 6, or 5) percent elongation in the MD or CD. In some embodiments, the substrate is not pleated. In other embodiments of the laminate made by the method of the present disclosure, one or more zones of the substrate may comprise one or more elastically extensible materials extending in at least one direction when a force is applied and returning to approximately their original dimension after the force is removed.
In some embodiments, the substrate may be extensible but non-elastic. In other words, the substrate may have an elongation of at least 5, 10, 15, 20, 25, 30, 40, or 50 percent but substantially no recovery from the elongation (e.g., up to 40, 25, 20, 10, or 5 percent recovery). The term “extensible” refers to a material that can be extended or elongated in the direction of an applied stretching force without destroying the structure of the material or material fibers. In some embodiments, an extensible substrate may be stretched to a length that is at least about 5, 10, 15, 20, 25, or 50 percent greater than its relaxed length without destroying the structure of the material or material fibers. Suitable extensible carriers may include nonwovens (e.g., spunbond, spunbond meltblown spunbond, or carded nonwovens). In some embodiments, the nonwoven may be a high elongation carded nonwoven (e.g., HEC). Other extensible, non-elastic carriers include thermoplastic films, including those made from any of the materials described above for the thermoplastic layer. The extensible, non-elastic film may be thinner than the thermoplastic layer in some embodiments.
In some embodiments of the method according to the present disclosure, the substrate comprises an elastic material. The term “elastic” refers to any material (such as a film that is 0.002 mm to 0.5 mm thick) that exhibits recovery from stretching or deformation. An elastic material is an extensible material that has recovery properties. In some embodiments, a material may be considered to be elastic if, upon application of a stretching force, it can be stretched to a length that is at least about 25 (in some embodiments, 50) percent larger than its initial length and can recover at least 40, 50, 60, 70, 80, or 90 percent of its elongation upon release of the stretching force. An elastic substrate may be a film or fibrous. Examples of polymers for making elastic films or fibrous carriers include thermoplastic elastomers such as ABA block copolymers, polyurethane elastomers, polyolefin elastomers (e.g., metallocene polyolefin elastomers), olefin block copolymers, polyamide elastomers, ethylene vinyl acetate elastomers, and polyester elastomers. An ABA block copolymer elastomer generally is one where the A blocks are polystyrenic, and the B blocks are prepared from conjugated dienes (e.g., lower alkylene dienes). The A block is generally formed predominantly of substituted (e.g., alkylated) or unsubstituted styrenic moieties (e.g., polystyrene, poly(alphamethylstyrene), or poly(t-butylstyrene)), having an average molecular weight from about 4,000 to 50,000 grams per mole. The B block(s) is generally formed predominantly of conjugated dienes (e.g., isoprene, 1,3-butadiene, or ethylene-butylene monomers), which may be substituted or unsubstituted, and has an average molecular weight from about 5,000 to 500,000 grams per mole. The A and B blocks may be configured, for example, in linear, radial, or star configurations. An ABA block copolymer may contain multiple A and/or B blocks, which blocks may be made from the same or different monomers. A typical block copolymer is a linear ABA block copolymer, where the A blocks may be the same or different, or a block copolymer having more than three blocks, predominantly terminating with A blocks. Multi-block copolymers may contain, for example, a certain proportion of AB diblock copolymer, which tends to form a more tacky elastomeric film segment. Other elastic polymers can be blended with block copolymer elastomers, and various elastic polymers may be blended to have varying degrees of elastic properties.
Many types of thermoplastic elastomers are commercially available, including those from BASF, Florham Park, N.J., under the trade designation “STYROFLEX”, from Kraton Polymers, Houston, Tex., under the trade designation “KRATON”, from Dow Chemical, Midland, Mich., under the trade designation “PELLETHANE”, “INFUSE”, VERSIFY”, or “NORDEL”, from DSM, Heerlen, Netherlands, under the trade designation “ARNITEL”, from E. I. duPont de Nemours and Company, Wilmington, Del., under the trade designation “HYTREL”, from ExxonMobil, Irving, Tex. under the trade designation “VISTAMAXX”, and more.
An elastic film substrate may have a single layer of an elastomer, or the substrate may have a core made with an elastomer and at least one skin layer from a relatively non-elastic polymer, such as any of those described above for the thermoplastic backing. The materials and thicknesses of the multi-layer elastic substrate may be selected such that when the substrate is extended to a certain degree, the skin layers undergo plastic deformation. When the elastic layer recovers, the relatively non-elastic skin layer forms a textured surface on the elastic core. Such elastic films are described, for example, in U.S. Pat. No. 5,691,034 (Krueger et al.).
The method according to the present disclosure is typically carried out a continuous web of the thermoplastic layer and a continuous web of the substrate. While the thermoplastic layer and substrate may have any useful width, the width of the thermoplastic layer and substrate may be selected so that it has a desired size for a given application. For example, in some embodiments, before stretching, the thermoplastic layer has a width of 10 millimeters (mm) to 60 mm (in some embodiments, 10 mm to 50 mm, 10 mm to 40 mm or 10 mm to 30 mm).
While a thermoplastic layer having a first surface bearing a plurality of male fastening elements can be made as described using any of the methods described above with a width of 10 mm to 60 mm, 10 mm to 40 mm, or 10 mm to 30 mm, in some embodiments, this narrow thermoplastic layer is cut from a thermoplastic layer having a wider width. (e.g., having a width of at least 100 mm, 200 mm, 250 mm, 500 mm, or 750 mm). For example, for a wide web having a width at least twice the desired distance between the two opposing side edges of the film, the method can further comprise slitting the wide web to form at least two of the thermoplastic layers. In these embodiments, the at least two of the thermoplastic layers can be stretched simultaneously. In some embodiments, the at least two of the thermoplastic layers remain connected to the wide web during at least a portion of the stretching. This is one way in which slitting the wide web, stretching the at least two of the thermoplastic layers, and laminating the thermoplastic layer to substrate can all be carried out in-line.
While it is understood that in the method of the present disclosure, a width of up to 60 mm (as described above in any of its embodiments) is achieved upon stretching, and a subsequent slitting step is not required to achieve this width before laminating, in some embodiments, the thermoplastic layer may be slit after stretching and before laminating. For example, it may be useful to slit a thermoplastic layer having a width up to 60 mm, 50 mm, 40 mm, or 30 mm in half and laminating each half in-line for use in the left and right portions of an absorbent article. In another example, it may be useful to slit a thermoplastic layer having a width up to 60 mm, 50 mm, 40 mm, or 30 mm into quarters and laminating each quarter in-line for use in the left and right portions of an absorbent article in two manufacturing lines running simultaneously. While cutting the thermoplastic layer into halves or quarters may be desirable, cutting the thermoplastic layer into more than four lanes is typically not carried out for in-line lamination.
As mentioned above, stretch-induced molecular orientation in the thermoplastic layer after stretching can be determined by standard spectrographic analysis of birefringent properties. When a narrow web (e.g., having a width of 10 mm to 50 mm, 10 mm to 40 mm, or 10 mm to 30 mm) is stretched, the thermoplastic layer can have different birefringent properties than when a wider web (e.g., having a width of at least 100 mm, 200 mm, 250 mm, 500 mm, or 750 mm) is stretched and subsequently slit to the dimensions of the narrower web. Since the center of a web is typically stretched more than the edges, the edges of a thermoplastic layer that is slit to a narrow dimension and subsequently stretched can have different retardance properties than the edges of a thermoplastic layer that formed by stretching a wider web and subsequently slitting it to a narrow dimension. Retardance refers to how out of phase the two polarization components of the light are that are refracted by a birefringent material. Birefringence can be calculated from retardance using the film thickness. It is observed that a web prepared by stretching a wider web and subsequently slitting to a narrow dimension can have a sharper drop-off in retardance near its slit edges than a thermoplastic layer prepared by stretching a narrow web. The drop-off in retardance from the edge can be determined by measuring the retardance in a film sample continuously along a line in the direction transverse to the stretching direction starting at the sample edge and ending 500 micrometers from the sample edge. The average retardance over this distance is then calculated. Next the distance from the edge at which the retardance reaches 75% of the average retardance is measured. This can be referred to as the 75% average retardance distance. The lower the change in retardance within 500 micrometers from the edge, the smaller this distance will be. On the other hand, a significant change in retardance within 500 micrometers from the edge of the thermoplastic layer results in a larger 75% average retardance distance and can indicate an “edge effect”.
The edge effect can also be described as a retardance profile in which there is an average retardance along a perpendicular line from the first edge to a location 500 micrometers from the first edge, and a distance from the first edge where 75% of the average retardance is observed is at least 10 micrometers. In general, there is also an average retardance along a perpendicular line from the second edge to a location 500 micrometers from the second edge, and a distance from the second edge where 75% of the average retardance is observed is at least 10 micrometers.
In some embodiments, the thermoplastic layer has a 75% average retardance of greater than 10 micrometers, 15 micrometers, or 20 micrometers. In some embodiments, the thermoplastic layer that is slit to a narrow dimension and subsequently stretched has a 75% average retardance distance of at least 1.5 times, at least twice, or at least 2.5 times 75% average retardance distance than a thermoplastic layer formed by stretching a wider web and subsequently slitting it to a narrow dimension. The measurements can be made using a polarization microscope such as a “LEICA DMRXE”, type TCS, obtained from Microsystems GmbH, Wetzlar, Germany, equipped with an LC-Polscope system from CRi Inc., now part of PerkinElmer Inc., Waltham, Mass., using a Q Imaging Retiga Exi FAST1394 camera. Further details are provided in the Examples, below. Further information about retardance profiles in stretched thermoplastic layers are described in Int. Appl. Pub. Nos. WO 2017/112601 (Gilbert et al.) and WO 2017/112604 (Gilbert et al.), incorporated herein by reference.
The laminate made by the method of the present disclosure can be cut in the cross-machine direction, for example, to provide a patch of any desired size for a given application. Such a patch can be considered a fastening patch.
Laminates made according the method of the present disclosure are useful, for example, in absorbent articles. In some embodiments, the substrate is a component of an absorbent article (e.g., a diaper or adult incontinence article). The component of the absorbent article can be, for example, a fastening tab or a diaper ear. A schematic, perspective view of one embodiment of an absorbent article 620 that can include a laminate made according to the present disclosure is shown in
At least one of the front waist region 666 or the rear waist region 665, more typically the rear waist region 665, comprises at least one fastening tab 640. The fastening tab in the embodiment illustrated in
In some embodiments, when attaching the absorbent article 620 to a wearer's body, the user's end of fastening tab can be attached to a target area 668 comprising fibrous material 672 which may be arranged on the back sheet 662 of the front waist region 666. Examples of loop tapes which may be applied to the target area 668 to provide an exposed fibrous material 672 are disclosed, for example, in U.S. Pat. No. 5,389,416 (Mody et al.) EP 0,341,993 (Gorman et al.) and EP 0,539,504 (Becker et al.). In other embodiments, the back sheet 662 comprises a woven or nonwoven fibrous layer which is capable of interacting with the thermoplastic layer 605 disclosed herein, which has male fastening elements on its first surface. Examples of such back sheets 662 are disclosed, for example, in U.S. Pat. No. 6,190,758 (Stopper) and U.S. Pat. No. 6,075,179 (McCormack et al.). In other embodiments, the size of the target area 668 may be smaller, may be in the form of two separate portions near the first and second longitudinal edges 664a, 664b.
While in the illustrated embodiment, the laminate is included in a fastening tab, in other embodiments, the laminate may be an integral ear portion of the absorbent article. The laminate made by the method according to the present disclosure may also be useful, for example, for disposable articles such as sanitary napkins. Laminates made by a method of the present disclosure may also be useful in many other fastening applications, for example, assembly of automotive parts or any other application in which releasable attachment may be desirable.
In a first embodiment, the present disclosure provides a method of making a laminate, the method comprising:
providing a thermoplastic layer having a first surface and a second surface opposite the first surface, the first surface of the thermoplastic layer bearing a plurality of male fastening elements;
stretching the thermoplastic layer in the machine direction so that it plastically deforms and decreases in width by at least 25 percent, wherein after the stretching, the thermoplastic layer has a width of up to 60 millimeters; and subsequently
laminating the second surface of the thermoplastic layer to a substrate to form the laminate, wherein the stretching and laminating are completed in-line.
In a second embodiment, the present disclosure provides the method of the first embodiment, wherein the thermoplastic layer is stretched in the machine direction by differential speed rolls.
In a third embodiment, the present disclosure provides the method of the second embodiment, wherein following stretching using a second roll having a speed sufficient to stretch the thermoplastic layer, the thermoplastic layer is not directed onto a third roll having a lower speed than the second roll before laminating.
In a fourth embodiment, the present disclosure provides method of making a laminate, the method comprising:
providing a thermoplastic layer having a first surface and a second surface opposite the first surface, the first surface of the thermoplastic layer bearing a plurality of male fastening elements;
stretching the thermoplastic layer in the machine direction by first and second rolls of different speeds so that it plastically deforms and decreases in width, wherein after the stretching, the thermoplastic layer has a width of less than 60 millimeters; and subsequently
laminating the second surface of the thermoplastic layer to a substrate to form the laminate, wherein the stretching and laminating are completed in-line,
wherein the second roll has a faster speed than the first roll, and wherein the thermoplastic layer is not directed onto a third roll having a slower speed than the second roll before the laminating.
In a fifth embodiment, the present disclosure provides the method of the fourth embodiment, wherein stretching the thermoplastic layer in the machine direction decreases its width by at least 10 percent, at least 20 percent, or at least 25 percent.
In a sixth embodiment, the present disclosure provides the method of any one of the first to fifth embodiments, wherein stretching the thermoplastic layer so that it plastically deforms comprises stretching to at least 20% elongation.
In a seventh embodiment, the present disclosure provides the method of any one of the first to sixth embodiments, wherein stretching the thermoplastic layer so that it plastically deforms comprises stretching to at least 25% elongation.
In an eighth embodiment, the present disclosure provides the method of any one of the first to seventh embodiments, wherein stretching the thermoplastic layer so that it plastically deforms comprises stretching to at least 30% elongation.
In a ninth embodiment, the present disclosure provides the method of any one of the first to eighth embodiments, wherein stretching the thermoplastic layer so that it plastically deforms comprises stretching to at least 50% elongation.
In a tenth embodiment, the present disclosure provides the method of any one of the first to ninth embodiments, wherein the thermoplastic layer is stretched by 1.25× to 5× in the machine direction.
In an eleventh embodiment, the present disclosure provides the method of any one of the first to tenth embodiments, wherein the thermoplastic layer is stretched by 1.5× to 4× in the machine direction.
In a twelfth embodiment, the present disclosure provides the method of any one of the first to eleventh embodiments, wherein stretching the thermoplastic layer in the machine direction decreases its width by at least 30 percent.
In a thirteenth embodiment, the present disclosure provides the method of any one of the first to twelfth embodiments, wherein stretching the thermoplastic layer in the machine direction decreases its width by at least 35 percent.
In a fourteenth embodiment, the present disclosure provides the method of any one of the first to thirteenth embodiments, wherein stretching the thermoplastic layer in the machine direction decreases its width by up to 50 percent.
In a fifteenth embodiment, the present disclosure provides the method of any one of the first to fourteenth embodiments, wherein stretching is carried out multiple times before laminating the second surface of the thermoplastic layer to a substrate.
In a sixteenth embodiment, the present disclosure provides the method of any one of the first to fifteenth embodiments, further comprising heating the thermoplastic layer before stretching, while stretching, after stretching, or a combination thereof.
In a seventeenth embodiment, the present disclosure provides the method of any one of the first to sixteenth embodiments, wherein the thermoplastic layer is laminated to the substrate by adhesive bonding, thermal bonding, point bonding, ultrasonic welding, laser welding, or combinations thereof.
In an eighteenth embodiment, the present disclosure provides the method of any one of the first to seventeenth embodiments, wherein the thermoplastic layer is stretched in at least the cross-direction before it is stretched in the machine direction.
In a nineteenth embodiment, the present disclosure provides the method of any one of the first to eighteenth embodiments, wherein the thermoplastic layer comprises at least one of a polyolefin, polyamide, or polyester.
In a twentieth embodiment, the present disclosure provides the method of the nineteenth embodiments, wherein the thermoplastic layer comprises at least one of polypropylene or polyethylene.
In a twenty-first embodiment, the present disclosure provides the method of the twentieth embodiment, wherein the thermoplastic layer comprises polypropylene and further comprises an impact modifier.
In a twenty-second embodiment, the present disclosure provides the method of the twentieth embodiment, wherein the thermoplastic layer comprises beta-phase polypropylene.
In a twenty-third embodiment, the present disclosure provides the method of any one of the first to twenty-second embodiments, wherein the substrate comprises at least one of a nonwoven material, a knit material, or a film.
In a twenty-fourth embodiment, the present disclosure provides the method of any one of the first to twenty-third embodiments, wherein the substrate comprises an elastic material.
In a twenty-fifth embodiment, the present disclosure provides the method of any one of the first to twenty-fourth embodiments, wherein the substrate is a component of a personal care product. In some embodiments, the component is a fastening tab or a diaper ear.
In a twenty-sixth embodiment, the present disclosure provides the method of any one of the first to twenty-fifth embodiments, wherein after stretching, the thermoplastic layer has a width of 5 to 50 millimeters.
In a twenty-seventh embodiment, the present disclosure provides the method of any one of the first to twenty-sixth embodiments, wherein after stretching, the thermoplastic layer has an average thickness of up to 75 micrometers.
In a twenty-eighth embodiment, the present disclosure provides the method of the twenty-seventh embodiment, wherein after stretching, the average thickness of the thermoplastic layer is up to 50 micrometers.
In a twenty-ninth embodiment, the present disclosure provides the method of any one of the first to twenty-eighth embodiments, wherein the thermoplastic layer has opposing side edges and a retardance profile extending between the side edges that drops off near each edge to create an edge effect.
In a thirtieth embodiment, the present disclosure provides the method of any one of the first to twenty-ninth embodiments, wherein the thermoplastic layer has a 75% average retardance of greater than 10 micrometers.
In a thirty-first embodiment, the present disclosure provides the method of any one of the first to thirtieth embodiments, wherein a density of the male fastening elements before stretching is in a range from 394/cm2 (2500/in2) to 1575/cm2 (10000/in2).
In a thirty-second embodiment, the present disclosure provides the method of any one of the first to thirty-first embodiments, wherein a density of the male fastening elements after stretching is in a range from 248/cm2 (1600/in2) to 550/cm2 (3500/in2).
In a thirty-third embodiment, the present disclosure provides the method of any one of the first to thirty-second embodiments, wherein stretching the thermoplastic film comprises adjusting a density of the male fastening elements to achieve a pre-determined density.
In a thirty-fourth embodiment, the present disclosure provides the method of the thirty-third embodiment, wherein the pre-determined density is selected based on a desired shear or peel strength to a fibrous substrate.
In a thirty-fifth embodiment, the present disclosure provides the method of any one of the first to thirty-fourth embodiments, wherein the thermoplastic layer has no through-holes.
In a thirty-sixth embodiment, the present disclosure provides the method of any one of the first to thirty-fifth embodiments, wherein the thermoplastic layer is substantially planar.
In a thirty-sixth embodiment, the present disclosure provides the method of any one of the first to thirty-sixth embodiments, further comprising slitting the stretched thermoplastic layer into halves or quarters before laminating.
In order that this disclosure can be more fully understood, the following examples are set forth. It should be understood that these examples are for illustrative purposes only and are not to be construed as limiting this disclosure in any manner.
Film grade polypropylene (PP) copolymer, a polypropylene impact copolymer, was obtained from the Dow Chemical Company, Midland, Mich., under the trade designation “DOW C700-35N POLYPROPYLENE RESIN”. The polymer density was reported to be 0.902 g/cc as measured according to ASTM D972 and the melt flow index (MFI) was reported to be 35 (at 230° C. and under the load of 2.16 kg) as measured according to ASTM D1238.
A substantially continuous thermoplastic layer was prepared with an array of upstanding posts integral with the thermoplastic layer. The upstanding posts were capped. The cap shapes were oval, and after they were made, they were deformed using the procedure described in U.S. Pat. No. 6,132,660 (Kampfer) to provide “hook heads with downwardly projecting fiber engaging portions”.
A thermoplastic layer with male fastening elements was prepared by feeding a stream of C700-35N Polypropylene Resin through a 2 inch single screw extruder. Barrel zones 1-7 were set at 176° C., 170° C., 180° C., 190° C., 200° C., 218° C., and 218° C., respectively. The molten resin was then fed through a sheet die to a rotating cylindrical mold. The temperature of the die was set at 218° C., and the temperature of cylindrical mold was set at 90° C. The screw speed was set at 80 rpm. Rapid flow of the resin into the mold cavities induced molecular orientation parallel to the direction of flow. The mold was water-cooled to provide rapid quenching that maintained the orientation in the polymer. The post density was 3500 posts per square inch (542 posts per square centimeter) arranged in a staggered array and the post shape was conical. The web was fed directly into a cap forming apparatus. The posts were capped with oval shaped caps using the procedure described in U.S. Pat. No. 5,845,375 (Miller et al.). The caps were subsequently deformed using the procedure described in U.S. Pat. No. 6,132,660 (Kampfer). The web was 140 mm wide and was wound into a roll.
The 140-mm wide web was then unwound and slit down to several 14-mm wide strands, each of which was wound into a roll.
One of the 14-mm wide rolls was then unwound and stretched in the machine direction using a series of draw ratios shown in Table 1, below, by passing the sample through a pair of rolls arranged with one roll on top of the other roll. The top roll was a rubber-coated roll at room temperature. The bottom roll was a metal roll that was heated at 70 degrees Celsius. The web was S-wrapped around the two rolls, with the male fastening elements positioned toward the rubber-coated roll and away from the metal roll. The gap between the rubber roll and the metal roll was 6 inches (15.2 cm). After stretching, while still in-line, the thermoplastic layer with male fastening elements was then laminated to the adhesive-coated side of a nonwoven adhesive tape obtained from 3M Company, St. Paul, Minn., under the trade designation “CFT-3003” at a nip point further down web. The final lamination line speed was 5 meters per minute. For each of Control Example 1 and Examples 2 to 4, the speed of bottom roll (Roll 2) relative to the top roll (Roll 1) and the resulting draw ratio is shown in Table 1, below. The final width of the web is also shown in Table 1, below.
Control Example 5 and Examples 6 to 8 were carried out using the procedure described for Control Example 1 and Examples 2 to 4, with the modification that the 140-mm wide web was slit into 30-mm wide webs. One of the 30-mm wide rolls was then unwound and stretched in the machine direction using a draw ratio shown in Table 2, below. For each of Control Example 5 and Examples 6 to 8, the speed of bottom roll (Roll 2) relative to the top roll (Roll 1) and the resulting draw ratio is shown in Table 2, below. The final width of the web is also shown in Table 2, below.
This disclosure is not limited to the above-described embodiments but is to be controlled by the limitations set forth in the following claims and any equivalents thereof. This disclosure may be suitably practiced in the absence of any element not specifically disclosed herein.
This application claims priority to U.S. Provisional Application No. 62/526,764, filed Jun. 29, 2017, the disclosure of which is incorporated by reference in its entirety herein.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/US2018/039400 | 6/26/2018 | WO | 00 |
| Number | Date | Country | |
|---|---|---|---|
| 62526764 | Jun 2017 | US |
