AU2007200188A1 - Electrostatic impregnation of powders on substrates - Google Patents

Description

1 -1-

AUSTRALIA

PATENTS ACT 1990 COMPLETE SPECIFICATION FOR A STANDARD PATENT

ORIGINAL

Name of Applicant/s: Actual Inventor/s: Johnson Johnson Consumer Companies, Inc.

Vipul Bhupendra Dave Address for Service is: SHELSTON IP Margaret Street SYDNEY NSW 2000 CCN: 3710000352 Attorney Code: SW Telephone No: Facsimile No.

(02) 97771111 (02) 9241 4666 Invention Title: ELECTROSTATIC IMPREGNATION OF POWDERS ON

SUBSTRATES

Details of Original Application No. 2001266727 dated 05 Jun 2001 The following statement is a full description of this invention, including the best method of performing it known to me/us:- File: 37605AUP01 501069753_1.DOC/5844 la Electrostatic Impregnation Of Powders On Substrates c The present invention relates to the use of electrostatic impregnation to load materials such as binders and flavors onto substrates such as fibers and medical devices made 00 from ceramics, metal alloys, and polymers. The invention also relates to substrates loaded with materials such as binders and flavors, wherein the materials are loaded into or on the substrates via electrostatic impregnation.

0 Many substrates are coated with materials such as polymers, polymeric binders, wax binders, flavors, and the like. For example, medical devices, such as stents, which are used in the human body, are frequently made of metal alloys. The stents require coating with a polymer or wax before use in the body. Another example of a substrate that is typically coated, with a polymer, a wax or the like, is dental floss.

Currently, dental floss has three main consumer needs that are not achieved in all products. These needs are (i) prevention/ minimization of fraying and shredding during use, (ii) easy insertion and sliding between tight teeth and (iii) gentleness to the gums. As used herein, "fraying" means the separation of fibers by the stress placed on the floss during use between the teeth. As used herein, "shredding" means the breaking of fibers by the stress placed on the floss during use between the teeth.

The minimization of fraying and shredding of dental floss is extremely important, as fraying and shredding are the most frequently encountered consumer complaints about floss.

2 O Traditionally, floss consists of continuous fibers coated CI with wax containing additives such as flavors, sweeteners and one or more active ingredients. The microcrystalline wax that is currently used holds the fibers together and facilitates the repetitive sliding motion of floss between teeth. Shear forces applied to floss during use lead to 00 00 fraying and shredding of the fibers. Such fraying and shredding occur primarily because the stresses applied to C the floss during use tend to exceed the cohesive forces of wax that help bond the fibers together.

There are two possible routes that can be adopted in order to overcome the floss shredding problem. These include making the floss from a monofilament of suitable size or a "psuedo-monofilament", bonding the plurality of filaments in a multifilament structure such that they are adhered together and function like a monofilament.

Pseudo-monofilament dental flosses are very similar to fiber-reinforced composites, in which fibers are impregnated with polymer matrices, which can be thermoset or thermoplastic in nature.

Composites are matrixes, a matrix comprising a polymeric resin, that are reinforced with another material. For fiber composites, the reinforcing material is fibers. The composite may be used as a dental floss.

A study of the available composite manufacturing techniques leads to the understanding that two important stages exist. In stage one, the fibers and binder polymers are brought into intimate contact. In stage two, heat and pressure are applied in order to impregnate and consolidate the components. Stage one is crucial, as it brings the matrix polymer and fiber in closer proximity to each other, thereby minimizing the flow length required during consolidation. This first stage is what makes 3 processing techniques used for thermoplastic composites C different from thermoset composites, due to their higher Ctviscosities.

It is known to overcome this problem by trying to reduce the viscosity of the resin in order to achieve rapid 00 00 impregnation of the reinforcing fibers. This is called a pre-impregnation processes.

Solvent or solution impregnation has been used primarily C where the high viscosity of the matrix material is reduced using solvents or plasticizers by dissolving the polymer in the solvent. The fibers are then made to pass through a dip bath filled with the solution of matrix material.

The fibers are coated and the coated fibers are then passed through a series of dryers in order to remove the solvent, thereby providing the finished composite. The biggest disadvantage of such a process is environmental concerns regarding use of the solvent. In addition, manufacturing speed is very low, and thus manufacturing costs:are increased.

The process described above requires dissolving a coating material in a solvent prior to coating a substrate.

Dissolving the coating material may be undesirable, as there is an environmental concern over volatile organic compounds. Therefore, there is a need for a process of coating a substrate that does not require dissolving a coating in a solvent.

Powder impregnation is a more versatile process, as it will process both low and high viscosity resins as long as they can be obtained in the powder form, and the process is relatively simple.

4 CI Investigators at Georgia Tech have developed a system Swherein glass fibers are spread using up to 8 Teflon* coated rollers after which the spread fibers have a powder deposited thereon using a deposition system developed by Electrostatic Technology Incorporated (ETI). In this 00 00 system, powder particles are charged and are then electrostatically deposited onto the glass fiber. The C above-mentioned rollers were found, however, to cause damage to the fiber and a transition was then made to a C different fiber spreading technology known as pneumatic venturi spreading. This effort lead to the issuance of United States Patent No. 5,094,883. In the patent, the importance of flexible fiber impregnation production was taught for applications such as braiding and weaving.

None of the dental floss patents of which the inventor is aware have applied a powder technology approach for coating the substrate fibers of the dental floss with polymers. There is a continuing need for a process of coating substrates such as fibers and medical devices which does not require dissolving a coating in a solvent.

The present invention provides a process including: providing a substrate; and electrostatically coating the substrate with at least one coating material. In another embodiment, the present invention provides a substrate coated by electrostatic impregnation. The invention utilizes electrostatic powder coating technology to coat a substrate with materials such as waxes; thermoplastic polymers; additives such as spray-dried flavors and sweeteners; active ingredients such as sodium fluoride; abrasives; etc. This method can be used for coating any substrate including, but not limited to films, non-wovens, 5 monofilament fibers, multi-filament fibers, medical CI devices, hair, sutures, and metal devices as long as the Ctcoating materials are in a powder form. The preferred substrates are monofilament fibers, multi-filament fibers, and medical devices. The coated fibers may be useful in applications such as, but not limited to, dental tapes and 00 00 dental floss. The medical devices may be made of ceramics, metal alloys, or polymers. The medical devices C- may be useful in applications such as, but not limited to, stents and polymer tubes such as catheters.

c-i The approach for electrostatically coating floss adopted in the present invention is to prepare a pseudomonofilament by using waxes or thermoplastic polymers to adhere the fibers to each other before coating the resulting pseudo-monofilament with a desired coating composition which may include, for example, waxes, thermoplastic polymers, flavors and other additives. Some of the advantages of using waxes or thermoplastic polymers as the coating materials are the ease of processability, toughness, durability, long shelf life, lack of crosslinking chemical reactions and relatively high manufacturing speed. The drawbacks, however, are very high melt viscosities (in the range of 10' poise) which lead to challenges in the areas of total fiber wet-out, interface control and mass production.

In the present invention, wax or polymer powder impregnation has been chosen to accomplish the challenge of bringing the fiber and matrix into contact by using an electrostatic deposition chamber. The technique has the ability to support continuous production of fibrous substrates which can then be integrated into a consolidation line that can use techniques such as 6 c calendering, hot-gun heating, filament winding and hand C- lay-up to apply pressure and heat in order to produce the Sfloss product. Once the fibers have been bonded together, wax and other additives can be applied to the bonded substrate.

00 00 The physics of charging.polymeric particles is not always easy to comprehend and is far from being completely tied C to the chemistry of the polymer powder. However, a considerable amount of research has been done in the area Swith regard to electrostatic spray guns in the painting c-i and coating industry.

Powders acquire charge in two ways: tribocharging and corona charging. Corona charging results when particles receive a charge from electrically charged air.

Tribocharging occurs when powder, during transportation from a reservoir to the spray gun or coater bed, undergoes frictional contact with an unsymmetrical surface. This unsymmetry could be due to velocity, temperature or chemical composition. The polarity and magnitude of the tribocharge depend on the nature of the powder, the travel velocity, and the nature of the contact tubing.

Formulation chemistry of the polymer could also determine the nature, positive or negative, of the acquired charge. Usually the charging is higher at lower transportation rates and decreases as transportation rates increase. On the other hand, corona charging occurs in the region between the corona glow and the substrate. For particles beyond a certain size microns) field charging predominates. Below a size of 0.2 microns however, the charge diffuses through the air.

7 0 According to theory, the saturation charge per ball-shaped C4 particle is directly proportional to the square of the Sparticle radius and inversely proportional to its mass.

The shape of the particle was found to not deviate in most cases from the ball-shape and so approximations made with regards to the spherical nature of the particle in 00 theoretical calculations are still fairly accurate. In regard to the sign positive or negative) and Smagnitude of the charge the electron affinity of the elements or functional groups bound to the carbon atoms and their stereometric arrangement in the macromolecule proves to be decisive.

A comparison shows that the increasing tendency to charge negatively moves in accordance with the increasing work function of the electron [poly methyl(methacrylate), polyethylene, poly (vinylchloride), poly (tetrafluoroethylene)], while materials with the lowest work functions tend to charge positively polyamide). In spray gun applications, aerodynamic forces are responsible for transporting the powder towards the object and electrostatic forces are responsible once the powder is near the substrate in order to facilitate good wrapping of the coating around the fibers.

Suitable fibers to be used in the present invention include, but are not limited to, natural fibers such as cellulose, cellulosic fibers, and rayon; polyolefins such as polyethylene and polypropylene; polyesters such as polycaprolactone poly(ethylene terephthalate) poly(butylene terephthalate) and Vectran (Trademark of Hoechst-Celanese); polyamides such as nylon 6, nylon 11, nylon 12, and nylon 6,6; poly(ether-amides) 8 O such as, but not limited to, Pebax® 4033 SA and Pebax® C 7233 SA (Trademark of Elf Atochem); poly(ether-esters) Ssuch as, but not limited to, Hytrel® 4056 (Trademark of DuPont) and Riteflex® (Trademark of Hoechst-Celanese); fluorinated polymers such as poly(vinylidine fluoride) and 00 poly(tetrafluoroethylene); and combinations thereof, 00 0_0 including bicomponent fibers, which may be core-sheath fibers. Texturized fibers may also be used.

The bicomponent fibers may have cross-sectional shapes such as round; trilobal; cross; and others known in the art. The core-sheath bicomponent fibers are typically made such that the sheath of the fibers utilizes a lower melting point polymer than the core polymer. Suitable polymers for the core include polyamides such as, but not limited to, nylon 6, nylon 11, nylon 12, and nylon 6,6; polyesters such as, but not limited to, PET and PBT; poly(ether-amides) such as, but not limited to, Pebax® 4033 SA and Pebax® 7233 SA (Trademark of Elf Atochem); poly (ether-esters) such as, but not limited to, Hytrel® 4056 (Trademark of DuPont) and Riteflex® (Trademark of Hoechst-Celanese); polyolefins such as, but not limited to, polypropylene and polyethylene; and fluorinated polymers, such as, but not limited to, poly(vinylidene fluoride); and mixtures thereof. Nylon 6 and polypropylene are preferred.

Suitable polymers for the sheath include polyolefins such as, but not limited to, polyethylene and polypropylene; polyesters such as, but not limited to, PCL; poly(ether-amides) such as, but not limited to, Pebax® 4033 SA and Pebax® 7233 SA (Trademark of Elf Atochem); poly(ether-esters) such as, but not limited to, 9 O Hytrel® 4056 (Trademark of DuPont) and Riteflex® C (Trademark of Hoechst-Celanese); elastomers made from c polyolefins, for example Engage® elastomers (Trademark of DuPont-Dow); poly(ether urethanes) such as, but not limited to, Estane® (Trademark of BF Goodrich); poly(ester 00 urethanes) such as, but not limited to, Estane® (Trademark 00 of BF Goodrich); Kraton® polymers (Trademark of Shell Chemical Company) such as, but not limited to poly(styrene-ethylene/butylene-styrene); and poly(vinylidene fluoride) copolymers, such as, but not limited to, KynarFlex® 2800, (Trademark of Elf Atochem).

Pebax® polymers, polyethylene, and PCL are preferred.

The ratio of the two components of the core-sheath fibers can be varied. All ratios used herein are based on volume percents. The ratio may range from about 10 percent core and about 90 percent sheath to about 90 percent core and about 10 percent sheath, preferably from about 20 percent core and about 80 percent sheath to about 80 percent core and about 20 percent sheath, more preferably from about percent core and about 70 percent sheath to about percent core and about 30 percent sheath. The sheaths of the bicomponent fibers may be fused prior to electrostatic coating.

The substrates are electrostatically coated with at least one coating composition. Suitable first coatings to be used in the present invention include, but are not limited to, poly(ethylene oxide); poly(ethylene glycol); hydroxyethyl cellulose; hydroxypropyl cellulose; polyethylene; waxes such as microcrystalline wax; polyvinylidene fluoride and polycaprolactone.

10 0 Suitable second coatings to be used in the present Cl invention include, but are not limited to, poly(ethylene Soxide), poly(ethylene glycol), hydroxyethyl cellulose, hydroxypropyl cellulose, polyethylene, waxes such as microcrystalline wax, and polycaprolactone. The coatings may contain flavors, such as, but not limited to, natural 00 00 and synthetic flavor oils, such as mint and cinnamon. The Sflavor oils may be used as is, or may be encapsulated in C- or supported on a carrier such as starch or modified starch.

The process of the invention may also be useful for orienting short bicomponent fibers perpendicular to the axis of a substrate, then fusing the short bicomponent fibers to the substrate. The length of the short bicomponent fibers may range from 1 mm to 5 mm. After the short bicomponent fibers are oriented onto the substrate by electrostatic impregnation, they are fused to the substrate by heat at a temperature appropriate to melt the outer surface of the bicomponent fiber.

Additional materials that may be included in the coatings include, but are not limited to, sweeteners such as bulk sweeteners, including sorbitol and mannitol, and intense sweeteners including aspartame and sodium saccharin, as taught by European Patent Application EP 919,208, hereby incorporated by reference for the disclosure relating to waxes and sweeteners; abrasives, such as silica; dentrifices; chemotherapeutic agents; cleaners; and whiteners. Examples of suitable additives are disclosed in United States Patent No. 5,908,039, the disclosure of which is hereby incorporated by reference. Any of the foregoing materials may be used in encapsulated form.

11 O The amount of wax, flavor,. and other additives typically CI coated on fibers to make floss is known in the art.

STypically, the coating composition is added at from 2 weight percent to 60 weight percent, based on the weight of the fibers.

00 00 Suitable medical devices to be used in the present invention include, but are not limited to, medical devices C made from ceramics, metal alloys, and polymers, such as stents, and polymer tubes such as catheters. The medical C devices may be coated with the same waxes and in the same manner as mentioned above.

Many factors were important in determining how to prepare examples of the present invention. The selection of materials was based on a number of chemical and physical parameters of the polymer and the fiber. Among these, the melting point (Tm) and degradation temperature (Td) are important as they determine issues regarding material selection and processing conditions. The chemical structure of the polymers will influence the adhesion of the deposited material to the substrate fibers.

Processing conditions further involve operating furnace temperature, residence time in the furnace (which influences line speed) and powder concentrations.

Physical parameters such as powder particle size (mean and distribution), density, melt viscosity, electrical conductivity, etc. are among the important ones that determine the deposition characteristics. Crystallization kinetics of the binder polymer also must be considered as it has an influence on the morphology/structure of the polymer once it is cooled down from the melt during the consolidation stage. Coating polymers and fibers were 12 chosen for the examples considering all the factors, and are summarized with their properties in Tables 1A and lB.

Table 1A Polymer Producer Parti ci T e Size-= Polycaprolactone Union 60 60 343 (Tone 767) Carbide Polyethylene Union 100 65 250 Oxide Carbide (WSR-N-10-100- Reg) Polyethylene Union 100 65 250 oxide Carbide (WSR-N-80-100- Nylon 11 Elf NT 185 436 (Besno) Atochem Poly(vinylidene Elf 200 165 374 Fluoride) Atochem (Kynar 711) PVDF Copolymer Elf 200 145 363 (Kynar-Flex Atochem 2801) Poly(ether- Elf NT 160 232 amide) Atochem (Pebax 4033-SA) High Density Hoechst- 120 130 NT Polyethylene Celanese (H-DPE GHR 8110) Hydroxypropyl Hercules 100 190 350 cellulose (Kiucel [EXS Pharm..]) (particle size is in mesh) NT not tested 13 Table 1B Tenaci T T_ Fiber Type Construction Denier tv (OC) (g/d) Nylon 6,6 Untwisted 630 8 255 442 Air- Entangled 3 dpf Nylon 6 Untwisted 1400 5 220 446 Air- Entangled 3 dpf Polypropyl Untwisted 630 8 162 301 ene Air- Entangled 3 dpf Teflon Monofilament 1200 5 N/A NT Polyester Untwisted 400 23 331 NT (Vectran) 5 dpf dpf denier/filament The powder coating process is shown schematically in Figure 1. The coating line consists of a feed spool, grounding unit, electrostatic coater, furnace/oven and take-up winder. The feed spool is mounted on a metallic post that facilitates easy unwind of the fiber during operation. The fiber is then made to pass through an eyelet that is connected to a ground source to allow for grounding of the fiber. The fiber then passes through a tensioning device made of ceramic rods that can be adjusted depending on the desired packing conditions of the powder in the fiber matrix. The fiber then passes through openings provided at each end of the coater.

A B-60 coater (available from Electrostatic Technology Incorporated, a subsidiary of Nordson Corporation, Branford, CT) was used to conduct the processes set forth in the examples. The coater comprises a powder feeder connected to it that feeds powder, which is held in a 14 hopper, into the rear end of the bed. A photohelic gauge CI placed in the bed measures the level of powder in the bed Sand ensures that a constant level of powder is maintained during the coating operation. A refrigerator unit ensures the delivery of clean, moisture and oil free air into the plenum of the coater, and a powder collector provides for 00 00 collection of powder that is vacuumed out of the bed during operation. The coater also comprises a fire C detection device and a vortex tube to assist in the formation of the powder cloud.

The powder coated fiber exits the deposition chamber and then passes through a furnace. A suitable furnace and is made by Lindberg and Glenro. The furnace has a spilt lid that is made to open and close via air actuated arms. The fiber then moves through an eyelet onto a core spool using a Leesona rewinder. The line speed can be controlled by the Leesona rewinder and is measured using a digital tachometer.

A layer of polymer powder was fluidized in the bed, which was constructed of a plastic material. The powder was fluidized by air that was charged negatively in the plenum of the coater. The air was kept clean and free of moisture and oil by passing it through a refrigeration unit. The air was then made to pass through the air plenum and encountered a mesh of electrodes that were charged by a highly negative direct current supply.

Negative coronas used as negatively charged powder particles tend to deposit more uniformly and efficiently than positively charged ones because of their relative resistance to electric breakdown. The electrons generated in the glow region of the negative corona quickly attach 15 themselves to electronegative gas molecules such as oxygen CI in the air to form negative ions. The negatively charged Sair then passed through a porous ceramic or plastic bed to contact the powder. Field charging or ion bombardment then transferred some of the ions to the powder particles thereby generating an aerated, negatively charged cloud of 00 00 powder in the bed. This indirect charging of the powder by the air along with the separation of the charging mesh C from the powder makes the fluidized bed process different from other powder techniques such as powder spray gun and C triboelectric charge guns. The substrate, which in the present case was the fiber, was then grounded in order to generate a sufficient potential difference to facilitate electrostatic deposition.

The amount of polymer binder added to the fibers was the main dependent variable for the design of experiments.

The powder coating variables that could have an impact on the add-on are bed fluidization flow rate electrostatic voltage (kilovolts, and line speed (meters per minute). The other variables that can be controlled on the coater are bed air pressure, vortex flow rate and vortex air pressure. It was determined that none of these latter variables influenced the add-on significantly.

The vortex tube settings were changed to create the powder cloud and once the cloud was generated, the settings were kept constant throughout the experiment. The bed agitator was turned on whenever needed, but was avoided as much as possible, as it was seen to reduce the add-on due to additional turbulence in the powder cloud. In general, wherever possible, a two parameter, three level design of 16 experiments was conducted. The variables were varied CI within the following limits: Bed fluidization flow rate (m 3 /sec): Low (0.006); Medium (0.010); and High (0.014) 00 00 Electrostatic voltage Low (0 or no voltage); Medium and High (40.4) It was important to determine the furnace temperature in C order to optimize the polymer fusion and bonding on the fiber. A visual experiment was carried out on nylon 6 fibers and polyethylene oxide binder. The residence time in the furnace for a line speed of 10 m/min was calculated based on the length of the furnace (approximately 1 meter) to be 6.3 seconds.

Fiber was coated at a bed flow rate of 0.014 m 3 /sec and electrostatic voltage of 40.2 kV and was then inserted into the furnace at a selected temperature and held there for 6.3 seconds. Optical microscopy was performed to check the melt morphology of the polymer on the fibers.

The furnace temperature was then raised and a freshly coated sample was exposed to the temperature. This was done until a temperature was reached at which melt occurred. It was observed that a good coating was formed on the fibers at a furnace temperature of 265 0

C.

The procedure described above was utilized to determine the furnace temperature for a given set of materials and process conditions. The residence time in the oven can be increased by using longer ovens or by wrapping the coated yarn in grooves of metallic rollers mounted on pulleys in the heated section of shorter ovens.

17 CI Example 1 Polvamide Multi-filaments/Water Soluble SPolymer Coating Systems Ct Nylon 6 Multi-filaments/Poly(Ethylene Oxide) 00 Poly(ethylene oxide) [PEO] N-80 grade was used to coat a nylon 6 multi-filament structure comprising 467 filaments, o each filament having a denier of 3. Tables 2 and 3 show the add-on of PEO as a function of electrostatic Svoltage and bed flow rate, respectively, at an oven temperature of 260°C and a line speed of 16 m/min. The add-on increases with increasing voltage but decreases beyond a voltage value of 40 kV. On the other hand, the trend with respect to bed flow rate indicates a strong monotonic dependence where the add-on increases with increasing flow rate. PEO powder was uniformly dispersed and fused on the nylon 6 fibers as was observed by scanning electron microscopy.

18 Bed Flow Rate 0.006 0.006 0.006 0 .006 0.010 0.010 0.010 0.010 0.014 0 .014 0.014 0.014 0.014 Table 2 W/ec Electrostatic 0KV 20 40.4 60.2 0 20 40.4 60.2 0 20 40.4 60.2 80.4 Voltag~e Add On 1.73 9.8 10.2 1 4 .17 22.64 24 .14 3 7 .14 28.57 36.21 5.35 Table 3 Bed Flow Rate Mn 3 /sec Add On Electrostatic Voltag~e (KV) 0 0 0 20.6 20.6 20.6 40.3 40.3 40.3 60.2 60.2 60.2 80.4 0.006 0.010 0 .014 0 .006 0.010 0.014 0.006 0 .010 0 .014 0.006 0.010 0 .014 0 .014 1 .73 4 .17 7 .14 9.8 22 .64 28.57 10.32 24. 14 36.21 1 3 5.35 19 Nylon 6,6 Multi-filaments/Poly(ethylene Oxide): cPEO N-80 was used to coat a nylon 6,6 multi-filament structure comprising 210 filaments, each having a denier of 3, at a furnace temperature of 237 0 C. Tables 4 and show the add-on of PEO as a function of voltage and flow 00 00 rate at line speeds of 11 m/min and 17 m/min, Srespectively. As seen from the Tables, regardless of the C1 line speed, the add-on is very sensitive to bed flow rate, with increasing flow rates resulting in higher add-on.

C1 The trend with voltage is the same as in the previous case with the existence of a saturation voltage beyond which increasing voltage results in a drop in add-on. The saturation voltage in the present case appeared to be kV. The add-on also seemed to be higher at 17 m/min as compared to llm/min, but higher speeds did not support this trend. Scanning electron micrographs showed that PEO was uniformly coated on the nylon 6,6 fibers.

Table 4 Add-On Voltage 0.006 mn/sec 0.014 m'/sec 0 5.13 19.23 7.14 22.22 3.33 15.69 3 15.38 20 Table Add-On Voltage 0.006 m 3 /sec 0.014 m'/sec 0 2.5 -17.07 3.64 24.1 3 26.67 1 22.73 0.6 23 A study was conducted after coating nylon 6,6 with 20% PEO at an oven temperature of 235°C, voltage of 30 kV, flow rate of 0.013 m 3 /sec, bed pressure of 45 psi, vortex pressure of 20 psi and line speed of 11 m/min. Table 6 summarizes the results of a consumer test of PEO coated nylon 6,6 floss. The data (percent of people who indicate the floss passes each test) shows that the PEO coated floss performed well, particularly at ease of sliding between teeth and being gentle on the gums.

Table 6 Property Sliding easily between teeth Being gentle to the gums Cleaning effectively between all teeth Percent Pass 63 24 21 0 Nylon 6,6 Multi-filaments/Hydroxypropyl Cellulose: SNylon 6,6 was coated with hydroxypropyl cellulose. Tables 7 (line speed of 11 m/min, oven 235 0 C) and 8 (line speed of 16 m/min, oven =255 0 C) show that the add-on of O0 hydroxypropyl cellulose was dependent on the bed 0 0 flow rate which was the dominant factor. HPC powder Spossessed large amounts of charge as received from the C supplier. The powder floated and tended to melt onto the fiber once deposited.

Table 7 Voltage Add-on at 0.006 Add-on at 0.014 (kV) m 3 /sec m 3 /sec 0 0 9.09 2 11.76 1.2 12.5 Table 8 Voltace Add-on at 0.006 Add-on at 0.014 (kV) m 3 /sec m 3 /sec 0 0 14.81 3.57 18.18 4 22 O Example 2 Polyester Multi-filaments/Water Insoluble C Polymer Coating Systems Vectran Multi-filaments/High Density Polyethylene: Vectran is a high performance/ high temperature fiber made 00 00 from liquid crystalline polyester and is commercially available from Hoechst-Celanese. A furnace temperature of C- 310 0 C was used to melt the water-insoluble polyethylene coating material onto the Vectran® fiber at a line speed Cq of 17 m/min. Table 9 shows that in order to achieve higher add-ons of polyethylene, high flow and voltage was essential.

Table 9 Voltage (KV) Add On 0 9.35 20.2 8.38 40.3 8.1 60.1 14.8 80.5 The flow rate required to achieve the above add-ons was 0.014 m 3 /sec.

Example 3 Fluoropolymer Monofilament/Water Soluble Polymer Coating Systems Poly(tetrafluoroethylene) ("PTFE") Monofilament/Poly(ethylene oxide): PTFE monofilament was coated with a non-wax water-soluble polymer, poly(ethylene oxide), to increase the coefficient of friction. The PTFE monofilament was generally rectangular in transverse cross-section, with a 23 C width of about 2-3 mm and a thickness of about 0.08 0.13 C mm. The temperature was 320 0 C at a line speed of 27 m/min.

cTable 10 shows the add-on of PEO on the PTFE monofilament tape, and it was observed that beyond 20 kV voltage the add-on drops as was seen earlier. This shows that the trend of add-on versus voltage is independent of substrate 00 00 geometry, cylindrical versus flat fibers. PTFE was 0 also successfully coated with a mixture of multiple CI powders such as PEO, spray-dried peppermint flavor and sodium saccharin.

Table Add-On Voltage 0.006 m 3 /sec 0.010 m'/sec 0.014 (kV) m/sec 0 10.26 10.22 NT 21.0 18.39 18.7 21.62 40.2 10.58 11.9 NT 60.2 7.5 9.1 NT 80.4 9.1 11.2 NT Tables 11A and 11B summarize all the coating experiments that were conducted on different classes of fibers using different polymer coating systems and the preferred conditions for each set of materials. The main variables were bed pressure (0.006 to 0.014 m'/sec), voltage (0 to kV) and line speed (6 to 64 m/min for Nylon 6/PEO and 11 to 17 m/min for the rest of the materials tested).

The furnace temperature was changed based on the fiber/polymer combination. If desired, further consolidation can be carried out on the powder-coated fibers in order to prepare a thoroughly impregnated product. A combination of heat and pressure can be used 24 00 00 to drive the polymer inside the fibers that will produce a void free product. Using the viscous f low of the polymer through the fibrous network and the elastic deformation of the fiber network, a consolidation model can be developed.

Table 11A _Prefeered Conditionsil Fiber Polymer' Pressu Voltacte Speed Comments Oven =260 0

C

Nylon PEC N80 0.014 40.4 kV 11 Binder 6 rn/min 1.75% to 31% Oven 237 0

C

PEO N180 0.014 20.2 kV 11 Binder in/mmn to 27% Reduced add on due to _______turbulence Nylon Larger 6,6 particle PEG size, 8000 High density poor floatation, Low molecular weight, good ____melt Powder was very fine, Kiucel 0.014 40.2 kV 17 Extremely rn/mmn cohesive, Agitator had to be used, Feed hopper could not be _u s 25 Table 11B Preferred Conditions Fiber Polymer Pressur Voltaq Sn~eed Comments Kynar powders Kynar high Nylon 711 densities, 6,6 Kynar fine particle Flex size, PCL did PCL not charge due to its size, grinding down was not _____possible Fiber Polypr PEO N80 0.010 20.2 11 performed opylen kV rn/mi very well, e low melting point made coating Vectra HDPE 0.014 80.2 17 Powder was n kV rn/min extremely heavy, oven ____310 0

C

Powder was HDPE 0.014 80.2 17 extremely kV rn/mmn heavy, oven Teflon 310*C, good PEO N80,melt but poor flavor, 0.006 ahso sacchari 20.2 27 Excellent n kV rn/mmn floatation, oven 320 0

C,

increased ratio 26 Example 4 Selection Process for Polymer Powders Based on Cl Powder Aeration It is necessary to understand powder aeration to predict the coating performance of polymer powders. In order to understand this quantitatively, experiments were carried 00 00 out on several powders to obtain their bulk and tapped densities. In this experiment, a clean graduated cylinder C was taken and weighed 50 cc. of powder was then poured into the cylinder and weighed again (W 2 Weights C were recorded to 5 decimal precision. The aerated/bulk density was then computed using equation Pb= W 2 1 where Pb is the bulk density in grams/cc.

In order to obtain the tapped density the same measurements were made with a minor difference. After the powder was poured into the cylinder, it was tapped times in order to compact it and powder was added to maintain a 50ml volume. The cylinder was then weighed

(W

3 Equation 1 was used after substituting W, for W 2 and the tapped density was obtained in grams/cc. Table 12 lists the bulk and tapped densities of the different polymers. The fused density in the table represents the density of a block of material.

27 Table 12 Bulk Density Tapped Density Fused Pymer (g/cc) (g/cc) Density (g/cc) Polyethylene Oxide WSR-N-10-100-Reg 0.46-0.50 0.54 1.2 WSR-N-80-100-NF Polycaprolactone 767 0.52 0.61 1.15 Polyethylene Glycol 0.54 0.82 1.03 Polyethylene GHR 8110 0.47 0.51 0.95 HPC (Klucel 0.32 0.39 1.16 The differential densities (fused density tapped density) of the polymer particles were plotted (log-log) as a function of mean particle size .(in microns). It appears that the relationship of these polymer properties is critical to the polymer's fluidization properties, such as aeratability, cohesiveness, sand-like properties, and spoutability. The data can be used as a guide in selecting powders for fluidized-bed coating applications.

For example, PEO and HPC are more aeratable than Polyethylene glycol and Polyethylene GHR 8110 (a high density polyethylene). Therefore, PEO and HPC are more easily fluidized.