Additive material for plastic, resin composite material and method for manufacturing them

Abstract

To provide a pulp-fiber-based plastic additive which can be simply manufactured, and can improve mechanical strength of a resin composite material by addition as a base, a resin composite material containing the additive material, and a method for manufacturing them.SOLUTION: Pulp used while being mixed with plastic is surface-treated pulp where an acid-modified resin layer composed of an acid-modified resin is formed in at least a part of a fiber surface. Since the pulp can improve compatibility with plastic having hydrophobicity on its surface, the strength of the plastic can be improved by adding the pulp together with the plastic and heating and kneading the pulp.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a plastic additive, a resin composite, and a method for producing the same, and more particularly to a plastic additive that is used by mixing with plastic, a resin composite containing the additive, and a method for producing the same. [Background technology]

[0002] Composite materials made by mixing natural wood materials (such as wood flour and pulp) with plastic (for example, a composite of wood flour and plastic is called WPC) are used for exterior applications because they have higher weather resistance than wood and can be given a more wood-like feel than plastic or metal. In recent years, composite materials have been attracting attention from the perspective of reducing the amount of plastic used in plastic product fields other than exterior applications, i.e., from the perspective of eliminating plastic. In addition, the range of products that can be used as composite materials is wide, and the required properties are also diverse.

[0003] In such composite materials, interfacial adhesion between the hydrophilic wood flour and the hydrophobic plastic is crucial for maximizing the reinforcing effect and other benefits of wood flour addition. Therefore, much research has been conducted on the compatibility of wood flour and plastic. For example, various resins (compatibilizing resins) that improve the compatibility between the two (wood flour and plastic) have been studied (e.g., Patent Documents 1 and 2). Maleic acid-modified resins, which possess both hydrophilic and hydrophobic properties, are commonly used as such compatibilizing resins. Furthermore, because pulp, a wood-based material, is more fibrous than wood flour, research aimed at improving the strength of composite materials has been ongoing. However, because pulp fibers are bulky and have a large specific surface area, simply mixing the pulp with a compatibilizing resin during heat mixing makes it difficult to adequately compatibilize the pulp fibers. As a result, aggregation of the pulp fibers occurs during heat mixing, resulting in insufficient reinforcing strength.

[0004] Therefore, in recent years, techniques have been proposed to improve the compatibility of fibrous wood materials (for example, Patent Documents 3 and 4). Patent Documents 3 and 4 describe the use of chemically modified cellulose fibers in which hydrophilic hydroxy groups present on the surface of cellulose fibers are substituted with hydrophobic functional groups (for example, carbamate groups). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2003-113280 [Patent Document 2] International Publication No. 2022 / 014539 [Patent Document 3] Japanese Patent Application Publication No. 2023-142300 [Patent Document 4] Japanese Patent Application Publication No. 2019-01876 Summary of the Invention [Problem to be solved by the invention]

[0006] However, the techniques of Patent Documents 3 and 4 require special facilities for chemically modifying cellulose fibers, and furthermore, the production of chemically modified cellulose fibers is extremely complicated and expensive. For this reason, there is a need for the development of a pulp-plastic composite (resin composite) that can use low-cost pulp, improve compatibility in a simple manner, and provide appropriate reinforcing strength.

[0007] In view of the above circumstances, the present invention aims to provide a pulp fiber-based plastic additive that can be easily manufactured and that can improve the mechanical strength of resin composites when added, a resin composite containing this additive, and methods for manufacturing these. [Means for solving the problem]

[0008] As a result of extensive research into how to solve the above problems, the present inventors discovered that the above problems could be solved by using pulp whose fiber surfaces have been surface-treated with a resin, leading to the completion of the present invention.

[0009] The plastic additive of the first invention is pulp that is mixed with plastic and used, and is characterized in that the pulp is surface-treated pulp in which an acid-modified resin layer made of an acid-modified resin is formed on at least a portion of the fiber surface. The plastic additive of the second invention is characterized in that the acid-modified resin is a resin having functional groups that chemically interact with the hydroxyl groups of the pulp and having polymer chains that exhibit intermolecular compatibility with plastics. The third invention is a plastic additive according to the first or second invention, characterized in that the surface-treated pulp has a coating rate of an acid-modified resin layer of 0.25 or less, and the coating rate is a value calculated by adding a predetermined amount of the surface-treated pulp to water at room temperature, mixing, and leaving it to stand for 24 hours, and then calculating the mass ratio of the surface-treated pulp that sinks in the water to the surface-treated pulp mixed in the water (mass of the surface-treated pulp that sinks / mass of the surface-treated pulp mixed in water). The plastic additive of the fourth invention is characterized in that, in the second invention, the functional group is one or more selected from the group consisting of a carboxy group, an amino group, an acid anhydride group, an amide group, an aldehyde group, a nitro group, a phosphate group, and a nitrate ester group. The plastic additive of the fifth invention is characterized in that, in the second invention, the polymer chain is selected from the group consisting of polyethylene, polypropylene, polystyrene, AS, ABS, polyester, polyurethane, phenolic resin, epoxy resin, urea resin, melamine resin, and low molecular weight resins thereof. A sixth aspect of the present invention is an additive for plastics according to the first or second aspect of the present invention, characterized in that the acid-modified resin has a melting point of 220° C. or less. A plastic additive according to a seventh aspect of the present invention is characterized in that, in the first or second aspect of the present invention, the acid-modified resin is a maleic acid-modified resin and / or an acrylic acid-modified resin. The resin composite material of the eighth invention comprises a plastic and a plastic additive, and is characterized in that the plastic additive is surface-treated pulp having an acid-modified resin layer formed on at least a portion of the fiber surface. The resin composite of the ninth invention is characterized in that, in the eighth invention, the acid-modified resin has functional groups that chemically interact with hydroxyl groups on the pulp surface of the surface-treated pulp, and has polymer chains that exhibit intermolecular compatibility with plastics. The resin composite material of the 10th invention is characterized in that, in the 8th or 9th invention, the surface-treated pulp has a coating rate of an acid-modified resin layer of 0.25 or less, and the coating rate is a value calculated by adding a predetermined amount of the surface-treated pulp to water at room temperature, mixing, and leaving it to stand for 24 hours, and then calculating the mass ratio of the surface-treated pulp that sinks in the water to the surface-treated pulp mixed in the water (mass of the surface-treated pulp that sinks / mass of the surface-treated pulp mixed in water). The resin composite material of the eleventh invention is the resin composite material of the eighth or ninth invention, characterized in that it contains wood flour, the content of the surface-treated pulp relative to the wood flour is 0.1 or more in mass ratio (mass of surface-treated pulp / mass of wood flour), and the total content of the wood flour and the surface-treated pulp relative to the plastic is 4.0 or less in mass ratio ((total mass of wood flour + surface-treated pulp) / mass of plastic). The resin composite material of the twelfth invention is the resin composite material of the eighth or ninth invention, characterized in that the reduction rate (%) of elongation at break after absorbing water for 70 days is 15% or less. The resin composite material of the thirteenth invention is the resin composite material of the eighth or ninth invention, characterized in that the viscosity increase at a shear rate of 132 (1 / s) is two times or less. The method for producing a plastic additive of the 14th invention is a method for producing a plastic additive as described in claim 1, which is used by mixing it with plastic, and is characterized in that it includes a surface treatment step in which pulp and an acid-modified resin are heated and kneaded to form an acid-modified resin layer on the surface of the pulp fibers, and in the surface treatment step, the mixing ratio of the acid-modified resin is adjusted to be 1 part by mass or more and 25 parts by mass or less per 100 parts by mass of the pulp. The method for producing a resin composite material of the 15th invention includes a compounding step of heating and kneading plastic, pulp, and a compatibilizing resin, and is characterized in that the pulp is surface-treated pulp having a resin layer on the fiber surface. [Effects of the Invention]

[0010] The plastic additive of the present invention can improve compatibility with plastics having hydrophobic surfaces, and by adding the additive to a plastic and kneading it under heat, the strength of the plastic can be improved. Furthermore, the plastic additive of the present invention can be appropriately produced using the method for producing the plastic additive of the present invention. According to the resin composite material of the present invention, the ST pulp fibers are uniformly dispersed in the plastic, which improves fluidity during heating. Furthermore, the resin composite material of the present invention can be appropriately produced by using the method for producing the resin composite material of the present invention. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a schematic production flow diagram of the plastic additive of this embodiment, the resin composite material of this embodiment, and wood plastic (WPC) of this embodiment. [Figure 2] 1A and 1B are schematic diagrams of ST pulp fiber, which is a plastic additive of this embodiment; (A) is a schematic diagram of a state in which an acid-modified resin layer is provided on the entire surface of the pulp fiber; (B) is a schematic diagram of a state in which there is a part of the surface of the pulp fiber where the acid-modified resin layer is not provided; and (C) is a schematic diagram of a state in which an acid-modified resin layer is provided on a part of the surface of the pulp fiber. [Figure 3] FIG. 1A is a schematic explanatory diagram of a resin composite material of the present embodiment, and FIG. 1B is a schematic explanatory diagram of a conventional resin composite material. [Figure 4] These are fiber surface images observed using an electron microscope. (A) is an image of the fiber surface of N pulp, and (B) is an image of the fiber surface of ST pulp. [Figure 5] FIG. 2 is a diagram showing the results of immersing ST pulp and N pulp, which are plastic additives of the present embodiment, in water. [Figure 6] FIG. 1A is a graph showing the relationship between shear rate and viscosity of the resin composite material of this embodiment, and FIG. 1B is a graph showing the relationship between shear rate and viscosity of the resin composite material to which N pulp has been added. [Figure 7] FIG. 1 is a diagram comparing the storage modulus of the resin composite material of the present embodiment, a resin composite material to which N pulp is added, and a resin composite material to which no pulp is added. [Figure 8] FIG. 1 is a graph comparing the relationship between the substitution rate of various pulps for wood flour and the tensile strength in the resin composite material of the present embodiment and a resin composite material to which N pulp has been added. [Figure 9] FIG. 1 is a graph comparing the relationship between the substitution rate of various pulps for wood flour and Young's modulus in the resin composite material of the present embodiment and a resin composite material to which N pulp has been added. [Figure 10] FIG. 1 is a graph comparing the relationship between the substitution rate of various pulps for wood flour and the breaking elongation in the resin composite material of the present embodiment and a resin composite material to which N pulp has been added. [Figure 11] FIG. 1 is a graph comparing the relationship between water immersion time and change in water absorption rate over time for the resin composite material of the present embodiment, a resin composite material with N pulp added, and a resin composite material with no pulp added. [Figure 12] FIG. 1 is a graph comparing the relationship between the substitution ratio of various pulps to wood flour and the rate of decrease in breaking elongation due to water absorption in the resin composite material of the present embodiment and a resin composite material to which N pulp has been added. DETAILED DESCRIPTION OF THE INVENTION

[0012] Next, an embodiment of the present invention will be described with reference to the drawings. The plastic additive of this embodiment is pulp that is mixed with plastic. This pulp is characterized in that a resin layer made of an acid-modified resin (hereinafter referred to as an acid-modified resin layer) is formed on the surface of the pulp fibers. That is, the plastic additive of this embodiment is surface-treated pulp (hereinafter referred to as ST pulp) in which an acid-modified resin layer is formed on the surface of the pulp fibers. In other words, ST pulp is pulp whose surface is modified by an acid-modified resin. The resin composite of this embodiment is formed by heat-kneading this ST pulp and plastic, and the natural fiber composite is formed by heat-molding the resin composite of this embodiment by injection molding or the like. The concept of natural fiber composite materials includes pulp and plastic composites and wood plastic (WPC). In this specification, pulp whose pulp fiber surfaces have not been subjected to a surface treatment is referred to as N pulp.

[0013] (Plastic additive and manufacturing method thereof according to this embodiment) First, a method for producing an additive for plastics according to this embodiment (hereinafter referred to as the method for producing the additive) will be described.

[0014] As shown in the flow diagram in Figure 1, the manufacturing method of this additive includes a surface treatment step. This surface treatment step is a step for forming an acid-modified resin layer on the surface of the pulp fibers. Specifically, it is a step in which pulp and an acid-modified resin are mixed and kneaded while being heated.

[0015] First, the pulp and acid-modified resin used in the surface treatment step will be described.

[0016] Pulp as used herein refers to cellulose fibers extracted from plant raw materials through mechanical or chemical processing, with each individual fiber being referred to as a pulp fiber, and the aggregate of these fibers being pulp. Pulp as used herein also includes fine fibers (e.g., fibers with a fiber width of several nm to several tens of nm or several tens of nm to several hundreds of μm, see FIG. 3(A)) that are generated when plant raw materials are chemically or physically pulverized to extract cellulose fibers. Each individual pulp fiber having an acid-modified resin layer formed on its surface is an ST pulp fiber, and the aggregate of these fibers is ST pulp.

[0017] The type of pulp is not particularly limited, and may include one or more types selected from the group consisting of the following types. In other words, it may be one type or a mixture of two or more types. Examples of such pulps include chemical pulps made from wood, such as hardwood pulp (hardwood kraft pulp (LKP)), softwood pulp (softwood kraft pulp (NKP)), sulfite pulp (SP), dissolving pulp (DP), soda pulp (AP), unbleached kraft pulp (UKP), and oxygen bleached kraft pulp (OKP); semi-chemical pulps, such as semi-chemical pulp (SCP) and chemi-groundwood pulp (CGP); and mechanical pulps, such as groundwood pulp (GP) and thermomechanical pulp (TMP, BCTMP). Other examples include cotton pulps such as cotton linter and cotton lint, which are made from plant or animal sources; non-wood pulps such as hemp, straw, and bagasse; and cellulose, chitin, and chitosan isolated from sea squirts and seaweed. Another example is recycled pulp, which is made from pulp that has already been made into paper. This includes waste paper generated during the manufacture of household paper, such as milk cartons and kitchen paper, as well as deinked pulp made from newspapers, magazines, cardboard, etc. In particular, broke paper generated during product changeover in the papermaking process in papermaking is a dry material, unused material with little deterioration of pulp fibers, and a high-quality material with stable quality, making it a preferable raw material for the plastic additive of this embodiment. Furthermore, since most of this broken paper is simply recycled as waste paper pulp, which is a raw material for paper products, using it as a raw material for the plastic additive of this embodiment will increase added value and enable it to be used for new applications in the paper industry (for example, as a raw material for additives for wood plastics).

[0018] There are no particular limitations on the acid-modified resin, so long as it is a resin that can modify the fiber surface of pulp and improve compatibility with plastics.

[0019] For example, the acid-modified resin may have both hydrophilic and hydrophobic properties. Specifically, from the viewpoint of bonding to the surface of pulp fibers, the acid-modified resin is preferably one in which functional groups having chemical interactions with hydroxy groups on the cellulose surface, such as ester bonds, are grafted onto the polymer molecules. Furthermore, from the viewpoint of compatibility with plastics of the resin composite material (the resin composite material of this embodiment) described below, it is preferable that the acid-modified resin have polymer chains that are highly compatible with plastics. In other words, the functional groups have chemical interactions with hydroxy groups in cellulose, and the polymer chains described below have molecular entanglement with resin components such as plastics (i.e., intermolecular compatibility).

[0020] Examples of the functional group include a carboxy group contained in a carboxylic acid, a carboxylic acid anhydride, or the like, an amino group contained in an aniline, or one or more groups selected from the group consisting of an acid anhydride group, an amide group, an aldehyde group, a nitro group, a phosphate group, a nitrate ester group, and the like. The polymer chain may be one or more selected from the group consisting of polyethylene, polypropylene, polystyrene, acrylonitrile-styrene resin (AS), acrylonitrile-butadiene-styrene copolymer (ABS), polyester (polylactic acid, PET, etc.), polyurethane, phenolic resin, epoxy resin, urea resin, melamine resin, etc., and low molecular weight resins such as oligomers thereof. This polymer chain is involved not only in terms of intermolecular compatibility with plastics but also in flow properties that affect coatability. However, while a low molecular weight results in high flow and improved coatability, there is a concern that mechanical properties may be reduced. Although it is difficult to define the fluidity by molecular weight because there are various types of polymer chains, it can be determined by the melting point, which is preferably 220°C or lower, more preferably 180°C or lower, and even more preferably 150°C or lower.

[0021] Examples of acid-modified resins that satisfy both of the above-mentioned requirements include maleic acid-modified resins and acrylic acid-modified resins, which have functional groups grafted onto the polymer chain that chemically interact with the hydroxyl groups in the cellulose, and are compatible with plastics.

[0022] The acid-modified resin includes one or more resins selected from the group consisting of resins having the above-mentioned functions. That is, the acid-modified resin may be one type or a mixture of two or more types. The acid-modified resin may be the same type of resin as the compatibilizing resin (for example, acid-modified resin) added when preparing the resin composite material described below.

[0023] Next, the step of heat-kneading the above-mentioned pulp and the resin containing the acid-modified resin will be described.

[0024] In this step, the equipment used for the heat kneading is not particularly limited as long as it can coat the molten acid-modified resin on the surface of the pulp fibers, i.e., it is not particularly limited as long as it can coat the surface of the pulp fibers with the acid-modified resin so that an acid-modified resin layer (see FIG. 2) can be formed on the surface of the pulp fibers when cooled. For example, a heating mixer generally used in kneading resins, a high-speed fluid mixer (a so-called Henschel mixer), an extrusion molding machine, etc. In particular, the use of a Henschel mixer is preferable because it can suppress aggregation of pulp particles during kneading, thereby improving the uniformity of the surface treatment.

[0025] The conditions for heating and kneading (for example, temperature and rotation speed) are not particularly limited as long as the acid-modified resin can be melted and the pulp fibers can be coated with the molten acid-modified resin. For example, the heating temperature is adjusted so that the acid-modified resin to be mixed can be melted and the pulp does not undergo thermal degradation, specifically, from 120°C to 250°C, preferably from 150°C to 220°C, and more preferably from 180°C to 200°C. The rotation speed is also not particularly limited. The rotation speed is adjusted so that the molten acid-modified resin flows smoothly within the kneading device and the pulp does not aggregate. The higher the shear within the device, the better the coating properties (i.e., surface treatment performance). The maximum rotation speed varies depending on the capacity of the kneading device, the shape of the kneading blades, etc. For example, when using a 10 L Henschel mixer, the rotation speed is adjusted to 500 rpm or higher. This value is preferably adjusted to 1000 rpm or higher, and more preferably 1500 rpm or higher.

[0026] In this specification, "coating the surface of pulp fibers to form an acid-modified resin layer" means that an acid-modified resin layer is formed on at least a portion of the surface of the pulp fibers. In other words, this concept includes not only a state in which the entire surface of surface-treated pulp (ST pulp) having an acid-modified resin layer formed on the fiber surface obtained by the manufacturing method of this additive is covered with an acid-modified resin layer (see FIG. 2(A)), but also a state in which the acid-modified resin layer is formed on only a portion of the surface (for example, a state in which the acid-modified resin layer is formed so as to be scattered on the surface of the pulp fiber) (see FIG. 2(C)), and a state in which the acid-modified resin layer is formed so that a portion of the surface of the pulp fiber is exposed from the surface where the acid-modified resin layer is formed (see FIG. 2(B)).

[0027] In the heat kneading in the surface treatment step, the blending ratio of pulp and resin is adjusted as follows. By increasing the proportion of this acid-modified resin, the area of ​​the pulp fiber surface that is coated can be increased. In other words, the proportion of the acid-modified resin is not particularly limited as long as it is adjusted so that the surface of the pulp fiber can be appropriately modified. For example, the amount of the acid-modified resin is adjusted to 1 part by mass or more per 100 parts by mass of pulp. From the viewpoint of increasing the treated surface area of ​​the pulp fiber, the blending ratio of the acid-modified resin is adjusted to preferably 1 part by mass or more, more preferably 4 parts by mass or more. The state in which the surface of the pulp fiber is modified by the acid-modified resin (the state in which the surface of the pulp fiber is surface-treated) is shown, for example, in the photograph of the surface observation of ST pulp in Figure 4 of the Examples. The enlarged area in this photograph (the area where the surface is smooth) is the area where the acid-modified resin layer is formed on the surface of the pulp fiber by the acid-modified resin.

[0028] The surface of the pulp fiber is "appropriately modified," for example, when surface-treated pulp (ST pulp) having an acid-modified resin layer formed on the surface of the pulp fiber is mixed with water at room temperature and left to stand for 24 hours, and the proportion of ST pulp that settles in the water is 0.25 or less in mass ratio relative to the ST pulp mixed in the water (see Figure 5 in the Examples). In other words, appropriately modified ST pulp has a fiber surface formed with an acid-modified resin layer, and the coating ratio is adjusted to 0.25 or less. This coating ratio is expressed as a value calculated by adding a predetermined amount of ST pulp (surface-treated pulp) to water at room temperature, mixing, and leaving it to stand for 24 hours, and then calculating the proportion of ST pulp (surface-treated pulp) that settles in the water relative to the ST pulp (surface-treated pulp) mixed in the water (mass of ST pulp (surface-treated pulp) that settles / mass of ST pulp (surface-treated pulp) mixed in the water). The coating rate of the ST pulp is not particularly limited, but is preferably adjusted to 0.2 or less, more preferably 0.15 or less, and even more preferably 0.1 or less.

[0029] As described above, by using this additive manufacturing method, it is possible to produce ST pulp having an acid-modified resin layer on the surface of the pulp fiber, as shown in Figure 2. The acid-modified resin that forms this acid-modified resin layer has both hydrophilic and hydrophobic properties. For this reason, in the acid-modified resin layer formed on the surface of the pulp fibers, many of the modified functional group portions (hydrophilic portions) bond with the hydroxyl groups on the surface of the pulp fibers, and many of the polymer chains (hydrophobic portions) can be arranged so that they come into contact with the plastic they are compounding (i.e., on the surface side of the acid-modified resin layer). In other words, the plastic additive of this embodiment is ST pulp that has been modified so that the surface properties of the pulp fibers shift from hydrophilic to hydrophobic or hydrophobic, and therefore has improved compatibility with plastics that have hydrophobic surfaces compared to ordinary pulp. Furthermore, when this ST pulp is heated and kneaded with plastic, it can be uniformly dispersed in the molten plastic, improving adhesion to the plastic. Therefore, if ST pulp is added together with plastic in the manufacturing method of the resin composite material of this embodiment described below, the ST pulp can be arranged in a uniformly dispersed state in the resin (plastic), and the ST pulp fibers can be in close contact with the surrounding plastic. This can improve the strength of the resin composite material of this embodiment manufactured. In other words, the plastic additive (ST pulp) of this embodiment manufactured using this additive manufacturing method is very suitable as an additive that can improve the strength of plastic by adding it to plastic and heating and kneading it.

[0030] It is preferable to adjust the amount of the acid-modified resin to be mixed in the surface treatment step so that it is not too much relative to the pulp. This is because the acid-modified resin having the above-described properties has a smaller molecular weight and weaker strength than the plastic in the resin composite (the resin composite of the present embodiment) described below, and therefore, if the amount of acid-modified resin in the resin composite becomes too large, it tends to have a negative effect on the reinforcing effect of the resin composite. In other words, the addition of an acid-modified resin to the additive manufacturing method can improve the modification level of the ST pulp, and can improve adhesion to plastic in the resin composite (the resin composite of this embodiment), but it also reduces the reinforcing effect of the resin composite, resulting in a trade-off. Therefore, when considering the production of a resin composite material using ST pulp, it is preferable to adjust the upper limit of the compounding ratio of the acid-modified resin to a level that can adequately exert a reinforcing effect on the resin composite material. For example, the upper limit of the amount of the acid-modified resin is adjusted to 25 parts by mass or less per 100 parts by mass of pulp, preferably 15 parts by mass or less, and more preferably 10 parts by mass or less.

[0031] When a compatibilizing resin is added in the preparation of a resin composite to which a hydrophilic material such as wood flour (for example, wood flour, calcium carbonate, talc, or other hydrophilic inorganic materials) is subsequently added, the acid-modified resin may be the same type of resin as the compatibilizing resin. In this case, from the viewpoint of compatibility between the two (the acid-modified resin layer of ST pulp and the compatibilizing resin), the advantage is obtained that the dispersibility of the pulp with the fibers or fillers in the resin composite can be improved.

[0032] Furthermore, the plastic additive of this embodiment can be easily produced using existing kneading equipment, etc., as described above, and the surface of the pulp fiber can be easily modified to be hydrophobic. This eliminates the need for complicated chemical modification treatments, such as replacing hydroxyl groups on the surface of the pulp fiber with hydrophobic functional groups, as in conventional techniques, and offers the advantage of significantly reducing production costs.

[0033] (Resin composite material and manufacturing method thereof according to this embodiment) Next, the resin composite material of this embodiment and its manufacturing method will be described. As described below, the resin composite of this embodiment can be produced by adding the ST pulp (the plastic additive of this embodiment) obtained by the additive manufacturing method described above together with plastic and then performing a heat-kneading process. Moreover, because the ST pulp is added together with the plastic, the ST pulp fibers can be uniformly dispersed and arranged in the plastic. This makes it possible to provide a resin composite with dramatically improved strength.

[0034] The resin composite material of this embodiment will be simply referred to as a resin composite material hereinafter. Furthermore, uniformly dispersing ST pulp fibers in a resin composite or in the plastic of the resin composite means uniformly dispersing and arranging the ST pulp fibers in the plastic that forms the resin composite (see Figure 3(A)). Furthermore, Figure 3(B) is a model dispersion diagram of a resin composite manufactured using N pulp that has not been surface-treated as used in conventional technology, showing the state of N pulp fibers arranged in the plastic of this resin composite.

[0035] As shown in FIG. 1, the method for producing a resin composite material of this embodiment (hereinafter referred to as the present composite material production method) is a method for producing a resin composite material of this embodiment, and includes a compounding process (compounding process) for adding desired functions to plastics. This compounding step involves blending plastic and components for imparting desired functions to the plastic (for example, strength, woody texture, etc.), and then heating and kneading the mixture. This composite manufacturing method is characterized by the inclusion of ST pulp in the mixed components. In other words, this composite manufacturing method is characterized by the addition of surface-treated pulp (ST pulp), in which the surface of the pulp fiber has been coated with an acid-modified resin in advance, to plastic. The compounded powder, spherical, rice-shaped, cylindrical, or lumpy pellets obtained after the heat kneading are the resin composite material of this embodiment. The pellets obtained here are also sometimes called compounds.

[0036] The scheme including the surface treatment step shown in Figure 1 is the additive manufacturing method of this embodiment, and the resulting ST pulp is the plastic additive of this embodiment, while the scheme including the compounding step shown in Figure 1 is the composite manufacturing method of this embodiment.

[0037] As shown in Figure 1, the components used in this composite manufacturing method can include, in addition to ST pulp, wood materials such as wood flour used in the production of general wood plastics (WPC), compatibilizing resins to improve compatibility, pigments to add color, etc. Furthermore, inorganic materials such as calcium carbonate and talc, glass fibers, carbon fibers, etc. may also be added to the components.

[0038] The equipment used for the heat kneading in this composite manufacturing method can be a heat mixer or extruder that is generally used for kneading resins. The conditions (for example, temperature and rotation speed) for heating and kneading in such equipment are not particularly limited as long as the plastic can be melted and appropriately kneaded with the mixing components. For example, the heating temperature is adjusted so that the plastic can be melted and the ST pulp and wood materials do not undergo thermal degradation. There are no particular restrictions on the rotation speed. The conditions for heating and kneading can be the same as those in the additive manufacturing method described above, and therefore will not be described here.

[0039] The plastics used include thermoplastic resins with a melting point of 250°C or less. Specific examples include polypropylene, polyethylene, ABS, polyvinyl chloride, polystyrene, and polylactic acid. In particular, olefin plastics such as polyethylene and polypropylene are preferred from the viewpoint of versatility, as they are used in many products. The plastic includes one or more types selected from the group consisting of these resins, that is, it may be one type or a mixture of two or more types.

[0040] In addition to the above-mentioned ST pulp, the wood material may also contain wood flour, pulp, natural fibers such as hemp and flax, etc. In other words, the wood material may contain, in addition to ST pulp, one or more members selected from the group consisting of these members. When wood flour is used, for example, wood flour of a size that passes through a predetermined sieve can be used. The size of the sieve opening is not particularly limited as long as it is one that is used in preparing general WPC. For example, a sieve with an opening of 5 mm or even smaller, such as about 1 mm, may be used.

[0041] The compatibilizing resin is preferably a resin having both hydrophilic and hydrophobic properties, such as an acid-modified resin, a chlorinated resin, etc. In particular, from the viewpoint of compatibilization with plastics, it is preferable to use a resin having a polymer chain that is highly compatible with the plastic to be composited.

[0042] In this composite manufacturing method, the blending ratio of each component is adjusted to obtain appropriate strength, texture, etc. depending on the application.

[0043] The blending ratio of each component corresponds to the content of each component in the resulting resin composite (the resin composite of this embodiment). For example, if the blending ratio of plastic is 10% by mass or more and 90% by mass or less of the total amount of components, the content of plastic in the resin composite can be interpreted as 10% by mass or more and 90% by mass or less of the total mass of the resin composite.

[0044] For example, from the viewpoint of molding flowability, the lower limit of the blending ratio of the plastic relative to the total mass of all components (plastic and mixed components) is preferably 10% by mass or more, more preferably 20% by mass or more, and even more preferably 30% by mass or more. Also, from the viewpoint of reducing petroleum-based resources, the upper limit is preferably 90% by mass or less, more preferably 85% by mass or less, even more preferably 80% by mass or less, still more preferably 75% by mass or less, and even more preferably 50% by mass or less.

[0045] For example, the blending ratio of the wood material is preferably 5% by mass or more, more preferably 10% by mass or more, and even more preferably 15% by mass or more, based on the total mass of all components (plastic and mixed components) from the viewpoints of imparting a woody texture and improving mechanical properties. Also, from the viewpoints of water resistance and molding fluidity, the blending ratio is preferably 70% by mass or less, more preferably 60% by mass or less, and even more preferably 50% by mass or less.

[0046] For example, from the viewpoint of reinforcing properties, the blending ratio of ST pulp is preferably 1% by mass or more (0.01 or more in mass ratio) of the total mass of all components (plastic and mixed components), more preferably 3% by mass or more, even more preferably 5% by mass or more, still more preferably 10% by mass or more, still more preferably 13% by mass or more, and even more preferably 20% by mass or more. The upper limit is the same as that of the wood material described above.

[0047] In particular, when the wood material is made of ST pulp and wood flour, the following adjustment may be made. For example, the blending ratio of ST pulp is adjusted, in relation to wood flour, so that the mass ratio of ST pulp / wood flour is 0.1 or more, from the viewpoint of reinforcing effect. This value is more preferably 0.25 or more, even more preferably 0.5 or more, even more preferably 1.0 or more, even more preferably 2.0 or more, even more preferably 3.0 or more, and even more preferably 4.0 or more. Furthermore, the mass ratio of wood flour / ST pulp is adjusted so that it is 10 or less. This value is preferably 6 or less, even more preferably 5 or less, even more preferably 4 or less, even more preferably 2.5 or less, even more preferably 1.5 or less, even more preferably 1 or less, and even more preferably 0.5 or less.

[0048] Furthermore, the blending ratio of the above-mentioned wood material (when composed of wood flour and ST pulp) to the plastic is adjusted so that the mass ratio ((wood flour + ST pulp) / plastic) of the wood material is 4.0 or less, from the viewpoint of fluidity and dispersibility. This value is preferably 2.0 or less, and more preferably 1.0 or less. To further improve fluidity, this value is preferably 0.95 or less, more preferably 0.7 or less, even more preferably 0.5 or less, and even more preferably 0.4 or less. Note that the fluidity is improved by reducing this value. Furthermore, the blending ratio of the above-mentioned wood material (when consisting of wood flour and ST pulp) in relation to the plastic is preferably such that the mass ratio (plastic / ST pulp) is 20 or less, more preferably 15 or less, even more preferably 14 or less, even more preferably 10 or less, even more preferably 7 or less, even more preferably 6 or less, even more preferably 4 or less, and even more preferably 3 or less.

[0049] The compatibilizing resin is a resin that improves the compatibility of wood materials with plastics, improving the dispersibility of wood materials in plastics. However, if the blending ratio is too high, the interfacial strength between the wood material and plastic decreases, limiting the reinforcing effect of the resin composite. Therefore, for example, from the viewpoint of the above-mentioned dispersibility and interfacial strength, the blending ratio of the compatibilizing resin is adjusted to 8% by mass or less (0.08% by mass or less) of the total mass of all components (plastic and mixed components). This value is preferably 5% by mass or less, more preferably 4% by mass or less, and even more preferably 3% by mass or less. Furthermore, when dispersibility and interfacial strength are more particularly taken into consideration, this value is preferably 2% by mass or less (0.02% by mass or less), more preferably 1.6% by mass or less, even more preferably 1% by mass or less, and even more preferably 0.5% by mass or less. In particular, in relation to wood materials (excluding ST pulp, which has already been surface treated), the compatibilizing resin / wood material (excluding ST pulp) mass ratio is adjusted to 0.4 or less. This value is preferably 0.2 or less, more preferably 0.12 or less, even more preferably 0.1 or less, and even more preferably 0.08 or less. An even smaller value is also possible.

[0050] As described above, by simultaneously adding ST pulp with surface-modified pulp fibers during heat-kneading of plastic, it is possible to produce a resin composite material (the resin composite material of this embodiment) in which the ST pulp fibers are uniformly dispersed in the plastic, as shown in Figure 3(A). Therefore, the resin composite material of this embodiment can prevent the ST pulp fibers from entangling or agglomerating with each other in the plastic, thereby improving the fluidity during heating. In other words, the resin composite of this embodiment can suppress an increase in viscosity when heated, thereby improving the handleability when using the resin composite of this embodiment to manufacture molded products. Specifically, since the viscosity can be reduced even when heated during molding, the resin can be poured evenly into the fine details of a mold, etc. Therefore, by using the resin composite of this embodiment, it is possible to manufacture plastic molded products with shapes that appropriately conform to the fine details of a mold, etc., even if the mold has a fine shape. Furthermore, as shown in Figure 3(A), the cooled molded product can be arranged with the ST pulp fibers uniformly dispersed throughout the plastic, improving the mechanical strength of the molded product. This mechanical strength can be improved compared to when normal pulp (N pulp) without any special surface treatment is used (see Figure 3(B)). The reason for this is that the fiber surface of the ST pulp added in the compounding process is pre-coated with an acid-modified resin, which improves compatibility with the plastic and allows the fibers to be uniformly dispersed throughout the resin (plastic) during heating and kneading.

[0051] When N-pulp is added to standard wood plastics, the bulkiness of N-pulp makes it impossible for the compatibilizing resin added during heat mixing to properly coat the surface of the N-pulp fibers. This causes adjacent N-pulp particles to become entangled and clump together during heat mixing (see part X in Figure 3(B)). As a result, the N-pulp is not uniformly dispersed throughout the plastic, which presumably results in a lower than expected reinforcing strength.

[0052] Furthermore, by using this composite manufacturing method, the compatibility between ST pulp and plastic can be improved as described above, and therefore the adhesion at the interface between ST pulp and plastic can be improved (see Figure 3(A)). Therefore, it is possible to prevent a decrease in functionality due to water absorption when the resin composite material (the resin composite material of this embodiment) is moistened. Specifically, a molded product using the resin composite material of this embodiment can suppress a phenomenon that occurs when wood plastics made from wood materials absorb water (shape change due to elongation when absorbing water, etc.).

[0053] For example, when a resin composite made with typical N pulp is used in exterior construction exposed to wind and rain (e.g., a deck), it absorbs moisture from rain and other factors, resulting in a decrease in mechanical strength. This is because the adhesion at the interface between the N pulp fiber and plastic in such a resin composite is low, allowing moisture to penetrate the interface between the two, making this the likely starting point for fracture. On the other hand, the resin composite produced by this composite production method (the resin composite of this embodiment) can improve the compatibility between the ST pulp fiber and plastic, thereby increasing the interfacial adhesion between the two. This allows the tensile strength to be maintained at a high level, thereby suppressing breakage due to water absorption. Specifically, the resin composite of this embodiment shows almost no decrease in the breaking elongation of the mechanical properties when absorbing water, compared to when N pulp is used. In other words, by adding ST pulp (the plastic additive of this embodiment) during the heat-kneading process in the compounding process, the decrease in toughness when absorbing water, which is one of the issues with conventional wood plastics, can be suppressed.

[0054] Furthermore, the interfacial adhesion between the ST pulp fiber and plastic can be improved, which significantly reduces dimensional change when moisture is added, improving dimensional stability when absorbing water.

[0055] Therefore, the resin composite material manufactured by this composite manufacturing method (the resin composite material of this embodiment) can appropriately exhibit the desired strength even when used for exterior construction purposes exposed to wind and rain. For example, the resin composite material of this embodiment has a reduction rate (%) in breaking elongation after absorbing water for 70 days of 15% or less, preferably 10% or less, more preferably 5% or less, even more preferably 3% or less, and even more preferably 2% or less. The percentage decrease in elongation at break after 70 days of water absorption (%) can be calculated by the method in the Examples.

[0056] In the above-described composite manufacturing method, the case where a compatibilizing resin is added has been described, but it is also possible to manufacture the resin composite of this embodiment without adding a compatibilizing resin. The reason for this is that the ST pulp (the plastic additive of this embodiment) added together with the plastic in this composite manufacturing method has its fiber surface modified with an acid-modified resin layer. This acid-modified resin layer contains polymer chains that are highly compatible with the plastic, and these polymer chains are arranged on the surface side of the acid-modified resin layer so that they come into contact with the plastic. Therefore, the ST pulp can perform the same function as a compatibilizing resin. For example, if the wood material used in this composite manufacturing method is only ST pulp, the acid-modified resin layer of the ST pulp fiber can provide adequate compatibility with plastics without the need for a compatibilizing resin. Furthermore, when the wood material contains wood flour in addition to ST pulp, the acid-modified resin layer of the ST pulp fiber can be made to bond the hydrophilic portion of the ST pulp fiber that is not bonded to the hydroxyl groups of the pulp fibers with the hydroxyl groups on the surface of the wood flour, thereby bonding the hydrophobic portion of the acid-modified resin layer with the plastic through interaction, thereby achieving the same function as a compatibilizing resin. [Example]

[0057] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples.

[0058] The waste paper pulp used was made by passing broke paper (manufactured by AIPA Co., Ltd.) through a 0.5 mm mesh in a crusher (model number ATOMZ-LABO / AT-200) manufactured by Ishikawa Soken Co., Ltd.

[0059] The surface of the recycled paper pulp was treated with an acid-modified resin (Rike-Aid MG-400W manufactured by Riken Vitamin Co., Ltd.). Furthermore, to create wood plastic (WPC), a polypropylene (PP, hereafter simply referred to as PP)-based masterbatch (Cellbrid manufactured by Toclas Corporation) with a wood flour filling rate of 70 was used, diluted with PP manufactured by Prime Polymer Co., Ltd. (Model No. J107G).

[0060] (Preparation of surface-treated pulp (ST pulp)) Acid-modified resin was added to the recycled paper pulp in an amount of 8% by mass, and the mixture was kneaded in a Henschel-type mixer (Super Mixer SMV-Ba, manufactured by Kawata Corporation) at 180°C and 1500 rpm until the material temperature exceeded 170°C, to obtain surface-treated pulp (ST pulp). Specifically, 24 g of acid-modified resin was added to 300 g of waste paper pulp, and the mixture was heated and mixed.

[0061] (Preparation of Resin Composites) The resin composite (sometimes called pulp-added WPC) was prepared by substituting ST pulp for the wood flour, with the raw material composition ratio of (wood flour + ST pulp): PP: acid-modified resin = 25:73:2. The blending ratio is shown in Table 1. In other words, "pulp in ST pulp" in Table 1 indicates the mass % of pulp in ST pulp after the pulp is coated with acid-modified resin, and the acid-modified resin used to coat the ST pulp is included in "compatibilizing resin" in Table 1. As shown in Table 1, each resin composite was prepared so that the total blending ratio of wood flour and recycled paper pulp (pulp in N pulp or ST pulp) was 25 mass%. The larger the sample number, the higher the blending ratio of N pulp or ST pulp. The blending ratio of recycled paper pulp (N pulp or ST pulp) is expressed as the degree of substitution (see Figure 6). For example, in Sample No. 1, the recycled paper pulp substitution rate is 0% ((0 / 25) x 100), and in Sample No. 2-ST, the pulp (ST pulp) substitution rate is 20% ((5 / 25) x 100).

[0062] Furthermore, as shown in Table 1, the mass ratio of the ST pulp content to the wood flour (mass of wood flour / mass of pulp in ST pulp) in each sample containing ST pulp was 4 (20 / 5) for sample No. 2-ST, 1 (12.5 / 12.5) for sample No. 3-ST, and 0.25 (5 / 20) for sample No. 4-ST. The total content of wood flour and ST pulp relative to the plastic was expressed as a mass ratio ((mass of wood flour + mass of ST pulp) / mass of plastic) of Sample No. 2-ST: 0.348 (20 + (5 + 0.4)) / 73), Sample No. 3-ST: 0.356 (12.5 + (12.5 + 1.0) / 73), Sample No. 4-ST: 0.364 (5 + (20 + 1.6) / 73), and Sample No. 5-ST: 0.370 (0 + (25 + 2.0) / 73). Furthermore, the mass ratio of the total content of wood flour and pulp in the ST pulp to plastic in each of these samples ((total mass of wood flour + pulp in ST pulp) / mass of plastic) was 0.342 in all cases (for example, 0.342((20+5) / 73) for Sample No. 2-ST).

[0063] Furthermore, the content of ST pulp (mass of pulp in ST pulp + mass of acid-modified resin layer) in each sample containing ST pulp relative to the entire resin composite was 0.054 ((5 + 0.4) / (20 + (5 + 0.4) + 73 + 1.6)) for sample No. 2-ST, 0.135 for sample No. 3-ST, 0.216 for sample No. 4-ST, and 0.27 for sample No. 5-ST, in terms of mass ratio. For wood flour, the mass ratio (mass of ST pulp (mass of pulp in ST pulp + mass of acid-modified resin layer) / mass of wood flour) was 0.270 ((5 + 0.4) / 20) for Sample No. 2-ST, 1.08 ((12.5 + 1.0) / 12.5) for Sample No. 3-ST, and 4.32 ((20 + 1.6) / 5) for Sample No. 4-ST. The mass ratio (mass of wood flour / mass of ST pulp (mass of pulp in ST pulp + mass of acid-modified resin layer)) was 3.704 (20 / (5 + 0.4)) for Sample No. 2-ST, 0.926 (12.5 / 13.5) for Sample No. 3-ST, and 0.231 (5 / 21.6) for Sample No. 4-ST. The mass ratio (mass of plastic / mass of ST pulp (mass of pulp in ST pulp + mass of acid-modified resin layer)) of the plastic was 13.52 (73 / (5+0.4)) for sample No. 2-ST, 5.41 (73 / (12.5+1.0)) for sample No. 3-ST, 3.38 (73 / (20+1.6)) for sample No. 4-ST, and 2.70 (73 / (25+2.0)) for sample No. 5-ST.

[0064] [Table 1]

[0065] The heat kneading was carried out using a Labo Plastomill manufactured by Toyo Seiki Seisakusho under conditions of 190°C, 60 rpm and 15 minutes to obtain a resin composite material.

[0066] (Preparation of test specimens) The obtained resin composite material was crushed to about 5 mm, and the crushed compound was molded into a dumbbell shape (JIS K 7139 A12) at a molding temperature of 190°C using an injection molding machine (Babyplast) manufactured by IOM Corporation to obtain a test piece.

[0067] As comparative examples, to confirm the effect of the surface treatment, resin composites were prepared in the same manner using untreated recycled paper pulp (N pulp), and test pieces were obtained (Samples No. 2-N to No. 5-N). In addition, a resin composite containing only wood flour was prepared in the same manner, and test pieces were obtained in the same manner (Sample No. 1).

[0068] (Testing and Evaluation Methods) The surface condition of the ST pulp was observed using an electron microscope, and the average fiber length was measured using a fiber length distribution analyzer. The resin composites prepared under various blending conditions were used to measure the relationship between shear rate and viscosity at 190°C using a capillary rheometer (Nippon Dynisco, LCR7000). The mechanical properties of each resin composite were evaluated by tensile tests using a tension-compression testing machine (manufactured by A&D Co., Ltd.) (in accordance with JIS K 7161). The dispersion state of the ST pulp was measured by measuring the storage modulus in the molded body at 180°C under shear strain using a cone rheometer (MCR702e, manufactured by Anton Paar). Water resistance was evaluated by immersing each resin composite in water at room temperature for 70 days and then conducting a tensile test using a tension and compression testing machine (manufactured by A&D Co., Ltd.).

[0069] (Experimental results) Next, the experimental results are shown.

[0070] (Surface observation) Figure 4 shows images of the fiber surfaces of ST pulp and N pulp observed using an electron microscope. As shown in Figure 4(B), it was confirmed that an acid-modified resin layer was formed on the fiber surface of ST pulp (see the area surrounded by the solid line in the left photograph of Figure 4(B) and the area surrounded by the dashed line in the right photograph of Figure 4(B) (enlarged version of the left photograph)).

[0071] In addition, in order to accurately grasp the treatment level of the surface treatment, the evaluation was carried out using a water immersion method. FIG. 5 is a photograph of the state after immersion in water for 24 hours using the water immersion method. In the experiment, 1 g of N pulp and 1 g of ST pulp were added to 100 ml of water at room temperature, and after leaving it to stand for 24 hours, the proportion of ST pulp (surface-treated pulp) that settled in the water was calculated as the mass ratio to the ST pulp (surface-treated pulp) mixed in the water (mass of ST pulp (surface-treated pulp) that settled / mass of ST pulp (surface-treated pulp) mixed in water). As shown in Figure 5, this evaluation method showed that N pulp settled immediately after immersion in water, but no settling was observed in ST pulp even after immersion for one day. In other words, the coating rate of the acid-modified resin on ST pulp was 0 (0 mg / 1 g). This confirmed that the surface of the ST pulp was properly coated with acid-modified resin and modified to be hydrophobic. Furthermore, it was confirmed that there was almost no difference in fiber length between the surface-treated and non-treated recycled paper pulps, with N pulp being approximately 600 μm and ST pulp being approximately 660 μm.

[0072] (fluidity in resin composites) Figure 6 shows the relationship between viscosity and shear rate for each resin composite. The relationship between the shear rate (1 / s) and viscosity thickening of each resin composite shown in Figure 6 can be expressed by the following approximate formula. For the WPC without pulp (Sample No. 1), the relationship between shear rate and viscosity was approximated as y = -238.1ln(x) + 1768.4. When the wood flour:N ratio was 20.0:5.0, the equation was approximately y = -324.8ln(x) + 2415.8; when the wood flour:N pulp ratio was 12.5:12.5, the equation was approximately y = -713.2ln(x) + 5058.7; when the wood flour:N pulp ratio was 5.0:20.0, the equation was approximately y = -459.4ln(x) + 3404.9; and when the wood flour:N pulp ratio was 0:100.0, the equation was approximately y = -1296ln(x) + 8612.7. For ST pulp, when the wood flour:ST pulp ratio was 20.0:5.0, it was approximately y = -294.3ln(x) + 2223.8; when the wood flour:ST pulp ratio was 12.5:12.5, it was approximately y = -384.7ln(x) + 2874.4; when the wood flour:ST pulp ratio was 5.0:20.0, it was approximately y = -443.7ln(x) + 3271.4; and when the wood flour:ST pulp ratio was 0:100.0, it was approximately -417.6ln(x) + 3089.9.

[0073] In Sample No. 1, shear dependency was observed, where the viscosity decreased as the shear rate increased. Because wood flour is not a completely isotropic shape but has an aspect ratio, it is thought that the increased shear rate caused the particles to become oriented, resulting in a decrease in viscosity. Furthermore, when non-surface-treated pulp (N pulp) was added (Figure 6(B)), a tendency for viscosity to increase in the low shear rate region was observed as the substitution amount of N pulp increased. Conversely, at high shear rates, the difference was small, with samples No. 3-N, No. 4-N, and No. 5-N, which have substitution rates of over 50%, having roughly the same viscosity. The reason for this viscosity trend is thought to be that the N pulp particles in the N pulp resin composite are dispersed in an entangled state (see Figure 3(B)). At low shear rates, this creates resistance, increasing viscosity, and as the shear rate increases, they become more oriented in the flow direction, resulting in a decrease in viscosity. Here, aggregation of N pulp particles is also suggested, but based on the results of tensile strength, etc., which will be described later, it can be determined that no strong aggregation has occurred, and it is expected that the entanglement is at a level that will disintegrate at high shear rates. Furthermore, the fact that the viscosity gradient with shear rate for samples No. 2-N and No. 3-N, which have low N pulp substitution, is similar to that of sample No. 1 also suggests that the state of the pulp affects the flow characteristics. On the other hand, the resin composite to which surface-treated pulp (ST pulp) was added also increased in viscosity as the amount of ST pulp substituted increased (Fig. 6(A)), but there was no difference between the high and low shear rate regions, and it was confirmed that the level of thickening was lower in the low shear rate region compared to the resin composite to which N pulp was added. As mentioned above, the difference between the two is that there is no significant difference in fiber shape between N pulp and ST pulp, so it is expected that this is due to the dispersion state of ST pulp in the resin composite. As shown in the bottom photo of Figure 4, the surface of ST pulp is coated with an acid-modified resin, which is thought to enable it to be uniformly dispersed in the resin during heating and kneading in the resin composite manufacturing process (compounding process). Therefore, there is little or no entanglement of the pulp particles, as there is in resin composites with added N pulp (see Figure 3(A)), and it is presumed that there is little resistance at low shear rates. In other words, pulp surface treatment with acid-modified resin can contribute to improving the dispersibility of pulp, which is difficult to disperse uniformly.

[0074] Furthermore, from the results of Figure 6 and the above approximations, it was confirmed that the resin composite material of the present invention in which all wood flour was replaced with ST pulp exhibited a viscosity increase at a shear rate of 132 (1 / s) that was less than two times that of the composite material without the replacement. This increase in viscosity was also proportional to the amount of ST pulp replacement. On the other hand, the resin composite material in which all wood flour was replaced with N pulp exhibited a viscosity increase at a shear rate of 132 (1 / s) that was more than four times that of the composite material. This value, particularly in the low shear region, is preferably less than three times, more preferably less than two times. The resin composite material with ST pulp added in this experiment exceeded both target values. It was also confirmed that the viscosity remained below specific values ​​at other shear rates.

[0075] As mentioned above, the fact that ST pulp is dispersed in the resin is also supported by the results of storage modulus measurements taken using a cone rheometer (Figure 7). Here, the storage modulus is evaluated when the PP is in a molten state, so if the samples have the same amount of PP added, the interactions between wood flour and fibers can be evaluated. Compared to sample No. 1, in which wood flour was not replaced with pulp, resin composites with a 50% replacement rate (samples No. 3-N and No. 3-ST) showed a high storage modulus regardless of whether or not the surface was treated. This is due to the addition of pulp, which has a higher aspect ratio and specific surface area than wood flour. On the other hand, at the same pulp substitution level, the resin composite with added N pulp (Sample No. 3-N) had a higher storage modulus than the resin composite with added ST pulp (Sample No. 3-ST). As mentioned above, there was no difference in pulp shape, so this difference is thought to reflect the state of the pulp. In other words, the resin composite with added N pulp (Sample No. 3-N) had a high storage modulus due to the entanglement of the pulp particles. This is consistent with the results of previous research, which showed that the storage modulus is higher when the pulp particles are dispersed in PP (resin) in an entangled state rather than aggregated.

[0076] (Mechanical properties of resin composite materials) FIG. 8 shows the relationship between the substitution ratio of various pulps to wood flour and the tensile strength of the test pieces of each resin composite material. The tensile strength of the injection-molded PP used in this experiment was 32.8 MPa, while that of Sample No. 1 was 39.5 MPa, demonstrating the reinforcing effect of the wood flour. In other words, in the base resin composite, the wood flour is a material that is uniformly dispersed and compatible within the PP. The experimental results showed that by replacing the wood flour in this resin composite with pulp, the strength of both N pulp and ST pulp improved, and the strength tended to increase as the amount of pulp substitution increased. In the viscosity test described above (see Figure 6), it was considered that the pulp in the resin composite material to which N pulp was added was in an entangled state. However, the fact that N pulp also improved tensile strength supports the conclusion that the entanglement is not in a state of significant aggregation. Furthermore, the resin composite with ST pulp exhibited higher tensile strength than the resin composite with N pulp, suggesting that the reinforcing effect of the pulp was more pronounced, and that the surface treatment improved the interfacial adhesion between the pulp surface and PP.

[0077] FIG. 9 shows the relationship between the substitution ratio of various pulps to wood flour and Young's modulus in test pieces of each resin composite material. As shown in Figure 9, no significant change in Young's modulus was observed even when the pulp substitution rate increased. Generally, methods of adding inorganic fillers and fibers to improve the strength of wood plastics (WPC) have been much studied, but in most cases the Young's modulus also increases along with the increased strength. Based on previous research and the experimental results in Figure 9, it is believed that the main factor in the relationship between the substitution rate of various pulps and Young's modulus is due to the dispersion state of the pulp fibers in the molded body.

[0078] FIG. 10 shows the relationship between the substitution ratio of various pulps to wood flour and the breaking elongation in the test pieces of each resin composite material. The resin composite with added N pulp showed a slight decrease in breaking elongation due to the substitution of N pulp. This is thought to be because there is no bonding strength at the contact points where the pulp pieces are intertwined, and these points are the starting points for fracture. On the other hand, in the resin composites containing ST pulp, the breaking elongation (%) was lower than that of Sample No. 1 at a substitution rate of 20% (Sample No. 2-ST) and 50% (Sample No. 3-ST), but as the substitution rate increased, it became equivalent to that of Sample No. 1. Furthermore, the resin composites containing ST pulp had a higher breaking elongation than the resin composites containing N pulp. The reasons for this are thought to be that ST pulp is more homogeneously dispersed than N pulp, as discussed in the viscosity test above (see Figure 6), and that its compatibility with PP is higher due to the surface treatment.

[0079] (Water absorption characteristics of resin composite materials) Table 2 shows the water absorption rate of test pieces of each resin composite after 70 days of water absorption and the results of tensile tests in the water-absorbed state.

[0080] [Table 2]

[0081] All resin composites showed a water absorption rate of around 2.5%, with no significant differences observed. Since the base plastic, PP, does not absorb water, it is thought that the wood flour and pulp absorbed water. Figure 11 shows the change in water absorption rate over time for Sample No. 1 and resin composites with a pulp replacement rate of 50% (Samples No. 3-N and No. 3-ST). Regarding water absorption behavior, no difference was observed between the presence or absence of pulp and the difference in surface treatment. Furthermore, since the water absorption rate increased even after 70 days of absorption, it is expected that water gradually penetrates into the interior. On the other hand, as shown in Table 3, the tensile strength and Young's modulus decreased due to water absorption, and the rate of decrease tended to be greater for each resin composite than for Sample No. 1. This is thought to be because the hydrogen bonds between the pulp fibers swelled with water, weakening the interfiber bonds. However, what we want to focus on here is the elongation at break.

[0082] [Table 3]

[0083] Figure 12 and Table 3 show the relationship between the substitution ratio of various pulps for wood flour in test pieces of each resin composite and the rate of decrease in breaking elongation due to water absorption. This rate of decrease was calculated by (breaking elongation before water absorption - breaking elongation after water absorption) / (breaking elongation before water absorption). Sample No. 1's breaking elongation decreased by approximately 30% due to water absorption. This is thought to be because water penetrates into the voids in the wood flour, causing the wood flour to expand, weakening the adhesion at the interface and causing breakage at these points, resulting in a decrease in breaking elongation. Furthermore, in resin composites with added N pulp, the reduction in breaking elongation (%) gradually decreased as the N pulp substitution rate increased. As shown in Table 2, the water absorption rate of samples with added N pulp remained almost unchanged, which suggests that pulp fibers have fewer voids than wood flour, and water adheres to the surface rather than inside the pulp, resulting in less swelling and affecting the breaking elongation. On the other hand, as shown in Figure 12, in the resin composite material with added ST pulp, the decrease in breaking elongation (%) was almost nonexistent when the ST pulp substitution rate was 20%, and even when the ST pulp substitution rate was further increased, almost no decrease in elongation was observed.As shown in Table 2, the resin composite material with added ST pulp has the same water absorption rate as the resin composite material with added N pulp, so it is thought that water penetrates through the pulp surface, just like the resin composite material with added N pulp. Based on the results of this experiment, it can be inferred that the high adhesion of ST pulp surface-treated with acid-modified resin to PP led to a lower rate of decrease in breaking elongation due to water absorption.

[0084] (summary) The plastic additive (ST pulp) of the present invention is a pulp surface that has been pre-coated with an acid-modified resin. The resin composite of this embodiment, obtained by adding this ST pulp to plastic and kneading it under heat, is manufactured so that the pulp fibers contain pulp that has been pre-surface-treated. This has been confirmed to suppress a decrease in fluidity and improve mechanical strength. Furthermore, with regard to the traditional issue of wood plastic (WPC) in terms of the decrease in toughness when absorbing water, the resin composite of this embodiment is manufactured so that the pulp fibers contain pulp that has been surface-treated in advance (ST pulp), and it has been found that the decrease in breaking elongation when absorbing water is suppressed. In addition, the broke paper generated in the papermaking process is used as recycled paper pulp. Since the broke paper is less likely to deteriorate with use and has stable quality, if the broke paper is used as a raw material for the plastic additive of the present invention, it can be expected to be used in applications with high added value. [Industrial Applicability]

[0085] The plastic additive of the present invention is suitable as an additive to be mixed with plastic, and the resin composite material of this embodiment can be used for various purposes as a composite material of pulp and plastic.

Claims

1. Pulp used in combination with plastics, The pulp is It is a surface-treated pulp in which an acid-modified resin layer made of an acid-modified resin is formed on at least a part of the fiber surface. A plastic additive characterized by:

2. The acid-modified resin is The resin has a functional group that chemically interacts with the hydroxyl group of the pulp and a polymer chain that exhibits intermolecular compatibility with plastics.

2. The plastic additive according to claim 1.

3. The surface-treated pulp is the coating rate of the acid-modified resin layer is 0.25 or less; The coating rate is A predetermined amount of the surface-treated pulp is added to water at room temperature, mixed, and left to stand for 24 hours. The proportion of the surface-treated pulp that settles in the water is calculated as a mass ratio (mass of the surface-treated pulp that settles / mass of the surface-treated pulp that is mixed in the water) of the surface-treated pulp that settles in the water.

3. The plastic additive according to claim 1 or 2.

4. The functional group is one or more selected from the group consisting of a carboxy group, an amino group, an acid anhydride group, an amide group, an aldehyde group, a nitro group, a phosphate group, and a nitrate ester group.

3. The plastic additive according to claim 2.

5. The polymer chain is selected from the group consisting of polyethylene, polypropylene, polystyrene, AS, ABS, polyester, polyurethane, phenolic resin, epoxy resin, urea resin, melamine resin, and low molecular weight resins thereof.

3. The plastic additive according to claim 2.

6. The acid-modified resin has a melting point of 220° C. or less.

3. The plastic additive according to claim 1 or 2.

7. The acid-modified resin is Maleic acid modified resin and / or acrylic acid modified resin 3. The plastic additive according to claim 1 or 2.

8. A plastic and a plastic additive, The plastic additive is It is a surface-treated pulp in which an acid-modified resin layer made of an acid-modified resin is formed on at least a part of the fiber surface. A resin composite material characterized by:

9. The acid-modified resin is The resin has a functional group that chemically interacts with the hydroxyl group on the surface of the surface-treated pulp, and has a polymer chain that exhibits intermolecular compatibility with plastics. The resin composite material according to claim 8.

10. The surface-treated pulp is the coating rate of the acid-modified resin layer is 0.25 or less; The coating rate is A predetermined amount of the surface-treated pulp is added to water at room temperature, mixed, and left to stand for 24 hours. The proportion of the surface-treated pulp that settles in the water is calculated as a mass ratio (mass of the surface-treated pulp that settles / mass of the surface-treated pulp that is mixed in the water) of the surface-treated pulp that settles in the water. The resin composite material according to claim 8 or 9.

11. Contains wood flour, the content of the surface-treated pulp relative to the wood flour is 0.1 or more in terms of mass ratio (mass of surface-treated pulp / mass of wood flour), The total content of the wood flour and the surface-treated pulp relative to the plastic is 4.0 or less in terms of mass ratio ((total mass of wood flour + surface-treated pulp) / mass of plastic). The resin composite material according to claim 8 or 9.

12. The reduction in elongation at break (%) after absorbing water for 70 days is 15% or less. The resin composite material according to claim 8 or 9.

13. Viscosity increase at a shear rate of 132 (1 / s) is less than 2 times The resin composite material according to claim 8 or 9.

14. 2. A method for producing the additive for plastics according to claim 1, which is used by mixing with plastics, The method includes a surface treatment step of heating and kneading pulp and an acid-modified resin to form an acid-modified resin layer on the surface of the pulp fibers, In the surface treatment step, The blending ratio of the acid-modified resin is adjusted to be 1 part by mass or more and 25 parts by mass or less with respect to 100 parts by mass of the pulp. A method for producing a plastic additive, comprising:

15. The method includes a compounding step of heating and kneading plastic, pulp, and a compatibilizing resin, The pulp is a surface-treated pulp having a resin layer on the fiber surface. A method for producing a resin composite material, comprising:

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