JPH05202200A - Latex rubber product and its production - Google Patents

Abstract

PURPOSE:To obtain the subject rubber product having a low content of chemical with irritation to skin by previously vulcanizing a latex with a specific compounding agent for vulcanization, then centrifuging, molding and processing and further vulcanizing. CONSTITUTION:A raw material latex such as natural rubber latex is mixed with a compounding agent for vulcanization containing a sulfur-based vulcanizing agent such as dipentamethylene thiuram tetrasulfide and previously vulcanized. Further at a point of time when the previous vulcanization is completed, the latex is centrifuged by using a centrifugal separator to remove the excessive compounding agent not participating in vulcanization. Then, the centrifuged latex is optionally blended with an antioxidant, a colorant, wax, etc., molded and processed and vulcanized to give the objective rubber product effective for prevention of air pollution and acidic rain measure and safely useful for gloves, etc.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a latex rubber product such as gloves and a method for producing the same, and more specifically, it contains a small amount of chemicals that are irritating to the skin, and the ash content during combustion and sulfur oxidation in combustion gas The present invention relates to a novel latex rubber product having a reduced amount of material and a method for producing the same.

[0002]

2. Description of the Related Art Conventionally, sulfur vulcanization, which uses sulfur or a substance containing sulfur as a vulcanizing agent, is the most common rubber vulcanization method, has a low cost, and is a facility. It is easy to use, and the obtained rubber has excellent physical properties. However, sulfur-vulcanized rubber products contain sulfur and non-combustible vulcanization activators (zinc oxide is the most common) in the rubber during combustion,
There are problems that sulfur oxides are generated during combustion and that a relatively large amount of ash remains. In particular, sulfur oxides generated when incineration of sulfur-vulcanized rubber causes air pollution, acid rain problems, and problems such as furnace corrosion. Also, if a large amount of ash remains after combustion,
It is a disadvantage in minimizing waste. In particular, rubber gloves for protection against radiation pollution used at nuclear power plants, etc.
Since it is incinerated after use and the ash containing radioactivity is stored, when a large number of gloves are incinerated, the amount of ash generated will be enormous and a large space will be required for storage. is there.

Further, since vulcanization accelerators such as zinc salt of mercaptobenzothiazole, tetramethylthiuram disulfide and tetraethylthiuram disulfide have skin irritant properties, a rubber product using the vulcanization accelerator is allergic to people with sensitive skin. May occur. However, these compounding agents are indispensable when performing sulfur vulcanization. Therefore, if at least the amount actually consumed for vulcanization is reduced, the vulcanization will not proceed and the physical properties will deteriorate.

On the other hand, instead of sulfur vulcanization, if a method of using a peroxide as a crosslinking agent or a method of crosslinking by radiation is adopted,
Since it does not contain sulfur or zinc oxide, the above problems can be solved. However, peroxide is not suitable for rubber products such as gloves that come into direct contact with human skin due to its skin irritation. Further, the odor of the decomposed product of peroxide remains. Furthermore, in the case of radiation crosslinking,
The equipment cost is enormous, and there are safety and environmental problems, and the physical properties of the obtained rubber, particularly those after immersion in water, are remarkably deteriorated, and the actual level has not yet been reached.

A main object of the present invention is to provide a latex rubber product in which the amount of sulfur oxides and ash generated by the combustion of vulcanized rubber is reduced, and a method for producing the latex rubber product. Another object of the present invention is to provide a latex rubber product which does not contain harmful compounding agents and therefore causes less skin irritation and a method for producing the same.

[0006]

Means and Actions for Solving the Problems The inventors of the present invention have conducted extensive studies to achieve the above object, and as a result,
A latex comprising a molded and vulcanized product of a latex that has been prevulcanized in the presence of a vulcanizing compounding agent containing a sulfur-based vulcanizing agent, and free compounding agent has been removed from the compounding agent used in the prevulcanization The present invention has been completed by discovering a new fact that a rubber product can achieve the above object.

That is, according to the present invention, as in the conventional case, the compounding agent for vulcanization containing the sulfur-based vulcanizing agent is not added to the latex and vulcanized as it is, but it is prevulcanized in advance and released. Since the vulcanization is performed using the latex from which the surplus vulcanizing compounding agent has been removed, the rubber compound obtained is less likely to retain the compounding agent, and therefore the amount of ash and sulfur oxides generated is reduced. It can also be reduced and less irritating to the skin due to harmful formulations.

In the present invention, a vulcanizing compounding agent containing a sulfur-based vulcanizing agent is added to the latex for prevulcanization, and then the free compounding agent in the latex is removed by centrifugation.
The present invention also provides a method for producing a latex rubber product characterized by molding and vulcanization. That is, the present inventors have noticed that the vulcanizing compounding agent containing the sulfur-based vulcanizing agent generally has a larger specific gravity than the rubber particles in the latex,
The inventors have found that such a compounding agent can be easily separated and removed from the rubber particles by centrifugation, and have completed the present invention.

As the raw latex in the present invention,
For example, natural rubber alone or natural rubber to which a stabilizer or a preservative is added, synthetic rubber such as acrylonitrile-butadiene rubber, styrene-butadiene rubber, isoprene rubber or chloroprene rubber, or an aqueous emulsion of a blend of two or more thereof. Suspension can be given. The rubber content in the latex is usually 40 to 70% by weight.

Examples of stabilizers for natural rubber include sodium carboxymethyl cellulose, saponified polyvinyl alcohol, casein, sodium alginate, and starch. The stabilizer is added in a proportion of 0.05 to 0.2% by weight based on the total amount of latex. Examples of the preservative include ammonia, tetramethylthiuram disulfide, zinc oxide, boric acid, lauric acid, and sodium salt of pentachlorophenol. The preservative is added in a proportion of 0.05 to 0.7% by weight based on the total amount of latex.

Typical examples of natural rubber latex depending on the type of preservative include high ammonia latex (containing 0.7% ammonia), low ammonia SPP latex (containing 0.2% ammonia and 0.2% sodium salt of pentachlorophenol), and low ammonia TZ. Latex (containing 0.2% ammonia, tetramethylthiuram disulfide 0.0125% and zinc white 0.0125%), low ammonia boric acid latex (0.2% ammonia, 0.2 boric acid)
% And lauric acid 0.05%), low ammonia ZD
C latex (containing 0.2% ammonia, 0.1% diethyl-dithiocarbamate zinc and 0.02% lauric acid) and the like.

The vulcanization compounding agent added to the latex includes, in addition to known vulcanizing agents, vulcanization accelerators, vulcanization retarders, vulcanization activators and the like. Examples of the vulcanizing agent include sulfur and compounds containing sulfur, such as 4,4'-dithiodimorpholine and dipentamethylene thiuram tetrasulfide. Examples of the vulcanization accelerator include amines such as hexamethylenetetramine and n-butyraldehydeaniline; guanidines such as diphenylguanidine and di-o-tolylguanidine; N, N′-diphenylthiourea;
N, N'-diethylthiourea, dibutylthiourea, dilaurylthiourea, meltcaptobenzothiazole, sodium salt, zinc salt or cyclohexylamine salt of meltcaptobenzothiazole, dibenzothiazole disulfide, tetramethylthiuram disulfide, tetraethylthiuram disulfide, tetrabutylthiuram Disulfide, tetramethylthiuram monosulfide, dipentamethylenethiuram tetrasulfide, pentamethylenedithiocarbamic acid piperidine salt, sodium diethyldithiocarbamate, sodium dibutyldithiocarbamate, zinc dimethyldithiocarbamate, zinc diethyldithiocarbamate, zinc dibutyldithiocarbamate, N-ethyl Sulfur compounds such as zinc N-phenyldithiocarbamate And the like.

Examples of the vulcanization retarder include organic acids such as phthalic anhydride, salicylic acid and benzoic acid; N-nitrosodiphenylamine, N- (cyclohexylthio) phthalimide, diphenylurea and sulfonamide derivatives. However, vulcanization retarders are rarely used in latex. Examples of the vulcanization activator include inorganic substances such as zinc oxide, lead oxide, magnesium oxide and zinc carbonate, stearic acid, oleic acid, lauric acid, zinc stearate, triethanolamine, diethanolamine, diethylene glycol and triethylene glycol. Organic substances are included.

The blending amount of each component is not particularly limited and may be within the range conventionally used.
Specifically, it is suitable to add about 0.5 to 2 parts by weight of the vulcanizing agent to 100 parts by weight of the rubber. Further, it is appropriate that about 0.5 to 2 parts by weight of the vulcanization accelerator is added to 100 parts by weight of the rubber. Vulcanization retarder is rubber 1
It is suitable to add about 0.3 to 1 part by weight to 00 parts by weight. The vulcanization activator is appropriately added in an amount of about 1 to 5 parts by weight based on 100 parts by weight of rubber.

The term "prevulcanization" as used in the present invention means that a rubber compound dispersed in water in a colloidal state has a compounding agent for vulcanization added in the state of a dispersion attached thereto or penetrates into the rubber particles to form particles. It means to proceed with vulcanization. Such pre-vulcanization is a kind of chemical reaction that is carried out by adding an amount of a compounding agent for vulcanization usually used to the raw latex, and the reaction proceeds rapidly when the temperature is raised, but even at room temperature, it takes only a few days. Pre-vulcanization is completed. Generally, pre-vulcanization is 30-80 ° C.
By aging for 1 hour to 1 day.

The physical properties of rubber products such as films made from latex depend largely on the degree of prevulcanization. When the pre-vulcanization is completed, centrifugation is performed to remove excess vulcanizing agent, vulcanization accelerator, vulcanization activator, etc., which were not involved in vulcanization. Then, if necessary, an antioxidant, a colorant, a weather resistance imparting agent (such as wax), a thickener and the like are added. This latex is molded and vulcanized to obtain a rubber product.

Regarding the molding process, the conventional latex processing method can be adopted as it is. Specifically, for example, a film forming method in which a molding die made of glass, metal, etc. is dipped in latex and dried, an adhesive method in which rubber particles are agglomerated on the surface of the die by using electrostatic force, and a heat-sensitive coagulant was contained. There are a heat-sensitive method using latex, an electrodeposition method in which a metal mold is used and positive charges are applied to the metal mold to attach rubber particles to the mold surface.

According to the above-mentioned adhesion method, cations (Ca
⁽²⁺ etc.), and then dip this mold in latex, and the negatively charged rubber particles in the latex are attracted by the above cations and aggregate on the surface of the mold to form a rubber layer. Is the way to do it. Further, the heat-sensitive method, by immersing the preheated mold in the latex containing the heat-sensitive coagulant, to solidify the latex containing the heat-sensitive coagulant on the surface of the mold, in this state pull up the mold from the latex, and dry. To do.
Examples of the heat-sensitive coagulant include polymeric substances such as polyvinyl methyl ether and polyalkylene glycol, various zinc ammonium complex salts, sodium silicofluoride, and ammonium nitrate.

Vulcanization is normally completed at 80 to 120 ° C. for about 0.2 to 1 hour. In the centrifugal separation, if the centrifugal force is too strong, the rubber particles will irreversibly aggregate and become useless as a latex. On the other hand, if it is too weak, the compounding agent cannot be sufficiently separated from the rubber particles, and the intended purpose of the present invention cannot be achieved. Therefore,
Depending on the type and amount of compounding agent used and the degree of pre-vulcanization,
It is necessary to determine the optimum centrifugal force. In general, the specific gravity of natural rubber is 0.91, whereas the specific gravity of vulcanizing compounding agents that are usually used is 2.1 for sulfur and 5.4-for zinc oxide.
5.7, titanium oxide 3.8-4.2, wax 0.9
Before and after. In addition, a zinc salt of 2-mercaptobenzothiazole (trade name "NOXCELLER MZ" manufactured by Ouchi Shinko Chemical Co., Ltd.) used as a vulcanization accelerator has a specific gravity of 1.70, a thiuram type, for example, tetraethylthiuram disulfide (Ouchi Shinko Chemical company product name "Nocceller TET") has a specific gravity of 1.31, zinc dithiocarbamate type, for example zinc dimethyldithiocarbamate (Ouchi Shinko Chemical Co., Ltd. product name "Noxceller PZ") has a specific gravity of 1.79, diethyldithiocarbamine Zinc acidate (trade name "NOXCELLER EZ" manufactured by Ouchi Shinko Chemical Co., Ltd.) has a specific gravity of 1.47, and zinc dibutyldithiocarbamate (trade name "NOXCELLER B manufactured by Ouchi Shinko Chemical Co., Ltd."
Z ”) has a specific gravity of 1.26, and all of them except wax have specific gravities greater than 1. Therefore, by centrifuging the latex containing the compounding agent for vulcanization, the rubber particles and the compounding agent for vulcanization can be separated. In particular, sulfur and zinc oxide having a large specific gravity quickly settle, so separation and removal Is extremely easy. Further, even a vulcanization accelerator having a relatively small specific gravity can be easily separated and removed by appropriately selecting the centrifugal force.

In this way, excess compounding agents not involved in vulcanization are removed in advance, and as a result, sulfur, non-combustible vulcanization activator (zinc oxide, etc.) It is possible to obtain a final rubber product that contains the minimum necessary vulcanization accelerator. Instead of the centrifugal separation, it is also possible to separate and remove the free compounding agent from the latex by natural sedimentation due to the difference in specific gravity. However,
Since it takes about one month for separation, it is not an industrially practical method. Further, among the compounding agents, water-soluble compounding agents (for example, ammonia casein, potassium hydroxide, etc.) cannot be removed by the above-mentioned centrifugal separation method, so that after vulcanization molding, extraction with water, so-called leaching may be performed.

Examples of the latex rubber product of the present invention include, for example, gloves, finger cots, condoms, catheters,
Examples thereof include overboots, but it goes without saying that the rubber product of the present invention is not limited to these applications.

[0022]

EXAMPLES The present invention will now be described in detail with reference to examples, but it goes without saying that the present invention is not limited to these examples. Example 1 A compounding agent for vulcanization was added to the natural rubber latex in the proportions shown below, and after stirring, the mixture was aged at 30 ° C. for 3 days to perform prevulcanization. In addition, all the compounding agents used below were added in the form of a dispersion (dispersion medium: water).

(Ingredients) (Dry parts by weight) Natural rubber latex (rubber content 60%) ^{* 1} 100 sulfur 1.0 zinc oxide 1.0 mercaptobenzothiazole zinc salt ^{* 2} 0.1 diethyldithiocarbamate zinc salt ^{* 2} 0.8 Titanium oxide 3.0 2,2'-methylenebis (4-methyl-6-t-butylphenol) ^{* 3} 1.0 * 1: Tetramethylthiuram disulfide and zinc oxide as preservatives and stabilizers, respectively. Raw ammonia type latex containing 0125% * 2: Vulcanization accelerator * 3: Anti-aging agent Pre-vulcanized latex (A) was placed in a centrifuge (type H100B2 manufactured by Domestic Centrifuge Co., Ltd.). Rotation speed 5000
Centrifugation was performed for 15 minutes at rpm. After the separation, the latex (B), which is the supernatant portion, was taken out so that the sediment was not mixed. The sediment is redispersed in water,
It was dried and analyzed.

With respect to the above latexes (A) and (B), the viscosity, pH and solid content were measured. Further, these latexes were cast on a glass plate and heated at 100 ° C. for 30 minutes for vulcanization to obtain films having a thickness of 0.4 to 0.5 mm. Breaking strength (T
_B ), elongation at break (E _B ), 300% modulus and degree of swelling with toluene were investigated. The results are shown in Table 1.

In Table 1, the viscosity was measured by using a BL type viscometer manufactured by Tokyo Keiki Co., Ltd. at 60 rpm.
Measured using a 1 rotor. Strength at break (T _B), elongation at break (E _B) and 300% modulus JIS K
6301 was measured. The degree of swelling with toluene is measured by measuring the weight change after immersion in toluene at 40 ° C. for 24 hours.

[0026]

[Table 1]

As shown in Table 1, after prevulcanization, the centrifugally separated latex (B) has a slightly lower viscosity when compared to the latex (A) not centrifuged, which is due to the use of thickeners. Is fully adjustable. Regarding the physical properties of the obtained film, the centrifugally separated latex (B) has a slightly higher swelling ratio (this is considered to be due to the slightly lower crosslink density). Then, a film having the same swelling ratio as the film using the latex (A) was obtained. On the other hand, regarding the breaking strength (T _B ) and the breaking elongation (E _B ), it can be seen that the centrifuged latex (B) is not inferior to the latex (A) not centrifuged.

In addition, each film has a concentration of 50 pp at 40 ° C.
The ozone resistance was examined by leaving it in the hm atmosphere for 100 hours. As a result, no difference was found between the films of latex (A) and (B). On the other hand, diethyldithiocarbamate zinc salt (Zn contained in each film)
EDC) with acetone: chloroform (1: 1) to 10
Time Soxhlet extraction and quantification by high performance liquid chromatography. As a result, ZnEDC was 7
321 μg / g was 1190 μg / g in the film obtained from latex (A), whereas ZnEDC was not detected in the film obtained from latex (B). Example 2 In natural rubber latex (high ammonia latex),
Add the compounding agent for vulcanization at the ratio shown below, and after stirring,
It was aged at 0 ° C. for 24 hours and prevulcanized. In addition, all the compounding agents used below were added in the form of a dispersion (dispersion medium: water).

(Blending Component) (Drying Weight Part) Natural Rubber Latex (Rubber Content 60%) 100 Sulfur 1.0 Zinc Oxide 1.0 Dibutyldithiocarbamate Zinc Salt 0.6 (Vulcanization Accelerator) Obtained Latex ( C) using a centrifuge (type H100B2 manufactured by Domestic Centrifuge Co., Ltd.) at a rotation speed of 50.
Centrifugation was carried out at 00 rpm for 30 minutes, and then the supernatant liquid (D) was taken out so that the precipitate was not mixed.

The above latexes (C) and (D) were separately cast on a glass plate and dried at room temperature to prepare a film, which was then vulcanized at 100 ° C. for 30 minutes. For each of the obtained films, the amount of ash and the amount of sulfur oxides generated in the combustion gas were measured. The results are shown in Table 2.

[0031]

[Table 2]

From Table 2, the latex (D) after pre-vulcanization and centrifugal separation shows that the amount of ash and sulfur oxide is latex (C).
It can be seen that it is reduced compared to. Example 3 A natural rubber latex was compounded with a compounding agent for vulcanization at the same compounding ratio as in Example 2, and then aged at 30 ° C. for 24 hours for prevulcanization. The obtained latex was centrifuged using a centrifuge (Type H200 manufactured by Domestic Centrifuge Co., Ltd.) by changing the centrifugal force or the centrifuging time, and the latex portion as a supernatant was taken out, A film was prepared in the same manner as in 2. Table 3 shows the relationship between centrifugal force and ash content when centrifugal separation was performed for 20 minutes under various centrifugal forces.

[0033]

[Table 3]

On the other hand, Table 4 shows the relationship between the centrifugal separation time and the ash content when the centrifugal separation time was changed while the centrifugal force was kept constant at 2700G.

[0035]

[Table 4]

It can be seen from Table 3 that the ash content is reduced to about 46% of the standard latex for control (the one which is not subjected to centrifugation after pre-vulcanization) by performing the centrifugation at 1300 G for 20 minutes. Recognize. Also, from Table 4, 2700
When centrifugation is performed by changing the separation time with the constant centrifugal force of G,
It can be seen that the ash content is reduced to 50% of the standard latex in about 10 minutes, and is reduced to about 40% when the centrifugation is continued. Example 4 A compounding agent for vulcanization was added to the synthetic isoprene latex in the ratio shown below, and after stirring, the mixture was aged at 30 ° C. for 24 hours and prevulcanized. In addition, all the compounding agents used below were added in the form of a dispersion (dispersion medium: water).

(Ingredients) (Dry parts by weight) Synthetic isoprene latex (rubber content 65%) 100 Sulfur 1.0 Zinc oxide 1.0 Dibutyldithiocarbamate zinc salt 0.6 Centrifugation was performed for 30 minutes at a rotation speed of 5000 rpm using a centrifuge (Type H-600 manufactured by Domestic Centrifuge Co., Ltd.). The flow rate of the latex (E) was adjusted so that the residence time was 20 minutes. The supernatant latex (F) was taken out automatically.

The above latexes (E) and (F) were separately poured onto a glass plate and dried at room temperature to prepare a film, which was then vulcanized at 100 ° C. for 30 minutes. The ash content and the total sulfur content of each of the obtained films were measured. The results are shown in Table 5.

[0039]

[Table 5]

From Table 5, it can be seen that the latex (F) after prevulcanization and centrifugal separation has reduced ash content and total sulfur content as compared with the latex (E).

[0041]

As described above, in the latex rubber product of the present invention, excess vulcanizing compounding agent unnecessary for vulcanization is removed by centrifuging after prevulcanization. The amount generated can be reduced. Therefore, it is most suitable for use in, for example, rubber gloves for protection against radiation pollution that are incinerated and disposed of after being used in a nuclear power plant or the like. In addition, since the amount of sulfur oxides generated by combustion is also reduced, in addition to preventing air pollution and acid rain measures,
It is also preferable for preventing the corrosion of the furnace.

Further, the latex rubber product of the present invention is
By the centrifugal separation, the skin-irritating compounding agent is also removed, and therefore it is safe for use in gloves and the like. The latex rubber product of the present invention is also effective in providing a transparent rubber product.

Claims (4)

[Claims] 1. Molding / vulcanization of a latex prevulcanized in the presence of a vulcanizing compounding agent containing a sulfur-based vulcanizing agent and free of the compounding agent used in the prevulcanization. Latex rubber products characterized by being made of vulcanized products. 2. The latex rubber product according to claim 1, wherein the latex is a natural rubber latex. 3. The latex rubber product according to claim 1, wherein the compounding agent for vulcanization contains, in addition to the vulcanizing agent, a vulcanization accelerator and a vulcanization activator. 4. A step of adding a compounding agent for vulcanization containing a sulfur-based vulcanizing agent to latex for prevulcanization, and a step of removing the compounding agent free in the prevulcanized latex by centrifugation. ,
A method for producing a latex rubber product, comprising a step of molding and processing the centrifugally separated latex and a step of vulcanizing the molded product.