WO1999065433A1

WO1999065433A1 - Orthopaedic casting tape and a method for preparing thereof

Info

Publication number: WO1999065433A1
Application number: PCT/KR1999/000324
Authority: WO
Inventors: Tae Hun Kim; Yil Woong Yi; Myoung Seok Koh; Chul Min Pai
Original assignee: Samyang Corporation
Priority date: 1998-06-19
Filing date: 1999-06-19
Publication date: 1999-12-23
Also published as: BR9911322A; CN1311650A; JP2002518094A; AU4398699A

Abstract

The present invention relates to an orthopaedic casting tape and a method for preparing thereof. More particularly, the casting tape containing a substrate prepared by heat shrinkage of a warp knitted fabric comprising a polyester fiber in a chain stitch and in a weft in-lay, a stretch yarn connecting the chain stitches and an elastic fiber, is coated with water-curable polyurethane prepolymer resin. As a result, the invention provides: 1) better conformability body shape due to multi-axial extension; 2) less constriction to the patient's limbs; 3) sufficient crush strength compared to that of fiberglass cast though it has a thinner layer and; 4) significantly reduced localization of coated resin during storage.

Description

ORTHOPAEDIC CASTING TAPE AND A METHOD FOR PREPARING THEREOF

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to an orthopaedic casting tape and a method for preparing thereof. More particularly, the casting tape containing a substrate prepared by heat shrinkage of a warp knitted fabric comprising a polyester fiber in a chain stitch and in a weft in-lay, a stretch yarn connecting the chain stitches and an elastic fiber, is coated with water-curable polyurethane prepolymer resin. As a result, the invention provides 1) better conformability body shape due to multi-axial extension, 2) less constriction to the patient's limbs, 3) sufficient crush strength compared to that of fiberglass cast though it has a thinner layer and 4) significantly reduced localization of coated resin during storage.

There are various ways to immobilize a broken bone or dislocated joint at the site of fracture in the body using a casting material such as plaster of Paris. The plaster of Paris, however, has several disadvantages in that a) the kneading process requiring water for casting is cumbersome, b) the heavy weight of the cast due to its low strength-to-weight ratio brings inconvenience to the patients, c) plaster cast loses the crush strength when it is wet, d) the poor evaporation of water may induce itching and e) the accurate diagnosis cannot be achieved due to its poor transmission of X-ray.

In an effort to improve the shortcomings of plaster of Paris, intensive studies have been made hitherto and, as a result, novel types of bandages or synthetic casting tapes have been recently developed as the substitutes of plaster of Paris.

U.S. Patent Nos. 3,241,501 and 3,881,473 disclose a casting tape formulated in such a manner that a sheet comprising a textile or knitted fabric is coated with a cast material that can be hardened by exposure to ultraviolet light. However, it requires using an ultraviolet lamp to cure the cast, and it takes a long time to complete the curing process. U.S. Patent No. 3,932,526 discloses a method of fixation by curable reaction between epoxy resin and water. U.S. Patent Nos. 4,131,114, 4,376,438, 4,411,262 and 4,502,479 disclose a method of immobilizing the body at the site of fracture with a synthetic casting tape that uses a sheet comprising fiberglass coated with polyurethane resin. The casting tape is used by dipping it in water and then applying it to the site of fracture. U.S. Patent No. 4,502,479 reportes that fiberglass and polyamide fiber having initial modulus of higher than 8x10⁶ psi were suitable fibers for a synthetic casting tape, since the cast with the high modulus fibers shows improved crush strength. The above patent discloses that a fabric knitted with fiberglass is the useful as a substrate of casting tape among various types of fibers.

Fiberglass casting tape has several disadvantages in that a) low flexibility brings inconformability to the fracture site, especially to curvatured site, b) harmful dusts of fiberglass, generated during the processes of knitting a substrate and removing the cast, give the risks of respiratory disease and cancer and c) environmental problems can be raised since casting tape is not completely burned up in the hospital incinerator. Accordingly, various efforts has been made to enhance the conformability of casting tape by incorporating other flexible fiber or replacing to other fibers.

U.S. Patent No. 4,668,563 discloses a substrate for the casting tape made with a combination of high modulus fibers (more than 8 x 10⁶ psi, e.g. fiberglass or polyamide fiber) and elastic fibers (e.g. spandex or rubber). In this case, the shelf life of a product is determined by the retention period of elastic properties for elastic fibers. However, the elasticity of the elastic fiber gradually decreases by lengthwise tension through long-time storage. Further, it may happen that casts are not conformable to the patient's body because elastic fiber in its substrate provides only lengthwise extension but widthwise extension is restricted by friction between neighboring fibers in configuration. Moreover, a high elastic recovery of casting tape may induce the constriction to the patient's body. The invention also has various disadvantages by using fiberglass substrate as mentioned above.

To replace fiberglass, U.S. Patent No. 5,027,804 discloses a substrate consisting polyester or polypropylene fibers having low heat-shrinkage combined with polyester or polyamide fibers having high heat-shrinkage. U.S. Patent Nos. 5,256,134 and 5,382,466 disclose a substrate for an orthopedic splinting bandage wherein each individual wale contains stitches formed from elastic and inelastic yarns. Further, U.S. Patent No. 5,403,267 reports the substrate for splinting bandage comprising low modulus polypropylene and polyurethane fibers. However, these inventions using nonfiberglass have several disadvantages in the low crush strength due to low modulus fiber and the increase of thickness of the substrate by using high denier yarns. In addition, the surface of the cast becomes rough due to foaming by excessive polyurethane prepolymer resin that has to be applied to maintain proper strength. In addition, localization of prepolymer resin may occur during the long-term storage. The loss of the elasticity, constriction to the patient's body and insufficient conformability, which is shown in U.S. Patent No. 4,668,563, are also the serious problems of the above inventions.

SUMMARY OF THE INVENTION

The objective of the present invention is to solve the above-mentioned problems of the prior arts by providing the casting tape wherein a substrate prepared by heat shrinkage of a warp knitted fabric comprising a polyester fiber in a chain stitch and in a weft in-lay, a stretch yarn connecting the chain stitches and an elastic fiber is coated with water-curable polyurethane prepolymer.

As a result, the invention provides 1) better conformability to the body shape due to multi-axial extension, 2) less constriction to the patient's limbs, 3) sufficient crush strength compared to that of fiberglass cast though it has a thinner layer and 4) significantly reduced localization of coated resin during storage.

Brief Description of the Drawings

Fig. 1 illustrates a 4-bar knitting configuration of substrate. Fig. 2 illustrates a 3-bar knitting configuration of substrate.

1. chain stitch 2. zigzag pattern connecting chain stitches

3. weft in-lay pattern

4. tucked in chain stitch

Detailed Description of the Invention The invention is therefore relates to a casting tape containing a substrate prepared by heat shrinkage of a warp knitted fabric comprising a polyester fiber, knitted in chain stitch and weft in-lay, a stretch yarn connecting the chain stitches and an elastic fiber, is coated with water-curable polyurethane prepolymer. The invention comprises a method for preparing a casting tape, wherein substrate prepared by heat shrinkage process of a warp knitted fabric for 1 to 5 minutes at 60 ~ 140 ^°C , is coated with 45 ~ 65 % by weight of the polyurethane prepolymer resin in the casting tape. The invention is explained in more detail as set forth hereunder.

The invention relates to an orthopaedic casting tape and a method for preparing thereof. More particularly, the casting tape wherein a substrate prepared by heat shrinkage of a warp knitted fabric comprising a polyester fiber in a chain stitch and in a weft in-lay, a stretch yarn connecting the chain stitches to give multi-axial extensibility and an elastic fiber to give the lengthwise extensibility, is coated with water-curable polyurethane prepolymer. The invention provides 1) better conformability to body shape due to multi- axial extension, 2) less constriction to the patient's limbs, 3) sufficient crush strength compared to that of fiberglass cast though it has a thinner layer and 4) significantly reduced localization of coated resin during storage.

Each component and its effect of the casting tape according to the invention are explained as set forth hereunder.

1. Substrate

The invention discloses the use of synthetic organic fibers instead of fiberglass in a substrate for a casting tape, therefore eliminating the harmful dusts of fiberglass generated during the manufacturing process and removal of the cast after use. In addition, the removed cast can be easily burned in a hospital incinerator.

Major factors in screening synthetic organic fibers are moisture content, mechanical properties (initial modulus, tenacity, elongation), fiber density and denier.

The moisture incorporated in a fiber can be a factor of shortening the shelf life of the casting tape because of reaction with the isocyanate group of polyurethane prepolymer. According to the invention, it is preferable to use polyolefin and polyester fibers with moisture content of lower than 0.5 wt.%.

Mechanical properties of the fibers are very important factors for the crush strength of the cast. It is well known the more high modulus fibers in FRP (fiber reinforced plastics), the better the strength of FRP. Although high modulus fibers increases crush strength in case of casting tape, it reduces conformability to the body. On the other hand, a substrate comprising low modulus fibers brings low crush strength after cured. Accordingly, the present invention discloses to use fibers with 50 ~ 120 g/den of initial modulus which is higher than that of fibers for clothing, preferably 60 ~ 110 g/den and 2 - 10 g/den of tensile strength, preferably 5 - 8 g/den.

Density and denier of fibers determines the thickness and the weight per unit area of substrate. In the casting tape prepared by using organic fibers, it needs much more resin content than that of using fiberglass to maintain the crush strength of the cast due to their low modulus. Since, it is necessary to use the substrate with high resin holding property, fiber with appropriate density and denier should be used to obtain sufficient weight per unit area. The thickness of substrate is an important factor on cast application and comfort of the patient. In general, 3 or 4 layers provide a strong nonweight- bearing cast and 5 to 8 layers are typically adequate for weight-bearing cast. However, when organic fiber is used, it needs additional 2 to 3 layers necessary for strength and causes uncomfortable to the patients. But, the casting tape according to the present invention can be applied with the same layers as fiberglass cast since it has sufficient crush strength compared to that of the fiberglass. The invention discloses that the substrate should have weight of 200 g/ irf, preferably higher than 220 g/ m^!. Therefore, the invention uses polyester which has higher density than that of polyolefin, selected from polyethylene terephthalate, poly(l,4-cyclohexanedimethyl) terephthalate and poly(ethyleneoxybenzoate) and more preferably polyethylene terephthalate. Appropriate range of fiber denier is 200 ~ 1000 denier, preferably 300 ~ 600 denier. In the invention, stretch fiber connecting polyester chain stitches gives conformability to the body shape. The stretch yarn is prepared by using thermoplastic property of organic fibers. Stretch yarn, prepared by eliminating one direction deformation after heat-set on the fibers, is characterized by spring structure with superior extensibility and recovery to deformation compared to non-stretch fibers.

There are in principle three main methods of making stretch yarns [Man Made Fibers, 6th ed., p 486 ~ 487, 712 ~ 713, Newnes-Butter Worths] :

1. False-twisting : Twist is inserted, the yarn in the twisted state is heat-set, and then it is untwisted. It kinks because of the "set" distortion. The fiber is crimped sinusodially.

2. Drawing over Hot Knife Edge : This imparts a spiral-like curl to the fiber, because one side of each fiber (that touching the hot knife) is treated differently from the other side. In one sense this copies the bicomponent structure of wool.

3. Stuffing Box Method : Fibers are forced into a stuffing-box or similar chamber, and the crimp heat-set in them. This imparts a saw-tooth crimp and gives the greatest bulk of all.

It is called as texturing yarn when it is crimped by using air jet instead of heat chamber. The stretch yarn is different from the elastic fiber, which has high extensibility and recovery by chemical structure.

In prior arts, widthwise extension of the substrates is determined by weft in-lay pattern. The extensibility by these configurations, however, is restricted by friction between neighboring fibers. Therefore, the invention provides the extensibility in lengthwise and diagonal as well as widthwise direction by connecting the chain stitches. The connecting configuration between chain stitches is straight or zigzag pattern, preferably zigzag pattern. Therefore, the invention provides that the substrate has multi-axial extensibility and improved conformability by the connecting pattern of stretch yarn. Stretch yarn used for the invention preferably includes false twist yarn or texturing yarn of polyester or nylon, more preferably includes polyester texturing yarn with 30 ~ 100 denier. In addition, preferable the zigzag connecting pattern imparts various directions of extension.

Generally, the conformability of a casting tape is expressed by extensibility in the lengthwise and widthwise direction of the substrate. The extensibility is determined at a load of 680grams per inch of width, substrate which is connected by stretch yarn has extensibility of 10 ~ 30 % in lengthwise direction, 10 ~ 60 % in widthwise direction and 30 ~ 80 % in diagonal direction. This structural extensibility solves the problems of the prior arts caused by using elastic fibers, which is loss of extensibility by tension in lengthwise direction during long time storage.

Because of high bending rigidity of fiberglass, the casting tape using this have desirable crush strength when it has a weight ratio of ca. 6:4 (substrate vs. water-curable resin). Since resin content is relatively lower than that of substrate, localization of resin is minimal during long-time storage. However, while in case using organic fiber for a casting substrate, the desirable crush strength cannot be obtained until weight ratio between substrate and resin reaches 4:6. This amount of resin is more than that of a substrate so that it causes localization of resin because the substrate has not enough resin holding property. As a result, carbon dioxide generated by the reaction between resin and moisture could be stayed as bubble or foam on the localized surface of a cast, resulting in poor appearance. Localization of resin is related to weight per unit area of substrate, uniformity of substrate density, resin-holding ability of fibers. According to the invention, stretch yarn with high resin-holding ability connects chain stitches to maintain uniformity of substrate density and to reduce localization. The substrate of the invention requires a weight per unit area of 200 ~ 300 g/ m^! , preferably 220 ~ 280 g/ m° to reduce the localization and maintain the crush strength compared to that of fiberglass cast.

The elastic fiber which is incorporated in warp direction is used to provide elasticity in a lengthwise direction to the substrate. Preferred elastic fibers include polyester or polyurethane elastic fiber. A covered or uncovered elastic fiber also can be employed. The covering fiber includes cotton, nylon and polyester, preferably polyester fibers.

U.S. Patent No. 4,668,563 discloses that an extensibility of 40-200 % may be provided in the lengthwise direction by the addition of a natural rubber yarn or polyurethane elastic fiber (Spandex) in the lengthwise direction. However, since a natural rubber yarn or polyurethane elastic fiber has a high reversible elongation and recovery power, it imparts a pressure to the patients' body during application of the casting tape. Further, a natural rubber yarn gives more pressure than polyurethane elastic fiber because it is difficult to produce below 100 denier. Polyester elastic fiber with 400 - 600 % of reversible elongation gives less constriction than polyurethane elastic fiber with 400 ~ 800 % of reversible elongation. When such constriction to the body is measured, the term "power" shall apply. The power is defined as a force needed for stretching a substrate in a certain elongation ratio; in the case of a substrate for the casting tape, the power is expressed by a tensile strength per unit inch width at 10 % or 30 % of the elongation [unit: gram per unit inch width]. The power of a substrate of the invention is preferably lower than 150 gram per inch width at 10% elongation, more preferably lower than 50 gram per inch width. The extensibility of the substrate is 20 - 80 %, preferably 30 - 70 % in lengthwise direction and 30 - 100 %, preferably 40 - 80 % in widthwise direction. The invention discloses the casting tape which comprises a polyurethane elastic fiber of 30 -100 denier and 0.5 - 3 wt.% or a polyester elastic fiber of 50 - 100 denier and 0.5 - 4 wt.%. In manufacturing the warp knitted fabric, in case of using high amount of elastic fiber at low tension during knitting, the extensibility of the substrate increases but recovery force is too high to have power below 50 gram. In case of using low amount of elastic fiber at high tension during knitting, it is difficult to have sufficient conformability. Moreover, loss of elasticity by tension during long-time storage may occur.

In the invention, the substrate with an appropriate extensibility and power is provided by heat shrinkage process.

When a knitted fabric is treated by heat, the loops of the chain stitches become denser due to the contraction of the fibers. Since the loop consisting the substrate has dense structure by the heat shrinkage of polyester fiber, the chain stitch loop is extended prior to the elastic fiber when the substrate is elongated. The extended state of chain stitch loop is maintained after the elongation load is released while extended deformation of the elastic fiber is recovered immediately. By reason of above, the eat shrinkage process brings on an effect of reducing the constriction power to the patients' body.

Two kinds of manufacturing process are as follows : One is dry heat- shrinkage process and the other is drying after wet heat-shrinkage process.

In case of dry heat-shrinkage process, there are two methods of stuffer box and hot air chamber. Wet heat-shrinkage process is a method to shrink in water by using steam or dyeing machine. Even though the shrinking effect is better than that of dry heat-shrinkage process, it requires another drying process and calendaring process because of widthwise shrinkage. According to the invention, dry heat-shrinkage process is more preferable. Dry heat- shrinkage process provides more than 10 % of shrinkage effect, improved extensibility with significantly reduced power. Above results can be obtained by following conditions; 60 - 140 ^°C for 1 - 5 minutes.

According to the invention, the substrate is prepared by a Raschel or Tricot warp knitting machine. The invention discloses a Raschel warp knitting machine using a 3-bar or 4-bar configuration with 6 - 28 needles per inch. Bar 1 in the knitting configuration executes a chain stitch, bar 2 connects the chain stitches, bar 3 lays in with chain stitch, bar 4 tucks in with chain stitch. The desired substrate which has reduced power according to the present invention is prepared by heat shrinking process with knit fabric having above structure.

The density and openness of a substrate affects the resin holding property. The density of a substrate is expressed by the number of courses per inch and the number of openness is the number of wales per inch multiplied by density. The substrate of the invention has 16 - 22 course/ inch of density and

160 - 220 openness/ inch².

2. Coating material

The curable prepolymer resin for the casting tape is prepared via the reaction between diisocyanate and polyol.

Any diisocyanate compound used for the invention may be selected from those in the literature (Polyurethanes: Chemistry and Technology II 453-607, pp. 609-659, Interscience Publishers). It is preferred to select an aromatic diisocyanate, e.g., phenylene 1,3-diisocyanate, phenylene 1,4- diisocyanate, a mixture of phenylene l,3-/l,4-diisocyanate, toluene 2,4- diisocyanate, toluene 2,6-diisocyanate, a mixture of toluene 2,4-/2,6- diisocyanate, diphenylmethane 2,4-diisocyanate, diphenylmethane 4,4- diisocyanate, a mixture of diphenylmethane 2,4-/ 2,6-diisocyanate, naphthalene 1,5-diisocyanate or diisocyanate polymer containing carbodiimide group, urethane group or alophanate group. Among them, it is most preferred to use diphenylmethane diisocyanate, which is commercially available.

All of the polyols, which have been generally used in the art for polyurethane prepolymer resins designed for the casting tapes can be applied to the invention. The physical properties based on the chemical structures and a person having ordinary skill in the art can readily adjust amount of polyol used without undue experimentation. In particular, if the polyether homopolymer with a molecular weight in the range of about 200 ~ 30,000, preferably in the range of 300 - 20,000 or a combination of such copolymers is used, a high strength cast can be maintained. If a hydrophilic polyol is employed, the amount of hydrophilic polyol should be in the range of less than 50% of the total weight of polyol. The hydrophilic polyol, when contacted with water, attracts water to the prepolymer resin and maintains a high strength of the cast. Preferably, the prepolymer comprises diisocyanate and polyol in a molar ratio of 2: 1 ~ 15: 1. If the molar ratio of diisocyanate and polyol is less than about 2:1, the adhesiveness of the substrate is weakened; if it exceeds the molar ratio of about 15: 1, a prolonged period of time is required for curing. The content of isocyanate in a prepolymer prepared via polymerization with the above molar ratio is preferably in the range of about 10 - 25% of the total weight of the prepolymer. Such a range is preferred in terms of curing time and adhesiveness.

To manufacture the prepolymer of the invention, one or more catalysts can be selected from the following groups, and they should be able to facilitate curing by the reaction with water: amines such as triethylamine, dimethylethanol amine, tetramethyl-l,3-buthane diamine, bis-2- dimethylaminoethyl ether, and triethylene diamine; morpholine-based derivative compounds such as N-methylmorpholine, N-ethylmorpholine, dimorpholinoethyether, dimorpholinodiethoxy ethane, bis(2,6- dimethylmorpholino)ethylether, morpholinoethyl-(2,6- dimethylmorpholinoethyl)ether, l-(2-morpholinoethoxy)-2-(2,6- dimethylmorpholinoethoxy)ethane; inorgaic materials such as sodium bicarbonate, sodium carbonate and calcium carbonate, which are insoluble in prepolymer but soluble in water. The amount of such catalyst to the total weight of prepolymer is in the range of about 0.5 - 15 wt.%, more preferably in the range of about 1 - 10 wt.%. If amount of such catalyst is below range, the curing may require a prolonged period of time. If it is above the range, the shelf life may be shortened because reaction occurs during storage.

Further, an appropriate amount of the commonly available additives such as stabilizer (e.g., acid anhydride or acid halide), anti-foaming agent, antioxidant and pigment can be added in a polymerization between the polyol and diisocyanate compounds.

3. Casting tape

The casting tape of the invention is prepared in such a manner that a substrate is coated with a water curable resin under a relative humidity of less than about 5%. Considering the reactability between the prepolymer and moisture in the air, the casting tape, immediately after the coating process, is placed and sealed in an air-tight package. It is preferred that the amount of resin coated onto the substrate be in the range of about 45 - 65 wt. % to the total weight of the casting tape. The amount expressed by weight is about 160 - 560 g/ in', more preferably about 180 - 520 g/ n . If the amount of resin is below the range, crush strength is lowered. On the other hand, if it is above the range, the localization of the coated resin causes bubbles on the surface of the cast, resulting in poor appearance.

The following examples illustrate various aspects of the invention but are not to be construed to limit the claims in any manner whatsoever.

Comparative example 1

As illustrated in Fig. 1, a knitted fabric substrate of 4-bar configuration was fabricated by a 12-gauge Raschel warp knitting machine. More specifically, bar 1 contained polyethylene terephthalate yarn of 350 denier with 47 ends executed chain stitch; bar 2 contained a polyester texturing yarn of 70 denier with 46 ends and performed connecting the chain stitches by zigzag pattern; bar 3 contained the same fiber of bar 1 to 0-0/3-3 patterns with 45 ends is weft in- lay; bar 4 contained a polyurethane elastic fiber. The substrate, so formulated, was 4 inches in width, 18 courses per inch and 235 g/ n in weight.

1000 g of isocyanate compound (Isonate-143LK, Kumho Mistui Chemicals, Inc.), 15 g of anti-foaming agent (DC ANTIFOAM 1400) and 2 g of stabilizer (benzoyl chloride, Aldrich) were carefully charged in a sequential order to a well dried glass vessel equipped with an agitator, Teflon impeller, thermometer and nitrogen line. The reaction mixture was stirred for 20 minutes under nitrogen atmosphere. 350 g of KONIX PP-750 (Korean polyol product), 50 g of KONIX PEG-400, 250 g of KONION PE-108 and a catalyst (bis(2,6- dimethylmorpholino) ethyl ether) were added to the mixture, and then the temperature was increased to 60 ^°C . The above mixture was reacted at 60 ^°C for 2 hours and then cooled at room temperature under nitrogen atmosphere to obtain a polyurethane prepolymer resin.

The substrate was coated with the aforementioned prepolymer resin by using one-roll type coating machine and was packaged into a moisture-proof aluminum pouch. The coated amount of resin was 58%.

Comparative example 2

In the same procedure as described in the comparative example 1, a knitted fabric substrate of 4-bar configuration was fabricated; bar 1, 3 contained polyethylene terephthalate of 420 denier; bar 4 contained polyester elastic fiber [NEOPA. SYC] of 80 denier with 47 ends. The substrate, so fabricated, was 4 inches in width, 17 courses/ inch in density and 240 g/ nr in weight. Polyurethane prepolymer prepared by the same procedure of comparative example 1 was coated. The coated amount of resin was 57 %.

Example 1

A 10 m of heating section equipped with 10 free rollers was installed in heating room to perform heat-shrinking the knit fabric prepared in above comparative example 1. The knit fabric passed the heating room, where inside temperature was controlled by circulating hot air, by wind-up roller from outside. The substrate, passed in such heating section for 2 minutes at 120 ^°C, was coated by the same procedure of comparative example 1. The coated amount of resin was 57% .

Example 2

The substrate prepared in comparative example 2 was heat shrunken and coated by the same procedure of example 1. The coated amount of resin was 59%.

Comparative example 3

As illustrated in Fig. 2, a knit fabric of 3-bar configuration was fabricated by a 12-gauge Raschel warp knitting machine used in comparative example 1; however, the fabric was knitted without using a stretch yarn compared to the above comparative example 1. More specifically, bar 1 contained polyester yarn of 350 denier with 47 ends; bar 2 contained the same fiber of bar 1 in 0-0/3-3 patterns with 46 ends; Bar 3 contained polyester elastic fiber of 80 denier with 47 ends. The substrate was coated with polyurethane prepolymer by the same procedure of comparative example 1. The coated amount of resin was 58%.

Comparative example 4

As illustrated in Fig. 2, a knit fabric of 3-bar configuration was prepared by the same procedure of comparative example 3; bar 1 contained a fiberglass of 68 tex with 47 ends; bar 2 contained the same fiber of bar 1; bar 3 contained polyurethane elastic fiber of 70 denier with 47 ends. The substrate, so formulated, was 4 inches in width, 14 courses per inch in density and 220 g/ in' in weight. The substrate was coated with resin by the same procedure of comparative example 1. The coated amount of resin was 42%.

Comparative example 5

As illustrated in Fig. 2, a knit fabric of 3-bar configuration was prepared by the same procedure of comparative example 3; bar 1 contained polypropylene fiber of 1000 dtex with 47 ends; bar 2 contained the same fiber of bar 1 with 45 ends; bar 3 contained polyurethane elastic fiber of 70 denier with 47 ends. The substrate, so formulated, was 4 inches in width, 16 courses per inch in density and 205 g/ in' in weight. The substrate was coated with resin by the same procedure of comparative example 1. The coated amount of resin was 59%.

Comparative example 6

As illustrated in Fig. 2, a knit fabric of 3-bar configuration was prepared by the same procedure of comparative example 3; bar 1 contained polyester stretch yarn of 150 denier with 47 ends; bar 2 contained polyester 2-ply spun yarn with 45 ends; bar 3 contained polyurethane elastic fiber of 70 denier with 47 ends. The substrate, so formulated, was 4 inches in width, 15 courses per inch in density and 155 g/ n in weight. The substrate was coated with resin by the same procedure of comparative example 1. The coated amount of resin was 60%.

Experimental example The physical properties on the products based on the above Examples and Comparative Examples were measured by the following methods, as shown in Table 1.

(1) Crush Strength

A roll of casting tape having a width of 4 inches, taken out of the aluminum package after 2-week storage, was immersed in room temperature water for 30 seconds and then, excess water was squeezed out using both hands. A cylindrical ring comprising 6 layers of casting tape was formed by wrapping the roll around a padding-covered mandrel having a diameter of 5 cm. The ring stood for 24 hours to be cured, and the mandrel was removed from the ring. The ring was placed under a fixing device (Instron Model 4204), and by lowering the cross-head, a given force was recorded when the casting tape was pressed by 1 cm. The lowering rate of the cross-head was predetermined at 2.8 mm/min.

(2) Extensibility and Power

After opening the casting tape of 4 inches in width, it was cut into a 15 cm length and was fixed at both clamps of the Instron. The Extensibility of the casting tape was determined as the percentage of elongation at 680 gram load per 1 inch of width. The power was determined as the force needed for stretching the casting tape at 10 % elongation.

(3) Content of resin After opening the casting tape having 4 inches in width, it was immersed in a beaker containing 1000 ml of acetone for 3 hours to dissolve the resin coated onto the substrate. It was washed 3 times with acetone. The weight of the dried substrate was measured and calculated by following equation 1. Equation 1

Weight of Resin

Content of Resin(%) x lOO

(Weight of substrate + Weight of Resin)

(4) Standard deviation of weight per site of casting tape (localization of resin)

A roll of a casting tape with 4 inches of width, being left in an oven at

50 ^°C for 30 days, was unrolled on a flat table covered with an aluminum film.

For a complete curing by moisture in the air, the tape was left for a sufficient period of time. Then, the cured tape was cut into pieces of 5.0 cm of width. The pieces were weighed and the standard deviation of weight was calculated.

Table 1

As mentioned above, the invention relates to an orthopedic casting tape and a method for preparing thereof. More particularly, the casting tape of the invention is prepared in such a manner that a substrate prepared by heat shrinkage of a warp knitted fabric comprising a polyester fiber in a chain stitch and in a weft in-lay, a stretch yarn connecting the chain stitches and an elastic fiber, is coated with water-curable polyurethane prepolymer. As a result, the invention provides 1) multi-axial extension and conformability to body shape, 2) less constriction to the patient's limbs, 3) sufficient crush strength compared to that of fiberglass cast and 4) significantly reduced localization of coated resin during storage.

Claims

CLAIMS What is claimed is :

1. An orthopaedic casting tape containing a substrate coated with a water- curable prepolymer resin, said substrate prepared by heat shrinkage of a warp knitted fabric comprising a polyester fiber in a chain stitch and in a weft in-lay, a stretch yarn connecting the chain stitches and an elastic fiber.

2. The orthopaedic casting tape according to claim 1, wherein said substrate is prepared by heat shrinkage of a warp knitted fabric comprising a polyester fiber in a chain stitch and in a weft in-lay, a stretch yarn connecting said chain stitches and an elastic fiber incorporated in said knitted fabric in warp direction, and has a weight per unit area of 200 ΓÇö 300 g/ n , a density of 16 ~ 22 courses per inch and 160 ~ 220 openings per square inch.

3. The orthopaedic casting tape according to claim 1 or 2, wherein said polyester fiber having a denier of 200 ΓÇö 1000, a modulus of 50 ~ 120 g/den and a tensile strength of 2 ΓÇö 10 g/den, is selected from the group consisting of polyethylene terephthalate, poly(l,4-cyclohexanedimethyl) terephthalate and poly(ethyleneoxybenzoate).

4. The orthopaedic casting tape according to claim 1 or 2, wherein said stretch yarn connecting the chain stitches by straight or zigzag pattern, is selected from polyester false twist yarn, polyester texturing yarn, nylon false twist yarn, and nylon texturing yarn.

5. The orthopaedic casting tape according to claim 1 or 2, wherein said substrate contains 0.5ΓÇö4 % by weight of said elastic fiber selected from polyester elastic fiber and polyurethane elastic fiber.

6. The orthopaedic casting tape according to claim 1, wherein said water- curable resin is a prepolymer prepared via reaction between an aromatic diisocyanate and polyol in a molar ratio of 2:1 ~ 15:1.

7. A method of preparing the casting tape wherein substrate prepared by heat shrinkage of a warp knitted fabric through heat shrinkage process for 1 to 5 minutes at 60 ΓÇö 140 ^┬░C, is coated with 45 to 65% by weight of the polyurethane prepolymer resin in the casting tape.