JP2010126816A - Polylactic acid fiber, fiber-based board, fiber-based board with film, and method for producing fiber-based board - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polylactic acid fiber holding excellent heat resistance, to provide a fiber-based board which uses the polylactic acid fibers and can prevent the softening of the polylactic acid by frictional heat on router processing or drill processing, and to provide a polylactic acid fiber-based board which improves the adhesion of processing blades to polylactic acid, the scrap adhesion and burrs of a processed board to cut surface, and is excellent in a cutting property. <P>SOLUTION: The polylactic acid fiber includes 0.1 to 5.0 mass% of a metal salt of a phosphonic acid having an aromatic ring in a fiber of polylactic acid resin. The fiber-based board having a crystallinity of not less than 10% in the surface layer portion and a crystallinity of not less than 40% in the middle layer portion comprises the polylactic acid fibers and natural fibers. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a fiber board.

  In recent years, all fields have been focused on environmental issues. For example, for the purpose of reducing the environmental impact at the time of disposal, polylactic acid resin and natural fibers are mixed and heated and pressurized, and the overall apparent density is in a specific range. A method for producing a fiber-based board molded into a sheet has been proposed (see, for example, Patent Document 1). This is because the biodegradable fiber is used as a raw material for the fiber-based board that is mixed with polylactic acid resin and natural fiber and heat-pressed, and because it is relatively easy to manufacture, The environmental load can be reduced. However, with the above technology, polylactic acid softens due to frictional heat and compression due to high-speed rotation during drilling of the board surface (drilling) and grooving with a cutting tool such as a router. There are disadvantages in that the machinability is inferior to that of general-purpose products such as lactic acid sticking, chip adhesion to the cutting surface of the processing board, and burrs (fluffing of the cutting part).

Further, from the viewpoint of improving the heat resistance of polylactic acid, a crystal nucleating agent having a high crystallization rate has been proposed for polylactic acid. (For example, see Patent Document 2) However, since the fiberization technology of polylactic acid using a crystal nucleating agent having a high crystallization rate is difficult and has not been established yet, the problem of heat resistance of polylactic acid fiber has not been solved. .
JP 2004-130796 A (Claim 1, 0027) International Publication No. 05/097894 (Claims 1, 0018, 0025)

  An object of the present invention is to provide a polylactic acid fiber having excellent heat resistance, and to suppress softening of polylactic acid due to frictional heat during router processing and drilling using the polylactic acid fiber. It is to provide a polylactic acid fiber-based board that is excellent in cutting workability by improving the adhesion of the polylactic acid to the processing blade, and the adhesion of chips to the cutting surface of the processing board and burrs. .

The present invention for solving the above-described problems is characterized by one of the following configurations.
(1) A polylactic acid fiber comprising 0.1 to 5.0% by mass of a phosphonic acid metal salt having an aromatic ring in a fiber made of a polylactic acid resin.
(2) A fiber-based board comprising the polylactic acid fiber according to (1) and a natural fiber, wherein the surface layer portion has a crystallinity of 10% or more and the middle layer portion is 40% or more. .
(3) The fiber board according to (2), wherein the density is 0.1 g / cm ³ or more.
(4) A fiber-based board with a film, wherein a film is laminated on at least one of the front and back surfaces of the fiber-based board according to (2) or (3).
(5) A method for producing a fiber-based board, comprising mixing the polylactic acid fiber according to (1) and natural fiber, heating and pressurizing and integrally forming, and then annealing.

  According to the present invention, a polylactic acid fiber having excellent heat resistance can be obtained. As a result, adhesion of polylactic acid to the processing blade, chip adhesion to the cutting surface of the processing board, and burr problems are improved, and cutting processing is performed. A polylactic acid fiber-based board having excellent properties can be obtained.

  Hereinafter, embodiments of the present invention will be described in detail.

  The polylactic acid fiber of the present invention is a fiber made of a polylactic acid resin and contains a phosphonic acid metal salt having an aromatic ring that acts as a crystal nucleating agent. The content of the phosphonic acid metal salt is important. It becomes. In the present invention, the polylactic acid fiber and the natural fiber are used to constitute a fiber-based board and a fiber-based board with a film. Details of the polylactic acid fiber, the fiber-based board, and the fiber-based board with a film will be described below. Will be explained.

A. Polylactic acid fiber (Polylactic acid resin)
Polylactic acid resin used in the fiber of the present _{invention, - (O-CHCH 3 -CO} ) n - is a polymer as a repeating unit, and is obtained by polymerizing lactic acid oligomers, such as lactic acid or lactide. Lactic acid has two optical isomers, D-lactic acid and L-lactic acid. The higher the optical purity of polylactic acid, the higher the melting point of polylactic acid, that is, the better the heat resistance. The optical purity of polylactic acid is preferably 90% or more. The melting point of polylactic acid is preferably 150 ° C. or higher in order to maintain the heat resistance of the fiber.

  When blending poly (L lactic acid) and poly (D lactic acid), it is preferable to form a stereo complex in which a racemic crystal is formed by performing high-temperature heat treatment at 140 ° C. or higher after forming into a fiber. Thereby, melting | fusing point can be raised to 220-230 degreeC. In this case, the blend ratio of poly (L lactic acid) and poly (D lactic acid) is preferably 40/60 to 60/40 because the ratio of stereocomplex crystals can be increased.

  Usually, residual lactide may be present as a low molecular weight residue in polylactic acid. The amount of residual lactide in polylactic acid is preferably 3000 ppm by mass or less, more preferably 1000 ppm by mass or less, and still more preferably 300 ppm by mass or less. By suppressing the amount of residual lactide in polylactic acid, it is possible to prevent hydrolysis of the fiber and maintain durability. Examples of a method for reducing the amount of residual lactide in polylactic acid include adopting solid-phase polymerization as a polymerization method and washing the pellet with warm water of about 80 ° C.

  In addition, components other than lactic acid may be copolymerized as long as the properties of polylactic acid are not impaired. The components to be copolymerized include polyalkylene ether glycols such as polyethylene glycol, aliphatic polyesters such as polybutylene succinate and polyglycolic acid, aromatic polyesters such as polyethylene isophthalate, and hydroxycarboxylic acids, lactones, dicarboxylic acids, and diols. An ester bond-forming monomer such as

  As a polymerization method of polylactic acid, a direct dehydration condensation method in which lactic acid is dehydrated and condensed as it is in the presence of an organic solvent and a catalyst, a method in which at least two homopolymers are copolymerized and transesterified in the presence of a polymerization catalyst, And an indirect polymerization method in which lactic acid is once dehydrated to form a cyclic dimer and then subjected to ring-opening polymerization.

  The weight average molecular weight of the polylactic acid is preferably 80,000 or more, more preferably 100,000 or more, and further preferably 120,000 or more in order to improve the wear resistance. On the other hand, in order to maintain spinnability and stretchability, the polylactic acid preferably has a weight average molecular weight of 350,000 or less, more preferably 300,000 or less, and even more preferably 250,000 or less.

  In polylactic acid, it is preferable that the carboxyl group terminal of a part of molecular chain is blocked. By blocking the terminal of some carboxyl groups of the molecular chain of polylactic acid, heat resistance and hydrolysis resistance can be improved. The carboxyl group terminal concentration of the polylactic acid including the residual monomer and residual oligomer is 10 equivalent / ton or less, preferably 5 equivalent / ton or less. By setting it to 10 equivalents / ton or less, heat resistance and hydrolysis resistance can be improved. On the other hand, in terms of production cost and productivity, it is preferably 1 equivalent / ton or more. The carboxyl group terminal of polylactic acid can be blocked by adding a carbodiimide compound or a compound having a glycidyl group. That is, the polylactic acid preferably has an addition reaction product with a carbodiimide group or a glycidyl group. A carbodiimide compound or a compound having a glycidyl group as a carboxyl group terminal blocker of polylactic acid may be used alone or in combination of two or more. The addition amount of the carbodiimide compound or the compound having a glycidyl group with respect to polylactic acid is preferably 0.1 to 10% by mass.

  It is important that polylactic acid contains a phosphonic acid metal salt having an aromatic ring, which acts as a crystal nucleating agent, in an amount of 0.1 to 5.0% by mass in the fiber.

  By mixing phosphonic acid metal salt having an aromatic ring with a high crystallization speed into polylactic acid resin, the polylactic acid resin can be made into fiber, and when used for fiber board, polylactic acid is crystallized. Since the degree becomes higher and the crystal size becomes smaller, the heat resistance in the vicinity of the softening point can be drastically improved, and a board excellent in cutting workability can be obtained. If the phosphonic acid metal salt having an aromatic ring in the fiber exceeds 5% by mass, an increase in crystallization promoting effect is hardly observed due to aggregation of the phosphonic acid metal salt having an aromatic ring, but due to an increase in filtration pressure during spinning. The pack life is shortened, and fuzz and yarn breakage occur frequently during spinning and drawing. If the amount is less than 0.1% by mass, the amount of the crystal nucleating agent is small, so that crystallization does not proceed due to rapid cooling during fiber board molding, and the heat resistance near the softening point of polylactic acid remains low. Due to the heat, the polylactic acid softens, causing the problem that the polylactic acid is attracted to the processing blade and the problem that chips are fixed to the cutting surface of the board.

  In the phosphonic acid metal salt having an aromatic ring, the aromatic ring may be any of a benzene ring, naphthalene ring, anthracene ring, thiophene ring, furan ring, pyrrole ring, pyrazole ring, pyridine ring, and pyran ring. In view of heat resistance and cost, a benzene ring, a naphthalene ring and an anthracene ring are preferable, and a benzene ring is more preferable. Specific examples of the phosphonic acid component having an aromatic ring that forms a phosphonic acid metal salt having an aromatic ring include phenylphosphonic acid, 2-methylphenylphosphonic acid, 3-methylphenylphosphonic acid, 4-methylphenylphosphonic acid, 4 -Ethylphenylphosphonic acid, 2-isopropylphenylphosphonic acid, 2-methoxyphenylphosphonic acid, 4-methoxyphenylphosphonic acid, 2-nitrophenylphosphonic acid, 3-nitrophenylphosphonic acid, 4-nitrophenylphosphonic acid, 2- Methyl-4-nitrophenylphosphonic acid, 3-methyl-5-nitrophenylphosphonic acid, 2-methoxy-4-nitrophenylphosphonic acid, 2-chloro-5-methylphenylphosphonic acid, 2-fluorophenylphosphonic acid, 4 -Chlorophenylphosphonic acid, 4-bromophenyl Examples include sulphonic acid, 2-iodophenylphosphonic acid, 2,3-xylylphosphonic acid, 2,4-xylylphosphonic acid, 2,5-xylylphosphonic acid, etc. You may use together.

  In the phosphonic acid metal salt having an aromatic ring, the metal species is not particularly limited, but light metals and heavy metals from Group 1A to Group 6B of the periodic table are preferable in terms of moldability, heat resistance and durability. From the viewpoints of heat resistance and heat resistance, a divalent metal is more preferable, and among these, any one of magnesium, calcium, iron, copper, and zinc is more preferable, and zinc is particularly preferable. These may be used alone or in combination of two or more. In particular, at least one of magnesium phenylphosphonate, calcium phenylphosphonate and zinc phenylphosphonate is preferable in terms of moldability and heat resistance, and zinc phenylphosphonate is more preferable in terms of durability. These may be used alone or in combination of two or more.

  The average particle diameter D50 (median diameter) of the phosphonic acid metal salt having an aromatic ring is 5 μm or less in order to increase the crystallinity and to ensure an increase in filtration pressure, spinnability and stretchability during yarn production. is required. As will be described later, the smaller the particle size of the phosphonic acid metal salt having an aromatic ring, the larger the specific surface area, and the effect as a crystal nucleating agent is greatly improved. Therefore, the particle diameter of the phosphonic acid metal salt having an aromatic ring is preferably 4 μm or less, and more preferably 3 μm or less. Most preferably, it is 2 μm or less. In addition, the lower limit of the average particle diameter D50 of the phosphonic acid metal salt having an aromatic ring is not particularly limited. However, as the particle diameter becomes smaller, the cohesiveness becomes higher and the dispersibility in the polymer becomes worse. It is preferably 2 μm or more.

  Moreover, it is preferable that the content rate of the phosphonic acid metal salt which has an aromatic ring with a particle diameter of 10 micrometers or more is 0 to 4.5 volume% or less with respect to the total amount of the phosphonic acid metal salt which has an aromatic ring. When using polylactic acid fiber for industrial materials, the fiber diameter of the single fiber is required to be 15 to 50 μm as a general-purpose grade. In our study, it was found that when the fiber diameter is less than twice the particle diameter of the phosphonic acid metal salt having an aromatic ring to be added, the fiber strength rapidly decreases and the strength distribution also shifts to the lower strength side. . Therefore, the content of the phosphonic acid metal salt having an aromatic ring having a particle diameter of 10 μm or more is preferably 0 to 4.5% by volume or less based on the total amount of the phosphonic acid metal salt having an aromatic ring. More preferably, it is 0-3 volume%, More preferably, it is 0-2 volume%, Most preferably, it is 0 volume%.

  In addition, the particle diameter of each phosphonic acid metal salt is measured by a laser diffraction method using SALD-7100 manufactured by Shimadzu Corporation, and the average particle diameter D50 and the content are obtained from the particle size distribution.

  The polylactic acid preferably has a cooling crystallization temperature T′c of 90 to 140 ° C. as measured by a differential scanning calorimeter (DSC). This can be achieved by including a predetermined amount of a phosphonic acid metal salt having an aromatic ring. T'c is a parameter for measuring the crystallization speed, and the higher the T'c, the faster the crystallization speed. Therefore, the higher the T′c, the faster the crystallization speed and the higher the ultimate crystallinity, so that high crystallization can be achieved to obtain the heat resistance required for cooling in the board manufacturing process, and the desired mechanical properties can be achieved. Be improved. T′c is preferably 100 to 140 ° C., more preferably 110 to 140 ° C., and most preferably 120 to 140 ° C.

  The crystallinity and T′c are measured using DSC. The measurement was performed on 2.0 mg of a sample at a rate of temperature increase of 10 ° C./min, a target temperature of 200 ° C., a hold time of 5 minutes, and then a temperature decrease rate of −10 ° C./min and a target temperature of 30 ° C. The extreme temperature at the time of temperature rise is the melting point (° C.), and the extreme temperature of the crystallization exothermic curve (at the time of temperature drop) is the temperature crystallization temperature. The crystallinity is calculated from the formula: crystallinity (%) = 100 × (melting enthalpy + crystallization enthalpy) / 93.

  In addition to the crystal nucleating agent, the polylactic acid may contain particles, flame retardants, plasticizers, antistatic agents, antioxidants, ultraviolet absorbers, lubricants such as ethylenebissteasanamide, and the like.

(Shape and dimensions of polylactic acid fiber)
In the present invention, the polylactic acid fiber has a cross-sectional shape such as a round cross-section, hollow cross-section, porous hollow cross-section, trilobal cross-section (triangular cross-section, Y cross-section, T cross-section, etc.), flat cross-section, W cross-section, X cross-section. Etc. can be adopted.

  The single fiber fiber degree of the polylactic acid fiber is preferably 0.5 to 100 dtex. More preferably, it is 0.8-80 dtex. When it is less than 0.5 dtex, spinning and carding passability are remarkably deteriorated, and it becomes difficult to obtain a spun yarn and a nonwoven fabric. On the other hand, if it exceeds 100 dtex, the fiber dispersibility in the nonwoven fabric production process is lowered.

  The polylactic acid fiber is preferably a short fiber of 5 to 150 mm. When the length is less than 5 mm, the fibers constituting the nonwoven fabric become insufficiently entangled, and the strength as the fiber board decreases. On the other hand, when it exceeds 150 mm, it is difficult to uniformly disperse in the nonwoven fabric manufacturing process, so that productivity is lowered and strength is not uniform, and strength may be partially reduced.

  The polylactic acid fiber is preferably provided with a spinning oil containing a smoothing agent. By adding an oil agent containing a smoothing agent to polylactic acid fiber, the slipperiness of polylactic acid fiber is improved, processability in spinning and drawing, carding and spinning, and crimping of the resulting fiber itself. While improving the quality of spots and fluff, it is possible to improve the spreadability of the fibers and the dispersibility of the fibers in the fiber structure. Examples of the smoothing agent include fatty acid esters, polyhydric alcohol esters, ether esters, polyethers, silicones, and mineral oils. These smoothing agents may be used as a single component, or a plurality of components may be mixed and used. Moreover, as an adhesion amount of an oil agent, 0.1-2.0 mass% is preferable with respect to a fiber, More preferably, it is 0.2-0.7 mass%. By setting it within the range, the process passability during carding can be improved. In addition to the smoothing agent, the oil agent is an emulsifier, an antistatic agent, an ionic surfactant, a bundling agent, a rust preventive agent that emulsifies the oil agent in water to lower the viscosity and improve adhesion to the yarn and permeability. It is also preferable to add a preservative, an antioxidant and the like.

  It is preferable to impart crimps to the polylactic acid fiber. By imparting crimps, the entanglement of fibers in the spun yarn can be strengthened, and the process passability during carding can be improved. The number of crimps is preferably 6 to 20 mountains / 25 mm, more preferably 8 to 15 mountains / 25 mm. The crimp rate is preferably 10 to 50%, and more preferably 15 to 30%.

(Method for producing polylactic acid fiber)
The polylactic acid fiber can be produced by melt spinning the polylactic acid resin in which a metal salt of phosphonic acid having an aromatic ring is mixed. The yarn made of the melted polylactic acid resin is cooled, provided with an oil agent, and taken off. The take-up speed is preferably 400 to 2,000 m / min. Next, the undrawn yarn of polylactic acid fiber is drawn and drawn. As for the alignment, the total fineness of the tow after stretching is preferably 50,000 to 1,000,000 dtex. The stretching of the polylactic acid fiber is preferably performed by liquid bath stretching using hot water at 60 to 100 ° C. in order to obtain a uniform tow. As a draw ratio in the drawing of the polylactic acid fiber, 1.5 to 6 times is preferable. By doing so, polylactic acid fibers having appropriate strength can be obtained. Moreover, you may provide an oil agent as a finishing agent after extending | stretching or after the crimping provision mentioned below as needed. Next, crimping is preferably applied to the drawn yarn. Examples of the crimping method include a stuffing box method, an indentation heating gear method, and a high-speed air injection indentation method. The polylactic acid fiber is preferably subjected to relaxation heat treatment (heat setting) in a tow state after crimping. By doing so, it is possible to obtain excellent dimensional stability and crimp retention. Thereafter, the polylactic acid fiber can be cut into a desired fiber length by a cutting device such as a rotary cutter.

B. Fiber board and fiber board with film (Composition)
The fiber-based board of the present invention is an aggregate composed of polylactic acid fibers and natural fibers as described above, and the crystallinity of the surface layer portion is 10% or more and the crystallinity of the middle layer portion is 40% or more.

  In the fiber-based board of the present invention, since the polylactic acid fiber and the natural fiber are mixed, the mechanical properties of the board such as bending strength are high, and the environmental load at the time of disposal is also suppressed.

  In addition, since the surface layer portion of the fiber board is usually rapidly cooled by cooling in the board forming process, the polylactic acid containing no crystal nucleating agent as described above has a degree of crystallinity of about 5% and increases the degree of crystallinity. Is difficult. However, since the fiber board of the present invention is composed of polylactic acid fibers containing a predetermined amount of a phosphonic acid metal salt having an aromatic ring, it can have a crystallinity of 10% or more in the surface layer portion. The strength of the surface portion is increased, and as a result, the generation of burrs during cutting can be suppressed. On the other hand, since the middle layer portion is cooled relatively slowly as compared with the surface layer portion, the crystallization degree tends to be high, but the crystallization degree is about 30% even when talc, which is a general-purpose crystal nucleating agent, is used. However, since the fiber board of the present invention is composed of polylactic acid fibers containing a predetermined amount of a phosphonic acid metal salt having an aromatic ring, the middle layer has a crystallinity of 40% or more, and the heat resistance is dramatically improved. In addition, it is possible to reduce the sticking of chips to the processing blade due to frictional heat during cutting and the attachment of chips to the end portion of the board. In addition, since the fiber board of the present invention is composed of polylactic acid fibers containing a predetermined amount of a phosphonic acid metal salt having an aromatic ring, the crystal size of the polylactic acid in the surface layer portion and the middle layer portion measured by a polarization micrograph Tends to be 100 μm or less, and the crystals are small and dense, so that they are stronger against heat and heat resistance is improved. The crystal size is more preferably 50 μm or less, and most preferably 10 μm or less. Such crystallinity improves the heat resistance of the polylactic acid fiber of the fiber-based board, and can solve the problem during cutting. In the present invention, the surface layer portion is a layer in the range of 2 mm from the surface, and the portion sandwiched between the surface layer portions is referred to as a middle layer portion.

The fiber-based board of the present invention preferably has a density of 0.1 g / cm ³ or more. By setting the density to 0.1 g / cm ³ or more, not only the strength of the board is improved, but also in the cutting process, the friction resistance between the cutting blade and the fiber-based board is increased, so that the natural fiber having high strength is high. Can be cut cleanly together with the fiber-based board, and burrs on the cut surface are suppressed. More preferably, it is 0.3 g / cm ³ or more, and further preferably 0.5 g / cm ³ or more. And a fiber board as described above becomes a fiber board with a film by laminating a film on at least one side. According to the fiber board with film, the hardness of the surface is increased, and burrs during processing are further eliminated.

(Natural fiber)
Examples of natural fibers used in the fiber board of the present invention include wood pulp, bagasse, wheat straw, reed, papyrus, bamboo, pulp, cotton, kenaf, roselle, Asa, flax, ramie, jute, hemp, sisal Asa, Manila Asa, palm , Banana, wool and the like, and these may be used alone or in combination of two or more. For example, adopting fibers collected from kenaf or jute belonging to herbs that are relatively long among natural fibers, are annual grasses, and grow very quickly and easily in tropical and temperate regions. Thus, an excellent strength can be obtained. In particular, kenaf bast contains cellulose at a high content of 60% by mass or more, has high strength, and is inexpensive, so kenaf fibers collected from kenaf bast are used. It is preferable.

  The natural fiber preferably has an average fiber length in the range of 5 to 150 mm. By constituting the fiber-based board with natural fibers having a certain fiber length, that is, short fibers, a fiber-based board having excellent bending strength and capable of suppressing the occurrence of burrs during cutting is obtained. When the short fiber length is less than 5 mm, the strength is remarkably lowered. On the other hand, if the short fiber length exceeds 150 mm, it becomes difficult to uniformly disperse natural fibers and polylactic acid fibers in the nonwoven fabric manufacturing process, resulting in a decrease in productivity and non-uniform strength. May fall. The average fiber length of the more preferable natural fiber is 20 to 130 mm, and the most preferable range is 50 to 100 mm.

(the film)
As a film constituting the fiber-based board with film, a film made of a thermoplastic resin is preferably used. For example, it is one or more kinds of resins selected from polylactic acid resins, polyester resins, polyolefin resins and the like. Among these, it is preferable to use a polylactic acid resin having good moldability, excellent strength, and environmentally friendly. The thickness of the film is preferably in the range of 30 to 500 μm. When the thickness of the film is less than 30 μm, there is a high possibility that natural fibers are mixed into the surface resin layer, and burrs may occur during cutting. In addition, in the case of a thick surface resin layer exceeding 500 μm, since a large amount of thermoplastic resin is present on the surface layer of the board, the chips soften due to the generation of frictional heat during the cutting process, and the chips on the board surface or the cutting machine. Becomes easier to stick. Furthermore, as a range of more preferable film thickness, it is 50-300 micrometers.

(Manufacturing method of fiber board and fiber board with film)
1. Nonwoven Fabric Manufacturing Method The fiber-based board of the present invention is formed by opening the polylactic acid fiber and the natural fiber by, for example, an opener, and then forming a web by a carding method or an airlaid method, and further laminating in 1 to 20 stages. . Then, the laminated body is put together and the fibers are intertwined by a needle punch method or the like to obtain a cloth-like nonwoven fabric having a high density. There is also a method of obtaining a nonwoven fabric by melting polylactic acid fibers and bonding the fibers with a known apparatus such as a heating furnace. At this time, the density is 0.03 to 0.40 g / cm ³ , the basis weight is 50 to 4500 g / m ² , and the cloth-like body is tightened with entangled fibers having a thickness of about ² to 400 mm. In this step, polylactic acid fibers and natural fibers are blended, opened, and entangled, so that they can be uniformly dispersed and are a fiber laminate in which two or more types of fibers are entangled with each other. A nonwoven fabric can be obtained.

2. Board forming method The fiber-based board of the present invention is hot-pressed for a certain time in order to form the nonwoven fabric obtained as described above into a board-like plate-like body. The press machine to be used may be a roll press machine that presses the material continuously between a pair of hot rolls, but a pair of upper and lower hot presses that can be heated with a high-frequency heat source to ensure sufficient hot press time. A hot press plate that presses the material through a platen is preferred.

  As for the timing of pressing and heating, after pressing, heating may be performed for a certain time in the next step, or these heating and compression may be performed simultaneously in one step. The pressing pressure is preferably in the range of 0.5 to 10 MPa. If it is less than 0.5 MPa, the time required for pressing becomes long, and the workability at the time of board molding is lowered, which is not preferable. If it exceeds 10 MPa, the pressing time is shortened, but the nonwoven fabric of the laminate is displaced and uniform. It is not preferable because there is a possibility that a new board cannot be molded. As the press temperature, the temperature conditions are set so that the platen temperature of the press and the internal temperature of the nonwoven fabric are within the range of minus 20 ° C. to plus 50 ° C. of the melting point of the polylactic acid fiber.

  Furthermore, it is more preferable to cool the fiber board thereafter. As a cooling method, the cooling press is performed under conditions of a pressure of 0.5 to 5 MPa and a temperature of 5 to 40 ° C. by a cooling press machine or the like. By appropriately manipulating these conditions, crystallization of polylactic acid is promoted, and a fiber-based board excellent in bending strength and cutting workability can be obtained.

  Moreover, a fiber board with a film can be obtained by laminating a film on the nonwoven fabric before pressing. As the press temperature when laminating the films, it is preferable that the platen temperature of the press machine be in the range of minus 20 ° C. to plus 35 ° C. of the melting point of the film.

3. Annealing treatment method Annealing treatment is preferably performed in order to improve the cutting workability of the board. The “annealing” treatment referred to in the present invention is a method of promoting recrystallization by reheating after board forming. As crystallization progresses, the macromolecules align with each other and the movement of the molecules is restricted, and even when the temperature is applied from the outside, the molecules do not move easily. Sticking of polylactic acid and adhesion of chips to the cutting surface can be suppressed. As a specific annealing treatment, the fiber-based board obtained after finishing the hot pressing step is put into a furnace such as a heating furnace or a hot air drying apparatus, and the temperature inside the furnace is adjusted to grow polylactic acid crystals. By heating at an accelerated temperature of 80 to 150 ° C. and heating for 2 to 400 minutes, it becomes possible to promote crystallization of polylactic acid and obtain a board that is resistant to frictional heat during cutting. Moreover, it is also preferable to perform press work again under the temperature of 80-150 degreeC.

  Even when the films are laminated, the annealing treatment can be performed under the above conditions.

  According to the present invention as described above, the polylactic acid adheres to the cutting blade, and chips adhere to the cutting surface due to frictional heat at the time of cutting the polylactic acid fiber-based board, which has been a problem until now. The fiber board which can suppress a burr | flash and was excellent in the intensity | strength can be obtained efficiently.

[Measuring method]
(1) Residual lactide amount 1 g of a sample is dissolved in 20 ml of dichloromethane, and 5 ml of acetone is added to this solution. Furthermore, it was made to deposit with cyclohexane, it was made to precipitate, it analyzed by the liquid chromatograph using Shimadzu GC17A, and the amount of lactide was calculated | required with the absolute calibration curve.

(2) Weight average molecular weight Polylactic acid was dissolved in chloroform to obtain a measurement solution, which was measured by gel permeation chromatography (GPC) to determine the weight average molecular weight in terms of polystyrene. The number of measurements was 5, and the average value was calculated.

(3) Carboxyl group end concentration A precisely weighed sample was dissolved in o-cresol (water 5%), and an appropriate amount of dichloromethane was added to this solution, followed by titration with a 0.02 N KOH methanol solution. . At this time, an oligomer such as lactide, which is a cyclic dimer of lactic acid, is hydrolyzed to generate a carboxyl group terminal, so that all of the carboxyl group terminal of the polymer, the monomer-derived carboxyl group terminal, and the oligomer-derived carboxyl group terminal are totaled. The carboxyl group terminal concentration obtained is obtained.

(4) Average particle diameter D50, content rate Average particle diameter D50 and content rate measured the average particle diameter D50 (micrometer) by the laser diffraction method using SALD-7100 by Shimadzu Corporation. Moreover, the content rate (volume%) of 10 micrometers or more was calculated | required from the obtained particle size distribution.

(5) Single yarn fineness Based on JIS L 1013 (1999) 8.3.1 A method, skein of 112.5m is sampled 5 times, the mass is measured, and the value (g) is 10,000 / 112. .5, the apparent fineness (dtex) was determined. From the apparent fineness, a positive fineness was determined by the following formula, and an average value was calculated.
Positive fineness (dtex) = D ′ × (100 + Rc) / (100 + Re)
Where D ′: apparent fineness (dtex)
Rc: Official moisture content (%)
Re: Equilibrium moisture content (%).

(6) Fiber length Measured according to JIS A 1015 (1999) 8.4.1. Weigh 800 mg of sample, create a staple diagram, divide the illustrated staple diagram into 50 fiber length groups, measure the boundary of each segment and the fiber length at both ends, and find 49 boundaries at the average fiber length at both ends The fiber length was added and divided by 50, the average fiber length (mm) was calculated, and the average value was taken twice.

(7) Tensile strength and tensile elongation Measured according to JIS A 1015 (1999) 8.7.1. The test was performed at a tensile speed of 20 mm / min and a gripping interval of 20 mm, and the tensile strength and tensile elongation were determined by the following formulas. The test number was tested 10 times, and the average value was calculated.
Tensile strength (cN / dtex) = SD / F0
Where SD: Maximum load (cN)
F0: Single yarn fineness of sample (dtex)
Tensile elongation (%) = (E1-E2) / (L + E1) × 100
Here, E1: Looseness (mm)
E2: Elongation at maximum load (mm)
L: Grasp interval (mm).

(8) Crimp number and crimp rate The crimp number was measured according to JIS L1015 (1999) 8.12.1, and the crimp rate was measured according to JIS L1015 (1999) 8.12.2.

(9) Melting point, crystallinity, temperature drop crystallization temperature Using a differential scanning calorimeter DSC-60, manufactured by Shimadzu Corporation, 2.0 mg of a sample was heated at a rate of 10 ° C / min, a target temperature of 200 ° C, and a hold time of 5 minutes. Thereafter, the measurement was performed at a temperature drop rate of −10 ° C./min and a target temperature of 30 ° C. The extreme temperature of the obtained melting endothermic curve (at the time of temperature rise) is the melting point (° C.), the enthalpy at that time is ΔHm (J / g), and the enthalpy of the crystallization exothermic curve (at the time of temperature rise) is ΔHc (J / g) The extreme temperature of the crystallization exothermic curve (at the time of cooling) was defined as the cooling crystallization temperature T′c (° C.). The number of tests was 5, and the average value was calculated. The crystallinity was calculated from the following formula.

Crystallinity (%) = 100 × (ΔHm + ΔHc) / 93
Where ΔHm: melting enthalpy (J / g)
ΔHc: crystallization enthalpy (j / g).

(10) Density and basis weight Density was measured according to JIS A 5905 (2003) 6.3. That is, after leaving the fiber board to stand for 24 hours in a standard state of a temperature of 20 ° C. and a humidity of 65% RH, three test pieces having an outer dimension of 10 cm × 10 cm were cut out. Next, the width, length, and thickness of one test piece were measured, the average values for each were obtained, the width, length, and thickness of the test piece were taken, and the volume (v) was obtained. Next, mass (g) was measured and calculated by the following formula. The thickness was measured to 0.05 mm, the width and length were 0.1 mm, the mass was measured to an accuracy of 0.01 g, and the density was calculated by the following formula up to 0.01 g / cm ³ units. After obtaining the density for each test piece, the average value of the three test pieces was obtained, and this value was taken as the density.

Density (g / cm ³ ) = m / v
Where m: mass (g)
v: Volume (cm ³ )
The basis weight is based on JIS L 1906 (2000) 5.2. Three test pieces of 20 cm × 25 cm were collected per 1 m width of the sample, and left for 24 hours in a standard condition of a temperature of 20 ° C. and a humidity of 65% RH. The mass (g) was measured, and the average value was expressed in terms of mass per 1 m ² (g / m ² ).

(11) Router processing The board was grooved with a router blade, and chip adhesion to the cutting surface of the processed board and the presence or absence of burrs were visually evaluated according to the following criteria.

[Cutting chips]
○: There is no chip adhesion on the board.

    X: Chips adhere to the board.

[Bari]
A: There is no burr on the board, and the surface of the board and the cutting surface are cut at right angles.

    ○: There is no burr on the board, but the surface of the board and the cutting surface are not cut at right angles.

    X: There are burrs on the board.

(12) Drilling The board was drilled with a drill blade, and whether or not chips and polylactic acid were fixed to the processing blade was visually evaluated according to the following criteria.

    ○: There is no chip and polylactic acid sticking to the blade.

    X: Chips and polylactic acid are fixed on the blade.

(Examples 1-3)
Polylactic acid chip (melting point 170 ° C., weight average molecular weight 150,000) and Nissan Chemical Industries, Ltd. zinc phenylphosphonate “ECOPROMOTE” having a particle diameter D50 of 3 μm as a crystal nucleating agent (content of particle diameter 10 μm or more Extruder-type spinning with 0% by volume based on the total amount) and 0.7% by weight of polycarbodiimide compound “LA-1” (1 equivalent of carbodiimide / 247 g of carbodiimide compound) manufactured by Nisshinbo Co., Ltd. The machine was melt spun at a spinning temperature of 230 ° C., the spun yarn was cooled, and after applying and converging the oil agent, it was taken up at 1000 m / min to obtain an undrawn yarn. In Examples 1 to 3, the content of the crystal nucleating agent in the fibers obtained was changed as shown in Table 1.

  The obtained undrawn yarn is converged to 800,000 dtex, drawn 4.0 times in a 90 ° C. liquid bath, mechanically crimped with a stuffer box, heat treated at 145 ° C. for 10 minutes, Was applied by a spray method so as to be 0.5% by weight with respect to the fiber, and cut to 51 mm to obtain a short polylactic acid fiber having a single particle fineness of 6.6 dtex. There was no yarn breakage or fluffing in the spinning and drawing processes, and the raw cotton could be obtained stably. The obtained polylactic acid short fibers have a tensile strength of 3.6 cN / dtex, a tensile elongation of 40%, a number of crimps of 10/25 mm, and a crimp rate of 11%, which are sufficiently practical mechanical properties, and T′c The crystallization rate was as fast as 129 ° C.

  On the other hand, kenaf bast fibers having an average fiber length of 75 mm were prepared as natural fibers.

The polylactic acid short fibers and kenaf bast fibers were mixed using a roller card at a weight ratio of 30:70, opened, and then entangled using a needle punch machine to obtain a nonwoven fabric. Next, this nonwoven fabric was laminated with a 13-layer stacking device to obtain a laminate having a basis weight of about 12,600 g / m ² . A hot plate heated at a platen temperature of 170 ° C. and a high-frequency press set so that the internal temperature of the laminate is 200 ° C., sandwiched with a spacer having a thickness of 18 mm, and at a pressure of 2.4 MPa Then, heating for 50 minutes and pressure molding were simultaneously performed, and then a cooling press was performed with a press machine having a platen temperature of 40 ° C. The thickness of the obtained fiber-based board was about 18.0 mm, and the density of the whole board was about 0.70 g / cm ³ .

Example 4
An unstretched polylactic acid film (melting point: 168 ° C.) having a thickness of 200 μm was laminated on both surfaces of the nonwoven fabric laminate used in Example 2, and a board was molded in the same manner as in Example 1.

(Comparative Example 1)
A board was molded in the same manner as in Example 1 except that the content of zinc phenylphosphonate in the polylactic acid short fibers was changed. (Comparative Example 2)
Except for changing the content of zinc phenylphosphonate in the polylactic acid fiber, an attempt was made to spin and stretch the polylactic acid short fiber in the same manner as in Example 1, but the fluff and yarn breakage occurred frequently, and the polylactic acid short fiber Could not be obtained stably.

(Comparative Example 3)
A board was formed in the same manner as in Example 1 except that polylactic acid short fibers were spun without adding a crystal nucleating agent.

(Comparative Example 4)
A board similar to that of Example 1 except that talc “SG-2000” manufactured by Nippon Talc Co., Ltd. having a particle diameter D50 of 2 μm (content of particle diameter of 10 μm or more is 0% by volume with respect to the total amount) is used as the crystal nucleating agent. Was molded.

  The results of Examples 1 to 4 and Comparative Examples 1 to 4 are shown in Table 1.

  It turns out that Examples 1-4 are excellent in "router workability" which is a board cutting process, and "drill workability". On the other hand, Comparative Examples 1 to 4 are deficient in both or either of the workability in the cutting process.

  In the fiber-based board of the present invention, the polylactic acid fiber has excellent heat resistance, the polylactic acid adheres to the processing blade, the chip adhesion to the cutting surface of the processing board and the burr problem are improved, and the processability is excellent. Therefore, it is useful as a gaming machine member, automobile member, building member, electric / electronic member, civil engineering member, agricultural material, and the like.

Claims (5)

  A polylactic acid fiber comprising 0.1 to 5.0% by mass of a phosphonic acid metal salt having an aromatic ring in a fiber made of a polylactic acid resin.   A fiber-based board comprising the polylactic acid fiber according to claim 1 and natural fibers, wherein the surface layer portion has a crystallinity of 10% or more and the middle layer portion is 40% or more. The fiber board according to claim 2, wherein the density is 0.1 g / cm ³ or more.   A fiber-based board with a film, wherein a film is laminated on at least one of the front and back surfaces of the fiber-based board according to claim 2 or 3.   A method for producing a fiber-based board, comprising mixing the polylactic acid fiber according to claim 1 and natural fiber, heating and pressurizing and integrally forming, and then annealing.