GLOVE
The invention relates to a glove made from a covalently cross-linked elastomer film, which elastomer film contains at least one layered silicate.
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The present application claims priority under 35 U.S.C. §119(a) of Austrian Patent Application No. A 858/2010 filed May 26, 2010, the disclosure of which is expressly incorporated by reference herein in its entirety.
BACKGROUND OF THE INVENTION1. Field of the Invention
The invention relates to a glove made from a covalently cross-linked elastomer film, which elastomer film contains at least one filler, and a method of producing this glove by immersing a glove mold in an immersing bath previously filled with latex, and the latex contains at least one filler.
2. Discussion of Background Information
There is a trend in the examination glove sector in particular—examination gloves are used in industry, in laboratories and also in medicine for example—towards thinner wall thicknesses due to the rising cost of raw materials. However, the protective function of the glove in particular has been affected by the thinner wall thickness. Since the requirements governing chemical protection have also become more stringent in recent years, this trend goes against the needs of the user.
In order to keep the cost of manufacturing such gloves under control, fillers are added to the gloves. Chalk is primarily used for this purpose. Chalk has the property of reducing the strength of the elastomer glove, both immediately after the manufacturing process and after aging, and is also massively detrimental to the capacity to withstand chemicals. Another disadvantage of such gloves is that they tend to turn gray in color after sterilization.
In order to improve the ability of such gloves to withstand chemicals, an approach known from the prior art is to use so-called laminates, in other words to opt for multi-layered glove structures. For example, patent specification US 2005/0044609 A1 describes a glove with a PVC substrate, to which a barrier coating based on an acrylic polymer with a glass transition temperature of between −30° C. and +30° C. is applied in order to improve the chemical permeation coefficient. The disadvantage of such multi-layered structures is that they are also associated with higher manufacturing costs due to the fact that the gloves have to undergo more dipping process.
SUMMARY OF THE EMBODIMENTSAccordingly, the objective of the invention is to propose a thin-walled examination glove which can be manufactured more cost-effectively.
This objective is achieved by the invention on the basis of the glove outlined above in which the filler is a layered silicate, and independently by the method of manufacturing this glove whereby a layered silicate is used as the filler and the filler is converted to an aqueous dispersion before being added to the latex, and also by the use of a filler containing a layered silicate, in particular kaolin, to produce a glove from an elastomer film.
Surprisingly, it has been found that replacing the usual filler of chalk with a layered silicate significantly improves permeation resistance to at least some chemicals. The reason for this probably resides in the fact that a sort of “barrier” can be built up in the glove material itself due to the layered silicate, in other words the individual layers, so that chemicals penetrating the glove material can be held back between these layers more effectively and for a longer time, especially due to the Van der Waals interaction between the atoms of the layers and the atoms of the chemicals. The chemicals penetrating between the layers can cause the layered silicate to swell slightly under certain circumstances so that a slight pressure is introduced into the surrounding elastomer material, thereby slowing down the permeation of these chemicals through the glove material itself. In this respect, it is of advantage if the elastomer molecules are covalently cross-linked with one another so that the elastomer film itself is prevented from swelling, at least for the most part, because the permeation times would otherwise by reduced again due to this increased swelling of the elastomer. With the gloves proposed by the invention, it is therefore possible to manufacture them with slimmer wall thicknesses than those of gloves filled with chalk and the mechanical properties are at least more or less comparable with those filled with chalk. Alternatively, it is possible to obtain higher permeation times whilst retaining the same wall thickness as that of gloves known from the prior art. Also of advantage is the fact that sterilizing the gloves, for example by means of electromagnetic radiation such as electron radiation or gamma radiation, does not cause them to turn gray in color. The filler, i.e. the layered silicate, is preferably converted into an aqueous dispersion before being added to the latex, thereby obtaining a more homogeneous distribution of this filler within the elastomer and in particular avoiding the formation of an agglomerate.
It is preferable if, for a layer thickness of 1 mm, the elastomer film has a permeation resistance in accordance with DIN EN 374-3 of at least 14 minutes, in particular at least 16 minutes, preferably at least 18 minutes, before the solvent isopropanol is broken down.
In particular, the glove may have a layer thickness selected from a range with a lower limit of 0.05 mm and an upper limit of 0.4 mm or selected from a range with a lower limit of 0.1 mm and an upper limit of 0.3 mm.
Based on one variant of the invention, the filler is a clay mineral. The advantage of clay minerals is that they are available more cheaply than synthetically manufactured layered silicates on the one hand, and secondly clay minerals offer an advantage in that they are already available to a large degree in very fine grains, in particular with particle sizes of less than 5 μm, in particular less than 2 μm. This makes it possible to obtain a correspondingly homogeneous, fine distribution of the grains of the filler through the elastomer film.
Particularly good results have been achieved in terms of increasing permeation resistance if the clay mineral used was a mineral selected from a group comprising kaolinite, dickite, nacrite, halloysite, allophane or imogolite or mixtures thereof and the clay mineral used in another embodiment was kaolin and/or talcum. Especially with kaolin, the mechanical properties of the elastomer glove can also be improved, especially with regard to the resistance to tearing and tear propagation of the glove. Using kaolin and/or talcum also reduces the permeability of the glove to gases.
In this respect, it is also of advantage if the kaolin contains a proportion of kaolin of at least 70% by weight, and the rest may be made up of the usual substances which occur in clay minerals, such as quartz or mica-like silicates. The kaolin preferably contains a proportion of kaolin of at least 80% by weight, in particular at least 90% by weight.
The clay mineral may also be hard-calcinated in order to further improve the mechanical properties of the glove.
In a preferred embodiment, the proportion of fillers in the elastomer film is selected from a range with a lower limit of 5 phr and an upper limit of 30 phr (phr: particles per 100 parts rubber). Below 5 phr, an improvement in the permeation resistance was observed but not to the degree desired for the purpose of the invention. With a proportion in excess of 30 phr, the resistance of the glove to tearing decreased so that the advantage of better resistance to chemicals, i.e. greater permeation resistance, does not outweigh the disadvantage of the reduced resistance of the glove to tearing.
In particular, the filler is used in a proportion selected from a range with a lower limit of 10 phr and an upper limit of 25 phr, preferably with a lower limit of 12 phr and an upper limit of 20 phr.
It is also of advantage if the filler is used in particulate form, in which case 50% of the particles have a particle diameter of at most 10 μm in order to obtain a better distribution in the elastomer film.
In particular, it is of advantage if at least 60% of the particles have a particle diameter of at most 10 μm, and more preferably if at least 75% of the particles have a particle diameter of at most 10 μm.
Based on another embodiment, the particle diameter of the biggest particles is at most 30 μm. In practice, it was found that particles with a diameter bigger than 30 μm represent impurities within the elastomer film and thus impair the mechanical properties.
The filler is preferably used in particulate form, in which case the particle diameter of the biggest particles is at most 20 μm, in particular at most 10 μm.
Based on yet another embodiment of the invention, the filler has a volume-specific surface of at most 40 m2/cm3, in particular at most 25 m2/cm3, preferably at most 20 m2/cm3, measured by the BET method (DIN ISO 9277:2003-05). Using fillers with higher volume-specific surfaces causes chemicals or solvents penetrating the elastomer film to bind with the filler to a higher degree, thereby leading to increased swelling of the layered silicate which impairs the mechanical properties, in particular resistance to tearing, especially if higher proportions of filler are used in the elastomer film.
The elastomer film is preferably made from a natural rubber latex because not only can it be produced relatively inexpensively, it also enables a specific interaction (Van der Waal) to be observed between the layered silicates and the natural rubber latex.
As mentioned above, it is of particular advantage if the glove can be made in a single layer from a single elastomer film, thereby resulting in a corresponding cost optimization.
Based on one embodiment of the method, the dispersion is added to the latex prior to the initial cross-linking process, thereby enabling the filler to be incorporated in the elastomer film more effectively.
In order to obtain the highest possible proportion of filler on the elastomer film and thus obtain a correspondingly high increase in permeation resistance, it is of advantage if the initial cross-linking is terminated with a degree of cross-linking of at most 96% (toluene swelling, 20° C., ISO 1817).
In particular, initial cross-linking takes place to a cross-linking degree of at most 85%, preferably to a cross-linking degree of at most 80%, because this enables the filler to be incorporated or embedded in the elastomer matrix more efficiently.
Another option is to bond the filler covalently onto the matrix, e.g. via silanes or such like.
To provide a clearer understanding, the invention will be explained in more detail below with reference to examples.
DETAILED DESCRIPTION OF THE EMBODIMENTSThe particulars shown herein are by way of example and for purposes of illustrative discussion of the embodiments of the present invention only and are presented in the cause of providing what is believed to be the most useful and readily understood description of the principles and conceptual aspects of the present invention. In this regard, no attempt is made to show structural details of the present invention in more detail than is necessary for the fundamental understanding of the present invention, the description taken with the drawings making apparent to those skilled in the art how the several forms of the present invention may be embodied in practice.
All the figures relating to ranges of values in the description should be construed as meaning that they include any and all part-ranges, in which case, for example, the range of 1 to 10 should be understood as including all part-ranges starting from the lower limit of 1 to the upper limit of 10, i.e. all part-ranges starting with a lower limit of 1 or more and ending with an upper limit of 10 or less, e.g. 1 to 1.7, or 3.2 to 8.1 or 5.5 to 10.
The way in which the gloves are manufactured is the same as that known from the prior art except that a layered silicate is used as a filler. Such a glove can therefore be produced by the immersion process described below.
During a compounding step, any chemicals which might be needed for an initial vulcanization step are mixed with the latex and the latex is homogenized if necessary. The optionally pre-vulcanized latex is then transferred to a chain immersion plant where it undergoes the steps of immersion, beading down, wet-leaching, dying, optionally dry-leaching, optionally powdering, drawing, packaging, quality control and optionally sterilization. The immersion molds are cleaned, filled with coagulant and dried before conducting another immersion process.
The immersion molds are usually made from porcelain but may also be made from glass, stainless steel or plastic. A clean surface of the immersion mold is a condition for obtaining a homogeneous deposition of the latex film during the subsequent immersion process. Both basic and acid solutions, oxidizing compounds, surfactants or often a combination of these cleaning chemicals are used to de-grease and clean the immersion molds.
Amongst other things, the composition of the coagulation bath is a parameter which determines the layer thickness of the deposited latex film. The coagulation bath is usually made up of coagulants (usually CaNO3, optionally also CaCl2), separating agent (CaCO3) and wetting agent (cationic surfactants). The separating agent makes it easier to pull the glove off the immersion mold, and in some poweder-free processes, other inorganic salts and to a certain extent polymers may also be used, in a manner known from the prior art.
The positive metal ions deposited on the surface of the immersion mold cause a discharge, followed by coagulation of the negatively stabilized latex as soon as the mold is immersed in the previously cross-linked latex. Different film thicknesses can be obtained depending on the immersion time and concentration of metal ions.
Gloves can be produced with a rolled rim at the bottom shaft end. To this end, a part of the film deposited during beading down is mechanically rolled together by rotating brushes. Due to the stickiness of the film, the rolled beaded edge remains intact during the entire manufacturing process.
Mechanical strength is imparted to the wet latex film by a brief drying process before wet-leaching. Immersing the latex films in a warm (˜50°) water bath causes proteins as well as the coagulant to be washed out.
In order to produce powder-free gloves, a surface treatment may be used instead of powdering, e.g. by chlorination, in order to make the gloves easier to pull on and pull off. However, it would also be possible to use anti-friction coatings.
The immersion process by which gloves are made is known from the prior art and the skilled person is referred to patent specification EP 0 856 294 A for example, in particular FIGS. 4 and 5 of this EP-A and the associated explanations in column 14, line 38 to column 18, line 51, especially the explanations relating to coagulation, immersion in latex, various washing processes, various finishing treatments such as chlorination or halogenation of the surface of the gloves and latex, the process of creating surface roughness and the processing used to obtain powder-free gloves, etc. To avoid unnecessarily repeating what is already known from the prior art in connection with this invention, no further description of this will be given. However, the disclosure of EP 0 856 294 A1 is expressly incorporated by reference herein in its entirety.
As explained above, the core of the invention is the production of gloves with increased permeation resistance to chemicals, i.e. these gloves afford a higher degree of resistance to the migration of chemicals through the elastomer film, thereby increasing the permeation time. This is achieved by using a layered silicate. In this respect, the layered silicate used is a clay mineral in particular, preferably selected from the group comprising kaolinites, dickite, nacrite, halloysite, allophane, imogolite. In particular, the clay mineral used may be kaolin and/or talcum, in which case the proportion of layered silicate filler may be between 5 phr and 30 phr. In the event that pure kaolinite is not used, it is of advantage if the kaolin contains a proportion of kaolin of at least 70% by weight. In addition to improved permeation times, i.e. longer permeation times, these gloves exhibit improved swelling behavior with respect to different solvents, in other words the swelling is less pronounced than is the case with gloves which do not contain the filler proposed by the invention. The permeability of such gloves to gases can also be improved.
It is also possible for the layered silicate to be surface-modified and/or hard-calcinated. For example, the layered silicate may be silanized. By modifying the OH groups with silanes, the interaction with polar rubbers can be influenced. For example, with mono-functional silanes such as triethoxypropyl silane, trimethoxyoctyl silane, triethoxyoctyl silane, a lower viscosity of the latex can be obtained by rendering it hydrophobic, thereby resulting in better film formation. By using bi-functional organo-silanes such as 3-chloropropyltriethoxysilane, to (3-triethoxysiliypropyl)tetrasulfane, triethoxy (3-thiocyanatopropyl)silane, in particular bi-functional organo-silanes with active cross-linking groups (e.g. vinyl or thiol groups), a covalent bonding of the layered silicate on the rubber can be achieved, thereby resulting in higher tensile strength for example.
The layered silicate filler is preferably converted into an aqueous dispersion first of all, and the fillers are used in particulate form in particular and the particle size, i.e. the particle diameter, is preferably selected so that at least 50% have a particle diameter of at most 10 μm and even more preferably the particle diameter of the biggest particles is at most 30 μm. In the context of the invention, however, fine particulate fillers are preferred, i.e. the maximum grain size or maximum particle diameter is less than 30 μm and at least 50% of the particles have a particle diameter of at most 3 μm.
The filler may also have a volume-specific surface corresponding to the values given above.
Before being added to the latex, the filler is preferably dispersed in a solvent, in particular water. This filler dispersion is preferably mixed with the latex before the latter is cross-linked. However, it would also be possible for the dispersion to be added to the mixture after maturing, in other words after the initial cross-linking.
It is also of advantage if the elastomer molecules of a glove proposed by the invention are covalently cross-linked, for example by means of sulfur, peroxides or other materials which lead to cross-linking, because this significantly reduces increased swelling of the film, which means that the permeation can be further improved, in other words the permeation times increased.
It is also of advantage if the initial process of cross-linking the elastomer is not too pronounced before the glove is immersed because this improves formation of the film when using higher filter contents. In particular, initial cross-linking degrees of at most 96% or at most 85%, preferably at most 80%, are preferred.
The degree of cross-linking is defined by the swelling when the filler is mixed in after the initial cross-linking, but if the filler is added prior to cross-linking, the degree of initial cross-linking may also be defined on the basis of the modulus for example.
The following basic formula may be used to produce a glove as proposed by the invention.
Latex: 100 phr Stabilizer: 0.1 phr to 0.5 phrZnO: 0.1 phr to 0.8 phr, preferably 0.3 phr
S: 0.4 phr to 1.2 phr, preferably 0.8 phr
Zinc diethyl dithiocarbamate: 0.1 phr to 1 phr, preferably 0.3 phr
Zinc dibutyl dithiocarbamate: 0.1 phr to 1 phr, preferably 0.2 phr
Zinc-2-mercaptobenzothiazol: 0 phr to 0.2 phr, preferably 0.05 phr
1,3-diphenyl guanidine: 0 phr to 0.5 phr, depending on the temperature of the initial cross-linking. at room temperature, preferably up to 0.2 phr
Anti-aging agent: 0.5 phr to 1.5 phr, preferably 0.8 phr
The stabilizer used may be KOH, for example, or any other stabilizer known from the prior art. Anti-aging agents known from the prior art may also be used.
This mixture is preferably matured, and this maturing process may take place at 30° C. for 24 hours, for example, or at 60° C. for 2 to 4 hours.
The latex used is preferably a natural rubber latex. However, it would also be possible to use other elastomers, e.g. styrene-butadiene rubbers, butadiene rubbers, isobutylene-isoprene rubbers, ethylene-propylene-diene monomers, nitrile-butadiene rubbers, chloroprene rubbers, fluoride rubbers, and mixtures thereof.
The aqueous kaolin dispersion can then be added.
As may be seen from the tables below, using a layered silicate, in particular kaolin, enables the permeation times to be lengthened.
Similar results were obtained with the minerals dickite, nacrite, halloysite, allophane, imogolite, and it should be pointed out that it is generally necessary to use natural substances and substances with a composition corresponding to them may also be used.
The embodiments described as examples represent possible variants of the glove, and it should be pointed out at this stage that the invention is not specifically limited to the variants specifically illustrated, and instead the individual variants may be used in different combinations with one another and these possible variations lie within the reach of the person skilled in this technical field given the disclosed technical teaching.
It is noted that the foregoing examples have been provided merely for the purpose of explanation and are in no way to be construed as limiting of the present invention. While the present invention has been described with reference to an exemplary embodiment, it is understood that the words which have been used herein are words of description and illustration, rather than words of limitation. Changes may be made, within the purview of the appended claims, as presently stated and as amended, without departing from the scope and spirit of the present invention in its aspects. Although the present invention has been described herein with reference to particular means, materials and embodiments, the present invention is not intended to be limited to the particulars disclosed herein; rather, the present invention extends to all functionally equivalent structures, methods and uses, such as are within the scope of the appended claims.
Claims
1. Glove made from a covalently cross-linked elastomer film, which elastomer film contains at least one filler, wherein the filler is a layered silicate.
2. Glove according to claim 1, wherein the elastomer film, having a layer thickness of 1 mm, has a permeation resistance in accordance with DIN EN 374-3 of at least 14 minutes before the solvent isopropanol is broken down.
3. Glove according to claim 1, wherein the at least one filler is a clay mineral.
4. Glove according to claim 3, wherein the clay mineral is selected from a group comprising kaolinite, dickite, nacrite, halloysite, allophane, imogolite
5. Glove according to claim 3, wherein the clay mineral is kaolin and/or talcum.
6. Glove according to claim 5, wherein the kaolin contains at least 70% by weight of kaolinite.
7. Glove according to claim 3, wherein the clay mineral is hard-calcinated.
8. Glove according to claim 1, wherein the filler is used in a proportion selected from a range with a lower limit of 5 phr and an upper limit of 30 phr.
9. Glove according to claim 1, wherein the filler is in particulate form and 50% of the particles have a particle diameter of at most 10 μm.
10. Glove according to claim 9, wherein the particle diameter of the biggest particle is at most 30 μm.
11. Glove according to claim 1, wherein the filler has a volume-specific surface of at most 40 m2/cm3, measured by the BET method.
12. Glove according to claim 1, wherein the elastomer film is made from natural rubber latex.
13. Glove according to claim 1, wherein the elastomer film comprises a single layer.
14. Method of producing a glove according to claim 1 by immersing a glove mold in an immersing bath containing latex, which latex contains at least one filler, wherein a layered silicate is used as the filler and the filler is converted into an aqueous dispersion before being added to the latex.
15. Method according to claim 14, wherein the dispersion is added to the latex prior to the initial cross-linking process.
16. Method according to claim 14, wherein the initial cross-linking process is run to a degree of cross-linking degree of at most 96% (swelling of the toluene).
17. Method of producing an elastomer, comprising:
- supplying a layered silicate as a filler to an elastomer,
- wherein a glove formed from a film of the elastomer has the layered silicate filler.
18. Method according to claim 17, wherein the layered silicate comprises kaolin.
Type: Application
Filed: May 25, 2011
Publication Date: Dec 1, 2011
Applicant: SEMPERIT AKTIENGESELLSCHAFT HOLDING (Wien)
Inventor: Raimund SCHALLER (Neunkirchen)
Application Number: 13/115,620
International Classification: A41D 19/00 (20060101); A41D 19/04 (20060101);
