CN110799687B - Nonwoven articles and methods of making the same - Google Patents

Abstract

A method includes exposing a particulate coating disposed on a nonwoven web comprising heat-softenable fibers to pulsed electromagnetic radiation having at least one wavelength in a range of 200nm to 1000 nm. The particle coating comprises different particles that are not chemically bonded to each other and that are not retained in a binder material other than the heat-softenable fibers. Also disclosed are nonwoven articles comprising a heat-softenable nonwoven web having a particulate coating disposed thereon. The particle coating comprises different particles that are not chemically bonded to each other and that are not retained in the binder material other than the heat-softenable nonwoven web. The particle coating remains at least 60% after one minute immersion in isopropanol at 22 ℃.

Description

Nonwoven articles and methods of making the same

Technical Field

The present disclosure broadly relates to methods for improving the durability of particulate coatings on nonwoven webs, and articles made therefrom.

Background

Coatings of powders (e.g., graphite) on nonwoven webs are well known; however, powders are often loosely bound to the fibers and are prone to shedding. Various methods have been devised to overcome this problem, including: 1) using a curable resin applied to the fibers prior to powder coating and when cured, firmly bonding the powder to the fibers; 2) in those instances where the nonwoven web is sufficiently durable, the powder may be rubbed onto it in a process known as friction adhesion (tribo-adhesion); and 3) the powder may be selected to include a binder component that fuses to the fibers upon heating.

However, each of these techniques has drawbacks if a particle coating consisting essentially of inorganic particles is desired. For example, in such cases, the presence of the binder component in methods 1) and 3) would be unacceptable, and the durability of the particulate coating produced by method 2 is often problematic, as the particulate coating is often susceptible to damage by methods such as milling and/or rinsing with solvents.

Disclosure of Invention

Advantageously, the present disclosure provides a simple method of enhancing the durability of a particle coating involving transient heating by exposure to pulsed electromagnetic radiation having at least one wavelength in the range of 200nm to 1000 nm. Without being bound by theory, the inventors believe that the modulated electromagnetic radiation that strikes the particles in the particle coating is converted to heat that is located in the vicinity of the particles, thereby softening adjacent fibers and increasing the adhesion between those fibers and particles.

In a first aspect, the present disclosure provides a method of making a nonwoven article, the method comprising exposing a particle coating disposed on a heat-softenable nonwoven web to pulsed electromagnetic radiation having at least one wavelength in a range from 200 nanometers to 1000 to nanometers, wherein the particle coating comprises loosely bound distinct particles that are not chemically bonded to each other and that are not retained in a binder material other than the heat-softenable nonwoven web, and wherein the pulsed electromagnetic radiation has a sufficient fluence and pulse width to increase a bonding force between at least a portion of the loosely bound distinct particles and the heat-softenable nonwoven web.

By this technique, the durability of the particulate coating is improved, while the alternative heating method is prone to damage (e.g., warping) the heat-softenable nonwoven web.

Accordingly, in a second aspect, the present disclosure provides a nonwoven article made according to the above-described method of the present disclosure.

In a third aspect, the present disclosure provides a nonwoven article comprising a heat-softenable nonwoven web having a particulate coating disposed thereon, wherein the particulate coating comprises different particulates that are not chemically bonded to each other and that are not retained in a binder material other than the heat-softenable nonwoven web, and wherein the particulate coating retains at least 60% after one minute of immersion in isopropanol at 22 ℃.

As used herein:

the term "visible light" refers to electromagnetic radiation having a wavelength of 400 nanometers (nm) to 700 nanometers (nm).

The term "powder" refers to a free-flowing collection of fine particles.

The term "pulsed electromagnetic radiation" refers to electromagnetic radiation that is modulated as a series of discrete peaks of increasing intensity. The peak may be relative to a background level of negligible or zero electromagnetic radiation, or the background level may be at a higher level that is substantially ineffective in increasing the adhesion of the particles to the fibers in the particle coating.

The term "heat softenable" means softenable when heated.

The term "particle coating" refers to a coating of small particles that may or may not be free-flowing.

The features and advantages of the present disclosure will be further understood upon consideration of the detailed description and appended claims.

Drawings

Fig. 1 is an enlarged schematic side view of anexemplary article 100 according to the present disclosure.

It should be understood that numerous other modifications and embodiments can be devised by those skilled in the art that will fall within the scope and spirit of the principles of this disclosure.

Detailed Description

Advantageously, the present disclosure provides a simple method of using transient heating to enhance the durability of a particulate coating on a nonwoven web by exposure to a modulated electromagnetic radiation source.

Referring now to fig. 1, anexemplary article 100 includes a heat-softenablenonwoven web 110 having aparticulate coating 120 disposed thereon.

Particulate coatings on heat-softenable nonwoven (e.g., thermoplastic) webs can be applied by a variety of known methods including, for example, exposure to an atomized particle cloud, contact with a powder bed, coating with a solvent-based particle-dispersed coating followed by evaporation of the solvent and/or powder abrasion (rubbing the dried particles against a substrate to form a coating of powder particles). Examples of powder abrasion methods can be found in U.S. Pat. Nos. 6,511,701B1 (Divigalpitiaya et al), 6,025,014(Stango) and 4,741,918(Nagybaczon et al). The remaining methods are familiar to those of ordinary skill in the art.

Useful particle coatings include small loosely-bound particles capable of absorbing at least one wavelength of pulsed electromagnetic radiation, preferably corresponding to a majority of the energy of the pulsed electromagnetic radiation. Suitable particles are preferably at least substantially impervious to electromagnetic radiation, yet robust to strong absorbers thereof. It is desirable to maximize light (electromagnetic radiation) to thermal conversion yield without changing the chemical nature of the particles.

Exemplary suitable particles include graphite, clay, hexagonal boron nitride, pigments, inorganic oxides (e.g., alumina, calcium oxide, silica, ceria, zinc oxide, or titanium dioxide), metals, organic polymer particles (e.g., polytetrafluoroethylene, polyvinylidene fluoride), carbides (e.g., silicon carbide), flame retardants (e.g., aluminum trihydrate, aluminum hydroxide, magnesium hydroxide, sodium hexametaphosphate, organophosphonates, and phosphates and esters thereof), carbonates (e.g., calcium carbonate, magnesium carbonate, sodium carbonate), dried biological powders (e.g., spores, bacteria), and combinations thereof. Preferably, the particles have an average particle size of from 0.1 to 100 microns, more preferably from 1 to 50 microns, and more preferably from 1 to 25 microns, although this is not essential. Graphite and hexagonal boron nitride are particularly preferred in many applications.

The particulate coating comprises loosely bound distinct particles that are not chemically bonded to each other and that do not remain in the binder material other than the heat-softenable nonwoven web itself prior to exposure to electromagnetic radiation.

The heat-softenable nonwoven web preferably comprises thermoplastic fibers, but non-thermoplastic fibers may be used alone or in combination with, for example, thermoplastic fibers. In a preferred embodiment, the fibers of the heat-softenable nonwoven web are non-tacky and/or non-thermosetting, but this is not required.

Exemplary suitable heat-softenable nonwoven webs include melt-spun webs, blown microfiber webs, needled staple fiber webs, thermally bonded airlaid webs, and hydroentangled webs. The heat-softenable nonwoven web may be prepared by any suitable nonwoven web preparation method. Examples include melt spinning, Blown Microfiber (BMF), air-laid processes, wet-laid processes, and hydroentangling. These and other methods will all be known to those skilled in the art. Alternatively, a variety of nonwoven webs comprising heat-softenable fibers are commercially available. The heat-softenable nonwoven web may have any basis weight and may, for example, be densely compacted or lofted and open.

Some examples of thermoplastic polymers that may be suitable for fiber formation include polycarbonates, polyesters, polyamides, polyurethanes, polyacrylics (e.g., polyacrylonitrile), block copolymers such as styrene-butadiene-styrene and styrene-isoprene-styrene block copolymers, polyolefins such as polyethylene, polypropylene, polybutylene, and poly (4-methyl-1-pentene), and combinations of such resins. Examples of thermoplastic polymeric materials that can be used to make nonwoven webs comprising thermoplastic fibers are disclosed in U.S. Pat. Nos. 5,706,804(Baumann et al), 4,419,993(Peterson), Re 28,102(Mayhew), 5,472,481(Jones et al), 5,411,576(Jones et al), and 5,908,598(Rousseau et al). In some preferred methods, at least a portion of the fibers in the thermoplastic web have a higher melting core and a lower melting sheath. In such cases, the higher melting core should preferably be at least 25 ℃.

The pulsed electromagnetic radiation can be from any source capable of generating sufficient fluence and pulse duration to achieve sufficient heating of the nonwoven web to more tightly bond the particulate coating thereto. At least three types of sources may be effective for this purpose: flash lamps, lasers, and shutter lamps. The selection of an appropriate source will typically be influenced by the desired process conditions (e.g., line speed, line width, spectral output, and cost).

Preferably, the pulsed electromagnetic radiation is generated using a flash lamp. Of which xenon flash lamps and krypton flash lamps are the most common. Both provide a broad continuous output in the wavelength range of 200 to 1000 nanometers, however krypton flash lamps have a higher relative output intensity in the wavelength range of 750 to 900nm compared to xenon flash lamps which have more relative output in the wavelength range of 300 to 750 nm. Xenon flash lamps are generally preferred for most applications, especially those involving graphite particles. Many suitable xenon and krypton flashlamps are commercially available from suppliers such as the Eleutida Technologies Corp. of Waltham, Mass and Hewley, Heraeus of Hanau, Germany, Haxan, Germany.

In another embodiment, the pulsed electromagnetic radiation may be generated using a pulsed laser. Suitable lasers may include, for example, excimer lasers (e.g., XeF (351nm), XeCl (308nm), and KrF (248nm)), solid-state lasers (e.g., ruby (694nm)), and nitrogen lasers (337.1 nm).

In yet another embodiment, the pulsed electromagnetic radiation is generated using a continuous light source and a shutter (preferably a rotating aperture/shutter to reduce overheating of the shutter). Suitable light sources may include high pressure mercury lamps, xenon lamps, and metal halide lamps.

To achieve maximum efficiency, the electromagnetic radiation spectrum is preferably most intense at wavelengths that are strongly absorbed by the particles, but this is not a requirement. Also, in the case of reflective particles, the electromagnetic radiation spectrum is preferably most intense in the region of the spectrum where the particles are least reflective, but this is not a requirement.

Preferably, the pulsed electromagnetic radiation source is capable of generating a high fluence (energy density) with a high intensity (high power/unit area), but this is not a requirement. These conditions ensure that sufficient heat is absorbed to achieve increased adherence of the particles to the fibers. However, the combination of intensity and fluence should not be too great/high to cause ablation, excessive degradation, or volatilization of the fibers in the nonwoven web. The selection of suitable conditions is within the ability of one of ordinary skill in the art.

To minimize heating of the interior portions of the fibers that are not capable of interacting with the particles on the nonwoven web, the pulse duration is preferably short; for example, less than 10 milliseconds, less than 1 millisecond, less than 100 microseconds, less than 10 microseconds, or even less than 1 microsecond, although this is not a requirement.

To achieve high line speeds in a continuous manufacturing process, not only should the pulsed electromagnetic radiation be preferably strong, but the exposure area is preferably large, and the pulse repetition rate is preferably fast (e.g., 100Hz to 500 Hz).

To evaluate durability, the resulting exposed particle coated nonwoven web can be immersed in a solvent such as isopropyl alcohol at about 22 ℃ (e.g., room temperature) for a fixed interval (e.g., 1, 2, 3, 4, or even 5 minutes or more), then removed, dried, and weighed. The weight loss of the powder can then be determined by subtraction. The solvent should be selected such that it does not dissolve the nonwoven web.

Preferably, the particulate coating of the nonwoven article is sufficiently bonded to the nonwoven web such that at least 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, or even at least 90% of the particulate coating remains bonded to the nonwoven web after one minute of immersion in isopropanol at 22 ℃.

Selected embodiments of the present disclosure

In a first embodiment, the present disclosure provides a method of making a nonwoven article, the method comprising exposing a particle coating disposed on a heat-softenable nonwoven web to pulsed electromagnetic radiation having at least one wavelength in a range from 200 nanometers to 1000 nanometers, wherein the particle coating comprises loosely bound distinct particles that are not chemically bonded to each other and that are not retained in a binder material other than the heat-softenable nonwoven web, and wherein the pulsed electromagnetic radiation has sufficient fluence and pulse width to increase a bonding force between at least a portion of the loosely bound distinct particles and the heat-softenable nonwoven web.

In a second embodiment, the present disclosure provides the method according to the first embodiment, wherein the particulate coating comprises at least one of graphite or hexagonal boron nitride.

In a third embodiment, the present disclosure provides the method of the first or second embodiment, wherein the particle coating consists essentially of graphite.

In a fourth embodiment, the present disclosure provides the method of any one of the first to third embodiments, wherein the pulsed electromagnetic radiation is generated using a flash lamp.

In a fifth embodiment, the present disclosure provides the method of any one of the first to third embodiments, wherein the pulsed electromagnetic radiation is generated using a pulsed laser.

In a sixth embodiment, the present disclosure provides the method of any one of the first to third embodiments, wherein the pulsed electromagnetic radiation is generated using a continuous light source and a shutter.

In a seventh embodiment, the present disclosure provides the method of any one of the first to sixth embodiments, wherein the heat-softenable nonwoven web comprises fibers having a higher melting point core and a lower melting point sheath.

In an eighth embodiment, the present disclosure provides a nonwoven article made according to any one of the first to seventh embodiments of the present disclosure.

In a ninth embodiment, the present disclosure provides a nonwoven article comprising a heat-softenable nonwoven web having a particulate coating disposed thereon, wherein the particulate coating comprises different particulates that are not chemically bonded to each other and that are not retained in a binder material other than the heat-softenable nonwoven web, and wherein the particulate coating retains at least 60% after one minute of immersion in isopropanol at 22 ℃.

In a tenth embodiment, the present disclosure provides a nonwoven article according to the ninth embodiment, wherein the particulate coating comprises at least one of graphite or hexagonal boron nitride.

In an eleventh embodiment, the present disclosure provides the nonwoven article of the ninth or tenth embodiment, wherein the particulate coating consists essentially of graphite.

In a twelfth embodiment, the present disclosure provides the nonwoven article of any one of the ninth to eleventh embodiments, wherein the particulate coating retains at least 90% after one minute immersion in isopropanol at 22 ℃.

In a thirteenth embodiment, the present disclosure provides a nonwoven article according to any one of the ninth to twelfth embodiments, wherein the heat-softenable nonwoven web comprises fibers having a higher melting point core and a lower melting point sheath.

Objects and advantages of this disclosure are further illustrated by the following non-limiting examples, but the particular materials and amounts thereof recited in these examples, as well as other conditions and details, should not be construed to unduly limit this disclosure.

Examples

Unless otherwise indicated, all parts, percentages, ratios, and the like in the examples and the remainder of the specification are by weight. All reagents used in the examples were obtained or purchased from general chemical suppliers, such as Sigma-Aldrich Company of st Louis, Missouri, or may be synthesized by conventional methods.

Materials used in the examples

General method for coating graphite onto a substrate

To prepare the examples and comparative examples described below, a graphite coating was applied to a PE nonwoven substrate by placing strips of nonwoven material of approximately 1.5 inch (3.8cm) by 10 inch (25.4cm) dimensions and a small amount of MICRO850 in a sealable plastic bag. The bag was then sealed and shaken until the PE nonwoven was visibly covered with graphite. The nonwoven material was then removed and excess graphite particles were removed by purging with compressed nitrogen at a pressure of 40 psi.

The relative amount of graphite coating deposited on the PE nonwoven film was determined by measuring the weight of the sample before and after the process.

General method for determining durability

The durability (elasticity of coating) of the samples prepared according to the examples and comparative examples described below was tested.

The nonwoven sample was completely immersed (i.e., submerged) in the IPA bath at room temperature (22 ℃) and stirred by hand for 1 minute. The sample was then removed and spread onto a clean surface in a chemical fume hood and allowed to dry completely.

All reported percent graphite retained (% R) are calculated from the following equation:

wherein M is_g,iIs the mass of graphite on the nonwoven just prior to immersion in isopropanol, and M_g,wIn order to maintain the quality of the graphite on the nonwoven material after the washing step.

Examples 1 to 11(EX-1 to EX-11) and comparative example A (CEX-A)

CEX-a and EX-1 to EX-12 are graphite coated PE nonwoven substrates prepared as described above. For CEX-a, the substrate was not subjected to IPL and was a control sample. EX-1 to EX-11 were prepared by subjecting the samples to intense pulsed light Irradiation (IPL). In the case of all IPLs, the source used was a Xe flash lamp, commercially available from Xeon Corporation, Wilmington, Mass as a SINTERON S-2100Xe flash lamp equipped with a type C bulb. The sample was placed under a quartz plate for the irradiation process.

For EX-1, at a pulse rate of 1Hz and 0.1J/cm²The substrate was treated 1 time with energy density of (1). The substrate is then removed and flipped over, and the process is repeated on the back side of the substrate.

For EX-2, at a pulse rate of 1Hz and 0.1J/cm²The substrate was treated 3 times with energy density. The substrate is then removed and flipped over, and the process is repeated on the back side of the substrate.

For EX-3, at a pulse rate of 1Hz and 0.1J/cm²The substrate was treated 5 times with energy density of (1). The substrate is then removed and flipped over, and the process is repeated on the back side of the substrate.

For EX-4, at a pulse rate of 1Hz and 0.2J/cm²The substrate was treated 1 time with energy density of (1). The substrate is then removed and flipped over, and the process is repeated on the back side of the substrate.

For EX-5, at a pulse rate of 1Hz and 0.2J/cm²The substrate was treated 3 times with energy density. The substrate is then removed and flipped over, and the process is repeated on the back side of the substrate.

For EX-6, at a pulse rate of 1Hz and 0.2J/cm²The substrate was treated 5 times with energy density of (1). The substrate is then removed and flipped over, and the process is repeated on the back side of the substrate.

For EX-7, at a pulse rate of 1Hz and 0.3J/cm²The substrate was treated 1 time with energy density of (1). The substrate is then removed and flipped over, and the process is repeated on the back side of the substrate.

For EX-8, at a pulse rate of 1Hz and 0.3J/cm²The substrate was treated 3 times with energy density. The substrate is then removed and flipped over, and the process is repeated on the back side of the substrate.

For EX-9, at a pulse rate of 1Hz and 0.3J/cm²The substrate was treated 5 times with energy density of (1). The substrate is then removed and flipped over, and the process is repeated on the back side of the substrate.

For EX-10, at a pulse rate of 1Hz and 0.4J/cm²The substrate was treated 1 time with energy density of (1). The substrate is then removed and flipped over, and the process is repeated on the back side of the substrate.

For EX-11, at a pulse rate of 1Hz and 0.4J/cm²The substrate was treated 3 times with energy density. The substrate is then removed and flipped over, and the process is repeated on the back side of the substrate.

Table 1 below reports the IPL effect on the PE nonwoven and the measured parts of the graphite coating remaining (f).

TABLE 1

Examples	IPL pulse/side	Energy density/pulse, J/cm2	％R
				CEX-A	0	0	4.9
EX-1	1	0.1	16.6
				EX-2	3	0.1	26.8
EX-3	5	0.1	31.5
				EX-4	1	0.2	18.6
EX-5	3	0.2	44.0
				EX-6	5	0.2	45.4
EX-7	1	0.3	16.5
				EX-8	3	0.3	52.3
EX-9	5	0.3	60.5
				EX-10	1	0.4	34.8
EX-11	3	0.4	91.0

Comparative examples B to D (CEX-B to CEX-D)

For CEX-B through CEX-D, samples of nonwoven PE were heated in a 725G Isotemp type laboratory oven (Fisher Scientific, Hampton, New Hampshire). The samples were placed on aluminum trays in a pre-heat oven for the specified amount of time. The results are reported in table 2 below.

TABLE 2

Examples	Temperature, C	Duration of time in minutes	％R
				CEX-B	105	5	27.5
CEX-C	105	15	37.0
				CEX-D	105	30	54.8

All cited references, patents, and patent applications in the above application for letters patent are incorporated by reference herein in their entirety in a consistent manner. In the event of inconsistencies or contradictions between the incorporated reference parts and the present application, the information in the preceding description shall prevail. The preceding description, given to enable one of ordinary skill in the art to practice the claimed disclosure, is not to be construed as limiting the scope of the disclosure, which is defined by the claims and all equivalents thereto.

Claims (13)

1. A method of making a nonwoven article, the method comprising exposing a particle coating disposed on a heat-softenable nonwoven web to pulsed electromagnetic radiation having at least one wavelength in a range from 200 nanometers to 1000 nanometers, wherein the pulse duration is less than 10 milliseconds, wherein the particle coating comprises loosely bound distinct particles that are not chemically bonded to each other and that are not retained in a binder material other than the heat-softenable nonwoven web, and wherein the pulsed electromagnetic radiation has sufficient fluence and pulse width to increase bonding forces between at least a portion of the loosely bound distinct particles and the heat-softenable nonwoven web.

2. The method of claim 1, wherein the particulate coating comprises at least one of graphite or hexagonal boron nitride.

3. The method of claim 1, wherein the particle coating is comprised of graphite.

4. The method of claim 1, wherein the pulsed electromagnetic radiation is generated using a flash lamp.

5. The method of claim 1, wherein the pulsed electromagnetic radiation is generated using a pulsed laser.

6. The method of claim 1, wherein the pulsed electromagnetic radiation is generated using a continuous light source and a shutter.

7. The method of claim 1, wherein the heat-softenable nonwoven web comprises fibers having a higher melting point core and a lower melting point sheath.

8. A nonwoven article prepared according to the method of any one of claims 1 to 7.

9. A nonwoven article comprising a heat-softenable nonwoven web having a particulate coating disposed thereon, wherein the particulate coating comprises distinct particulates that are not chemically bonded to one another and that are not retained in a binder material other than the heat-softenable nonwoven web, and wherein the particulate coating is retained after one minute immersion in isopropanol at 22 ℃ by at least 60%.

10. The nonwoven article of claim 9, wherein the particulate coating comprises at least one of graphite or hexagonal boron nitride.

11. The nonwoven article of claim 9, wherein the particulate coating is comprised of graphite.

12. The nonwoven article of claim 9, wherein the particulate coating retains at least 90% after one minute immersion in isopropanol at 22 ℃.

13. The nonwoven article of claim 9, wherein the heat-softenable nonwoven web comprises fibers having a higher melting point core and a lower melting point sheath.

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