US20200157734A1

US20200157734A1 - Nonwoven article and method of making the same

Info

Publication number: US20200157734A1
Application number: US16/626,244
Authority: US
Inventors: Megan A. Creighton; Emily S. Goenner; Raymond P. Johnston; Morgan A. Priolo; Joel A. Getschel
Original assignee: 3M Innovative Properties Co
Current assignee: 3M Innovative Properties Co
Priority date: 2017-06-29
Filing date: 2018-06-26
Publication date: 2020-05-21
Also published as: CN110799687A; WO2019003115A1; KR20200024163A; EP3645776B1; EP3645776A1; CN110799687B; KR102492536B1

Abstract

A method comprises exposing a particle coating disposed on a nonwoven fiber web comprising thermally-softenable fibers to pulsed electromagnetic radiation having at least one wavelength in the range of 200 nm to 1000 nm. The particle coating comprises distinct particles that are not chemically bonded to each other, and are not retained in a binder material other than the thermally-softenable fibers. Also disclosed are nonwoven articles comprising a thermally-softenable nonwoven fiber web having a particle coating disposed thereon. The particle coating comprises distinct particles that are not chemically bonded to each other and are not retained in a binder material other than the thermally-softenable nonwoven fiber web. The particle coating is at least 60 percent retained after a one minute immersion in isopropanol at 22° C.

Description

TECHNICAL FIELD

The present disclosure broadly relates to methods for improving the durability of particle coatings on nonwoven fiber webs, and articles preparable thereby.

BACKGROUND

Coatings of powders (e.g., graphite) on nonwoven fiber webs are widely known; however, the powders are typically loosely bound to the fibers and are prone to falling off. Various methods have been devised to overcome this problem, including: 1) use of a curable resin applied to the fibers prior to powder coating, and that when cured securely binds the powder to the fibers; 2) in those cases where the nonwoven fiber web is durable enough, the powder may be rubbed onto it in a process known as triboadhesion; and 3) the powders can be selected to contain binder components that can fuse to the fibers on heating.
However, each of these techniques has disadvantages if a particle coating consisting essentially of inorganic particles is desired. For example, the presence of binder components in approaches 1) and 3) would be unacceptable in such a situation, and durability of particle coatings made by approach 2) is generally problematic as particle coatings are typically prone to damage by methods such as abrasion and/or rinsing with solvent.

SUMMARY

Advantageously, the present disclosure provides an easy method to enhance the durability of particle coatings that involves instantaneous heating by exposure to pulsed electromagnetic radiation having at least one wavelength in the range of 200 nm to 1000 nm. Without wishing to be bound by theory, the present inventors believe that the modulated electromagnetic radiation hitting the particles in the particle coating is converted to heat that is localized adjacent to the particles thereby softening the adjacent fibers and increasing adhesion between those fibers and the 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 thermally-softenable nonwoven fiber web to pulsed electromagnetic radiation having at least one wavelength in the range of 200 to 1000 nanometers, wherein the particle coating comprises loosely bound distinct particles that are not chemically bonded to each other and are not retained in a binder material other than the thermally-softenable nonwoven fiber web, and wherein the pulsed electromagnetic radiation has sufficient fluence and pulse width to increase bonding force between at least a portion of the loosely bound distinct particles and the thermally-softenable nonwoven fiber web.
By this technique, durability of the particle coating is improved, while alternative heating methods were prone to damaging (e.g., warping) the thermally-softenable nonwoven fiber web.
Accordingly, in a second aspect, the present disclosure provides a nonwoven article made according to the foregoing method of the present disclosure.
In a third aspect, the present disclosure provides a nonwoven article comprising a thermally-softenable nonwoven fiber web having a particle coating disposed thereon, wherein the particle coating comprises distinct particles that are not chemically bonded to each other and are not retained in a binder material other than the thermally-softenable nonwoven fiber web, and wherein the particle coating is at least 60 percent retained after a one minute immersion in isopropanol at 22° C.
As used herein:
The term “visible light” refers to electromagnetic radiation having a wavelength of 400 to 700 nanometers (nm).
The term “powder” refers to a free-flowing collection of minute particles.
The term “pulsed electromagnetic radiation” refers to electromagnetic radiation that is modulated to become a series of discrete spikes with increased intensity. The spikes may be relative to a background level of electromagnetic radiation that is negligible or zero, or the background level may be at a higher level that is substantially ineffective to increase adhesion of particles in the particle coating to the fiber.
The term “thermally-softenable” means softenable upon heating.
The term “particle coating” refers to a coating of minute particles which may or may not be free-flowing.
Features and advantages of the present disclosure will be further understood upon consideration of the detailed description as well as the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an enlarged schematic side view of an exemplary 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, which fall within the scope and spirit of the principles of the disclosure.

DETAILED DESCRIPTION

Advantageously, the present disclosure provides an easy method to enhance the durability of particle coatings on nonwoven fiber webs using instantaneous heating by exposure to a modulated source of electromagnetic radiation.
Referring now to FIG. 1, exemplary article 100 comprises a thermally-softenable nonwoven fiber web 110 having a particle coating 120 disposed thereon.
Particle coatings on thermally-softenable nonwoven (e.g., thermoplastic) fiber webs can be carried out by various known methods including, for example, exposure to an aerosolized particle cloud, contact with a powder bed, coating with a solvent-based particle dispersion coating followed by evaporation of solvent, and/or powder-rubbed (rubbing dry particles against a substrate to form a coating of the powder particles). Examples of powder-rubbing methods can be found in U.S. Pat. No. 6,511,701 B1 (Divigalpitiya et al.), U.S. Pat. No. 6,025,014 (Stango), and U.S. Pat. No. 4,741,918 (Nagybaczon et al.). The remaining methods will be familiar to those of ordinary skill in the art.
Useful particle coatings comprise minute loosely bound particles capable of absorbing at least one wavelength of the pulsed electromagnetic radiation, preferably corresponding to a majority of the energy of the pulsed electromagnetic radiation. Suitable particles are preferably at least substantially unaffected by electromagnetic radiation, but are moderate to strong absorbers of it. This is desirable to maximize the light (electromagnetic radiation) to heat conversion yield without altering the chemical nature of the particles.
Exemplary suitable particles include graphite, clays, hexagonal boron nitride, pigments, inorganic oxides (e.g., alumina, calcia, silica, ceria, zinc oxide, or titania), metal(s), organic polymeric particles (e.g., polytetrafluoroethylene, polyvinylidene difluoride), carbides (e.g., silicon carbide), flame retardants (e.g., aluminum trihydrate, aluminum hydroxide, magnesium hydroxide, sodium hexametaphosphate, organic phosphonates and phosphates and ester thereof), carbonates (e.g., calcium carbonate, magnesium carbonate, sodium carbonate), dry biological powders (e.g., spores, bacteria), and combinations thereof. Preferably, the particles have an average particle size of 0.1 to 100 micrometers, more preferably 1 to 50 micrometers, and more preferably 1 to 25 micrometers, although this is not a requirement. Graphite and hexagonal boron nitride are particularly preferred in many applications
Prior to exposure to the electromagnetic radiation the particle coating comprises loosely bound distinct particles that are not chemically bonded to each other, and are not retained in a binder material other than the thermally-softenable nonwoven fiber web itself.
The thermally-softenable nonwoven fiber web preferably comprises thermoplastic fibers, although non-thermoplastic fibers may be used alone or in combination with thermoplastic fibers, for example. In preferred embodiments, the fibers of the thermally-softenable nonwoven fiber web are non-tacky and/or non-thermosetting, although this is not a requirement.
Exemplary suitable thermally-softenable nonwoven fiber webs include meltspun fiber webs, blown microfiber webs, needletacked staple fiber webs, thermally bonded airlaid webs, and spunlace webs. The thermally-softenable nonwoven fiber web may be made by any suitable nonwoven fiber web making process. Examples include meltspun, blown microfiber (BMF), air-laid processes, wet-laid processes, and spunlace. These and other methods will be known to those of skill in the art. Alternatively, a wide array of nonwoven fiber web comprising thermally-softenable fibers are commercially available. The thermally-softenable nonwoven fiber web may be of any basis weight and may be densely compacted or lofty and open, for example.
Some examples of thermoplastic polymers that may be suitable for fiber-forming 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 polymers materials that may be used to make nonwoven fiber web comprising thermoplastic fibers are disclosed in U.S. Pat. No. 5,706,804 (Baumann et al.), U.S. Pat. No. 4,419,993 (Peterson), Re 28,102 (Mayhew), U.S. Pat. No. 5,472,481 (Jones et al.), U.S. Pat. No. 5,411,576 (Jones et al.), and U.S. Pat. No. 5,908,598 (Rousseau et al.). In some preferred methods, at least a portion of the fibers in the thermoplastic fiber web have a higher melting core and a lower melting sheath. In such cases, the higher melting core should preferably be at least 25° C.
The pulsed electromagnetic radiation may come from any source(s) capable of generating sufficient fluence and pulse duration to effect sufficient heating of the nonwoven fiber web to cause the particle coating to bind more tightly to it. At least three types of sources may be effective for this purpose: flashlamps, lasers, and shuttered lamps. The selection of appropriate sources will typically be influenced by desired process conditions such as, for example, line speed, line width, spectral output, and cost.
Preferably, the pulsed electromagnetic radiation is generated using a flashlamp. Of these, xenon and krypton flashlamps are the most common. Both provide a broad continuous output over the wavelength range 200 to 1000 nanometers, however the krypton flashlamps have higher relative output intensity in the 750-900 nm wavelength range as compared to xenon flashlamps which have more relative output in the 300 to 750 nm wavelength range. In general, xenon flashlamps are preferred for most applications, and especially those involving graphite particles. Many suitable xenon and krypton flashlamps are commercially available from vendors such as Excelitas Technologies Corp. of Waltham, Mass. and Heraeus of Hanau, Germany.
In another embodiment, the pulsed electromagnetic radiation can be generated using a pulsed laser. Suitable lasers may include, for example, excimer lasers (e.g., XeF (351 nm), XeCl (308 nm), and KrF (248 nm)), solid state lasers (e.g., ruby 694 nm)), 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.
For maximum efficiency, the electromagnetic radiation spectrum is preferably most intense at wavelength(s) that are strongly absorbed by the particles, although this is not a requirement. Likewise, in the case of reflective particles, the electromagnetic radiation spectrum is preferably most intense in spectral regions in which the particles are least reflective, although this is not a requirement.
Preferably, the source of pulsed electromagnetic radiation is capable of generating a high fluence (energy density) with high intensity (high power per unit area), although this is not a requirement. These conditions assure that the sufficient heat is absorbed to effect increased adhesion of the particles to the fibers. However, the combination of intensity and fluence should not be so great/high as to cause ablation, excessive degradation, or volatilization of fibers in the nonwoven fiber web. Selection of appropriate conditions is within the capability of one of ordinary skill in the art.
To minimize heating of interior portions of the fibers that cannot interact with the particles on the nonwoven fiber web, the pulse duration is preferably short; e.g., 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 speed in continuous manufacturing processes, not only should the pulsed electromagnetic radiation preferably be powerful, but the exposure area is preferably large and the pulse repetition rate is preferably fast (e.g., 100 to 500 Hz).
In order to evaluate durability, the resultant exposed particle-coated nonwoven fiber web may be immersed in a solvent such as, e.g., isopropanol for a fixed interval (e.g., 1, 2, 3, 4, or even 5 minutes, or longer) at about 22° C. (e.g., room temperature), and then removed, dried, and weighed. Weight loss of powder can then be determined by subtraction. The solvent should be selected such that it does not dissolve the nonwoven fiber web.
Preferably, the particulate coating of the nonwoven article is sufficiently bonded to the nonwoven fiber web so that after one minute of immersion in isopropanol at 22° C. at least 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, or even at least 90 percent of the particulate coating remains bonded to the nonwoven fiber web.

SELECT 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 thermally-softenable nonwoven fiber web to pulsed electromagnetic radiation having at least one wavelength in the range of 200 to 1000 nanometers, wherein the particle coating comprises loosely bound distinct particles that are not chemically bonded to each other and are not retained in a binder material other than the thermally-softenable nonwoven fiber web, and wherein the pulsed electromagnetic radiation has sufficient fluence and pulse width to increase bonding force between at least a portion of the loosely bound distinct particles and the thermally-softenable nonwoven fiber web.
In a second embodiment, the present disclosure provides a method according to the first embodiment, wherein the particle coating comprises at least one of graphite or hexagonal boron nitride.
In a third embodiment, the present disclosure provides a method according to the first or second embodiment, wherein the particle coating consists essentially of graphite.
In a fourth embodiment, the present disclosure provides a method according to any one of the first to third embodiments, wherein the pulsed electromagnetic radiation is generated using a flashlamp.
In a fifth embodiment, the present disclosure provides a method according to 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 a method according to 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 a method according to any one of the first to sixth embodiments, wherein the thermally-softenable nonwoven fiber web comprises fibers having a higher melting core and a lower melting 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 thermally-softenable nonwoven fiber web having a particle coating disposed thereon, wherein the particle coating comprises distinct particles that are not chemically bonded to each other and are not retained in a binder material other than the thermally-softenable nonwoven fiber web, and wherein the particle coating is at least 60 percent retained after a one minute immersion in isopropanol at 22° C.
In a tenth embodiment, the present disclosure provides a nonwoven article according to the ninth embodiment, wherein the particle coating comprises at least one of graphite or hexagonal boron nitride.
In an eleventh embodiment, the present disclosure provides a nonwoven article according to the ninth or tenth embodiment, wherein the particle coating consists essentially of graphite.
In a twelfth embodiment, the present disclosure provides a nonwoven article according to any one of the ninth to eleventh embodiments, wherein the particle coating is at least 90 percent retained after the one minute immersion in isopropanol at 22° C.
In a thirteenth embodiment, the present disclosure provides a nonwoven article according to any one of the ninth to twelfth embodiments, wherein the thermally-softenable nonwoven fiber web comprises fibers having a higher melting core and a lower melting 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 noted, all parts, percentages, ratios, etc. in the Examples and the rest of the specification are by weight. All reagents used in the examples were obtained, or are available, from general chemical suppliers such as, for example, Sigma-Aldrich Company, Saint Louis, Missouri, or may be synthesized by conventional methods.

Materials used in the Examples


DESIGNATION	DESCRIPTION

PE nonwoven	Meltblown linear low density polyethylene
	nonwoven fiber web, basis weight = 63 g/m²,
	0.33 mm thickness
MICRO 850	Graphite powder, 3-5 micrometer particle size,
	13 m²/g surface area, 0.088 ohm · cm resistivity,
	obtained from Ashbury Graphite Mills, Inc.,
	Kittanning, Pennsylvania as MICR0850
Isopropanol (IPA)	solvent, obtained from Aldrich Chemical
	Company Milwaukee, Wisconsin

General Method for Coating Graphite onto Substrates

To make Examples and Comparative Examples described below, graphite coatings were applied on PE nonwoven substrates by placing a strip of nonwoven approximately 1.5 inches (3.8 cm) by 10 inches (25.4 cm) in dimension 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 in graphite. The nonwoven was then removed, and excess graphite particles were removed by blowing with compressed nitrogen at a pressure of 40 pounds per square inch.
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 Methods for Determining Durability

The samples prepared according to Examples and Comparative Examples described below, were tested for durability (resilience of coatings).
Nonwoven samples were completely immersed (i.e., submerged) in a bath of IPA at room temperature (22° C.) and stirred by hand for 1 minute. The samples were then removed and spread onto a clean surface in a chemical hood and allowed to dry completely.
All reported percentages of graphite retained (% R) were calculations from the following equation:
$% R = 100 \times \frac{M_{g, i} - M_{g, w}}{M_{g, i}}$
Where M_g,iis the mass of graphite on the nonwoven just prior to immersion in isopropanol, and M_g,wis the mass of graphite remaining on the nonwoven after the wash step.

Examples 1-11 (EX-1 to EX-11) and Comparative Example A (CEX-A)

CEX-A and EX-1 to EX-12 were 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 an intense pulsed light irradiation (IPL). In all cases of IPL, the source used was a Xe flashlamp, commercially obtained from Xenon Corporation, Wilmington, Mass., as a SINTERON S-2100 Xe flashlamp equipped with Type C bulb. Samples were placed beneath a quartz plate for the irradiation process.
For EX-1, the substrate was treated 1 time at a pulse rate of 1 Hz and an energy density of 0.1 J/cm². The substrate was then removed and flipped over, and the treatment was repeated on the backside of the substrate.
For EX-2, the substrate was treated 3 times at a pulse rate of 1 Hz and an energy density of 0.1 J/cm². The substrate was then removed and flipped over, and the treatment was repeated on the backside of the substrate.
For EX-3, the substrate was treated 5 times at a pulse rate of 1 Hz and an energy density of 0.1 J/cm². The substrate was then removed and flipped over, and the treatment was repeated on the backside of the substrate.
For EX-4, the substrate was treated 1 time at a pulse rate of 1 Hz and an energy density of 0.2 J/cm². The substrate was then removed and flipped over, and the treatment was repeated on the backside of the substrate.
For EX-5, the substrate was treated 3 times at a pulse rate of 1 Hz and an energy density of 0.2
J/cm². The substrate was then removed and flipped over, and the treatment was repeated on the backside of the substrate.
For EX-6, the substrate was treated 5 times at a pulse rate of 1 Hz and an energy density of 0.2 J/cm². The substrate was then removed and flipped over, and the treatment was repeated on the backside of the substrate.
For EX-7, the substrate was treated 1 time at a pulse rate of 1 Hz and an energy density of 0.3 J/cm². The substrate was then removed and flipped over, and the treatment was repeated on the backside of the substrate.
For EX-8, the substrate was treated 3 times at a pulse rate of 1 Hz and an energy density of 0.3 J/cm². The substrate was then removed and flipped over, and the treatment was repeated on the backside of the substrate.
For EX-9, the substrate was treated 5 times at a pulse rate of 1 Hz and an energy density of 0.3 J/cm². The substrate was then removed and flipped over, and the treatment was repeated on the backside of the substrate.
For EX-10, the substrate was treated 1 time at a pulse rate of 1 Hz and an energy density of 0.4
J/cm². The substrate was then removed and flipped over, and the treatment was repeated on the backside of the substrate.
For EX-11, the substrate was treated 3 times at a pulse rate of 1 Hz and an energy density of 0.4 J/cm². The substrate was then removed and flipped over, and the treatment was repeated on the backside of the substrate.
Table 1, below, reports the IPL effects on PE nonwoven and the measured fraction (f) of the graphite coating retained.

TABLE 1

		ENERGY
		DENSITY
	IPL PULSES	PER PULSE,
EXAMPLE	PER SIDE	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-D (CEX-B to CEX-D)
For CEX-B to CEX-D, samples of nonwoven PE were subjected to heating in a Model 725G Isotemp laboratory oven (Fisher Scientific, Hampton, New Hampshire). Samples were placed on an aluminum tray in a preheated oven for the specified amount of time. Results are reported in Table 2, below.

TABLE 2

	TEMPERATURE,	DURATION,
EXAMPLE	° C.	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 herein incorporated by reference in their entirety in a consistent manner. In the event of inconsistencies or contradictions between portions of the incorporated references and this application, the information in the preceding description shall control. The preceding description, given in order 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

1-13. (canceled)

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

15. The method of claim 14 wherein the particle coating comprises at least one of graphite or hexagonal boron nitride.

16. The method of claim 14, wherein the particle coating consists essentially of graphite.

17. The method of claim 14, wherein the pulsed electromagnetic radiation is generated using a flashlamp.

18. The method of claim 14, wherein the pulsed electromagnetic radiation is generated using a pulsed laser.

19. The method of claim 14, wherein the pulsed electromagnetic radiation is generated using a continuous light source and a shutter.

20. The method of claim 14, wherein the thermally-softenable nonwoven fiber web comprises fibers having a higher melting core and a lower melting sheath.

21. A nonwoven article made according to the method of claim 1.

22. A nonwoven article comprising a thermally-softenable nonwoven fiber web having a particle coating disposed thereon, wherein the particle coating comprises distinct particles that are not chemically bonded to each other and are not retained in a binder material other than the thermally-softenable nonwoven fiber web, and wherein the particle coating is at least 60 percent retained after a one minute immersion in isopropanol at 22° C.

23. The nonwoven article of claim 22, wherein the particle coating comprises at least one of graphite or hexagonal boron nitride.

24. The nonwoven article of claim 22, wherein the particle coating consists essentially of graphite.

25. The nonwoven article of claim 22, wherein the particle coating is at least 90 percent retained after the one minute immersion in isopropanol at 22° C.

26. The nonwoven article of claim 22, wherein the thermally-softenable nonwoven fiber web comprises fibers having a higher melting core and a lower melting sheath.