Coated sewing thread

Abstract
Processes for coating sewing thread using a radiation curable composition and the resultant coated sewing thread. Sewing thread is coated with a radiation curable composition, which exhibits a self sustaining cure after exposure to radiation. The composition is applied using contact coating techniques to coat and impregnate the thread with resin. The coated thread is then exposed to radiation to cure the coating. Because the cure is self sustaining, the composition more fully and completely reacts to form a coating with increased durability and reduced susceptibility to stripping or flaking during use in demanding industrial applications.
Description




FIELD OF THE INVENTION




This invention relates to processes for coating sewing thread, and in particular to processes for coating sewing thread using solventless systems.




BACKGROUND OF THE INVENTION




Sewing thread is typically constructed from multiple continuous filament multifilament plies which are individually twisted in one direction and then combined by twisting in the opposite direction to produce a multiple ply final thread. In general, this causes the separate plies to act as a single unitary ply during the sewing process.




In many highly demanding industrial environments, it can be necessary to further treat sewing thread prior to its use. Such treatments can improve the integrity and retention of individual filaments within the sewing thread under conditions of high abrasion, improve the adhesion of the plies or individual filaments to each other in monocord or multicord constructions, and improve durability of the thread in its final end use. In these instances, the thread is coated with a bonding agent in the form of a lacquer or other plastic material which essentially forms a solid yet flexible film or sheath surrounding the thread. This allows the thread to retain substantial flexibility because the individual filaments of the thread retain the ability to have some movement relative to each other.




If the bonding agent fully penetrates the cross-section of the thread, however, the individual filaments are bound to each other and a stiff thread results. Such a stiff thread performs similar to a monofilament thread and can be unacceptable for many end use applications.




Conventionally, sewing thread is coated by passing the thread through a suitable resin in a solvent and then through a heating oven which evaporates the solvent and leaves the film. This operation, however, can be slow and releases organic solvent materials into the atmosphere. In addition, the film or sheath tends to flake off the sewing thread when used in demanding applications. The flaking is highly undesirable because it produces a visible dandruff-like deposit on the product. Further, energy required to remove the solvent can increase production costs.




Solventless systems can avoid many problems associated with solvent based coatings. In an exemplary solventless system, sewing thread is coated with a prepolymer material (such as a monomer plus a catalyst) which is capable of reacting to form a film when exposed to ultraviolet (UV) radiation. However, radiation curable systems also tend to flake off the sewing thread when the sewing thread is used in demanding applications. Other problems which can be associated with the use of many solventless systems include incomplete cure, tackiness, low adhesion and low production speeds.




SUMMARY OF THE INVENTION




The present invention provides processes for coating sewing thread using solventless systems. The solventless systems are generally more environmentally acceptable than conventional solvent based systems. In addition, the solventless systems can be applied to the thread and then cured in an in-line process at a greatly increased rate as compared to solvent based processes, which can reduce production costs. Solvent or water does not have to be removed from the solventless system after coating, thus reducing energy costs. In addition, sewing thread can be coated using smaller sized equipment, thus reduction production space.




In contrast to prior solventless systems, however, the coated sewing thread exhibits improved resistance to flaking and powdering. In addition, the coated sewing threads of the invention can have excellent adhesion properties which can protect the thread surface during demanding high speed industrial applications.




In the invention, a radiation curable material or resin system is applied in-line to a continuous threadline. When the thus coated thread is exposed to radiation, the radiation initiates polymerization or cure of the resin. In contrast to prior solventless systems, however, the radiation initiates a reaction that is self sustaining following initiation, as explained below.




Preferably, the radiation curable system is a cationic initiated system in which the radiation initiates a self sustaining crosslinking reaction following initiation, in contrast to many radiation cured polymers which are based upon a free radical mechanism. In the latter type mechanism, it is currently believed that the reaction only proceeds in the presence of UV radiation. However, in the case of a sewing thread, it is believed that at least a portion of the resin applied to the thread is shielded from the UV radiation by the individual filaments in the thread. Thus, for free radical initiated UV resins, the shielded portion of the resin is never fully reacted and hardened.




In contrast, for cationic initiated resins, the shielded portion of the resin is hardened as a result of the self sustaining thermal reaction initiated by the UV radiation even though the shielded portion of the resin is never irradiated directly. As a result, the cationic initiated systems cure or react more completely and as a result do not suffer from the tacking and flaking problems associated with free radical radiation curable resins.




In the invention, to coat the sewing thread, the sewing thread is passed through a cavity in a coating apparatus which contains the radiation curable material under pressure. The radiation curable material is applied to the thread in the cavity using a “contact coating” process in which the pressurized radiation curable resin is applied to the exterior of the sewing thread as the sewing thread is contacted by a surface so as to impregnate resin into the periphery of the sewing thread. In one embodiment of the invention, contact coating is achieved by employing a coating die having an orifice of smaller diameter than the diameter of the sewing thread. Alternatively, a deformable porous media can be provided in the die cavity so that it surrounds and contacts the sewing thread as it passes through the cavity. As a result of contact coating, the resultant sewing thread exhibits a thin layer of radiation curable material that has been impregnated into the periphery of the sewing thread.




Following curing of the radiation curable coating, the sewing thread of the invention differs structurally from conventional organic solvent based coated sewing thread because the radiation curable composition is applied so that the composition penetrates into the periphery of the sewing thread, preferably to a depth of one to about three single filament layers (or diameters), and the peripheral filaments are bonded to each other and in some cases to the next interior level of filaments. Although the composition penetrates the thread, the degree of penetration is controlled to prevent the thread from becoming unduly stiff. Thus, a continuous sheath of resin is not formed around the sewing thread, in contrast with conventional coated sewing thread; instead, the coating extends into the periphery of the thread. This can advantageously minimize or prevent stripping of the coating caused by abrasive forces such as are encountered in sewing processes.











BRIEF DESCRIPTION OF THE DRAWINGS




Some of the features and advantages of the invention having been described, others will become apparent from the detailed description which follows, and from the accompanying drawings, in which:





FIG. 1

is a top view of an exemplary apparatus for coating sewing thread in accordance with the invention;





FIG. 2

is a side view of the apparatus of

FIG. 1

;





FIG. 3

is a cross sectional view of a sewing thread coating apparatus of the apparatus of

FIG. 1

, taken along line


3





3


thereof;





FIG. 4

is a partially broken top view of the coating apparatus of

FIG. 3

, taken along line


4





4


thereof;





FIG. 5

is an enlarged top view of the broken away portion of the apparatus of

FIG. 4

illustrating a resin reservoir therein;





FIG. 6

is a greatly enlarged cross-sectional view of a cavity of the coating apparatus of

FIG. 3

, taken along line


6





6


thereof;





FIG. 7

is a greatly enlarged cross-sectional view of an alternative embodiment of a cavity of the coating apparatus of

FIG. 3

illustrating the use of a porous, deformable contact media in the cavity;





FIG. 8

a cross-sectional view of an ultraviolet (UV) radiation curing chamber of the apparatus of

FIG. 1

, taken along line


8





8


thereof;





FIG. 9

is a top view of the UV radiation curing chamber of

FIG. 8

, taken along line


9





9


thereof;





FIG. 10

is cross-sectional end view of the UV radiation curing chamber of

FIG. 8

, taken along line


10





10


thereof;





FIGS. 11

,


12


and


13


are photographs illustrating a perspective view of a coated sewing thread of the invention and further illustrate penetration of the coating into the periphery of the sewing thread;





FIG. 14

is a photograph illustrating a perspective view of a sewing thread prepared using a conventional solvent based coating system and illustrates how the conventional coating surrounds the thread without substantial penetration of the coating into the thread;





FIG. 15

is a photograph illustrating a perspective view of an abraded prior art sewing thread coated with a conventional solvent based system and illustrates stripping of the coating caused by abrasive forces such as are encountered in sewing processes; and





FIG. 16

is a photograph illustrating a perspective view of an abraded coated sewing thread of the invention and illustrates the absence of any substantial stripping of the coating.











DETAILED DESCRIPTION OF THE INVENTION




In the following, a detailed description of the preferred embodiment of the invention is given. It will be recognized that although specific terms are used, they are used in a descriptive and not in a limiting sense in that the invention is susceptible to numerous variations and equivalents within the spirit and scope of the description of the invention.




Referring to

FIGS. 1 and 2

, an exemplary process and apparatus for coating sewing thread in accordance with the invention is illustrated.

FIGS. 1 and 2

illustrate a system for in-line coating of multiple threadlines. The skilled artisan, however, will appreciate that the invention can include coating more or fewer threadlines than illustrated.




The threadlines, designated generally as


10


, are directed from supply packages


12


into a coating apparatus, designated generally as


20


, via entry ports


22


. The threadlines can be preconditioned or pretreated to provide moisture levels desirable for a particular resin system, for example, by minimizing exposure of the threadlines to atmospheric humidity and/or removing moisture from the threadlines prior to coating. The threadlines can be preheated, for example, using a standard UV unit, prior to entry into the coating apparatus.




Typically, a threadline comprises one or more multifilament plies which are individually twisted in a first direction and then combined by twisting in an opposite direction to produce a multi-ply thread construction. The threadline, however, can include one, two, or more than three multifilament plies or other structures used to form sewing thread as will be apparent to the skilled artisan. The multifilament plies are typically composed of a relatively high tenacity multifilament continuous filaments such as nylon, polyester or the like. By way of illustration, the individual or single multifilament plies typically have a denier (decitex) within the range of from about 50 to about 500 denier (56-556 decitex). Thus, the thread illustrated in

FIG. 1

(comprising three individual multifilament plies) typically has a total denier ranging from about 150 to about 2,000 denier (167 to about 2,222 decitex).




As illustrated in

FIG. 2

, a resin supply source


24


supplies a radiation curable composition (which also can be preheated) to a resin distribution manifold via line


26


and into coating apparatus


20


. As used herein, and as will be appreciated by the skilled artisan, the term “radiation curable composition” refers to compositions which photopolymerize or cure upon exposure to radiation. Generally the composition includes polymerizable compounds, including monomers, oligomers, polymers, prepolymers, resinous materials, and mixtures thereof, and a photoinitiator, which when exposed to a source of radiation, initiates a reaction of the polymerizable materials. The radiation curable composition may be polymerized to form homopolymers or copolymerized with various other monomers.




In the invention, the preferred polymerizable compounds cure cationically, and the photoinitiator generates a proton on exposure to radiation, typically ultraviolet (UV) radiation. This cation causes the polymerizable compounds to crosslink. The cationic cure is advantageous because it is self generating. In contrast, most radiation curable compositions that are widely used in commerce are cured via a free radical mechanism in which the photoinitiator generates free radicals upon exposure to radiation, which in turn attack and initiate polymerization of unsaturated polymerizable compounds. For the polymerization to take place, the composition must be exposed to the radiation source; once the radiation source is removed, the reaction stops because free radicals are no longer generated. Thus unreacted material can remain in the coating unless all of the coating is exposed to radiation. In such cases, the coating tends to flake and/or tack.




In contrast, the cationic initiated reaction is self generating, i.e., the reaction continues after the radiation source is removed. Such compositions can provide an improved protective coating for sewing thread because the composition can more fully cure, that is, essentially all available polymerizable components of the composition are reacted. As result, essentially no flaking is observed when the thread is used.




Preferred cationically curable compounds include epoxy resins. As the skilled artisan will appreciate, radiation curable compounds other than epoxy resins can be used in the invention so long as the curing or polymerization thereof is self sustaining after the reaction is initiated by exposure to radiation. Epoxy compounds or resins suitable for use in the invention include those materials having at least one polymerizable epoxy group per molecule, and preferably two or more such groups per molecule. The epoxides can be monomeric or polymeric, saturated or unsaturated, and include aliphatic, cycloaliphatic, aromatic and heterocyclic epoxides, and mixtures thereof, and may be substituted with various substituents, such as halogen atoms, hydroxyl groups, ether radicals, and the like.




Preferably the epoxide is a cycloaliphatic epoxide. Exemplary cycloaliphatic epoxides include diepoxides of cycloaliphatic esters of dicarboxylic acids such as bis(3,4-epoxycyclohexylmethyl)adipate, bis(3,4-epoxycyclohexylmethyl)oxalate, bis(3,4-epoxy-6-methylcyclohexylmethyl)adipate, bis(3,4-epoxycyclohexylmethyl)pimelate, and the like. Other cycloaliphatic epoxides include 3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexane carboxylates such as 3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexane carboxylate, 3,4-epoxy-1-methylcyclohexylmethyl-3,4-epoxy-1-methylcyclohexane carboxylate, 6-methyl-3,4-epoxycyclohexylmethyl-6-methyl-3,4-epoxycyclohexane carboxylate, 3,4-epoxy-2-methylcyclohexylmethyl-3,4-epoxy-2-methylcyclohexane carboxylate, 3,4-epoxy-3-methylcyclohexylmethyl-3,4-epoxy-3-methylcyclohexane carboxylate, 3,4-epoxy-5-methylcyclohexylmethyl-3,4-epoxy-5-methylcyclohexane carboxylate and the like. Commercially available cycloaliphatic epoxides useful in the invention include epoxides available from Union Carbide Corporation as the “Cyracure” series of materials, epoxides available from UCB Chemicals as the “UVACURE® series of materials, and the like.




Preferably the moisture content of the threadlines is controlled to maximize performance of a particular resin system. For example, the threadlines can be preconditioned or pretreated prior to coating to minimize moisture uptake and/or reduce moisture content. Alternatively, or in addition to preconditioning, the percent humidity of the coating environment can be controlled to maintain a percent relative humidity desirable for performance of a particular resin.




The cycloaliphatic epoxies can be used alone, as mixtures with one another, and as mixtures thereof with other types of epoxides, such as glycidyl type epoxides, aliphatic epoxides, epoxy resol novolac resins, epoxy phenol novolac resins, polynuclear phenol-glycidyl ether derived resins, aromatic and heterocyclic glycidyl amine resins, hydantoin epoxy resins, and the like and mixtures thereof. These epoxides are well known in the art and many are commercially available.




The epoxy can be present in amounts between about 99.9 and about 85 percent by weight of the composition.




Suitable photoinitiators include onium salts as known in the art for photoinitiating cure of epoxy resins. Such onium salts can have the general formula: R


2


I


+


MX


n







, R


3


S


+


MX


n







, R


3


Se


+


MX


n







, R


4


P


+


MX


n







, R


4


N


+


MX


n







, wherein different radicals represented by R can be the same or different organic radicals containing 1 to 30 carbon atoms, including aromatic carbocyclic radicals containing 6 to 20 carbon atoms, which can be substituted with 1 to 4 monovalent radicals selected from the group consisting of C1-C8 alkoxyl, C1-C8 alkyl, nitro, chloro, bromo, cyano, carboxy, mercapto, and the like, and also including aromatic heterocyclic radicals including pyridyl, thiophenyl, pyranyl, and the like; and MX


hu −


is a non-basic, non-nucleophilic anion such as BF


4







, PF


6







, AsF


6







, SbF


6







, HSO


4







, ClO


4







and the like as known in the art. The term “hetero” as used herein refers to linear or cyclic organic radicals having incorporated therein at least one non-carbon and non-hydrogen atom, and is not meant to be limited to the specific examples contained herein. Exemplary photoinitiators include triarylsulfonium complex salts, aromatic sulfonium or iodonium salts of halogen-containing complex ions, aromatic onium salts of Group VIa elements, aromatic onium salts of Group Va elements, and the like. Currently preferred photoinitiators include triarylsulfonium hexafluoroantimonate salts, triarylsulfonium hexafluorophosphate salts, mixtures thereof and the like. The photoinitiator is present in the radiation curable composition in conventional amounts, typically ranging from about 0.1% to about 15% by weight, based on the total weight of the composition.




Suitable radiation curable compositions are disclosed, for example, in U.S. Pat. Nos. 4,874,798; 4,593,051; and 4,818,776, the entire disclosure of each of which is hereby incorporated by reference.




In addition, the radiation curable composition can include a pigment capable of imparting color to the threadline. The pigment can be an organic or inorganic pigment, or a mixture thereof, as known in the art. Useful inorganic pigments include without limitation metallic oxides (iron, titanium, zinc, cobalt, chromium, and the like), metal powder suspensions (gold, aluminum, and the like), earth colors (siennas, ochers, umbers, and the like), lead chromates, carbon black, and the like and mixtures thereof. Useful organic pigments include without limitation animal pigments (rhodopsin, melanin, and the like), vegetable or plant pigments (chlorophylls, carotenoids, such as carotene and xanthophyll, flavanoids, such as catechins, flavones, flavanols, and anthocyanins, flavanones, leucoanthocyanidins, flavonols, indigo, and the like), synthetic organic pigments (phthalocyanone, lithos, toluidine, para red, toners, lakes, and the like), and the like and mixtures thereof.





FIG. 3

illustrates a cross-sectional view of coating apparatus


20


of

FIG. 1

taken along line


3





3


. Coating apparatus


20


includes a horizontally split coating die


28


with upper and lower members


30


and


32


, respectively, each member having a generally elongate shape with a rectangular or square cross-section. Die


34


is provided with a plurality of cavities or reservoirs


34


which are each in communication with a corresponding threadline entry port


22


and a threadline exit port


36


. Lower member


32


of die


28


is also provided with a plurality of radial bores


38


, each in fluid communication with an individual reservoir


34


and with the resin distribution manifold via one of a plurality of lines


40


to allow the radiation curable composition from source


24


to be fed into each reservoir


34


. Each reservoir


34


preferably has a generally cylindrical shape which is tapered at the entry and exit ports, although other reservoir configurations can be used.




Each threadline enters the coating apparatus via a discrete entry port


22


into a reservoir


34


and then exits the coating apparatus via an exit port


36


. As best seen in

FIGS. 5 and 6

, the split coating die


22


is divided into the upper and lower members


30


and


32


along a plane that extends through the entry and exit ports


22


and


36


of each die cavity


34


. This construction allows easy threading at start-up of the coating process when the upper member


30


of the split die is removed. The threadlines can be alternatively threaded through the coating apparatus


20


using an aspirator or other suitable means.




Pressurized radiation curable composition is directed from resin supply source


24


through line


26


to the resin distribution manifold and into each reservoir


34


via lines


40


. As threadlines


10


pass through the coating apparatus, and in particular through reservoirs


34


filled with pressurized radiation curable composition, the threadlines are coated with the composition.




The pressure of the radiation curable composition within reservoirs


34


can vary, depending upon factors such as the working viscosity of the composition, the desired level of pickup, and the like. Advantageously, the composition is pressurized to assist with control of the desired level of pickup.




The inventors have also found that the invention can be used with a wide range of radiation curable composition viscosities, ranging from about 100 centipoise (cP) to about 8000 cP, and higher at room temperature. Preferably, the viscosity and pressure of the radiation curable composition within reservoir


56


are selected to provide a threadline pickup of about 1 to about 20 percent, and more preferably about 5 to about 12 percent. For example, in one advantageous embodiment of the invention, a radiation curable composition having a viscosity of about 500 to about 2000 cP is supplied within reservoir


56


at a pressure less than about 5 pounds per square inch (psi). Radiation curable compositions having higher viscosities can also be used in combination with higher pressures (for example, a viscosity of about 5000 to about 7000 cP at a pressure of about 30 to about 50 psi), to achieve comparable degree of resin pickup onto the threadline.




In addition to varying and controlling composition viscosity and pressure within reservoirs


34


to control pickup of the composition by the threadline, the coating process of the invention also includes a “contact coating” step to control pickup. As used herein, the term “contact coating” refers to applying the pressurized radiation curable composition to the exterior of the threadline within the coating apparatus


20


while also contacting the coated threadline with a suitable surface to impregnate the composition into the periphery of the threadline.




In one embodiment of the invention, each exit port


36


of coating die


28


has a diameter which is slightly smaller than the cross sectional dimension of each of the threadlines


10


. In this embodiment of the invention, the coated threadline contacts the edge of port


36


as the threadline passes therethrough. In another embodiment of the invention, a deformable porous media can be inserted into reservoir


34


which surrounds and contacts the threadline as it passes through the reservoir. For example, as illustrated in

FIG. 7

, a felt material


42


can be formed into a shape corresponding to the interior configuration of the reservoir


34


, although other conformable, porous media can also be used. In this embodiment of the invention, this contact in effect “wipes” the coated threadline so as to control pickup. As a result of the contact coating step, the resultant threadline exhibits a thin layer of radiation curable composition that has been impregnated into the periphery of the threadline to provide a coated sewing thread which is structurally distinct from conventional sewing thread, as described in more detail below. Impregnation can be controlled, however, so that the resultant thread is not undesirably stiff due to excessive penetration of the resin into the thread structure.




This contact coating step contrasts with conventional processes for coating continuous substrates. For example, typically sewing thread is immersed in a low solids content solution of the bonding agent, passed through cooperating rotating rolls to remove excess bonding agent, and then heated to evaporate the solvent. However, this process can result in undesirable levels of resin pickup, which can result in excessively thick coating sheaths, wasted material, and the like. The pressure of the nip can be controlled to remove excess resin, but excessive pressure can cause the resin to impregnate the thread. This is typically avoided because of the resulting increased stiffness.




On the other hand, conventional die coating processes for coating wires, optical fibers and the like with a radiation curable composition typically include directing the optical fibers through a coating apparatus which includes a cavity filled with a pressurized radiation curable composition. However, in contrast to the present invention, typical wire and optical fiber coating processes do not include a contact coating step. Instead, the exit orifice of the die has a diameter greater than the diameter of the fiber or wire and acts as a cylindrical doctor blade to apply a continuous sheathlike coating of the composition to the wire or optical fiber. Great efforts are taken in these processes to prevent the coated fiber from contacting or touching any surface to prevent harming the optic fiber.




Also as illustrated in

FIGS. 3 and 4

, coating apparatus


20


can include a clamping element


44


for applying substantially equalized clamping pressure to each reservoir


34


. The clamping element


44


includes a pair of pivoting arms


46


, each positioned for movement between a position that is non-aligned with the coating die


28


, and a die contacting and pressure distributing position aligned with an upper outer surface of the coating die (illustrated by the arrows in FIG.


4


). Each arm preferably applies clamping pressure to the upper portion of the split die via a pressure distributing bar


48


attached thereto via suitable fastening means, such as a threaded bolt


50


.




When actuated, each arm


46


rotates from the noncontacting position inwardly towards coating die


28


until pressure distributing bars


48


rest upon an upper outer surface of the coating die


28


. The pressure distributing bars advantageously provides substantially equalized pressure across each cavity


34


so as to control and equalize pickup of resin by individual threadlines passing therethrough.




Returning again to

FIGS. 1 and 2

, after exiting the coating apparatus


20


, the coated threadlines


10


are directed into a radiation curing chamber


50


via a plurality of conventional guides, not shown. As illustrated in

FIG. 8

, radiation curing chamber


50


includes a housing


52


comprising a base


54


and a cover


56


mounted for movement about a pivot


58


. Disposed within the housing


52


is an elongate radiation source


60


oriented perpendicular to the path of the threadlines


10


, which emits radiation of a suitable wavelength and intensity to initiate cure of the radiation curable composition on the threadlines. The radiation source


60


is mounted in a reflecting chamber within housing


52


to focus radiation emitted by the radiation source about each threadline. In a preferred embodiment as illustrated in

FIGS. 8 and 10

, the reflecting chamber includes an upper focusing reflector


62


oriented in the direction of the threadlines and a single elongate bottom diffusing reflector


64


oriented in the direction of the radiation source


60


. Reflectors


62


and


64


can be formed of any of the types of material known in the art suitable for reflecting radiation.




The upper focusing reflector


62


includes a plurality of individual semicircular reflector cavities, each extending from a threadline entry port into the housing


52


to a threadline exit port out of the housing


52


, and each having a longitudinal axis parallel to the path of the threadlines


10


through the radiation chamber. The bottom diffusing reflector


64


(

FIG. 10

) is preferably a single channel shaped cavity having a longitudinal axis perpendicular to the path of the threadline through the radiation chamber. The radiation source


60


and the reflecting chamber, including top focusing reflector


62


and bottom diffusing reflector


64


, through which the threadlines travel are positioned so that substantially all of the periphery of the moving threadline is impinged by radiation emitted by the radiation source


60


. Although not required, the curing chamber


50


can be continuously flooded or purged with an inert fluid, such as nitrogen, argon, helium, and the like to prevent or minimize adverse effects on the curing due to the presence of oxygen in the curing chamber.




If desired, housing


52


can be adapted to receive a suitable monitoring device to monitor energy levels emitted by radiation source


60


, such as a probe


66


in FIG.


8


. In addition, the curing chamber can include an exhaust duct


68


and cooling vent


70


to exhaust heat generated by the process from the chamber and to introduce cooling fluid into the chamber to thereby control temperature within the chamber.




Although the curing chamber as illustrated includes one radiation source, more than one radiation source can be included within the chamber. Alternatively, as illustrated in

FIGS. 1 and 2

, more than one curing chamber, designated as chambers


72


and


74


, can be provided. In addition, although an elongate radiation source is illustrated perpendicular to the path of the threadlines, in an alterative embodiment of the invention, one or more elongate radiation sources can be used which are parallel to the threadlines.




The active energy beams used in accordance with the present invention may be ultraviolet light or may contain in their spectra both visible and ultraviolet light. The polymerization may be activated by irradiating the composition with ultraviolet light using any of the techniques known in the art for providing ultraviolet radiation, i.e., in the range of 240 nm and 420 nm ultraviolet radiation, or by irradiating the composition with radiation outside of the ultraviolet spectrum. The radiation may be natural or artificial, monochromatic or polychromatic, incoherent or coherent and should be sufficiently intense to activate polymerization. Conventional radiation sources include fluorescent lamps, mercury, metal additive and arc lamps. Variable irradiant platform lamps available from Fusion Systems, which emit a narrow wavelength band of 308 nm, are also advantageous in the present invention to more closely match the chemistry of the radiation curable composition. Coherent light sources are the pulsed nitrogen, xenon, argon ion- and ionized neon lasers whose emissions fall within or overlap the ultraviolet or visible absorption bands of the compounds of the invention.




The radiation time can depend on the intensity of the radiation source, the type and amount of photosensitizer and the permeability of the composition and the threadline to radiation. The threadline can be exposed to radiation for a period ranging from about 0.05 second to about 5 minutes. Irradiation can be carried out in an inert gas atmosphere but this is not required.




Returning to

FIGS. 1 and 2

, threadlines


10


exit the curing chamber(s), are directed between the nip of a capstan device defined by cooperating idle rolls


76


and


78


, and taken up via a plurality of individual winders


80


for storage. Alternatively, the threadlines can be directed to additional downstream processing.




Also as illustrated in

FIGS. 1 and 2

, a computer control system


82


can be used to monitor threadline tension and detect breakage of a threadline. If a break is detected, the control system can actuate a value to close off the specific resin supply line


40


to the reservoir


34


associated with the broken threadline to stop resin feed into the reservoir to minimize resin loss. The control system can also deactivate the power supply to the threadline supply and/or wind up rolls associated with the broken threadline. Additionally, the control system can also monitor the coating resin supply.




The resultant coated sewing thread of the invention differs structurally from conventional coated sewing thread. As noted above, the radiation curable coating is applied so that the resin penetrates into the periphery of the sewing thread, preferably to a depth of one to about three single filament layers (or diameters). As a result, the peripheral filaments of the sewing thread are bonded to each other and in some cases to the next interior level of filaments. However, even though resin penetrates the thread, the sewing thread can be flexible and is suitable for conventional applications, and in particular for highly demanding industrial applications, such as assembly of densely woven fabrics used to produce shoes, soft luggage, and the like, and other dense materials such as leather.





FIGS. 11 through 16

illustrate the structural differences between sewing thread coated with a conventional solvent system and sewing thread of the invention which is coated with a radiation curable, self sustaining polymerizable composition.

FIGS. 11-13

are photographs illustrating perspective views of sewing thread coated in accordance with the present invention. As demonstrated by

FIGS. 11-13

, the resin penetrates into the periphery of the sewing thread for a distance of from one and up to about three filament diameters (and more in some cases), thus bonding the outer filaments to one another and to some of the immediately underlying interior filaments as well. Thus, in the coated sewing thread of the invention, the sheath or coating is integrated into the exterior filaments of the thread. Further, as illustrated by

FIGS. 11-13

, the thickness of the coating is not uniform, but rather can vary, for example, depending upon the degree of penetration of resin in a given location along the periphery of the thread. Further, for thread comprising more than one multifilament ply, the coating can fill in the gaps between plies, in contrast to thread coated with a solvent system in which the cast resin bridges the gap between plies. Still further, the thickness of the coating can vary depending upon the percent pickup, the denier of the thread, the number of filaments per cross section of the ply, and the like.




In contrast, as demonstrated by

FIG. 14

, which is a greatly enlarged perspective view of a solvent coated sewing thread (again using the Elvamide system), a continuous sheath of resin is formed around the sewing thread and does not extend substantially into the thread. In essence, the solvent based system is cast as a separate film surrounding the periphery of the thread, which remains as the continuous sheath after the solvent is evaporated.





FIG. 15

is a perspective view of an abraded sewing thread which was coated with a nylon solvent based system, commercially available as the Elvamide series from DuPont. When the sewing thread was subjected to an abrasion test that simulates abrasion applied to the thread by a sewing needle, the coating is removed as strips. These strips are sometimes visible as a white powder or flakes on sewn products. In contrast, as illustrated in

FIG. 16

, when the coated sewing thread of the invention is subjected to the same abrasion conditions, minimal displacement of the coating is observed.




The foregoing is illustrative of the present invention and is not to be construed as limiting thereof.



Claims
  • 1. A coated sewing thread comprising:a plurality of filaments twisted to form a unitary thread; and a coating material coating the exterior periphery of the unitary thread and penetrating into said thread to a depth of about one to about three single filament diameters, wherein said coating material is a substantially fully reacted radiation curable composition comprising cationically polymerized compounds.
  • 2. The coated sewing thread of claim 1, wherein said cationically polymerized compounds comprise reacted epoxy resin.
  • 3. The coated sewing thread of claim 1, wherein said sewing thread comprises three multifilament plies which are individually twisted in a first direction and then combined by twisting in an opposite direction to produce a multiple ply thread, wherein the multiple ply thread includes longitudinally extending gaps between each of the three multifilament plies; and wherein said coating material is present in the gaps between the plies.
  • 4. The coated sewing thread of claim 1, wherein said coating further comprises a pigment.
  • 5. A coated sewing thread comprising:a plurality of filaments twisted to form a unitary thread; and a coating material comprising a substantially fully reacted radiation curable composition coating the exterior periphery of the unitary thread and penetrating into said thread to a depth of at least about one to about three single filament diameters, wherein said radiation curable composition comprises cationically polymerized compounds.
  • 6. The coated sewing thread of claim 5, wherein said cationically polymerized compounds comprise reacted epoxy resin.
  • 7. The coated sewing thread of claim 5, wherein said radiation curable composition comprises compounds that exhibit a self sustaining reaction when exposed to radiation.
  • 8. The coated sewing thread of claim 5, wherein said sewing thread comprises three multifilament plies which are individually twisted in a first direction and then combined by twisting in an opposite direction to produce a multiple ply thread, wherein the multiple ply thread includes longitudinally extending gaps between each of the three multifilament plies; and wherein said coating material is present in the gaps between the plies.
  • 9. The coated sewing thread of claim 5, wherein said coating further comprises a pigment.
  • 10. A coated sewing thread comprising:a plurality of filaments twisted to form a unitary thread; and a coating material comprising a radiation curable composition comprising cationically polymerized compounds coating the exterior periphery of the unitary thread.
  • 11. The coated sewing thread of claim 10, wherein said cationically polymerized compounds comprise reacted epoxy resin.
  • 12. The coated sewing thread of claim 10, wherein said sewing thread comprises three multifilament plies which are individually twisted in a first direction and then combined by twisting in an opposite direction to produce a multiple ply thread, wherein the multiple ply thread includes longitudinally extending gaps between each of the three multifilament plies; and wherein said coating material is present in the gaps between the plies.
  • 13. The coated sewing thread of claim 10, wherein said coating further comprises a pigment.
  • 14. The coated sewing thread of claim 10, wherein said coating penetrates into said thread to a depth of at least about one to about three single filament diameters.
Parent Case Info

Divisional of prior application Ser. No. 08/987,655; filed Dec. 9, 1997 now U.S. Pat. No. 6,436,484.

US Referenced Citations (83)
Number Name Date Kind
1943818 Fantone et al. Aug 1934 A
2647488 Shive Aug 1953 A
2787980 McDermott Apr 1957 A
2875092 Cline Feb 1959 A
RE25164 Cline Feb 1962 E
3090664 Cline et al. May 1963 A
3179485 Kawasaki Apr 1965 A
3247043 Cardina Apr 1966 A
3332393 Hoover Jul 1967 A
3502495 Akamatsu Mar 1970 A
3507608 Eirich Apr 1970 A
3698899 Giberstein Oct 1972 A
3775150 McClary Nov 1973 A
3882819 Skeeters May 1975 A
3952552 Rozner Apr 1976 A
3988108 Segoshi et al. Oct 1976 A
4076510 Mracek et al. Feb 1978 A
4108748 Portnoy et al. Aug 1978 A
4175972 Crivello Nov 1979 A
4194462 Knowles Mar 1980 A
4230766 Gaussens et al. Oct 1980 A
4239868 Bonnet et al. Dec 1980 A
4258646 Kloczewski et al. Mar 1981 A
4263337 Login Apr 1981 A
4263370 Login Apr 1981 A
4264483 Laufer et al. Apr 1981 A
4287228 Schlesinger Sep 1981 A
4294190 Ohis Oct 1981 A
4333963 Emmons et al. Jun 1982 A
4342794 Völker et al. Aug 1982 A
4390238 Van Der Hoek Jun 1983 A
4430853 Scott et al. Feb 1984 A
4440802 Irving Apr 1984 A
4479984 Levy et al. Oct 1984 A
4501588 Suzuki et al. Feb 1985 A
4507350 Hendrix et al. Mar 1985 A
4533570 Iyengar Aug 1985 A
4593051 Koleske Jun 1986 A
4652488 Willemsen et al. Mar 1987 A
4662307 Amos et al. May 1987 A
4818776 Koleske Apr 1989 A
4835193 Hayase et al. May 1989 A
4874798 Koleske et al. Oct 1989 A
4892764 Drain et al. Jan 1990 A
4932978 Gavend et al. Jun 1990 A
4963300 Meier et al. Oct 1990 A
5000981 McGarry et al. Mar 1991 A
5034279 Wilson, Jr. et al. Jul 1991 A
RE33677 Vazirani Aug 1991 E
5039549 Nguyen et al. Aug 1991 A
5140054 Miller et al. Aug 1992 A
5171609 Ury Dec 1992 A
5219623 Petisce Jun 1993 A
5227229 McMahan McCoy et al. Jul 1993 A
5236464 Green et al. Aug 1993 A
5237917 Traut et al. Aug 1993 A
5240971 Eckberg et al. Aug 1993 A
5247147 Boniort et al. Sep 1993 A
5287606 Ruef Feb 1994 A
5298361 Bonham Mar 1994 A
5318808 Crivello et al. Jun 1994 A
5334421 McNutt Aug 1994 A
5350604 Crivello Sep 1994 A
5352392 Johnson et al. Oct 1994 A
5369205 Eckberg et al. Nov 1994 A
5372858 Saylor, III Dec 1994 A
5390400 Jacob et al. Feb 1995 A
5409504 Fritzsche Apr 1995 A
5409740 Brann Apr 1995 A
5447797 Stapp et al. Sep 1995 A
5449408 Kkoaizawa et al. Sep 1995 A
5451355 Boissonnat et al. Sep 1995 A
5501734 Oliphant Mar 1996 A
5534558 Minns Jul 1996 A
5539013 Eckberg et al. Jul 1996 A
5679115 Fritzsche et al. Oct 1997 A
5869182 Ebert et al. Feb 1999 A
6117547 Kelmartin et al. Sep 2000 A
6187224 Kreuder et al. Feb 2001 B1
6265476 Krongauz et al. Jul 2001 B1
6294592 Herrmann et al. Sep 2001 B1
6436484 Broome et al. Aug 2002 B1
20020168481 Broome et al. Nov 2002 A1
Foreign Referenced Citations (24)
Number Date Country
44 20 088 Dec 1995 DE
0 153 829 Sep 1985 EP
153829 Sep 1985 EP
0 492 649 Dec 1991 EP
0 496 117 Dec 1991 EP
1300057 Dec 1962 FR
1435755 Jun 1966 FR
2031719 Nov 1970 FR
917437 Feb 1963 GB
49-034972 Mar 1974 JP
50-095854 Jul 1975 JP
50-115277 Sep 1975 JP
51-136732 Nov 1976 JP
58-057199 Dec 1983 JP
60-65748 Apr 1985 JP
63-270864 Nov 1988 JP
3-68475 Mar 1991 JP
3-294592 Dec 1991 JP
4-108132 Apr 1992 JP
4-202846 Jul 1992 JP
4-202865 Jul 1992 JP
4-202868 Jul 1992 JP
4-316678 Nov 1992 JP
WO 9322943 Nov 1993 WO
Non-Patent Literature Citations (2)
Entry
“Cyracure,” Cycloaliphatic Epoxides, Union Carbide.
“Uvacure,” Epoxide Resin Systems for Cationic UV Cure, Radcure.