Apparatus and method for coating of objects using a porous resilient matrix

Abstract: An apparatus (10) for applying a coating to an object (12) includes a pair of reciprocating members (14A,14B) which each include a porous resilient pad (16A,16B) mounted for movement toward and away from each other. The apparatus (10) includes a coating supply system (24) for supplying coating to the resilient pads (16A,16B). The pads (16A,16B) have a movement sequence from an initial rest position where the pads (16A,16B) are spaced apart from one another to a coating loading position where the pads (16A,16B) are in physical contact and have a degree of compression with each other to load the coating onto the pads, then the pads (16A,16B) are moved to an intermediate rest position with the pads (16A,16B) spaced apart an the object (12) to be coated is moved between the pads (16A,16B). The sequence then includes a coating delivery position where the pads (16A,16B) are in physical contact with each other and the object (12) so that the pads (16A,16B) have a degree of compression with each other and the object (12) thereby applying the coating to the object.

Description: Field of Invention This invention relates to the coating of objects and more particularly relates to methods and apparatus for applying lubricants to medical devices such as over-the-needle peripheral venous catheters, hypodermic needles, blades and the like. Background of the Invention Medical devices are often assembled from components formed from many different materials. It often is necessary to apply a coating of a lubricant to one or more of the components so that a component of one material will readily slide against a component of another material. Examples of this type of application are catheters with guidewires, over-needle catheters, syringe plunger stopper within a syringe barrel, needles for penetration of blood collection tube stoppers and the like. In other medical device applications, a lubricant is applied to a device to ease its penetration into the body. Examples of these applications are surgical blades, hypodermic needles, peripheral venous catheters and the like. In all of these medical device lubrication applications, there are strict requirements on the amounts of lubricant, the uniformity of the application and a need to avoid contamination of the device with foreign material other than the lubricant. A further requirement on application of lubricant results from the high volume production requirements often resulting in the use of high speed assembly equipment. Thus, any lubricant application must be precise and compatible with high volume production. Currently, a commonly used lubricant for medical devices is "silicone," i e., polydimethyl siloxane having a Brookfield viscosity between about 1,000 and 20,000 centistokes (cs). For some applications, the silicone is applied "neat", i.e., without solvent. An example of neat application of silicone to syringe plunger stoppers is disclosed in United States Patent 5,207,293 to Eden et al. This patent discloses a method and apparatus for lubricating syringe stoppers by moving the stoppers between a pair of wheels which are positioned partially in a reservoir containing lubricant so that with rotation of the wheels, lubricant is transferred to the stoppers. Another commonly used neat application method is tumbling a measured quantity of small parts, such as stoppers, with a measured quantity of lubricant so that the parts acquire a coating of the lubricant. Silicone lubricant also may be sprayed onto the parts either neat or in a carrier solvent. Neat spraying has been found to work well for interior surfaces such as inside syringe barrels. Solvent based dipping or spraying is commonly used for coating hypodermic needles and catheters. Chlorofluorcarbon solvents have proven to be very satisfactory for the delivery of silicone onto medical devices because they are non-toxic, non-flammable, inert, evaporate rapidly without leaving residue and are available in very high purity. Unfortunately, because of the belief that chlorofluorocarbon solvents are responsible for destruction of ozone in the upper atmosphere, most commonly used chlorofluorocarbon solvents will no longer be available. Alternate solvents such as hydrocarbons are flammable, and aqueous based systems generally are not practical for silicones. Thus, there is a need for an apparatus that is compatible with high production volume and capable of uniformly delivering precise quantities of lubricant to medical devices. DE-A 304590 describes a process and device for siliconising friction surfaces of needles, wherein the silicone is applied to the needle by a rotational movement, translational movement or combination of both movements. During rotational movement, different surface areas of a transfer element come into contact one after the other with different surface areas of the surface to be siliconised, and the transfer occurs with the concurrent action of different adhesion forces of the silicone on the transfer element and on the surface to be siliconised. In the case of wiping on, the silicone adhering to the transfer element is wiped onto the area to be siliconised and thus transferred onto it. In so doing, the same surface area of the transfer element can come into contact with different surface areas of the surface to be siliconised. SUMMARY OF THE INVENTION The present invention relates to apparatus according to claim 1. An apparatus for applying a coating to an object includes a pair of reciprocating members each having a porous resilient pad. The members are mounted for movement toward and away from each other. The apparatus further includes a coating supply system for supplying the coating to the resilient pads. The members have sequential movement positions starting from an initial rest position with the resilient pads spaced apart from each other. The movement sequence then includes a coating loading position where the resilient pads are in physical contact and have a degree of compression with each other loading the coating into the pads. There is an intermediate rest position where the pads are spaced apart and the object to be coated is placed between the resilient pads. The movement sequence includes a coating delivery position with the resilient pads in physical contact with each other and the object being coated, the resilient pads additionally having a degree of compression with each other and the object, thereby applying the coating to the object. A method for applying a coating to an object includes placing an object to be coated between two reciprocating members each including a resilient pad mounted for motion toward and away from each other. The object is placed between the pads when the pads are spaced apart from each other and are loaded with the coating to be applied to the object. The method then includes moving the pads from the pads spaced apart position to a position where the pads are in physical contact with each other and the object to be coated so that the pads have a degree of compression with each other and the object to be coated thereby applying the coating to the object. The apparatus and method of the present invention provide a precise coating of neat lubricant to objects such as hypodermic needles, catheters, guidewires and the like. The invention is compatible with high volume assembly and can be built into a compact station to be fit into existing assembly machinery. The method of the present invention leaves no residual solvent and is simple to practice and maintain. Brief Description of the Drawings Fig. 1 is a partially sectioned perspective view of the preferred apparatus of the present invention for applying a coating to an object; and Figs. 2A to 2E are partial cross-section schematic views of the apparatus of Fig. 1 along the line 2-2 showing the reciprocating members in the several positions of a movement sequence. Detailed Description While this invention is satisfied by embodiments in many different forms, there are shown in the drawings and herein described in detail preferred embodiments of the invention with the understanding that the present disclosure is to be considered exemplary of the principles of the invention and is not considered to limit the invention to the embodiments illustrated. Referring to Figs. 1 and 2A to 2E, an apparatus 10 for coating an object 12 of the present invention includes a pair of reciprocating members 14A and 14B. In order to facilitate and simplify the present description, the reciprocating members and other parts of apparatus 10 which are present in pairs are described as symmetrical or identical and are identified with suffixes "A" and "B." For particular applications, such as when object 12 is not symmetrical, the present invention is intended to encompass embodiments where parts of the apparatus, herein described in pairs to simplify the description, are not symmetrical or identical. Reciprocating members 14A and 14B each further include porous resilient pads 16A and 16B. Members 14A and 14B are preferably mounted on a base 20 and include drive mechanisms 30A, 30B, and supports 31A, 31B. Pads 16A, 16B are mounted for movement toward and away from each other. Apparatus 10 includes a coating supply system 24 for supplying a coating to resilient pads 16A, 16B. Preferably resilient pads 16A, 16B each include backing plates 40A, 40B each having a first side 42A, 42B and a second side 44A, 44B and having a plurality of holes 46A, 46B therethrough. Pads 16A, 16B each further preferably include reticulated elastomeric foam layers 48A, 48B having front sides 52A, 52B and back sides 56A, 56B. Back sides 56A, 56B of preferred foam layer 48A, 48B preferably are fixedly attached to first sides 42A, 42B of the backing plates. Members 14A, 14B have a movement sequence schematically illustrated in Figs. 2A to 2E including an initial rest position with resilient pads 16A, 16B spaced apart a distance "m" from each other. The movement sequence then includes a coating loading position where resilient pads 16A, 16B are in physical contact and have a degree of compression with each other. The degree of compression is determined by comparing the thickness t 1 of pads 16A, 16B in the initial rest position as shown in Fig 2B to thickness t 2 of pads 16A, 16B in Fig. 2B showing the coating loading position. The compression of the pads serves to spread the coating onto pads 16A, 16B. The compression of the pads in the coating loading step followed by the release of the compression in the intermediate rest position serves to load the coating onto the pads and also to distribute it. The movement sequence then includes movement to an intermediate rest position where resilient pads are again spaced apart distance "m" as shown in Fig. 2C, allowing placement of the object to be coated between the pads.The movement sequence then includes a coating delivery position where pads 16A, 16B are in physical contact with each other and the object being coated. In the coating delivery position, the pads have a thickness t 3 and a degree of compression with each other and the object being coated as represented in Fig. 2D. The degree of compression is determined by comparing the ratio of pad thickness t 3 with thickness t 1 of the initial rest position. In the coating delivery position the coating is transferred from pads 16A, 16B to the object. Preferably, the degree of compression of pads 16A, 16B in the coating loading position (t 2 /t 1 ) is greater than the degree of compression in the coating delivery position (t 3 /t 1 ). When the degree of compression for coating delivery is less than the degree of compression for coating loading, results show more uniform and precise transfer of the coating to the objects being coated. Preferably, coating supply system 24 includes a reservoir 26 for holding a coating 27 and a transport system 28A, 28B transporting the coating to the pads through holes 46A, 46B. Each of the preferred reciprocating members 14A, 14B include drive mechanisms 30A, 30B for reciprocal movement of the pads through the movement sequence. Preferably apparatus 10 includes an object placement system 34 for placing objects 12 between the pads and then removing the objects. Preferred apparatus 10 includes a control system 32 for controlling the coating supply system, the reciprocating member drive system and the object placing system. The preferred coating supply system includes having coating transport system 28A, 28B in fluid communication with second sides 44A, 44B of the backing plates 40A, 40B so that a relatively constant supply of coating is maintained at holes 46A, 46B at back sides 56A, 56B of the foam layers 48A, 48B to load the resilient foam layers. Control system 32 preferably adjusts coating supply system 28A, 28B so that there is a sufficient amount of coating available for delivery to the object. The control system may be mechanical, electromechanical, digital and the like to control the coating delivery, the movement of the reciprocating members and the object placement and removal. A suitable material for the porous foam layer is a reticulated polyurethane foam with between about 300 to about 1250 pores per square centimeter. In applications where the object to be coated is a medical device such a catheter or a hypodermic needle, a preferred foam is a reticulated polyurethane foam which has been permanently thermally sintered from an as-blown height of between about 5cm to 25cm to a height of about 2.5cm. One skilled in the art of polymeric foams recognizes that the thermal sintering is also described as "felting," and further described as "firmness" or "firmness ratio" of between 2 and 10. Thermal sintering involves compressing the foam from the as-blown thickness to a desired thickness, then heating. When the compression then is released, the foam retains the compressed thickness. This sintering has the effect of increasing the density of the foam by reducing the void volume of the pores in the foam. In the preferred present apparatus, where the object being coated is a medical device such as a catheter, hypodermic needle, a catheter mounted over a hypodermic needle and the like, preferred resilient foam pads 16A, 16B have a thickness t 1 between about 0.25cm to about 2.5cm and most preferably between about 0.4cm to about 0.8cm. Preferably the object being coated is placed substantially centrally between the resilient foam pads so that when the pads are in the coating delivery position, the object is not substantially deflected. The positioning of the object is particularly important when the object being coated is pointed, e.g., a hypodermic needle or a catheter mounted over a needle. If a pointed object is deflected during the coating delivery compression, there may be a tendency to cause the point to partially imbed in one pad or the other, potentially damaging the point, reducing the service life of the pad and generating undesirable particles. Preferably the foam has about 10 to about 100 pores per linear cm with a firmness about 4. This preferred foam will have about 85% to about 90% void volume or open pore space. Suitable reticulated polyurethane foams, which are available in a range of firmness between 2 and 10, are available as "Foamex SIF felt" from Speciality Polyurethane, 1500 E. Second Street, Eddystone, PA 19013 and from E. E. Murray Co., 707 Umatilla Street, Denver, CO 80204. Other foams having similar properties are expected to perform satisfactorily. In cases where the objects to be coated are not medical devices such as needles, blades, catheters and the like, foams having different properties may be desired. In the preferred coating system, the coating is a lubricant. The apparatus of the invention is suitable for application of other coatings including, but not limited to, colorants, pesticides and the like. For these other applications, foams having different composition and properties may be selected and are included in the scope of the invention. In the preferred application, the degree of compression between resilient pads 16A, 16B in the coating loading position is greater than the degree of compression in the coating delivery position. These compression positions have the effect of reducing the void volume or open space within the foam. When the compression is released from the coating loading position, the foam returns to the original uncompressed volume, and at least a portion of the void volume is occupied by the coating charge. When the foam having a charge of coating is compressed into the coating delivery position, the foam preferably substantially engulfs the object being coated, the coating in the portion of the void volume is displaced and transferred to the object being coated. One skilled in the art of lubricating medical devices recognizes that a coating of polydimethyl siloxane is often used as a lubricant on medical devices such as hypodermic needles, scalpels and guidewires made from metal and on medical devices formed from polymeric materials such as catheters and probes. The purpose of the lubricant coating is to reduce the sliding friction between the device and tissue or the sliding friction between one component of the device and another. In almost all applications of silicone lubricant to medical devices there are two conflicting requirements governing the amount applied; there should be some uniform minimum amount applied over the entire surface where the sliding friction is to be reduced; and there should not be excess or visible silicone present on the device. These requirements are often in conflict with each other since polydimethyl siloxane with viscosity above about 500cs applied by direct dipping into the neat material, while providing complete coverage, generally results in an undesirable excess that leads to visible droplet formation Currently, many silicone lubricant applications rely on use of a volatile solvent carrier to dilute the silicone, insure complete coverage of the object and avoid deposition of excess lubricant. Since polydimethyl siloxane is non-polar, many solvents otherwise suitable for its delivery are quite flammable and the medical device industry evolved toward non-flammable chlorofluorocarbon solvents. With the recent recognition of the ozone depletion problem and its attribution to chlorofluorocarbons, many of these solvent based dilution systems for application of silicone are no longer practical. As an example, data is presented related to coating four 14 gauge catheters at a time with 12,500cs. polydimethyl siloxane (silicone) using the preferred embodiment of the present invention illustrated in Figs. 1-2. The control used in this study was standard commercial product having identical components. The control product was lubricated with identical silicone applied using a chlorofluorocarbon solvent based application system. While the preferred embodiment of the present invention is well suited for the lubrication of cylindrical objects with a length at least three times longer than their diameter such as needles and catheters, this example is not to be considered limitative of the invention to 14g catheters, rather it is intended to show the utility and repeatability of the apparatus and method in use over a 24 hour period. In this example, the foam used was firmness 4 polyurethane Foamex. Preferably, pads 16A, 16B are each divided into four sections 17A, 17B, the sections being mounted on each reciprocating member to facilitate easy replacement. Each section 17A, 17B is about 0.635 cm thick (t 1 ) by 1.27 cm wide by 6.35 cm long giving an uncompressed 16A, 16B volume of 41 cm 3 . The preferred apparatus was set up so that in the coating loading position pads 16A, 16B were compressed to a thickness of 0.158 cm (t 2 ), a 75% compression (t 2 /t 1 = 0.25). In the coating delivery position, the pads 16A, 16B were compressed to a thickness of 0.312 cm (t 3 ), a 50% compression (t 3 /t 1 = 0.5). The void volume, i.e., the pores, in the uncompressed state of the foam is about 88% of 41 cm 3 . When the foam is under 75% compression, the void volume decreases from 88% to a value of 76%. When the foam returns to the uncompressed state the increase in void volume is 12% of 41 cm 3 or 4.92 cm 3 at least a portion of the void volume then is filled by the preferred coating material, polydimethyl siloxane having a viscosity of 12,500cs. While the preferred polydimethyl siloxane has a viscosity about 12.500cs, the present invention is suitable for application of polydimethyl siloxanes or other coatings with Brookfield viscosities at 25°C. between about 10cs to about 1,000,000cs. The 24 hour trial run of the apparatus of the present invention was conducted to apply 12,500cs polydimethyl siloxane for lubrication to the 14g peripheral venous catheters mounted over needles. Samples of the coated catheters were taken at regular intervals and the amount of silicone lubricant present on their surface was determined by extraction. In the preferred configuration used in the trial, the reciprocating members are mounted so that the pads are vertical with the motion toward and away from each other being horizontal. Preferably, top surfaces 19A, 19B of the resilient pads are sealed so that when the pads are in the compressed state the coating cannot pass through the top surface of the pad and pool on surfaces 19A, 19B of the pads. The top surface may be sealed by adhesive, fusing by heat, ultrasound and the like. Preferably top surfaces 19A, 19B are fused by pressing against a smooth surfaced heated above the melting point of the polyurethane foam forming a skin. When the apparatus is operating in a steady state, control system 32 is preferably adjusted so that the amount of coating material delivered to the foam pads is only a slight excess to the desired amount being applied to the catheters. The slight excess cannot pool on the top surface because of the sealed surfaces 19A, 19B and migrates to the bottom of the pads where it may be collected without effecting the amount present on the catheters. The slight excess delivery to the pads ensures that the distribution into the pads during the coating loading cycle is sufficient to provide substantially uniform coverage of the object being coated. The results show that the preferred apparatus of the present invention was able to reliably and repeatedly apply 0.30 ± 0.075 mg polydimethyl siloxane to more than 20,000 catheters over a 24 hour period. Comparisons in standard laboratory performance testing for penetration force and drag force show generally similar behavior between these experimental catheters lubricated by the preferred apparatus of the present invention and standard commercial product lubricated by application of the same silicone in chlorofluorocarbon solvent. A constant concern in manufacture of over needle catheters is damage to the point of the needle during lubrication of the catheter and introduction of foreign matter onto the catheter or needle point during lubrication. In the trial, there was overall comparable performance of the catheters lubricated by the preferred present invention to standard commercial product indicating that the lubrication levels were comparable and that there was no detectable degradation in needle point quality. Careful microscopic examination showed that there was little evidence of introduction of particulates resulting from the contact between the resilient foam and the catheter. Further, there was no additional microbial background contamination or bioburden on catheters lubricated in the trial of the preferred apparatus when compared to the standard commercial product. The coating apparatus of the present invention may be compactly built to fit on assembly machines into space currently used for solvent based coating apparatus. The apparatus and method for its use demonstrate a capability to produce product having similar quality and performance properties to standard commercial product produced with solvent based coating. The apparatus of the present invention is also compatible with the assembly rate requirements and efficiency of current assembly machines using solvent based coating systems. The present invention provides a simple and reliable coating station for medical device assembly machines allowing manufacturers to eliminate the use of solvent based coating systems in many applications.

Claims: An apparatus (10) for applying a coating to an object (12) comprising a coating supply system (24) for supplying a coating to said resilient pads (16A, 16B) and members (14A, 14B) having sequential movement; characterised in that : the members are reciprocating members (14A, 14B) each comprising a porous resilient pad (16A, 16B), the members being mounted for movement toward and away from each other; and the sequential movement positions comprise an initial rest position wherein said resilient pads (16A, 16B) are spaced apart from each other, a coating loading position wherein said resilient pads (16A, 16B) are spaced apart from each other, a coating loading position wherein said resilient pads (16A, 16B) are in physical contact and have a degree of compression with each other thereby loading the coating into the pads (16A, 16B), an intermediate rest position wherein said resilient pads (16A, 16B) are spaced apart from each other so that an object (12) to be coated is placeable between said resilient pads (16A, 16B), a coating delivery position wherein said resilient pads (16A, 16B) are in physical contact with each other and with the object (12) to be coated, said pads (16A, 16B) having a degree of compression with each other and the object (12) to be coated in order to apply the coating to the object (12). The apparatus of claim 1 wherein said degree of compression in said coating loading position is greater than said degree of compression in said coating delivery position. The apparatus of claim 1 wherein said coating supply system (24) comprises a reservoir (26) and a transport system (28A, 28B) for supplying the coating to the resilient pads (16A, 16B). The apparatus of claim 1 wherein each of said reciprocating members (14A, 14B) further includes a drive mechanism (30A, 30B) and a backing plate (40A, 40B) for mounting said resilient pads (16A, 16B). The apparatus of claim 4 wherein said backing plates (40A, 40B) have a first side (42A, 42B) and a second side (44A, 44B) and further include a plurality of openings therethrough, said first side (42A, 42B) having said resilient pads (16A, 16B) mounted thereon and said openings being in fluid communication with said second side (44A, 44B) to said coating supply system (24) for supplying said coating to said resilient pads (16A, 16B). The apparatus of claim I wherein said resilient pads (16A, 16B) are foam and have a sealed top edge surface, said sealed top edge surface serving substantially to prevent said coating from pooling on said top edge surface of said pad (16A, 16B) when said pads (16A, 16B) are compressed in said coating loading position. The apparatus of claim 1 wherein said coating is a lubricant comprising polydimethyl siloxane having a Brookfield viscosity between about 100 centistokes to about 1,000,000 centistokes. A method for applying a coating to an object (12) comprising: placing an object (12) to be coated between two reciprocating members (14A, 14B) each comprising a porous resilient pad (16A, 16B) mounted for motion toward any away from each other, said placing occurring when said pads (16A, 16B) are in a position having said pads (16A, 16B) spaced a distance apart from each other and having a loading of a coating to be applied to the object (12); and moving said pads (16A, 16B) from said position having said pads (16A, 16B) spaced apart to a position having said pads (16A, 16B) in physical contact with each other and the object (12) to be coated, so that said pads (16A, 16B) have a degree of compression with each other and the object (12) to be coated, thereby applying the coating to the object (12). The method of claim 8 wherein the object (12) is a cylinder having a ratio of length to diameter greater than three to one and said placing step comprises placing the object (12) intermediate said pads (16A, 16B) when said pads (16A, 16B) are spaced apart so that when said pads (16A, 16B) are moved to said position having said pads (16A, 16B) in physical contact with each other and the object (12), said degree of compression between said pads (16A, 16B) and the object (12) being similar from each pad (16A, 16B) so that said object (12) is not substantially deflected. The method of claim 9 wherein said reciprocating members (14A, 14B) further include a coating supply system (24) and said loading of said coating of said resilient pads (16A, 16B) further comprises moving said pads (16A, 16B) from a position having said pads (16A, 16B) spaced apart to a coating loading position having said pads (16A, 16B) in physical contact with each other and having a degree of compression with each other, the coating thereby being loaded into said pads (16A, 16B), said coating loading step occurring before said object (12) placing step.

Inventors: LAMBERT JEANNE E, LEE MIN SHIU, TALLER ROBERT A, WILLIAMITIS VICTOR A, LAMBERT, JEANNE E., LEE, MIN SHIU, TALLER, ROBERT A., WILLIAMITIS, VICTOR A.
Applicants: BECTON DICKINSON CO, BECTON, DICKINSON AND COMPANY
Application year: 1996
Main classification: B05C1
IPC codes: B05C11, B05C1, A61M5