JPH0812813A - Natural rubber composition - Google Patents

Abstract

PURPOSE:To obtain the subject composition useful as rubber products such as rubber glove, balloon, etc., having physical properties of natural rubber of its own, improved decomposition properties with a microorganism, environmental adaptability by dispersing fine particles of a microorganism decomposable resin into a natural rubber latex. CONSTITUTION:This composition is obtained by dispersing (B) fine particles of a microorganism decomposable resin such as polyhydroxybutyrate or polyhydroxyvalerate into (A) a natural rubber latex such as one blended with a rubber chemical, e.g. a vulcanizing agent for rubber. The component B has preferably >=100 deg.C melting point and <=10mum particle diameter in the component A and the blended amount of the component B is 10-100 pts.wt. based on 100 pts.wt. of the component A.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a natural rubber composition used for producing a natural rubber product having improved microbial degradability.

[0002]

2. Description of the Related Art It has been known that natural rubber is a biodegradable substance because it is a natural product. However, natural rubber products that use natural rubber contain natural rubber with vulcanizing agents such as sulfur, vulcanization accelerators, and anti-aging agents to improve physical properties such as rubber elasticity. Therefore, microbial degradability is reduced, and it is generally regarded as a hardly degradable substance. Marine organisms swallow natural rubber products such as rubber balloons and are damaged because rubber balloons are persistent substances.

Originally, natural rubber products such as balloons, condoms, rubber gloves and the like are produced from natural rubber latex, and improvement of microbial degradability thereof has hardly been studied. However, cross-linking of rubber has been studied, and attempts have been made to improve decomposability in terms of, for example, reducing the amount of vulcanizing agent and performing cross-linking by radiation cross-linking. However, because of the deterioration of physical properties and the difficulty of manufacturing,
There is still room for improvement.

Under these circumstances, studies have recently been made on imparting microbial degradability to natural rubber products obtained by blending natural rubber and a microbial degradable resin with hot rolls. This product melts a solid rubber generally called raw rubber and a microbial degradable thermoplastic resin to form a sea / island structure, and has a microbial degradable thermoplastic resin in the sea and natural rubber on the island in a roll. It is a blend.

[0005]

However, since the physical properties of this natural rubber product are dominated by the sea part occupied by the microbial-degradable thermoplastic resin, the natural rubber has almost the original elasticity. Absent. However, since the rubber particles are dispersed, the impact resistance of the product is improved. The role of the natural rubber component in this case is rather that of the thermoplastic resin as a filler.

[0006] The present invention has been made in view of such conventional circumstances, and if the same manufacturing method as the conventional one is used, that is, when the conventional natural rubber product is produced, it is applied to the natural rubber latex. It is an object of the present invention to provide a natural rubber composition capable of obtaining a natural rubber product which is excellent in microbial degradability and has physical properties inherent to natural rubber, particularly elasticity when subjected to the same treatment as the above treatment. .

[0007]

Means and Actions for Solving the Problems The natural rubber composition provided by the present invention is a liquid in which a microbial degradable resin is stably dispersed as fine particles in a natural rubber latex. By subjecting this liquid to vulcanization and other similar treatments as in conventional manufacturing methods, it is possible to obtain natural rubber products that have physical properties equivalent to those of conventional products and that have a significantly improved microbial decomposition rate. You can

[0008] Since natural rubber and microbial degradable resin, and aliphatic polyester resin as a representative thereof, have poor compatibility, if the amount of the microbial degradable resin is more than 100 parts by weight based on 100 parts by weight of natural rubber, the sea is The natural rubber that forms the structure is unlikely to form a continuous phase, and the biodegradable resin that forms the island structure does not form a continuous phase either, and the physical properties are extremely weak, and the state becomes disjointed. It is difficult to become an elastic natural rubber product. Therefore, the optimum amount of the biodegradable resin is 100 parts by weight or less with respect to 100 parts by weight of natural rubber.

Although it is possible to control the sea / island structure of the natural rubber and the microbial degradable resin in the natural rubber product by adjusting the blending amount of the microbial degradable resin, it is necessary to give the natural rubber product rubber elasticity. Should be the sea and the island should be a biodegradable resin. In this case, the more natural rubber that is, the more clearly the sea is formed,
The rate of microbial decomposition of the product will decrease, but if natural rubber deteriorates due to oxygen (especially ozone), ultraviolet rays, etc. and cracks etc., the microbial decomposable resin that is an island will be exposed, so
It is considered that the decomposition of the product is promoted and the decomposition rate does not decrease so much. However, when the compounding amount of the microbial-degradable resin becomes less than 10 parts by weight with respect to 100 parts by weight of natural rubber, the substance becomes a hardly decomposable substance close to a natural rubber product produced from conventional natural rubber latex. Therefore, the lower limit of the amount of the biodegradable resin blended is appropriately 10 parts by weight.

The particle size of the microbial degradable resin dispersed in the natural rubber latex is preferably 10 μm or less, and even about 1 μm is stable and is preferable for obtaining a good quality natural rubber product. When the particle size is 10 μm or more, the resin particles settle. For example, when a mold for rubber gloves is immersed in natural rubber latex, resin particles settle in the latex liquid film attached to the mold and do not disperse uniformly in the film, resulting in a non-uniform film of resin particles. I won't. In order to prevent the sedimentation of such resin particles, it is possible to increase the viscosity of the latex itself, or to add a dispersant, but even in such a case, the resin to be added is If the specific gravity of the group polyester is large, it will settle over time.

Examples of the biodegradable resin include aliphatic polyesters, block copolymers of low molecular weight polyamides for the purpose of improving the melting point of low melting point aliphatic polyesters, and polylactic acid. . The aliphatic polyester includes a polycondensation product of a polyvalent carboxylic acid containing an aliphatic divalent carboxylic acid and a polyhydric alcohol containing an aliphatic diol, a polycondensation product of a hydroxyaliphatic carboxylic acid, and a ring opening of a lactone. Polymers are included, and specific examples thereof include homopolymers and copolymers derived from ethylene diadipate, propiolactone, caprolactone, β-hydroxybutyrate and the like. β
Examples of the copolymer derived from -hydroxybutyrate include a copolymer of β-hydroxybutyrate and β-hydroxyvalerate.

However, considering the processing temperature of the natural rubber composition, the microbial degradable resin usable in the present invention is
Of the above resins, those having a melting point (Mp) of 100 ° C. or higher are limited, and all of them are decomposed by a microbial enzyme such as lipase. This is because heating in excess of 100 ° C. is performed in the vulcanization and drying steps of the natural rubber composition. Therefore, if the biodegradable resin has a melting point of less than 100 ° C., its fine particles are processed into the natural rubber composition. This is because it is melted and agglomerated therein, or is fused to the molding die to prevent uniform dispersion.

Unlike general synthetic resin products, natural rubber products have the characteristic that the rubber part swells due to moisture,
If the molecular spacing of the rubber is widened, microbes are likely to enter the gaps, which promotes the decomposition, and the biodegradable resin that forms the islands is also susceptible to the decomposition, which promotes the decomposition. It Further, the natural rubber composition of the present invention,
Since the fine particles of the biodegradable resin are dispersed in the natural rubber latex, the fine particles of the biodegradable resin are exposed on the surface of the processed natural rubber product. Therefore, the biodegradability is remarkably improved as compared with the conventional single rubber product.

The natural rubber composition according to the present invention can be used as a material for conventional natural rubber products produced from natural rubber latex, such as rubber gloves, condoms and balloons. The natural rubber product using the natural rubber composition of the present invention has improved biodegradability even after being disposed of after use and landfilled, so that it is easily decomposed and enters a natural cycle. . Therefore, it is possible to use the same landfill for a long time. Moreover, even if it is dumped in the ocean, it will be decomposed with the passage of time, and the harm to wildlife will be reduced. Further, even if it is incinerated, no harmful gas is generated, so that adverse effects on the environment are reduced as compared with the conventional case.

[0015]

EXAMPLES Examples of the present invention will be described below together with comparative examples.

First, the natural rubber latex and the microbial degradable resin used in the examples and comparative examples, the compounding amount of the microbial degradable resin with respect to the natural rubber, and the preparation procedure of the natural rubber composition using both compositions will be described.

(1) The natural rubber latex was prepared by mixing a predetermined amount of general rubber chemicals such as sulfur, a vulcanization accelerator and a stabilizer in advance.

(2) As the microbial degradable resin, those shown in Table 1 were used.

[0019]

[Table 1]

(3) The blending amount (W / W%) of the biodegradable resin with respect to the natural rubber was calculated by the weight of the resin with respect to the weight of the natural rubber when water in the natural rubber latex was evaporated and dried. . For reference, Table 8 shows a table converted into parts by weight (w / w%) as a blending unit.

[0021]

[Table 8]

(4) The blending amount of the biodegradable resin with respect to the natural rubber is shown in Table 2.

[0023]

[Table 2]

(5) The natural rubber compositions are the natural rubber latices of Examples 1 to 5 and Comparative Examples 1 to 6 shown in Table 2 and the corresponding water dispersion Nos. 1 to No. 4 and 4 were made by uniformly mixing.

PHB or PCL aqueous dispersion Nos. 1 to No. No. 4 was prepared by dispersing PHB or PCL finely divided by the method shown in Table 3 in water.

[0026]

[Table 3]

Table 4 shows the results of observing the sedimentation state of the resin particles when the natural rubber compositions of Example 1 and Comparative Examples 1 to 3 were left standing for 24 hours.

[0028]

[Table 4]

Next, using the natural rubber compositions of Examples 1 to 5 and Comparative Examples 1 to 6 and the natural rubber latex of Comparative Example 7, natural rubber sheets were prepared by the following procedure.

(1) The natural rubber compositions of Examples 1 to 5 and Comparative Examples 1 to 6 and the natural rubber latex of Comparative Example 7 were aged at 40 ° C. for 48 hours.

(2) The obtained aged natural rubber composition was applied onto a glass plate and uniformly cast, and this was placed in an oven for 1 hour.
After vulcanization at 30 ° C. for 20 minutes, it was peeled from the glass plate.

(3) The obtained rubber sheet was washed with running water for 1 hour to remove the water-soluble substance, and then heated in an oven for 10 hours.
It was dried at 5 ° C for 1 hour, and this was used as a final product, a natural rubber sheet.

The appearance and evaluation of the physical properties of the obtained natural rubber sheet were carried out, and the results shown in Table 5 were obtained.

[0034]

[Table 5]

The tensile strength, elongation and 300% modulus in Table 5 were measured on a rubber sheet piece obtained by punching out the natural rubber sheet prepared by the above procedure with JIS No. 1 dumbbell. A tensile tester with a chuck interval of 4 cm and a pulling speed of 500 mm / mm was used for the measurement.

When the obtained natural rubber sheet was subjected to a microbial degradability test, the results shown in Table 6 were obtained. The test was conducted as follows.

The biodegradability test was carried out using a natural rubber sheet 1
The cut pieces of 0 cm x 10 cm were generally buried in soil (in this case, on the factory premises) to a depth of 15 cm underground and dug out at regular intervals to observe the appearance and the like.

[0038]

[Table 6]

For reference, the weight loss of the polyester component, which is a biodegradable resin, was measured by alkaline hydrolysis, and the results shown in Table 7 were obtained. For hydrolysis, potassium hydroxide (KOH) / ethyl alcohol (EtO
H) / purified water = 5/75/20 W / W% of the treatment liquid was used, and the weight-measured natural rubber sheet pieces were immersed therein at 20 ° C. for 24 hours.

[0040]

[Table 7]

PH for general-purpose thermoplastic resin such as PE
In the case of a product in which B, PCL, etc. are blended in an island structure, almost no weight loss is observed by the alkaline hydrolysis treatment as in the reference comparative example. This fact indicates that the product does not biodegrade even when buried in real soil.

However, the natural rubber sheet is hydrolyzed and its weight is reduced depending on the blending amount. This indicates that the sheet is microbially decomposed even when it is buried in actual soil.

[0043]

As described above, since the natural rubber composition of the present invention has the above-mentioned constitution, it is excellent in biodegradability by using the conventional method for producing a natural rubber product. In addition, it is possible to produce a natural rubber product having the original physical properties of natural rubber.

Claims (7)

[Claims] 1. A natural rubber composition obtained by dispersing a microbial degradable resin in the natural rubber latex as fine particles. 2. The natural rubber composition according to claim 1, wherein a natural rubber latex is compounded with a rubber chemical such as a rubber vulcanizing agent which is usually used. 3. The natural rubber according to claim 1, wherein the microbial-degradable resin is at least one selected from the group consisting of an aliphatic polyester and / or a copolymer of an aliphatic polyester and another microbial-degradable resin. Composition. 4. The aliphatic polyester is at least one selected from the group consisting of polyhydroxybutyrate or / and polyhydroxyvalerate or / and a copolymer of β-hydroxybutyrate and β-hydroxybrylate. The natural rubber composition according to claim 3. 5. The natural rubber composition according to claim 1, wherein the biodegradable resin is fine particles having a particle size of 10 μm or less in a natural rubber latex. 6. The natural rubber composition according to claim 1, wherein the amount of the biodegradable resin is 10 parts by weight to 100 parts by weight based on 100 parts by weight of the natural rubber. 7. The melting point of the biodegradable resin is 100 degrees Celsius.
The natural rubber composition according to claim 1, which has a temperature of not less than ° C.