JPH0881502A - Production of deproteinized natural rubber latex - Google Patents

Abstract

PURPOSE: To improve the film-forming characteristics, mechanical stability, and green strengths of a deproteinized natural rubber latex by adding thereto specific fine natural rubber particles. CONSTITUTION: A natural rubber latex such as a field latex or an ammonia- treated latex is deproteinized by adding thereto 0.001-10wt.% anionic and/or nonionic surfactant and 0.01-10wt.% protease and keeping it at a standstill for from a few minutes to one week at 5-90 deg.C, giving a deproteinized natural rubber latex having a nitrogen content of 0.02wt.% or lower. Fine natural rubber particles having an average particle size of 0.1-0.5μm are added to the deproteinized latex in an amt. of 1-15wt.% based on the latex.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a deproteinized natural rubber latex which is excellent in film-forming properties, mechanical stability and green strength and which is substantially free of protein.

[0002]

2. Description of the Related Art Natural rubber latex is industrially used as a raw material for foamed foam rubber products, dipping products such as gloves and condoms, and adhesives and adhesives. Natural rubber latex is obtained as a sap of rubber trees such as Hevea brasiliens cultivated in farms. In addition to about 30% of rubber content, about several% of each of proteins, fatty acids, polysaccharides, minerals, etc. Contains rubber components and is called field latex.

As a raw material for industrial use, a field latex containing impurities is concentrated and purified by a creaming method or a centrifugal separation method to a rubber content of about 60%.
Purified natural rubber latex with 2 to 0.7% ammonia added is used. As a purification method, a centrifugal separation method with high purification efficiency is often used. In the purified natural rubber latex, about 2% of protein remains, about half of which is water-soluble protein, and the remaining amount is chemically bound to rubber particles. The hydrophilic protein bound to the rubber particles contributes to stability in water and, at the same time, is susceptible to oxidation and prevents oxidative deterioration of the rubber. The water-soluble protein also contributes to the stabilization of the rubber latex as a protective colloid. In addition, a small amount of remaining fatty acid reacts with ammonia added to prevent spoilage to form a fatty acid ammonium which is an amphoteric ionic surfactant, and contributes to stabilization of the latex.

However, in recent years, it has been found that the use of natural rubber medical devices causes immediate allergy, and it has been determined that the causative substance is a protein present in natural rubber. Immediate allergies due to the protein of this natural rubber, in addition to the protein originally contained in natural rubber,
It has been pointed out that the protein modified by the addition of ammonia is also a causative substance. The protein that is the causative agent is 1
Since it is denatured and becomes harmless at 70 ° C or higher, it is rendered harmless in the processing process of products such as tires using solid natural rubber as a starting material, but at most 130 in the processing process of latex products.
Since it is heated at ℃, the causative protein does not change and becomes a problem.
This immediate allergy occurs when a protein that is a causative agent is contacted and a patient who develops antibodies in the body again contacts the causative protein.

Therefore, it is possible that a large number of potential patients have developed among those who are constantly using natural rubber latex products containing allergens. In particular, there are some reports that the morbidity rate reaches as high as 10% in medical personnel who regularly use surgical gloves and inspection gloves that are excellent in workability and fit, which is a serious social problem. In order to fundamentally solve this problem, the present inventors have succeeded in developing a technique for producing a natural rubber latex from which a protein which is a causative substance of immediate allergy is almost completely removed.

As described above, proteins play an important role in stabilizing the latex. Therefore, how to stabilize the latex at the same time as efficiently removing the protein from natural rubber is an important issue. . There are two types of stability of natural rubber latex: stability against chemicals and stability against mechanical irritation. Insufficient chemical stability of the former causes inconveniences such as solidification when blending chemicals and fillers. On the other hand, if the stability is excessively high, a disadvantage such as the inability to form a film by the coagulation method using a coagulating agent at the time of molding occurs, and thus a delicate balance is required. Insufficient mechanical stability of the latter causes disadvantages such as solidification during transportation and solidification at an unexpected stage during processing operation.
In general, the higher the mechanical stability, the better.

The present inventors have also proposed a stabilizer for deproteinized natural rubber. However, as is often experienced in synthetic rubber latex, deproteinized natural rubber latex with improved mechanical stability using a surfactant stabilizer is the most important film forming property among processing properties. However, it has a drawback that it is inferior to the ordinary natural rubber latex, and particularly in the so-called direct method of forming a film by dipping and drying without using a coagulant, this tendency is strong and it is difficult to produce a uniform film.

Therefore, the conventional deproteinized natural rubber latex is inferior in film-forming properties and is not suitable as a raw material for a direct method for producing a thin film product such as a condom or a catheter without using a coagulant. Therefore, the present inventors
In an effort to improve the deproteinized natural rubber latex, after degrading the protein of natural rubber latex with a proteolytic enzyme in the presence of a surfactant, filtering only the degradation residue of the protein with an ultrafiltration membrane. It was found that a deproteinized natural rubber latex having less of the above-mentioned defects can be obtained by leaving the fine particle component originally present in the latex, and as a manufacturing method therefor, a manufacturing method using a rotary flat membrane device was proposed (Japanese Patent Application No. -52989).

[0009]

The production of deproteinized natural rubber latex by the ultrafiltration method using the above rotary flat sheet membrane device has the advantages described above, and it is easy to obtain a high-concentration latex. Although it has many advantages such as easy automation of operation, it has the disadvantage that the equipment cost is high and the initial investment becomes too large.Therefore, there is a big economic problem that the equipment cost is not high for small-scale production. Have

An object of the present invention is to provide a method for producing a deproteinized natural rubber latex, which is capable of economically and easily producing a deproteinized natural rubber latex having excellent film-forming properties and mechanical properties even in small-scale production. That is.

[0011]

Means and Actions for Solving the Problems As a result of intensive studies aimed at achieving the above object, the present inventors have found that deproteinized natural rubber latex prepared separately is added to deproteinized natural rubber latex. The present invention has completed the present invention by discovering the new fact that a deproteinized natural rubber latex having improved mechanical stability and film-forming characteristics and further improved green strength can be easily obtained when the latex is added. Came to do.

That is, in the method for producing a deproteinized natural rubber latex of the present invention, the deproteinized natural rubber latex is added in an amount of 1 to 15% by weight based on the rubber component and an average particle size of 0.1. It is characterized in that natural rubber fine particles of 1 to 0.5 μm are added. The deproteinized natural rubber latex used in the present invention preferably has a nitrogen content of 0.02% or less. Here, the nitrogen content is an index showing the amount of protein contained in the rubber molecule, and if the nitrogen content is 0.02% or less, it is considered that substantially no protein is contained. Examples of the deproteinization treatment method include the method disclosed in JP-A-6-56902. That is, after proteolytic enzyme is added to latex such as field latex and ammonia-treated latex to decompose the protein, it is repeatedly washed with a surfactant for purification. A centrifugation method is preferably adopted for washing.

The proteolytic enzyme may be, for example, one derived from bacteria, one derived from filamentous fungi, one derived from yeast, etc., but is not particularly limited, but a protease derived from bacteria is used. Preferably. Such a decomposition treatment with a proteolytic enzyme can be usually performed by adding the proteolytic enzyme to natural rubber latex in a proportion of 0.01 to 10% by weight, and allowing it to stand or stir for several minutes to one week. . Proteolytic treatment is 5 to 90
Suitably, it is carried out at a temperature of 0 ° C, preferably 20-60 ° C.

The surfactant may be added either during the proteolytic treatment or after the treatment. As a surfactant,
For example, anionic and / or nonionic surfactants can be used. Examples of the anionic surfactant include carboxylic acid type, sulfonic acid type, sulfuric acid ester type and phosphoric acid ester type. Examples of nonionic surfactants include polyoxyalkylene ether-based, polyoxyalkylene ester-based, polyhydric alcohol fatty acid ester-based, sugar fatty acid ester-based, and alkyl polyglycoside-based agents. The amount of the surfactant added is 0.001 to 10% by weight of the natural rubber latex.
Is appropriate.

The natural rubber fine particles in the present invention include:
It is possible to concentrate and use the rubber component contained in the serum (heavy liquid component) generated during the concentration and purification by centrifugation in the deproteinization process of natural rubber latex. This serum contains 2 to 5% by weight of natural rubber fine particles having an average particle diameter of 0.1 to 0.5 μm. Alternatively, the serum containing 4-8% of fine rubber particles generated during the production of purified latex by centrifuging the field latex may be subjected to proteolytic treatment by the above-mentioned method, concentrated and purified before use.

The method for concentrating and purifying the above-mentioned serum is not particularly limited. For example, a method of concentrating by adding a water-soluble compound having a high specific gravity to the serum and then centrifuging, or an ultrafiltration method such as a flat membrane type or a tube type is used. A method of concentrating and purifying by an illegal method can be adopted. Since the latter is difficult to concentrate to a high concentration, it is preferable to use a centrifugally purified latex on the side of addition, which has a high concentration.

As the natural rubber fine particle component used in the present invention, the rubber component contained in the serum generated during the production of the conventional purified latex obtained by concentrating the field latex by centrifugation can also be recovered and utilized. Since the above-mentioned serum contains 4 to 8% of fine rubber particles having an average particle size of 0.1 to 0.5 μm, it is usually precipitated after addition of an acid and recovered as a solid rubber. It is used as a price grade. In the present invention, a proteolytic enzyme and a surfactant may be added to this serum, and it can be used in the same manner as the serum at the time of proteolytic treatment, centrifugation, and purification of the above deproteinized natural rubber.

In the purification and concentration of the above-mentioned fine rubber particles by the centrifugal separation method, in order to enhance the efficiency of the centrifugal separation, a water-soluble compound having a high specific gravity is added and dissolved in the serum at a ratio of 5 to 10% by weight based on the total amount. It is preferable to centrifuge it after allowing it to stand. The above-mentioned water-soluble compound to be added does not coagulate the latex, does not deteriorate the properties of the latex, and may be an inorganic compound or an organic compound as long as it does not have a bad influence even if a trace amount remains in the final product. good. Usually, inorganic salts such as ammonium sulfate and sodium carbonate, and water-soluble polymers such as polyethylene glycol are preferably used.

The method of centrifugation is not particularly limited, but in order to reduce the contamination of amino acid proteolytic residues and water-soluble compounds added to increase the specific gravity of the serum, the number of revolutions should be increased or retention during centrifugation should be performed. It is desirable to improve the separation efficiency by a method such as lengthening the time and to concentrate the rubber component as high as possible. In the concentration and purification by ultrafiltration, the flat membrane method and the tube method as well as the rotary flat membrane method can be used, and the method is not particularly limited, but the flat membrane method and the tube method can achieve high concentration without coagulation. It is difficult to concentrate and it is usually necessary to keep the solid content below 20% by weight. However, even in such a low-concentration latex, no problem occurs in practice by using a natural rubber latex having a high solid content as the natural rubber latex.

As the ultrafiltration membrane, any membrane capable of permeating a proteolytic residue may be used, and one having a molecular weight cutoff of about 700,000 or more is preferable. By adding the natural rubber fine particles, the raw rubber film can have a green strength of 5 MPa or more, preferably 6 MPa or more, and particularly 7 MPa or more.

In the present invention, it is necessary to add natural rubber fine particles to the deproteinized natural rubber latex in a proportion of 1 to 15% by weight based on the rubber component.
If the amount of the natural rubber fine particles added is less than this range, it is impossible to improve various characteristics such as film forming characteristics and mechanical stability. On the other hand, when the amount of the natural rubber fine particles added exceeds the above range, it is uneconomical since the sufficient addition effect has already been obtained and the cost of recovering the fine particle components is high.

The deproteinized natural rubber latex obtained by the method of the present invention may be adjusted to an appropriate rubber solid content concentration, and may be in the state of the latex or in the form of a sheet or film made of a dehydrated product thereof. As a deproteinized natural rubber in an appropriate form such as a bulk form, a powder form, etc., it can be used for the production of various rubber products.

[0023]

The present invention will be specifically described below based on Reference Examples and Examples, but the present invention is not limited to these Examples. Reference Example Proteolytic treatment and concentration / purification of natural rubber latex were carried out according to the method described in JP-A 06-56902. That is, in the field latex (rubber solid content 30% by weight) obtained from Malaysia FELDA Co., Ltd., nonionic anion composite surfactant (NeoPerex F-25 manufactured by Kao Corporation and Emulgen manufactured by Kao Corporation) was added to the rubber solid content. A mixture of 109P and 60P in a weight ratio of 60:38) was added so as to be 1% by weight, and a proteolytic enzyme (alkaline protease manufactured by Kao Corporation) was added at 0.02% by weight. Then, after enzyme treatment at 40 ° C. for 24 hours, the mixture was diluted with water so that the rubber solid content concentration became 10% by weight, and then the solid rubber content was obtained using a DeLaval continuous centrifuge (about 10,000 G). It was concentrated and purified until the concentration reached 65% by weight. The obtained cream was diluted again with water so that the rubber solid content concentration became 10% by weight, and then centrifuged again to obtain a rubber solid content concentration of 65% by weight and a mechanical stability of 120 seconds (machine in the evaluation test described later). Measurement in the same way as the evaluation method of dynamic stability),
A deproteinized natural rubber latex (hereinafter referred to as latex A) having a N content of the raw rubber of 0.007% by weight was obtained.

This latex A was used in each of the following examples. In the above process, a serum having a rubber solid content of about 5% by weight (hereinafter referred to as serum B) obtained by the first centrifugation was used as a raw material for obtaining the natural rubber fine particle components of Examples 1 and 2. Example 1 Ammonium sulfate was added to and dissolved in the serum B so as to be 10% by weight, and then concentrated using a DeLaval continuous centrifuge (about 10,000 G) to give a rubber solid content of about 50.
A weight percent cream was obtained. This cream was diluted with water in which 5% by weight of ammonium sulfate was dissolved so that the rubber solid content was 10% by weight, and then centrifuged again to obtain a cream having a rubber solid content of 50% by weight. This cream is 0.1
The latex consisted of rubber particles of 1 μm, and the average particle diameter of the rubber particles was 0.38 μm.

5 g and 1 latex of this fine particle component
Latex C-1a and C-1b were prepared by adding 0 g to 100 g of the latex A. Example 2 Using the cross-flow type flat membrane cell equipped with a polysulfone ultrafiltration membrane having a nominal molecular weight cut-off of 3,000,000, the above-mentioned serum B was added up to about 20% by weight of rubber solid content, that is, the total amount was the same. It was concentrated to 1/4. This was diluted to the original concentration with water and then concentrated again to 1/4. Do this operation 2
Repeated times. The obtained latex is 0.05-1 μm
The latex was rubber particles having an average particle diameter of 0.30 μm.

20 g of the above latex is added to the latex A
Latex C-2 was obtained by adding to 100 g. Example 3 The same field latex as used in the reference example was concentrated and purified using a DeLaval continuous centrifuge (about 10,000 G) until the solid rubber content concentration became 60% by weight. At that time, a soy sauce containing about 6% by weight of rubber particles having a maximum particle size of 1 μm or less was by-produced. To the whole amount of this serum, the same nonionic anion complex type surfactant as in the reference example was added.
5% by weight and proteolytic enzyme were added to a concentration of 0.01% by weight. After treating this at 40 ° C. for 24 hours, ammonium sulfate was added and dissolved so as to be 10% by weight, and then a DeLaval continuous centrifuge (about 10,
000G) to obtain a cream having a rubber solid content of about 50% by weight. This cream was diluted with water in which 5% by weight of ammonium sulfate was dissolved to a rubber solid content of 10% by weight, and then centrifuged again to give a rubber solid content of 52% by weight.
Got the cream. This cream was a latex composed of rubber particles of 0.1 to 1 μm, and the average particle size of the rubber particles was 0.30 μm. 5 g of this fine particle component latex was added to 100 g of the above latex A to prepare latex C-3. [Evaluation Test] The mechanical stability, green strength, and film forming characteristics of each latex obtained were evaluated.

Here, the mechanical stability is JIS-K-6.
MST (Mechanical Stab)
ility Time, unit: seconds) was measured. At the time of measurement, adjust the emulsifier concentration to 1.0% of the rubber solids, and
The T. measuring device used was manufactured by Craxon. Further, 36 g of each latex was cast on a glass plate of 18 cm × 12 cm, left to dry at room temperature, peeled off from the glass plate, and the surface in contact with the glass surface was dried for one day. Then, it was dried under vacuum to obtain a raw rubber test film sample. The strength (green strength) of the obtained raw rubber film as a test sample was measured at a test speed of 500 mm / min using a JIS No. 4 dumbbell.

Film forming characteristics for forming a test film were evaluated during the above green strength measurement. As an evaluation criterion, a film that was difficult to be formed due to cracking or the like during film formation was regarded as a poor film-forming property, and a film that could be formed into a uniform film was evaluated as good. As a comparative example, the latex A obtained in the reference example was used to evaluate the mechanical stability, green strength and film forming characteristics in the same manner as above.

The test results are shown in Table 1.

[0030]

[Table 1]

As is clear from Table 1, the deproteinized natural rubber latexes obtained in Examples are superior to the latexes of Comparative Examples in mechanical stability, green strength and film forming characteristics. Recognize.

[0032]

Industrial Applicability The method for producing a deproteinized natural rubber latex of the present invention comprises adding fine natural rubber particles to the deproteinized natural rubber latex to obtain various characteristics such as film forming characteristics, mechanical stability and green strength. A latex having improved properties can be easily obtained without causing problems such as increase in equipment cost.

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Yasuyuki Tanaka 1481-184 Uchikoshi-cho, Hachioji-shi, Tokyo (72) Inventor Shin-ichi Nakade 3-31 Kasugaoka, Itami-shi, Hyogo (72) Inventor Toshiaki Sakaki Kakogawa, Hyogo 1314, 1314 Yoda, Onoue-shi, Ichi (72) Inventor, Shoji Hayashi 133-5, Enohara, Wakayama, Wakayama Prefecture (72) Akihito Kuga, 3-19, Kandanishikicho, Chiyoda-ku, Tokyo 1 Fuji Latex Co., Ltd. (72) Inventor Kazuhiko Shibata 1-2-1, Shimohozumi, Ibaraki City, Osaka Prefecture Nitto Denko Corporation

Claims (3)

[Claims] 1. Addition of natural rubber fine particles having an average particle diameter of 0.1 to 0.5 μm to a deproteinized natural rubber latex in a proportion of 1 to 15% by weight based on the rubber component. A method for producing a deproteinized natural rubber latex, which comprises: 2. The method for producing a deproteinized natural rubber latex according to claim 1, wherein the nitrogen content is 0.02% by weight or less. 3. The method for producing a deproteinized natural rubber latex according to claim 1, wherein the natural rubber fine particles are deproteinized.