阅读说明：本技术 树脂组合物的制造方法 (Method for producing resin composition ) 是由 福田雄二郎 角田惟绪 于 2020-07-30 设计创作，主要内容包括：具有如下第一混炼工序,其中,将加权平均纤维长度为0.20mm～1.50mm的纤维素纤维、增容树脂和尿素投入到混炼机中并进行混炼。(The method comprises a first kneading step in which a cellulose fiber having a weighted average fiber length of 0.20 to 1.50mm, a compatibilizing resin and urea are fed into a kneader and kneaded.)

1. A method for producing a resin composition, comprising a first mixing step of: cellulose fibers having a weight average fiber length of 0.20mm to 1.50mm, a compatibilizing resin and urea are fed into a kneader and kneaded.

2. The method for producing a resin composition according to claim 1, further comprising a second kneading step of: the kneaded product obtained in the first kneading step is kneaded with a diluting resin.

3. The method for producing a resin composition according to claim 1 or 2, wherein in the first kneading step, the amount of the urea to be fed into the kneader is 10% by weight to 100% by weight relative to 100% by weight of the amount of the cellulose fiber component including cellulose and hemicellulose in total among the cellulose fibers.

4. The method for producing a resin composition according to any one of claims 1 to 3, wherein in the first kneading step, the amount of the cellulose fiber component, which is the total of cellulose and hemicellulose, among the cellulose fibers fed into the kneader is 35 to 85% by weight based on the total amount of the cellulose fibers, the compatibilizing resin, and the urea.

Technical Field

The present invention relates to a method for producing a polyolefin resin, particularly a polypropylene resin composition, containing fine cellulose fibers.

Background

The microfibrous cellulose obtained by finely unraveling the plant fibers contains microfibrous cellulose and cellulose nanofibers, and is microfine fibers having a fiber diameter of about 1nm to about several 10 μm. Microfibrous cellulose is lightweight, has high strength and high elastic modulus, and has a low coefficient of linear thermal expansion, and therefore is suitable as a reinforcing material for resin compositions.

The microfibrous cellulose is usually obtained in a state of being dispersed in water, and is difficult to be uniformly mixed with a resin or the like. Therefore, in order to improve the affinity and miscibility with the resin, chemical modification of the cellulose raw material has been attempted.

For example, in patent document 1, a cellulose raw material in which a part of hydroxyl groups of cellulose is substituted with carbamate groups is obtained by heat treatment of a cellulose raw material and urea, and the obtained material is refined by mechanical treatment to obtain microfibrous cellulose. The microfibrous cellulose obtained by this method has lower hydrophilicity and higher affinity with a resin or the like having a lower polarity than conventional microfibrous cellulose, and therefore is uniformly dispersed in the resin to provide a composite having high strength.

However, a method for producing a resin composition capable of obtaining a resin molded article having a higher flexural modulus and a higher flexural strength is required.

Documents of the prior art

Patent document

Patent document 1: japanese patent laid-open publication No. 2019-1876

Disclosure of Invention

Problems to be solved by the invention

An object of the present invention is to provide a method for producing a resin composition capable of obtaining a resin molded article having a high flexural modulus and a high flexural strength.

Means for solving the problems

The present invention provides the following (1) to (4).

(1) A method for producing a resin composition, comprising a first mixing step of: cellulose fibers having a weighted average fiber length (length average fiber length) of 0.20mm to 1.50mm, a compatibilizing resin, and urea are fed into a kneader and kneaded.

(2) The method for producing a resin composition according to (1), further comprising a second kneading step of: the kneaded product obtained in the first kneading step is kneaded with a diluting resin.

(3) The method for producing a resin composition according to (1) or (2), wherein in the first kneading step, the amount of the urea to be fed into the kneader is 10 to 100% by weight based on 100% by weight of the total amount of cellulose and hemicellulose in the cellulose fibers.

(4) The method for producing a resin composition according to any one of (1) to (3), wherein in the first kneading step, the amount of the cellulose fiber component, which is the total of cellulose and hemicellulose, among the cellulose fibers charged into the kneader is 35 to 85% by weight based on the total amount of the cellulose fibers, the compatibilizing resin, and the urea.

Effects of the invention

According to the present invention, a method for producing a resin composition capable of obtaining a resin molded article having a high flexural modulus and a high flexural strength can be provided.

Drawings

FIG. 1 is a schematic view showing a pulverizer usable in the production method of the present invention.

Detailed Description

Hereinafter, a method for producing the resin composition of the present invention will be described with reference to the drawings. In the present invention, "to" includes end values. That is, "X to Y" includes values X and Y at both ends thereof.

The method for producing a resin composition of the present invention comprises a first kneading step in which a cellulose fiber having a weighted average fiber length (length-average fiber length) of 0.20mm to 1.50mm, a compatibilizing resin, and urea are fed into a kneader and kneaded.

(cellulose fiber)

The cellulose fibers used in the present invention have a weighted average fiber length (length average fiber length) in the range of 0.2mm to 1.5mm, preferably in the range of 0.3mm to 1.0 mm. Such cellulose fibers can be obtained by, for example, pulverizing or beating a cellulose raw material.

(cellulose Material)

In the present invention, the cellulose raw material refers to various forms of materials mainly composed of cellulose, and includes lignocellulose (NUKP), and examples thereof include pulp (bleached or unbleached wood pulp, bleached or unbleached non-wood pulp, refined linter, jute, abaca, kenaf and other herbal pulp), natural cellulose such as cellulose produced by microorganisms such as acetic acid bacteria, regenerated cellulose obtained by dissolving cellulose in a certain solvent such as cuprammonium solution or morpholine derivative and then reprecipitating, fine cellulose obtained by depolymerizing cellulose by subjecting the cellulose raw material to hydrolysis, alkaline hydrolysis, enzymatic decomposition, crushing treatment, mechanical treatment by vibration ball mill or the like, and various cellulose derivatives.

Lignocellulose is a complex carbohydrate polymer constituting the cell wall of a plant, and is mainly composed of cellulose and hemicellulose, which are polysaccharides, and lignin, which is an aromatic polymer. The lignin content can be adjusted by delignifying or bleaching pulp or the like as a raw material.

In the present invention, in the case of using pulp as the cellulose raw material, either unblending or beating may be used, but it is preferable to use pulp subjected to beating treatment. This can increase the specific surface area of the pulp and increase the amount of urea reaction. The degree of beating treatment is preferably 400mL or less, more preferably about 100mL to about 200mL, in terms of drainage (c.s.f). When the drainage degree exceeds 400mL, the effect cannot be exhibited, and when the drainage degree is less than 100mL, the effect of improving strength is inhibited when a reinforced resin is produced due to formation of short fibers caused by damage to cellulose fibers. When the beating process is performed, the pulverizing step described later can be omitted if the weighted average fiber length (length average fiber length) falls within the range of 0.2mm to 1.5mm, preferably 0.3mm to 1.0mm, in the washing process and the drying process described later.

As a method of the beating treatment, for example, a mechanical (mechanical) treatment of pulp fibers using a known beater can be cited. As the beater, a beater generally used in the case of beating pulp fibers can be used, and examples thereof include nija beater, PFI mill, disc mill, conical refiner, ball mill, stone bowl mill, sand mill, impact mill, high pressure homogenizer, low pressure homogenizer, Dyno mill (ダイノーミル), ultrasonic mill, kanda mill (カンダグラインダ), attritor, vibration mill, chopper, jet mill, crusher, home juicer mixer, and mortar. Among them, a Niagara beater, a disc refiner, and a conical refiner are preferable, and a disc refiner and a conical refiner are more preferable.

(dehydration)

In the cleaning treatment, dehydration may be performed as necessary. The dehydration method may be performed by a pressure dehydration method using a screw press, a reduced pressure dehydration method using volatilization or the like, but a centrifugal dehydration method is preferable from the viewpoint of efficiency. Dehydration is preferably carried out to a solids content of about 10% to about 60% in the solvent.

(drying)

The cellulose fibers used in the present invention are subjected to a drying treatment after the above-mentioned dehydration step and, if necessary, before being used in the pulverization step to be carried out. The drying process can be carried out using, for example, a microwave dryer, an air blower dryer, or a vacuum dryer, but a dryer capable of drying while stirring, such as a drum dryer, a paddle dryer, a nauta mixer (ナウターミキサー), or a batch dryer with stirring blades, is preferable. Drying is preferably carried out until the cellulose fibers have a moisture content of about 1% to about 5%.

One of the features of the present invention is kneading by adding urea together with cellulose fibers and a compatibilizing resin. The mechanism of the strength improvement phenomenon by the cellulose fibers in the polyolefin resin due to this operation is not known at present, but some of them can be explained by the following examination. That is, it is considered that urea is decomposed into ammonia and isocyanic acid at a temperature exceeding 135 ℃, urea and cellulose fibers are simultaneously kneaded, and unmodified hydroxyl groups newly appearing from the inside of the cellulose fibers are kneaded to react with the generated isocyanic acid, thereby promoting the formation of urethane bonds. Further, it is considered that by melt-kneading the cellulose fiber and the compatibilizing resin having an acid anhydride at the same time, the ionic bond between the amino group newly introduced on the surface of the cellulose fiber by the urea treatment and the carboxylic acid of the compatibilizing resin is promoted, and a composite of the cellulose fiber and the compatibilizing resin can be formed more firmly.

From the viewpoint of improving the flexural modulus and from the viewpoint of suppressing fiber aggregation and reduction in flexural strength due to an excessive amount of urea to be blended, the amount of urea to be blended is preferably 10 to 100% by weight, more preferably 20 to 100% by weight, and still more preferably 30 to 70% by weight, based on 100% by weight of the total amount of cellulose fiber components (hereinafter, sometimes referred to as "cellulose amount") contained in the cellulose fibers, and necessary for achieving the above-described mechanism.

(Compatibilizing resin)

One of the features of the present invention is kneading by adding a compatibilizing resin together with cellulose fibers and urea. The compatibilizer resin functions to improve the uniform mixing and adhesion between the hydrophilic cellulose fibers and the hydrophobic diluent resin, which is polyolefin. The compatibilizing resin (hereinafter, sometimes referred to as "resin for masterbatch") used in the present invention is a polymer resin having a polyolefin chain such as polypropylene or polyethylene and a dicarboxylic acid having a low molecular weight and capable of forming an acid anhydride, such as maleic acid, succinic acid or glutaric acid, and among these, maleic anhydride-modified polypropylene (MAPP) to which maleic acid is added and maleic anhydride-modified polyethylene (MAPE) are preferably used together with polypropylene or polyethylene, respectively.

The factors that determine the characteristics of the compatibilized resin include the amount of dicarboxylic acid added and the weight average molecular weight of the polyolefin resin as the base material. A polyolefin resin containing a large amount of added dicarboxylic acid improves compatibility with a hydrophilic polymer such as cellulose, but the molecular weight of the resin decreases during the addition process, and the strength of the molded product decreases. The optimum balance is such that the amount of dicarboxylic acid added is from 20mgKOH/g to 100mgKOH/g, more preferably from 45mgKOH/g to 65 mgKOH/g. When the amount of addition is small, the amount of ionic bonds with urea in the resin becomes small. In addition, when the amount of addition is large, the strength as a reinforcing resin cannot be achieved due to self-aggregation caused by hydrogen bonds between carboxyl groups in the resin or the like, or due to a decrease in the molecular weight of the olefin resin as a base material caused by an excessive addition reaction. The polyolefin resin preferably has a molecular weight of 35000 to 250000, more preferably 50000 to 100000. When the molecular weight is less than this range, the strength of the resin decreases, and when the molecular weight is more than this range, the viscosity at the time of melting greatly increases, the workability at the time of kneading decreases, and the molding becomes a cause of a molding failure.

The amount of the compatibilizing resin having the above characteristics is preferably 10 to 70% by weight, more preferably 20 to 50% by weight, based on the amount of the cellulose. If the amount of the isocyanate added exceeds 70% by weight, the incorporation of the isocyanate derived from urea into the cellulose fibers is inhibited, and the formation of a composite of the compatibilizer and urea is promoted, and the effects of the present invention cannot be exhibited.

The compatibilizing resin may be used alone or in the form of a mixture of two or more resins.

(first kneading step pretreatment-pulverization step)

In the present invention, a pulverization step may be provided before the first kneading step described later. By using the cellulose fibers pulverized in the pulverizing step, the fiber cake of the cellulose fibers is appropriately loosened when the cellulose fibers are put into the kneader, and bridging (clogging) at the inlet (chute section) and occurrence of a failure in biting pulp into the screw can be suppressed.

Fig. 1 schematically shows a pulverizer that can be used in the pulverizing step of the present invention. The pulverizer 2 shown in fig. 1 has: a main body 6, the main body 6 having an input port 4 for inputting a material to be pulverized; the fixed knife 8, the said fixed knife 8 is fixed on body 6; a rotary cutter 12, the rotary cutter 12 having a blade 12a, the rotary cutter 12 introducing the material to be pulverized, which is thrown from the throw-in port 4, into the pulverizing chamber 10; a screen 14, the screen 14 adjusting a discharge particle size of the pulverized material.

In the pulverizing step of the present invention, the flocculent mass 3 of cellulose fibers in a dry state is fed from the inlet 4 of the pulverizer 2. The thrown flocked mass 3 of cellulose fibers is introduced into the pulverization chamber 10 by the rotary cutter 12, and is pulverized by a shearing force acting between the blade 12a of the rotary cutter 12 and the fixed cutter 8. The whole of the rotary cutter 12 crushes the cellulose fibers while pressing them against the screen 14, and when the diameter of the cellulose fibers is smaller than the diameter of the screen 14, the cellulose fibers are discharged from the crusher 2. The cellulose fibers having a diameter not smaller than the diameter of the mesh 14 are lifted by the rotary cutter 12 and repeatedly crushed.

Here, in the present invention, the screen 14 having an aperture of 1mm or more and 5mm or less, preferably 3mm or more and 5mm or less, is preferably used. When the pore diameter of the screen is too small, the average fiber length of the cellulose fibers obtained by the screen becomes too short, and thus the bending strength of the obtained formed body becomes low. When the mesh opening size is too large, the average fiber length is long and the amount of flocky lumps increases, so that the workability is deteriorated due to poor biting into the kneader, and the amount of undeveloped fibers in the obtained molded body is increased to lower the strength. The cellulose fibers obtained in this manner preferably have a weighted average fiber length (length average fiber length) of about 0.20mm to about 1.5mm, and more preferably 0.3mm to 1.0 mm.

From the viewpoint of reducing the drying load during kneading, dried fibers are preferably used for the cellulose fibers to be pulverized in the pulverization step. The dried cellulose fibers in the previous stage are usually flocculent fiber blocks fed to the pulverizer 2.

Examples of the pulverizer that can be used in the pulverizing step of the present invention include UGO3-280XKFT manufactured by HORAI.

(first mixing step)

In the first kneading step of the present invention, cellulose fibers having a weighted average fiber length of 0.20mm to 1.50mm, preferably 0.30mm to 1.00mm, a compatibilizing resin and urea are simultaneously fed into a kneader and melt-kneaded. The weighted average fiber length (length average fiber length) of the cellulose fibers can be measured using a fiber tester (manufactured by L & W company) or the like. When the mixture is fed into a mixer, various commercially available feeders and side feeders can be used. When the compatibilizing resin and urea are powdered in advance, the cellulose fibers, the compatibilizing resin and urea may be mixed and then charged by a commercially available mixer or the like before charging. Even when the compatibilizing resin or the like is not powdered, it may be charged by preparing a plurality of feeders such as a pellet feeder and a cellulose fiber feeder, for example. In the first kneading step, the amount of the cellulose fiber component added to the kneader is preferably 35 to 85 wt%, more preferably 40 to 75 wt%, based on the total amount of the cellulose fiber, the compatibilizing resin and urea.

(mixing roll)

As the kneading machine used in the first kneading step of the present invention, a kneading machine having a strong kneading force capable of melt-kneading the compatibilizing resin and urea and promoting the nanocrystallization of the cellulose fiber is preferable, a multi-screw kneading machine such as a twin-screw kneading machine or a four-screw kneading machine is preferably used, and a configuration in which a plurality of kneading sections, rotors and the like are included in a portion constituting a screw is preferable. As long as the kneading force equivalent to the above can be ensured, for example, a kneading machine such as a roll stand (bench roll), a banbury mixer, a kneader, or a planetary mixer can be used.

The set temperature for melt kneading can be adjusted according to the melting temperature of the compatibilizing resin to be used. When the maleic anhydride-modified polypropylene suitable for the present invention is used as the compatibilizing resin, the temperature is preferably 135 ℃ or higher in order to promote decomposition of urea, and more preferably 160 ℃ or higher in which the compatibilizing resin having a dicarboxylic acid residue capable of forming an acid anhydride is melted and a part of the terminal is closed by dehydration. By setting the temperature as described above, isocyanic acid is produced from urea, and urethane bonds are formed with unmodified hydroxyl groups on the cellulose fibers. This can introduce an amino group into the cellulose fiber and promote ionic interaction with the compatibilizing resin. Further, at the above temperature, the dicarboxylic acid residue in the compatibilizing resin is closed to form an acid anhydride, and thereby an esterification reaction with the cellulose fiber is caused, and a more firm resin composite can be formed. On the other hand, when the kneading temperature exceeds 200 ℃, the polypropylene resin as the base material starts to deteriorate, and the strength decreases.

In the present invention, the cellulose fibers, the compatibilizing resin and urea fed into the kneader are melt-kneaded in the first kneading step, and at least a part of the cellulose fibers are defibrated by a shear force generated during the melt-kneading, thereby preparing a resin composition containing cellulose nanofibers.

The cellulose nanofibers are preferably microfibers having a fiber diameter of about 1nm to about 1000nm and an aspect ratio of 100 or more. The cellulose nanofibers may be present in excess in the resin composition according to the present invention, and the resin composition may contain fibers that have not been fibrillated.

(second kneading step)

The method for producing a resin composition of the present invention may further include a second kneading step of kneading the kneaded product obtained in the first kneading step and a diluting resin. When the second mixing step is included, the kneaded product produced in the first mixing step may be used as a master batch.

(resin for dilution)

As the diluting resin, a thermoplastic resin which contains a polyolefin resin such as polyethylene, polypropylene (hereinafter also referred to as "PP"), an ethylene-propylene copolymer, polyisobutylene, polyisoprene, or polybutadiene as a main component, has a hydrophobicity relatively equivalent to that of the polyolefin resin according to the purpose, and has a melting temperature of about 100 to about 200 ℃. Examples of thermoplastic resins that may be added include: polystyrene, polyvinylidene chloride, a fluororesin, (meth) acrylic resin, polyamide (PA, nylon resin), polyester, polylactic acid, polyglycolic acid, a copolymer resin of lactic acid and ester, an acrylonitrile-butadiene-styrene copolymer (ABS resin), polycarbonate, polyphenylene ether, (thermoplastic) polyurethane, polyacetal, a vinyl ether resin, a polysulfone-based resin, a cellulose-based resin (triacetyl cellulose, diacetyl cellulose, etc.), and the like.

In the case of using MAPP as the compatibilizing resin (resin for masterbatch), polypropylene is preferably used as the resin for dilution.

When the kneaded product obtained in the first kneading step is used as a master batch, a resin composition further containing a diluent resin can be obtained by adding the diluent resin to the master batch and melt-kneading the mixture. When the diluting resin is added and melt-kneaded, the two components may be mixed at room temperature without heating and then melt-kneaded, or may be mixed while heating and melt-kneaded.

As a kneading machine in the case of adding a diluting resin and melt-kneading the mixture, the same kneading machine as that used in the first kneading step can be used. The melt kneading temperature can be adjusted according to the compatibilizing resin used in the first kneading step. The heating set temperature at the time of melt kneading is preferably within a range of about 10 ℃ from the minimum processing temperature recommended by the supplier of the thermoplastic resin. When polypropylene is used as the diluting resin, the melt kneading temperature is preferably 140 to 230 ℃ and more preferably 160 to 200 ℃. By setting the mixing temperature within this temperature range, the cellulose fibers and the resin can be uniformly mixed.

The resin composition produced by the production method of the present invention may further contain, for example, a surfactant; polysaccharides such as starch and alginic acid; natural proteins such as gelatin, casein, and the like; inorganic compounds such as tannins, zeolites, ceramics, metal powders, and the like; a colorant; a plasticizer; a fragrance; a pigment; a flow modifier; leveling agent; a conductive agent; an antistatic agent; an ultraviolet absorber; an ultraviolet light dispersing agent; deodorant, antioxidant, etc. The content ratio of the optional additives may be appropriately set within a range not impairing the effects of the present invention.

(resin composition)

The resin composition obtained by the production method of the present invention may be a kneaded product (master batch) obtained in the first kneading step, or may be a resin composition obtained in the second kneading step of kneading the kneaded product (master batch) obtained in the first kneading step and a diluting resin.

According to the present invention, a method for producing a resin composition capable of obtaining a resin molded article having a high flexural modulus and a high flexural strength can be provided.

Examples

The present invention will be described in further detail below with reference to examples, but the present invention is not limited to these examples.

(measurement of flexural modulus and flexural Strength)

The resin compositions obtained in examples and comparative examples were charged into a pelletizer to obtain pellet-shaped resin molded bodies. A pellet-shaped resin molding (150 g) was charged into a small molding machine ("MC 15" manufactured by Xplore Instruments) and a bar test piece was molded at a heating cylinder (cylinder) temperature of 200 ℃ and a mold temperature of 40 ℃. The flexural modulus and flexural strength were measured at a test speed of 10 mm/min and a distance between the points of 64mm using a precision universal tester ("Autograph AG-Xplus" manufactured by Shimadzu corporation) for the test piece (thickness: 4mm, length of the parallel portion: 80 mm). The reinforcement ratio was determined as the ratio of the measured values of each sample when the flexural modulus and flexural strength values of PP as a diluted resin in the measured values were set to 100, and the results are shown in table 1. A flexural modulus of 130 or more and a flexural strength of 118 or more indicates excellent strength.

(kneading machine and operating conditions used for production of masterbatch and resin composition)

"MFU 15TW-45 HG-NH" screw diameter of twin-screw kneader manufactured by Technovel corporation: 15mm, L/D: 45, processing speed: 300 g/hour

The screw speed was 200 rpm.

(example 1)

(preparation of cellulose fiber)

20kg (solid content 10kg) of hydrous conifer unbleached kraft pulp (NUKP) which was not subjected to beating treatment was put into a stirrer (manufactured by Nippon coke Industrial Co., Ltd. "FM 150L"), and then stirring was started, and dehydration under reduced pressure was performed at 80 ℃. The moisture content of the obtained cellulose fibers was measured by an infrared moisture meter. The water content was 2.5% by weight. The weighted average fiber length obtained by measuring the fiber length of the cellulose fiber by a fiber tester (manufactured by L & W) was 1.00 mm.

(materials used for production of Master batch and resin composition)

(a) Cellulose fiber

(b) Compatibilizing resin (resin for master batch)

Maleic anhydride modified polypropylene (MAPP): (Toyo Tac PMA-H1000P manufactured by Toyo Boseki Co., Ltd.; addition amount of dicarboxylic acid 57mgKOH/g)

(c) Urea: (He Guang Chun chemical industries Co., Ltd.)

(d) Resin for dilution

Polypropylene (PP): (PP MA04A manufactured by Japan Polypropylene corporation)

(production of Master batch)

The above cellulose fibers (22 g in terms of an absolute dry matter, the total cellulose amount of cellulose and hemicellulose: 20g), a powdered compatibilizing resin (MAPP: 6g), and a powdered urea (6 g: a blending amount of 30% relative to the cellulose amount) were put in a polyethylene bag, and mixed by shaking. The obtained mixture (34 g) was fed into a kneader by using a feeder (manufactured by Technovel corporation) attached to the twin-screw kneader, and kneaded at 180 ℃ to prepare a master batch.

(production of resin composition)

The obtained master batch and the diluting resin (PP) were mixed in a proportion of 10% of the total amount of the resin (the compatibilizing resin and the diluting resin) and the cellulose fiber and urea, based on the amount of the cellulose fiber component derived from the cellulose fiber, and kneaded at 180 ℃ by the above-mentioned twin-screw kneader, to obtain a resin composition.

(example 2)

The master batch and the resin composition were produced in the same manner as in example 1, except that the amount of urea was changed to 14g (70% of the amount of urea blended with respect to the amount of cellulose).

(example 3)

The master batch and the resin composition were produced in the same manner as in example 1, except that the amount of urea was changed to 20g (the amount of urea added to the cellulose was 100%).

(example 4)

(preparation of cellulose fiber)

20kg (solid content 10kg) of hydrous conifer unbleached kraft pulp (NUKP) subjected to beating treatment until CSF becomes 150mL was put into a stirrer (manufactured by Nippon coke Industrial Co., Ltd. "FM 150L"), and then stirring was started, followed by dehydration under reduced pressure at 80 ℃. The moisture content of the obtained cellulose fibers was measured by an infrared moisture meter. The water content was 2.5% by weight. The fiber length of the cellulose fiber was measured by a fiber tester (manufactured by L & W corporation) and the weighted average fiber length was 0.31 mm.

The masterbatch and the resin composition were produced in the same manner as in example 1, except that the cellulose fibers obtained in the above-described manner were used.

(example 5)

The master batch and the resin composition were produced in the same manner as in example 4, except that the amount of urea was changed to 14g (70% of the amount of urea added to the cellulose).

(example 6)

The master batch and the resin composition were produced in the same manner as in example 1, except that the amount of urea was changed to 2g (10% of the amount of urea added to the cellulose).

Comparative example 1

The master batch and the resin composition were produced in the same manner as in example 1, except that urea was not blended.

Comparative example 2

The cellulose fiber of example 1 (22 g as an absolute dry matter), powdered PP (6g) in place of the compatibilizer resin, and powdered urea (6 g: a blending amount of 30% based on the amount of cellulose) were put in a polyethylene bag, and mixed by shaking. The obtained mixture (34 g) was fed into a kneader by using a feeder (manufactured by Technovel corporation) attached to the twin-screw kneader, and kneaded at 180 ℃ to produce a kneaded product containing cellulose fibers and PP.

The obtained kneaded material, MAPP and diluting resin (PP) were mixed in a proportion of 10% of the total amount of the resin (PP and diluting resin (PP) used in place of MAPP and compatibilizing resin) and the cellulose fiber component derived from cellulose fibers, and kneaded at 180 ℃ using the above twin-screw kneader to obtain a resin composition. The blending ratio of MAPP and PP (the sum of PP used as a compatibilizing resin and PP used as a diluting resin) was set to 3: 83.

comparative example 3

The kneaded product containing the cellulose fibers and PP obtained in comparative example 2 and the diluting resin (PP) were mixed in a proportion such that the amount of the cellulose fiber component derived from the cellulose fibers became 10% of the total amount of the resin, the cellulose fibers, and urea, and kneaded at 180 ℃ by the above twin-screw kneader, to obtain a resin composition.

Comparative example 4

The master batch and the resin composition were produced in the same manner as in example 4, except that urea was not blended.

Comparative example 5

Cellulose fibers (22 g in terms of an absolute dry matter, the total cellulose amount of cellulose and hemicellulose therein: 20g) subjected to beating treatment until the CSF became 150mL and powdered urea (6g in terms of a blending amount of 30% relative to the cellulose amount) were put into a polyethylene bag and mixed by shaking. 28g of the obtained mixture was fed into a kneader by using a feeder (manufactured by Technovel Co., Ltd.) attached to the twin-screw kneader and kneaded at 180 ℃.

As shown in table 1, according to the method for producing a resin composition having the first kneading step of charging and kneading cellulose fibers, a compatibilizing resin and urea in a kneader of the present invention, a resin composition providing an excellent molded article having an improved flexural modulus can be obtained by adding urea in an amount of 10 to 100% by weight based on 100% by weight of cellulose in an amount of the urea added. Further, by adding urea in an amount of 10 to 30 wt% based on 100 wt% of the cellulose, a resin composition providing an excellent molded article with improved flexural strength can be obtained. It is also found that this effect is further improved in flexural modulus by beating the pulp used. On the other hand, it is found that the improvement effect is small in comparative examples 1 and 4 in which urea is not added. In addition, it is found that the strength improvement effect is small in comparative examples 2 and 3 in which the compatibilizing resin is not added together with urea.