Classifications

• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
  • C08J5/00—Manufacture of articles or shaped materials containing macromolecular substances
  • C08J5/02—Direct processing of dispersions, e.g. latex, to articles
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
  • C08L7/00—Compositions of natural rubber
  • C08L7/02—Latex
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
  • C08J2307/00—Characterised by the use of natural rubber
  • C08J2307/02—Latex
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
  • C08J2309/00—Characterised by the use of homopolymers or copolymers of conjugated diene hydrocarbons
  • C08J2309/10—Latex

Definitions

• the present invention relates to the field of manufacturing latex products. More particularly the present invention relates to a method of manufacturing latex products through binary process using Rubber Lattices such as Natural Rubber Latex including Hevea brasiliensis and Guayule latex and Synthetic Rubber Lattices including Nitrile, Polychloroprene and Polyisoprene.
• Rubber Lattices such as Natural Rubber Latex including Hevea brasiliensis and Guayule latex
• Synthetic Rubber Lattices including Nitrile, Polychloroprene and Polyisoprene.
• Dipped latex products such as gloves, condoms, balloons and finger cots are made by well-established manufacturing process where the curing agent typically sulphur, accelerators, activators, surfactants are added to one or more of the lattices, namely: Natural Rubber Lattices including Hevea brasiliensis and Guayule latex and Synthetic Rubber Lattices including Nitrile, Polychloroprene and Synthetic Polyisoprene to prepare a liquid compound used in the dipping process. Dipping is a process where formers, which are articles having the shape of the required finished articles such as gloves, condoms, balloons, etc., are dipped into a liquid compound of the selected latex. When the formers are withdrawn from the compounded latex, a thin film of the latex compound remains coated on the formers. Then the film is dried and heated to cure the polymer to form the dipped article.
• the curing agent typically sulphur, accelerators, activators, surfactants are added to
• successive layers are applied by carrying out repeated dipping of the coated formers into latex compound again and then drying the film.
• the process is ' repeated on the dried film to improve physical properties of the finished product and / or add colour to the film.
• Two or more repetitions of dipping is carried out depending upon the nature of Formulation of compound, intended level of thickness and physical properties, colour addition to the coating of the film etc.
• the coated film is removed from the former in the shape of the required article.
• the dipping process is automated so that a number of formers are mounted on an endless conveyor chain that carries the formers through stages of immersion into latex compound (termed dipping) followed by drying in heated ovens and eventually removal of article from the formers.
• the majority of the dipped latex products manufacturers use the dipping process broadly described above.
• the overall machinery inclusive of latex compound storing vessels and related automation to carry out the dipping process is called a dipping plant.
• the latex holding vessels in which the latex compound is held to enable formers to be dipped are called dippers or dipping tanks. These dippers have built-in cooling provisions to maintain latex temperature within predetermined range.
• the plant would have two or more dippers and associated drying ovens. For example, if two coatings of latex compound are to be made on the former then there could be two different dippers. In some designs the same formers are repeatedly immersed into the dippers twice. This is achieved by routing the formers carried by endless conveyor chain twice into the same dipper.
• condoms which are manufactured from the rubber lattices by employing dipping process, are commonly used during sexual intercourse to reduce the probability of pregnancy and / or prevent spreading sexually transmitted diseases.
• condoms have been made from natural rubber latex but more recently condoms made from various synthetic elastomers have been introduced.
• condoms made from synthetically prepared polyisoprene have been found to offer a number of advantages over traditional condoms.
• the synthetically prepared polyisoprene serves as a suitable substitute of natural latex for manufacturing condoms.
• the synthetic polyisoprene is known to cure very fast. This pre-disposes manufacturing process to be designed such that the cure rate is kept well controlled until conversion into condoms by dipping process.
• the fast curing is managed through lowering the temperature of the latex in the plant. As compared to natural rubber latex where the compound is maintained at about 25°C the synthetic latex needs to be maintained at 15°C. Therefore, while manufacturing dipped latex articles from the synthetic lattices the temperature is required to be maintained at 15°C so that reduction in the rate of curing (in this case pre-vulcanisation) can be achieved.
• One of the methods disclosed in Patent publication WO2007113463 requires the latex to be stored and used in low temperature preferably at 15°C or less to slow down curing. This process of cooling is expensive.
• Patent publication US10/085,890 In another method of preventing the fast cure is disclosed in Patent publication US10/085,890. That patent requires the use of unusual compounding ingredients some of which are considered toxic.
• the present invention provides a binary process for manufacturing dipped latex product.
• the binary process includes preparing a first latex mixture Formulation A comprising latex, one or accelerators, and one or more surfactants, and preparing a second latex mixture Formulation B comprising latex, one or more curing agents, and one or more surfactants. Further, dipping one or more formers into the Formulation A and B separately in order to form a plurality of coatings/layers of the Formulation A and B, and later on curing the plurality of coatings/layers on the formers to form the dipped latex products.
• the present invention provides a binary process for manufacturing of dipped latex products.
• the disclosed binary process is advantageous; both in cases of using synthetic and natural lattices for manufacturing of dipped latex products. It is particularly advantageous when used for manufacturing from fast curing synthetic lattices such as, but not limited to, nitrile, polychloroprene and synthetic polyisoprene.
• the present invention overcomes the disadvantages inherent in the use of synthetic rubber lattices, which are namely fast curing rate and requirement of maintaining low temperature at 15°C or less to overcome the problem of fast curing rate.
• the present . invention provides for the binary process for manufacturing . dipped latex products including following steps: - 1 ) Preparing two separate mixtures of the latex in two different dippers each held at a temperature of 24°C to 30°C, wherein the first mixture is designated as Formulation A including the latex and an accelerator, such as, but not limited to, zinc dibutyl dithiocarbamate and other surfactants and the second mixture is designated as Formulation B including the latex and curing agents, such as, but not limited to, sulphur and other surfactants.
• an accelerator such as, but not limited to, zinc dibutyl dithiocarbamate and other surfactants
• Formulation B including the latex and curing agents, such as, but not limited to, sulphur and other surfactants.
• sulphur donors such as thiuram sulphides and dithiomorpholine can also be used.
• this invention envisages coating formers initially with the Formulation A including the accelerator compound only in the first dip by immersing them to a depth sufficient to yield the finished latex product of desired length. The first coating is then partially dried on the formers.
• the formers already coated with Formulation A, are then dipped into the Formulation B including the curing agent compound in the second dip.
• the second coating is then dried.
• the formers are then heated to appropriately initiate vulcanization of the two layers to form cross linking.
• the process of vulcanization initiates automatically once the accelerator and curing agent compounds come in contact with each other.
• Subsequent heating of the film formed on the formers by the two coats at 60°C to 12Q°C in the ovens accelerates the ' process of vulcanization and cross linking takes place to form the cured film * ..
• the dipping process is adjusted to achieve the desired thickness and length as per the dipped latex product to be manufactured.
• Subsequent steps in the manufacturing process such as exposure to vulcanizing ovens, leaching, stripping of product from the formers etc., are similar to those employed in the normal manufacture of dipped latex products.
• the formers are first dipped into the Formulation A having accelerator compound, preferably kept at 24°C to 30°C.
• the first dipping stage forms a thin coating of the Formulation A containing the accelerator compound on the former.
• This accelerator coating is dried in a hot oven.
• the coating remains as a dry film, on the formers while the formers are dipped into the Formulation B containing the curing agents, preferably kept at 24°C to 30°C in the next dipper.
• the formers While coming out of the second dipper the formers have an over-coating of the curing agent compound on the previously made accelerator coating. Further, the coatings so formed are dried and vulcanized by heating.
• the coat formed over the formers dipped in the Formulation A is not allowed to dry completely, and the formers are dipped into the Formulation B to form another coat and then the coatings so formed are dried and vulcanized by heating.
• three sequential dips are allowed.
• a sandwich of curing compound film made by the Formulation B between two accelerator compound films made by the Formulation A is created.
• the formers are first dipped into the Formulation A having accelerator compound to form a thin coating of the Formulation A on the formers and the accelerator coating is dried in a hot oven.
• the said formers having dry film of latex formed by Formulation A is again dipped in the Formulation B to form a thin over coating of Formulation B, which is then dried in the hot oven.
• the said formers, having dried film formed by coatings of Formulation A and B are again dipped in the Formulation A to form a thin over coating of the Formulation A. Thereafter, all the coatings are dried in the hot oven and curing is performed.
• three sequential dips are allowed with alterations in drying pattern of the coats formed by Formulation A and B.
• a sandwich of curing compound film made by the Formulation B between two accelerator compound films made by the Formulation A is created.
• the formers are first dipped into the Formulation A having accelerator compound to form a thin coating of the Formulation A on the formers and the accelerator coating is dried in a hot oven.
• the said formers having dry film of latex formed by Formulation A is again dipped in the Formulation B to form a thin over coating of Formulation B, which are then are again dipped in the Formulation A to form a thin over coating of the Formulation A without drying the coating formed by Formulation B. Thereafter, all the coatings are dried in the hot oven and curing is performed.
• the products manufactured by the disclosed process have physical properties similar to that of the products made from lattices mixed with curing agent and accelerator stored at low temperature through conventional method.
• the binary process significantly improves the degree of control over the state of any pre-vulcanization of the latex at the time of dipping. This means that products have more reproducible properties and there is less lot-to-lot variability.
• the process can also be used to dip with a lower degree of pre-vulcanization. This improves film integration leading to improved properties and improved product reproducibility.
• the binary process disclosed in the present invention is useful in manufacturing variety of dipped latex products including, but not limited to, medical gloves, condoms, balloons, male external urinary drainage catheters, surgical tubing, contraceptive diaphragms, finger cots, catheter balloons and cuffs, uterine thermal ablation balloons, drug infusion bladders, tissue retrieval pouches, medical tubing, baby bottle nipples, infant pacifiers, anesthesia breather bags, resuscitation bags, rubber dental dams, and exercise bands.
• the invention can be applied to any latex material used for making dipped products.
• a key advantage of dipped articles produced from synthetic latex is the absence of natural rubber latex proteins that can lead to Type I allergic reactions. If both natural rubber latex and synthetic rubber latex products are made in same plant it is essential while switching between the lattices to use cleaning measures to prevent cross-contamination of the synthetic latex products with natural latex and its components. All equipment should be thoroughly cleaned before preparation of dispersions and solutions. Ensure that the cleaning removes all residues / traces of any natural latex and related proteins. While handling synthetic latex plant operators and technicians should wear hitrile rubber .gloves throughout manufacture. The present invention is explained further in the following specific examples which are only by way of illustration and are not to be construed as limiting the scope of the invention.
• the compounding ingredients were added to the latex in the form of dispersions in water. Standard procedures that are well established in the art can be used for the preparation of these dispersions.
• the solutions were prepared as follows:
• Emulgin® B2 solution surfactant - Cetyl stearyl alcohol etherified with 20 mol Ethylene Oxide
• the pH of the above dispersions were adjusted to be > 11.5 by adding 0 % KOH solution if necessary.
• Step B COMPOUNDING OF SYNTHETIC LATEX
• the synthetic polyisoprene latex is used in this example.
• a key element of the invention is the preparation of two separate mixtures, one designated as "Formulation A” containing synthetic latex and accelerator mixture and the other designated as "Formulation B” containing synthetic latex and curing agents' mixture.
• the required quantity of synthetic latex (Kraton® IR 401) was transferred into a compounding vessel (designated for "Formulation A") using a designated pump. During transfer the latex was filtered through 40 micron filter.
• the latex was stirred using a mechanical stirrer with a speed of rotation within the range of 30 to 60 rpm.
• the temperature of the compounded latex was maintained within (27 ⁇ 3)°C throughout this process until the compounded latex was transferred to the Dipping Line.
• the addition of solutions to late was performed in the following manner: The required quantity of the 20% Emulgin® B2 solution was weighed into a SS (stainless steel) container. The pH of the solution was adjusted to a range between 11.5 to 12.5 by adding 10% KOH solution as needed. The Emulgin®B2 solution was then added to the Kraton® IR - 401 latex at a slow rate over 5 minutes. The SS container was then rinsed with 0.01 % of KHWS solution which was then added to Kraton IR - 401 latex. The latex was then allowed to mix for 15 minutes.
• the required quantity of 10% potassium oleate was weighed into in an SS container and added to the Kraton IR - 401 latex at a slow rate over 15 minutes.
• the SS container was rinsed with 0.01% of KHWS solution which was then added to Kraton® IR - 401 latex.
• the latex was then allowed to mix for a duration of 45 minutes.
• the required quantity of the 15% Anilan solution was weighed into the SS container and added to the Kraton® IR - 401 latex at a slow rate over 15 minutes.
• the SS container was rinsed with the 0.01 % of KHWS solution which was then added to the Kraton® IR - 401 latex.
• the latex was then allowed to mix for 15 minutes.
• the required quantity of the 5% Potassium Hydroxide solution was weighed into the SS container and then added to the Kraton® IR - 401 latex at a slow rate over 15 minutes.
• the SS container was rinsed with the 0.01% of KHWS solution which was added to the Kraton IR - 401 latex.
• the required quantity of the 40% Struktol® LA229 was weighed into a SS container.
• the pH of the paste was adjusted to a range between 11.5 and 12.5 by adding the 10% of KOH solution as needed.
• the paste was then added to the Kraton® IR - 401 latex at a slow rate over 15 minutes under mixing.
• the lid of the compounding tank was then closed.
• the compounded latex was continually stirred for a duration of 24 hours and afterwards kept without agitation for further duration of 24 hours.
• the properties of the compounded latex such as total solids content, total alkalinity, pH, and viscosity were measured.
• the Formulation A was then transferred to the Dipping Line.
• the latex was stirred using a rnechanical stirrer with a speed of rotation within the range of 30 to 60 rpm.
• the temperature of the compounded latex was maintained within (27 ⁇ 3)°C throughout this process until the compounded latex was transferred to the Dipping Line.
• the addition of solutions to the latex was performed in the following manner: The required quantity of the 20% Emulgin® B2 was weighed into a SS container. The pH of the solution was adjusted to a range between .5 to 12.5 by adding the 10% of KOH solution as needed. The solution was then added to the Kraton® IR - 401 latex at a slow rate over 15. minutes. The SS container was rinsed with the 0.01 % of KHWS solution which was then added to the Kraton® IR - 401. The latex was then allowed to mix for a duration of 15 minutes.
• the required quantity of the 10% potassium Oleate was weighed into the SS container and then added to the Kraton® IR - 401 latex at a slow rate over 15 minutes.
• the SS container was rinsed with the 0.01% of KHWS solution which was then added to the Kraton® IR - 401 latex.
• the latex was then allowed to mix for a duration of 45 minutes.
• the required quantity of the 15% Anilan solution was weighed into the SS container and added to the Kraton® IR - 401 latex at a slow rate over 15 minutes.
• the SS container was rinsed with the 0.01% of KHWS solution which was then added to the Kraton® IR - 401 latex.
• the latex was then allowed to mix for a duration of 15 minutes.
• the required quantity of the 5% Potassium Hydroxide solution was weighed into the SS container and added to the Kraton® IR - 401 latex at a slow rate over 15 minutes.
• the SS container was sensed with the 0.01% of KHWS solution which was then added to Kraton® IR - 401 latex.
• the required quantity of the 50% sulphur paste dispersion was weighed into a SS container.
• the sulphur paste dispersion was well mixed and homogenized before use.
• the pH of the paste was adjusted to between 11.5 to 12.5 by adding the 10% of KOH solution as needed.
• The. sulphur pasted then added to the Kraton® IR - 401 latex at a slow, rate over 5 minutes.
• the SS container was rinsed with the 0.01% of KHWS solution which was then added to Kraton® IR - 401 latex.
• the latex was then allowed to mix for a duration of 15 minutes.
• the required quantity of the 40% Struktol® LA229 was weighed into the SS container.
• the pH of the dispersion was adjusted to between .5 to 12.5 by adding the 10% of KOH solution as needed.
• the dispersion was then added to the Kraton® IR - 401 latex at a slow rate for over 15 minutes under mixing.
• the lid of the compounding tank containing the Formulation B was then closed.
• the compounded latex, after addition of all the dispersions, was continually stirred for about 24 hours and then kept it without agitation for a further 24 hours.
• the properties of the compounded latex such as total solids content, total alkalinity, pH, and viscosity were measured.
• Step C CONDOM DIPPING PROCESS
• the compounded Formulation A from the compounding tank 1 and the compounded Formulation B from the compounding tank 2 were transferred to dipping tank 1 and dipping tank 2 respectively 3-6 hours before use to allow air bubbles to vent out from the latex compound.
• the temperature of the compounds in the dipping vessels and their respective reserve tanks was maintained within (27 ⁇ 3)°C throughout the Dipping Process. This temperature regulation is needed to maintain physical properties such as viscosity, total solids content etc. and to minimize loss of water due to evaporation and is not critical to control vulcanization / pre-vulcanisation : As such no significant vulcanization / pre-vulcanisation takes place at this stage. Dipping was carried out using the above compounds independently, the Formulation A in the first dipper and Formulation B in the second dipper. The dippers were distinctly separated from each other to prevent cross contamination. Dipping was performed as per previously established methods for making condoms using conventional dipping processes.
• the films of latex compound coated on the formers were dried by means of electrical heaters set to achieve film temperatures of 60°C to 120°C.
• the accelerator compound (Formulation A) coating had an over coating of sulphur compound (Formulation B) and vulcanization was initiated at this stage.
• the dried film was immersed in 1% slurry of composite paste with accelerator in the third dip to prevent surface stickiness.
• the condoms were collected in wet slurry for further processing. The condoms will then be removed from the formers and will undergo washing and drying processes, called post-treatment, in the same way as conventionally manufactured condoms.
• condoms are collected every hour from the formers, washed in slurry and dried by means of air-heating. At this stage, further vulcanizing occurs giving the condoms necessary strength.
• the strength of the condoms can be measured by the established air inflation test where the condoms are inflated with air until they burst. The volume of air inflated and the pressure achieved at the point of bursting are indicators of how good the film / condom is and the consistency of the process of manufacturing.
• EXAMPLE 2 USING SYNTHETIC POLYISOPRENE LATEX - Different method of dipping Step A: Preparation of Dispersions and Solutions and Step B: Compounding of Synthetic Latex will be same as in Example 1
• the Dipping was carried out using the above compounds independently, the Formulation A in the first dipper and Formulation B in the second dipper.
• the dippers were distinctly separated from each other to prevent cross contamination. Dipping was performed as per previously established methods for making condoms using conventional dipping processes.
• the films of latex compound coated on the formers were not dried before forming the next coating.
• the accelerator compound (Formulation A) coating gets an over coating of sulphur compound (Formulation B) when the first coating is still in nearly wet condition and vulcanization was initiated at this stage.
• the process was to dip1 - dryl then dip2 and dry2. But in this it is to dip1 - dip 2 and then dry / vulcanise.
• Step A Preparation of Dispersions and Solutions and Step B: Compounding of Synthetic Latex will be same as in Example 1
• the Dipping was carried out using the above compounds independently, the Formulation A in the first dipper, Formulation B in the second dipper and again Formulation A in the third dipper.
• the dippers were distinctly separated from each other to prevent cross contamination. Dipping was performed as per previously established methods for making condoms using conventional dipping processes.
• the films of latex compound coated on the formers were dried by means of electrical heaters set to achieve film temperatures of 60°C to 120°C.
• the accelerator compound (Formulation A) coating had an over coating of sulphur compound (Formulation B) and vulcanization was initiated at this stage.
• the dried film was coated in Formulation A again to build a sandwich of sulphur compound inside.
• the condoms were collected in wet slurry for further processing.
• Step A Preparation of Dispersions and Solutions and Step B: Compounding of Synthetic Latex will be same as in Example 1.
• Dipping was carried out using the above compounds independently, the Formulation A in the first dipper, Formulation B in the second dipper and again Formulation A in the third dipper.
• the dippers were distinctly separated from each other to prevent cross contamination. Dipping was performed as per previously established methods for making condoms using conventional dipping processes.
• the variation is to make the third coating on the second coating without drying the second coating. That is dipl - dry 1 - dip 2 - dip 3 - dry / vulcanise.
• the advantages were on thickness control on different layers.
• EXAMPLE 5 USING NATURAL RUBBER LATEX
• natural rubber latex - derived from Hevea brasiliensis is used - as against previous examples wherein synthetic polysisoprene was used.
• formulations A, B are same as before but the differences would be in the type of surfactants and other ingredients added.
• Step A PREPARATION OF LATEX FORMULATION A
• the required quantity of natural rubber latex was transferred into a compounding vessel (designated for "Formulation A") using a designated pump. During transfer the latex was filtered through 40 micron filter.
• the latex was stirred using a mechanical stirrer with a speed of rotation within the range of 30 to 60 rpm.
• the temperature of the compounded latex was maintained within (27 ⁇ 3) °C throughout this process until the compounded latex was transferred to the Dipping Line.
• Step B PREPARATION OF LATEX FORMULATION B
• the required quantity of natural rubber latex was transferred into a compounding vessel (designated for "Formulation B") using a designated pump. During transfer the latex was filtered through 40 micron filter.
• the latex was stirred using a mechanical stirrer with a speed of rotation within the range of 30 to 60 rpm.
• the temperature of the compounded latex was maintained within (27 ⁇ 3) °C throughout this process until the compounded latex was transferred to the Dipping Line.
• the two formulations A, B are taken for dipping.
• Condoms made using the disclosed binary method should be allowed to undergo further maturation in room temperature storage for 4 weeks. The physical properties improve further during this period due to continued curing of the latex film. After maturation the condoms can be tested electronically for defects such as pin-holes etc. and any defectives found segregated and disposed off. Those that be free from manufacturing defects can be packed in foil packing as rs' requirements, .
• features of condoms manufactured by the binary process and conventional process were compared and it was found that both types of condoms have similar swelling index, burst volume and burst pressure.
• Physical properties of the finished products are determined by how much of the sulphur has formed cross links within and between the polyisoprene chains or the lattices. For Lattices this process is termed as "vulcanization".
• pre- vulcanization is used to refer to the vulcanization taking place at the stage of preparing liquid compound using the lattices.
• curing is generally used in place of "vulcanization” in the document.

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