Method for heat-setting spandex-containing garments

A method of heat-setting garments by boarding the garment and subjecting it to preselected temperatures that are different for different parts of the garment and an apparatus for carrying out this method are provided.

BACKGROUND OF THE INVENTION
 This invention pertains to a method of heat-setting a garment by boarding
 the garment and subjecting it to preselected thermal conditions that are
 different for different parts of the garment.
 DISCUSSION OF BACKGROUND ART
 Methods have been proposed to modify stockings so that the pressure felt by
 different parts of a leg of a wearer are different. Japanese Kokai Patent
 No.'s Hei 3(1991)-287801, No. Hei 3(1991)-279403 and No. Hei 4(1992)-18102
 each discloses a method for making stockings in which the knitting is
 changed for different parts of the stocking so that mesh size, yarn
 denier, and/or length of yarn per course is different and correspond to
 different parts of a wearer's leg. As a result, the pressure experienced
 by the wearer is different for different parts of the leg. However, such
 methods require complex knitting procedures in order to vary the stitch
 density (mesh size), length of yarn fed per course, and yarn denier.
 A variety of methods have also been proposed to board and heat-set
 garments, including stockings. British Patent Number 719,795 discloses an
 apparatus for heat-setting stockings which do not contain spandex by
 passing them through a tunnel-like oven on an endless conveyor. Baffle
 plates are disclosed to direct the hot air onto the welt (knitted
 non-raveling edge) of the stocking. However, this is an imprecise method
 in that the hot air merely enters at that point and is not prevented from
 affecting the rest of the stocking.
 Japanese Kokai Patent No. Hei 4(1992)-108181 discloses a method of exposing
 different parts of a stocking to UV radiation in addition to uniformly
 heating the entire stocking in order to adjust the stretch in different
 parts of the stocking. However, this method can result in undesirable
 deterioration of the fibers in parts of the stocking that have been
 exposed to the radiation.
 A versatile and simple method of making stockings so that the pressure on
 the wearer's leg is different in several parts of the leg is still needed,
 as is a practical apparatus for carrying out such method.
 SUMMARY OF THE INVENTION
 The method of the present invention for heat-setting a garment containing
 spandex comprises the steps of:
 mounting the garment comprising a plurality of garment parts on a boarding
 form;
 heating the mounted garment by subjecting the garment to a plurality of
 preselected elevated temperatures corresponding spatially to the garment
 parts; and
 removing the garment so heat-set from the form.
 The apparatus of the present invention for heat-setting garments comprises:
 at least one chamber;
 a plurality of heating zones within the chamber;
 a plurality of heating means, each heating means being positioned in a
 heating zone; and
 a boarding form for mounting the garment, the form being supported within
 the chamber so that the heating zones correspond spatially to the garment
 parts.

DETAILED DESCRIPTION OF THE INVENTION
 As used herein, "spandex" means a manufactured fiber in which the
 fiber-forming substance is a long chain synthetic elastomer comprised of
 at least 85% by weight of a segmented polyurethane. "Part" of a garment
 means a section of the garment attached to another section of the garment,
 each section being associated with a corresponding body part of a wearer,
 for example foot, calf, thigh, arm, back, and the like.
 Knit garments are often heat-set under tension to stabilize their
 dimensions. In the case of garments containing spandex, such heat-setting
 can generally be performed at temperatures in the range of about
 40.degree. C. to 300.degree. C., preferably 60.degree. C. to 200.degree.
 C. When the garment is a pair of stockings, such heat-setting can be
 performed on a boarding form in the shape of a leg. Stockings, such as
 pantyhose, which exert different pressures on different parts of the body,
 such as the foot (toes and ankle), calf, knee, thigh and abdomen, are more
 comfortable to the wearer.
 By means of the present invention, garments with excellent comfort, feel
 and fatigue alleviating effects can be obtained from a greige knit fabric
 made with a relatively simple knitting design and without adopting
 complicated knitting methods. Because of the resulting high knitting
 productivity, cost can be reduced markedly. In the past, the part of the
 garment where the pressure was intended to be low has been realized by
 increasing the amount of yarn fed to the knitting machine, changing the
 yarn denier, and/or changing the knit mesh size (stitch density). It has
 now been found that substantially the same result can be realized by
 raising the level of heat-setting by selectively increasing the
 temperature to which each such part of a garment is exposed. Conversely,
 where in the past the part of the garment where the pressure was intended
 to be high has been realized by, for example, decreasing the amount of
 yarn feed on the knitting machine, substantially the same result can now
 be realized by lowering the level of heat-setting by lowering the
 temperature to which such part is exposed.
 The method and apparatus of the present invention can be applied to
 garments having substantially the same mesh size throughout the garment.
 Such garments can include brassieres, girdles, pants, shirts, gloves,
 pantyhose, and stockings. The length of yarn fed into each course and the
 tension with which the yarn is knit determine the mesh size in each
 course. When the mesh size (stitch density) or length of yarn fed is
 substantially the same throughout the garment, the method and apparatus of
 this invention can be used to alter the compressive force exerted by
 different parts of the garment when it is worn.
 This way, knitting adjustments can be significantly reduced, because even
 when the mesh size or amount of yarn fed is changed for various parts of
 the garment (for example a stocking or pantyhose), the method and
 apparatus of the invention can be combined with such knitting changes to
 further adjust and optimize the resulting compressive force, thereby
 significantly reducing the need for such changes.
 For example, the pressure or binding force of stockings has traditionally
 been adjusted by varying the amount of yarn fed to the knitting machine in
 more than twenty steps in the lengthwise (wale) direction of the
 stockings. In contrast, by means of the method of this invention, a greige
 stocking of simplified knitting design, wherein the toe-to-lower calf part
 has substantially the same amount of yarn feed, the upper calf-to-lower
 thigh part has a substantially constant but proportionally increased
 amount of yarn feed (compared to the toe-to-lower calf), and the
 thigh-to-abdomen part has substantially the same amount of yarn feed but
 at a higher level than the other parts, can be heat-set by varying the
 heat-setting conditions in the lengthwise (wale) direction according to
 this invention to obtain the requisite pressure, even though only three
 knitting changes are used. The knitting complexity is thus considerably
 reduced compared to the traditional method, but the resulting stockings
 are comparable in the pressure exerted at different parts of the leg.
 Use of yarns having higher heat-set efficiency requires even fewer
 adjustments of the knitting process so that a tubular knit stocking can be
 manufactured with substantially the same amount of yarn feed from toe to
 abdomen.
 In the present method, a spandex-containing garment to be heat-set is
 mounted on a boarding form (for example a leg form), and the mounted
 garment is exposed to a plurality of preselected temperatures. At least
 two, preferably at least three, and more preferably at least four
 different preselected temperatures can be applied so that different parts
 of the garment experience different temperatures. The heat must be
 sufficient to heat-set spandex, but to differing extents depending on the
 temperature. As a result, the thermal histories of the different parts of
 the garment will be different, and the compressive force will also be
 different in various parts of the garment.
 The temperatures can differ in the vertical direction of the garment (i.e.
 in the direction of wales of stockings) or in the horizontal direction
 (i.e., in the direction of courses in stockings). For most purposes,
 temperatures differing in the vertical direction of the garment are
 preferred, so that in the case of stockings or pantyhose the compressive
 force decreases in the order: foot, calf, knee, and thigh. Preferably, the
 pressure experienced by the wearer on the foot, calf, knee and thigh is
 adjusted to within a range of 40-57 grams-force per square centimeter
 (gf/cm.sup.2), 27-47 gf/cm.sup.2, 20-32 gf/cm.sup.2, and 19-29
 gf/cm.sup.2, respectively.
 Fibers in various parts of garments treated by the process of the present
 invention shrink by different percentages in boiling water as a result of
 their differing thermal histories, and their stress recovery from
 elongation is also different if they are taken from differing parts of a
 stocking which has been heat-set by the present method.
 The garments, particularly stockings, processed by this method include
 those made from conventional knits. For instance, they can be made of a
 knitting yarn that contains spandex, polybutylene terephthalate fibers,
 polyesterether fibers, or polyester elastic fibers. The elastic fiber can
 be bare (100% elastic yarn), a combination (covered) elastic yarn that is
 made from non-elastic fibers such as polyamide, polyester, or cotton
 fibers over a core of elastic fibers, or mixtures of elastic fibers and
 non-elastic fibers. For stockings, the knitting yarn has a total denier
 (d) of 5-300, preferably 10-200. These yarns can be a mixture of heavy
 denier fibers and fine denier fibers, and the fibers with a fine denier
 can also include super-fine fibers with a single-fiber denier of 0.1 or
 less.
 Heat-setting of garments can be by dry heat or wet heat, or a combination
 of the two. The heating means include electrothermal heaters,
 electron-beam heaters, infrared-ray heaters, steam, and hot water.
 Infrared-ray sources and far infrared sources (both of which provide dry
 heat) are preferred because more precise local heating of any garment part
 is possible.
 Heat-setting can be performed at a temperature of about 40.degree.
 C.-300.degree. C., preferably 60.degree. C.-200.degree. C. The compressive
 force of the heat-set yarn varies with the type of heat used and,
 therefore, the temperature range must be changed depending on the type of
 heat and the part of the garment being heat-set. For instance, when
 heat-setting stockings, a temperature range of about 60.degree.
 C.-150.degree. C. is preferred when steam is used and a temperature range
 of about 80.degree. C.-200.degree. C. is preferred when dry heat is used.
 The preferred setting temperature for each part of the stockings when dry
 heat is used is about 100.degree. C.-140.degree. C. for the foot,
 110.degree. C.-150.degree. C. for the calf, 130.degree. C.-170.degree. C.
 for the knee, and 150.degree. C.-200.degree. C. for the thigh.
 A combination of wet-heat treatment and dry-heat treatment can also be
 employed. For instance, pre-treatment of stockings with wet heat, followed
 by dry-heat, affords stockings which can be heat-set and finished so that
 they feel softer.
 Turning to FIG. 1, a side view of the apparatus of the present invention is
 shown with a boarding form 3 in profile, mounted on holder 4 inside
 chamber 1. Heat sources 2 are shown arranged so as to provide different
 temperatures to different parts of form 3.
 FIG. 2 shows a front view of the apparatus with boarding form 3 shown on
 edge and mounted on holder 4. As in FIG. 1, heat sources 2 are mounted so
 that they apply heat to heating zones that are oriented in the course
 direction of the garment. Two heat sources are shown for each zone and are
 placed facing each other on either side of form 3. Sub-chambers 1-1, 1-2,
 1-3, 1-4, and 1-5 correspond to the heating zones and are separated from
 each other by barriers 5 so that they are in no substantial thermal
 communication with each other.
 The apparatus of this invention can heat each part of the stocking to be
 set as needed while limiting diffusion of heat between heating zones by
 using a barrier, for example a diaphragm, between the zones, the barrier
 being arranged so that it does not touch the stocking being heat-set. Thus
 at least two sub-chambers are formed within the main chamber, without the
 sub-chambers being in substantial thermal communication with other
 sub-chambers. Thus the apparatus can have several different and
 substantially independent zones oriented in the direction of horizontal
 and/or vertical rows, each zone corresponding spatially to a sub-chamber.
 The garments can be set on a form where the heat is precisely and finely
 varied at specific points between the zones corresponding to selected
 parts of the garment, or they can be set on a form where the different
 heat conditions vary more continuously from one zone to the next. It is
 preferred that there be several separate heating zones and corresponding
 heating means inside at least one chamber or housing. Each such heating
 means may comprise a pair of heat sources, preferably positioned on
 opposite sides of the boarding form. However, it is possible to use
 heating means that are separated in two or more separate chambers. As many
 heating zones and means as needed can be used to heat-set the garment as
 desired in accordance with the shape and function of the garment.
 For stockings, the leg form can have a telescoping mechanism and a
 collapsing mechanism for reducing and increasing volume. This makes easier
 to perform the stretching-and-relaxation treatments that are useful in
 adjusting the force used during setting of the stockings. It also makes it
 easier to put the stocking onto the form and take it off the form after
 heat-setting.
 In a preferred embodiment of the apparatus of the invention, the
 heat-setting device of this invention comprises at least three separate
 heating zones and corresponding sub-chambers arranged one above another
 along the length of a stocking board form and separated by a heat
 diffusion barrier between each zone. The barrier does not touch the
 stockings. A different temperature can be used in each sub-chamber. Dry
 heat is provided by infrared or far-infrared heat sources positioned in
 each sub-chamber.
 The shape and structure of the apparatus and the heating zones can vary
 with the garment to be heat-set. Any shape and heat source can be used as
 long as it is capable of setting each part of the garment to be treated.
 EXAMPLE
 Covered yarn having a core of 15 d polyurethane elastic yarn covered with
 12 d polyamide fibers was knitted on a pantyhose knitting machine. After
 pre-setting the knit for 20 minutes using steam at 100.degree. C., the
 toes and seams of the knit were then sewed to make pantyhose. The
 pantyhose was then dyed beige with acid dye using a drum-dyeing device.
 The amount of yarn feed of the dyed pantyhose was 100 cm/horizontal row
 (or course) for the toe and the ankle and 130 cm/horizontal row (or
 course) for the thigh.
 The dyed pantyhose was placed on a stainless steel leg form and the edges
 of the hip section of the pantyhose were fixed with an elastic band. This
 was then placed in the heat-setting apparatus, which had the following
 four sub-chambers in one chamber: a sub-chamber for the foot (including
 toes and ankle) in which the temperature was adjusted to 130.degree. C., a
 sub-chamber for the calf in which the temperature was 150.degree. C., a
 sub-chamber for the knee in which the temperature was 160.degree. C., and
 a sub-chamber for the thigh in which the temperature was 170.degree. C.
 The heating time was 2 minutes.
 The pressure of the pantyhose on a leg form after heat-setting was 45
 gf/cm.sup.2 on the foot (toes and ankle), 35 gf/cm.sup.2 on the calf, 25
 gf/cm.sup.2 on the knee, and 20 gf/cm.sup.2 on the thigh. These values
 were determined from the compressive force of each part of the pantyhose
 on the form with a PS-B pressure sensor made by Kyowa Denkyo (Japan).