JP2013185085A - Foam containing modified microfibrillated plant fibers - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a foam, in which microfibrillated plant fibers are dispersed in a highly hydrophobic thermoplastic resin component or a rubber component uniformly, and which has excellent mechanical strength and fine foam diameters; and to provide a method for producing a foam having excellent mechanical strength.SOLUTION: The present invention relates to a foam comprising: (A) at least one component selected from the group consisting of a thermoplastic resin and a rubber; and (B) microfibrillated plant fibers each esterified with an alkyl or alkenyl succinate anhydride.

Description

  The present invention relates to a foam containing a microfibrillated plant fiber modified with alkyl or alkenyl succinic anhydride and a resin component and / or a rubber component, and a method for producing the same.

  Thermoplastic resins such as polyethylene and polypropylene are widely used for containers, piping, films, medical uses, and the like from the viewpoint of being inexpensive and excellent in flexibility and chemical resistance. Rubber is a material excellent in elastic modulus and impact resistance, and is widely used not only for industrial purposes but also for general purposes.

  In addition to the above-mentioned properties, foams obtained by foaming a thermoplastic resin or rubber are conventionally known in order to further reduce weight, heat insulation, and shock absorption.

  As described above, the foam of thermoplastic resin or rubber is lighter than the unfoamed state, and is excellent in heat insulation and shock absorption, but has a problem that strength is lowered. doing. In order to give strength to such a thermoplastic resin or rubber foam, a reinforcing material such as a filler is blended.

  By the way, in order to improve physical properties such as the strength of resin and rubber, it is known to use microfibrillated plant fibers in which cellulose fibers are microfibrillated and the fiber diameter is reduced to the nano order as fillers ( For example, Patent Document 1).

  The microfibrillated plant fiber is very useful as a reinforcing material such as a filler because of its light mass and high strength. However, microfibrillated plant fibers have a very strong cohesive force and generally poor compatibility with resin components and rubber components, so that it is possible to obtain a uniform molding material in which microfibrillated plant fibers are uniformly dispersed. Have difficulty. In addition, the foam obtained by foaming the molding material also has a problem that the mechanical strength cannot be sufficiently exhibited. For such problems, attempts have been made to improve the dispersibility in the resin or rubber component by modifying the surface of the microfibrillated plant fiber with a chemical modifier or the like.

  For example, Patent Document 2 describes that a compound containing a quaternary ammonium group is used to cation-modify microfibrillated plant fibers and suppress aggregation of microfibrillated plant fibers by electrostatic repulsion of cations. In addition, a composite material in which the modified microfibrillated plant fiber is combined with a thermoplastic resin is described.

  However, the above-mentioned cation-modified microfibrillated plant fiber is uniformly dispersed in a resin having a relatively high polarity such as a polyester-based resin. On the other hand, there is a problem that it is difficult to sufficiently disperse and the mechanical strength cannot be sufficiently exhibited.

  Patent Document 3 discloses a foam having an average cell diameter of 0.3 mm to 1.5 mm in which a resin composition composed of a thermoplastic resin composed of a polyolefin resin and an organic fiber is foamed. Yes. In Patent Document 3, cellulose fibers and the like are exemplified as the organic fibers, the average fiber diameter of the organic fibers is 0.1 to 1000 μm and the average fiber length is 0.01 to 5 mm, the organic fibers are a surface treatment agent, For example, it is also described that the surface treatment may be performed with a coupling agent (such as a silane coupling agent having a functional group such as an amino group, a substituted amino group, an epoxy group, or a glycidyl group).

  However, Patent Document 3 does not specifically examine the effect of the fiber surface treatment, and does not refer to the foam having excellent mechanical strength in detail. Even in fiber-reinforced foams, the poor compatibility between cellulose fibers and resin deteriorates the dispersibility of the fibers and the fiber / resin interface strength, lowers the fiber reinforcement effect, and increases the strength due to coarse growth of bubbles during foaming. There is room for improvement in the modification of the fibers suitable for hydrophobic resins because they cause a decrease.

JP 2008-297364 A JP 2011-162608 A JP 2007-56176 A

  The present invention provides a foam having a fine foam diameter excellent in mechanical strength, in which microfibrillated plant fibers are uniformly dispersed in a highly hydrophobic thermoplastic resin component or rubber component. An object of the present invention is to provide a method for producing a foam excellent in mechanical strength.

  As a result of intensive studies to solve the above problems, the present inventors have used alkyl or alkenyl succinic anhydride in order to improve mechanical strength in thermoplastic resin components and rubber components with high hydrophobicity. Use of modified microfibrillated plant fibers (hereinafter also referred to as ASA modified microfibrillated plant fibers) obtained by esterification as a reinforcing material makes it possible to uniformly modify modified microfibrillated plant fibers in thermoplastic resins and rubber. It was found to be useful in terms of dispersion in Further, by foaming a thermoplastic resin or rubber in which such ASA-modified microfibrillated plant fibers are uniformly dispersed, a fine foam having a very small foam diameter in the foam can be obtained. I found. From such knowledge, it was possible to reduce the weight of the resin or rubber foam without causing a decrease in mechanical strength, which is a problem in conventional foams.

  The present invention is an invention that has been completed through further studies based on such findings. That is, this invention provides the foam shown to the following term, and its manufacturing method.

Item 1. At least one component (A) selected from the group consisting of thermoplastic resin and rubber, and microfibrillated plant fiber (B) esterified with alkyl or alkenyl succinic anhydride
Foam containing.

  Item 2. Item 2. The content of the modified microfibrillated plant fiber (B) esterified with alkyl or alkenyl succinic anhydride is 0.1 to 200 parts by mass with respect to 100 parts by mass of the component (A). Foam.

  Item 3. Item 3. The foam according to Item 1 or 2, wherein the specific gravity is 0.03 to 0.9.

  Item 4. Item 4. The foam according to any one of Items 1 to 3, wherein an average value of the foam diameter in the foam is 0.1 to 100 μm.

  Item 5. Item 5. The foam according to any one of Items 1 to 4, wherein the component (A) is a polyolefin resin.

  Item 6. Item 6. The foam according to any one of Items 1 to 5, wherein the component (A) is polyethylene.

Item 7. (1) Mixing at least one component (A) selected from the group consisting of a resin and rubber with a modified microfibrillated plant fiber (B) esterified with alkyl or alkenyl succinic anhydride, and / or resin and / or A method for producing a foam, comprising a step of preparing a rubber composition, and (2) a step of foaming a resin and / or a rubber composition.

  Item 8. The step of foaming the resin and / or rubber composition in step (2) encloses the resin and / or rubber composition and an inert gas in a high-pressure vessel, and impregnates the resin and / or rubber composition with the inert gas. Item 8. The method for producing a foam according to Item 7, which is a step of causing the resin and / or the rubber composition to foam by rapid decompression.

  Item 9. Item 9. The method for producing a foam according to Item 8, wherein the inert gas is carbon dioxide.

Item 10. Item 10. The method for producing a foam according to Item 8 or 9, wherein the pressure in the high-pressure vessel is 1 to 30 MPa, and the pressure after rapid decompression is 0.5 × 10 ⁵ to 2 × 10 ⁵ Pa.

  According to the foam of the present invention, the ASA-modified microfibrillated plant fiber obtained by esterification with alkyl or alkenyl succinic anhydride is uniformly dispersed in the thermoplastic resin or rubber. And / or the reduction in mechanical strength, which is regarded as a problem in foaming of the rubber composition, is not impaired. Moreover, when the foam is produced, the foam diameter can be controlled to be small by improving the viscoelasticity due to the inclusion of the ASA-modified microfibrillated plant fiber. Therefore, the foam diameter in the obtained foam becomes fine, and a lightweight foam having a small specific gravity can be obtained without impairing the decrease in mechanical strength.

  In addition, in the thermoplastic resin and the rubber component, the foam in which the conventional microfibrillated plant fiber or the modified microfibrillated plant fiber is dispersed does not provide sufficient mechanical strength. In the foam of the resin component or rubber component, since the ASA-modified microfibrillated plant fiber is used as the modified microfibrillated plant fiber in the resin or rubber component, it is possible to dramatically improve the mechanical strength. It becomes.

  Hereinafter, the foam of this invention and its manufacturing method are explained in full detail.

<Foam>
The foam of the present invention comprises at least one component (A) selected from the group consisting of a thermoplastic resin and rubber, and a modified microfibrillated plant fiber (B) esterified with alkyl or alkenyl succinic anhydride. contains.

  As the thermoplastic resin component in component (A), olefin resin, polyamide resin, polyacetal resin, vinyl ether resin, polyamide resin, polycarbonate resin, polyester resin, polysulfone resin, polylactic acid, triacetylated cellulose, diacetylated Examples thereof include cellulose resins such as cellulose.

  Examples of the olefin resin include polyethylene, vinyl chloride resin, styrene resin, (meth) acrylic resin, and the like.

  Examples of the polyethylene include high density polyethylene (HDPE) and low density polyethylene (LDPE), and examples of the LDPE include branched low density polyethylene and linear low density polyethylene. Among these, it is preferable to use HDPE from the viewpoint of high rigidity and high heat resistance.

  The number average molecular weight of polyethylene is preferably about 10,000 to 1,000,000, more preferably about 50,000 to 500,000. By setting the number average molecular weight of polyethylene to 10,000 or more, the fluidity at the time of melting is lowered, the foam diameter of the foam can be reduced, and the weight of the resin can be reduced without impairing the mechanical strength. The effect that you can do it. Moreover, by setting the number average molecular weight of polyethylene to 1,000,000 or less, the foaming ratio of the resin can be increased, and the effect of reducing the weight can be obtained.

  The specific gravity of polyethylene is preferably about 0.91 to 0.98, more preferably about 0.91 to 0.94. In particular, when HDPE is used as polyethylene, the specific gravity of HDPE is preferably about 0.94 to 0.98. Moreover, when using LDPE as polyethylene, as a specific gravity of LDPE, about 0.91-0.935 is preferable.

  Moreover, it is good also as a copolymer which has an ethylene unit and another olefin unit in the range by which the characteristic as polyethylene is not impaired. Examples of other olefins include propylene, 1-butene, 1-hexene, 4-methyl-1-pentene, 1-octene, 1-pentene, norbornene, vinyl acetate, and ethyl acrylate.

  Examples of the rubber component in component (A) include those of diene rubber components. Specifically, natural rubber (NR), butadiene rubber (BR), styrene-butadiene copolymer rubber (SBR), isoprene rubber. (IR), butyl rubber (IIR), acrylonitrile-butadiene rubber (NBR), acrylonitrile-styrene-butadiene copolymer rubber, chloroprene rubber, styrene-isoprene copolymer rubber, styrene-isoprene-butadiene copolymer rubber, isoprene- Examples include butadiene copolymer rubber, hydrogenated natural rubber, and deproteinized natural rubber. Examples of the rubber component other than the diene rubber component include ethylene-propylene copolymer rubber, acrylic rubber, epichlorohydrin rubber, polysulfide rubber, silicone rubber, fluorine rubber, and urethane rubber. These rubber components may be used alone or in combination of two or more. What is necessary is just to mix | blend suitably also in the blend ratio in the case of blending according to various uses.

  Materials (plant fiber-containing materials) containing plant fibers used as raw materials for ASA-modified microfibrillated plant fibers (B) include wood, bamboo, hemp, jute, kenaf, cotton, beet, agricultural residue, and cloth. Examples thereof include pulp obtained from natural plant fiber materials, regenerated cellulose fibers such as rayon and cellophane. In particular, pulp is a preferable raw material.

  The pulp includes chemical pulp (kraft pulp (KP), sulfite pulp (SP)), semi-chemical pulp (SCP) obtained by pulping plant raw materials chemically or mechanically, or a combination of both. ), Chemi-Grand Pulp (CGP), Chemi-Mechanical Pulp (CMP), Groundwood Pulp (GP), Refiner Mechanical Pulp (RMP), Thermo-Mechanical Pulp (TMP), Chemi-thermo-Mechanical Pulp (CTMP), and these plant fibers Preferred examples include deinked waste paper pulp, corrugated waste paper pulp, and magazine waste paper pulp as the main component. These raw materials can be delignified or bleached as necessary to adjust the amount of lignin in the plant fiber.

  Among these pulps, various kraft pulps derived from conifers with strong fiber strength (coniferous unbleached kraft pulps (hereinafter sometimes referred to as NUKP), softwood oxygen-bleached unbleached kraft pulps (hereinafter sometimes referred to as NOKPs), Softwood bleached kraft pulp (hereinafter sometimes referred to as NBKP)) is particularly preferred.

  The plant fiber used as a raw material is mainly composed of cellulose, hemicellulose, and lignin. The lignin content in the plant fiber-containing material is usually about 0 to 40% by mass, preferably about 0 to 10% by mass. The lignin content can be measured by the Klason method.

  In the cell wall of the plant, microfibrillated plant fibers having a width of about 4 nm are present as a minimum unit. This is the basic skeletal material (basic element) of plants. The cellulose microfibrils gather to form a plant skeleton. In the present invention, the “microfibrillated plant fiber” is a fiber (a fiber that has been defibrated) obtained by unraveling the fiber of the material containing the plant fiber to the nano-size level.

  Examples of a method for producing microfibrillated plant fibers include a method of defibrating a material containing plant fibers used as a raw material for the above-mentioned plant fibers by a known defibrating method. For example, water of cellulose fiber-containing material is used. Examples of the method include pulverizing a suspension or slurry by mechanically grinding or beating them with a refiner, a high-pressure homogenizer, a grinder, a uniaxial or multiaxial (for example, biaxial) kneader, or a bead mill. You may process combining these defibrating methods as needed.

  More specifically, for example, a method described in JP2011-162608A can be used.

  In the ASA-modified microfibrillated plant fiber (B) of the present invention, the hydroxyl group of the microfibrillated plant fiber reacts with alkyl or alkenyl succinic anhydride to form an ester bond. Here, since alkyl or alkenyl succinic anhydride becomes a half ester of succinic acid in which the alkyl group or alkenyl group is substituted by reaction with a hydroxyl group, a carboxylic acid group is also introduced into the modified microfibrillated plant fiber.

  More specifically, examples of the alkenyl succinic anhydride include compounds having a skeleton derived from an olefin having 4 to 30 carbon atoms and a maleic anhydride skeleton. Specifically, octyl succinic anhydride, dodecyl succinic anhydride, hexadecyl succinic anhydride, alkyl succinic anhydride such as octadecyl succinic anhydride, pentenyl succinic anhydride, hexenyl succinic anhydride, octenyl succinic anhydride, decenyl succinic anhydride, Examples include undecenyl succinic anhydride, dodecenyl succinic anhydride, tridecenyl succinic anhydride, hexadecenyl succinic anhydride, octadecenyl succinic anhydride and the like. These may be used alone or in combination. Two or more types may be used in combination from the viewpoint that properties such as hydrophobicity and water resistance can be controlled.

  Examples of the alkyl succinic anhydride include hydrogenated products obtained by adding hydrogen to the unsaturated bond of the alkenyl succinic anhydride.

  The method for producing the ASA-modified microfibrillated plant fiber (B) is not particularly limited. For example, a method of reacting the microfibrillated plant fiber with alkyl or alkenyl succinic anhydride, pulp, etc. Examples thereof include a method in which a cellulose fiber-containing material is reacted with alkyl or alkenyl succinic anhydride, and the resulting ASA-modified cellulose fiber is defibrated by the above-described method.

  The degree of ester substitution (DS) of the ASA-modified microfibrillated plant fiber (B) is to uniformly disperse the highly hydrophilic microfibrillated plant fiber in polyethylene or to improve the water resistance of the microfibrillated plant fiber. Therefore, about 0.05 to 2.0 is preferable, about 0.1 to 2.0 is more preferable, and about 0.1 to 0.8 is still more preferable.

In addition, DS removes by-products such as alkyl or alkenyl succinic anhydride used as a raw material by washing or a hydrolyzate thereof, then increases in weight, elemental analysis, neutralization titration method, FT-IR , And can be analyzed by various analysis methods such as ¹ H-NMR.

  The content of the ASA-modified microfibrillated plant fiber (B) is preferably about 0.1 to 200 parts by weight, more preferably about 0.5 to 100 parts by weight, with respect to 100 parts by weight of the component (A). About 50 mass parts is more preferable. By setting the content of the ASA-modified microfibrillated plant fiber (B) to 0.1 parts by mass or more, the viscosity and elasticity at the time of melting increase, the elastic modulus and strength of the thermoplastic resin and / or rubber composition, etc. Is obtained. Moreover, the effect of maintaining the heat moldability of the resin and / or rubber composition can be obtained by setting the content of the ASA-modified microfibrillated plant fiber (B) to 200 parts by mass or less.

  Further, in the foam of the present invention, a resin in which a polar group is introduced by adding maleic anhydride, epoxy or the like as a compatibilizing agent within a range not impairing the effects of the present invention, for example, maleic anhydride-modified polyethylene resin, maleic anhydride An acid-modified polypropylene resin and various commercially available compatibilizers may be used in combination.

  As content of these compatibilizing agents, about 0.1-50 mass parts is preferable with respect to 100 mass parts of component (A), and about 0.5-20 mass parts is more preferable.

  Further, the foam of the present invention may further contain an inorganic salt (C), and by containing the inorganic salt (C), the modified microfibrillated plant fiber (B) interacts with the inorganic particles. The effect that the strength, elastic modulus, etc. of the resin and / or rubber composition are improved is obtained.

  Examples of the inorganic salt (C) include salts composed of Group 1 or Group 2 metals. Specifically, acetates, carbonates, sulfates composed of Group 1 or Group 2 metals, Examples thereof include nitrates. Examples of the Group 1 metal include sodium and potassium. Examples of the Group 2 metal include magnesium, calcium, strontium, barium, and the like. More specifically, magnesium sulfate, barium sulfate, barium carbonate, carbonic acid. Examples include potassium and calcium carbonate. The particle diameter of the inorganic salt can be arbitrarily selected according to the purpose, but in general, a smaller one is preferable. Among these, carbonate is preferable in that it has an excellent effect of improving the elastic modulus, and a powder having a relatively large surface area of particle diameter / crystal diameter can be easily obtained and modified microfibrillated plant fiber (B). Calcium carbonate and barium carbonate are more preferable from the viewpoint of easy interaction with each other and that the obtained molded product is less colored.

  The content of the inorganic salt (C) is 0.1 to 20 parts by mass, preferably about 0.5 to 20 parts by mass, and more preferably about 1 to 10 parts by mass with respect to 100 parts by mass of the component (A). preferable. By setting the content of the inorganic salt (C) to 0.1 parts by mass or more, the mechanical properties of the molded article can be improved by the interaction with the ASA-modified microfibrillated plant fiber (B). Moreover, by setting the content of the inorganic salt (C) to 20 parts by mass or less, the relative amounts of polyethylene and ASA-modified microfibrillated plant fiber (B) are not reduced, and mechanical properties such as strength and elastic modulus are reduced. Can be prevented and deterioration of moldability can be prevented.

  Further, the foam of the present invention may contain any additive other than the above-described components.

  For example, surfactants; polysaccharides such as starches and alginic acids; natural proteins such as gelatin, glue and casein; inorganic compounds such as tannins, zeolites, ceramics and metal powders; colorants; plasticizers; fragrances; pigments; Additives such as agents, leveling agents, conductive agents, antistatic agents, ultraviolet absorbers, ultraviolet dispersants, deodorants, and flame retardants may be appropriately blended.

  As a content ratio of an arbitrary additive, it may be appropriately contained within a range in which the effect of the present invention is not impaired. For example, about 0.01 to 10% by mass with respect to 100 parts by mass of the component (A). Preferably, about 1-5 mass% is more preferable.

  The specific gravity of the foam of the present invention is preferably about 0.03 to 0.9, more preferably about 0.1 to 0.8, and even more preferably about 0.3 to 0.8. By setting the specific gravity of the foamed body of the present invention to 0.03 or more, an effect that a decrease in mechanical strength can be suppressed is obtained. In addition, by setting the specific gravity of the foam to 0.9 or less, it is possible to achieve the effect that the weight of the foam can be reduced and the heat insulation and insulation are improved.

<Method for producing foam>
The production method of the present invention comprises (1) a modified microfibrillated plant fiber (B) esterified with at least one component (A) selected from the group consisting of a thermoplastic resin and rubber and an alkyl or alkenyl succinic anhydride. ) To prepare a resin and / or rubber composition, and (2) to foam the resin and / or rubber composition.

  The component (A) used in the step (1) and the modified microfibrillated plant fiber (B) esterified with alkyl or alkenyl succinic anhydride are the same as those mentioned in the above <foam>. Things can be used.

  The blending amount of the ASA-modified microfibrillated plant fiber (B) is set so as to be the content of the ASA-modified microfibrillated plant fiber (B) of the <foam>, for example, the component (A) 100 About 0.1-200 mass parts is preferable with respect to mass parts, about 0.5-100 mass parts is more preferable, and about 1-50 mass parts is further more preferable.

  The method of mixing the component (A), the ASA-modified microfibrillated plant fiber (B), and the compatibilizer, inorganic salt (C), and optional additives described above is not particularly limited, For example, after the ASA-modified microfibrillated plant fiber is dried in advance, a thermoplastic powder, pellets, or other optional additives are mixed in a mixer, blender twin-screw kneader, kneader, lab. Plast mill, homogenizer, high-speed homogenizer, high-pressure homogenizer, planetary stirrer, mixing with 3 rolls, etc., or mixing and stirring with a stirrable device, followed by heating and stirring with a twin-screw kneader, kneader solid-phase shear extruder, etc. A method of melt-kneading with an apparatus capable of ASA, an ASA-modified microfibrillated plant fiber (B) containing a component (A) and a solvent such as water, and any other arbitrary Utilizing a method in which solvent removal and melt-kneading are performed simultaneously with a device capable of heating and stirring, such as a twin-screw kneader, a kneader solid-phase shear extruder, etc., after the additive is mixed in the above apparatus I can do it. Moreover, you may mix a component (A), after grind | pulverizing with a well-known grinder.

  The kneading temperature in the melt kneading is preferably about 160 to 200 ° C., for example.

  In addition, a method of mixing a part of the component (A) and the ASA-modified microfibrillated plant fiber (B) to prepare a master batch, and mixing the obtained master batch and the remaining component (A), This is preferable in that the ASA-modified microfibrillated plant fiber (B) is more uniformly dispersed in the component (A). The mixing ratio of the component (A) used for mixing with the ASA-modified microfibrillated plant fiber (B) when preparing the masterbatch is preferably 0.1 to 50% by mass with respect to the total amount of the component (A). About, more preferably, about 0.5 to 30% by mass is used.

  Moreover, when mixing a component (A) and modified | denatured microfibrillated plant fiber (B), you may mix | blend a compatibilizing agent, inorganic salt (C), and arbitrary additives, These addition amount is What is necessary is just to mix | blend suitably so that it may become the range of each content contained in the said foam.

  A thermoplastic resin and / or rubber composition is obtained by the step (1), and a foam is obtained by foaming the thermoplastic resin and / or rubber composition in the step (2). As a method of foaming the thermoplastic resin and / or rubber composition, for example, the thermoplastic resin and / or rubber composition and an inert gas are sealed in a high-pressure container, and the thermoplastic resin and / or rubber composition is not used. Method of foaming thermoplastic resin and / or rubber composition by impregnating with active gas and rapid decompression (foaming method 1), foaming agent is contained in thermoplastic resin and / or rubber composition, and foaming A method in which carbon dioxide or nitrogen gas is generated by thermally decomposing the agent and foamed (foaming method 2), a solvent having a low boiling point is contained in the thermoplastic resin and / or rubber composition, and a low boiling point solvent is obtained by heating. Examples include a method of evaporating and foaming a thermoplastic resin and / or a rubber composition (foaming method 3), a method of taking a gas such as air as bubbles by stirring and foaming (foaming method 4), and the like.Among these, the foamed diameter in the thermoplastic resin and / or rubber composition can be reduced, the foamed diameter does not vary, the foam can be uniformly foamed, and the decomposition residue of the foaming agent is Foaming method 1 is preferable from the standpoint that it does not remain and that no odor is generated.

  In the foaming method 1, specific examples of the foaming medium used include carbon dioxide and nitrogen. Among these, carbon dioxide is preferable from the viewpoint of high solubility in the component (A), and it is more preferable to use supercritical carbon dioxide from the viewpoint that a denser foam can be formed.

  The pressure in the high-pressure vessel after enclosing the foaming medium is preferably about 1 to 30 MPa, more preferably about 3 to 25 MPa, and further preferably about 5 to 25 MPa. By setting the pressure in the high-pressure vessel to 1 MPa or more, the resin and / or rubber composition can be more impregnated with an inert gas, and the dissolved inert gas is a thermoplastic resin and / or rubber. Since the composition is plasticized, the foaming temperature can be lowered. Furthermore, the apparatus cost concerning a pressure-resistant container can be lowered | hung by setting the pressure in a high pressure container to 30 Mpa or less.

  The temperature in the high-pressure vessel is preferably about 100 to 160 ° C, more preferably about 110 to 150 ° C, and further preferably about 120 to 140 ° C. By setting the temperature in the high-pressure vessel to be near the melting point of the resin, the expansion ratio is increased and the weight can be reduced. Moreover, by setting the temperature in the high-pressure vessel in the vicinity of the melting point of the component (A), the expansion ratio can be reduced, and the decrease in mechanical strength can be suppressed.

  A thermoplastic resin and / or rubber composition and an inert gas are enclosed in the high-pressure vessel, and the thermoplastic resin and / or rubber composition are sealed under a high-pressure and high-temperature condition as described above, and then rapidly decompressed. Things can be foamed.

Examples of the method of rapidly depressurizing include a method of opening a high-pressure vessel at a time and reducing the pressure to atmospheric pressure. The pressure after sudden pressure reduction is preferably about 0.5 × 10 ⁵ to 2 × 10 ⁵ Pa, more preferably atmospheric pressure (1.01325 × 10 ⁵ Pa).

<Molding material and molded body>
The foam of the present invention can be molded into a desired shape and used as a molding material. Examples of the shape of the molding material include sheets, pellets, and powders. The molding material having these shapes can be obtained by using, for example, mold molding, injection molding, extrusion molding, hollow molding, foam molding and the like.

  The molding material obtained by molding the foam of the present invention is used in a field where a polyethylene molded body containing microfibrillated plant fibers has been used, particularly in a field where weight reduction is required. For example, interior materials, exterior materials, structural materials, etc. for transportation equipment such as automobiles, trains, ships, airplanes, etc .; housings, structural materials, internal parts, etc. for electrical appliances such as personal computers, televisions, telephones, watches, etc .; mobile phones, etc. Housing, structural materials, internal parts, etc. for mobile communication equipment; portable music playback equipment, video playback equipment, printing equipment, copying equipment, housing for sports equipment, etc .; construction materials, office equipment such as stationery It can be used effectively as a container, a container, etc.

  It can be suitably used for automotive ceiling materials, door trims, sound absorbing materials, seal materials, air conditioner insulation materials, building joint materials, and other industrial products, such as cushioning materials and heat insulation / cooling materials, especially used in foamed polyethylene. . Further, it can be suitably used for joint materials such as construction, civil engineering, vehicles, electrical equipment, and housing equipment, airtightness, seals, packing materials, heat insulation and heat insulation materials, which are used with foamed rubber components.

3 is a cross-sectional SEM photograph of the foam obtained in Example 2. 6 is a cross-sectional SEM photograph of a foam obtained in Comparative Example 5. It is the graph which plotted specific gravity and the bending elastic modulus on the vertical axis | shaft about the foam and unfoamed body obtained in Examples 1-4 and Comparative Examples 1-6. It is the graph which plotted specific gravity and the bending strength on the vertical axis | shaft about the foam and unfoamed body obtained in Examples 1-4 and Comparative Examples 1-6. It is the graph which plotted the storage elastic modulus (G ') in the frequency of 1 Hz of the sheet-like molding before foaming of Example 1 and Comparative Examples 4 and 6. It is the graph which plotted the loss elastic modulus (G '') in the frequency of 1 Hz of the sheet-like molding before foaming of Example 1 and Comparative Examples 4 and 6.

[Example]
EXAMPLES Hereinafter, although an Example and a comparative example are given and this invention is demonstrated further in detail, this invention is not limited to these.

-Examples 1-4
<Preparation of microfibrillated plant fiber by bead mill>
A slurry of softwood bleached kraft pulp (NBKP) (slurry concentration: 2% by mass) is passed through a single disc refiner (manufactured by Kumagai Riki Kogyo Co., Ltd.) and repeatedly refined until the Canadian Standard Freeness (CSF) is 100 ml or less. Went. Next, the obtained slurry was concentrated to 20% by mass using a centrifuge (manufactured by Kokusan Co., Ltd.) to prepare NBKP (refiner treatment).

  Next, water was added to 375 g of NBKP (refiner treatment, concentration: 20% by mass) to make the total amount 10 kg (slurry concentration: 0.75% by mass). The obtained refiner-treated NBKP slurry was subjected to mechanical defibrating treatment with a bead mill (NVM-2, manufactured by Imex Corp.) under the following conditions.

[Defining conditions]
Beads: Zirconia beads (diameter: 1mm)
Vessel capacity: 2 liters Bead filling: 1216 ml (4612 g)
Rotation speed: 2,000rpm
Vessel temperature: 20 ° C
Discharge rate: 600 ml / min.

  The obtained slurry of microfibrillated plant fibers was filtered under pressure with a filter press (manufactured by Nippon Filtration Equipment Co., Ltd.) to obtain water-containing microfibrillated plant fibers having a solid content concentration of 25% by mass.

<Preparation of specific surface area measurement sample>
4 g (1 g of solid content) of the water-containing microfibrillated plant fiber obtained above was sampled, ethanol was added to 0.5 mass%, the mixture was stirred with a stirrer for 30 minutes, transferred to a centrifuge tube, and manufactured by Kokusan Co., Ltd. Centrifugation was performed using a cooling high-speed centrifuge “HR-9”. After centrifugation, the supernatant was removed by decantation, and then the residue was again dispersed in ethanol to 0.5 mass%, and stirred with a stirrer, and then the slurry was centrifuged. This operation was repeated three times each with ethanol and tert-butanol, and after solvent substitution, 200 g of a tert-butanol dispersion (concentration: 0.5% by mass) of microfibrillated plant fiber was transferred to an eggplant flask, and the flask was liquid. The whole was immersed in a nitrogen bath and frozen. Subsequently, this eggplant flask was set in a freeze dryer (FDU-1200, Tokyo Rika Kikai Co., Ltd.) and freeze-dried.

<Measurement of specific surface area of microfibrillated plant fiber>
Measurement of the BET specific surface area of the obtained microfibrillated plant fiber after freeze-drying by a nitrogen gas adsorption method using an automatic specific surface area / pore diameter distribution measuring device “BELSORP-mini II” (manufactured by Nippon Bell Co., Ltd.) As a result, it was 138 m ² / g.

<Preparation of Alkenyl Succinic Anhydride (ASA) Modified Microfibrillated Plant Fiber>
After adding 300 g of N-methylpyrrolidone (NMP) to the above-mentioned water-containing microfibrillated plant fiber (solid content: 75 g), the mixture was added to Trimix TX-5 (manufactured by Inoue Seisakusho Co., Ltd.). Dehydrated under reduced pressure at -50 ° C. Next, 75 g of T-NS135 (ASA having 16 carbon atoms other than succinic anhydride, manufactured by Seiko PMC), 5.6 g of dimethylaminopyridine (DMAP), 25.6 g of potassium carbonate, and 50 g of NMP are added. , Reacted at 62 ° C. for 1.5 hours. After the reaction, it was washed successively with acetone, ethanol, acetic acid water and water to obtain hydrous ASA-modified microfibrillated plant fiber. The degree of substitution was measured by the following method and found to be 0.40.

<Calculation of substitution degree (DS) of ASA (C16) modified microfibrillated plant fiber>
The substitution degree (DS) of ASA modification was hydrolyzed by heating and stirring the ester bond of ASA and cellulose in the ASA-modified microfibrillated plant fiber at 70 ° C. in a sodium hydroxide solution. Then, it calculated after calculating | requiring the amount of ASA produced | generated by hydrolysis by back titrating with 0.1N hydrochloric acid aqueous solution. In addition, phenolphthalein was used as an indicator for back titration.

  Specifically, about 0.5 g of a dried product of ASA-modified microfibrillated plant fiber was precisely weighed into a 100 ml beaker, 15 ml of ethanol and 5 ml of distilled water were added, and the mixture was stirred at room temperature for 30 minutes. Thereafter, 10 ml of 0.5N sodium hydroxide solution was added and stirred at 70 ° C. for 15 minutes, then cooled to room temperature and further stirred overnight. A few drops of an 85% phenolphthalein ethanol solution were added to the resulting mixture, followed by back titration with a 0.1N aqueous hydrochloric acid solution, and the amount of ASA produced by hydrolysis was measured. The degree of substitution was calculated from the amount of ASA-modified microfibrillated plant fiber used and the amount of ASA measured by titration.

<Composite of ASA-modified microfibrillated plant fiber and polyethylene>
After the ASA-modified microfibrillated plant fiber obtained in <Preparation of ASA-modified microfibrillated plant fiber> was washed twice with ethanol, ethanol was added to adjust the solid content concentration to 3.0% by mass. To this ASA-modified microfibrillated plant fiber (solid content 54 g) dispersed in ethanol, maleic anhydride-modified polypropylene (MAPP, Toyo Tac PMA H1000P manufactured by Toyobo Co., Ltd., acid content 5.7 mass%, melt Flow rate: 110 g / 10 min (190 ° C., 2.16 kg)) 12.9 g, calcium carbonate (CaCO ₃ ) 4 g, and high density polyethylene (HDPE) (Sumitomo Seika Co., Ltd. flow beads HE3040, melting point : 130 ° C.) Ethanol was added to 29.2 g of each, and a dispersion prepared to a solid content concentration of 10.0% by mass was mixed in a beaker with propeller stirring. The obtained resin mixture dispersion was subjected to suction filtration, and then dried under reduced pressure while stirring with a trimix to prepare a master batch.

  Subsequently, a mixture of the obtained master batch and HDPE (Suntech-HD J320 manufactured by Asahi Kasei Chemicals Corporation) was mixed with a twin screw kneader (KZW, screw diameter: 15 mm, L / D: 45 manufactured by Technobel). And screw rotation: 200 rpm, damming structure: 0, treatment speed 200 g / hour) at 140 ° C. for one pass, and the resulting melt-kneaded product is pelletized using a pelletizer (manufactured by Technobel Co., Ltd.). The obtained pellets were put into an injection molding machine (NPX7-1F, manufactured by Nissei Resin Co., Ltd.) to obtain a dumbbell-shaped molded product. The heating cylinder temperature was 160 ° C., and the mold temperature was 40 ° C. Table 1 shows the blending ratio of each component contained in the obtained molded product.

<Manufacture of foam>
The dumbbell-shaped molded product obtained in <Composite of ASA-modified microfibrillated plant fiber and polyethylene> was cut to prepare a test piece having a length of 35 mm, a width of 5 mm, and a thickness of 1 mm. . The obtained test piece was placed in a mold, further placed in a high-pressure vessel, filled with carbon dioxide, and held at the temperature and pressure shown in Table 2 for 300 minutes until the test piece was sufficiently dissolved in carbon dioxide. Thereafter, carbon dioxide was released at once into the atmosphere (1.01325 × 10 ⁵ Pa), and the test piece was foamed to obtain a foam.

Comparative example 1
In Example 1, the sheet-like molded article prepared in <Composite of ASA-modified microfibrillated plant fiber and polyethylene> was not foamed, and was not foamed in the same manner as in Example 1 with the blending ratio shown in Table 1. The test piece was manufactured.

Comparative example 2
In Example 3, the sheet-like molded product prepared in <Composite of ASA-modified microfibrillated plant fiber and polyethylene> was not foamed, and was not foamed in the same manner as in Example 3 with the blending ratio shown in Table 1. The test piece was manufactured.

Comparative example 3
A test piece was produced in the same manner as in Example 1 except that only HDPE used in Example 1 was formed into a sheet and an unfoamed test piece was produced without foaming.

Comparative examples 4 and 5
Only HDPE used in Example 1 was formed into a sheet shape, and a foam was produced by the same method as in <Production of foam> in Example 1 above. Table 2 shows the temperature and pressure in the high-pressure vessel, which are the foaming conditions.

Comparative Example 6
The refiner-treated pulp used in Example 1 was not subjected to ASA modification, and the pulp was defibrillated by the same method as in Example 1 to prepare unmodified microfibrillated plant fibers, and ASA modified microfibrils. Unmodified microfibrillated plant fibers were used in place of the modified plant fibers. Otherwise, a foam was produced in the same manner as in Example 1. Table 2 shows the temperature and pressure in the high-pressure vessel, which are the foaming conditions.

<Physical property evaluation>
Cross-sectional SEM photographs of the foams obtained in Example 2 and Comparative Example 5 are shown in FIGS. 1 and 2, respectively.

  The average value, specific gravity, bending elastic modulus, bending strength, and dynamic viscoelasticity of the foam diameter of the samples obtained in Examples 1 to 4 and Comparative Examples 1 to 6 were measured. The measurement results are shown in Table 2. In addition, the average value of foam diameter, specific gravity, bending elastic modulus, bending strength, and dynamic viscoelasticity measurement were measured by the following conditions and measuring methods.

-Average value of foam diameter After copying only the outline of bubbles from a cross-sectional SEM image of the foam onto a film, etc., and converting it to image data with a scanner, etc., the area of the bubbles was imaged and the equivalent circle diameter was calculated. . The average equivalent circle diameter calculated for 50 or more bubbles per sample was taken as the average foam diameter.

-Specific gravity The weight of the molded body in air and in water was measured, the density was determined by the Archimedes method, and the specific gravity was determined by dividing by the density value of water.

Bending elastic modulus and bending strength The bending elastic modulus and bending strength of the molded body were measured at a deformation rate of 5 mm / min (load cell 100N). A universal testing machine Autograph AG-5000E [AG-X refreshed] (manufactured by Shimadzu Corporation) was used as a measuring instrument.

  Moreover, about Examples 1-4 and Comparative Examples 1-6, the graph which plotted specific gravity on the horizontal axis and the bending elastic modulus on the vertical axis | shaft is shown in FIG. In FIG. 3, Δ is Examples 1-2, ◇ is Examples 3-4, ▲ is Comparative Example 1, ♦ is Comparative Example 2, ■ is Comparative Example 3, □ is Comparative Examples 4-5, and ○ is Comparative Each of Example 6 is plotted.

  And about Examples 1-4 and Comparative Examples 1-6, the graph which plotted specific gravity on the horizontal axis and bending strength on the vertical axis | shaft is shown in FIG. In FIG. 4, Δ is Examples 1-2, ◇ is Examples 3-4, ▲ is Comparative Example 1, ◆ is Comparative Example 2, ■ is Comparative Example 3, □ is Comparative Examples 4-5, and ○ is Comparative. Each of Example 6 is plotted.

Dynamic viscoelasticity measurement ASA-modified microfibrillated plant fiber / PE resin of Example 1, PE resin of Comparative Example 4 and microfibrillated plant fiber / PE resin of Comparative Example 6 before foaming The test piece was set in a dynamic viscoelasticity measuring device “ARES” manufactured by TA Instruments Japan Co., Ltd., and the storage elastic modulus (G ') And loss modulus (G ") were measured.

  FIG. 5 shows a graph in which the storage elastic modulus (G ′) versus temperature of Example 1, Comparative Example 4, and Comparative Example 6 is plotted. FIG. 6 shows the results of Example 1, Comparative Example 4, and Comparative Example 6. The graph which plotted the loss elastic modulus (G ") with respect to temperature is shown.

<Discussion>
1 and 2, it can be seen that when a resin composition of ASA-modified microfibrillated plant fiber and polyethylene is foamed, a dense foam having a small foam diameter is formed. Such a foam having a small foam diameter is considered to be obtained by suppressing the expansion of the foam diameter because the ASA-modified microfibrillated plant fiber is uniformly mixed in polyethylene in the resin composition before foaming. It is done.

  From Table 2, FIG. 3 and FIG. 4, Examples 1-4 in which ASA-modified microfibrillated plant fibers and polyethylene were combined and further foamed were Comparative Examples 1 in which ASA-modified microfibrillated plant fibers and polyethylene were not foamed. And compared with the comparative example 3 of non-foamed polyethylene, the specific reduction of specific gravity was seen and it turns out that weight reduction has been achieved. Moreover, compared with Comparative Examples 4-5 in which Examples 1-4 foamed only polyethylene, the bending elastic modulus and bending strength improved. From this, the ASA-modified microfibrillated plant fiber is uniformly dispersed in polyethylene and a dense foam is formed by the ASA-modified microfibrillated plant fiber, and further, as a filler by the ASA-modified microfibrillated plant fiber. It is considered that the reinforcing effect was sufficiently exhibited. And Examples 3-4 with a high content rate of ASA modified | denatured microfibrillated plant fiber compared with Examples 1-2 further increase the reinforcement effect, and the bending elastic modulus and bending strength are improving.

  Furthermore, in the foam of the unmodified microfibrillated plant fiber of Comparative Example 6 and polyethylene, the flexural modulus and flexural strength are inferior although the specific gravity is higher than that of Example 1. This result is considered that the unmodified microfibrillated plant fiber is not sufficiently dispersed in polyethylene and the mechanical strength is lowered.

  Furthermore, from FIG. 5 and FIG. 6, Example 1 shows that in the sheet-like molded product before foaming, ASA-modified microfibrillated plant fibers are uniformly mixed as a filler in polyethylene. It can be seen that the viscosity and elasticity values in the molten state are significantly higher than those of Comparative Example 4 in which only polyethylene is used, compared to Comparative Example 6 using fibrillated plant fibers. Therefore, it turns out that the foam diameter of the obtained foam is small and can be foamed densely.

Claims (10)

At least one component (A) selected from the group consisting of thermoplastic resin and rubber, and microfibrillated plant fiber (B) esterified with alkyl or alkenyl succinic anhydride
Foam containing. The content of the modified microfibrillated plant fiber (B) esterified with alkyl or alkenyl succinic anhydride is 0.1 to 200 parts by mass with respect to 100 parts by mass of the component (A). The foam described. The foam according to claim 1 or 2, wherein the specific gravity is 0.03 to 0.9. The foam according to any one of claims 1 to 3, wherein an average value of the foam diameter in the foam is 0.1 to 100 µm. The foam according to any one of claims 1 to 4, wherein the component (A) is a polyolefin resin. The foam according to any one of claims 1 to 5, wherein the component (A) is polyethylene. (1) Mixing at least one component (A) selected from the group consisting of a resin and rubber with a modified microfibrillated plant fiber (B) esterified with alkyl or alkenyl succinic anhydride, and / or resin and / or A method for producing a foam, comprising a step of preparing a rubber composition, and (2) a step of foaming a resin and / or a rubber composition. The step of foaming the resin and / or rubber composition in step (2) encloses the resin and / or rubber composition and an inert gas in a high-pressure vessel, and impregnates the resin and / or rubber composition with the inert gas. The method for producing a foam according to claim 7, wherein the resin and / or the rubber composition is foamed by rapidly reducing pressure. The method for producing a foam according to claim 8, wherein the inert gas is carbon dioxide. The method for producing a foam according to claim 8 or 9, wherein the pressure in the high-pressure vessel is 1 to 30 MPa, and the pressure after rapid decompression is 0.5 x 10 ⁵ to 2 x 10 ⁵ Pa.

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