WO2006038761A1

WO2006038761A1 - Antibacterial latex foam containing nano-silver particles and method of producing the same

Info

Publication number: WO2006038761A1
Application number: PCT/KR2005/001890
Authority: WO
Inventors: Seon-Woo Noh
Original assignee: Individual
Current assignee: Individual
Priority date: 2004-10-05
Filing date: 2005-06-17
Publication date: 2006-04-13
Anticipated expiration: 2007-04-05
Also published as: KR100495530B1

Abstract

The present invention relates to a method of producing antibacterial latex foam containing nano-silver particles and antibacterial latex foam produced by the method. The method of producing antibacterial latex foam according to the present invention is an im¬ provement of a conventional method of producing antibacterial latex foam and is performed through a series of steps of: preparing a latex solution by mixing rubber latex as a base material with subsidiary materials; separately preparing an aqueous emulsion solution containing fine silver powder; mixing the latex solution and the aqueous emulsion solution with each other and aging the mixture to prepare an antibacterial latex raw material; and foaming, curing and gelating the antibacterial latex raw material to obtain antibacterial latex foam. The present invention incorporates nanometer-sized silver particles into latex foam at a low concentration so that the latex foam has superior antibacterial activity. Accordingly, the latex foam of the present invention can be variously applied to a variety of latex foam and products obtained by processing the latex foam, which intend to prevent bacterial reproduction.

Description

ANTIBACTERIAL LATEX FOAM CONTAINING NANO- SILVER PARTICLES AND METHOD OF PRODUCING THE

SAME

Technical Field

[1] The present invention relates to latex foam and a method of producing the same, and more particularly, to latex foam with antibacterial activity and a method of producing the same.

[2]

Background Art

[3] Latex foam is generally produced by adding various additives such as a vul¬ canization accelerator, a vulcanizing agent, a hardener, a hardening accelerator and a foaming agent to rubber as a main component, and foaming the mixture to generate minute bubbles.

[4] Since latex foam is obtained by using rubber with high elasticity as a main component, generating minute bubbles therein and curing the material, it has a property of high softness and has been employed in various fields. Today, latex foam has been used for a latex mattress that is a kind of health care article.

[5] Since latex foam itself does not have antibacterial activity, there have been recently developed several methods to impart antibacterial activity to latex foam or a rubber product close to its raw material. The representative methods for imparting an¬ tibacterial activity to a rubber product are disclosed in Japanese Patent Laid-Open Publication No. (Hei)9-111053, and Korean Patent Laid-Open Publication Nos. 2002-1896 and 2004-64467.

[6] Japanese Patent Laid-Open Publication No. (Hei)9-111053 is directed to Rubber containing an antibacterial agent, rubber gloves and a rubber finger thimble containing an antibacterial agent, and a method of producing the same, wherein the antibacterial agent is prepared by impregnating zeolite or silica gel with silver, copper, zinc or the like. Although this cited invention employs a metal component such as silver, copper or zinc with high antibacterial activity, the metal component is employed not as it is but in a state where a carrier such as zeolite or silica gel is impregnated with the metal component. Thus, there is a disadvantage in that it is impossible to sufficiently utilize antibacterial activity of the silver component itself. Further, this cited invention has a disadvantage in that an additional process for preparing the aforementioned silver- zeolite or silver-silica gel is required. Therefore, even though the cited invention uses silver exhibiting high antibacterial activity, zeolite or silica gel contains the silver component or the like therein and functions as a kind of complex. Thus, there is an intrinsic disadvantage in that it is impossible to fully use antibacterial activity exhibited by the silver component itself.

[7] Further, Korean Patent Laid-Open Publication No. 2002- 1896 is directed to "A method of preparing an antibacterial sanitary article using natural rubber latex," and discloses a method of preparing a sanitary article using natural rubber latex, which can inhibit the propagation and reproduction of microorganisms at a contact region with a human body. However, since Korean Patent Laid-Open Publication No. 2002-1896 also uses zeolite that bears silver ions or zinc ions as an antibacterial agent, it has the same disadvantage as the invention disclosed in Japanese Patent Laid-Open Publication No. (Hei)9-111053.

[8] Furthermore, Korean Patent Laid-Open Publication No. 2004-64467 is directed to

"A functional latex mattress, and a method and apparatus for producing a functional latex mattress, and discloses a method comprising the steps of aging an undiluted solution for latex for 12 to 36 hours, adding components such as vulcanization ac¬ celerators, vulcanizing agents, hardeners, hardening agents, oxidizing agents, fillers and charcoal powders to the solution in a colloidal state, foaming the aged latex solution for 30 to 40 minutes, molding the latex solution in a mold, and washing a resultant molded product. Although this cited invention asserts that the addition of charcoal powders gives beneficial effects to a human body, the description of the publication does not provide objective data capable of supporting the assertion. Therefore, it is considered that the cited invention gives consequence to the mass- production of a latex mattress rather than imparting of functionality to the latex mattress, and the accompanying drawings also support such presumption.

[9]

Disclosure of Invention Technical Problem

[10] As described above, there have been provided several techniques and methods for imparting antibacterial activity to latex products. However, there have not yet been developed a method enabling an inorganic antibacterial agent made of an inorganic material to directly provide antibacterial activity, and a latex product and latex foam produced by the method.

[11] Accordingly, it is an object of the present invention to provide a method of producing a latex product, particularly, antibacterial latex foam that is formed with a plurality of minute bubbles using latex as a base material and contains nano-silver particles capable of exhibiting its own antibacterial activity.

[12] It is another object of the present invention to provide antibacterial latex foam containing nano-silver particles produced by the above method. Technical Solution

[13] The present invention is directed to a method of producing antibacterial latex foam containing nano-silver particles, and antibacterial latex foam produced by the method.

[14] The method of the present invention comprises the steps of: preparing a latex solution by mixing rubber latex as a base material with subsidiary materials according to a conventional method, wherein the subsidiary materials comprise 1.0 to 5.0 PHR of vulcanizing agent, 0.5 to 2.0 PHR of antioxidant, 0.2 to 5.0 PHR of vulcanization ac¬ celerator, 0.5 to 2.0 PHR of foaming stabilizer and 5 to 200 PHR of filler based on 100 weight parts of rubber latex; preparing an aqueous silver emulsion solution consisting of 0.005 to 0.1 weight parts of silver powder and 1 to 10 weight parts of silver dispersion for dispersing the silver powder therein based on 100 weight parts of rubber latex; preparing an antibacterial latex material by mixing the latex solution with the aqueous silver emulsion solution and aging the mixture; producing latex foam by foaming, vulcanizing and curing the antibacterial latex material; and post-processing the latex foam by molding, cooling, releasing and washing the produced latex foam according to a conventional method.

[15] Further, the present invention provides antibacterial latex foam produced by the above method, which contains 0.005 to 0.1 weight parts of silver powder based on 100 weight parts of rubber latex.

[16]

Advantageous Effects

[17] Since the method of producing the antibacterial latex foam according to the present invention can directly use silver powder, it has an advantage in that there is no need for additional preparation of a carrier containing a silver component contrary to con¬ ventional methods. Therefore, according to the method of the present invention, there are advantages in that it is not necessary to perform a process of additionally preparing a silver carrier (i.e., zeolite or silica gel containing a silver component) and to purchase the silver carrier at high expense.

[18] Further, the method of producing the antibacterial latex foam according to the present invention has an advantage in that the amount of a silver component to be used can be significantly reduced. This means that even though the method of the present invention uses the amount of an effective component smaller than that in a con¬ ventional method, it can produce latex foam with antibacterial activity comparable to that of an existing product. In particular, the method of producing the latex foam according to the present invention can sufficiently exhibit high antibacterial activity in a low concentration range that has been considered to be inappropriate in the prior art. Accordingly, the method of producing the latex foam according to the present invention has a significant advantage in view of the efficient use of finite resources.

[19] Further, the latex foam produced by the method of the present invention exhibits significantly high antibacterial activity. In particular, in a case of using the latex foam as a material for cosmetic puffs, there is an advantage in that such cosmetic puff can exert sterilizing effects on bacteria that infect the skin with which the cosmetic puffs are in contact, and thus, they can be very effectively used.

[20] Furthermore, since the latex foam produced by the method of the present invention exhibits high antibacterial activity, there is an advantage in that sterilizing effects thereof on bacterial infection can be applied to various uses. For example, in a case where the latex foam of the present invention is used for soles of sneakers, since the soles of sneakers themselves have antibacterial activity, it is possible to manufacture antibacterial sneakers that can sterilize various types of bacteria infecting the interiors of the sneakers without using an additional antibacterial agent. Accordingly, there is an advantage in that the latex foam of the present invention can be widely used for prevention of bacterial infection. Brief Description of the Drawings

[21] Fig. 1 shows measurement data of an antibacterial activity test for antibacterial latex foam of the present invention using Staphylococcus aureus at the FITI Testing & Research Institute in Korea.

[22] Fig. 2 shows measurement data of an antibacterial activity test for antibacterial latex foam of the present invention using E. coli at the FTTI Testing & Research Institute in Korea.

[23] Fig. 3 shows measurement data of an antibacterial activity test for antibacterial latex foam of the present invention using Klebsiella pneumoniae at the FITI Testing & Research Institute in Korea.

[24]

Mode for the Invention

[25] Hereinafter, the present invention will be specifically described on a step basis.

[26]

[27] 1. Step of preparing a latex solution:

[28] The present invention uses rubber latex as a base material. Unless specifically mentioned herein, the contents of components are based on 100 weight parts of rubber latex. The term "rubber latex" herein includes synthetic rubber latex, natural rubber latex and a mixture thereof.

[29] The synthetic rubber latex is preferably used since a product made thereof through emulsion polymerization at low temperature has uniform particles and low surface tension. It is preferred that the synthetic rubber latex can be easily mixed with natural rubber latex and low viscosity be maintained by regulating its solid content to a range of 60 to 80%. The synthetic rubber latex includes chloroprene latex, oil-resistant latex (NBR LATEX) and the like.

[30] Meanwhile, the natural rubber latex includes ammonia-treated natural rubber latex and non-treated natural rubber latex. It is preferred that the ammonia-treated natural rubber latex be concentrated to have its solid content of about 60% through cen- trifugation and contain about 0.6 to 0.8% of ammonia as an antiseptic. In contrast, the non-treated natural rubber latex has no ammonia added as an antiseptic through an additional process.

[31] In the present invention, if the ammonia-treated natural rubber latex is used as a base material, a "deammoniation" process is inevitably required. If the concentration of the ammonia component is high, the ammonia component contained in the latex hinders gelation upon production of latex foam. Thus, it is preferred that the ammonia component be removed in advance.

[32] In the present invention, the "deammoniation"process can be effectively performed by slowly stirring the natural rubber latex at a low speed of about 30 to 70 rpm and causing the surface of the latex to come into contact with humid air. In order to reduce time required for the deammoniation process, it is preferred that the natural rubber latex be heated to about 40°C However, if the natural rubber latex is heated to 40°C or more, it adversely affects the stability of the latex. Thus, it is desirable to heat the latex to less than 40°C. After the deammoniation process, the concentration of ammonia in the latex is preferably about 0.12 to 0.2%.

[33] Since the concentration of ammonia in the latex has a direct effect on a fine cell

(bubble) structure of the latex during a subsequent gelation process for the latex in the present invention, it is very important to measure the content of ammonia in the latex.

[34] In the present invention, a method of measuring the content of ammonia in the latex can be performed as follows:

[35] i) Add 10 g of natural rubber latex into a beaker of 500 D;

[36] ii) Dilute it with water to a final volume of 300 D;

[37] iii) Add about 1 % of nonionic surfactant into the beaker and mix them therein;

[38] iv) Titrate the mixture with 1 N HCl(based on pH= 5.2); and

[39] v) Ammonia concentration(%)

[40] = { HCl(D)xactor(HCl)/sample concentration } x 100

[41]

[42] In the present invention, the rubber latex as a base material may comprise subsidiary components such as a vulcanizing agent, a vulcanization accelerator, an an¬ tioxidant, a foaming stabilizer, a filler and the like in the same manner as an ordinary case.

[43] When the latex raw material is vulcanized, the vulcanization accelerator is used to shorten vulcanization time and to lower vulcanization temperature. Preferably, 0.1 to 3.0 PHR of EZ (zinc diethyl dithiocarbarmate) is used as a primary accelerator, and 0.1 to 2.0 PHR of MZ (zinc mercaptobenzothiazol) is used as a secondary accelerator. Instead of EZ, zinc dibuthyl dithiocarbarmate may be used as the primary accelerator. Here, the term "PHR"means a percentage to the dry weight of the rubber latex raw material used in the present invention.

[44] In the present invention, 1 to 5 PHR of sulfur is used as a vulcanization agent. In case of less than 1 PHR, a cross-linking rate is too low to properly exhibit the performance of latex foam. In case of greater than 5 PHR, the degree of hardness of the latex foam is excessive, which is not desirable. In particular, when sulfur is excessively used, it improves the hardness of a final product but causes a disadvantage in that a shrinkage phenomenon of bubbles cannot be avoided. Preferably, sulfur is normally used in the form of a 50 to 60 % dispersion.

[45] In the present invention, the antioxidant includes phenols, preferably, styrenated phenol (SP) or 3,2-metylen bis 4-methyl-6-tert buthyl phenol. If a highly antioxidant function is required, it is preferred that a p-phenylenediamine-based antioxidant be used even though some stains may be generated. The antioxidant is used in an amount of 0.5 to 2.0 PHR and in the form of an emulsion or dispersion.

[46] In the present invention, the foaming stabilizer is a gel sensitizer and also called a secondary hardener. A major function thereof is to smoothly perform a gelation reaction and an additional function thereof is to prevent collapse of bubbles and shrinkage of gel. Preferably, the foaming stabilizer includes TRIMEN BASE available from Naugatuck Chemical Co. or VULCAFOR EFT available from LCI. Ltd. These compounds are a reaction product of ethylene chloride, formaldehyde and ammonia, and are preferably used in an amount of 0.5 to 2.0 PHR. In addition, cyclohexamine diphenylguanidine (DPG) or quaternary ammonium salts may be effectively used. Such compounds can also act as a vulcanization accelerating adjuvant.

[47] In the present invention, the foam stabilizer contributes to stabilization of bubbles according to the following principle. Naturally, pH of the rubber latex is high, and a nonionic surfactant of soap maintains an emulsified state as an emulsifying agent under such a condition. However, in a low pH condition, anions and cations of soap interact with each other, resulting in loss of an emulsifying function of the surfactant. When SSF (sodium silicofluoride) as a hardener is added to the rubber latex, the fluoric acid (SSF) lowers pH of the rubber latex, so that the rubber latex is placed in a very unstable state due to the loss of its emulsified state. At this time, the foaming stabilizer (TRIMENE B ASE) hinders the interaction of soap even in a low pH condition so that the latex raw material can continuously perform a gelation reaction in a stable state, thereby beforehand preventing bubbles from aggregating, breaking or shrinking.

[48] In the present invention, if the foaming stabilizer is used in an amount of less than

0.5 PHR, it does not sufficiently exhibit its function in a low pH condition, in case of 2.0 PHR or more, Zn⁺⁺interact with alkyl groups of soap. Thus, latex foam with rough surfaces is produced undesirably.

[49] In the present invention, the filler may be employed in view of cost reduction. The filler may include inorganic components typically used, e.g., clay, calcium carbonate, talc, aluminum hydrate and the like, and powdery mica and magnesium silicate may also be used. The filler is selected in consideration of the strength and processability of the latex foam before it is mixed with the rubber latex. Since a filler with a relatively larger particle size has a less harmful effect on the processing of latex foam rather than that with a relatively smaller particle size, it is desirable to use a filler with a larger particle size, more preferably, an average particle size of about 5 D. The amount of the filler to be input may be determined in consideration of the composition of the latex foam, a production method, the type of the latex foam, and the like. For example, in case of latex form used for a cosmetic mask pack, it is desirable to use the filler in an amount of 5 to 20 PHR. In case of that used for slab stocks, it is desirable to use the filler in an amount of 40 to 60 PHR. In case of that used for a carpet, it is desirable to use the filler in an amount of 50 to 200 PHR.

[50] In the step of preparing the latex solution of the method of the present invention, the rubber latex as the base material and the aforementioned various subsidiary components are weighed and then mixed with each other according to a conventional method to obtain a latex raw material in the form of a milky liquid. The latex raw material in the form of a milky liquid thus prepared is referred herein to as a latex solution. By doing so, the preparation of the latex solution is completed.

[51]

[52] <Example 1 : Step of preparing a latex solution>

[53] 800 g of SBR and 200 g of NBR as rubber latex were weighed and uniformly mixed. At this time, SBR had an average particle size of about 3,000 and its solid content was adjusted to about 67% to maintain low viscosity; and NBR containing 0.7% of ammonia as an antiseptic was employed.

[54] Further, as subsidiary components, 3.2 PHR of sulfur as a cross-linking agent of latex, 1.5 PHR of EZ and 1.5 PHR of MZ as vulcanization accelerators, 1.8 PHR of SP as an antioxidant, 2.2 PHR of TRIMEN BASE as a bubble stabilizer and 12 PHR of talc as a filler were prepared, respectively.

[55]

[56] 2. Step of preparing an aqueous silver emulsion solution: [57] The present invention comprises the step of preparing an aqueous silver emulsion solution containing 0.005 to 0.1 weight parts of silver powder and 1 to 10 weight parts of silver dispersion for dispersing the silver powder based on 100 weight parts of rubber latex as a base material.

[58] In the present invention, the silver powder is included in an amount of 0.005 to 0.1 weight parts based on 100 weight parts of rubber latex as the base material. The present invention is characterized by direct use of nanometer-sized fine silver particles as the silver powder. In case of direct use of the fine silver particles, even the addition of the minimum amount of silver particles also enables the use of intact antibacterial activity of the fine silver particles. (However, the prior arts do not directly use a silver component but uses it in the form of a carrier containing the silver component.)

[59] In the present invention, it is desirable to use silver powder with a particle size of about 1 to 100 nanometer(D). Further, the silver powder preferably has physical properties such as a tap density of about 1.0 to 5.0 g/D and a specific surface area of about 0.5 to 5.0 D/g.

[60] In the present invention, if the content of the silver powder is too low such as less than 0.005 weight parts, a composition ratio of the silver component impregnated into a final latex foam product is too low, whereby the latex foam cannot have antibacterial activity. On the other hand, if the content of the silver component is too high such as greater than 0.1 weight parts, it is also undesirable because the antibacterial activity of a final product is not improved in proportion to the increased silver content. Further, the excessive silver component interacts with sulfur, which undesirably becomes a cause of generation of black spots on the surface of a final product.

[61] It can be seen that the content of the silver powder in the present invention is sig¬ nificantly lower than that in the invention of Japanese Patent Laid-Open Publication No. (Hei)9-111053 that is the related art. More specifically, the Japanese Patent Laid- Open Publication No. (Hei)9-111053 clearly discloses that the content of an inorganic antibacterial agent ranges from 0.1 to 3.0 weight parts with respect to rubber latex, and the antibacterial agent has no antibacterial activity if the content of the inorganic an¬ tibacterial agent is in a range of less than 0.1 weight%. In contrast, although the content of the silver powder in the present invention is only 0.005 to 0.1 weight parts based on 100 weight parts of rubber latex, it is possible to impart antibacterial activity to a final latex foam product. This fact shows that the method of the present invention overcomes technical difficulties that cannot be solved by a conventional method and sufficiently achieves significant effects.

[62] In order to disperse the silver powder in the present invention, 1 to 10 weight parts of silver dispersion are included with respect to 100 weight parts of rubber latex. In the present invention, the silver dispersion comprises 50 to 90 weight% of aqueous solution and 10 to 50 weight% of silver dispersing agent, based on the silver dispersion itself. The silver dispersing agent may comprise an alkali component such as potassium hydroxide (KOH) and sodium hydroxide (NaOH) and an organic acid. At this time, it is desirable to use oleic acid or rosin acid as the organic acid, and castor oil may also be used. Further, it is preferred that the alkali component and the organic acid be used together in the aforementioned aqueous solution.

[63] In the present invention, the silver emulsion solution is preferably prepared by uniformly mixing the alkali component and the organic acid in the aqueous solution, adding the silver powder thereto, and uniformly dispersing the mixture.

[64]

[65] <Example 2: Preparation of an aqueous antibacterial silver emulsion solution>

[66] Silver powder was purchased from Nano MS Inc. in Korea and had granularity of 1 to 20 D. The silver powder was prepared by weighing 0.1 g of 100% pure silver (purity 99.9%) powder in a flake form. Further, 75 g of water was prepared in a mixing container, 32 g of oleic acid and 18 g of potassium hydroxide were added thereto, and the mixture was then uniformly mixed. Thereafter, the silver powder was added to the mixing container and the mixture was stirred at 50 to 70 rpm for about 2 hours.

[67]

[68] 3. Step of preparing an antibacterial latex raw material:

[69] An antibacterial latex raw material is prepared in the present invention by mixing the latex solution obtained in the step of preparing the latex solution with the aqueous silver emulsion obtained in the step of preparing the aqueous silver emulsion solution, and aging the mixture.

[70] In the present invention, the mixing of the latex solution with the aqueous silver emulsion solution can be conducted according to a conventional method.

[71] If natural rubber (NR) latex is used as a base material in the present invention, it is desirable to perform an aging process for the NR latex. The aging process is performed by gently stirring the antibacterial latex raw material at a temperature of 25 to 30°C for 10 to 24 hours. When the aging process has been performed, a gelation reaction is more smoothly performed, the hardness of latex foam as a final product increases, and the occurrence of a shrinkage phenomenon decreases during a drying process, thereby avoiding the occurrence of a loose skin phenomenon in a final product. However, if the reaction temperature or the stirring time exceeds a proper range, the tensile strength of a final product obtained after the vulcanization is undesirably lowered and the tensile force thereof is decreased during a gelation reaction. If the aging process has been carried out, it is desirable to immediately use the latex raw material. If the aging process has been carried out but the latex raw material is not intended to be used im¬ mediately, it is important to store the aged antibacterial latex raw material at a temperature of 10 to 13°C.

[72] Meanwhile, it is preferred that a zinc oxidation process be performed before the vulcanization of the antibacterial latex raw material.

[73] In the present invention, a standard mixing ratio for the zinc oxidation ranges from

1 to 7 PHR. The zinc oxidation performs two functions: one is to promote cross- linking caused by sulfur and the other is to support a gelation reaction due to the cross- linking. It is desirable to carry out the zinc oxidation in a 45 to 55% dispersion, and the dispersion should be input after stirring and filtration thereof because it easily pre¬ cipitates.

[74] Further, in the present invention, the zinc oxidation process can be applied to the latex raw material or antibacterial latex raw material. More preferably, the zinc oxidation process is applied at the step of preparing the latex solution if synthetic rubber latex is used as the latex raw material, whereas the zinc oxidation process is applied at this step if natural rubber latex is used as the latex raw material. This is because the natural rubber latex may be immediately cured by the zinc oxidation if the latex raw material is the natural rubber latex. In order to prevent these harmful effects, the zinc oxidation is applied just before the curing reaction caused by sulfur.

[75]

[76] <Example 3: Preparation of an antibacterial latex raw material>

[77] 1 kg of latex solution prepared in Example 1 was mixed with 80 g of aqueous silver emulsion solution prepared in Example 2. This step was performed according to a con¬ ventional method.

[78]

[79] 4. Step of preparing antibacterial latex foam:

[80] The present invention comprises the steps of foaming and vulcanizing the an¬ tibacterial latex raw material thus prepared above.

[81] In the present invention, the foaming process may be performed according to a con¬ ventional method and in a batch or continuous mode. In case of a continuous mode, there are advantages in that it is very economic because loss of latex can be prevented, and homogenous latex foam can be completely injected into a molding machine. Thus, the continuous mode is preferred to the batch mode. In order to obtain high-quality lat ex foam, it is very important to control temperature during the foaming process. After various subsidiary components are added to the latex raw material, it is desirable to maintain the temperature of a workroom to be higher than that of the latex raw material. Specifically, if the temperature of the latex raw material ranges from 20 to 25°C, it is preferred that the temperature of a workroom be in a range of about 25 to 30°C.

[82] In the present invention, the vulcanization process is to cause the rubber latex raw material to be cross-linked and is carried out by using sulfur. The vulcanization process is also carried out according to a conventional method. [83]

[84] <Example 4: Preparation of antibacterial latex foam>

[85] 1 kg of antibacterial latex raw material prepared in Example 3 was foamed in a continuous mode according to a Dunlop method. The inner pressure of a mixing head was 2.3 kg/D, and the latex raw material was injected into a molding machine within 1 minute. [86]

[87] 5. Step of post-processing antibacterial latex foam:

[88] The present invention comprises the step of performing post-processing, such as curing, cooling, releasing and washing, for the antibacterial latex raw material after the vulcanization process. [89] The present invention performs a curing process through a gelation reaction after the vulcanization process. In the present invention, it is desirable to use SSF (sodium silicofluoride) as a gelling agent. This is because SSF shows superior stability in pH value and is gradually hydrolyzed so that the latex foam can be gradually cured to be a final product.

[90] SSF is slowly hydrolyzed according to the following reactions:

[91] Na 2 SiF 6 + 3H 2 O « 6HF + Na 2 SiO 3

[92] HF « H⁺ + F

[93] Na 2SiO3 + 3H2O ^ Si(OH) 4 + 2Na 2OH

[94] 2NaOH + 2HF « 2NaF + 2H O

[95]

[96] As SSF is subjected to such a gradual hydrolysis reaction, the antibacterial latex foam is gradually gelated.

[97] In the present invention, it is desirable to use SSF in an amount of 0.5 to 5 PHR under a normal condition. If SSF is used in an amount of less than 0.5 PHR, the curing reaction is too weak to obtain desired effects. If SSF is used in an amount of greater than 5 PHR, the antibacterial latex raw material is partially gelated, which leads to un¬ desirable results. SSF is typically prepared in the form of a 50% dispersion and is preferably used by diluting it to a 20 to 30% dispersion. Further, in case of the use of SSF, stirring and filtration thereof is necessary to prevent precipitation thereof.

[98] In the present invention, the amount of SSF to be used is determined depending on several factors such as the kind of latex raw material, the amount of the silver emulsion solution to be used, the temperature of the antibacterial latex raw material during the aging process, the temperature of a workroom, and the inner temperature of the molding machine, regardless of the use of a filler. Further, in order to determine the amount of SSF to be used, time required for gelation of the antibacterial latex foam should be consecutively checked and tested, and then taken into consideration. Preferably, the time required for gelation of SSF after injected into a head of the molding machine is 3 to 7 minutes. Consequently, the amount of SSF to be used is not always fixed but is specifically determined case by case to conform to working conditions or environments.

[99] In the present invention, it is preferred that the gelation process be performed within the molding machine. A proper material for the molding machine is an aluminum alloy that is inexpensive and lightweight and has resistance to chemical corrosion. Since there is a tendency for cured latex foam to be shrunk smaller than a desired size after the drying process, it is desirable to prepare a molding machine with a size larger by about 5 to 15% than a desired product size.

[100] Thereafter, in the present invention, cooling, releasing and washing steps are performed according to a conventional method.

[101] [102] 6. Antibacterial test for antibacterial latex foam product [103] The inventor prepared finally a latex foam product by going through all the steps described in Examples 1 to 4, and obtained a test sample thereof and measured an¬ tibacterial activity of the sample to confirm the performance of the latex foam product.

[104] [105] <Example 5: Antibacterial effects of antibacterial latex foam product> [106] In order to objectively confirm the antibacterial activity of the latex foam product prepared according to the method of the present invention, the present inventor requested an antibacterial test to the FITI Testing & Research Institute in Korea. The FTTI Testing & Research Institute measured the antibacterial activity of the latex foam product according to a SHAKE FLASK METHOD (KS M 0146-2003). Specifically, a test bacterial solution was subjected to shaking culture at 37+l°C for 24 hours, and the number of bacteria within the culture solution was counted. A surface area of a test sample was 60 D, and Tween 80 (0.05%) was used as an non-ionic surfactant, i) Staphylococcus aureus (ATCC 6538), ii) E. coli (ATCC 25922), and iii) Klebsiella pneumoniae (ATCC 4352) were used as test strains.

[107] As a result, the antibacterial activity was measured as follows:

[108] Table 1

[109] Note: CFU = Colony Forming Unit [HO] Objective data on the test are shown as follows: [111] Fig. 1 shows measurement results of a test for the antibacterial activity of Staphylococcus aureus conducted by the FIΗ Testing & Research Institute;

[112] Fig. 2 shows measurement results of a test for the antibacterial activity of E. coli conducted by the FIΗ Testing & Research Institute; and [113] Fig. 3 shows measurement results of a test for the antibacterial activity of Klebsiella pneumoniae conducted by the FIΗ Testing & Research Institute. [114] From the results of the antibacterial tests, it was found that all the samples of the present invention show more than 99.9% destruction of the test strains. These results suggest that the test strains hardly grow and cannot survive on the surface of the latex foam of the present invention. Accordingly, it can be known from these results that the latex foam prepared by the method of the present invention has superior antibacterial activity.

[115] Although the method of producing antibacterial latex foam, and the latex foam produced by the method according to the present invention have been specifically described above, the description is only for the most preferred embodiment of the present invention and the present invention is not limited thereto. The scope of the present invention is determined and defined by the appended claims.

[116] Further, it will be apparent to those skilled in the art that various modifications and changes can be made thereto based on the description, but it is clear that these modi¬ fications and changes also fall within the scope of the invention.

[117]

Industrial Applicability [118] Since the present invention exhibits high antibacterial activity, the latex foam of the present invention can be applied to various uses. For example, it can be used for soles of sneakers, cosmetic puffs, and latext mattress. Accordingly, there is an advantage in that the latex foam of the present invention can be widely used for prevention of bacterial infection.

[119]

Claims

[1] A method of producing antibacterial latex foam containing nano-silver particles, the method comprising the steps of: preparing a latex solution by mixing rubber latex as a base material with subsidiary materials according to a conventional method, wherein the subsidiary materials comprise 1.0 to 5.0 PHR of vulcanizing agent, 0.5 to 2.0 PHR of an¬ tioxidant, 0.2 to 5.0 PHR of vulcanization accelerator, 0.5 to 2.0 PHR of foaming stabilizer and 5 to 200 PHR of filler based on 100 weight parts of rubber latex; preparing an aqueous solution of silver emulsion consisting of 0.005 to 0.1 weight parts of silver powder and 1 to 10 weight parts of silver dispersion for dispersing the silver powder therein based on 100 weight parts of rubber latex; preparing an antibacterial latex material by mixing the latex solution with the aqueous solution of silver emulsion and aging the mixture; producing latex foam by foaming, vulcanizing and curing the antibacterial latex material; and post-processing the latex foam by molding, cooling, releasing and washing the produced latex foam.

[2] The method as claimed in claim 1, further comprising, if rubber latex as a base material is natural rubber latex treated with ammonia, a deammoniation step of removing ammonia existing in the latex by slowly stirring the latex at a low speed of 30 to 70 rpm at a temperature of 40°C or less in .

[3] The method as claimed in claim 1, wherein the silver powder in the step of preparing the aqueous silver emulsion solution has physical properties such that a particle size ranges from 1 to 100 D, a tap density ranges from 1.0 to 5.0 g/D and a specific surface area ranges from 0.5 to 5.0 D/g.

[4] The method as claimed in claim 1, wherein the silver dispersion in the step of preparing the aqueous silver emulsion solution comprises 50 to 90 weight% of aqueous solution and 10 to 50 weight% of silver dispersing agent based on the silver dispersion itself; and the silver dispersing agent is composed of alkali components including potassium hydroxide (KOH) or sodium hydroxide (NaOH), and an organic acid selected from the group consisting of oleic acid, rosin acid and castor oil.

[5] Antibacterial latex foam containing nano-silver particles produced by the method according to any one of claims 1 to 4.