Plastic article or earthenware shaping or treating: apparatus – Press forming means – press reshaping means – or vulcanizing... – Including means to adjust relative position of a roll
Reexamination Certificate
1999-08-05
2002-04-09
Nguyen, Nam (Department: 1722)
Plastic article or earthenware shaping or treating: apparatus
Press forming means, press reshaping means, or vulcanizing...
Including means to adjust relative position of a roll
C425S363000, C425S371000, C425S374000, C425S394000
Reexamination Certificate
active
06368097
ABSTRACT:
FIELD OF THE INVENTION
The present invention is directed to a method and apparatus for capping headed stem fasteners, and more particularly, to a method and apparatus for controlling the nip profile and for increasing the nip length.
BACKGROUND OF THE INVENTION
Various fasteners that releasably interengage with other articles are widely used as low cost garment fasteners, such as on disposable diapers. One type of headed stem fastener is the hook portion of a hook-and-loop fastener. Although the hook portion of a hook-and-loop fastener is typically designed to engage with a loop strip, the hook portion can be used by itself to become releasably fastened to fabrics that are easily penetrated by the hook. Another type of heated stem fastener that is particularly suited for this purpose is a mushroom-headed fastener, such as available under the product designation XMH-4152 from Minnesota Mining & Manufacturing Company of St. Paul, Minn. Mushroom-headed fasteners can be designated to become releasably fastened to burlap, Terri cloth, and tricot.
Stem fasteners are typically formed by capping polymeric stems extending distally from a backing layer. The precursor web containing the stems can be prepared according to a variety of techniques, such as disclosed in U.S. Pat. No. 4,290,174 (Kalleberg) and U.S. patent application Ser. No. 08/048,874 (Miller), entitled Mushroom-Type Hook Strip for a Mechanical Fastener (WO 94/23610).
FIGS. 1 and 3
are schematic illustrations of two commonly used methods for capping stems projecting upward from a precursor web. In the embodiment of
FIG. 1
, a precursor web
20
is fed through a gap in a nip
21
between two calender rolls
22
and
24
. The heated calender roll
22
contacts a predetermined portion of a distal end
26
of the stems
28
projecting upward from a backing
30
. The temperature of the heated calender roll
22
is maintained at a temperature that will readily deform the distal ends
26
under mechanical pressure in the nip
21
.
Maintaining the distal ends
26
at this temperature allows melting and molecular disorientation of the stems
28
. During such contact and/or upon subsequent cooling, a head
32
is formed on the distal ends
26
. The heads
37
can be a variety of shapes, such as mushroom-shaped heads, “umbrella,” “nail head,” “golf tee” and “J-shaped.” Mushroom shaped heads typically have a flat, planar or slightly convex upper surface and a maximum cross-section larger than the diameter of the stem immediately below the head (see FIGS.
8
A and
8
B).
The capping mechanism is generally a time-temperature-pressure phenomenon, although it is possible that some heat may be transmitted to the stems by convection. In practice, the height of the stems
28
and the finished height of the capped stem
32
are determined by the product design. The upper temperature at the roll
22
is generally limited to the temperature at which the polymer of the stems
28
sticks to the roll.
FIG. 2
is a diagram illustrating the size of the capping surface
34
(see
FIG. 1
) of a conventional calendering system. In
FIG. 2
, R is the radius of the heated roll, X is the distance over which the precursor web
20
is capped, t
2
is the height of the capped stem
32
, and t
1
is the height of the stem
28
. For a typical product, t
2
is approximately 0.51 mm and t
1
is approximately 0.74 mm. Using the following equation, the capping surface or distance
34
for a calender roll with a diameter of 45.7 cm (18 inches) is approximately 7.2 mm.
x
=
2
π
R
360
[
cos
-
1
[
d
-
t
1
2
R
]
]
FIG. 3
is a schematic illustration of an alternate method and apparatus for forming headed stems
42
. The precursor web
20
is positioned so that a heated platen
40
is located above the stems
28
. The heated platen
40
heats the air near the distal ends
26
of the stems
28
to cause the ends to soften by convection. The stems are deformed into generally hemispherical-shaped heads
42
. In order to achieve controlled deformation of the distal ends
26
, the temperature at which the heated platen
40
can be operated is limited by the polymer from which the stems
28
are constructed. Additionally, the ability to control the shapes of the heads
42
is limited.
BRIEF SUMMARY OF THE INVENTION
The present invention is directed to a method and apparatus for capping headed stem fasteners. The present method and apparatus controls the nip profile and increases the nip length.
The present method of capping a headed stem fastener includes providing a precursor web having a backing with a rear surface, a front surface, and a multiplicity of polymeric stems projecting distally from the front surface of the backing. A heated member is positioned opposite a support surface to form a variable nip having a variable nip length. The support surface has a shape generally conforming to a contour of the heated member. The precursor web is fed along the length of the variable nip to compressively engage the polymeric stems between the heated member and the support surface so that distal ends of the polymeric stems are deformed.
A variety of nip profiles may be configured using the present heated member and support surface. The nip gap may decrease along the variable nip length. The nip gap may have a generally constant rate of decreases along the variable nip length. The nip gap may decrease more rapidly near a nip inlet than near a nip outlet or the nip gap may decrease more rapidly near a nip outlet than near a nip inlet. The nip gap may have a generally constant rate of decrease near a nip inlet and a nonuniform rate of increase near a nip outlet. The nip gap may remain constant along a portion of the variable nip length and vary elsewhere along the variable nip length.
The curved support structure forms a variable nip having a variable nip length that is significantly longer than can be achieved using a pair of rolls of a comparable diameter. Therefore, without changing the diameter of the heated roll, the present curved support structure permits the variable nip length to be increased. Since capping is generally a time-temperature-pressure phenomenon, for a given time, temperature and pressure, the line speed of the precursor web through the present variable nip is greater using the present curved support structure than using a conventional two roll nip. The combination of the present heated roll and curved support structure define a variable nip length preferably at least 1.25 times greater than the nip length defined by a pair of rolls having the same diameter as the heated roll, and more preferably at least 1.5 times greater, and most preferably at least 3.0 times greater.
The present invention is also directed to an apparatus for capping a precursor web. The precursor web has a multiplicity of polymeric stems projecting distally from a front surface of a backing. The apparatus includes a heated member opposite a support surface forming a variable nip having a variable nip length. The support surface has a shape generally conforming to a contour of the heated member. A feeding mechanism feeds the precursor film through the variable nip along the variable nip length to compressively engage the polymeric stems between the heated member and the support surface supports so that distal ends of the polymeric stems are deformed.
The heated member may be a heated roll opposite a curved support surface. The curved support surface preferably has a radius of curvature generally conforming to a radius of curvature of the heated roll. The support surface may be slid or rotated into engagement with the heat roll.
In an alternate embodiment, the heated member may be a heated belt opposite the support surface. The support surface may be a support belt. The shape of the heated belt may optionally be altered by a support roll or a curvilinear slide plate. The heated belt and the support surface define at least two tapered zones. Alternatively, the heated belt has a generally planar configuration.
The present invention incl
LaLiberte Thomas R.
Miller Philip
3M Innovative Properties Company
Bond William J.
Griswold Gary L.
Heckenberg Donald
Sprague Robert W.
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