阅读说明：本技术 含有纤维素黄原酸酯微细纤维的树脂组合物 (Resin composition containing cellulose xanthate microfine fibers ) 是由 久保纯一 中坪朋文 正清孝一 田嶋宏邦 佐佐木彰三 于 2018-06-21 设计创作，主要内容包括：本发明提供一种纤维素微细纤维能够以高均匀性对树脂、橡胶发挥适当的作用且对添加的树脂组合物的作用更优异的材料。使树脂组合物、树脂分散液含有纤维素黄原酸酯微细纤维。(The invention provides a material which can exert proper action on resin and rubber with high uniformity and has more excellent action on added resin composition. The resin composition and the resin dispersion liquid contain cellulose xanthate microfine fibers.)

1. A resin composition contains cellulose xanthate microfine fibers.

2. The resin composition according to claim 1, wherein a sulfur component which is not a part of a xanthate group and which is insoluble in carbon disulfide is present.

3. The resin composition according to claim 1 or 2, wherein the cellulose xanthate microfine fibers comprise cellulose xanthate nanofibers having a fiber diameter of 3 to 200 nm.

4. A resin dispersion contains cellulose xanthate microfine fibers.

5. The resin dispersion liquid according to claim 4, wherein the cellulose xanthate microfine fiber has a sulfur component generated by a reaction of a xanthate group with an oxidizing agent.

6. A master batch obtained by drying or acid setting the resin dispersion according to claim 4 or 5.

7. A rubber composition obtained by vulcanizing a rubber mixture containing the master batch according to claim 6, wherein the resin dispersion is a dispersion of the rubber composition.

8. The rubber composition of claim 7, wherein the rubber compound comprises carbon black.

9. The rubber composition according to claim 7 or 8, wherein the cellulose xanthate microfine fibers comprise cellulose xanthate nanofibers having a fiber diameter of 3 to 200 nm.

10. A process for producing a rubber molded article, which comprises obtaining a master batch from a rubber latex containing cellulose xanthate microfine fibers,

the rubber mixture containing the master batch is heated to be vulcanized.

11. The method for producing a rubber molding according to claim 10, comprising a step of oxidizing and modifying a part of the cellulose xanthate microfine fibers by adding an oxidizing agent.

12. A cellulose xanthate microfine fiber having a sulfur component which is not a part of xanthate groups and which is insoluble in carbon disulfide.

Technical Field

The present invention relates to a resin composition containing cellulose xanthate microfine fibers.

Background

Cellulose is known to have a reinforcing effect on resins and rubbers (patent document 1). However, such cellulose powder is in a particle form in which fibers are entangled with each other, and a high reinforcing effect by the fine fiber shape of cellulose cannot be obtained.

Further, the following patent document 2 discloses the following: in order to improve the reinforcing property of the rubber composition, short fibers such as cellulose are fibrillated and mixed with a rubber latex under stirring, and water is removed from the mixed liquid to obtain a rubber/short fiber master batch. However, fibrillated cellulose fibers tend to aggregate and are difficult to disperse uniformly in the rubber component.

Further, as an additive to the rubber composition, there is known an example of adding cellulose microfibers having a smaller fiber diameter and a nanometer size than fibrillated cellulose (for example, patent documents 3 to 5 below). They are considered to have a higher reinforcing effect than particulate cellulose and fibrillated cellulose.

On the other hand, patent document 6 discloses the following method: mixing natural rubber latex and cellulose xanthate solution, and coagulating in sulfuric acid/zinc sulfate solution to obtain the rubber-regenerated cellulose nano composite material.

Disclosure of Invention

However, the cellulose microfibers described in patent documents 3 to 5 are likely to aggregate to have the same size as fibrillated cellulose or, in some cases, are likely to aggregate to have a size equal to or larger than fibrillated cellulose, and therefore, it is difficult to ensure dispersibility, and there is a possibility that a sufficient reinforcing effect cannot be obtained due to unevenness.

In addition, in the method described in patent document 6, since cellulose II is a type and cannot be made into fine fibers when it is co-coagulated in an acid solution, a sufficient reinforcing effect cannot be exhibited unless the amount of the cellulose xanthate solution is increased.

Accordingly, an object of the present invention is to provide a material in which fine fibers can exert an appropriate effect on a resin or a rubber with high uniformity and which has an excellent effect on an added resin composition.

The present invention solves the above problems by incorporating cellulose xanthate microfibers into a resin composition or a resin dispersion. Cellulose xanthate is a cellulose xanthate in which xanthate (-OCSS) groups are introduced into any of the hydroxyl groups at the 2, 3, and 6 positions of cellulose^－Mⁿ⁺) The compound of (1). Note that M isⁿ⁺Is Na⁺A typical cation (n is an integer of 1 or more). The xanthate group undergoes ionic dissociation, and exerts an effect of making it easy to defibrate and not easy to aggregate due to electrostatic repulsion. Therefore, the uniformity is higher than that of the cellulose microfine fibers and the aspect ratio is sufficiently high, and therefore the strength-improving effect of the resin is excellent. Further, since the rubber composition contains a component derived from the introduced xanthate group, the vulcanization acceleration effect is exhibited when the rubber composition is directly introduced into the rubber composition.

The masterbatch obtained by heating and drying the resin dispersion containing the cellulose xanthate microfine fibers has a structure with high uniformity in which the cellulose xanthate microfine fibers are properly dispersed in the resin. However, depending on the heating conditions, a part or most of xanthate groups in the cellulose xanthate microfine fibers are detached and recovered as cellulose, and the cellulose microfine fibers are sometimes obtained. Even in this case, the fine fibers in the masterbatch can maintain the original dispersibility and uniformity. When this master batch is mixed with another chemical and vulcanized, a rubber composition is obtained which exhibits a vulcanization-accelerating effect by the xanthogenate group-derived component derived from the cellulose xanthogenate microfine fiber.

On the other hand, when a resin dispersion containing cellulose xanthate microfibers is treated with an acid, xanthate groups of the cellulose xanthate microfibers are detached and converted into cellulose microfibers. The masterbatch after fixing also can achieve higher uniformity than a resin composition containing only cellulose microfibers, since the original cellulose xanthate microfibers are dispersed in the composition with good dispersibility. Unlike the cellulose microfibers obtained by regenerating a cellulose xanthate solution (viscose), the cellulose microfibers obtained by removing the xanthate groups have cellulose I-type crystallinity and retain the structure of the fibers.

In addition, the rubber composition containing carbon black in addition to the cellulose xanthate microfine fibers can obtain a synergistic reinforcing effect. When the strain is low elongation of 100% or less, the cellulose xanthate microfine fibers after sufficient defibration can obtain almost the same reinforcing effect with an amount of about one fourth of the amount of carbon black added.

In the above-described configuration, the xanthogenate group of the cellulose xanthogenate microfine fiber can be oxidized and modified by adding an oxidizing agent, and the cellulose xanthogenate microfine fiber can have a structure having a bond such as sulfur or disulfide. A part of the xanthate group is oxidatively modified by adding an oxidizing agent to become sulfur, a reaction product more stable than the xanthate group. The sulfur and the reaction product remain in the cellulose xanthate microfine fibers and are not removed as much as xanthate groups even by acid regeneration treatment or heat regeneration treatment, and therefore, it is expected that the properties such as stress of the rubber are improved when contained in the masterbatch. The sulfur and reaction products may remain within, intramolecularly, or intermolecularly in the cellulose xanthate microfibers. Examples of the method of performing the oxidative modification include adding an oxidizing agent such as hydrogen peroxide. The above-mentioned oxidative modification is preferably carried out at the stage of slurry before the drying step for obtaining a master batch.

According to the present invention, cellulose xanthate microfibers dispersed in a resin or latex or cellulose microfibers from which xanthate groups have been removed are less likely to aggregate, and therefore, the present invention exerts an excellent reinforcing effect also in a resin composition or a resin molded body using the same as a masterbatch.

Drawings

In fig. 1, (a) is a 10 ten thousand TEM photograph of the cellulose xanthate nanofiber, and (b) is a 40 ten thousand TEM photograph of (a).

Fig. 2 is a graph showing the difference in stress deformation due to the XCNF addition amount in natural rubber in the examples.

Fig. 3 is a graph showing the difference in stress deformation due to the XCNF addition amount in the hydrogenated nitrile rubber in the examples.

Fig. 4 is a graph showing the difference in stress deformation due to the difference in the degree of defibration of XCNF in the embodiment.

Fig. 5 is a graph showing the difference in stress deformation due to the difference in defibering time of XCNF for defibering in the rubber latex in the example.

In fig. 6, (a) is a 40-ten-thousand TEM photograph of the latex and the cellulose xanthate nanofibers in the slurry for defibration in the latex, and (b) is a 2-ten-thousand TEM photograph of the cellulose xanthate microfibers in the masterbatch.

Fig. 7 is a graph showing the difference in stress deformation caused by the cases of adding XCNF, adding TOCN, and not adding to natural rubber in the examples.

Fig. 8 is a graph showing the difference in stress deformation caused by the addition of XCNF, the addition of TOCN and the absence of addition in the hydrogenated nitrile rubber in the examples.

Fig. 9 is a graph showing the difference in stress deformation caused by the cases of adding XCNF, adding CB, and not adding to natural rubber in the examples.

Fig. 10 is an X-ray CT photograph showing the state of the microfine fibers after recovery to cellulose in the masterbatch of example 16.

Fig. 11 is a diagram showing the difference in stress deformation due to the difference in the method for producing the master batch of the example.

Fig. 12 is a diagram showing synergistic effects of XCNF and CB in the embodiment.

Fig. 13 is a graph showing the effect due to the oxidation modification reaction in the example.

FIG. 14 is an optical micrograph of the surface of the XCNF oxidized product in example.

FIG. 15 shows a Raman spectrum of the particle portion of the XCNF oxidation-treated product in the example.

Figure 16 is a raman spectrum of the XCNF oxidant treatment in the examples.

Fig. 17 is a graph showing effects due to differences in the treatment methods of hydrogen peroxide in the examples.

Detailed Description

The present invention will be described in detail below. The present invention relates to a resin composition or a resin dispersion containing cellulose xanthate microfibers, a resin product group such as a masterbatch using the resin composition or the resin dispersion, and a method for producing a molded article.

The cellulose xanthate microfine fibers are basically produced by processing cellulose materials, and the cellulose materials used as the material are α -cellulose materials containing cellulose in a crystalline state I, and even α -cellulose materials completely converted to cellulose II cannot be suitably used.

In the production method according to the present invention, the cellulose material may be treated with an alkali such as an aqueous solution of an alkali metal hydroxide such as sodium hydroxide or potassium hydroxide to obtain alkali cellulose. Among them, sodium hydroxide is preferably used. The concentration of the alkali metal hydroxide aqueous solution needs to be 4 mass% or more, preferably 5 mass% or more. If the amount is less than 4% by mass, the mercerization of cellulose does not proceed sufficiently, and the amount of by-products generated in the subsequent xanthation cannot be ignored, resulting in a decrease in yield. Further, the effect of facilitating the defibration process described later is insufficient. On the other hand, the concentration of the alkali metal hydroxide aqueous solution is preferably 9 mass% or less. If the amount exceeds 9 mass%, the alkali metal hydroxide solution does not stay in the mercerizing step, but penetrates into the crystalline region of cellulose to fail to maintain the crystalline structure of cellulose I, and finally, it is difficult to obtain nanofibers.

The time for the alkali treatment is preferably 30 minutes or more, and more preferably 1 hour or more. If the amount is less than 30 minutes, mercerization may not sufficiently proceed, and the final yield may be excessively decreased. On the other hand, it is preferably 6 hours or less, and more preferably 5 hours or less. When the mercerization is performed for more than 6 hours, the amount of the alkali cellulose to be produced does not increase with time, and there is a possibility that the productivity decreases and the degree of polymerization of the cellulose decreases.

The temperature of the alkali treatment may be around room temperature or from room temperature to a temperature at which the heat is heated by heat generation. However, if the treatment temperature is extremely low, such as under refrigeration conditions, the permeability of the alkali solution into the cellulose tends to increase, and even at an alkali concentration in the above range, the alkali metal hydroxide solution may penetrate into the crystalline region of the cellulose, making it difficult to maintain the crystalline structure of the cellulose I-form. Therefore, when the temperature at which the alkali treatment is performed is not lower than the freezing temperature but lower than 10 ℃, the alkali metal hydroxide solution concentration is particularly preferably in the range of 4 to 7 mass%. This tendency is not particularly observed at 10 ℃ or higher, and as described above, an aqueous solution of an alkali metal hydroxide of 4 to 9 mass% is preferred. On the other hand, if the heating is excessively performed, the degree of polymerization of the cellulose may decrease.

The alkali cellulose obtained by the alkali treatment is preferably subjected to solid-liquid separation in advance to remove the aqueous solution component as much as possible. This is because the reaction proceeds more easily as the amount of water decreases in the subsequent xanthogenic esterification treatment. As a method for solid-liquid separation, for example, a general dehydration method such as centrifugal separation or filtration can be used. The alkali cellulose after solid-liquid separation preferably contains an alkali metal hydroxide in a concentration of about 3 mass% to 8 mass%. The efficiency of operation is deteriorated when the concentration is too low or too high.

After the alkali treatment, carbon disulfide (CS) is added₂) Reacting with the above alkali cellulose to make (-O)^－Na⁺) Conversion of the radical into (-OCSS)^－Na⁺) And xanthating treatment to obtain cellulose xanthate. Although Na is described as an alkali metal, the same treatment is performed when an alkali metal other than Na is used.

The average xanthogenate substitution degree per glucose unit in the xanthogenate conversion treatment is preferably 0.1 or more. That is, it is preferable that the cellulose has (-OCSS) of at least 10 on average out of 100 glucose units in the original cellulose^－Na⁺) The radicals are substituted. This is because (-OCSS) is contained if xanthogenate esterification is insufficient^－Na⁺) If the amount of the base is too small, the effect of promoting the subsequent defibration treatment cannot be sufficiently obtained. On the other hand, it is considered that if the substitution degree of xanthate exceeds 0.4, the hydrophilic property of each cellulose xanthate polymer is attributed to xanthate groupThe degree of substitution with xanthate is preferably 0.4 or less because the cellulose xanthate polymer is excessively high and moves in the direction of dissolution during the defibration treatment. In addition, when the average xanthate substitution degree is 0.33 or less, the average of at most 33 (-OCSS) out of 100 glucose units in the original cellulose is introduced^－Na⁺) In this case, the yield and efficiency are preferable. That is, the xanthate substitution degree is preferably 0.1 or more, preferably 0.4 or less, and more preferably 0.33 or less.

In order to increase the above average degree of xanthate substitution, it is preferred to provide a sufficient amount of carbon disulphide. Specifically, it is preferable to supply carbon disulfide in an amount of 10 mass% or more based on the mass of the cellulose contained in the alkali cellulose. If the amount is too small, the substitution degree of xanthate is excessively decreased, and cellulose xanthate microfibers cannot be obtained in a treatment with a light load as described later. In addition, the dispersibility of the cellulose xanthate microfine fibers after the defibration treatment may not be sufficiently obtained. On the other hand, although it is preferable to add carbon disulfide in an amount of 0.4 or less in the average degree of substitution with xanthate, even if an excessive amount of carbon disulfide is supplied, it cannot react with alkali cellulose and is wasted, and the supply of carbon disulfide takes an excessive cost.

In order to increase the average xanthate substitution degree, the contact time of carbon disulfide with alkali cellulose is preferably 30 minutes or longer, and more preferably 1 hour or longer. This is because, although xanthogenation based on contact of carbon disulfide proceeds rapidly, it takes time for carbon disulfide to penetrate into the inside of alkali cellulose. On the other hand, if it is 6 hours, the block of dehydrated alkali cellulose can be sufficiently permeated, and xanthation which can be reacted is almost completed, so that it is preferably 6 hours or less.

In the xanthation treatment, it is preferable to supply carbon disulfide to the dehydrated alkali cellulose and react the carbon disulfide in the gas with the alkali cellulose at a temperature of 46 ℃ or lower. When the temperature exceeds 46 ℃, there is a possibility that the degree of polymerization is lowered due to the decomposition of the alkali cellulose, and the reaction is difficult to be performed uniformly, so that there is a possibility that problems such as an increase in the amount of by-products and the detachment of the produced xanthate group occur.

It is considered that the xanthogenate esterification treatment increases the polarity of the cellulose fiber (cellulose xanthogenate molecule) in which crystallinity remains, increases the hydrophilicity, and improves the dispersibility due to electrostatic repulsion of the xanthogenate group. Therefore, compared to a method in which cellulose is directly subjected to a defibering treatment, the above-described cellulose xanthate can be produced into cellulose xanthate microfibers while maintaining crystallinity, that is, a crystalline structure of cellulose I type, originally contained in the cellulose material, by the mechanical defibering treatment under a slight load.

The cellulose xanthate subjected to xanthate esterification treatment described above facilitates the defibration treatment directly by the electrostatic repulsion due to the xanthate group. Here, after the xanthation treatment, the fibers are washed once to remove impurities, alkali, carbon disulfide, and the like, whereby the load and the number of times required for the defibration treatment can be reduced. The use of water for washing is preferable because there is little possibility that the cellulose xanthate fiber itself is damaged while the pH is lowered by the alkali. In the washing, washing with running water or washing with repeated addition of water and dehydration may be employed, but the influence on the fiber length is small. When sodium hydroxide, potassium hydroxide, or the like is used as the alkali metal hydroxide as the degree of washing, the pH of the slurry for defibration after washing is preferably 10.5 or less, more preferably 9.5 or less. When sodium hydroxide is used, the concentration of NaOH in the slurry is preferably 40ppm or less, more preferably 8ppm or less.

However, as described later, fibers washed with an aqueous solution of ammonia, an aliphatic or aromatic amine, or the like and subjected to solution substitution can be defibrated even when the pH exceeds 10.5. When ammonia or amine is used for washing, Na, which is a cation corresponding to a xanthate group, can be used⁺、K⁺And replacing the alkali metal ions with ammonium ions. If the alkali metal ions are sufficiently removed, the defibration can be easily performed even if the pH is high to some extent.

In order to obtain a resin composition and a resin dispersion containing the cellulose xanthate microfibers according to the present invention, any of a method of introducing cellulose xanthate microfibers, which have been previously made into microfibers by defibering cellulose xanthate, into a resin or a dispersion medium, and a method of once introducing cellulose xanthate before defibering into a resin or a dispersion medium and then defibering in a resin or a dispersion medium to make cellulose xanthate microfibers, can be used. If the defibration degree is to be increased, it is preferable to perform preliminary defibration in water as compared with a resin or a dispersion medium. Alternatively, an alkali solution such as sodium hydroxide may be added to the cellulose xanthate microfiber slurry to reduce the viscosity of the cellulose xanthate microfiber slurry, and then the cellulose xanthate microfiber slurry may be introduced into a resin or a dispersion medium. On the other hand, when the fibers are defibered in the resin dispersion (including the rubber latex), the defibering is mild and becomes fine fibers having a wide fiber diameter distribution. Further, it is considered that the dispersibility of the cellulose xanthate fine fibers and the latex particles produced by the defibration in the dispersion liquid is good, the contact interface is increased, and the increase in the contact interface brings about the following advantages: the chemical bond or high affinity between the xanthate group and the latex is easily obtained during the masterbatch preparation.

First, when the cellulose xanthate is subjected to the defibering treatment, it is preferably dispersed in water before introduction. Other components such as inorganic substances, surfactants, and water-soluble polymers may coexist in the water. As a method of the defibration treatment, a general method can be used as long as it does not cause a significant decrease in the fiber length. For example, a method of dispersing the fiber in water and defibrating the fiber by a rotary homogenizer, a bead mill, an ultrasonic disperser, a high-pressure homogenizer, a disc refiner, or the like is exemplified. However, the energy required in either method is significantly less than that required in a method in which cellulose is directly subjected to defibration treatment. Therefore, the load such as the pressure and the rotational speed can be reduced, and the time required for the treatment can be shortened. In addition, it is also preferable to perform the treatment under a low load in order to maintain the fiber length as much as possible.

Alternatively, the cellulose xanthate before the defibration treatment may be usedNa contained in xanthate group of acid ester or cellulose xanthate microfine fiber⁺Some or all of the alkali metal ions are ion-exchanged with other cations. Examples of the cation include hydrogen ion and K⁺、Li⁺Etc. other alkali metal ion, Ag⁺And the like 1 valent metal ion, ammonium ion, aliphatic or aromatic ammonium, and the like, and 1 or 2 or more species may be combined. Further, polyvalent ions such as zinc, calcium, and magnesium may be contained as necessary. For example, the hydrophobicity of the cellulose xanthate microfine fibers can be increased by performing salt exchange instead of the quaternary ammonium cation, and it is expected that the affinity between the resin and the cellulose xanthate microfine fibers is improved when the cellulose xanthate microfine fibers are mixed with a resin dispersion to prepare a master batch. Further, the quaternary ammonium cation makes it easy to dissociate the ions, and the cellulose xanthate is easily defibered, and the dispersibility of the cellulose xanthate fine fibers is improved.

Examples of the quaternary ammonium cation include tetrabutylammonium cation, tetrapropylammonium cation, tetraethylammonium cation, decyltrimethylammonium cation, dodecyltrimethylammonium cation, hexyldimethyloctylammonium cation, benzyltriethylammonium cation, triethylphenylammonium cation, and the like.

The cellulose xanthate microfine fibers after defibration may be subjected to an ion exchange of alkali metal ions or cations temporarily substituted therefor contained therein, and then subjected to a desorption treatment described later. Here, as the cation M to be subjected to ion exchangeⁿ⁺(n is an integer of 1 or more, preferably 3 or less), examples of which include hydrogen ion and Li⁺、Na⁺、K⁺Alkali metal ions, Ag, etc. different from the original alkali metal ions⁺Other monovalent metal ions, ammonium ions, aliphatic or aromatic ammonium ions, etc., and 1 or 2 or more species may be combined. Further, polyvalent ions such as zinc, calcium, and magnesium may be contained as necessary. Furthermore, the xanthogenated cellulose may contain other functional groups than hydroxyl groups.

On the other hand, a resin or a resin dispersion containing cellulose xanthate microfibers can be obtained by introducing cellulose xanthate before defibration into a liquid of a hot-melted thermoplastic resin, a liquid resin mixture before solidification reaction, or a resin dispersion, and performing defibration treatment in the same manner. Examples of the dispersion liquid of the resin include rubber latex.

Here, the cellulose xanthate microfine fibers are a mixture of cellulose xanthate nanofibers fully fibrillated to the extent that they are contained in the centrifugal supernatant during the centrifugal separation treatment and an undeveloped material that is not completely fibrillated. Specifically, the cellulose xanthate nanofibers are defined as having a fiber diameter of 3nm to 200 nm. The cellulose xanthate microfine fibers preferably contain 50% or more of the cellulose xanthate nanofibers, and the higher the content, the better the content in many cases. Since the cellulose xanthate nanofibers are suitably obtained as a centrifugal supernatant, the cellulose xanthate nanofibers contained in the centrifugal supernatant may be referred to when the cellulose xanthate nanofibers are described as "centrifugal supernatant" in the following description.

In any step, the size of the cellulose xanthate microfine fibers after defibration can be appropriately selected, but the average fiber length is preferably 25nm or more, more preferably 100nm or more, and still more preferably 150nm or more. If the length is too short, the fiber properties are not exhibited, and the effect of improving strength is reduced because the fiber approaches the particle-like cellulose. On the other hand, the average fiber length is preferably 100 μm or less, more preferably 70 μm or less, and further preferably 20 μm or less. When the average fiber length is too long, there is a possibility that fibers remaining due to insufficient defibration remain, and the surface area may be small and it may be difficult to form a network structure. In particular, when the fibers are preliminarily fibrillated in an aqueous system, the fibers can be fibrillated at a lower energy than in the conventional method, and thus the production can be easily performed within this range.

The average fiber diameter of the fibrillated cellulose xanthate microfine fibers is preferably 3nm or more, and more preferably 5nm or more. If the average particle diameter is less than 3nm, the average particle diameter is too small and approaches the limit of the fiber retaining crystallinity, and the strength of the fine fiber itself may be weakened. On the other hand, it is preferably 500nm or less, and more preferably 250nm or less. The reason for this is that: if the thickness is too large, the mixing of fibers that are insufficiently defibred cannot be avoided, and the network structure in the resin composition is destroyed.

The average fiber length and the average fiber diameter of the cellulose xanthate microfine fibers are calculated by the following formulas (1) and (2).

Cellulose xanthate microfiber slurry average fiber length (μm) as a whole (centrifugal supernatant number average fiber length × nanofiber production rate) + { undetilled number average fiber length x (100% -nanofiber production rate) } · (1)

Cellulose xanthate microfiber slurry average fiber diameter (nm) as a whole (centrifugal supernatant number average fiber diameter × nanofiber formation rate) + { undetilled material number average fiber diameter x (100% -nanofiber formation rate) } · (2)

The average xanthogenate substitution degree of the cellulose xanthogenate microfine fibers after defibration can be adjusted to 0.001 to 0.4 according to the purpose.

When the cellulose xanthate microfine fibers after defibration are contained in the resin composition or the resin dispersion in the above range, the cellulose xanthate microfine fibers (or the cellulose microfine fibers after the removal of the xanthate group thereof) can be uniformly dispersed in the masterbatch produced using the above resin composition or the resin dispersion, and the properties improving effect such as strength improvement can be suitably exerted in the molded article produced using the masterbatch.

The cellulose xanthate microfine fibers contained in the resin dispersion may be subjected to the following release treatment: reacting xanthate (-OCSS)^－M⁺) Become (-OH) groups to restore the cellulose xanthate to cellulose microfibers. The removal treatment may be carried out by an acid treatment. The reaction of converting xanthate groups into hydroxyl groups without decreasing the fiber length can be carried out by the action of an acid. The acid used herein includes inorganic acids or organic acids, preferably inorganic acids, and salts thereofAcids, sulfuric acids, nitric acids, and the like. The pH of the acid to be treated is preferably 6 or less, more preferably 5 or less. Even if the cellulose microfibers are recovered by the removal treatment with an acid in this manner, the cellulose xanthate microfibers are uniformly dispersed as cellulose xanthate microfibers, and the dispersed state is not easily coagulated, and can be maintained for a long period of time. This is considered to be because: since the cellulose xanthate microfine fibers are dispersed and present, and the acid coagulation rate of the resin is higher than that of the cellulose xanthate microfine fibers, the resin is appropriately distributed widely around the resin in the resin dispersion even after the cellulose xanthate microfine fibers are recovered.

Since the stripping treatment with an acid is carried out substantially once, most of the components stripped from the xanthate groups are removed from the system together with the cleaning. Thereafter, the reaction mixture was dried to obtain a master batch.

On the other hand, cellulose xanthate microfine fibers can be heated to convert xanthate (-OCSS)^－M⁺) A separation treatment in which a part or all of them are converted into (-OH) groups to restore the cellulose xanthate to cellulose microfibers. When the desorption is carried out by heating, the degree of desorption can be adjusted depending on the heating time and temperature, but the heating temperature is preferably 40 ℃ or higher. Although the treatment time is shorter as the temperature is higher, it is necessary to appropriately set conditions so as to avoid excessive heating in order to prevent the cellulose fibers from being cut and the degree of polymerization from decreasing. The heated cellulose xanthate microfine fibers may be in the form of a dry product or a slurry. The cellulose microfibers from which xanthate groups have been removed by the acid/heat treatment have an average fiber diameter and an average fiber length that are substantially the same as those of the cellulose xanthate microfibers.

When cellulose xanthate microfine fibers are used, the oxidizing agent may be added at any stage prior to the production of a masterbatch, which will be described later. The time for adding the oxidizing agent may be before or during introduction of the cellulose xanthate microfine fiber subjected to the defibering treatment into the resin dispersion liquid, or after the defibering treatment in the resin dispersion liquid. In addition, it is preferable to perform the reaction in a liquid before drying because the reaction generated by the oxidizing agent becomes difficult to proceed after drying the resin dispersion liquid or adding an acid to solidify the resin dispersion liquid in order to obtain the master batch.

In particular, when the oxidizing agent is added in a large amount, it is preferable to add the oxidizing agent to the resin dispersion liquid or to carry out the reaction in a state where the cellulose xanthate microfibers are sufficiently dispersed in the resin dispersion liquid, as compared with a method in which the oxidizing agent is added before the cellulose xanthate microfibers are introduced into the resin dispersion liquid. This is because: when a large number of reactions are performed in the state of cellulose xanthate microfibers before mixing with the resin dispersion, adjacent fibers agglomerate together, and it is difficult to obtain a dense network structure in the resin, and there is a possibility that the reinforcing effect by the cellulose xanthate microfibers after the treatment with the oxidizing agent cannot be sufficiently obtained.

The oxidizing agent to be added is preferably an oxidizing agent that does not cause a reaction of cutting the main chain of the cellulose xanthate microfine fiber and that has a negligible degree of reduction in the degree of polymerization. Specifically, hydrogen peroxide, iodine, a (acid of (a) phenylene ハロゲン), a salt thereof, and the like are mentioned, and hydrogen peroxide is preferable from the viewpoint of residual components.

When hydrogen peroxide is added as the oxidizing agent, the amount of hydrogen peroxide added may be 5 mol% or more based on the molar amount of xanthate groups in the cellulose xanthate microfine fibers. When the amount is less than 5 mol%, the reaction does not proceed sufficiently, and the effect is not sufficient. On the other hand, hydrogen peroxide is preferably added in a range of 2000 mol% or less. This is because: even if the amount exceeds 2000 mol%, the reaction is hardly observed, and there is a high possibility that the reaction is wasted, or the fibers are agglomerated due to aggregation, and thus a sufficient reinforcing effect cannot be obtained.

The modification reaction by adding an oxidizing agent can release xanthate groups to generate sulfur, a sulfur compound, or both, or 2 xanthate groups can react to form a substance having an-S-bond or the like in or between the molecules of the cellulose xanthate microfine fiber. Among them, in particular, sulfur particles tend to be easily formed.

Thereby, the bonds of sulfur, disulfide, and the like are generated by the oxidant treatment of the cellulose xanthate microfine fibers. Since the sulfur and disulfide formed by the present treatment are not decomposed by the action of acid, if the sulfur content is measured after the addition of acid, it can be distinguished from the sulfur component (sulfur component) derived from the xanthate group. In addition, while sulfur is generally readily soluble in carbon disulfide, the sulfur and/or disulfide formed by the above-described treatment with an oxidizing agent is insoluble in carbon disulfide. Here, it is considered that the sulfur component remains as a part of the xanthate group and does not dissolve in carbon disulfide because it remains in the fiber and in the matrix. In addition, the disulfide is considered to be insoluble due to bonding with the cellulose molecular chain. Consider that: the sulfur component soluble in carbon disulfide contributes to strength improvement in vulcanization also when contained in the masterbatch, and the sulfur component which is not a part of the xanthate group and insoluble in carbon disulfide is more stable than the xanthate group and remains due to firm interaction with cellulose xanthate microfine fibers, and when the resin is a rubber, the content of interaction can be increased to further improve the reinforcing effect.

When fibers are used in which cellulose xanthate microfibers are treated with an oxidizing agent, the xanthogenate group modification ratio is the ratio of the xanthogenate group-derived sulfur component not derived from the xanthogenate group, but derived from the modification reaction in the sulfur component derived from the xanthogenate group originally contained in the cellulose xanthate microfibers. The modification ratio is defined as the following variables and formulas.

A (1): sulfur content in fiber after treatment with oxidizing agent and separation of xanthate group with acid

A (2): the sulfur content in the carbon disulfide-insoluble fiber in A (1)

B: total sulfur content of cellulose xanthate microfine fibers before treatment with an oxidizing agent

Modification ratio (1): sulphur components other than xanthate groups, contributing to increased strength

Modification ratio (1) (%) ═ a (1) ÷ B × 100

Modification ratio (2): carbon disulphide-insoluble sulphur fraction, in addition to xanthate groups, particularly contributing to increased strength

Modification ratio (2) (%) ═ a (2) ÷ B × 100

A (1) is preferably 0.1% or more. When the content is less than 0.1%, the effect by modification is not sufficiently exhibited. On the other hand, when the latex is mixed after the oxidizing agent treatment, the dispersibility tends to decrease when the content exceeds 8%, and therefore, the content is preferably 8% or less. Further, when the latex is dispersed and treated with an oxidizing agent, aggregation is suppressed to some extent, and therefore, even if the amount exceeds 8%, the dispersibility tends to be easily maintained, and the strength-improving effect with respect to the amount of the oxidizing agent added is limited, and is actually 8% or less. On the other hand, since a part or the most part of the xanthate group can be converted into a stable sulfur component by the treatment with the oxidizing agent, the generation of odor due to the decomposition of the xanthate group in the processing step or the like is suppressed. The upper limit of the sulfur content by the oxidation treatment is not limited to the above-described case where odor control or the like is prioritized.

Similarly to a (1), a (2) is preferably 0.1% or more. When the content is less than 0.1%, the effect by modification is not sufficiently exhibited. On the other hand, when the latex is mixed after the oxidizing agent treatment, dispersibility tends to decrease when it exceeds 8%, and therefore 8% or less is preferable. When the latex is dispersed in an oxidizing agent, aggregation is suppressed to some extent, and therefore, the dispersibility tends to be maintained even if the amount of the polymer exceeds 8%.

The resin dispersion containing the cellulose xanthate microfine fibers can be dried by heating to obtain a masterbatch which is coagulated by removing water. At this time, when the cellulose fiber is heated to 40 ℃ or higher and dried, part or all of the xanthate groups are removed and the cellulose fiber is solidified in a state recovered to cellulose. Since the cellulose microfine fibers do not aggregate in the coagulated state, the master batch can be stored in a state in which the dispersion state is proper. Further, compared with the case where an acid is used in this state, the xanthogenate group is less likely to be detached, and therefore components derived from the xanthogenate group tend to remain in the master batch. The xanthate-derived component can exert a vulcanization acceleration effect in a vulcanization step before a final rubber product is obtained, particularly when the resin is a rubber. Further, the vulcanization-accelerating effect can be exhibited similarly when the masterbatch is stored.

As the resin which can be used in the form of the resin dispersion, a resin which is produced by polymerization of synthetic rubber to isoprene rubber, styrene-butadiene rubber, methyl methacrylate-butadiene rubber, 2-vinylpyridine-styrene-butadiene rubber, acrylonitrile-butadiene rubber, chloroprene rubber, silicone rubber, fluororubber, or the like can be used, and a latex of natural rubber can also be used. In order to form a dispersion, a surfactant is preferably contained. In the case of synthetic rubbers, the surfactants used for the synthesis of the emulsions may be contained directly. In addition to rubber, aqueous polyurethane, acrylic resin, acrylonitrile, or the like may be used.

In addition, when rubber is used as the above resin, a vulcanization accelerator, a vulcanizing agent, an aging inhibitor, a filler, a wax, a reinforcing agent, a softener, a filler, a colorant, a flame retardant, a lubricant, a plasticizer, and other additives other than the cellulose xanthate microfine fiber may be contained according to the use. Examples of the filler include carbon black, silica, and calcium carbonate. Examples of the vulcanizing agent include a sulfur component separately added thereto.

The preferable resin content of the resin dispersion depends on the resin. However, when the fibers are defibrated in the resin dispersion, the viscosity is preferably not excessively high.

The proportion of the cellulose xanthate microfine fibers (or cellulose microfine fibers having xanthogenate groups partially or completely removed) to the resin contained in the resin dispersion or the resin composition is not particularly limited, but is preferably 1 to 50% by mass in view of the reinforcing effect. If too small, the effect of hardly showing addition is exhibited, and if too large, the viscosity excessively increases when the resin dispersion is defibered, and the rubber becomes too hard in the case of a masterbatch, and handling may be difficult, and is preferably 20% by mass or less. Here, the cellulose xanthate microfibers that satisfy the above-described conditions of mass range mean cellulose xanthate microfibers that contain 50% or more of cellulose xanthate nanofibers having a fiber diameter of 3nm to 200nm and that contain cellulose xanthate nanofibers and an undecellulated material, and the average fiber diameter of the entire cellulose xanthate microfibers is 3nm to 500 nm.

In any of the above steps, the resin composition can be used as a general resin composition for producing a resin molded body after the master batch is prepared. In the resin molded article finally obtained, particularly in the case of a material requiring strength, the effect of the addition of the cellulose xanthate microfine fiber is easily exhibited.

In addition, in the case of a masterbatch in which acid coagulation is not performed or a masterbatch in which a component derived from xanthate groups remains even when acid coagulation is performed, cellulose xanthate microfibers exert useful effects particularly in a rubber composition in which the resin is rubber. First, when the rubber is vulcanized, the cellulose xanthate microfine fibers can exert a vulcanization acceleration effect by the component derived from the xanthate group thereof.

In addition, a synergistic effect may be exerted by using cellulose xanthate microfine fibers and other fillers in combination in the rubber composition. In particular, in the above filler, carbon black and cellulose xanthate microfine fibers exert a synergistic effect, and a high reinforcing effect can be achieved for the rubber composition. This is considered to be because: the carbon black is fine particles having a particle size of about 20 to 100nm, and the fine particles are fused together as a whole to form a complex aggregated form having chain-like or irregular chain-like branches. The aggregated form is called a primary aggregate (aggregate) and has a size of about 100 to 300 nm. The reinforcing effect of the rubber exerted by adding carbon black to the rubber composition is considered to be both the effect based on the chemical interaction of the functional groups on the surface of the carbon black and the effect based on the aggregate structure. The carbon black contained in the rubber composition is considered to be a secondary aggregate (aggregate) obtained by aggregating the aggregates or a structure obtained by further aggregating the secondary aggregate. These aggregate structures provide a reinforcing effect of the rubber composition.

It is considered that when both of the carbon black and the cellulose xanthate microfine fibers are contained in the rubber composition, the following effects are exhibited. The cellulose xanthate microfine fibers contain a large number of cellulose xanthate nanofibers having a fiber diameter of about 3 to 200nm, and are smaller than the aggregates of carbon black, so that the formation of secondary aggregates is not hindered. Therefore, it is considered that the secondary agglomerate of carbon black is entangled with the cellulose xanthate microfiber, and a synergistic reinforcing effect of both carbon black and cellulose xanthate microfiber is obtained.

However, in order to exhibit the synergistic reinforcing effect appropriately, it is necessary to sufficiently progress the defibration of the cellulose xanthate microfine fibers contained in the rubber composition, that is, to include at least cellulose xanthate nanofibers having a fiber diameter of 3nm to 200 nm. The average fiber diameter of the cellulose xanthate microfine fibers contained in the rubber composition is preferably 3nm or more. On the other hand, the average fiber diameter is preferably 500nm or less, more preferably 250nm or less. This is because: the fiber diameter is sufficiently small compared to the aggregate, and it becomes easy to exert a synergistic effect. On the contrary, it is considered that the following problem is caused when the fiber remains in the fiber remaining portion where the defibration is insufficient and the value of the average fiber diameter is increased.

For example, when cellulose xanthate is defibrated in NR latex, it is assumed that the rate of formation of cellulose xanthate nanofibers is about 60%, and nanofibers and undeveloped material are mixed together. When cellulose xanthate microfibers that have been insufficiently defibered are contained, there is a possibility that the undelivered matter of large-sized cellulose xanthate partially inhibits the formation of secondary aggregates of carbon black having a similar size. Therefore, in order to exert a synergistic reinforcing effect, it is preferable to add cellulose xanthate microfibers after sufficient defibration or to sufficiently defibrate the fibers in the latex.

The carbon black exerting such effects is contained in the resin composition preferably at least 10 mass%, more preferably at least 15 mass%, based on the mass of the resin. When the amount is less than 10% by mass, the effect of addition is hardly seen. When the content is 15% by mass or more, the synergistic effect is particularly preferably exhibited. On the other hand, it is preferably 60% by mass or less, and more preferably 55% by mass or less. This is because: if the amount exceeds 60 mass%, the amount of carbon black components is too large, and the properties inherent in the resin composition may be impaired.

When carbon black and the above cellulose xanthate microfine fibers are used in combination, the cellulose xanthate nanofibers having a fiber diameter of 3 to 200nm contained in the cellulose xanthate microfine fibers are preferably mixed in a mass ratio of 10: 1-1: 1. this is because: even if the amount of the one is too large, the synergistic effect is insufficient. The reason for this is as follows: in particular, when the strain is 100% or less, the effect of reinforcing the cellulose xanthate microfine fibers alone is about four times that of the carbon black alone, and therefore, if the amount of the carbon black is less than that of the cellulose xanthate nanofibers, the reinforcing effect of the cellulose xanthate nanofibers becomes too strong, and it is difficult to obtain a synergistic effect with the carbon black in combination.

The resin dispersion to which the cellulose xanthate microfine fibers are added can be applied to paper, nonwoven fabric, woven fabric, or the like to impart a surface-modifying effect or a heat resistance-improving effect, in addition to being processed into a masterbatch. For example, when the surface after coating is heated, the effect of preventing the occurrence of blocking is exerted by containing the dispersed cellulose xanthate microfibers. In addition, although the additive is contained, since the cellulose xanthate microfibers (or cellulose microfibers after the removal of xanthate groups) are uniformly dispersed, the possibility of further roughening the surface is low.

In addition to the masterbatch, when the coating is performed, when the cellulose xanthate microfine fiber is used alone, or when other applications are performed, the resin dispersion is finally dried, and an oxidizing agent is added to the resin dispersion before drying to perform a modification reaction, and the xanthate group is formed in advance to have a stable bond such as sulfur and/or disulfide, whereby the strength-improving effect can be enhanced in either case. In either case, A (1) and A (2) are preferably 0.1% or more. In addition, when mixing with latex after the oxide treatment, a (1) and a (2) are preferably 8% or less in order to maintain dispersibility. When the latex is dispersed in the oxidizing agent and treated with the oxidizing agent, aggregation is suppressed to some extent even if the amount exceeds 8%, but the amount is preferably 8% or less in view of the efficiency of adding the oxidizing agent.