WO2016099307A1

WO2016099307A1 - A latex composition for the manufacture of insulation gloves which withstand voltage of 40 v

Info

Publication number: WO2016099307A1
Application number: PCT/PL2014/000155
Authority: WO
Inventors: Urszula BORKOWSKA; Monika MALESA; Jan MICHALAK; Włodzimierz PIŁACIŃSKI; Janusz ROSLON
Original assignee: Secura B.C. Sp. Z O.O.
Priority date: 2014-12-19
Filing date: 2014-12-23
Publication date: 2016-06-23
Also published as: PL410673A1

Abstract

The subject of the invention is a latex composition for the manufacture of insulation products of high quality, a method for preparing a mixture of latex and latex gloves made from this mixture. The disclosed latex composition and method for preparing thereof provides products having good and stable in time electrical resistance, with good mechanical properties of the gloves with an acceptably thin wall thickness.

Description

A latex composition for the manufacture of insulation gloves which withstand voltage of 40 V

FIELD OF INVENTION

The subject of the invention is a latex composition for the manufacture of insulation products of high quality, a method for preparing a mixture of latex and latex gloves made from this mixture, which withstand voltage of 40 V.

BACKGROUND OF INVENTION

For the production of high quality gloves providing electrical insulation, natural latex is used. It ensures obtaining excellent mechanical properties of the resulted product. Gloves made of natural latex maintain a high degree of flexibility over a wide temperature range, have a high abrasion resistance and good electrical insulating properties. Gloves are formed by various techniques from so-called the latex mixture. The dispersion of latex mixture is composed of natural latex emulsion and different functional additives.

In the prior art different latex compositions are known, for example as those described in patents PL 161 721 , KR20030020998 and GB846290, for use in forming articles by dipping.

PL 61844 discloses a latex mixture and a method of preparing the gloves providing electrical insulation from natural latex comprising immersing the metal mold in latex composition, which includes natural rubber latex in an amount of 100 parts by weight dry rubber, a non-ionic stabilizer such as an aromatic polyether glycol, or a condensation product of ethylene oxide with alkylphenols in an amount of 0.1 -0.6 parts by weight, a crosslinking agent such as sulfur in an amount of 0.5-1.5 parts by weight, the vulcanization accelerator such as zinc or dietyloditiokarbamiman etylofenyloditiokarbamiman zinc in an amount of 0,2-0, 8 parts by weight of vulcanization activator, zinc oxide in an amount of 1.0-2.0 parts by weight, 40% aqueous formaldehyde solution, the coagulant substance from the group of polyorganosiloxanes or polyvinyl methyl ether in an amount of 0.5-2.5 parts by weight, drying the applied latex gel , zwulkanizowaniu, image of a glove form, elution of the components of electrical insulating properties and lowering again thorough drying of the glove, in which process heated to a temperature of 40°C - 80°C metal mold in which the stick is complete, widely spaced and the thickness of the walls of the palm and cuff is differentiated once immersed in the latex composition labeled with a viscosity of Ford cup with a diameter of 4 mm from 16 to 20 seconds pH 7.6 - 9.2 at the time of 5-60 seconds and then placed into a metal mold coated with a wet gel whose consistency decreases from the metal mold to the outer surface of the gel, in an aqueous wash bath with continuous flow at 18°C - 28°C for at least 30 minutes, removed the metal mold with a gel latex washed out and placed at 70°C 1-3 hours and then cured in hot air at 100°C - 140°C for 10-30 minutes, and after removing the glove from the metal mold product is washed in water at 18°C-28°C for 1 -4 hours and then dried in air heated to a temperature of 80°C for at least 2 hours.

P.286528 discloses manufacture method of thin-walled hollow polymeric articles or method for preparing a polymer coating on a substrate which comprises contacting a suitably shaped mold or substrate to be coated with a solution of the amine- terminated prepolymer having a functionality of at least 2, in an organic solvent to form coating on a substrate, drying the coating on the substrate and then contacting the coating on the substrate with a solution of multifunctional cross-linking agent (vulcanizing) which is capable of reacting with the amino end groups of the prepolymer, chain-extending and/or crosslinking.

P.312038 describes thin-walled rubber article with a high tear strength, prepared by dipping, which consists of a polymer blend comprising 10-75 wt.% of a triblock copolymer of styrene-isoprene-styrene (SIS) 1-90 wt.% of a styrene triblock copolymer butadiene-styrene (SBS) and 0-25 wt.% of a triblock copolymer of styrene- olefin-styrene (SOS).

P.404565 discloses a composition for the preparation of an elastomeric thin-walled articles by dipping, in particular all-rubber gloves, wherein said compositoin consists of a latex of a carboxyiated acrylonitrile butadiene rubber with acrylonitrile contents of not less than 20 mole% and the content of carboxyl groups of not less than 3 mol% and per 100 wt. parts of rubber in the latex of 0.5 to 0.7 wt. parts of 2,2'-methylene- bis[6-(1-methylcyclohexyl) -p-cresol], 0.3 to 0.6 wt. parts of the sodium salt of formaldehyde condensate of naphthalenesulfonic acid, from 0.5 to 1.0 wt. parts of polyether alkiloaryloglikolowego, from 1.5 to 8.0 wt. parts of crosslinker selected from the group consisting of ground sulfur or magnesium oxide, from 5.0 to 10.0 wt. parts of nanofiller from the group of layered aluminosilicates, modified dimethylbenzyl chloride (C12-18) alkylammonium chloride or dimetylobenzylostearyloamonium, wherein interlamellar distance is of > 15 A, not more than 8.0 wt. parts of zinc oxide and/or from 1.0 to 1.5 wt. parts of zinc diethyldithocarbamate, wherein the amounts indicated relate to the weight of components excluding water, zinc oxide and zinc diethylcarbamate are used in the case of crosslinked mixtures with sulfur.

In CN101822432 the latex gloves are described that providing electrical insulation and process for the preparation of the gloves. The gloves are cured as a whole. The method comprises preparing a mixture consisting of 90-96% natural rubber, a vulcanizing agent, accelerating PC, accelerating agent ZDC, a plasticizer Y, zinc oxide, antioxidants DNP and DOP, stabilizers, water, which are mixed to form a plastic material, then a coagulant including calcium chloride, leveling agent, detergent and water is prepared, and then the ingredients are mixed thoroughly. The glove mould is immersed in a coagulant solution, and then heated and dried. This is followed by vulcanizing and aging. JP2006257610 shows the production method of compositions for the glove production, wherein said gloves protect against static electricity. The method comprises the addition to natural rubber latex up to 10% or more of acrylonitrile- butadiene derivative of the latex, known as NBR latex. This compound provides adequate resistance to gloves protected against static electricity.

The document EP0378380 describes layers made of a latex having improved tear resistance properties. According to the illustrated embodiment the natural latex is modified by the addition of copolymer styrene-butadiene with high content of styrene. It is known from the prior art that in the vulcanized products polysulfides bridges forming during the vulcanization process provide stiffening and reinforcement of rubber. Sulfur can be incorporated into the latex composition in the form of polysulfides.

Polysulfides is a group of compounds containing anions of formula S_n ^?" (n = 2-8), characterized by a linear structure: ^"SS_n-2S\

US8464719 describes an article made of latex and its production process by immersing the matrix in the synthetic latex emulsion of the pre-vulcanization, without use of any coagulants and curing the article so produced. The method of obtaining the sulfur is used in a soluble form ring structure S8, in particular diisopropyl xanthogen polysulfide.

EP2687629 discloses a vulcanizing agent for latex mixture selected from among oxides, mercapto, sulfenamides, tiuramow, thiocarbamates, amines, thiophosphates, thiourea, thiazoles, and guanidines, preferably zinc bis(dibuthylodithiocarbamate), zinc dietylodithiocarbamate, zinc dimetylodithiocarbamate or zinc 2- mercaptobenzothiazole or the sodium salt of 2-mercaptobenzothiazole, 2,2'- dithiobenzothiazolu disulfide, N-cykloheksylobenzotiazolo-2-sulfenamide, N-tert- butylobenzotiazolo-2-sulfenamide, bis (triethoxysilylpropyl) tetrasulfide, tetraethylthiuram disulfide, tetramethylthiuram disulfide, tetramethylthiuram monosulfide, tetramethylthiuram polysulfide, thiuram hexasulfide, dimetylodithiocarbamate, N, N'-ethylene thiourea, 2- (morpholinothio) benzothiazole, sulfur, N, N'-diphenyl, N, N'-di-o-toliloguanidine, zinc sulfide, dibutyl and/or diphenylguanidine.

US3723239 describes laminate polymer latex with a mono-filament with a large radius of curvature or cross-sectional line formed by twisting the mono-filaments or the organic polymer layer prepared using an aqueous adhesive consisting of a mixture of the adhesive base mainly composed of a polyhydric phenol polysulfide solution dissolved in a resorcinol-formaldehyde condensate and RFL solution comprising a resorcinol-formaldehyde resin obtained by reacting resorcinol and formaldehyde and latex.

Unfortunately, despite the development of so many different solutions, the prior art production techniques fail to provide a high resistance of latex coatings to high voltage of 40-50 kV. With such a large electric current through a coating made of latex gradually begins to flow current, whose intensity increases with increasing voltage and puncture occurs, the flow of electric spark perforation latex coating and the destruction of the glove. It is not known exactly what the direct cause of the puncture is. There cannot also be determined in advance, at which point the glow will be punctured. It is believed that the internal moisture, increased hydrophilicity of the coating and microcracks contribute to the deterioration of the electrical strength of the gloves. This phenomenon can be prevented by producing more and more thicker latex coatings. Thick gloves, however, limit feeling, limit movement of the hand and fingers, are heavy and uncomfortable.

Therefore, there is still a need to produce a sensible thin gloves providing lasting protection against high voltage. Gloves that provide insulation from electricity may be formed thermosensitizable latex composition on a mold replicating the shape of the finished product. Latex composition outside the natural latex contains additional corrective measures pH, additives for vulcanization, accelerators, and more. For the process of vulcanization of natural rubber latex or chemical polymerization process of the latex particles, the addition of sulfur is responsible. The sulfur is introduced into the latex in the form of a fine aqueous dispersion. Sulfur itself is poorly wettable material. The presence of sulfur in the latex composition may lead to local unevenness in the degree of polymerization and in the structure of the latex sulfur crystals can remain unreacted. Said crystals do not provide full consistency of the polymer forming the layer, and can contribute to the formation of microcracks, in particular during the mechanical deformation of the article.

In the course of research on the composition used in the manufacture of latex gloves providing protection against high voltages, it was unexpectedly discovered that by modifying the composition of the latex gloves, they can be produced with good and stable in time electrical resistance, with good mechanical properties of the gloves with an acceptably thin wall thickness.

Summary of the Invention

The subject of the invention is latex composition for use in products providing electrical insulation wherein said composition comprises 85-95 wt.% of natural latex with high ammonium content and dry content of 61%; 1.5-2.9 wt.% coagulant, 0.2-0.3 wt.% surfactant, 0.8-1.5 wt.% formalin, and vulcanization dispersant to an amount of 2.8-3.5 wt.%, comprising 13-15 wt.% NaOH, 34-36 wt.% sulfur, 36-37 wt.% zinc oxide, 0.1-0.2 wt.% Lavinox and 0.1-0.2 wt.% Tamol, and the latex composition comprises a paraffin wax emulsion in an amount of 0.05-0.06 wt.%, wherein the pH of the mixture is between 8 and 1 1. Preferably sulfur is in the form of a fine crystalline or in the form of a polysulfide, more preferably sulfur is in the form of a fine crystalline or in the form of polysulfide of an alkali metal or an alkaline earth metal or ammonium, preferably polysulfide of sodium, potassium or ammonium.

In a preferred embodiment the pH of the mixture is 10.3, adjusted by the addition of 7% NaOH solution or a 35% solution of ammonium chloride to form an ammonium buffer.

In another preferred embodiment the surfactant comprises a mixture of potassium palmitate or mixture of sodium stearate and sodium palmitate in a ratio of 1 :1.

The latex composition according to the invention comprises the paraffin emulsion comprises water and at least one compound selected from the group consisting of paraffin oil, white petroleum jelly, hard paraffin, silicone oil, and, as an emulsifying agent, a mixture of polyethylene glycol PEG 400, polyethylene glycol PEG 1600, glycerol monooleate, sodium palmitate and borax, or a mixture of polyethylene glycol PEG 400, polyethylene glycol PEG 1600, glycerol monooleate, sodium palmitate and potassium stearate.

In a preferred embodiment the paraffin emulsion comprises a mixture of 40-45% paraffin oil and the remaining part distilled water.

In further preferred embodiment the paraffin emulsion comprises a mixture of 20-25% paraffin oil, 10-15% white petroleum jelly and 10-15% hard paraffin and the remainder as distilled water.

In further preferred embodiment the paraffin emulsion comprises a mixture of 50% distilled water, 25% paraffin oil, and 25% white petroleum jelly.

In further preferred embodiment the paraffin emulsion comprises 50-60% distilled water and 40-50% silicone oil.

In the preferred latex composition the paraffin emulsion comprises an emulsifying agent as a mixture of 0.09-0.15% polyethylene glycol PEG 400, 0.09-0.15% polyethylene glycol PEG 1600, 0.07-0.12% g glyceryl monooleate, 0.10-0.16% sodium palmitate 0.003-0.006% borax or potassium stearate.

In further preferred embodiment the latex composition comprises 72.18 wt.% of natural latex with high ammonium content and dry content of 61 %, 2.10 wt%. coagulant, 0.19 wt.% surfactant in the form of potassium palmitate, 0.87 wt.% formalin, and vulcanization dispersant to an amount of 2.48 wt.%, containing 22 wt.% NaOH, 55.9 wt%. of sulfur in the form of sodium polysulfide or ammonium polysulfide, further, the latex composition comprises 21.79 wt.% zinc oxide, 0.11 wt.% Lavinox and 0.03 wt.% Tamol and paraffin emulsion in an amount of 0.25 wt%, wherein the pH of the mixture is 10.3, adjusted by the addition of 7% NaOH solution.

The present invention also provides a method for preparing a latex composition comprising the steps of adding 265 kg of natural latex with a high ammonium content and dry content of 61 % to a container equipped with a water jacket and ribbon agitator, introducing 7.7 kg coagulant after stabilization of the temperature at 32°C, then adding 0.68 kg of the surfactant and all the time adjusting the pH of the mixture to 10.3, then adding in portions 37% formalin solution in an amount of 3.2 kg, at the end adding vulcanization dispersion to the container in an amount of 9.1 kg, said vulcanization dispersion is prepared separately, and finally adding paraffin in an amount of 0.9 kg to the latex composition.

In a preferred embodiment the vulcanization dispersion is generated by introducing into the 120 liter container equipped with a stirrer, heated by a diaphragm with water vapor, 60 kg of 50% NaOH solution, then 76 kg of sulfur, and heating the container under reflux to a gentle boiling for 4 hours, followed by hot filtration of the contents of the container and cooling to a temperature of 30°C, adding 80 kg of zinc oxide, 0.42 kg Lavinox and 0.12 kg Tamol to the cooled mixture and then stirring the mixture vigorously for 40 minutes to achieve high homogeneity and then degassing the mixture three times using a vacuum of 10 kPa and removing air bubbles suspended in the mixture. Preferably the sulfur is in the form of a fine crystalline or in the form of a polysulfide, more preferably the sulfur is in the form of an alkali metal polysulfide or an alkaline earth metal polysulfide or ammonium polysulfide, preferably in the form of polysulfide of sodium, potassium or ammonium.

In further preferred embodiment potassium palmitate, a mixture of sodium stearate and sodium palmitate in a ratio of 1 : 1 is used as a surfactant.

In further preferred embodiment the paraffin emulsion is prepared separately in a high shear industrial mixer with a 12 liter tank, by mixing for 20 minutes 5 kg of distilled water, 2 kg of paraffin oil, 1 kg of white petroleum jelly and 1 kg of hard paraffin and using as the emulsifier a mixture of 10 g of polyethylene glycol PEG 400, 10 g of polyethylene glycol PEG 1600, 8 g of glyceryl monooleate, 11 g of sodium palmitate and 4 g of borax.

In further preferred embodiment paraffin emulsion is prepared separately in a high shear industrial mixer with a 12 liter tank, by mixing for 20 minutes, 5 kg of distilled water, 2.5 kg of paraffin oil, 2.5 kg white petroleum jelly without hard paraffin, using as the emulsifier a mixture of 10 g of polyethylene glycol PEG 400, 10 g of polyethylene glycol PEG 1600, 10 g of glyceryl monooleate, 15 g of sodium palmitate and 3 g of borax.

In further preferred embodiment the paraffin emulsion is prepared separately in a high shear industrial mixer with a 12 liter tank, by mixing at the high temperature of 85°C for 20 minutes, 5 kg of distilled water, 4 kg of silicone oil, using as the emulsifier a mixture of 10 g of polyethylene glycol PEG 400, 10 g of polyethylene glycol PEG 1600, 10 g of glyceryl monooleate, 15 g of sodium palmitate and potassium stearate 5 Preferably the pH of the mixture is maintained at 10.3 all the time by the addition of 7% NaOH solution or by introducing stepwise 35% ammonium chloride solution forming ammonia buffer, wherein the solution of ammonium chloride is added in an amount of 1.6 kg or by the addition of an appropriate amount of a 10% solution of CHES.

The present invention further provides a latex article made from a blend according to the invention and made from a mixture obtained by the method according the invention.

Preferably the product is a glove providing electrical insulation. EXAMPLES

The invention will be illustrated in the examples which describe in detail preferred embodiments of the invention.

Example 1 - comparative, a mixture known from the prior art

To the container with water jacket and ribbon agitator 265 kg natural latex with high ammonium content and a dry matter content of 61 % was added. After stabilizing the temperature at 32°C, 7.7 kg of coagulant providing sensitivity of the mixture to elevated temperature and enabling gelling the mixture was added. Then, 0.52 kg of anionic surfactant in the form of a 22% aqueous solution of sodium lauryl ether sulfate. The pH of the mixture was adjusted constantly to 10.3 using 7% NaOH solution. Then 37% formalin solution in an amount of 3.2 kg was added portionwise. At the end, the vulcanization dispersion was introduced into the tank in an amount of 9.1 kg. Vulcanization dispersion was prepared separately. To the ball mill with 146 kg of water, 66 kg sulfur fine crystalline, 80 kg zinc oxide, 0.42 kg Lavinox and 0.12 kg Tamolu were added. The suspension was milled for 24 hours in order to achieve an appropriate level of fragmentation of the particles.

In the latex mixture, prepared as described above, a glove mold made of duralumin was dipped wherein said mold was preheated to the right temperature, enabling forming of a coagulate layer with a thickness appropriate to the specific kind of glove that provide reaching the appropriate level of electrical insulation. The molds with the coagulant were removed and further treated by drying and vulcanization, as for latex products.

The quality parameters for the obtained latex coatings were tested using the research form, so-called thumb, thus a form of a cylinder in rounded shape at the end with a diameter of 25 mm, length of 30 cm and made of duralumin. Support mold was heated to a temperature of 75°C and immersed in the latex composition to a depth of 20 cm for 30 seconds. Then the mold coated with coagulated mixture was removed from the container filled with a latex mixture, dried and then vulcanized for 20 minutes at 110°C. Sample No. 1 of cured latex was collected from the cooled mold reflecting the shape of the mold (toe). The thickness of the product has been studied at the tip of the finger and along the thumb in the intervals of 4 cm. A second sample prepared in the same way as Sample No. 1 was tested for tearing. Third Sample No. 1 was tested for electrical insulation measured as leakage current values when immersed in water at different voltages being applied. The test results are shown in Tables 1-3.

Example 2

In the container with water jacket and ribbon stirrer 265 kg natural latex with high ammonium content a dry matter content of 61 % was introduced. After stabilizing the temperature at 32°C, 7.7 kg of the mixture of coagulant was added, providing sensitivity to elevated temperature and making the mixture gelling. Then, 0.68 kg of the surfactant in the form of potassium palmitate was introduced. The pH of the mixture was adjusted constantly to 10.3 using 7% NaOH solution. Then 37% formalin solution in an amount of 3.2 kg was added portionwise. At the end, the vulcanization dispersion was added into the tank in an amount of 9.1 kg.

Vulcanizing dispersion was prepared separately. To the tank having a volume of 120 liters with a stirrer, heated with a diaphragm steam, 60 kg of 50% NaOH solution was introduced. Then, 76 kg of fine crystalline sulfur was added and the tank was heated under reflux to a gentle boiling for 4 hours. Then the contents of the container was hot filtered to remove any impurities and to clear the solution and then cooled to 30°C. To the cooled mixture 80 kg of zinc oxide, 0.42 kg Lavinox and 0.12 kg Tamolu were added. The mixture was then stirred vigorously for 40 minutes to achieve a high homogeneity and then degassed three times using a vacuum of 10 kPa and removing air bubbles suspended in the mixture.

The last component introduced to the latex was an emulsion of paraffin in an amount of 0.9 kg. Paraffin emulsion was prepared separately in such a way that, in industrial high speed mixer with a tank volume of 12 liters 5 kg of distilled water, 2 kg of paraffin oil, 1 kg of white petrolatum and 1 kg of hard paraffin was mixed for 20 minutes. A mixture of 10 g of polyethylene glycol PEG 400, 10 g of polyethylene glycol PEG 1600, 8 g of glyceryl monooleate, 11 g of sodium palmitate and 4 g of borax was used as the emulsifying agent.

From the resulted latex mixture the gloves that provide electrical insulation were formed as in Example 1. For the research purpose, a sample from this mixture using the thumb mold as in Example 1 to obtain Sample No. 2. Sample No. 2 was tested for wall thickness, strength and elongation as well as electrical insulation such as in Example 1. The results of the tests were shown in Tables 1-3. Example 3

In the container with water jacket and ribbon stirrer 265 kg natural latex with high ammonium content a dry matter content of 61% was introduced. After stabilizing the temperature at 32°C, 7.7 kg of the mixture of coagulant was added, providing sensitivity to elevated temperature and making the mixture gelling. Then, 0.68 kg of the surfactant in the form of potassium palmitate was introduced. The pH of the mixture was adjusted constantly to 10.3 using 7% NaOH solution. Then 37% formalin solution in an amount of 3.2 kg was added portionwise. At the end, the vulcanization dispersion was added into the tank in an amount of 9.1 kg.

Vulcanizing dispersion was prepared separately. To the tank having a volume of 120 liters with a stirrer, heated with a diaphragm steam, 60 kg of 50% NaOH solution was introduced. Then, 76 kg of sulfur in form of sodium polysulfide was added and the container was heated under reflux to a gentle boiling for 4 hours. Then the contents of the container was hot filtered to remove any impurities and to clear the solution and then cooled to 30°C. To the cooled mixture 80 kg of zinc oxide, 0.42 kg Lavinox and 0.12 kg Tamolu were added. The mixture was then stirred vigorously for 40 minutes to achieve a high homogeneity and then degassed three times using a vacuum of 10 kPa and removing air bubbles suspended in the mixture

The last component introduced to the latex was an emulsion of paraffin in an amount of 0.9 kg. Paraffin emulsion was prepared separately in such a way that, in industrial high speed mixer with a tank volume of 12 liters 5 kg of distilled water, 2 kg of paraffin oil, 1 kg of white petrolatum and 1 kg of hard paraffin was mixed for 20 minutes. A mixture of 10 g of polyethylene glycol PEG 400, 10 g of polyethylene glycol PEG 1600, 8 g of glyceryl monooleate, 11 g of sodium palmitate and 4 g of borax was used as the emulsifying agent. From the resulted latex mixture the gloves that provide electrical insulation were formed as in Example 1. For the research purpose, a sample from this mixture using the thumb mold as in Example 1 to obtain Sample No. 3. Sample No. 3 was tested for wall thickness, strength and elongation as well as electrical insulation such as in Example 1. The results of the tests were shown in Tables 1-3.

Example 3A

Example 4 was carried out analogously to Example 3 except that the sulfur is administered in the form of ammonium polysulfide (the amount of sodium polysulfide introduced corresponds to 76 g of elemental sulfur).

The use of ammonium polysulfide has the advantage that the gaseous ammonia formed in this example can be driven off from the mixture and does not remain in the mixture during the coagulation process, leading to a much lower content of impurities.

Example 4

In the container with water jacket and ribbon stirrer 270 kg natural latex with high ammonium content a dry matter content of 61 % was introduced. After stabilizing the temperature at 31 °C, 7.8 kg of the mixture of coagulant was added, providing sensitivity to elevated temperature and making the mixture gelling. Then, 0.68 kg of the surfactant in the form of mixture of sodium stearate and sodium palmitate in a ratio of 1 :1 was introduced. The pH of the mixture was adjusted constantly to 10.3 using ammonium chloride solution forming ammonium buffer. For this purpose to the mixture the 35% ammonium chloride solution was introduced portionwise in amount of 1.6 kg. To rapid introduction of this solution could cause coagulation of the latex mixture. In the next step, the vulcanization dispersion was added into the tank in an amount of 9.3 kg. Vulcanization dispersion was prepared separately according to Example 2. The last component introduced to the latex was an emulsion of paraffin in an amount of 1.1 kg. Paraffin emulsion was prepared separately in such a way that, in industrial high speed mixer with a tank volume of 12 liters 5 kg of distilled water, 2,5 kg of paraffin oil, 2,5 kg of white petrolatum without hard paraffin was mixed for 20 minutes. A mixture of 10 g of polyethylene glycol PEG 400, 10 g of polyethylene glycol PEG 1600, 10 g of glyceryl monooleate, 15 g of sodium palmitate and 3 g of borax was used as the emulsifying agent.

From the resulted latex mixture the gloves that provide electrical insulation were formed as in Example 1. For the research purpose, a sample from this mixture using the thumb mold as in Example 1 to obtain Sample No. 4. Sample No. 4 was tested for wall thickness, strength and elongation as well as electrical insulation such as in Example 1. The results of the tests were shown in Tables 1-3.

Example 5

In the container with water jacket and ribbon stirrer 270 kg natural latex with high ammonium content a dry matter content of 61 % was introduced. After stabilizing the temperature at 31 °C, 7.8 kg of the mixture of coagulant was added, providing sensitivity to elevated temperature and making the mixture gelling. Then, 0.68 kg of the surfactant in the form of mixture of sodium stearate and sodium palmitate in a ratio of 1 :1 was introduced. Then 37% formalin solution in an amount of 2.8 kg was added portionwise. The pH of the mixture was adjusted constantly to 10.3 using ammonium chloride solution forming ammonium buffer. For this purpose to the mixture the 35% ammonium chloride solution was introduced portionwise in amount of 1.6 kg. To rapid introduction of this solution could cause coagulation of the latex mixture. In the next step, the vulcanization dispersion was added into the tank in an amount of 9.3 kg. Vulcanization dispersion was prepared separately according to Example 2. The last component introduced to the latex was an emulsion of paraffin in an amount of 1.1 kg. Paraffin emulsion was prepared separately in such a way that, in industrial high speed mixer with a tank volume of 12 liters 5 kg of distilled water, 2,5 kg of paraffin oil, 2,5 kg of white petrolatum without hard paraffin was mixed at high temperature of 85°C for 20 minutes. A mixture of 10 g of polyethylene glycol PEG 400, 10 g of polyethylene glycol PEG 1600, 10 g of glyceryl monooleate, 15 g of sodium palmitate and 5 g of potassium stearate was used as the emulsifying agent. From the resulted latex mixture the gloves that provide electrical insulation were formed as in Example 1. For the research purpose, a sample from this mixture using the thumb mold as in Example 1 to obtain Sample No. 5. Sample No. 5 was tested for wall thickness, strength and elongation as well as electrical insulation such as in Example 1. The results of the tests were shown in Tables 1-3.

Example 6

In the container with water jacket and ribbon stirrer 270 kg natural latex with high ammonium content a dry matter content of 61 % was introduced. After stabilizing the temperature at 31 °C, 7.8 kg of the mixture of coagulant was added, providing sensitivity to elevated temperature and making the mixture gelling. Then, 0.68 kg of the surfactant in the form of mixture of potassium oleinate and potassium palmitate in a ratio of 3:1 was introduced. Then 37% formalin solution in an amount of 2.8 kg was added portionwise. The pH of the mixture was adjusted constantly to 10.3 by the addition of an appropriate amount of a 10% CHES solution.

At the end, the amount of 9.3 kg of vulcanizing dispersion was introduced to the container. Vulcanizing dispersion was prepared separately. To the tank having a volume of 120 liters with a stirrer, heated with a diaphragm steam, 60 kg of 50% KOH solution was introduced. Then, 65 kg of sulfur in form of sodium polysulfide was added and the container was heated under reflux to a gentle boiling for 6 hours. Then the contents of the container was hot filtered to remove any impurities and to clear the solution and then cooled to 30°C. To the cooled mixture 80 kg of zinc oxide, 0.42 kg Lavinox and 0.12 kg Tamolu were added. The mixture was then stirred vigorously for 40 minutes to achieve a high homogeneity and then degassed three times using a vacuum of 10 kPa and removing air bubbles suspended in the mixture

The last component introduced to the latex was an oil emulsion in an amount of 1.3 kg. The oil emulsion was prepared separately in such a way that, in industrial high speed mixer with a tank volume of 12 liters, 5 kg of distilled water, 4 kg of paraffin oil were mixed at high temperature of 85°C for 20 minutes. A mixture of 10 g of polyethylene glycol PEG 400, 10 g of polyethylene glycol PEG 1600, 10 g of glyceryl monooleate, 15 g of sodium palmitate and 5 g of potassium stearate was used as the emulsifying agent.

From the resulted latex mixture the gloves that provide electrical insulation were formed as in Example .

Table 1. Results of thickness measurements of the latex layer of the article

Table 2. Results of tensile stren th measurements

Table 3. Results of electrical insulation measurements. he leakage current for a given voltage [mA].

Voltage [V] Sample 1 Sample 3 Sample 4 Sample 5 Sample 6

5000 0.41 0.40 0.33 0.34 0.35

10000 0.52 0.51 0.42 0.40 0.41

20000 0.73 0.72 0.61 0.59 0.60

30000 0.94 0.91 0.80 0.77 0.78

Claims

We claim:

1. Latex composition for use in products providing electrical insulation characterized in that it comprises 85-95 wt.% of natural latex with high ammonium content and dry content of 61%; 1.5-2.9 wt.% coagulant, 0.2-0.3 wt.% surfactant, 0.8-1.5 wt.% formalin, and vulcanization dispersant to an amount of 2.8-3.5 wt.%, comprising 13- 15 wt.% NaOH, 34-36 wt.% sulfur, 36-37 wt.% zinc oxide, 0.1-0.2 wt.% Lavinox and 0.1-0.2 wt.% Tamol, and the latex composition comprises a paraffin wax emulsion in an amount of 0.05-0.06 wt.%, wherein the pH of the mixture is between 8 and 11.

2. The latex composition according to claim 1 , wherein the sulfur is in the form of a fine crystalline or in the form of a polysulfide.

3. The latex composition according to claim 2, wherein the sulfur is in the form of a fine crystalline or in the form of polysulfide of an alkali metal or an alkaline earth metal or ammonium, preferably polysulfide of sodium, potassium or ammonium.

4. The latex composition according to any one of claims 1-3, wherein the pH of the mixture is 10.3, adjusted by the addition of 7% NaOH solution.

5. The latex composition according to any one of claims 1-4, wherein the pH of the mixture is 10.3 adjusted by adding a 35% solution of ammonium chloride to form an ammonium buffer.

6. The latex composition according to any one of claims 1-5, wherein the surfactant comprises a mixture of potassium palmitate or mixture of sodium stearate and sodium palmitate in a ratio of 1 :1.

7. The latex composition according to any one of claims 1-6, wherein the paraffin emulsion comprises water and at least one compound selected from the group consisting of paraffin oil, white petroleum jelly, hard paraffin, silicone oil, and, as an emulsifying agent, a mixture of polyethylene glycol PEG 400, polyethylene glycol PEG 1600, glycerol monooleate, sodium palmitate and borax, or a mixture of polyethylene glycol PEG 400, polyethylene glycol PEG 1600, glycerol monooleate, sodium palmitate and potassium stearate.

8. The latex composition according to claim 7, wherein the paraffin emulsion comprises a mixture of 40-45% paraffin oil and the remaining part distilled water.

9. The latex composition according to claim 7, wherein the paraffin emulsion comprises a mixture of 20-25% paraffin oil, 10-15% white petroleum jelly and 10-15% hard paraffin and the remainder as distilled water.

10. The latex composition according to claim 7, wherein the paraffin emulsion comprises a mixture of 50% distilled water, 25% paraffin oil, and 25% white petroleum jelly.

11. The latex composition according to claim 7, wherein the paraffin emulsion comprises 50-60% distilled water and 40-50% silicone oil.

12. The latex composition according to any one of claims 7-11 , wherein the paraffin emulsion comprises an emulsifying agent as a mixture of 0.09-0.15% polyethylene glycol PEG 400, 0.09-0.15% polyethylene glycol PEG 1600, 0.07-0.12% g glyceryl monooleate, 0.10-0.16% sodium palmitate 0.003-0.006% borax or potassium stearate.

13. The latex composition according to claim 1 , wherein it comprises 72.18 wt.% of natural latex with high ammonium content and dry content of 61 %, 2.10 wt%. coagulant, 0.19 wt.% surfactant in the form of potassium palmitate, 0.87 wt.% formalin, and vulcanization dispersant to an amount of 2.48 wt.%, containing 22 wt % NaOH, 55.9 wt%. of sulfur in the form of sodium polysulfide or ammonium polysulfide, further, the latex composition comprises 21.79 wt.% zinc oxide, 0.1 1 wt.% Lavinox and 0.03 wt.% Tamol and paraffin emulsion in an amount of 0.25 wt%, wherein the pH of the mixture is 10.3, adjusted by the addition of 7% NaOH solution.

14. A method for preparing a latex composition comprising the steps of adding 265 kg of natural latex with a high ammonium content and dry content of 61 % to a container equipped with a water jacket and ribbon agitator, introducing 7.7 kg coagulant after stabilization of the temperature at 32°C, then adding 0.68 kg of the surfactant and all the time adjusting the pH of the mixture to 10.3, then adding in portions 37% formalin solution in an amount of 3.2 kg, at the end adding vulcanization dispersion to the container in an amount of 9.1 kg, said vulcanization dispersion is prepared separately, and finally adding paraffin in an amount of 0.9 kg to the latex composition.

15. The method according to claim 14, wherein the vulcanization dispersion is generated by introducing into the 120 liter container equipped with a stirrer, heated by a diaphragm with water vapor, 60 kg of 50% NaOH solution, then 76 kg of sulfur, and heating the container under reflux to a gentle boiling for 4 hours, followed by hot filtration of the contents of the container and cooling to a temperature of 30°C, adding 80 kg of zinc oxide, 0.42 kg Lavinox and 0.12 kg Tamol to the cooled mixture and then stirring the mixture vigorously for 40 minutes to achieve high homogeneity and then degassing the mixture three times using a vacuum of 10 kPa and removing air bubbles suspended in the mixture

16. The method according to claim 14 or 15, wherein the sulfur is in the form of a fine crystalline or in the form of a polysulfide.

17. The method according to claim 16, wherein the sulfur is in the form of an alkali metal polysulfide or an alkaline earth metal polysulfide or ammonium polysulfide, preferably in the form of polysulfide of sodium, potassium or ammonium.

18. The method according to claim 14-17, wherein potassium palmitate, a mixture of sodium stearate and sodium palmitate in a ratio of 1 : 1 is used as a surfactant.

19. The method according to claim 14-18, wherein the paraffin emulsion is prepared separately in a high shear industrial mixer with a 12 liter tank, by mixing for 20 minutes 5 kg of distilled water, 2 kg of paraffin oil, 1 kg of white petroleum jelly and 1 kg of hard paraffin and using as the emulsifier a mixture of 10 g of polyethylene glycol PEG 400, 10 g of polyethylene glycol PEG 1600, 8 g of glyceryl monooleate, 1 1 g of sodium palmitate and 4 g of borax.

20. The method according to claim 14-18, wherein the paraffin emulsion is prepared separately in a high shear industrial mixer with a 12 liter tank, by mixing for 20 minutes, 5 kg of distilled water, 2.5 kg of paraffin oil, 2.5 kg white petroleum jelly without hard paraffin, using as the emulsifier a mixture of 10 g of polyethylene glycol PEG 400, 10 g of polyethylene glycol PEG 1600, 10 g of glyceryl monooleate, 15 g of sodium palmitate and 3 g of borax.

21. The method according to claim 14-18, w wherein the paraffin emulsion is prepared separately in a high shear industrial mixer with a 12 liter tank, by mixing at the high temperature of 85°C for 20 minutes, 5 kg of distilled water, 4 kg of silicone oil, using as the emulsifier a mixture of 10 g of polyethylene glycol PEG 400, 10 g of polyethylene glycol PEG 600, 10 g of glyceryl monooleate, 15 g of sodium palmitate and potassium stearate 5 g.

22. The method according to claim 14-21 , wherein the pH of the mixture is maintained at 10.3 all the time by the addition of 7% NaOH solution.

23. The method according to claim 14-21 , wherein the pH of the mixture is maintained at 10.3 all the time, introducing stepwise 35% ammonium chloride solution forming ammonia buffer, wherein the solution of ammonium chloride is added in an amount of 1.6 kg.

24. The method according to claim 14-21 , wherein the pH of the mixture is maintained at 10.3 all the time by the addition of an appropriate amount of a 10% solution of CHES.

25. A latex article made from a blend as defined in the claims 1-13.

26. A latex article made from a mixture obtained by the method according to claim 14- 24.

27. A article of claims 25-26, wherein the product is a glove providing electrical insulation.