# Patent

## Title
Coating system, articles and assembly using the same and methods of reducing sticktion

## Abstract

The present invention provides a coating system for an article including a first component having a surface in frictional engagement with a surface of a second component, wherein at least a portion of at least one surface of the component(s) is coated with a coating prepared from a composition including a first, curable organopolysiloxane comprising at least two alkenyl groups; and a second, curable organopolysiloxane comprising at least two polar groups, the second organopolysiloxane being different from the first organopolysiloxane, which can provide low breakloose force when used in syringe assemblies.

## Background
CROSS REFERENCE TO RELATED APPLICATIONS
The present application claims priority to provisional application No. 60/787,366 filed on Mar. 30, 2006.


BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a coating system for an article, such as a syringe assembly, comprising curable organopolysiloxane(s), methods to reduce static and kinetic friction between slidable surfaces, and articles of low friction prepared thereby.
2. Description of Related Art
Certain devices require slow and controlled initiation and maintenance of sliding movement of one surface over another surface. It is well known that two stationary surfaces having a sliding relationship often exhibit sufficient resistance to initiation of movement that gradually increased pressure applied to one of the surfaces does not cause movement until a threshold pressure is reached, at which point a sudden sliding separation of the surfaces takes place. This sudden separation of stationary surfaces into a sliding relationship is herein referred to as “breakout”.
A less well known, but important frictional force is “breakloose force”, which refers to the force required to overcome static friction between surfaces of a syringe assembly that has been subjected to autoclaving and may have a slight deformation in one or both of the contacting surfaces of the syringe assembly, for example in the syringe barrel. In addition to autoclaving, parking of the assembly can further increase the breakloose force.
Breakout and breakloose forces are particularly troublesome in liquid dispensing devices, such as syringes, used to deliver small, accurately measured quantities of a liquid by smooth incremental line to line advancement of one surface over a graduated second surface. The problem is also encountered in devices using stopcocks, such as burets, pipets, addition funnels and the like where careful dropwise control of flow is desired.
The problems of excessive breakout and breakloose forces are related to friction. Friction is generally defined as the resisting force that arises when a surface of one substance slides, or tends to slide, over an adjoining surface of itself or another substance. Between surfaces of solids in contact, there may be two kinds of friction: (1) the resistance opposing the force required to start to move one surface over another, conventionally known as static friction, and (2) the resistance opposing the force required to move one surface over another at a variable, fixed, or predetermined speed, conventionally known as kinetic friction.
The force required to overcome static friction and induce breakout is referred to as the “breakout force”, and the force required to maintain steady slide of one surface over another after breakout or breakloose is referred to as the “sustaining force”. Two main factors contribute to static friction and thus to the breakout or breakloose force. The term “stick” as used herein denotes the tendency of two surfaces in stationary contact to develop a degree of adherence to each other. The term “inertia” is conventionally defined as the indisposition to motion which must be overcome to set a mass in motion. In the context of the present invention, inertia is understood to denote that component of the breakout force which does not involve adherence.
Breakout or breakloose forces, in particular the degree of stick, vary according to the composition of the surfaces. In general, materials having elasticity show greater stick than non-elastic materials, particularly when the surfaces are of dissimilar composition. The length of time that surfaces have been in stationary contact with each other also influences breakout and/or breakloose forces. In the syringe art, the term “parking” denotes storage time, shelf time, or the interval between filling and discharge. Parking generally increases breakout or breakloose force, particularly if the syringe has been refrigerated during parking.
A conventional approach to overcoming breakout has been application of a lubricant to a surface to surface interface. Common lubricants used are hydrocarbon oils, such as mineral oils, peanut oil, vegetable oils and the like. Such products have the disadvantage of being soluble in a variety of fluids, such as vehicles commonly used to dispense medicaments. In addition, these lubricants are subject to air oxidation resulting in viscosity changes and objectionable color development. Further, they are particularly likely to migrate from the surface to surface interface. Such lubricant migration is generally thought to be responsible for the increase in breakout force with time in parking.
Silicone oils are also commonly used as lubricants. They are poor solvents and are not subject to oxidation, but migration and stick do occur, and high breakout forces are a problem. Polytetrafluoroethylene surfaces provide some reduction in breakout forces, but this material is very expensive, and the approach has not been totally effective.
Thus there is a need for a better system to overcome high breakout and breakloose forces whereby smooth transition of two surfaces from stationary contact into sliding contact can be achieved.
SUMMARY OF THE INVENTION
In some embodiments, the present invention provides a coating system for an article comprising a first component having a surface in frictional engagement with a surface of a second component, wherein at least a portion of at least one surface of the component(s) is coated with a coating prepared from a composition comprising:
(a) a first, curable organopolysiloxane comprising at least two alkenyl groups; and
(b) a second, curable organopolysiloxane comprising at least two polar groups, the second organopolysiloxane being different from the first organopolysiloxane.
In some embodiments, the present invention provides articles of manufacture, such as syringe assemblies, having the coating system of the present invention applied to at least one surface of the article of manufacture that is in frictional engagement with another surface of the article of manufacture.
In some embodiments, the present invention provides a method for lubricating the interface between a first component having a surface in frictional engagement with a surface of a second component, comprising the steps of:
(a) applying the coating system according to the present invention to at least a portion of at least one surface of the component(s) to form a coating upon the portion of the surface; and
(b) irradiating the coating of step (a) to at least partially cure the coating.
In some embodiments, the present invention provides a method for reducing breakout and/or sustaining forces of slidable surfaces in the interior of a syringe assembly comprising:
(a) applying a coating system according to the present invention to the interior wall of the syringe barrel to form a coating thereon; and
(b) irradiating the coating of step (a) to at least partially cure the coating.



BRIEF DESCRIPTION OF THE DRAWINGS
The present invention will best be understood from the following description of specific embodiments when read in connection with the accompanying drawings:
FIG. 1 is a graph of infusion pump actuation force test results at a feed rate of 10 ml/hr for a prior art syringe assembly;
FIG. 2 is a graph of infusion pump actuation force test results at a feed rate of 10 ml/hr for a syringe assembly according to the present invention;
FIG. 3 is a graph of infusion pump actuation force test results at a feed rate of 1.0 ml/hr for a syringe assembly according to the present invention;
FIG. 4 is a graph of infusion pump actuation force test results at a feed rate of 0.1 ml/hr for a syringe assembly according to the present invention;
FIG. 5 is a graph of infusion pump actuation force test results at a feed rate of 1.0 ml/hr for a syringe assembly according to the present invention;
FIG. 6 is a graph of infusion pump actuation force test results at a feed rate of 10 ml/hr for a syringe assembly according to the present invention;
FIG. 7 is a graph of infusion pump actuation force test results at a feed rate of 0.1 ml/hr for a syringe assembly according to the present invention;
FIG. 8 is a graph of infusion pump actuation force test results at a feed rate of 1.0 ml/hr for a syringe assembly according to the present invention;
FIG. 9 is a graph of infusion pump actuation force test results at a feed rate of 10 ml/hr for a syringe assembly according to the present invention;
FIG. 10 is a graph of infusion pump actuation force test results at a feed rate of 0.1 ml/hr for a syringe assembly according to the present invention;
FIG. 11 is a graph of infusion pump actuation force test results at a feed rate of 1.0 ml/hr for a syringe assembly according to the present invention; and
FIG. 12 is a graph of infusion pump actuation force test results at a feed rate of 10 ml/hr for a syringe assembly according to the present invention.



DETAILED DESCRIPTION OF THE INVENTION
Other than in the operating examples, or where otherwise indicated, all numbers expressing quantities of ingredients, reaction conditions, and so forth used in the specification and claims are to be understood as being modified in all instances by the term “about.” Accordingly, unless indicated to the contrary, the numerical parameters set forth in the following specification and attached claims are approximations that may vary depending upon the desired properties sought to be obtained by the present invention. At the very least, and not as an attempt to limit the application of the doctrine of equivalents to the scope of the claims, each numerical parameter should at least be construed in light of the number of reported significant digits and by applying ordinary rounding techniques.
Notwithstanding that the numerical ranges and parameters setting forth the broad scope of the invention are approximations, the numerical values set forth in the specific examples are reported as precisely as possible. Any numerical value, however, inherently contain certain errors necessarily resulting from the standard deviation found in their respective testing measurements. Furthermore, when numerical ranges of varying scope are set forth herein, it is contemplated that any combination of these values inclusive of the recited values may be used.
Also, it should be understood that any numerical range recited herein is intended to include all sub-ranges subsumed therein. For example, a range of “1 to 10” is intended to include all sub-ranges between and including the recited minimum value of 1 and the recited maximum value of 10, that is, having a minimum value equal to or greater than 1 and a maximum value of equal to or less than 10.
The present invention provides a coating system for an article comprising a first component having a surface in frictional engagement with a surface of a second component. In accordance with the system and methods of the invention, the force required to achieve breakout, breakloose and/or sustaining forces can be greatly reduced, whereby transition of surfaces from stationary contact to sliding contact occurs without a sudden surge. When breakout or breakloose is complete and the surfaces are in sliding contact, they slide smoothly upon application of very low sustaining force. Substantially less lubricant may be required and lubricant migration is reduced or eliminated. The effect achieved by the system and methods of the present invention can be of long duration, and articles, such as syringes, can retain the advantages of low breakout, breakloose and sustaining forces throughout any parking period. When the surfaces are part of a liquid dispensing device, small highly accurate increments of liquid may be dispensed repeatedly without sudden surges. Thus, a syringe treated according to the method of the invention can be used to administer a medicament to a patient without the danger of surges whereby accurate control of dosage and greatly enhanced patient safety are realized.
Non-limiting examples of articles that can be treated with the coating system of the present invention include articles comprising a first component having a surface in frictional engagement with a surface of a second component, including for example medical devices such as syringe assemblies, syringe pumps, drug cartridges, needleless injectors, liquid dispensing devices and liquid metering devices. In some embodiments, the medical device is a syringe assembly comprising a first component which is a syringe barrel and a second component which is a sealing member.
The first component of the coating system can be formed from glass, metal, ceramic, plastic, rubber or combinations thereof. In some embodiments, the first component is prepared from one or more olefinic polymers, such as polyethylene, polypropylene, poly(1-butene), poly(2-methyl-1-pentene) and/or cyclic polyolefin. For example, the polyolefin can be a homopolymer or a copolymer of an aliphatic monoolefin, the aliphatic monoolefin preferably having about 2 to 6 carbon atoms, such as polypropylene. In some embodiments, the polyolefin can be basically linear, but optionally may contain side chains such as are found, for instance, in conventional, low density polyethylene. In some embodiments, the polyolefin is at least 50% isotactic. In other embodiments, the polyolefin is at least about 90% isotactic in structure. In some embodiments, syndiotactic polymers can be used. A non-limiting example of a suitable cyclic polyolefin includes an ethylene-norbornene copolymer such as TOPAS® ethylene-norbornene copolymer commercially available from Ticona Engineering Polymers of Florence, Ky.
The polyolefin can contain a small amount, generally from about 0.1 to 10 percent, of an additional polymer incorporated into the composition by copolymerization with the appropriate monomer. Such copolymers may be added to the composition to enhance other characteristics of the final composition, and may be, for example, polyacrylate, polyvinyl, polystyrene and the like.
In some embodiments, the first component may be constructed of a polyolefin composition which includes a radiation stabilizing additive to impart radiation stability to the container, such as a mobilizing additive which contributes to the radiation stability of the container, such as for example those disclosed in U.S. Pat. Nos. 4,959,402 and 4,994,552, assigned to Becton, Dickinson and Company and both of which are incorporated herein by reference.
The second component can be formed from any material such as is discussed above for the first component, but preferably is formed from an elastomeric material. Elastomers are used in many important and critical applications in medical devices and pharmaceutical packaging. As a class of materials, their unique characteristics, such as flexibility, resilience, extendibility, and sealability, have proven particularly well suited for products such as catheters, syringe tips, drug vial articles, injection sites, tubing, gloves and hoses. Three primary synthetic thermoset elastomers typically are used in medical applications: polyisoprene rubber, silicone rubber, and butyl rubber. Of the three rubbers, butyl rubber has been the most common choice for articles due to its high cleanness and permeation resistance which enables the rubber to protect oxygen- and water-sensitive drugs.
Suitable butyl rubbers useful in the method of the present invention include copolymers of isobutylene (about 97-98%) and isoprene (about 2-3%). The butyl rubber can be halogenated with chlorine or bromine. Suitable butyl rubber vulcanizates can provide good abrasion resistance, excellent impermeability to gases, a high dielectric constant, excellent resistance to aging and sunlight, and superior shock-absorbing and vibration-damping qualities to articles formed therefrom.
Other useful elastomeric copolymers include, without limitation, styrene copolymers such as styrene-butadiene (SBR or SBS) copolymers, styrene-isoprene (SIS) block polymers or styrene-isoprene/butadiene (SIBS), in which the content of styrene in the styrene block copolymer ranges from about 10% to about 70%, and preferably from about 20% to about 50%. The rubber composition can include, without limitation, antioxidants and/or inorganic reinforcing agents to preserve the stability of the rubber composition.
In some embodiments, the second component can be a sealing member, such as a stopper, O-ring, plunger tip or piston. Syringe plunger tips or pistons typically are made of a compressible, resilient material such as butyl rubber, because of the vulcanized rubber's ability to provide a seal between the plunger and interior housing of the syringe. Syringe plungers, like other equipment used in the care and treatment of patients, have to meet high performance standards, such as the ability to provide a tight seal between the plunger and the barrel of the syringe.
The coating is applied to at least a portion of at least one surface of the component(s) in frictional engagement with an opposed surface of another component. In some embodiments, at least a portion of at least one surface of the component(s) is coated with the coating. In other embodiments, at least a portion of a surface of the first component and at least a portion of a surface of the second component are coated with the coating. In some embodiments in which the first component is prepared from a non-cyclic polyolefin, the portion of the surface of the first component is uncoated, and the portion of the surface of the second component is coated with the coating. In some embodiments in which the syringe barrel is prepared from polypropylene and the sealing member is prepared from butyl rubber, the surface of the syringe barrel is uncoated and the at least one portion of the surface of the sealing member is coated with the coating. In other embodiments in which the syringe barrel is prepared from polypropylene and the sealing member is prepared from butyl rubber, the at least one portion of the surface of the sealing member can be coated with the coating. Methods for coating the surface(s) are discussed in detail below.
The coating system of the present invention comprises a cured coating prepared from a composition comprising one or more first, curable organopolysiloxane(s) comprising at least two alkenyl groups and one or more second, curable organopolysiloxane(s) comprising at least two polar groups, as described below. As used herein, the term “cure” as used in connection with a composition, e.g., a “cured composition” or a “cured coating” shall mean that at least a portion of the crosslinkable components which form the composition are at least partially crosslinked. As used herein, the term “curable”, as used in connection with a component of the composition, means that the component has functional groups capable of being crosslinked, for example alkenyl groups such as vinyl groups. In certain embodiments of the present invention, the crosslink density of the crosslinkable components, i.e., the degree of crosslinking, ranges from 5% to 100% of complete crosslinking. One skilled in the art will understand that the presence and degree of crosslinking, i.e., the crosslink density, can be determined by a variety of methods, such as dynamic mechanical thermal analysis (DMTA) using a TA Instruments DMA 2980 DMTA analyzer conducted under nitrogen. This method determines the glass transition temperature and crosslink density of free films of coatings or polymers. These physical properties of a cured material are related to the structure of the crosslinked network.
As discussed above, the coating system of the present invention comprises a cured coating prepared from a composition comprising one or more first, curable organopolysiloxane(s) comprising at least two alkenyl groups. Each alkenyl group of the first organopolysiloxane (a) can be independently selected from the group consisting of vinyl, allyl, propenyl, butenyl, pentenyl, hexenyl, heptenyl, octenyl, nonenyl and decenyl. One skilled in the art would understand that the first organopolysiloxane (a) can comprise one or more of any of the above types of alkenyl groups and mixtures thereof. In some embodiments, at least one alkenyl group is vinyl. Higher alkenyl or vinyl content provides more efficient crosslinking.
In some embodiments, the first organopolysiloxane (a) can be represented by the following structural formulae (I) or (II):




wherein R is alkyl, haloalkyl, aryl, haloaryl, cycloalkyl, silacyclopentyl, aralkyl, fluoro, fluoroalkyl, and mixtures thereof; X is about 60 to about 1000, preferably about 200 to about 320; and y is about 3 to about 25. Copolymers and mixtures of these polymers are also contemplated.

Non-limiting examples of useful first organopolysiloxanes (a) include: vinyldimethyl terminated polydimethylsiloxanes; vinylmethyl, dimethylpolysiloxane copolymers; vinyldimethyl terminated vinylmethyl, dimethylpolysiloxane copolymers; divinylmethyl terminated polydimethylsiloxanes; polydimethylsiloxane, mono vinyl, mono n-butyldimethyl terminated; and vinylphenylmethyl terminated polydimethylsiloxanes.
In some embodiments, a mixture of siloxane polymers selected from those of Formulae I and/or II can be used. For example, the mixture can comprise two different molecular weight vinyldimethylsilyl terminated polydimethylsiloxane polymers, wherein one of the polymers has an average molecular weight of about 5,000 to about 25,000 and preferably about 16,000, and the other polymer has an average molecular weight of about 30,000 to about 75,000 and preferably about 38,000. Generally, the lower molecular weight siloxane can be present in amounts of about 20% to about 80%, such as about 60% by weight of this mixture; and the higher molecular weight siloxane can be present in amounts of about 80% to about 20%, such as about 40% by weight of this mixture.
Another non-limiting example of a suitable first organopolysiloxane (a) is (7.0-8.0% vinylmethylsiloxane)-dimethylsiloxane copolymer, trimethylsiloxy terminated, such as VDT-731 vinylmethylsiloxane copolymer which is commercially available from Gelest, Inc. of Morrisville, Pa.
In some embodiments, the first organopolysiloxane (a) can further comprise one or more fluoro groups, such as —F or fluoroalkyl groups such as trifluoromethyl groups.
In some embodiments, the first organopolysiloxane (a) can further comprise one or more alkyl and/or one or more aryl groups, such as methyl groups, ethyl groups or phenyl groups, respectively.
Generally, the viscosity of the alkenyl-substituted siloxanes can range from about 200 to about 1,000,000 cst.
In some embodiments, the first organopolysiloxane (a) comprises about 10 to about 80 weight percent of the composition. In other embodiments, the first organopolysiloxane (a) comprises about 15 to about 50 weight percent of the composition. In other embodiments, the first organopolysiloxane (a) comprises about 20 to about 40 weight percent of the composition.
While not wishing to be bound by any theory, it is believed that the alkenyl functional siloxanes can increase the viscosity of the coating and improve binding between the coating and the coated surface.
The composition also comprises one or more second, curable organopolysiloxane(s) comprising at least two polar groups, the second organopolysiloxane(s) being different from the first organopolysiloxane(s), for example having different types of atom(s) or different numbers of atoms in the respective organopolysiloxanes.
Each polar group of the second organopolysiloxane (b) is independently selected from the group consisting of acrylate, methacrylate, amino, imino, hydroxy, epoxy, ester, alkyloxy, isocyanate, phenolic, polyurethane oligomeric, polyamide oligomeric, polyester oligomeric, polyether oligomeric, polyol, carboxypropyl, and fluoro groups. One skilled in the art would understand that the second organopolysiloxane (b) can comprise one or more of any of the above polar groups and mixtures thereof. Preferably, these organopolysiloxanes are not moisture-curable.
In some embodiments, the polar groups are acrylate groups, for example acryloxypropyl groups. In other embodiments, the polar groups are methacrylate groups, such as methacryloxypropyl groups.
The organopolysiloxane having polar groups can further comprise one or more alkyl groups and/or aryl groups, such as methyl groups, ethyl groups or phenyl groups.
A non-limiting example of a suitable organopolysiloxane (b) is [15-20% (acryloxypropyl)methylsiloxane]-dimethylsiloxane copolymer, such as UMS-182 acrylate functional siloxane which is commercially available from Gelest, Inc. of Morrisville, Pa. Other useful organopolysiloxanes (b) include polyfluoroalkylmethyl siloxanes and fluoralkyl, dimethyl siloxanecopolymers.
In other embodiments, the second organopolysiloxane (b) can be represented by the formula (III):




wherein R1 is selected from the group consisting of acrylate, methacrylate, amino, imino, hydroxy, epoxy, ester, alkyloxy, isocyanate, phenolic, polyurethane oligomeric, polyamide oligomeric, polyester oligomeric, polyether oligomeric, polyol, carboxypropyl, and fluoro groups; and R2 is alkyl, n ranges from 2 to 4, and x is an integer sufficient to give the lubricant a viscosity of about 10 to 2,000,000 cst.

In some embodiments, the second organopolysiloxane (b) comprises about 1 to about 40 weight percent of the composition. In other embodiments, the second organopolysiloxane (b) comprises about 3 to about 20 weight percent of the composition. In other embodiments, the second organopolysiloxane (b) comprises about 1 to about 20 weight percent of the composition.
While not wishing to be bound by any theory, it is believed that the polar siloxanes may be present on top of the coated surface to help reduce the coefficient of friction between the engaged surfaces. Also, after irradiation, it is believed that the viscosity of the polar siloxane may increase and improve the binding of the coating to substrate.
In some embodiments, the composition further comprises one or more organopolysiloxane(s) different from the first and second organopolysiloxanes, for example siloxanes of Formula (IV) shown below, such as alkyl siloxanes, and/or organopolysiloxanes comprising at least two pendant hydrogen groups.
Non-limiting examples of such organopolysiloxanes can be represented by the following structural formula (IV):




wherein R is alkyl, haloalkyl, aryl, haloaryl, cycloalkyl, silacyclopentyl, aralkyl and mixtures thereof; and Z is about 20 to about 1,800. In some embodiments, the organopolysiloxanes of Formula (IV) can be represented by the following structural formula (IVA):





wherein Z can be as above, or for example can be about 70 to about 1800 or about 70 to about 1,350. The average molecular weight of the organopolysiloxane of Formula (IV) can be about 1900 to about 100,000, and preferably about 5,000 to about 100,000. Generally, this corresponds with a viscosity of about 20 to about 300,000 centistokes (cst).

A non-limiting example of a suitable alkyl organosiloxane is polydimethylsiloxane. The viscosity of the alkyl organosiloxane can range from about 100 to about 1,000,000 cst, and in some embodiments can range from about 12,500 to about 100,000 cst. In some embodiments, the alkyl organosiloxane comprises about 1 to about 20 weight percent of the composition. In other embodiments, the alkyl organosiloxane comprises about 1 to about 10 weight percent of the composition. In other embodiments, the alkyl organosiloxane comprises about 1 to about 5 weight percent of the composition.
Non-limiting examples of suitable organopolysiloxanes comprising at least two pendant hydrogen groups include organopolysiloxanes having pendant hydrogen groups along the polymer backbone or terminal hydrogen groups. In some embodiments, the organopolysiloxane can be represented by the following structural formulae (V):




wherein p is about 8 to about 12, for example about 10. In other embodiments, the organopolysiloxane can be represented by the following structural formula (VI):

HMe2SiO(Me2SiO)pSiMe2H  (VI)

wherein p is about 140 to about 170, for example about 150 to about 160. A mixture of these polymers can be used comprising two different molecular weight materials. For example, about 2% to about 5% by weight of the mixture of a trimethyl silyl terminated polymethylhydrogensiloxane having an average molecular weight of about 400 to about 7,500, for example about 1900, can be used in admixture with about 98% to about 95% of a dimethylhydrogen silyl-terminated polymethylhydrogensiloxane having an average molecular weight of about 400 to about 37,000 and preferably about 12,000. In some embodiments, the mole ratio of vinyl groups to hydrogen groups in the reactive component is about 0.010:1 to about 0.20:1. In some embodiments, the mole ratio of hydrogen groups of the crosslinking polymer to hydrogen groups of the chain-extending polymer is about 5.0:1 to about 20:1. Non-limiting example of useful organopolysiloxanes comprising at least two pendant hydrogen groups include dimethylhydro terminated polydimethylsiloxanes; methylhydro, dimethylpolysiloxanecopolymers; methylhydro terminated methyloctyl siloxane copolymers; and methylhydro, phenylmethyl siloxane copolymers.

In some embodiments, the hydrogen organopolysiloxane can further comprise one or more fluoro groups, such as —F or fluoroalkyl groups such as trifluoromethyl groups.
In some embodiments, the hydrogen organopolysiloxane can further comprise one or more alkyl and/or one or more aryl groups, such as methyl groups, ethyl groups or phenyl groups, respectively.
Generally, the viscosity of the hydrogen organopolysiloxane can range from about 100 to about 1,000,000 cst.
In some embodiments, the hydrogen organopolysiloxane comprises about 1 to about 40 weight percent of the composition. In other embodiments, the hydrogen organopolysiloxane comprises about 5 to about 30 weight percent of the composition. In other embodiments, the hydrogen organopolysiloxane comprises about 10 to about 30 weight percent of the composition.
In some embodiments, the composition is essentially free of moisture-curable siloxanes, for example a moisture-curable siloxane comprising at least two hydroxyl groups, such as for example:




wherein R2 is alkyl, n ranges from 2 to 4, and x is an integer sufficient to give the lubricant a viscosity of about 10 to 2,000,000 cst. Other moisture-curable siloxanes which have moisture-curing character as a result of functionality include siloxanes having functional groups such as: alkoxy, aryloxy; oxime; epoxy; —OOCR13, N,N-dialkylamino; N,N-dialkylaminoxy; N-alkylamido; —O—NH—C(O)—R13; —O—C(═NCH3)—NH—CH3, —O—C(CH3)═CH2; and —S—C3H6Si(OCH3)3; wherein R13 is H or hydrocarbyl. As used herein, “moisture-curable” means that the siloxane is curable at ambient conditions in the presence of atmospheric moisture. As used herein, “essentially free of moisture-curable siloxanes” means that the composition includes less than about 5 weight percent of moisture-curable siloxanes, in some embodiments less than about 2 weight percent, and in other embodiments is free of moisture-curable siloxanes.

In accordance with the methods of the invention, surfaces which have a sliding relationship with each other are treated with the coating system of the present invention which is cured. The coating system of the invention may be applied to any surface which slides in contact with another surface. Application of a film of coating to the sliding surfaces may be accomplished by any suitable method, as, for example, dipping, brushing, spraying and the like. The lubricant may be applied neat or it may be applied in a solvent, such as low molecular weight silicone, non-toxic chlorinated or fluorinated hydrocarbons, for example, 1,1,2-trichloro-1,2,2-trifluoroethane, freon or conventional hydrocarbon solvents such as alkanes, toluene, petroleum ether and the like where toxicology is not considered important. The solvent is subsequently removed by evaporation. The lubricant film may be of any convenient thickness and, in practice, the thickness will be determined by such factors as the viscosity of the lubricant and the temperature of application. For reasons of economy, the film preferably is applied as thinly as practical, since no significant advantage is gained by thicker films.
The inventive compositions can be fully cured after application or partially cured to attach them to the substrate, and then fully cured at a later time. For example, air drying will permit partial cure. The compositions are initially fluid and can be applied directly to the substrate in any suitable manner, for example by dipping, brushing or spraying. The exact thickness of the coating does not appear to be critical and very thin coatings, e.g., one or two microns exhibit effective lubricating properties. While not necessary for operability, it is desirable that the thickness of the coating be substantially uniform throughout.
Curing of the reactive portion can be accomplished by conventional methods well known in the art. For example, curing by use of a catalyst, heat curing via oven or radio frequency (RF) are useful methods as well as the use of gamma, e-beam or ultraviolet radiation. Any mechanism which will initiate the hydrosilylation reaction is a useful curing technique.
In some embodiments, the coating is at least partially cured by irradiation with an isotope or electron beam. Radiation sterilization in the form of ionizing radiation commonly is used in hospitals for medical devices such as catheters, surgical items and critical care tools. Gamma irradiation is the most popular form of radiation sterilization and typically is used when materials are sensitive to the high temperature of autoclaving but are compatible with ionizing radiation. The bactericidal effect of gamma irradiation exerts its microbicidal effect by oxidizing biological tissue, and thus provides a simple, rapid and efficacious method of sterilization. Gamma rays are used either from a cobalt-60 (60Co) isotope source or from a machine-generated accelerated electron source. Sufficient exposures are achieved when the materials to be sterilized are moved around an exposed 60Co source for a defined period of time. The most commonly used validated dose for sterilizing medical devices is about 10 to about 100 kGy, for example 20-50 kGy.
In some embodiments, the composition further comprises a catalytic amount of a catalyst for promoting crosslinking of the first organopolysilaxane (a) and the second organopolysiloxane (b). Non-limiting examples of suitable catalysts for promoting heat cure include platinum or rhodium group metal catalysts, such as Karstedt catalyst Pt2{[(CH2═CH)Me2Si]2O}3 or peroxide catalysts, such as dicumyl peroxide The catalyst can be present in an amount ranging from about 0.001 to about 0.05 weight percent of the composition.
In the case of oven curing, temperatures should range from about 150° to about 180° C. and residence time in the oven is generally about 30 to about 40 seconds, depending on the precise formulation. If RF techniques are used, the coil should conduct enough heat to obtain a substrate surface temperature of about 180° to about 240° C. At these temperatures, only about 2 to about 4 seconds are required for cure. If gamma radiation techniques are used, the need for hydrosilylation initiating catalyst is eliminated, since the radiation will start the cure. This technique has the advantage of sterilizing as well, which is useful in medical applications.
In some embodiments, the coated articles are subjected to a sterilization treatment. Many sterilization techniques are available today to sterilize medical devices to eliminate living organisms such as bacteria, yeasts, mold and viruses. Commonly used sterilization techniques used for medical devices include autoclaving, ethylene oxide (EtO) or gamma irradiation, as well as more recently introduced systems that involve low-temperature gas plasma and vapor phase sterilants.
One common sterilization technique is steam sterilization or autoclaving, which is a relatively simple process that exposes a device, for example, to saturated steam at temperatures of over 120° C. for a minimum of twenty minutes at a pressure of about 120 kPa. The process is usually carried out in a pressure vessel designed to withstand the elevated temperature and pressure to kill microorganisms by destroying metabolic and structural components essential to their replication. Autoclaving is the method of choice for sterilization of heat-resistant surgical equipment and intravenous fluid as it is an efficient, reliable, rapid, relatively simple process that does not result in toxic residues.
Thus, in some embodiments, the present invention provides a method for lubricating the interface between a first component having a surface in frictional engagement with a surface of a second component, comprising the steps of: (a) applying a coating system according to claim 1 to at least a portion of at least one surface of the component(s) to form a coating upon the portion of the surface; and (b) irradiating the coating of step (a) to at least partially cure the coating.
In other embodiments, the present invention provides a method for reducing breakout force of a surface adapted for slidable engagement with another surface comprising: (a) applying a coating system according to claim 1 to at least a portion of at least one surface to form a coating upon the portion of the surface; and (b) irradiating the coating of step (a) to at least partially cure the coating.
In other embodiments, the present invention provides a method for reducing sustaining force of a surface adapted for slidable engagement with another surface comprising: (a) applying a coating system according to claim 1 to at least a portion of at least one surface to form a coating upon the portion of the surface; and (b) irradiating the coating of step (a) to at least partially cure the coating.
In other embodiments, the present invention provides a method for reducing breakout and sustaining forces of slidable surfaces in the interior of a syringe assembly comprising: (a) applying a coating system according to claim 1 to the interior wall of the syringe barrel to form a coating thereon; and (b) irradiating the coating of step (a) to at least partially cure the coating.
Breakout forces, breakloose forces and sustaining forces may be conveniently measured on a universal mechanical tester or on a testing machine of the type having a constant rate of cross-head movement, as, for example an Instron model 1122, as described in detail below.
The present invention is more particularly described in the following examples, which are intended to be illustrative only, as numerous modifications and variations therein will be apparent to those skilled in the art.
EXAMPLES
Example 1
In this example, 10 ml syringe components were coated with a conventional polydimethylsiloxane or a coating composition according to the present invention, subjected to irradiation, and evaluated for breakloose force and infusion pump actuation force (sticktion) relating to pump performance.
Each syringe barrel was lubricated with a conventional polydimethylsiloxane having a viscosity of 12,500 cst. Helvoet FM457 butyl rubber syringe stoppers were coated with a conventional polydimethylsiloxane having a viscosity of 100,000 cst (“Control”) or a coating composition according to the present invention (“Formulation A”) consisting of 20 weight percent of VDT-731 (7.0-8.0% vinylmethylsiloxane)-dimethylsiloxane copolymer, trimethylsiloxy terminated, available from Gelest, Inc. of Morrisville, Pa., 5 weight percent of UMS-182 [15-20% (acryloxypropyl)methylsiloxane]-dimethylsiloxane copolymer, available from Gelest, Inc., and 75 weight percent of DC 360 polydimethylsiloxane having a viscosity of about 100,000 cst, available from NuSil.
Each component was irradiated with cobalt at 45 kGy. Each syringe was assembled and filled with 10 ml of saline solution available from VWR Products and autoclaved at 124° C. for 30 minutes.
The breakloose force (in Newtons) of each sample syringe to simulate fast speed injection was determined by an Instron Model No. 1122 in compression (injection) mode using a 50 kg compression load cell at a cross head speed of 100 mm/min. The breakloose force is visually determined as the highest peak of the curve or point of where the slope of the curve changes on the graph. The minimum sustaining force is determined as the lowest or smooth section of the curve after the breakloose force. The maximum sustaining force is determined as the highest section of the curve after the breakloose force. The values reported in Table 1 below are the average of five samples for each of Sample A (coated with Formulation A) and the Control.
The infusion pump actuation force and fluid delivery characteristics for each test syringe were evaluated using a Becton Dickinson Program 2 eight pump data acquisition system. Each syringe is filled with 10 ml of Deionized water. All air bubbles in the syringe were removed and the plunger rod was advanced until the sealing rib of the stopper coincided with the desired test volume marking on the scale. Microbore tubing (0.020′′ ID×60′′ length) was connected to the syringe and the other end was connected to a 23 gauge×1 inch length needle. The needle was inserted into a beaker. The tubing set was manually filled with water from the syringe and the syringe was mounted in the pump. The flange of the barrel contected the front of the flange slot. The syringe plunger rod was positioned against the syringe pusher. There was no gap between the load cell and the plunger rod. The pump was purged by setting the flow rate at the maximum speed allowed by the pump. Once fluid is flowing freely through the tubing and needle into the beaker, the specified flow rate was set on the pump and infusion was begun. A chart of force over time for each syringe was generated, as shown in FIGS. 1-3. A visual determination of sticktion or no sticktion was made by viewing each chart for the smoothness of the curve. A smooth curve indicated no sticktion and an irregularly-shaped curve (for example with discernable peaks) indicated sticktion.










TABLE 1







Sample A
Control


















Breakloose Force
23 ± 1
36 ± 1


(N)










Pump Actuation
 1.0 ml/hr: no sticktion
1.0 ml/hr:
no sticktion


Force
10.0 ml/hr: no sticktion
10.0 ml/hr:
sticktion









As shown in Table 1 above, Sample A coated with a coating system according to the present invention exhibit lower breakloose force and reduced sticktion, even at 10.0 ml/hr pumping conditions.
Example 2
In this example, 10 ml syringe components were evaluated in the same manner as in Example 1 above, however the syringe barrel was formed from cyclic polyolefin. Both the stopper and barrel were coated as in Example 1 and each component was irradiated with cobalt at 20 kGy. Each syringe was assembled and filled with 10 ml of deionized water and autoclaved at 124° C. for 30 minutes. The test results reported in Table 2 below are an average of the test results for five samples each. The infusion pump actuation force test results are shown in FIGS. 4-6.










TABLE 2







Sample A
Control


















Breakloose Force
15 ± 1
49 ± 1


(N)










Pump
0.1 ml/hr: no sticktion
0.1 ml/hr:
sticktion


Performance
1.0 ml/hr: no sticktion
1.0 ml/hr:
no sticktion



10.0 ml/hr: no sticktion 
10.0 ml/hr:
sticktion









As shown in Table 2 above, Sample A coated with a coating system according to the present invention exhibit lower breakloose force and reduced sticktion at 0.1 ml/hr pumping conditions.
Example 3
In this example, 10 ml syringe components were evaluated in the same manner as in Example 1 above, the syringe barrel being formed from the cyclic polyolefin. Each stopper was coated with 100,000 cst polydimethylsiloxane. Each barrel was coated with a coating of Formulation B consisting of 20 weight percent of VDT-731 (7.0-8.0% vinylmethylsiloxane)-dimethylsiloxane copolymer, trimethylsiloxy terminated, 10 weight percent of UMS-182 [15-20% (acryloxypropyl)methylsiloxane]-dimethylsiloxane copolymer, and 70 weight percent of DC 360 polydimethylsiloxane having a viscosity of about 100,000 cst (“Sample B”); or Formulation C consisting of 20 weight percent of VDT-731 (7.0-8.0% vinylmethylsiloxane)-dimethylsiloxane copolymer, trimethylsiloxy terminated, 20 weight percent of UMS-182 [15-20% (acryloxypropyl)methylsiloxane]-dimethylsiloxane copolymer, and 60 weight percent of DC 360 polydimethylsiloxane having a viscosity of about 100,000 cst (“Sample C”). Each component was irradiated with cobalt at 20 kGy. Each syringe was assembled and filled with 10 ml of deionized water and autoclaved at 124° C. for 30 minutes. The test results reported in Table 3 below are an average of the test results for five samples each. The infusion pump actuation force test results are shown in FIGS. 7-12.










TABLE 3







Sample B
Sample C


















Breakloose Force
16 ± 1
15 ± 1


(N)










Pump
0.1 ml/hr: no sticktion
0.1 ml/hr:
no sticktion


Performance
1.0 ml/hr: no sticktion
1.0 ml/hr:
no sticktion



10.0 ml/hr: no sticktion 
10.0 ml/hr:
sticktion









As shown in Table 3 above, Samples B and C coated with a coating system according to the present invention exhibit low breakloose force and no sticktion at 0.1, 1.0 and 10 ml/hr pumping conditions.
Example 4
In this example, 10 ml syringe components were evaluated in the same manner as in Example 1 above, the syringe barrel being formed from polypropylene. Each stopper was coated with 100,000 cst polydimethylsiloxane. Each barrel was coated with a coating of a formulation as shown in Table 4. Sample Ref. 1-3 were each coated with polydimethylsiloxane having the respective viscosities indicated in Table 4. Samples A-I, E2 and F2 were coated with compositions including VDT-731 (7.0-8.0% vinylmethylsiloxane)-dimethylsiloxane copolymer, trimethylsiloxy terminated, and/or UMS-182 [15-20% (acryloxypropyl)methylsiloxane]-dimethylsiloxane copolymer, and DC 360 polydimethylsiloxane having a viscosity as indicated in Table 4. Each component was irradiated with cobalt at a dosage specified in Table 4. Each syringe was assembled and filled with 10 ml of deionized water and autoclaved at 124° C. for 30 minutes. The test results reported in Table 4 below are an average of the test results for five samples each.
As shown in Table 4, Samples E, F, E2 and F2 according to the present invention had low breakloose and sustaining forces. Also, Samples E and F had no sticktion at a pump rate of 10 ml/hr.









TABLE 4









Sample ID






















Ref
Ref
Ref














1
2
3
A
B
C
D
E
F
G
H
I
E2
F2











Formulation





















DC 360,

100


25
50
75
75
50
95
90
85




1,000 Cst


DC 360,


12,500 Cst


DC 360,
100

100









75
50


100,000 Cst


VDT-731



100
75
50
25
20
40



20
40


(Vinyl)


UMS-182







5
10
5
10
15
5
10


(Acrylate)







Radiation





















Dose, kGy
0
45
45
45
45
45
45
45
45
45
45
45
45
45







Functional Test





















Breakout
33/1  
24/3  
36/0.8
39/2  
44/3  
41/2  
45/3  
27/4  
25/2
33/3  
30/2  
32/1
23/0.8
34/2  


force, N


Sustaining
5/0.2
5/0.3
 7/0.6
8/0.5
7/0.3
6/0.2
7/0.2
5/0.4
 6/1
5/0.5
4/0.5
 5/1
 6/0.6
6/0.4


force, N







Pump Test (sticktion: Yes or No)





















10 mL/hr
Y
Y
Y


Y

Y
Y
Y
Y
Y
N
N


Sustaining







(reduced)
(reduced)


force, N


1.0 mL/hr












N
N


Sustaining


force, N









The present invention has been described with reference to specific details of particular embodiments thereof. It is not intended that such details be regarded as limitations upon the scope of the invention except insofar as and to the extent that they are included in the accompanying claims.

## Claims

1. A coating system for an article comprising a first component having a surface in frictional engagement with a surface of a second component, wherein at least a portion of at least one surface of the component(s) is coated with a coating prepared from a composition comprising:
(a) a first, curable organopolysiloxane comprising at least two alkenyl groups; and
(b) a second, curable organopolysiloxane comprising at least two polar groups, the second organopolysiloxane being different from the first organopolysiloxane, each polar group of the second organopolysiloxane (b) being independently selected from the group consisting of acrylate and methacrylate.

2. The coating system according to claim 1, wherein the article is a medical device selected from the group consisting of syringe assemblies, syringe pumps, drug cartridges, needleless injectors, liquid dispensing devices and liquid metering devices.

3. The coating system according to claim 2, wherein the medical device is a syringe assembly comprising a first component which is a syringe barrel and a second component which is a sealing member.

4. The coating system according to claim 1, wherein the first component is formed from glass, metal, ceramic, plastic, rubber or combinations thereof.

5. The coating system according to claim 4, wherein the first component is prepared from an olefinic polymer.

6. The coating system according to claim 5, wherein the olefinic polymer is selected from the group consisting of polyethylene, polypropylene, poly(1-butene), poly(2-methyl-1-pentene) and cyclic polyolefins.

7. The coating system according to claim 1, wherein the second component is a sealing member selected from the group consisting of a stopper, O-ring, plunger tip and piston.

8. The coating system according to claim 1, wherein the second component is prepared from a rubber material.

9. The coating system according to claim 8, wherein the rubber material is butyl rubber.

10. The coating system according to claim 1, wherein at least a portion of a surface of the first component and at least a portion of a surface of the second component are coated with the coating according to claim 1.

11. The coating system according to claim 1, wherein the first component is prepared from a non-cyclic polyolefin, the portion of the surface of the first component is uncoated, and the portion of the surface of the second component is coated with the coating according to claim 1.

12. The coating system according to claim 1, wherein each alkenyl group of the first organopolysiloxane (a) is independently selected from the group consisting of vinyl, allyl, propenyl, butenyl, pentenyl, hexenyl, heptenyl, octenyl, nonenyl and decenyl.

13. The coating system according to claim 1, wherein at least one alkenyl group of the first organopolysiloxane (a) is vinyl.

14. A coating system for an article comprising a first component having a surface in frictional engagement with a surface of a second component, wherein at least a portion of at least one surface of the component(s) is coated with a coating prepared from a composition comprising:
(a) a first, curable organopolysiloxane comprising at least two alkenyl groups; and
(b) a second, curable organopolysiloxane comprising at least two polar groups, the second organopolysiloxane being different from the first organopolysiloxane, wherein the first organopolysiloxane (a) is (7.0-8.0% vinylmethylsiloxane)-dimethylsiloxane copolymer, trimethylsiloxy terminated.

15. The coating system according to claim 1, wherein the first organopolysiloxane (a) comprises about 10 to about 80 weight percent of the composition.

16. A coating system for an article comprising a first component having a surface in frictional engagement with a surface of a second component, wherein at least a portion of at least one surface of the component(s) is coated with a coating prepared from a composition comprising:
(a) a first, curable organopolysiloxane comprising at least two alkenyl groups; and
(b) a second, curable organopolysiloxane comprising at least two polar groups, the second organopolysiloxane being different from the first organopolysiloxane, wherein the organopolysiloxane (b) is [15-20% (acryloxypropyl)methylsiloxane]-dimethylsiloxane copolymer.

17. The coating system according to claim 1, wherein the second organopolysiloxane (b) comprises about 1 to about 40 weight percent of the composition.

18. The coating system according to claim 1, wherein the composition further comprises an organopolysiloxane selected from the group consisting of an alkyl siloxane and an organopolysiloxane comprising at least two pendant hydrogen groups, the organopolysiloxane being different from the first and second organopolysiloxanes.

19. The coating system according to claim 1, wherein the coating is at least partially cured by irradiation with an isotope or electron beam.

20. The coating system according to claim 1, wherein the composition is essentially free of moisture-curable siloxanes.

21. The coating system according to claim 20, wherein the moisture-curable siloxane comprises at least two hydroxyl groups.