JP2020200907A - Transmission belt - Google Patents

Abstract

To provide a transmission belt composed of a rubber composition excellent in elasticity and low loss properties.SOLUTION: A transmission belt is composed of a rubber composition. The rubber composition contains, based on a sulfur-modified chloroprene rubber 100 pts.wt., 1.8-3.0 pts.wt. of a cellulose nanofiber that is fibrillated by mechanical treatment without modifying a hydroxymethyl group of the cellulose nanofiber with carboxylic acid or carboxylate.SELECTED DRAWING: None

Description

The present invention relates to a transmission belt.

Chloroprene rubber is used in a wide range of applications because it has a good balance of physical properties among various synthetic rubbers. Among them, sulfur-modified chloroprene rubber, which is a copolymer of sulfur, is used as one of the raw materials for transmission belts due to its excellent dynamic properties. However, due to the recent demand for higher performance and improved fuel efficiency, it has even higher elasticity. There is a demand for lower loss and lower loss.

Examples of elasticity include dynamic viscoelasticity obtained from the stress change when a constant vibration is applied to the sample, and tangent loss, which is the elastic ratio of the viscoelasticity. The smaller the tangent loss, the more the transmission belt is used. The transmission efficiency becomes high.

When producing vulcanized rubber, it is usually possible to increase the strength and elastic modulus by blending a reinforcing material such as carbon black or silica, but when reinforcing by blending these granular reinforcing materials, the vulcanized rubber is used. At the same time, the hardness of the rubber increases remarkably, the processability of the rubber product decreases, and the vulcanization loss increases as the elastic modulus increases. Therefore, there is a limit to the reinforcing effect in order to maintain an appropriate rubber hardness.

On the other hand, fiber-shaped reinforcing materials have been proposed, and tires and the like containing cellulose fibers have been proposed. (For example, Patent Document 1) However, hydrophilic cellulose has a lower reinforcing effect than hydrophobic rubber because it has poor dispersibility. As a countermeasure, a tire in which nano-order cellulose and a dispersant for dispersing the cellulose and a silane coupling agent for fixing the cellulose are blended with natural rubber latex has been proposed. (Patent Documents 2 to 3) However, these methods require a separate agent for dispersing rubber and cellulose, such as a dispersant, which increases the cost. In addition, the fact is that chloroprene rubber has not been studied much.

Japanese Unexamined Patent Publication No. 2006-206864 JP-A-2009-191197 JP-A-2009-191198

The present invention has been made in view of this problem, and an object of the present invention is to provide a transmission belt made of a rubber composition having a high elastic modulus and a low tangent loss.

Against this background, as a result of diligent studies to solve the above problems, the present inventor has made a rubber composition containing sulfur-modified chloroprene rubber and cellulose nanofibers, which show a low tangent loss while having a high elastic modulus in the transmission belt. It was found that the transmission belt with excellent transmission efficiency can be obtained by using. That is, in the present invention, the hydroxymethyl group of the cellulose nanofibers is not modified with a carboxylic acid or a carboxylic acid salt with respect to 100 parts by weight of the sulfur-modified chloroprene rubber, and the cellulose nanofibers are defibrated by mechanical treatment 1.8. A transmission belt made of a rubber composition, which comprises ~ 3.0 parts by weight.

Hereinafter, the present invention will be described in detail.

In the rubber composition used for the transmission belt of the present invention, the hydroxymethyl group of cellulose is not modified with a carboxylic acid or a carboxylic acid salt with respect to 100 parts by weight of sulfur-modified chloroprene rubber, and the cellulose nano is defibrated only by mechanical defibration. It contains 1.8 to 3.0 parts by weight of fiber.

Sulfur-modified chloroprene rubber can be obtained by emulsion polymerization of a chloroprene monomer and sulfur.

The amount of sulfur used is not particularly limited, but if it is added in an excessive amount, the heat resistance is adversely affected. Therefore, the total amount of chloroprene monomer or chloroprene monomer and a monomer copolymerizable with chloroprene is 100 parts by weight. On the other hand, it is 0.2 to 1 part by weight.

In the emulsion polymerization of chloroprene rubber, for example, the above-mentioned monomer is mixed with an emulsifier, water, a polymerization initiator, a chain transfer agent, other stabilizers, etc., polymerized at a predetermined temperature, and polymerized at a predetermined polymerization conversion rate. Examples thereof include a method of adding a terminator to terminate the polymerization.

As the emulsion polymerization initiator, known free radical substances such as peroxides such as potassium persulfate and ammonium persulfate, and inorganic or organic peroxides such as hydrogen peroxide and tertiary butyl hydroperoxide are used. be able to. In addition, these may be used alone or in a combined redox system with a reducing substance such as thiosulfate, thiosulfite, hydrosulfite, or organic amine.

The polymerization temperature is not particularly limited, but is preferably in the range of 10 to 50 ° C.

In the method for producing chloroprene rubber, the time at which the polymerization is completed is not particularly limited, but from the viewpoint of productivity, the polymerization is generally carried out so that the conversion rate of the monomer is 60% or more and 95%. If it is 60% or less, the production amount is small and the solid content of latex is low, the drying cost of water is high, and if it is 95% or more, the polymerization time becomes very long.

The polymerization terminator is not particularly limited as long as it is a commonly used terminator, and for example, phenothiazine, 2,6-t-butyl-4-methylphenol, hydroxylamine and the like can be used.

Further, it is possible to adjust the Mooney viscosity so as to obtain an appropriate Mooney viscosity by adding a defibrating agent and a defibrating aid to the latex having been polymerized. Examples of the glazing agent include thiuram compounds such as tetraethyl thiuram disulfide, tetrabutyl thiuram disulfide, and tetraoctyl thiuram disulfide. Examples of the anti-glutinating agent include thiocarbamic acid compounds such as sodium dibutyldithiocarbamate and ammonium dimethyldithiocarbamate.

The Mooney viscosity for terminating the thawing reaction is not particularly limited as long as it satisfies the high elastic stress of the present invention, but is preferably 20 to 80 in consideration of kneading workability.

Cellulose nanofibers are defibrated cellulose fibers contained in wood to an average fiber diameter of several nanometers to several tens of nanometers. Cellulose defibration treatment is mainly performed by mechanical treatment and chemical treatment to add various functional groups, and by using mechanical treatment together, aggregation of cellulose nanofibers is suppressed and it is carried out to a finer single nano level. However, in the present invention, the one obtained only by mechanical treatment without chemical treatment is used. Generally, it is difficult to set the average fiber diameter to 10 nm or less only by mechanical defibration, but in the present invention, it is preferably 10 to 300 nm, and more preferably 30 to 200 nm. When the average fiber diameter is 10 nm or more, the physical properties are good, and when the average fiber diameter is 300 nm or less, the molding processability and physical properties of the vulcanized rubber are good. The fiber length varies from 0.5 μm to several μm, but cellulose nanofibers having an average fiber length of 0.5 μm or more are excellent in processability and physical properties of vulcanized rubber, and have an average fiber length of less than 1500 μm. Is preferably 10 to 1500 μm because the molding processability of the cellulose nanofiber-containing rubber is improved. Further, when the cellulose nanofibers have a carboxylate or a carboxylic acid, the dispersed state of the cellulose nanofibers in the rubber deteriorates and aggregates, so that the effect of increasing the tensile stress of the obtained vulcanized rubber is reduced or handling is performed. Decreases. Therefore, cellulose containing no carboxylate or carboxylic acid is used.

In the present invention, the content of the cellulose nanofibers is 1.8 to 3.0 parts by weight, preferably 2.0 to 2.5 parts by weight, based on 100 parts by weight of the chloroprene rubber. When the cellulose nanofiber content is 1.8 parts by weight or more, the elastic modulus is excellent, and when the cellulose nanofiber content is 3.0 parts by weight or less, the handleability when the cellulose nanofibers are mixed is good. ..

The rubber composition can be obtained by mixing an aqueous dispersion of cellulose nanofibers with a latex of sulfur-modified chloroprene rubber to prepare a cellulose nanofiber dispersion liquid, and removing water from the dispersion.

Sulfur-modified chloroprene rubber latex is a polymer of chloroprene monomer and sulfur, or chloroprene monomer and sulfur and a monomer copolymerizable therewith, emulsified and dispersed with an alkali metal salt of carboxylic acid. The production method thereof is not particularly limited, and a reaction solution obtained by emulsion polymerization of a chloroprene monomer and a polymer of sulfur, a chloroprene monomer and sulfur and a monomer copolymerizable therewith, or sulfur modification. A solution obtained by dissolving chloroprene rubber in a solvent and then emulsifying and dispersing it with an alkali metal salt of a carboxylic acid can be used.

An aqueous dispersion of cellulose nanofibers is obtained by defibrating wood, pulp, or the like to a predetermined fiber diameter and fiber length by mechanical treatment.

The method for mixing the aqueous dispersion of the sulfur-modified chloroprene rubber latex and the cellulose nanofibers is not particularly limited, and the aqueous dispersion of the chloroprene latex and the cellulose nanofibers is performed using a propeller-type stirrer, a homomixer, a high-pressure homogenizer, or the like. It can be obtained by mixing until the body becomes uniform in appearance (no lumps or the like).

Methods for removing water from the cellulose nanofiber-dispersed rubber latex mixture (drying method) include heat drying, coagulation with acid and salt, and freeze-drying, but emulsifiers, coagulation liquid, and water remain inside the rubber. Since drying becomes difficult, the freeze-drying method in which rubber is precipitated (freeze-solidified) by freezing, excess emulsifiers and the like are washed with water and then dried with hot air is the most efficient and easy to dry. Further, it is more preferable to freeze-dry the cellulose nanofiber-dispersed rubber latex mixed solution at a pH of 10 or less so that the rubber can be easily precipitated.

In the method of freeze-coagulating and drying from the cellulose nanofiber-dispersed rubber latex mixture, the viscosity of the cellulose nanofiber-dispersed rubber latex mixture is preferably 1000 mPa · s or less. When the viscosity is 1000 mPa · s or more, the dispersion liquid can be easily handled.

The obtained cellulose nanofiber-containing rubber composition can be made into a vulcanized rubber by blending and kneading various compounding agents in the same manner as ordinary chloroprene rubber and heating.

The obtained vulcanized rubber has a high elastic modulus and a low tangent loss. The transmission belt is required to have various characteristics such as appropriate frictional resistance and wear resistance in order to enhance its transmission efficiency and durability. Elastic modulus and tangent loss are also important factors in the belt, but it was difficult to achieve both because improving one property would reduce other properties, but a rubber composition in which the ratio of elastic modulus to tangent loss increases. By using it, a transmission belt having excellent transmission efficiency can be obtained.

According to the present invention, a transmission belt having excellent transmission efficiency can be obtained by using a vulcanized rubber having a high elastic modulus and a low tangent loss.

Hereinafter, the present invention will be specifically described with reference to Examples, but the present invention is not limited to these Examples.

<Creation of sulfur-modified chloroprene rubber latex>
As a monomer mixture, 0.3 parts by weight of sulfur was added to 100 parts by weight of chloroprene, 4.0 parts by weight of potassium salt of phosphoric acid, 0.5 parts by weight of sodium salt of a condensate of naphthalene sulfonic acid and formaldehyde, It is mixed and stirred with an emulsified aqueous solution containing 0.05 parts by weight of sodium hydroxide, 1.0 part by weight of sodium orthophosphate, and 100 parts by weight of water, and the mixture is emulsified with 1.0 part by weight of potassium persulfate and anthraquinone-β-sulfonic acid. A polymerization catalyst consisting of 0.01 part by weight of sodium and 30 parts by weight of water was added at a constant rate by a pump to carry out the polymerization. The polymerization was carried out by adding a polymerization catalyst until the polymerization conversion rate reached 70%, to which 0.01 part by weight of thiodiphenylamine, 4-t-butylcatechol, 2,2'-methylenebis-4-methyl-6-t-. Polymerization was stopped by adding a polymerization inhibitor consisting of 0.05 parts by weight of butylphenol, 0.1 part by weight of diethylhydroxylamine, 0.05 part by weight of sodium lauryl sulfate, 5.0 parts by weight of chloroprene, and 1.0 part by weight of water. I let you. Subsequently, 2 parts by weight of a toluene solution of tetraethylthiuram disulfide emulsified with potassium loginate and 0.3 part by weight of sodium dibutyldithiocarbamate were added thereto, and the mixture was deflocculated at 40 ° C. until the Mooney viscosity reached 60. After that, unreacted chloroprene was removed and recovered by steam stripping under reduced pressure to obtain a sulfur-modified chloroprene rubber latex. The pH of the obtained sulfur-modified chloroprene rubber latex was 11.3.

<Preparation of cellulose nanofiber dispersion liquid and rubber composition>
A predetermined amount of an aqueous dispersion of cellulose nanofibers was added to the sulfur-modified chloroprene rubber latex, and the mixture was mixed with an autohomo mixer (manufactured by PRIMIX) at 2,000 rpm for 10 minutes. Then, the pH was adjusted to 6.5 with 15 wt% dilute acetic acid, and then the polymer was precipitated by freeze-coagulation and dried to prepare a rubber composition.

<Viscosity, pH>
The viscosity was measured with a Bismetron viscometer (manufactured by Shibaura Semtech Co., Ltd .: VD2).

The pH of the latex at 23 ° C. was measured with a pH meter (manufactured by HORIBA, Ltd.).

<Making rubber compound>

Open roll kneading of magnesium oxide, stearic acid, carbon black (FEF), plasticizer (DOA) and zinc oxide in parts by weight shown in Table 1 with respect to 100 parts by weight of the chloroprene rubber component of the chloroprene rubber containing cellulose nanofiber (CNF). It was added by machine to obtain a rubber compound.

<Creation of vulcanized product>
The obtained rubber compound was press-vulcanized at 160 ° C. for 15 minutes to prepare a vulcanized sheet.

<Measurement of mechanical properties of vulcanized products>
The elastic modulus (dynamic viscoelasticity E') and tangent loss (tan δ) of the obtained vulcanized sheet were determined by using a dynamic viscoelasticity tester VR-7120 (manufactured by Ueshima Seisakusho) with an initial strain of 5% and a dynamic strain. The value at 100 ° C. was measured under the conditions of 1% and a frequency of 1 Hz.

Example 1
An aqueous dispersion of cellulose nanofibers (Mori Machinery grade: C-100, fiber diameter: 30 to 200 nm, average fiber length: 100 μm) produced by mechanical defibration means on a sulfur-modified chloroprene rubber latex. Was mixed so as to be 2.5 parts by weight with respect to 100 parts by weight of the sulfur-modified chloroprene rubber converted into solid, and stirred for 10 minutes by the above method to obtain a cellulose nanofiber dispersion liquid. The viscosity of the dispersion was 540 mPa · s, there was no problem in handling, and a rubber composition was obtained by freeze-drying.

This rubber composition was used as a rubber compound, then a vulcanized product was prepared, and the elastic modulus and tangent loss were measured. The results are shown in Table 2. From Table 2, the elastic modulus was 15.7 MPa, the tangent loss (Tanδ) was 0.09, the elastic modulus was high, the tangent loss was low, and the ratio of the elastic modulus to the tangent loss was large and good results were obtained.

Example 2
A cellulose nanofiber dispersion was obtained in the same manner as in Example 1 except that the aqueous dispersion of cellulose nanofibers used was changed to KY-100G (fiber diameter: 10 to 100 nm, average fiber length: 10 to 1500 μm) manufactured by Daicel Finechem Ltd. A rubber composition and a vulcanized product were prepared, and the elastic modulus and the tangential loss were measured. The elastic modulus was high, the tangent loss was low, and the ratio of the elastic modulus to the tangent loss was large, which was a good result.

Comparative Example 1
A rubber composition and a vulcanized product were prepared in the same manner as in Example 1 except that the cellulose nanofibers were not mixed, and the elastic modulus and the tangent loss were measured. Both the elastic modulus and the tangent loss were low, and the ratio of the elastic modulus to the tangent loss was small.

Comparative Example 2
A rubber composition and a vulcanized product were prepared in the same manner as in Example 1 except that the mixing amount of the cellulose nanofibers was 1.5%, and the elastic modulus and the tangent loss were measured. Both the elastic modulus and the tangent loss were low, and the ratio of the elastic modulus to the tangent loss was small.

Comparative Example 3
A cellulose nanofiber dispersion was obtained in the same manner as in Example 1 except that the mixing amount of the cellulose nanofibers was 4%, but the viscosity of the dispersion was 1070 mPa · s, and the handleability was poor.

Claims (2)

A rubber composition containing 1.8 to 3.0 parts by weight of cellulose nanofibers defibrated by mechanical treatment without modifying the hydroxymethyl group with a carboxylic acid or a carboxylic acid salt with respect to 100 parts by weight of sulfur-modified chloroprene rubber. Transmission belt made of things. The transmission belt according to claim 1, wherein the average fiber diameter of the cellulose nanofibers is 10 to 300 nm.