Patent Application
20150128329
1. Field of the Invention
Embodiments of the present invention generally relate to polymeric compositions and articles made therefrom and, more particularly, to elastomeric articles having improved physical properties and methods of fabricating such articles.
2. Description of the Related Art
Latex, elastomeric, or polymeric formulations are used to make flexible products having barrier properties. Such articles, for example, elastomeric articles, include condoms and gloves. Gloves are used in many industries, such as construction, industrial, and medical, as well as households, to protect the hands of users. Many such gloves comprise synthetic or natural latex or thermoplastic elastomers, such as nitrile butadiene rubber, polychloroprene, or polyurethanes.
For medical applications, such as examination and surgical gloves, gloves promote protection against germs, viruses, and microbes. Particularly for surgical gloves, it is important that the gloves have high resistance to tears, such as can be caused by tensile forces, abrasions, and the like during procedures in which scalpels, forceps, scissors, hemostats, and the like are used. However, gloves made from synthetic polyisoprene are relatively weaker than gloves made from natural rubber latex, i.e., of the Hevea brasiliensis or guayule origin, and are susceptible to breaches during use and particularly extended use, increasing the risk of infection from doctor to patient and vice versa. As a consequence, healthcare personnel must double glove, i.e., don two gloves on each hand for procedures, which leads to a loss in tactile sensitivity and adds expense to surgical procedures. Moreover, wearing two gloves can tire medical personnel because of the need to overcome the stiffness of both gloves and decreases dexterity.
Also, elastomeric articles that are thin and flexible are more comfortable to users. However, the thinness and flexibility of elastomeric articles, such as gloves and condoms, comes at the expense of tear resistance properties.
Attempts to strengthen the physical properties of polyisoprene for elastomeric articles have largely failed. For example, various accelerators, have been used in rubber formulations to improve abrasion- and tear-resistance. However, high levels of thioureas have strong, undesirable odors and, moreover, some of these additives, such as thioureas, diphenyl guanidine (DPG), and/or casein, which is a stabilizer, are carcinogens and/or allergens. Although DPG provides curing and scorch times that are generally longer than other accelerators, the reaction is nonetheless too quick. Additionally, the use of DPG as an accelerator and casein as a stabilizer in polymeric, elastomeric, or latex compositions is considered to have a Human Health risk characterization ratio >1 as per REACH-CLP unit. Accordingly, a casein and/or DPG-free glove is desirable for health-related concerns. Moreover, high amounts of thioureas produce malodorous compositions and are allergenic. Also, curing and scorch times, periods during which rubber compositions can be worked before curing begins, are short.
Therefore, polymeric, elastomeric, or latex compositions, which can be used to make thin, flexible elastomeric articles, having improved tensile strength, tear- and abrasion-resistance, and processes capable of producing thin, flexible elastomeric articles having improved tensile strength, as well as abrasion- and/or tear-resistance, represent an advance in the art.
A glove, including a polymeric, elastomeric, or latex composition, having a water-based emulsion of a polyisoprene polymer; a first accelerator comprising at least one of a thiourea, a benzothiazole sulphenamide, a thiazole, or a dialkyl dithiocarbamate, or combinations thereof, a second accelerator comprising a thiuram or a xanthogen, or a combination thereof, at least one anti-oxidant, at least one vulcanizing agent; and an activator, wherein a total amount of the first accelerator and the second accelerator ranges from 0.2 to 2.5 PHR of the polymeric, elastomeric, or latex composition and the polymeric, elastomeric, or latex composition is substantially free of diphenyl guanidine and/or casein, are disclosed and/or described in connection with at least one of the figures disclosed herein, as set forth more completely in the claims. Various advantages and features of the present invention will be more fully understood from the following description and drawings.
So that the manner in which the above recited features of the present invention can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only illustrative embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments. It is to be understood that elements and features of one embodiment may be in other embodiments without further recitation. It is further understood that, where possible, identical reference numerals have been used to indicate comparable elements that are common to the figures.
Embodiments of the present invention comprise polymeric, elastomeric, and/or latex compositions, from which elastomeric articles, such as supported gloves, unsupported gloves, and condoms, are formed. Embodiments according to the present invention further comprise methods for compounding compositions and for fabricating such articles having improved physical properties, particularly gloves and condoms, having enhanced physical properties, such as substantially enhanced unaged and aged tensile properties, as well as tear resistance. The compositions, in accordance with embodiments of the invention, comprise novel polymeric, elastomeric, and/or latex compositions that are DPG and casein free.
The polymeric, elastomeric, and/or latex composition comprises, for example, natural or synthetic polyisoprenes. For example, synthetic, water-based polyisoprene emulsions, such as a KRATON® IR401 formulation materials, which have a high-cis 1,4 content and a high degree of linearity, such as blends comprising polybutadiene and polystyrene. In some embodiments of the invention, the polymeric, elastomeric, or latex composition includes styrenic block copolymers of polybutadiene, and polyisoprene also sold under the brand KRATON®.
Embodiments according to the invention also comprise, for e.g., at least one of naturally occurring polyisoprenes, synthetic cis 1,4-polyisoprene, carboxylated acrylonitrile butadiene, non-carboxylated acrylonitrile butadiene, nitrilebutadiene, polychloroprene, polyvinyls, butyl latex, styrene-butadiene (SBR), styrene-butadiene latex, styrene-isoprene-styrene (SIS), styrene-ethylene/butylene-styrene (SEBS), styrene-acrylonitrile (SAN), polyethylene-propylene-diene, waterbased polyurethane, solvent-based polyurethane, or combinations or blends thereof.
Furthermore, natural and synthetic isoprene latexes, inherently, produce flocculations, which are agglomerations of polymeric particles. The agglomeration of the particles prevents a uniform and complete vulcanization of the composition. Without intending to be bound by theory, it is believed that conventional rubber accelerators typically used in the pre-vulcanization of natural rubber and other synthetic rubber lattices, for example, DPG with casein as a stabilizer, promote the fast vulcanization of the agglomerated polymeric particles so that external portions are vulcanized while internal portions remain un-vulcanized (because once the external portions are vulcanized, sulfur or other crosslinking agents cannot penetrate the vulcanized external portions to reach the internal portions), causing a drop in overall intra- and inter-molecular crosslinking and therefore produces sub-optimal physical properties.
The polymeric, elastomeric, and/or latex compositions according to the invention further comprise additives, such as sulfur and zinc oxide, which provide chemical reactions for crosslinking the isoprene molecules.
Embodiment according to the invention further comprise polymeric, elastomeric, and/or latex compositions having at least two accelerator groups, of which a first accelerator is at least one of thioureas, thiazoles, and dialkyl dithiocarbamates, or combinations thereof; while a second accelerator comprises thiurams and xanthogens, or combinations thereof. For example, polymeric, elastomeric, or latex compositions comprise wherein the total amount of accelerators range from 0.2% to 2.5% by weight based on dry weight of polymer (PHR, parts per hundred rubber) of which thioureas comprise between 0.2-0.4% PHR.
Dialkyl dithiocarbamates according to the invention comprise sodium dimethyldithiocarbamate, zinc dimethyldithiocarbamate, zinc diethyl dithiocarbamate, zinc dibutyldithiocarbamate, sodium diethyldithiocarbamate, sodium dibutyldithiocarbamate, zinc dibenzyldithiocarbamate and combinations thereof.
Thiurams according to the invention comprise tetramethyl thiuramdisulfide, tetraethyl thiuramdisulfide, tetrabutyl thiuramdisulfide, dipentamethylene thiuramtetrasulfide and combinations thereof.
Xanthogens according to the invention comprise diisopropyl xanthogen polysulfide, dihydrocarbyl xanthogen polysulfide, dibutyl xanthogen polysulfide, and combinations thereof.
Thiazoles according to the invention comprise mercaptobenzothiazole, zinc mercaptobenzothiazole, dibenzothiazyl disulphide, N-cyclohexyl sulphenamido-2-benzothiazole, N-tert-butyl sulphenamide-2-benzothiazole (TBBS), N-morpholino-thio-2-benzothiazole, and combinations thereof.
Thioureas according to the invention comprise N,N′-diphenyl thiourea (DPTU), N-phenyl-N-cyclohexylthiourea, N-phenyl-N-alpha-phenylethylthiourea, N-phenyl-N′-ethylthiourea, N-para-methoxyphenyl N′-ethylthiourea, and combinations thereof.
The use of low amounts of a thiazole and a thiourea accelerator in combination in polymeric, elastomeric, and/or latex compositions provides a particularly long scorch time. In this context, a low amount means wherein the total amount of accelerators range from 0.2% to 2.5% PHR. Also, a comparatively longer composition pot life is possible when DPG, with milk casein as a stabilizer, is not used, thereby increasing the operating window of the composition during processing to manufacture elastomeric articles therewith.
Without intending to be limited by the theory or mechanism of operation, it is believed that the novel use of a thiazole and a thiourea accelerator in combination in low amounts, for example, TBBS and DPTU, slows the pre-curing and vulcanization reaction rates to a level unrealized with previous accelerator combinations, i.e., longer scorch times. Moreover, because the vulcanization is so slowed, a range of polymeric, elastomeric, or latex composition temperatures may be employed. This range of temperatures, such as approximately 20° C. to 35° C., allows the crosslink density to be optionally varied, as needed, to impart different desired physical properties, thereby allowing various compositions to be “tuned” for different service applications. Because the amount of crosslink density can be varied, i.e., physical properties, such as tear resistance, as well as substantially enhanced unaged and aged tensile strength, of the resulting article, e.g., a surgical glove, examination glove, supported glove, condom, or the like, are now possible. It is believed, without being bound by theory, that because DPTU and TBBS slows the vulcanization, longer polysulphide (polysulfide) bonding is created, resulting in higher tensile strength at relatively low crosslink densities.
It is further believed that the film architecture of a polymeric, elastomeric, or latex film, vulcanized using sulfur as a crosslinking agent, is made of sulfur cross links occurring between the polymer molecules within the particles (intra-molecular) as well as between the particles (inter-molecular) due to the mobility of polymeric chains. This results in a partially pre-vulcanized film or coating, which may be formed on a mold, for example, a ceramic mold, i.e., aluminosilicates, glasses, etc., in the shape of a glove or condom, which is dipped into a polymeric, elastomeric, or latex composition. Embodiments according to the invention comprise pre-vulcanizing the polymeric, elastomeric, or latex composition at a range of 20°-35° C. to achieve an acceptable degree of crosslinking, which, in some embodiments according to the invention, requires between 10 and 20 hours. In at least one exemplary embodiment, approximately 20 hours is appropriate.
The film or coating disposed on the mold is post-vulcanized in, for example, an oven ranging in temperature from approximately 110° C. to 130° C. The nature of cross links (short chain mono-, and di- and long-chain polysulphide cross links) as well as types of cross links that form between particles by control, for example, shear control, of degree of pre-vulcanization in polymeric, elastomeric, or latex composition and post processing conditions dictates the film architecture.
Moreover, it is believed that the use of TBBS and DPTU, which provides a long scorch time, as discussed above, also mitigates the vulcanization of the outer portions of polymeric, elastomeric, or latex flocculations (also known as peripheral crosslinking), and thereby promotes the vulcanization of the inner portions of the flocculations, providing a stronger polymeric structure. Furthermore, it is believed that the use of TBBS and DPTU promotes crosslinking while the polymeric, elastomeric, or latex composition ages, resulting in further increases in tensile strength, as opposed to the use of other accelerators, such as DPG, which exhibit a drop in tensile strength during aging. Even further, polymeric, elastomeric, or latex compositions comprising between approximately 0.2 PHR to approximately 2.5 PHR total of a thiazole accelerator and a thiourea accelerator are substantially less malodorous. And, as discussed above, such compositions are also substantially less allergenic.
As can be seen in
The polymeric compositions in
In some embodiments of the invention, the polymeric, elastomeric, and/or latex compositions are foamed, so that air cells dispersed in the range of 5-50 volumetric percentage are formed. When a composition is disposed on a former as a coating, closed cells or open cells may be formed, as is described in commonly-assigned U.S. Pat. Nos. 8,192,834, 8,001,809, and 7,814,571, which are herein incorporated by reference in their entireties. In some embodiments of the invention, the cells are interconnected in the polymeric latex layer. Closed cells provide a liquid proof polymeric latex coating that is highly flexible, soft and spongy, and provides good dry and wet grip. Closed cells, generally, have air content ranging from 5-15 volumetric percent. Open cells, which are interconnected, generally range from approximately 15-50 volumetric percentage range and provide a breathable artile, i.e., a glove, through the foamed polymeric latex layer. This foamed polymeric latex layer may penetrate half or more of the thickness of the knitted liner, though the polymeric latex layer does not penetrate the entire thickness, thereby substantially avoiding strike-through, i.e., skin contact with the polymeric latex.
The polymeric composition may contain additional surfactants such as TWEEN® 20 to stabilize the latex foam. Once the composition is foamed with appropriate air content and the viscosity is adjusted, refinement of the foam is undertaken by using an impeller at a suitable speed as is known to those in the art. Air bubble size may be refined using a different impeller at a reduced speed. The elastomeric coating, irrespective of whether foamed, may be applied by dipping a former, or a former having a knitted liner dressed thereon, into a latex emulsion or spraying the coating onto the liner or, for unsupported gloves, dipping the former directly into the latex emulsion or spraying the former with the latex emulsion.
A process for making a dipped article, in accordance with embodiments of the invention as discussed below, comprises the steps of dipping the former into a coagulant, for example, a strong coagulant, such as calcium nitrate, dipping the former into the polymeric, elastomeric, or latex composition to form a dipped article, such as a surgical or examination glove or condom. In some embodiments of the invention, the former is dipped into a weak coagulant, such as a weak acid, such as an aqueous solution of acetic acid or formic acid. The article may then be optionally dipped into a strong coagulant. Without intending to be bound or limited by theory, it is believed that strong coagulants acting on the outer layers promote the fast gelling of the outer layers, resulting in a case-hardening. A solidified outer surface prevents the coagulant from migrating into the interior of the layer of the film or coating, resulting in the incomplete gelling of the interior. In other words, strong coagulants acting on the outer layer of the film or coating promote the fast gelling of the outer layers, thereby not allowing the coagulant to reach the interior. Therefore, gelling of the interior of, for example, a coating is incomplete. Alternatively, a weak acid promotes the gelling of the interior of film or coating, because a weak acid slowly gels the exterior surface and migrates slowly into the interior of the latex layer, resulting in slower and complete gelling. After dipping in a weak acid, optionally dipping the article into a strong coagulant hardens the exterior surface.
It is further believed that where the interior of the article is allowed to more completely gel, the polymeric molecules get closer and, for example, zinc, zinc oxide, or sulfur crosslinks are enhanced. It is believed that an increase in crosslinking results in significant and unexpected increases in abrasion resistance. As discussed above, in some embodiments of the invention, the application of the weak acid is followed by the application of a strong coagulant, such as 2-15 wt % calcium nitrate aqueous coagulant solution.
The coagulant solution, which destabilizes and coagulates a polymeric, elastomeric, or latex composition, comprises one or more of calcium nitrate, calcium chloride, sodium chloride, potassium chloride, aluminum chloride, aluminum sulfate, and like salts. These coagulants are highly soluble in water and are strong coagulants. Also, water-based, polymeric, coagulant coatings, for coating the former, capable of producing a thickness in the range of about 5 to 50 micrometers on a former, may be used in embodiments of the invention. The polymeric coagulant coating solution possesses adequate former surface-wetting properties and sufficient viscosity or rheology characteristics so as to form a thin layer of polymeric coagulant coating. At least one way to accomplish this is by adding wetting agents and viscosity modifiers to the polymeric coagulant coating solution.
The polymeric coagulant coating dries at a reasonable rate, providing a well-defined operating time period, during which the polymeric coagulant coating remains tacky to accept the application of discrete coagulant particles defining the size, shape and distribution of the desired geometrical texture of the glove surface. One exemplary polymeric coagulant coating solution includes polymers selected from poly N-vinyl-2-pyrrolidone (PVP), polyvinyl alcohol (PVA), polyacrylic acids (PAA), polyacrylamide (PAC), and/or a copolymer or derivative of PVP, PVA, PAA or PAC. The amount of polymer present is in the range of approximately 0.1 to 10 dry weight percent, and in some embodiments of the invention, in the range of about 0.5 to 1.5 dry weight percent, as is described in commonly-assigned U.S. Pat. No. 7,814,570, which is herein incorporated by reference in its entirety.
At step 112, optionally, a decision as to whether to add a colorant is made, such as titanium dioxide, which is added at step 114. The method 100 then proceeds to step 116, at which point one or more accelerators is added, for example, a thiazole and a thiourea. In at least one embodiment according to the invention, the thiazole comprises TBBS and the thiourea comprises DPTU, and may further comprise a dithiocrbamate, such as dipentamethylene thiuramtetrasulfide (DPTT), which are added to the tank and mixed. At step 118, optionally, the above mixture is cooled to, for example, 28-32° C. At step 120, a surfactant is optionally introduced into the mixture. At step 122, optionally, another accelerator, for example, a dithiocarbamate, such as zinc diethyl dithiocarbamate (ZDEC), is mixed into the tank. At step 124, optionally, an alkalized chilled water is mixed into the mixture. At step 126, an anti-oxidant is mixed in and at step 128, a solution of ammonium hydroxide is mixed into the tank. At step 130, the mixture is mixed for a period of time. At step 132, the method 100 ends.
At least one exemplary method for compounding the compositions shown in
In at least one embodiment according to the invention, an appropriate amount of dithiocarbamate, such as at least one of sodium dibutyldithiocarbamate, such as 5% Butyl Namate® or zinc diethyl dithiocarbamate, followed by a xanthogen polysulphide, such as ROBAC AS100, is introduced into the mixing tank. Chilled alkalized water is optionally added to the mixing tank. An antioxidant methylmercaptobenzimidazole dispersion of soft water and ammonia is mixed slowly when the temperature of the composition drops to approximately 22° C. An appropriate amount of a titanium dioxide dispersion, for example, Ralox LC, a potassium caprylate, e.g., Alkon 8627, and/or styrene/maleic anhydride copolymer, esterified with a low molecular weight sec. butyl ester, e.g., Scripset 550 5% solution is introduced to the mixing tank and stirred.
At process step 310, the former having a first elastomeric coating disposed thereon is dipped into a tank having a coagulant, for example, an aqueous solution containing a strong or weak acid for a few seconds to several minutes. In some embodiments of the invention, the weak acid is a solution of acetic acid. At process step 312, the former having the coating disposed thereon is optionally dipped into a strong coagulant such as calcium citrate, calcium nitrate, or another coagulant as is known by those in the art, and removed. At process step 314, it is determined whether to add a second coating of onto the first elastomeric coating. If the answer is yes, the method 300 returns to step 308. Also, either the first of second coating may be foamed or unfoamed, irrespective of whether the first layer is foamed or unfoamed, and vice versa. If no second coating is to be added, the method 300 proceeds to process step 316. At step 316, the glove is optionally leached of impurities and proteins, for example, in an aqueous solution 35-50° C. for approximately 1-3 minutes. At process step 318, the glove is allowed to dry in air. At process step 320, the glove is placed in an oven for curing, for example, at 80-100° C. for 30 to 40 minutes. At process step 322, the method 300 ends.
The use of the terms “a” and “an” and “the” and other referents describing embodiments of the invention are to be construed both in the singular and plural unless otherwise indicated or clearly contradicted by context. Ranges of values herein are merely intended to serve as a shorthand method of referring to each separate value falling within the range; unless otherwise indicated herein, and each range value is incorporated into the specification as if individually recited herein. All methods described herein can be performed in any suitable order unless otherwise indicated herein or clearly contradicted by context. The use of any and all examples, or exemplary language (e.g., “such as”) provided herein, is intended merely to better illustrate the invention and does not pose a limitation on the scope of the invention unless otherwise claimed. No language in the specification should be construed as indicating any non-claimed element as essential to the practice of the invention. While the invention is described herein by way of example using several embodiments and illustrative drawings, those skilled in the art will recognize that the invention is not limited to the embodiments of drawing or drawings described.
The headings used herein are for organizational purposes only and are not meant to be used to limit the scope of the description or the claims. As used throughout this application, the word “may” is used in a permissive sense (i.e., meaning having the potential to), rather than the mandatory sense (i.e., meaning must). Similarly, the words “include,” “including,” and “includes” mean including, but not limited to. The word “glove” means glove or glove liner. The terms dispersion, emulsion, and composition may also be used interchangeably herein.
All ranges recited herein include values therebetween and can be inclusive or exclusive of the endpoints. Optional included ranges are from integer values therebetween (or inclusive of one original endpoint), at the order of magnitude recited or the next smaller order of magnitude. For example, if the lower range value is 0.2, optional included endpoints can be 0.3, 0.4, . . . 1.1, 1.2, and the like, as well as 1, 2, 3 and the like; if the higher range is 8, optional included endpoints can be 7, 6, and the like, as well as 7.9, 7.8, and the like. One-sided boundaries, such as 3 or more, similarly include consistent boundaries (or ranges) starting at integer values at the recited order of magnitude or one lower. For example, 3 or more includes 4 or more, or 3.1 or more.
Although a few exemplary embodiments of the invention have been described in detail above, those skilled in the art will appreciate that many modifications are possible in embodiments without materially departing from the teachings disclosed herein. Any and all such modifications are intended to be included within the embodiments of the invention, and other embodiments may be devised without departing from the scope thereof, and the scope thereof is determined by the following claims. Therefore, it should be understood that the drawings and detailed description thereto are not intended to limit the invention to the particular form disclosed, but on the contrary, the invention is to cover all equivalents and alternatives falling within the spirit and scope of the present invention as defined by the appended claims.
This application claims the benefit of priority to U.S. Provisional Application Ser. No. 61/904,267, filed Nov. 14, 2013, which is incorporated by reference in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| 61904267 | Nov 2013 | US |
