Button for articles of clothing

The present invention relates to a button that has improved strength and an improved resistance to deterioration. The button is preferably made from a ceramic material, such as partially stabilized zirconia, alumina, zirconia-alumina composites, or silicon carbide whisker reinforced ceramics. The button has a high strength, durability, and will often out-last the article of clothing on which it is placed.

FIELD OF THE INVENTION 
The present invention relates to an improved button that is useful for 
articles of clothing and the like. More particularly, the present 
invention relates to a button having improved properties that is 
fabricated from a ceramic material. 
BACKGROUND OF THE INVENTION 
In the past, buttons, particularly buttons for dress shirts, were 
fabricated from mother-of-pearl. The mother-of-pearl was durable and met 
the requirements of the clothing industry for many years. Nonetheless, 
much of the clothing industry switched to a less expensive polyester resin 
material when easy-care permanent-press fabrics were introduced in the 
1960's 
While the polyester resin buttons are sufficient for shirts that do not 
require pressing, they do not perform well when subjected to the hot 
presses and commercial laundering detergents that are now widely used, 
particularly for all-cotton shirts. Commercial laundering subjects the 
buttons to significant wear and stress, and the polyester resin tends to 
become brittle with age. A men's dress shirt is particularly prone to 
these problems because the smaller collar and cuff buttons are more likely 
to break than larger buttons. 
Button breakage presents a significant problem for the commercial 
laundering business, as well as the consumer Commercial laundries must 
often replace the buttons that are broken during the laundering process. 
Commercial laundries use a large number of buttons due to this problem and 
often employ one or more persons whose sole responsibility is to replace 
broken buttons. This costs the laundry a great deal of money for manpower 
and materials. 
The dress shirt industry has recognized this problem and has expended a 
great deal of time and effort to identify a practical solution. See, for 
example, the article "Scramble Is On to Develop the Unbreakable Button," 
published in the New York Times on Sep. 11, 1989. It is disclosed therein 
that experts have experimented with buttons having different materials, 
shapes, sizes, and thicknesses. Also see the article "All broken up: Shirt 
maker tackles that button problem," in the Milwaukee Journal, Dec. 27, 
1989. 
Despite this long felt need by the clothing industry and the efforts 
exerted by the industry, a practical solution to the problem has not 
previously been identified. 
For the button to be useful, the button must have a high strength and be 
resistant to corrosion from extremely hot steam presses, high 
concentrations of dry cleaning solvents or detergents, and the like. 
SUMMARY OF THE INVENTION 
The present invention provides a button for an article of clothing, wherein 
the button includes a ceramic material. Preferably, the ceramic material 
has a strength of at least about 250 MPa and a critical stress-intensity 
factor of at least about 3 to 4 MPam.sup.1/2. In one embodiment, the 
ceramic material has the strength of at least about 300 MPa. The ceramic 
material is preferably selected from the group consisting of partially 
stabilized zirconia alumina, alumina-zirconia composites, and silicon 
carbide (SiC) whisker-reinforced composites. In a more preferred 
embodiment, the button consists essentially of magnesia-partially 
stabilized zirconia. In yet another embodiment, the button is 
substantially white in color. 
The button according to the present invention is highly resistant to 
deterioration caused by dry cleaning solvents and detergents. Further, it 
is able to withstand high temperatures and high stresses that it can be 
exposed to during cleaning and pressing operations and during use. 
In a more preferred embodiment, the button consists essentially of a 
magnesia-partially stabilized zirconia having a strength greater than 
about 350 MPa and a critical stress-intensity factor greater than about 8 
MPam.sup.1/2, and the button is substantially white. 
The present invention also provides a dress shirt having a torso section 
with a plurality of buttons and a pair of sleeves attached to the torso 
section. The buttons consist essentially of a ceramic material having a 
strength of at least about 350 MPa and a critical stress-intensity factor 
of at least 8 MPam.sup.1/2. In one embodiment, the dress shirt is 
fabricated from substantially 100% cotton.

DESCRIPTION OF PREFERRED EMBODIMENTS 
The present invention is directed to a button fabricated from a ceramic 
material that is particularly useful for clothing. The ceramic material 
preferably has sufficient strength to remain intact when subjected to high 
stresses, is highly resistant to heat, and is highly resistant to 
degradation when subjected to chemicals such as dry-cleaning solvents, and 
the like. 
The ceramic material preferably has sufficiently high strength and fracture 
toughness such that there is a high probability of survival under severe 
stresses. Such severe stresses can occur, for example, when a shirt is 
pressed in a commercial press or tumbled in a hot dryer. An acceptable 
ceramic material preferably possesses a tensile strength, measured 
according to ACMA Test No. 4, of more than about 250 MPa, preferably more 
than about 300 MPa, and most preferably more than about 350 MPa. The 
ceramic material has a critical stress intensity factor of greater than 
about 3 to 4 MPam.sup.1/2, preferably greater than about 6 MPam.sup.1/2, 
more preferably greater than about 8 MPam.sup.1/2, and most preferably 
greater than about 12 MPam.sup.1/2. The critical stress intensity factor 
can be measured according to the single-edge notched beam (SENB) test, as 
described in Evans, A. G., "Fracture Mechanics Determinations" in Fracture 
Mechanics of Ceramics, Volume 1, edited by R. C. Bradt, D.P.H. Hasselman 
and F.F. Lange, Plenum Press, NY, pg. 17, (1974), incorporated herein by 
reference in its entirety. 
Examples of ceramic materials which can preferably be used in producing the 
ceramic button according to the present invention include zirconias, 
particularly partially stabilized zirconias, such as magnesia-, calcia-, 
yttria-or ceria-partially stabilized zirconias. Examples of these 
materials are described in: European Patent Application No. 8030025.6, 
Publication No. 0013599, filed Mar. 1, 1980 by Commonwealth Scientific and 
Industrial Research Organization; U.S. Pat. No. 4,067,745, by Garvie et 
al., issued Jan. 10, 1978, entitled "Ceramic Materials"; U.S. Pat. No. 
4,885,266 by Hughan et al., issued Dec. 5, 1989, entitled "Zirconia 
Ceramic Materials and Method for Making Same"; and Canadian Patent No. 
1,154,793, by Otagiri et al., issued Nov. 4, 1983, entitled "Zirconia 
Ceramics and Method of Producing the Same." All of the foregoing documents 
are incorporated herein by reference in their entirety. 
A preferred method for fabricating magnesia-partially stabilized zirconia 
according to the present invention is described in U.S. Pat. No. 
4,939,996, by Dinkha et al., incorporated herein by reference in its 
entirety. 
In this method, sufficient magnesium oxide or a material capable of forming 
magnesium oxide such as magnesium carbonate, is combined with the 
zirconium dioxide powder to provide an effective magnesium oxide level in 
the ceramic of from about 2.6 to about 3.8 weight percent. These mixed 
powders are preferably calcined between about 1000.degree. C. and about 
1700.degree. C., more preferably between about 1000.degree. C. and about 
1500.degree. C., for between about 4 and about 12 hours, preferably from 
about 6 to about 10 hours. The resulting calcined mixture is wet milled 
until the average particle size is preferably between about 0.8 and 2.5 
micrometers, more preferably about 1.5 micrometers. If needed, a 
sufficient amount of fugitive organic binder is added to allow formation 
of a compact green body. The amount needed depends on the method of 
formation and the particular binder used. Ordinarily the level of the 
binder is between 0.1 and about 7 weight percent of the calcined mixture 
with the preferred level being about 1.5 to about 2.8 percent. The mixture 
is then dried by evaporation of the water, preferably by spray drying. The 
dried powder is then formed into a compact of the desired shape, such as a 
button having four thread holes, preferably by dry pressing. Dry pressing 
will permit the button to have a contour and/or ridge, if desired. 
The formed compact is then heated from ambient temperature at a rate of 
between about 25.degree. C. per hour and about 250.degree. C. per hour, 
preferably about 100.degree. C. per hour, to a soak temperature of between 
about 1675.degree. C. and about 1800.degree. C., preferably between about 
1700.degree. C. and 1750.degree. C. This soak temperature is held for 
between about 1 and about 10 hours, preferably for about 2 to about 6 
hours. The sintered article is then cooled using a cooling procedure such 
as described in Robert R. Hughan, "Precipitation During Controlled Cooling 
of Magnesia-Partially Stabilized Zirconia," J. Am. Ceram. Soc. 69, 556-563 
(1986), incorporated herein by reference in its entirety. A preferred 
procedure involves cooling the sintered body at a rate of between about 
250.degree. C. and about 800.degree. C. per hour, preferably between about 
350.degree. C. and about 500.degree. C. per hour, to a temperature between 
about 800.degree. C. and about 1400.degree. C., preferably between about 
800.degree. C. and about 1000.degree. C. The sintered article can then be 
furnace cooled to room temperature. 
The sintered ceramic buttons according to the present invention are 
preferably polished in, for example, a geocentrifugal polisher. The 
polishing step gives the ceramic buttons a smooth and pleasing surface 
finish. 
Other materials that can be useful for producing the button according to 
the present invention include alumina, alumina-zirconia composites 
(Al.sub.2 O.sub.3 --ZrO.sub.2) having 5 to 90 weight percent ZrO.sub.2 and 
10 to 95 weight percent Al.sub.2 O.sub.3, the ZrO.sub.2 fraction 
containing from 0 to 6 weight percent Y.sub.2 O.sub.3 ; and SiC 
Whisker-reinforced ceramics, e.g., SiC whisker-reinforced alumina or SiC 
whisker-reinforced mullite. 
It has been found that magnesia-partially stabilized zirconia is less 
susceptible to flawing from stresses typically incurred during use than, 
for example, yttria-partially stabilized zirconia. Magnesia-partially 
stabilized zirconia has increased critical stress-intensity values 
(K.sub.IC) for millimeter-scale flaw sizes, when compared with 
yttria-partially stabilized zirconia, even though yttria-partially 
stabilized zirconia is often superior for small flaw sizes. Thus, 
magnesia-partially stabilized zirconia is a preferred ceramic material for 
use in the button. An example of magnesia-partially stabilized zirconia is 
transformation-toughened zirconia (TTZ) produced by the Coors Ceramics 
Company, Golden, CO, having a tensile strength at 25.degree. C. (ACMA Test 
No. 4) of about 352 MPa and a critical stress-intensity factor (single 
edged notched beam test) of at least about 8 MPam.sup.1/2. 
Partially stabilized zirconias are particularly useful since very low 
structural failure rates are desired, such as on the order of less than a 
few parts per million. It has been found that the preferred zirconia 
materials, such as magnesia-partially stabilized zirconia, may have a 
lower average strength than less preferred materials when analyzed at a 
high failure rate level such as 50 percent, but that these same preferred 
materials will provide a better average strength when analyzed at a lower 
level of failure rate, such as 5 to 100 parts per million, or less. That 
is, when articles fabricated from the preferred materials are subjected to 
the stress levels typically encountered by a button, the probability of 
failure (breakage) will be very low. 
Zirconia materials provide an additional advantage according to the present 
invention, since these materials sinter to a white or substantially white 
finish. This is desirable since the largest percentage of buttons produced 
for the clothing industry have a white or substantially white color. As 
used herein, the term substantially white includes shades such as ivory. 
One advantage to using an alumina based ceramic for the ceramic button 
according to the present invention, is that the alumina is more readily 
colored than other materials. For example, small amounts of rare earth 
oxides or other metal oxides can be added to the alumina without 
substantially changing the strength characteristics of the material. 
Zirconia materials, particularly magnesia-partially stabilized zirconia, 
are difficult to color without applying an external coating. 
FIGS. 1 and 2 depict an embodiment of a button 10 according to the present 
invention. The button includes holes 14 useful for attaching the button to 
an article of clothing. The button is also contoured and has a ridge 16 
for a pleasing aesthetic appearance. 
The buttons of the present invention have been tested to compare their 
properties to buttons of the prior art. The results of this test are shown 
in Table I. 
TABLE I 
______________________________________ 
Impact Test 
Compression 
Button Type (oz./in.) Test (lb.) 
______________________________________ 
Plastic 5.35 1850 
4-hole 
Plastic 4.95 2058 
2-hole 
Ceramic 30.52 2401 
______________________________________ 
The impact strength is measured by a swing-arm test. The compression test 
is performed on a laboratory press equipped with two self-aligning flat 
plates. The button being tested is centered on a lower plate and pressure 
is applied. The first audible crack indicates part failure. 
Table I shows that a ceramic button according to the present invention can 
have an impact strength of almost six times the impact strength of the 
plastic buttons. The compressive strength of the ceramic button shows an 
increase of from 17 to 30 percent over the prior art. 
The buttons were also tested in a washing and pressing operation. The 
ceramic buttons and plastic buttons were attached to two test shirts, and 
then washed and pressed on nine different washer/press set-ups. This was 
done to evaluate each button when processed through variations in wash, as 
well as press conditions. 
The shirts were monitored for button breakage at each wash and press cycle 
for fracturing. Both the first and second fracture of a plastic button 
occurred at the first pressing step, in a 13 ligne (0.325 inch diameter) 
collar button. Comparatively, the first fracture of one ceramic button 
according to the present invention occurred in a 13 ligne button on the 
fifteenth washing. No additional fracturing of any other ceramic buttons 
was detected for 32 consecutive cycles, and the test was stopped due to 
shirt deterioration. Thus, the buttons according to the present invention 
will often outlive the shirt on which they are sewn. 
The buttons according to the present invention are stronger than typical 
mass produced buttons that are presently available and are highly 
resistant to detergents and dry-cleaning solvents used in present 
commercial cleaning processes. The present invention satisfies a long-felt 
need by the clothing industry for a button having these characteristics. 
While various embodiments of the present invention have been described in 
detail, it is apparent that modifications and adaptations of those 
embodiments will occur to those skilled in the art. However, it is to be 
expressly understood that such modifications and adaptations are within 
the spirit and scope of the present invention.