RU2392362C2 - Two-component polymer fibre with modified surface - Google Patents

Abstract

FIELD: chemistry. ^ SUBSTANCE: fibre includes first polymer and composite. Composite forms layer comprising at least a part of fibre surface. Composite is comprised of polymer and filler with mean particle size exceeding thickness of layer formed of composite. Fibres can be of round, elliptic, three-foil, triangular, dumbbell, flat or hollow shape and symmetric or asymmetric shell/core or side-by-side configuration. Method of fibre obtainment involves composite formation by mixing first polymer and filler and joint extrusion of second polymer and composite in thermal binding conditions, with second polymer forming core and composite forming a layer at fibre surface. ^ EFFECT: improved fibre properties. ^ 28 cl, 6 dwg, 5 tbl, 10 ex

Description

Technical field

The invention relates to fibers and methods for their preparation. More specifically, the invention relates to synthetic fibers having an increased surface roughness and an improved touch to the touch.

State of the art

Many forms of fibers and fabrics were made from thermoplastics. The properties of fibers and fabrics are functions, at least in part, of the polymer (s) from which they are made, and the ways in which they are made. Representatives of these various types of polymers, fibers and fabrics and methods for their preparation are described in U.S. Patent Nos. 4076698, 4644045, 4830907, 4909975, 4578414, 4842922, 4990204, 5112686, 5322728, 4425393, 5068141 and 6190768, the combination of which is presented as a reference.

Mineral additives can be advantageously used to influence the properties of fibers obtained from thermoplastics. For example, in US Pat. No. 4,254,182, fibers are obtained by incorporating silica with a particle size ranging from 10 to 200 nanometers. Silica is then removed from the fiber to produce surface irregularities or cavities in the fiber. As a result, the fiber’s working surface area and friction coefficient can be increased, which can reduce smoothness, greasy touch, brilliant appearance and color depth perception.

Minerals were also encapsulated in the polymer to form a composite and to achieve the desired result from the physical property. US patent No. 6797377 describes fibers made of a thermoplastic polymer (in particular polypropylene) containing titanium dioxide, wax and at least one mineral filler such as kaolin or calcium carbonate. Fillers are added in such quantities that they are encapsulated in a polymeric substance. It is also noted in the patent that when a mixture of oil and minerals is added together to the polypropylene, the softness of the tape improves, while the tensile strength of the fabric tends to decrease.

US patents Nos. 5413655 and 5344862 describe the use of silica as an encapsulated additive in monocomponent fibers for nonwoven applications. The additive system includes two components: polysiloxane ether and hydrophobic colloidal silica. Silica is added in an amount of from 3 to 1,500 million parts of a thermoplastic polyether, and polyester is added in an amount of from 0.1 to 3 percent by weight of a thermoplastic polyester. The claimed result is a significant increase in the tensile strength of non-woven synthetic fabrics.

Thus, there is a need to improve tissue-like perception (touch of natural fibers) of synthetic fibers.

SUMMARY OF THE INVENTION

In one aspect, the present invention relates to a bicomponent fiber having an increased surface roughness. The bicomponent fiber may include a first polymer and a composite. The composite may form a layer that forms at least a portion of the surface of the fiber. The composite may include a second polymer and a filler. The average particle size of the filler may be greater than the thickness of the layer formed by the composite.

The present invention also provides a method for producing a bicomponent fiber, comprising the steps of mixing the first polymer and the filler to form a composite, and coextrusion under thermal bonding conditions of the second polymer and the composite to form a bicomponent fiber. The second polymer can form a polymer core, and the composite can form a layer that forms at least part of the surface of the fiber. The average particle size of the filler may be greater than the thickness of the composite layer.

The present invention also provides an improved method for producing bicomponent fiber, comprising coextrusion under thermal bonding conditions of (a) a first polymer and (b) a second polymer, which forms a layer that forms at least part of the surface of the fiber. The improvement includes mixing the filler with the second polymer to form a composite, where the average particle size of the filler is greater than the thickness of the layer formed by the composite.

Other aspects and advantages of the invention will be apparent from the following description and the appended claims.

Brief Description of the Drawings

1 is a schematic illustration of a core / cladding embodiment in a bicomponent fiber of the present invention.

Figure 2 is a schematic illustration of an embodiment where the bicomponent fiber of the present invention is configured side-by-side.

Figure 3 illustrates simplified filler particle distribution formats used in developing a model useful in manufacturing embodiments of the bicomponent fibers of the present invention.

Figures 4-6 are SEM images of embodiments of bicomponent fibers of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Conventional synthetic fibers that are extruded and stretched have a very smooth surface with very slight discontinuities, thus creating a smooth, oily touch. In one aspect, embodiments of the invention relate to modified surface roughness of a fiber to improve the perception of the sample by touch of synthetic fibers. The present invention provides a method for roughening the surface of synthetic fibers, where the surface roughness extends outside the shell of the bicomponent fibers, which leads to improved perception of the sample by touch, reducing the smoothness, oil test to the touch of the fiber. In one embodiment, the addition of mineral fillers, such as calcium carbonate (CaCO ₃ ), to the polymer shell, where the mineral fillers have an average particle diameter greater than the shell thickness, can provide a “protruding” effect, providing a rougher surface and improved touch perception of the sample.

General definitions

As used herein, “fiber” means a material in which the ratio of length to diameter is greater than about 10. Fibers are generally classified according to their diameter. A filament fiber is generally defined as having an individual fiber diameter of about more than 15 denier, usually about more than 30 denier. Excellent denier fiber generally refers to a fiber having a diameter of less than 15 denier. A microfinishing fiber is defined as a fiber having a diameter of about less than 100 microns.

"Filament fiber" or "single filament fiber" means a continuous filament of a substance of indefinite (i.e., unspecified) length, as opposed to "staple fiber", which is an intermittent filament of a material of a specified length (that is, a thread that has been cut or otherwise segmented into a given lengths).

"Polyolefin polymer" means a thermoplastic polymer derived from one or more olefins. The polyolefin polymer may have one or more substituents, for example, a functional group such as carbonyl, sulfide, and so on. For the purposes of this invention, “olefins” include aliphatic, alicyclic and aromatic compounds having one or more double bonds. Examples of olefins include ethylene, propylene, butene-1, hexene-1, octene-1, 4-methylpentene-1, butadiene, cyclohexene, dicyclopentadiene, styrene, toluene, alpha-methylstyrene and the like.

“Thermostable” and similar terms mean that a fiber or other structure or article comprising the polyolefin polymer of the present invention will retain substantially its elasticity during repeated stretching and contracting after heat exposure at about 90 ° C (about 200 ° F), for example, temperatures that are transferred during the production, processing (e.g. dyeing) and / or cleaning of a fabric made from a structure or article.

“Elastic” means that the fiber will restore at least 50 percent of its elongated length, after the first stretching, and after the fourth, 100 percent deformation (doubling the length). Elasticity can also be described by "permanent deformation" of the fiber. Residual deformation is the opposite of elasticity. The fiber is stretched to a certain value and subsequently released to its original position before stretching, and then stretched again. The value at which the fiber begins to pull the load is indicated as the percentage of permanent deformation. "Elastic substances" in this area are also called "elastomers" and "elastomeric". An elastic substance (sometimes referred to as an elastic article) includes an isolated polyolefin polymer, as well as, but is not limited to, a polyolefin polymer in the form of a fiber, film, strip, tape, braid, sheet, coating, molded product and the like. A preferred elastic material is fiber. The elastic material may be vulcanized or unvulcanized, irradiated or unirradiated and / or crosslinked or uncrosslinked.

"Inelastic substance" means a substance, such as a fiber, which is not elastic, as defined above.

“Significantly crosslinked” and similar terms mean that a polyolefin polymer, having a specific shape or in the form of an article, has a recoverable xylene equivalent to or less than 70 percent by weight (i.e., equivalent to or more than 30 percent by weight of the gel content), preferably equivalent or less than 40 percent by weight (i.e., equivalent to or more than 60 percent by weight of the gel content). Recoverable xylene (and gel content) are determined according to ASTM D-2765.

“Vulcanized” and “substantially vulcanized” means that a polyolefin polymer having a specific shape or product shape has been exposed to or subjected to a treatment that results in a significant degree of crosslinking. The fibers of the present invention can be vulcanized or crosslinked in various ways known to specialists in this field.

"Vulcanizable" and "crosslinkable" means that the polymer of the polyolefin of a certain shape or in the form of an article is not vulcanized or crosslinked, and has not been subjected to a treatment that has led to a significant degree of crosslinking (although the polyolefin polymer of a certain shape or in the shape the product includes additive (s) or functionality that will lead to a significant degree of crosslinking when it is exposed or subjected to such processing). In the application of this invention, vulcanization, irradiation or crosslinking can be carried out by UV radiation.

"Single component fiber" means a fiber that has a single region or domain of a polymer and does not have any other distinct regions of the polymer (which have bicomponent fibers).

“Bicomponent fiber” means a fiber that has two or more different regions or domains of a polymer. Bicomponent fibers are also known as conjugated or multicomponent fibers. The polymers are usually different from each other, although two or more components may include the same polymer. The polymers are located substantially in different zones in the cross section of the bicomponent fiber and usually stretch continuously along the length of the bicomponent fiber. A bicomponent fiber configuration may be, for example, a shell / core arrangement (in which one polymer is surrounded by another), a side-by-side arrangement, a pie arrangement, or an island in the sea arrangement. Bicomponent fibers are further described in US Pat. Nos. 6,225,243, 6,140,442, 5,382,400, 5,336,552 and 5,108,820. These patents are incorporated by reference in their entirety.

“Melt-blown fibers” are fibers formed by extruding a molten thermoplastic polymer composition through a plurality of small holes, typically round, capillary extruder heads, as molten filaments or fibers converging at high gas flow rates (eg, air), whose function is to attenuate thickness of threads or fibers to smaller diameters. The filaments or fibers are obtained at high gas flow rates and are placed on the collecting surface to form randomly dispersed fibers with average diameters of typically less than 10 microns.

“Melt spun fibers” are fibers formed by melting at least one polymer and then drawing the fibers in the molten state to a diameter (or other cross-sectional shape) less than the diameter (or other cross-sectional shape) of the extruder head.

“Non-woven synthetic fibers” are fibers formed by extruding a molten thermoplastic polymer composition through a plurality of small holes, typically round, capillary heads of a multichannel extruder mouthpiece. The diameter of the extruded fibers rapidly decreases, and then the fibers are placed on the collecting surface to form a tissue of randomly dispersed fibers with average diameters, typically between about 7 and about 30 microns.

"Nonwoven fabric" means a tape or fabric having the structure of individual fibers or threads that are randomly layered, but not in an identifiable manner, as in the case of knitted fabric. The elastic fiber of the present invention can be used to prepare nonwoven fabric structures, as well as composite structures of an elastic nonwoven fabric in combination with inelastic materials.

“Yarn” means a continuous thread of woven or otherwise bound threads that may be used in the manufacture of woven and knitted fabrics and other articles. Yarn can be coated and uncovered. Coated yarn is a yarn at least partially wrapped in an outer coating of another fiber or substance, usually a natural fiber, such as cotton or wool. As used herein, “fiber” or “fibrous” means a particular material in which the ratio of length to diameter of this material is greater than about 10. Conversely, “non-fiber” or “not fibrous” means a particular material in which the ratio of length to diameter this material is less than about 10.

Getting fiber and other products

The inventors have found that bicomponent fibers having an improved touch test can be obtained by modifying the surface roughness of the fiber. A bicomponent fiber may include at least two components, for example, having at least two different polymer systems. The first component, for example "component A", typically serves the purpose of maintaining the shape of the fiber during thermal bonding at elevated temperatures. The second component, for example "component B", serves as an adhesive. Component A may have a higher melting point than component B. For example, in one embodiment, component A may have a melting point of at least about 20 ° C, preferably at least 40 ° C higher than the melting point of component B. In others embodiments, component A and component B may have similar melting points. In addition, in other embodiments, component B may have a higher melting point than component A.

To simplify, the structure of bicomponent fibers in this description will be called the structure of the core / cladding. However, the fiber structure may have any one of the multi-component configurations described above, for example, the core / shell, side-by-side, “pie” or “islands in the sea” configuration, where component B forms a layer that forms at least part of the surface of the fiber.

In some embodiments, the core (component A) may include a thermoplastic polymer, such as a polyolefin. In other embodiments, the core may include an elastomeric polymer, illustrated by homogeneous branched polymers, two-block, three-block or multi-block elastomeric copolymers, such as olefin copolymers, for example styrene-isoprene-styrene, styrene-butadiene-styrene, styrene-ethylene / butylene-styrene or styrene-ethylene / propylene-styrene; polyurethanes; polyamides; and polyesters. In certain embodiments, the core may include olefin block copolymers disclosed in WO2005 / 090427, incorporated herein by reference.

The shell (adhesive or component B) may also be elastomeric, for example, a homogeneous branched polymer, preferably homogeneous branched ethylene or propylene. These materials are well known. For example, US Pat. No. 6,140,442 provides an excellent description of homogeneous branched, substantially linear polyolefins, especially ethylene polymers; the contents of which are incorporated herein by reference.

Mineral fillers can be added to the shell to obtain a composite and improve the desired properties. In preferred embodiments, the average particle size of the natural filler is greater than the shell thickness, with a “sticking” effect. A “protruding” effect can be illustrated for a bicomponent fiber core / cladding, as shown in figure 1, where the polymer core 10 is surrounded by a shell of the composite, which includes a polymer matrix 12 and a natural filler 14. Figure 2 illustrates the “protruding” effect for a two-component fiber side side by side. Other forms of bicomponent fibers will have similar characteristics when the composite of component B forms at least a portion of the surface of the fiber in order to provide a “sticking” effect that causes surface roughness on the fiber.

In certain embodiments, the mineral filler may comprise from about 1 to about 25 percent by weight of the shell. In other embodiments, the natural bulking agent may be from about 2 to about 20 percent; from about 3 to about 15 percent; or from about 5 to about 10 percent by weight of the shell. The shell may also include other additives ranging from about 0 to about 5 percent by weight of the shell, including plasticizers, compatibilizers and other additives known in the art.

Fillers useful in the present invention to improve the friction coefficient of a fiber or to produce a “sticking out” effect include, but are not limited to, untreated and treated silica, alumina, silica, talc, calcium carbonate and clay. In certain embodiments, the preferred natural bulking agent is calcium carbonate (CaCO ₃ ). In other embodiments, the natural filler may be a compatible mineral substance, where the mineral substance is coated with a compound to improve the dispersion and compatibility of the mineral substance in the polymer matrix. For example, the mineral substance may be calcium carbonate, where calcium carbonate is coated with stearic acid to improve the dispersion and compatibility of calcium carbonate in the polymer matrix.

The average particle size of the mineral filler used in the shell composite can be selected based on the desired shell thickness and can typically range from about 0.1 to about 20 microns. For example, for a fiber having a shell thickness of 1 micron, a natural filler having an average particle size of greater than about 1 micron can produce the desired “sticking out” effect. In some embodiments, the ratio of the average particle size of the natural filler to the shell thickness may be approximately equivalent to or greater than 1.0. In other embodiments, the ratio may be greater than about 1, but less than about 2; in other embodiments, the ratio may be greater than about 1.2, but less than about 1.8.

The natural filler may have a particle size distribution, where some particles are smaller than the average particle size and other particles larger than the average particle size. Particle size distribution can affect the implementation of the "sticking out" effect; for example, many particles are smaller than the shell thickness, therefore, can be encapsulated inside the shell, such as particles 16 in figures 1 and 2. Particles having a size much larger than the shell thickness can lead to adhesion problems where the particles do not remain in the composite matrix. A larger particle size distribution can also lead to a greater distance between particles protruding from the shell (as described below). In some embodiments, the preferred particle size distribution may be less than about 5. In other embodiments, the preferred particle size distribution may be less than about 3, less than about 2.5, less than about 2.0, or less than about 1.5 in other embodiments.

The fiber diameter can be measured and presented in various forms. Typically, fiber diameter is measured in denier per thread. Denier is a textile term that is defined as grams of fiber per 9000 meters of length of this fiber. Monofilament generally refers to an extruded fiber having a denier per thread greater than 15, typically greater than 30. Fine denier fiber typically refers to a fiber having a denier of about 15 or less. Microdeny (or microfibre) generally refers to a fiber having a diameter of not more than about 100 micrometers. For the fibers of the present invention, the diameter can vary widely with little effect on the elasticity of the fibers. The denier of the fiber, however, can be varied to suit the characteristics of the final product, and for this reason, the fiber should preferably be from about 0.5 to about 30 denier / thread for the meltblown fiber; from about 1 to about 30 denier / thread for a non-woven synthetic fiber; and from about 1 to about 20,000 denier / thread for a continuous wound thread. The shell thickness and average particle size of the natural filler can be selected based on the desired strand diameter or denier.

The bicomponent fibers of the present invention may have a core that comprises from 80 to 99 percent by weight of the fiber. In other embodiments, the core may be from 85 to 95 percent by weight of the fiber. The bicomponent fibers of the present invention may have a sheath that comprises from about 1 to about 20 percent by weight of the fiber. In other embodiments, the sheath comprises from about 5 to about 15 percent by weight of the fiber.

The shape of the fiber is not limited. For example, ordinary fibers have a circular cross-sectional shape, but sometimes the fibers have excellent shapes, for example a three-bladed shape or a flat shape (for example, similar to a "braid"). The bicomponent fibers disclosed herein are not limited to the shape of the fiber.

The bicomponent fiber of the present invention can be used with other fibers, such as PET, nylon, cotton, KEVLAR® (available from E.I. Du Pont de Nemours Co.) and so on, to obtain elastic fabrics. As an added benefit, the heat and moisture resistance of certain bicomponent fibers can allow polyester-PET fibers to dye under normal PET dyeing conditions. Other commonly used fibers, especially spandex (e.g. LYCRA®, spandex available from E.I. Du Pont de Nemours Co.), are commonly used under less stringent PET staining conditions to prevent deterioration.

Fabrics made from the bicomponent fibers of the present invention include woven, non-woven and knitted fabrics. Non-woven fabrics can be made in various ways, for example, stitching, molding (or hydrodynamic weaving), as disclosed in US patent No. 3485706 and 4939016, carding and thermal binding of staple fibers; bonding, spinning continuous fibers in one continuous process or blowing molten fibers into a fabric and subsequent calendaring or thermal bonding of the resulting tape. These various nonwoven fabric manufacturing techniques are well known to those skilled in the art, and the scope of the present invention is not limited in any particular way. Other structures made from such fibers are also included in the scope of the invention, including, for example, mixtures of the fibers of the present invention with other fibers (e.g. PET, cotton, and so on).

Manufactured products that can be made using the bicomponent fibers and fabrics of the present invention include elastic composite products (eg, diapers) that have elastic parts. For example, the elastic portions are typically constructed in the diaper waist belt portion to prevent the diaper from falling and in the leg portion to prevent leakage (as shown in US Pat. No. 4,381,781, which is incorporated herein by reference in its entirety). Often, elastic parts contribute to a better form of assembly and / or fastening systems for a good combination of comfort and reliability. The fibers and fabrics of the present invention can also produce structures in which elasticity is combined with breathability. For example, the elastic fibers, fabrics, and / or films of the invention may be included in the structures disclosed in US Pat. No. 6,176,952, which is incorporated herein by reference in its entirety.

The elastic fibers and fabrics of the invention can be used in various structures, as described in US patent No. 2957512 (patent '512), which is incorporated into this description by reference. For example, layer 50 of the structure described in the '512 patent (e.g., an elastic component) can be replaced by the elastic fibers and fabrics of the invention, especially where flat, folded, creped, corrugated and so on inelastic materials are assembled into elastic structures. The attachment of the elastic fibers and / or fabrics of the invention to inelastic fibers, fabrics or other structures can be carried out by melt bonding or by adhesives. Assembled or coated elastic structures can be made from the elastic fibers and / or fabrics of the invention and the inelastic component by pleating the inelastic component (as described in the '512 patent) prior to joining, pre-stretching the elastic component before joining, or pulling together the elastic component after joining when heated.

The fibers of the invention can also be used in the process of crosslinking by molding (or hydrodynamic weaving) to create new structures. For example, US Patent No. 4,801,482, which is incorporated herein by reference in its entirety, discloses an elastic sheet (12) that can be made using the new elastic fibers and / or fabrics described herein. Continuous elastic threads, which are described here, can also be used in woven applications where high elasticity is desired.

US Pat. No. 5,037,416 ('416 patent), which is incorporated herein by reference, describes advantageous methods for forming a contour top sheet using elastic woven strips (see element 19 of the' 416 patent). The elastic fibers of the invention can serve as element 19 of the '416 patent or can be used in the form of a fabric, providing the desired elasticity.

The elastic panels can also be made of the elastic fibers and fabrics of the invention disclosed herein, and can be used, for example, as elements 18, 20, 14 and / or 26 of US Pat. No. 4,940,464 ('464 patent), which is included in this description by reference. The elastic fibers and fabrics of the invention described herein can also be used as an elastic component of a side panel composite (e.g., layer 86 of the '464 patent).

The elastic materials of the present invention can also be made permeable or "breathable" by any method well known in the art, including aperture, slitting, microperforation, blending with fibers or foams or the like, and combinations thereof. Examples of such methods include US patent No. 3156242 Crowe, Jr., US patent No. 3881489 Hartwell, US patent No. 3989867 Sisson and US patent No. 5085654 Buell, each of which is incorporated into this description by reference in its entirety.

Model of the rough surface of a shell filled with calcium carbonate

As described above, the bicomponent fibers of the present invention may include a sheath, which includes a polymeric material and a filler, producing a "sticking out" effect. A simple model describing the surface roughness of a fiber in terms of the ratio of particle size to shell thickness and distance between particles in the shell is presented below to allow a better understanding of the present invention.

The perception of a sample to the touch of a PP non-woven fabric may be due to the roughness of the fabric surface at the microscopic level, as in the Kawabata measurement system. The surface roughness can be defined as the deviation of the surface shape from some ideal or given shape. Thus, for a nominally flat surface, the roughness can be defined in terms of the ratio of the true total area to the intended nominal area, or as the steepness of a profile taken along a predetermined line, or as the distance between the upper points and the lower points of the surface. In this document, two terms are used to describe the surface roughness of a fiber: the ratio of the average particle size to the shell thickness and the distance between particles in the shell. As will be shown below, roughness directly correlates with the physical properties of the fiber and filler. To establish a simple mathematical model for the thickness of the composite micro-shell, it is assumed that the shell is a filled two-phase composite system, while the core is assumed to be a homogeneous polymer resin, such as homogeneous polypropylene (hPP).

Correlation between mass and volume of component content in a two-phase composite

For a two-phase composite system, it can be shown that the following formula can be used to convert percent by mass to percent by volume:

α _av = 1 / (1+ (1 / α _aw -1) ρ _a / ρ _b ) (1)

or equation (2) can be used to convert percent by volume to percent by mass:

α _aw = 1 / (1+ (1 / α _av -1) ρ _b / ρ _a ) (2)

where α _av is the percent by volume of component a, α _aw is the percent by weight of component a, ρ _a is the density of component a, and ρ _b is the density of component b.

For example, for an hPP composite filled with calcium carbonate, it is assumed that the density of PP is 0.90, the density of calcium carbonate is 2.7 and 2 percent by volume of CaCO ₃ will be used. From equation (2), the filling level of calcium carbonate filled hPP composite is equivalent to 5.77 percent by weight.

Prediction of the thickness of a two-phase composite sheath for a bicomponent fiber

Assumptions used to predict thickness include: (1) the cross section of a bicomponent fiber consists of two perfect concentric circles; and (2) sections of the shell of the composite and the homogeneous core of the bicomponent fiber are formed as two different phases without interfering from one to the other.

When the contents of the sheath in a bicomponent fiber are given as a percentage by weight, the necessary formulas for estimating the thickness of the composite sheath are

ρ _s = A _f ρ _filler + (lA _f ) ρ _m

k = 0.5 {(ρ _c w _s / ρ _s w _c ) ^0.5 -1}

h = 11.894k [dpf / (ρ _c + 4ρ _s k (l + k))] ^0.5

D _c = h / k

D _f = D _c + 2h

where ρ _filler is the filler density in g / cm ³ ; ρ _m is the density of the polymer matrix in g / cm ³ ; A _f - percent by volume of filler in the microcomposite; w _f - percent by weight of the filler in the microcomposite; ρ _c is the density of the polymer in the core section of a bicomponent fiber in g / cm ³ ; ρ _s is the density of the polymer in the cladding section of the bicomponent fiber in g / cm ³ ; w _c is the percentage by weight of the core section; w _s is the percentage by weight of the shell section (note that: w _c + w _s = 1); V _c - percent by volume of the core section; V _s - percent by volume of the shell section (note that V _c + V _s = 1); dpf - denier per thread or grams of thread at 9000 meters; k is the parameter of the ratio of the shell to the core; h is the shell thickness in microns; D _c is the diameter of the core section in microns; and D _f is the diameter of the bicomponent fiber in microns.

Examples of calculated shell thickness values of a bicomponent hPP fiber filled with calcium carbonate, based on the known filler content, in percent by weight (w _f ), are shown in Table 1. The core is an hPP polymer (density = ρ _c = 0.90 g / cm ³ ), while the shell is a shell of calcium carbonate (density = 2.70 g / cm ³ ) filled with hPP microcomposite, the resulting shell density, ρ _s , is greater than the density of the core, ρ _c .

Table 1
The calculated shell thickness for the shell of calcium carbonate filled with PP based on w _f .

When the sheath content in a bicomponent fiber is known as percent by volume, the expression for the formula for calculating the thickness of the composite sheath is changed based on the ratio between percent by volume and percent by weight, which is given above.

The filler content in the shell can be expressed either as a percentage by weight or as a percentage by volume, so the formulas for calculating the thickness of the shell can be developed accordingly. It should be noted that the formulas only approximate the shell thickness as the included volume of the “sticking out” part of the particles, as if it were immersed in a polymer matrix. As a result, the actual shell thicknesses must be less than the predicted thickness. However, since the percentage by volume of filler in the shell is usually low (15% or less), the possible error is small and can be neglected in most cases.

From table 1 it is seen that for a constant sheath content in percent by weight in a bicomponent fiber with the largest diameter of the bicomponent fiber (or the largest dpf), the thickness of the shell of the microcomposite will be the largest. Further, for a constant diameter (or dpf) of a bicomponent fiber at the highest percent by weight of the sheath content, the sheath thickness will be the largest. Ultimately, the effect of the filler content in the shell on the shell thickness is relatively small. With increasing filler content, the shell thickness increases to a small extent. Similar observation results can be obtained with respect to the thickness of the shell when considering percent by volume.

The surface roughness of the fiber, represented by the “sticking out” effect of the filler particles, can be partially described in terms of the ratio of the filler particle size to the shell thickness. If this ratio is less than 1, the particles will be immersed in the matrix of the polymer shell and will be less effective in creating surface irregularities. On the other hand, if the ratio exceeds 2, more than half of the volume of the particles of the mineral substance can stick out of the shell and be exposed to air, which may lead to the shell losing its fixability with respect to the submerged particle. It should be noted, however, that this approximation does not consider mechanical effects and adhesion effects, which, when present, can make the ratio substantially higher. In one embodiment, the ratio of the filler particle size to the shell thickness may vary from about 1 to about 2. In other embodiments, the ratio may vary from about 1.2 to about 1.8. In addition, in other embodiments, the ratio may be greater than about 2.

Calculation of the distance between particles in a two-phase shell of a bicomponent fiber composite

From the above reasoning, the importance of choosing the appropriate particle size to provide a “sticking out” effect has been clearly demonstrated. Another factor affecting the perception of the sample by touch at the microscale is the distance between the particles in the shell, which can be correlated with the particle size, percent by volume of the fillers and the spatial arrangement of the particles. Wang and others proposed the following models representing the average distance between spherical filler particles (Meng-Jiao Wang, Siegfried Wolff, and Ewe-Hong Tan, "Filler-Elastomer Interactions. Part VIII. The Role of the Distance Between Filler Aggregates in the Dynamic Properties of Filled Vulcanizers," Rubber Chemistry and Technology, VoI 66, 178-195 (1993)). In the case of a loose, for example cubic, shape of the arrangement of the particle, the distance between the centers of the particles is described as

L = 0.805φ ^-1/3 d

where ϕ is the percentage by volume of the filler, and d is the characteristic of the particle length.

For a dense arrangement of particles, for example a face-centered cubic structure, the distance between the centers of the particles is described as

L = 0.906ϕ ^-1/3 d

For an unordered package arrangement, an average value of 0.86ϕ ^-1/3 d can be used.

Fluctuations in particle size in the thickness direction (or z-axis direction) can be effectively eliminated by assuming that the particle size is in the same order as the shell thickness; as a result, the model is simplified to a flat or two-dimensional size distribution of the filler particles. Four possible cases are considered: a particle in cubic and spherical shapes and a distribution of the arrangement of particles in the form of a square and an equilateral triangle.

Four assumptions were made to calculate the distance between particles in space. First: the shell thickness is in the same order as the average particle size of the CaCO ₃ filler, for example, if the average particle size is 1 μm, then the shell thickness is also 1 μm. Thus, the distribution of the filler in the shell can be considered as two-dimensional. Second: filler particles are evenly distributed in the polymer matrix of the shell. Third: all particles are evenly distributed in the shell, either in the form of squares, or in the form of equilateral triangles. And fourth: the particle size has a very narrow distribution, so only the average particle size is used to model the distance in space.

The distance between particles can then be calculated based on the formatting of particles in space. Particles can be in the format of a square or in the format of an equilateral triangle, as illustrated on the left and right sides of figure 3, respectively. The results also depend on whether the particles are considered as spheres or cubes (affecting the characteristic length of the particle). The resulting formulas for calculating the distance between particles are given in Table 2, where L is the distance between particles, d is the particle size (characteristic length: side length for a cubic particle or diameter for a spherical particle), and α _av is the ratio of percent by volume of particles to percent by volume of the polymer matrix.

table 2
Calculation of the distance between the filler particles

For each of the above formulas, the distance between the particles is directly proportional to the size of the particle. Thus, with a constant volumetric content of the filler, the distance between the particles is determined by the characteristic particle size for each of the above formulas. The ratio of the distance between the particles to the characteristic particle size (L / d) is listed in Table 3 for systems having 3-15 percent by weight of the filler. It should be noted that the maximum content of filler particles in the polymer matrix will also depend on the mixing ability of the extruder.

Table 3
L / d ratio for 3-15% by weight of filler

Some observational results can be obtained from the data shown in table 3. First, when the filler content increases, the level of particle concentration increases; thus the distance between the particles becomes shorter. Second, while maintaining the filler content, the arrangement of particles, the characteristic particle sizes are constant, the distance between spherical particles is less than the distance between cubic particles (by definition, the volume of a cubic particle is greater than the volume of a spherical particle having the same characteristic length d). On the contrary, there is a greater number of spherical particles than cubic particles with the same filling content, so the distance between the particles becomes shorter.

For this simplified model, filler particles are modeled as small cubes or spheres. The distribution of particles in the shell is treated as an arrangement of a square or an equilateral triangle. In reality, it is most likely that the particles are randomly packed and the shapes of the particles are more or less irregular. One way to handle this variation is to use the average packing location. The particle diameter is also replaced by the total diameter (as described by Wang and others). For simplicity, the average particle spacing was adopted for the model by averaging four values for the particle spacing shown in Table 3 (alternatively, L / d≈ (0.8 / α _av ) ^1/2 ).

It has been disclosed that fiber surface roughness of 1-10 microns will form an improved perception of the sample by touch. To form a fiber roughness, the required ratio of the distance between particles in space to the particle size, L / d, can be changed based on the particle size. In certain embodiments, the L / d ratio can vary from 1 to 10. For example, if the particle size is less than 1 micron, the ratio can be selected from 3 to 6 to form the desired roughness. If the particle size is equivalent to or greater than 1 micron, the ratio can be selected from 2 to 4. Thus, it can be seen from table 3 that when the filling level of the filler is less than 5 percent by mass, the distance between the particles in space may be too large to effectively increase tactile properties of the fiber.

The actual particle size is usually not the same for all filler particles, since generally available fillers have an average particle size and a particle size distribution from narrow to wide. The above calculations regarding the ratio of particle size to shell thickness can be determined using the average (or average) particle size, it should be noted that the particle size distribution will affect the actual distance in space and the surface roughness of the fiber. For natural fillers with a narrow particle size distribution (approximately less than 2.0), the particle size distribution effect can be neglected. For fillers with a wider particle size distribution (approximately greater than 3.0), a wider particle size distribution would lead to a greater distance between the particles. For example, the surface roughness of a fiber with a narrower particle size distribution will differ from the surface roughness of a fiber with a wider particle size distribution, since a fiber including a wide particle size distribution has more particles that are smaller than the average particle size. Thus, these smaller particles may possibly sink into the shell, potentially leading to a decrease in the “sticking out” effect. A wide particle size distribution also has a larger number of particles larger than the average particle size than a narrow distribution. However, the effect that occurs when a larger number of particles is larger than the average particle size can be refuted by the increased distance between the particles for the particles that actually create the “sticking out” effect and the increased likelihood of potential adhesion problems.

Although the above model can be used to calculate the ratio of the average particle size to the shell thickness and the distance between particles in the shell, the model should be used more qualitatively than quantitatively, since a large number of approximations were used to obtain the formulas. The general principles for using a mineral filler to alter the surface morphology of a fiber, however, are clearly presented by the model, and the model can provide initial design guidance.

Examples

An extrusion experiment was conducted to produce a bicomponent fiber with a shell of calcium carbonate filled with a polymer microcomposite. The core of Polypropylene 5D49 is a commercially available homopolymer available from the Dow Chemical Company (38 MFR; density 0.90 g / cm ³ ). The 5D49 sheath was compounded with various grades of calcium carbonate, as shown in Table 4. These fibers were compared with a single-filled 5D49 fiber (2 or 4 dpf, as appropriate) as a control (comparative) example.

The choice of calcium carbonate . Three commercially available grades of calcium carbonate having average particle sizes ranging from 0.4 to 1.2 microns were selected to study the “sticking out” effect: TUFFGARD® (precipitated calcium carbonate having an average particle size of 0.4 microns and an upper cut of about 2 micron, commercially available from Specialty Minerals Inc., Adams, MA); SUPER-PFLEX® 200 (precipitated calcium carbonate having an average particle size of 0.7 microns and an upper cut of about 4 microns, with a surface coated with 2% stearic acid to promote dispersion in the polymer, also commercially available from Specialty Minerals Inc., Adams, MA ); and FILMLINK® 400 (ground calcium carbonate having an average particle size of 1.2 microns and an upper cut of about 4 microns, with a surface coated with 2% stearic acid, commercially available from Imerys, Roswell, GA).

Compounding . Compounding was carried out in two stages to ensure dispersion of calcium carbonate in hPP. In a first step, calcium carbonate was compounded with hPP (5D49) at a weight ratio of 40/60 to form concentrates using a Banbury® mixer. In a second step, calcium carbonate concentrates — hPP — were diluted to the desired compositions in accordance with the formulas in Table 4 using a HAAKE® 1 "twin screw extruder with moderate torque and melting point settings (approximately 210 ° C).

Extruding fiber . Fiber samples were prepared using a fiber extrusion line consisting of two 1 "single screw extruders, two Zenith gear pumps, a 144-hole multi-channel mouthpiece, a fiber blower shaft and a twisting unit. A multi-channel mouthpiece hole capillary in diameter was 0.65 mm with a ratio of length length to a diameter of 4: 1. The melting point was set at 240 ° C. The productivity was 0.4 grams per hole per minute, the extrusion speed was set at 1000 m / min to produce 4 dpf (denier per thread) fiber and 2000 m / min for 2 dpf fibers, respectively. The fibers were collected in coils for subsequent testing of the property. The extrusion of the fiber was very uniform and no breaks were observed in the production of any sample.

Table 4
Samples of bicomponent fibers with a modified CaCO ₃ surface

SEM analysis for fiber surface morphology . Small fibers were cut and the sample was placed in an aluminum scanning electron microscope (SEM) cartridge to obtain surface and cross-sectional images. Samples were plated twice with gold, palladium for 20 seconds. Second electron images of the sample surface were obtained on a Hitachi S4100 scanning electron microscope using an accelerating voltage of 5 kV.

Images of the SEM surface of three characteristic modified surfaces of bicomponent fibers, samples 4, 8 and 10, are shown in figures 4-6, respectively. All three fibers are 2 dpf (17.7 microns in diameter) and contain 10% sheath by volume.

Referring to Figure 4, the SEM image of sample 4 fiber shows that the calcium carbonate particles in this sample are smaller and more concentrated compared to the SEM images of two other fiber samples (figures 5 and 6). This observation is consistent with the predictions of the model, because the calcium carbonate brand, TUFFGARD®, has a smaller particle size (0.4 microns), and the ratio of particle size to shell thickness is less than 1, the model predicts a less significant “sticking out” effect and closer particle spacing in space. Further, differences in topography were not visible between samples 5% (sample 2, SEM image not shown) and 10% with images of fiber surfaces, which have a very similar appearance.

Referring to FIG. 5, an SEM image of a sample 8 fiber indicates that this fiber has the highest overall surface roughness. The fiber not only has "bulges" of calcium carbonate, but also has craters or depressions formed around calcium carbonate particles that were not apparent in Figure 4. The calcium carbonate contained in sample 8, SUPER-PFLEX® 100, has a particle size of 0, 7 microns. Thus, the ratio of the size to the shell thickness is greater than 1, and the improvement in the “sticking out” effect over the sample 4 is allowed by the model.

Referring to FIG. 6, the particle size of the sample 10 is the largest and least concentrated on the fiber. There are some signs of hollows or craters on it, but less strong than that of sample 8. Calcium carbonate, FILMLINK® 400, has the largest particle size (1.2 microns) in this fiber, and the ratio of particle size to shell thickness is greater than 1. Images SEM have the form confirming the correctness of the model, so the “sticking out” effect looks the strongest of the three fiber samples, and the distance between the particles also looks the greatest.

The formation of craters or depressions on the surface of the fiber is partially not clear. One hypothesis is that craters or depressions can form when some large particles of calcium carbonate show off due to centrifugal force or other reasons encountered during the extrusion process. The loss of some calcium carbonate particles during fiber extrusion does not prevent the formation of surface roughness, since craters are formed by loose particles, they do provide surface roughness. However, particles falling off during the extrusion process can cause dusting problems. For a non-woven synthetic fiber line, dusting should not be a problem, therefore, exhaust fans are placed under the forming tape, where the fibers collide with the tape, and form a non-woven preform. In other applications, improved ventilation conditions around the production line may be needed; however, since the content of calcium carbonate filler in the fiber is low, about 1% fiber by weight, any dusting that may occur should not be strong and can be easily overcome.

Knitted socks

Samples of 2 dpf fiber, including the hPP standard, were knitted on a Lawson-Hemphill knitting machine. The number of columns and the number of rows per inch (wpi and cpi) is a measure of the density of the knitwear. Columns extend in the longitudinal direction of the fabric, rows in the transverse direction. The density of the fabric is defined as the product of columns and rows. The wpi and cpi of the six samples were measured as 26 and 32, respectively. The density of each sample was 832.

Touch test results . The perception of the touch test of knitted socks made of 2 dpf fibers is presented in Table 5. Samples 2 and 4 with a particle size to shell thickness ratio of less than 1 did not form a significant touch improvement. There was no significant “sticking out” effect predicted by the model and observed in the SEM image of sample 4 in Figure 4. Samples 8 and 10 did not have improved touch perception compared to the standard sample, which is made of hPP (5D49) monofilaments without surface modifications.

Table 5
Touch sample evaluation for selected fiber samples

As shown by the above description of examples, bicomponent fibers having a microcomposite surface component can improve the perception of the sample by touch of synthetic fibers. The inclusion of mineral fillers having a particle size greater than the thickness of the microcomposite polymer matrix, can be obtained "sticking out" effect, which leads to surface roughness and improved touch. In certain embodiments, bicomponent fibers having improved tactility are useful in end products such as carpets, synthetic hair, feminine hygiene products, diapers, athletic sportswear, clothing, upholstery, dressings and sterilized medical clothing, and tool wrappers.

While the invention has been described by a limited number of embodiments, those skilled in the art who benefit from this disclosure will appreciate that other embodiments may be devised that do not deviate from the scope of the invention disclosed herein. Thus, the scope of the invention should not be limited only by the attached claims.

All priority documents are fully incorporated herein by reference for all jurisdictions in which such inclusion is permitted. Additionally, all documents cited in this description, including test methods, are fully incorporated herein by reference for all jurisdictions in which such inclusion is permitted.

Claims (30)

1. A bicomponent fiber having an increased surface roughness, including
the first polymer, where the first polymer is a polyolefin, and a composite containing a second polymer and a filler, where the composite forms a layer that forms at least part of the surface of the fiber, and where the average particle size of the filler is greater than the thickness of the layer formed by the composite. 2. The bicomponent fiber according to claim 1, where the bicomponent fiber has a core / shell configuration, where the shell includes a composite, the core includes a first polymer, and where the shell thickness is less than the average particle size of the filler. 3. The bicomponent fiber according to claim 1, where the first polymer is selected from the group consisting of polyolefin, diblock, triblock, or multiblock elastomeric copolymer, polyurethane, polyamide, polyester, or a combination thereof. 4. The bicomponent fiber according to claim 3, wherein the diblock, triblock, or multiblock elastomeric copolymer is selected from the group consisting of styrene-isoprene-styrene, styrene-butadiene-styrene, styrene-ethylene / butylene-styrene or styrene-ethylene / propylene-styrene or combinations thereof. 5. The bicomponent fiber according to claim 1, where the polyolefin is a homogeneous branched polyolefin. 6. The bicomponent fiber according to claim 1, where the polyolefin is obtained from at least one monomer selected from the group consisting of ethylene, propylene, butene-1, hexene-1, octene-1, 4-methylpentene-1, butadiene , cyclohexene, dicyclopentadiene, styrene, toluene, alpha-methylstyrene or a combination thereof. 7. The bicomponent fiber according to claim 1, where the second polymer is an elastomeric polymer. 8. The bicomponent fiber according to claim 7, where the elastomeric polymer is selected from the group consisting of a homogeneous branched polyolefin, diblock, triblock or multiblock elastomeric copolymer, polyurethane, polyamide, polyester or a combination thereof. 9. The bicomponent fiber of claim 8, where the polyolefin is obtained from at least one monomer selected from the group consisting of ethylene, propylene, butene-1, hexene-1, octene-1, 4-methylpentene-1, butadiene , cyclohexene, dicyclopentadiene, styrene, toluene, alpha-methylstyrene or a combination thereof. 10. The bicomponent fiber according to claim 1, where the filler is selected from the group consisting of silica, alumina, calcium carbonate, silicon dioxide, clay, or a combination thereof. 11. The bicomponent fiber according to claim 1, where the filler includes calcium carbonate. 12. The bicomponent fiber of claim 10, wherein the filler is coated with a compatibilizer. 13. The bicomponent fiber of claim 12, wherein the compatibilizer is stearic acid. 14. The bicomponent fiber according to claim 1, where the composite contains from about 1% to about 20 wt.% By weight of the fiber. 15. The bicomponent fiber according to 14, where the composite contains from about 5% to about 20 wt.% By weight of the fiber. 16. The bicomponent fiber according to claim 1, where the filler contains from about 1% to about 25 wt.% By weight of the composite. 17. The bicomponent fiber according to claim 1, where the filler contains from about 3% to about 15 wt.% By weight of the composite. 18. The bicomponent fiber according to claim 1, where the average particle size of the filler varies from about 0.1 to about 20 microns. 19. The bicomponent fiber according to claim 1, where the ratio of the average particle size of the filler to the thickness of the composite layer is more than 1 and less than 2. 20. The two-component fiber according to claim 19, where the ratio of the average particle size of the filler to the thickness of the composite layer is from 1.2 to 1.8. 21. The two-component fiber according to claim 1, where the particle size distribution of the filler is less than 3.0. 22. The two-component fiber according to item 21, where the particle size distribution of the filler is less than 2.0. 23. The bicomponent fiber according to claim 1, where the ratio of the distance between the centers of the particles (L) to the average particle size (d) of the filler
a) between about 3 and about 6, when the average particle size is less than 1 μm, or
b) between about 2 and about 4, when the average particle size is 1 μm or more,
where the distance between the centers of the particles (L) is calculated as equal to (0.8 / α _av ) ^1/2 d,
where α _av is the ratio of percent by volume of particles to percent by volume of the polymer matrix. 24. The bicomponent fiber according to claim 1, where the fiber is elastic. 25. The bicomponent fiber according to claim 1, where the fiber is crosslinked. 26. An article comprising fiber according to claim 1. 27. A method of producing a bicomponent fiber according to claims 1 to 25, comprising coextrusion under thermal bonding conditions of (a) the first polymer and (b) the second polymer, which forms a layer that forms at least part of the surface of the fiber, where the filler is mixed with the second polymer with the formation of the composite is carried out before co-extrusion and where the average particle size of the filler is greater than the thickness of the composite layer. 28. The method according to item 27, where the co-extrusion includes obtaining a fiber having a round, oval, three-bladed, triangular, dumbbell, flat or hollow shape and a symmetric or asymmetric configuration of the shell / core or side-by-side. 29. The method of claim 28, wherein the bicomponent fiber has a rounded shape and a sheath / core. 30. A two-component fiber comprising a composite comprising a polymer and a filler, where the composite forms a layer that forms at least part of the surface of the fiber, and where the average particle size of the filler is greater than the thickness of the layer formed by the composite.

Images