WO2010046789A1

WO2010046789A1 - Elastomeric polymer/spinel nanoparticle composites to introduce special properties to dipped articles

Info

Publication number: WO2010046789A1
Application number: PCT/IB2009/051158
Authority: WO
Inventors: Sunil Fernando; Lakshman Nethsinghe; Nilwala Swetlana Kottegoda; M. T. Imalka Shanika Munaweera
Original assignee: Dipped Products Plc
Priority date: 2008-10-20
Filing date: 2009-03-19
Publication date: 2010-04-29

Abstract

Latex dipped article prepared using an elastomeric polymer/nanoparticle composite are disclosed. The articles based on nanomaterials display special properties such as antistatic and magnetic. The article is produced by direct dipping of the formers of the desired shape in the elastomeric polymer nanocomposite dispersion. The nanocomposite layer so formed may also be coated with other suitable elastomers.

Description

Field of invention

The invention relates to elastomeric dipped articles having antistatic and magnetic properties produced using nanoparticle/polymer composites, in particularly to elastomeric latex matrixes containing nanoparticles.

Background of the invention

Polymer/latex elastomer nanocomposites represent a new class of materials alternative to conventional filled polymers. In this new class of materials, nanosized inorganic fillers are dispersed in a polymer matrix offering tremendous improvement in performance or introducing new performance properties to the parent polymer/latex elastomer. Therefore, elastomeric articles based on nanocomposites will have number of new potential applications due to the presence of the nanomaterials. This invention relates to introducing antistatic properties into an article made using nanoparticles containing natural or synthetic elastomeric material, for special applications in different industries. The said antistatic property to the elastomeric dipped articles is imparted by the presence of the nanomaterial. In the event of the presence of unpaired electrons in the nanomaterial additionally imparts magnetic property to the article, and allows the article to be detected under a magnetic field.

It is desirable to prevent static electricity build up on objects to be handled specifically with electronic equipments and sensitive photographs since the static charges are known to be very detrimental to the said objects. Also, in electro-painting industry an electrostatic potential is generated in between the object and the paint and this discharge may cause injuries to the painter. Likewise in spray painting industry electrostatic charge generated at the nozzle can cause injuries to the painter. It is therefore, desirable to wear hand protection capable of electrostatic discharge in the above mentioned industries. In addition polymeric articles used in clean room, medical and food applications require a minimum dust and particulate contamination. The use of antistatic polymeric films reduces the tendency of dust and other particles to be attracted through electrostatic forces.

Elastomeric articles particularly gloves with magnetically detectable properties are widely used in industries such as food packaging, pharmaceutical, baby consumer goods. The operatives working in such industries are recommended to wear safety articles in order to maintain high standards of hygiene and cleanness. During the process of manufacturing snagging of elastomeric article can cause pieces to tear off and thereby contaminate the product. Such foreign bodies should be readily detected.

Articles with both antistatic and magnetic properties offer the combined advantage of preventing the products specifically pharmaceutical and food products from the contamination by dust particles and also allowing any snagged pieces to be detected by a magnetic field. The prior art describes several attempts to render antistatic properties to elastomeric polymers. US patent application no 2002/0002227 discloses a process for preparing antistatic film comprising a conductivity inducing material into the polymeric film where the conductivity inducing material is a non volatile ionisable metallic salt. During service life an elastomeric polymer article such as a glove undergoes constant bending, flexing and stretching which could increase the tendency of afore mentioned material to bloom, transfer or flake off the surface. This situation may cause damage in critical environments where antistatic properties are desired. In addition in some traditional products carbon black, fibers and other inorganic metals such as wires are used as static charge dissipative materials. These materials can stiffen the article leading to restricted flexibility and alternation of physical properties which is not desired for hand protection. In US patent no 5677357 discloses the use of anti statically effective amount of a hexahalogenated compound in polyurathene. The most widely used method for rendering polymers anti static properties is to incorporate polyethyleneglycol graft copolymers with the polymer matrix. US patent numbers 4302558 and 4384078 relate to antistatic graft polymers obtained by graft polymerization of vinyl or vinylidene monomer onto rubber polymer. However graft co-polymers are unsuitable for manufacture of dipped latex articles. These adverse effects will not be exhibited by the materials used for our invention as the nanofillers are designed to be compatible with the elastomeric polymer.

Currently the problem of detecting snagged elastomeric article pieces in food packages is addressed by sending the final product through a magnetic field or by visual detection by use of article of colour that contrasts the colour of the product. The prior art describes gloves used in food and pharmaceutical industry. The US patent 5922482 discloses a process for preparing a glove containing metal powders selected from nobel metals. The magnetic material has been directly mixed with the natural rubber matrix. US patent 7122593 discloses the use of magnetically detectable chromium oxide and/or ferrite in the latex article and a process for the manufacturing of such articles. Also afore mention active material limits the colour selection for the article and only uni-coloured article manufacturing is possible. However all the methods described in prior art do not address the issues related to compatibility between the two matrixes. Furthermore direct addition of salts of d-block elements into certain elastomeric materials in particular natural and synthetic rubber accelerate the aging of the elastomeric article. There are therefore needs for elastomeric articles having magnetic properties that have better compatibility between the filler and the matrix and with improved detection limits. Additionally all the methods used in prior art do not refer to the availability of articles with both magnetic and antistatic properties and use of any modified nanomaterials which offer a wide range of advantages over the submicron or micron size fillers.

Detailed Description

The present invention discloses an article made using an elastomeric polymer latex and nanoparticle composite and the process for making the same, which display both magnetic and antistatic properties. The said properties have been observed with nanofillers of less than 5% loading and more preferably with less than 2% loadings. The article having the said behavior does not exhibit significant modification in the unaged mechanical properties such as tensile, tear or flexibility. After aging for seven days at 70 ⁰C over 70% of the original performances retained.

In accordance with the present invention an article is prepared as outlined below.

1. Synthesis of nanomaterial.

2. Functionalisation of the nanomaterial with organic functional materials.

3. Preparation of the functionalised nanoparticle/elastomeric material nanocomposite

4. Preparation of the article.

The antistatic and magnetic properties to the parent polymer have been introduced in step 3 above using functionalized nanoparticles of spinel like materials which are solid solutions of cations of different valency.

In accordance with the present invention, the said nanomaterial has been synthesized in situ with a particle size between 1 - 100 nm, preferably below 50 nm, more preferably below 25 nm. The said nanomaterial is a spinel or inverse spinel like material containing a single or combination of para-, ferro-, ferri- or anti ferro- magnetic metal ions of different valency preferably di and trivalent cations, where divalent cations are distributed in octahedral sites and the trivalent cations in tetrahedral sites or in both tetra and octahedral sites. The divalent cations in the present invention are selected from d and/or f block elements and/or Ba, Ca, Sr and/or any cation that fits in octahedral voids of the structure. The trivalent cations selected from either ferric, chromium or tetra valent cations such as Sn with unpaired spins, are topotactically introduced in to the octahedral and/or tetrahedral voids of the said spinel or inverse spinel structures. The magnetic properties of the nanoparticles are controlled by the type of di and trivalent cation combination and their distribution between the two types of holes. Alternatively nanoparticles based on single metal cations which posses unpaired spins can be used to introduce said properties to the articles. The anion can be selected from group vi elements of the periodic table. Additionally the nanoparticles can be purchased or extracted from a natural source followed by converting in to nano-range by top-down approach for nanoparticle synthesis. Nanoparticle agglomeration occurs in the absence of surface modification. The particle size is controlled by optimizing the experimental conditions such as rate of addition of the reactants, concentration ratio between the two types of cationic solutions and temperature. Figures 1, 2, 3 represents the surface modification process of stabilization of the nanoparticles, using a suitable functional molecules. Surface modification of the nanoparticles can be carried out using preferably monocarboxylic acids selected from Cl - C20 long carbon backbone chains or the related versions of the di or tri carboxylic acids or any organic or inorganic molecule having functional groups that are capable of interacting with the surface hydroxyl groups of the particles and a tail which is compatible with latex matrix. Alternatively bulky molecules such as ethylene diamine tetra acetate can be used to chelate the nanoparticles in order to prevent attractive interactions between the nanoparticles. While the functional head group of the modifier interacts with the nanoparticle organic chain of the modifier would make it possible to unable favorable interactions between the polymer/elastomeric latex matrix and the nanoparticles. More preferably the presence of a double bond in the organic modifier would assist further chemical compatebilisation of the nanomaterial with the latex matrix during vulcanization of the said latex dispersion. Further improved bonding between the two films can be achieved by using special binding agents such as acrylic binders or any organic molecule that makes strong physical or chemical interactions between the latex matrix and the nanocomposite layer.

The filler loading in the present embodiment is 0.5% to 5% more preferably below 2% of the dry weight. The functionalised nanoparticle dispersions are stable for prolong periods of storage.

The ferrofluid containing organic nanoparticles can be added into any synthetic or natural elastomeric latex compound along with the other ingredients under mechanical stress in order to result a nanocomposite where the organic nanoparticles are uniformly distributed as nanoparticles through out the polymer matrix. The organic tail of the nanoparticle makes favorable chemical or strong physical interactions with the polymer matrix and thereby improves the compatibility between two matrixes.

Using the specifically prepared functionalised nanoparticle/elastomeric latex composite dipped articles such as gloves can be prepared by conventional dipping techniques with different variations in the method of coating the elastomeric nanocomposite layer. The nanocomposite layer can be applied as a coating on or sandwiched in between any synthetic/natural or blends of natural and/or synthetic elastomeric dipped films which sans nano materials.

Articles that can be made are

1. Nanocomposite on the outer surface only.

2. Nanocomposite on the outer and inner surface.

3. Nanocomposite as half dipped on the outer surface or to any other length from the finger tips to the cuff.

4. Nanomaterial trapped as an intermediate dip between two other dips.

5. Nanomaterial between fabric liners made from any natural or synthetic fibers such as cotton, polyester cotton, nylon, dinemer, Kevlar, and engineering fibers, and an elastomeric coating.

6. And permutations of the above with the liner.

The article may be unlined or flock lined.

A dipped article such as a glove can be made by dipping ceramic, steel, aluminium or plastic hand shaped formers into dipping tanks containing the said nanocomposite compounds. The nanocomposite layer can be dipped as fractions of the total article such as fingers alone, wrist down ward and wrist to cuff. It naturally follows that this invention could be applied to other elastomeric articles where the ordinary skill in the art is understood to be similar to the process involved in manufacture of articles. Further this invention enables the material to be uniformly distributed as nanomaterials in the finished product and also during the process operations the contents in the dipping tanks are less prone to settling issues. Further by using this invention we are not restricted to employing specific colours. In the later content it may be preferable to use the nanoelastomeric composite as an intermediate layer. According to the present invention nanocomposites based on various loadings of the nanoparticles were prepared. A preferred nanocomposite is based on oleic acid functionalised ferrous and ferric spinel like materials respectively dispersed in natural and nitrile latex. The examples given below are solely to illustrate the subject of the invention and they in no way constitute any limitation to the type of nanoparticle, functional group or elastomeric material which may be utilized.

Preparation of the functionalised nanoparticles:

2M ferrous ammonium sulphate solution was added drop-wise with stirring to a IM ferric chloride solution whilst controlling the pH at 9.0 at 30 ⁰C. The resulting ferrofluid was then treated with 50% oleic acid to functionalize and stabilize the nanoparticles. The presence of nanoparticles in the ferrofluid was checked using light scattering experiments and TEM imaging techniques. The presence of nanoparticles with narrow size distribution between 10 - 25 nm is evidenced from the TEM image and the particle size distribution graph given in the figure 4. The successful functionalisation of the nanoparticles was confirmed by FTIR technique.

Preparation of the nanocomposite

The organo-functionalized nanodispersion is added in small portions into the natural rubber latex and nitrile rubber formulations respectively whilst stirring. Referring to the TEM images and particle size distribution experiments it was evident that the particle size of the nanomaterial within the latex article is below 100 nm more preferably below 50 nm and most preferably below 25 nm.

Natural rubber formulation for the nanocomposite phr

Natural rubber 100

KOH 0.15

Accelerators + Sulphur dispersion 0.9

Antioxidant 0.7

Antifoaming agent 0.10

Oleic functionalised ferrofluid 1.5

Pigment As required

Nitrile rubber formulation for the nanocomposite phr

Nitrile Rubber 100

KOH 0.54 Accelerators + Sulphur dispersion 5.524

ZnO dispersion 3.0

Non ionic surfactant 0.3

TiO2 0.75

Pigment As required

Antifoaming agent 0.03

Oleic functionalised ferro fluid 1.5 Pigment as required

Metal detection sensitivity

1. 2 mm x 3 mm article fragments prepared from above formulations were detected by a metal detector rated for detecting 1.2 mm diameter meal sphere.

2. The dimensions of the fragment detected did not vary along the article length.

3. 2 mm x 3 mm article fragments were also be detected when it is buried inside a 1 cm diameter sausage roll.

Measurement of static charge dissipating properties.

Volume resistivity measurements carried out based on an ISO method suggest that the readings are within the volume resistivity values recommended for charge dissipative materials.

Claims

What is claimed is;

1) An elastomeric latex dipped product wherein the elastomeric latex polymer matrix is reinforced with ogano-functionalised inorganic nanomaterials.

2) A latex dipped product as claimed in 1 can also be applied to a glove which will have the benefit of the antistatic and magnetic properties and is comprised of one or multi layers of nanocomposite based on elastomeric polymer and organo- functionalised nanoparticles or alternatively the nanocomposite layer is coated on a neat elastomeric film.

3) An article manufactured using the nanocomposite as claimed in claims 1 and 2 wherein inorganic nanomaterial has spinel or inverse spinel like or metal oxide structures which have been modified with suitable organic functional groups.

4) The organo functionalised nanoparticles used in manufacture of dipped article as claimed in claim 3 contains nanoparticles with particle size below 100 nm, preferably below 50 nm more preferably below 25 nm.

5) An article manufactured according to claims 1 and 2 wherein the elastomeric polymer is any natural or synthetic elastomer or a blend of natural and/or synthetic elastomers.

6) An article manufactured as claimed in claims 1 and 2 wherein particle size of the inorganic nanoparticle is below 100 nm more preferably below 50 nm, and most preferably below 25 nm.

7) An article manufactured using the nanoparticles as claimed in claim 3 wherein the spinel or inverse spinel like nanoparticle is a solid solution of a divalent cation or a combination of divalent cations and tri or terra valent cation.

8) The nanoparticles as claimed in claim 3 and claim 7 wherein the divalent cations are dia, ferro, ferri, anti ferro or para magnetic and tri/tetra valent cations are para, ferro, ferri, anti ferri magnetic.

9) The divalent cations as claimed in claim 8 are selected from lanthanide and / or d- block and / or Ba , Ca , Sr or any divalent cations which fits with the octahedral voids of the spinel like structure and trivalent cations are ferric or chromium.

10) An article manufactured using the nanoparticles as claimed in claim 3 wherein the metal oxide nanomaterial is any metal that has unpaired spins. H)An article manufactured using the nanoparticles as claimed in claims 1 and 2 wherein the anion of the nanoparticles are selected from oxide, sulphide, selenide or telluride.

12) An article manufactured according to claim 1 wherein the nanomaterial is functionalized in order to prevent particle agglomeration.

13) An article manufactured according to claim 1 wherein the functionalised nanomaterial is physically compatible through strong intermolecular attractions or chemically compatible with the elastomeric polymer matrix.

14) Nanoparticles as claimed in claims 12 and 13 are functionalised using a mono/di or multi carboxylic acid group containing organic molecules selected from Cl- C20 carbon chain length or any organic molecules containing functional groups that can make physical or chemical bonds between the matrix material and nanoparticle.

15) Alternatively, nanoparticles as claimed in claim 12 are chelated using suitable chelating agents in order to prevent particle agglomeration.

16) An article as claimed in claims 1 and 2 wherein the nanoparticles are synthesized in situ or extracted from a natural source as solid materials and obtained nano particles by top down approach followed by functionalisation with suitable organic functional groups. Alternately the nanomaterial is purchased and functionalized followed by addition to the latex matrix.

17) An article as claimed in claims 1 and 2 wherein the nanocomposite is prepared using functionalised nanoparticles which are in situ synthesized and added to the elastomeric polymer dispersion/latex as nanodispersion.

18) An article as claimed in claims 1 and 2 wherein the article is produced with natural or synthetic rubber latex and ferrous ferric containing nanoparticles modified with long chain carboxylate acids.

19) An article as claimed in claims 1 and 2 wherein the article displays magnetically detectable and antistatic properties. 20) An article as claimed in claims 1 and 2 wherein the functionalised nanoparticle loading is between 0.1% to 5% by dry weight, preferably below 2% by dry weight.

2I)An article as claimed in claims 1 and 2 wherein the nanoparticle/elastomeric polymer latex composite is coated with a layer of elastomer sans the nanomaterial; the latter may contain coloured pigments of any choice; the coating may be on one side or either sides of the nanocomposite layer and could be of any thickness up to the thickness of the nanocomposite layer.

22) An article as claimed in claim 21 wherein the elastomeric layer coating is a blend of natural and/or synthetic elastomeric latexes, in particular natural rubber latex and synthetic latex such as neoprene, nitrile, polyurathene and others.

23) An article as claimed in claim 22 wherein the elastomeric coating/s is chemically bonded through a functional molecule to the nanocomposite layer.

24) The functional molecule as claimed in claim 23 is an acrylic binder or any organic molecule that is physically or chemically compatible with both the nanocomposite layer and the pure latex layer.

25) An article as claimed in claims 1 and 2 wherein the nanocomposite layer is coated with elastomeric polymer on one side and a fabric support on other side of the nanocomposite, in particular liners cut and sewn or woven.

26) An article as claimed in claim 25 wherein the fabric support is made from any natural or synthetic fibers.

27) An article as claimed in claims 1 and 2 wherein the article is composed of an elastomeric polymer layer, a middle nanocomposite layer, and an inner elastomeric polymer layer containing flock. The flock is cotton or blends of synthetic fibers.

28) An article as claimed in claims 1 and 2 wherein the nanocomposite layer is between two elastomeric layers or in between an elastomeric layer and a fabric support as a fraction of the total article.