JP2004001577A - Compression oriented molded product and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fine compression oriented molded product which is almost free from anisotropy in terms of strength and has large strength on the whole compared with a thick molded product monoaxially stretched in the major axial direction and no voids even in the form of a composite body containing powder filler, and a manufacturing method for the molded product. <P>SOLUTION: This compression oriented molded product l is obtained by compressing a crystalline thermoplastic polymer material, and has a molecular chain(crystal) M substantially oriented obliquely toward the axis L of the molded product or a face including the axis L. A billet obtained by melt-molding the crystalline thermoplastic polymer material is forcibly packed at the crystallization temperature of the polymer material into a molding cavity with a small cross-section area from the billet storage cavity of a molding die through a drawing part with a tapered inner peripheral face or a drawing part at least with both sloping inner faces and the molecular chain(crystal) is oriented. <P>COPYRIGHT: (C)2004,JPO

Description

{Circle over (1)} The present invention relates to a compression-oriented molded article made of a crystalline thermoplastic polymer material and having high mechanical strength, and a method for producing the same.

Conventionally, in the field of synthetic resin fibers, a technique has been employed in which molecules are axially oriented by stretching to improve tensile strength. Also, in the field of synthetic resin films, a technique is employed in which molecules are axially or planarly oriented by uniaxial or biaxial stretching to improve unidirectional or multidirectional tensile strength in the film plane.

However, in a plate-shaped or block-shaped synthetic resin molded article having a large thickness or a thick rod-shaped or column-shaped synthetic resin molded article, much research has not been conducted to improve mechanical strength by using molecular orientation. Recently, there has been proposed a method of obtaining a osteosynthesis pin having a large bending strength by, for example, stretching a melt-molded product of a biodegradable and absorbable polymer material in a long axis direction while heating. Is a rare example.

However, in the rod-shaped molded body elongated in the long axis direction like the above-mentioned osteosynthesis pin, molecules are uniaxially oriented in a direction parallel to the long axis direction [machine direction (drawing direction; MD; machine (drawn) direction]). ), The transverse direction (TD; transversal direction) perpendicular to the long axis direction.
direction) and the molecular chain (crystal) orientation is large. Therefore, although the tensile strength in the long axis direction is remarkably improved, the tearing force in the long axis direction is reduced, and the shearing force in the transverse (oblique) direction is not significantly improved. Torsion force (torque
force) is relatively weak.

問題 Such a problem is not limited to a round bar extending in the long axis direction, but can be similarly applied to a columnar molded product or a plate-shaped molded product having a polygonal cross section. In particular, the higher the degree of stretching, the more the polymer material shifts from the spherulite structure to the fibrous structure and the degree of fibrillation progresses, and the tendency becomes more remarkable.

In addition, if the polymer material contains a powder filler, voids (voids) are formed at the front and rear portions of the powder filler along the stretching axis during stretching, and the density of the compact decreases. In addition, there is a problem that the strength is reduced due to the thin body.

The present invention has been made in view of the above-described problem, and has as its object the purpose of the present invention to have a small anisotropy in strength, and to provide a greater overall strength than a thick molded body uniaxially stretched in the major axis direction. To provide a dense compression-oriented molded article having no voids even if it is a composite containing powder filler (paticule reinforced composites), and to provide a method for producing the same. is there.

In order to achieve the object, the compression-oriented molded article of the present invention is a compacted article having a high strength that is made of a crystalline thermoplastic polymer material, and the molecular chains or crystals are substantially formed of the molded article. It is characterized by being obliquely oriented toward the axis or a plane containing the axis. Since the thermoplastic polymer material constituting this molded article is essentially a crystalline polymer, the crystals generated by the orientation of the molecular chains as described above are similarly oriented, and the form also contributes to the strength. . According to the compression-orientation molded product of the present invention, in the amorphous region, the molecular chains are partially oriented, and in the crystal region, the crystals containing the molecular chains (main chains) are oriented in the compression direction. Molecular chain orientation is used as a synonym for crystal orientation.

In the compression-oriented molded article of the present invention, the axis to which the obliquely oriented molecular chains (crystals) are directed is the axis that becomes the mechanical core of the molded article, that is, the point where the external force applied during molding is concentrated in the material advancing direction. A continuously configured axis, which is at the center or off-center of the compact. The plane to which the molecular chain (crystal) is directed is a plane including the axis, and is a boundary plane where external forces are balanced on both sides.

The main aspects of the compression-oriented molded article of the present invention include (1) molecular chains (crystals) oriented obliquely toward an axis located at the center or off-center from the outer peripheral surface of the substantially cylindrical shaped article. (2) The molecular chains (crystals) are oriented obliquely toward the axis or the plane containing the center at or off the center from each side surface of the prismatic shaped body. (3) the molecular chains (crystals) are oriented obliquely from both sides of the plate-like molded body toward a plane including a center or an off-centered axis and parallel to both surfaces of the molded body. And the like. Further, the compression-oriented molded article of the present invention contains a powder filler (may be a system containing fine short fibers for enhancing physical properties) as necessary. As the powder filler, one suitable for the use of the molded body is used. For example, when the use is a biomaterial, a bioceramic powder or the like is preferably used.

As in the case of the compression-oriented molded article of the present invention, those in which molecular chains (crystals) are substantially obliquely oriented toward an axis or a plane containing the axis which is a mechanical core of the molded article are referred to as an axial direction. The anisotropy of the molecular chain (crystal) orientation between the transverse direction perpendicular to the film is smaller than that of a so-called uniaxially stretched product stretched in the major axis direction. Therefore, not only bending strength and tensile strength in the axial direction, but also tear strength in the axial direction (longitudinal cracking resistance), shear strength in the lateral (oblique) direction (horizontal cracking resistance), and torsional strength around the axis For example, the strength against forces in various directions is improved as a whole, and the strength is less anisotropic.

In particular, a columnar or prismatic compression-orientation molded body in which molecular chains (crystals) are oriented obliquely toward a central axis has a torsion strength because the molecular chains (crystals) take a radially arranged form in a cross section. Notably improved. And, among the plate-shaped compression-oriented molded products, those in which molecular chains (crystals) are obliquely oriented toward a plane including an axis at a position off the center (a plane parallel to both surfaces of the molded product) Since the orientation angles of the molecules on both sides of the surface are different, the mechanical properties are different on both sides, and a plate-like molded body as if two sheets having different physical properties were laminated is obtained. By changing the position of the bias, the overall mechanical properties of the plate-shaped molded body can be variously adjusted according to the application.

Because the molded article of the present invention is compressed, it has a higher density, a higher mechanical strength and a larger surface hardness than conventional uniaxially stretched uncompressed molded articles. Further, even in the molded body containing the powder filler, voids are not generated unlike in the case of stretching, so that the strength is not reduced by the voids.

According to the production method of the present invention for producing the above-described compression-oriented molded body, the inner peripheral surface is truncated between the billet accommodating cavity having a large cross-sectional area and the bottomed molding cavity having a small cross-sectional area. Using a mold having a constricted constricted portion or a constricted portion in which at least both inner surfaces are flat inclined surfaces, and using a crystalline thermoplastic polymer material in a billet accommodating cavity of the formed die. A melt-molded essentially amorphous billet is accommodated, and the billet is passed through a constriction at a crystallization temperature higher than the glass transition point of the thermoplastic polymer material and lower than the melting temperature. And press-fit filling in a so-called cold state.

As in the production method of the present invention, when a billet obtained by melt-molding a crystalline thermoplastic polymer material is press-filled from a billet accommodating cavity of a mold through a narrowing portion at a crystallization temperature into a bottomed cavity, the billet is formed. When passing through the constricted portion, a large shear force is generated due to frictional resistance between the tapered surface or the inclined surface of the constricted portion, and this is an external force in a material traveling direction (MD: Mechanical Direction) and a transverse direction (TD: Transversal Direction) for orienting molecules. Therefore, the molecular chain (crystal) is compressed while being obliquely oriented toward the MD axis of the billet or a plane including the axis. Then, even after being filled in the molding cavity, a back pressure is applied by the inner surface and the bottom surface of the molding cavity, so that the molded body is fixed while maintaining the molecular chain (crystal) orientation and the compressed state. Therefore, the obtained molded body is compressed to be dense, and the molecular chains (crystals) maintain the shape of the oriented body having an oblique angle toward the axis of the molded body or a plane including the axis. . In this case, the orientation angle of the molecular chain (crystal) [the orientation angle of the molecular chain (crystal) with respect to the axis of the molded body or a plane including the axis] is determined by the inclination angle of the tapered surface or the inclined surface of the narrowed portion, and the inclination angle of both cavities. It is essentially determined by approximating the area ratio of the cross section. This will be described in detail later.

Further, when the billet is press-filled at the crystallization temperature as described above, the press-filling property is good, the molecules are effectively oriented, and the crystallinity can be adjusted as desired.

In the manufacturing method of the present invention, the inclination angle of the tapered surface or the inclined surface of the drawn portion with respect to the center axis of the molding die is set to 10 to 60 °, and the area of the cross section of the billet accommodating cavity is set to the cross sectional area of the molding cavity. It is desirable to set 1.5 to 6 times the area. When the inclination angle is less than 10 °, a large shearing force due to frictional resistance between the billet and the tapered surface or the inclined surface is less likely to occur, and the outer peripheral portion of the billet is liable to slide. Orientation cannot be achieved effectively. On the other hand, if the inclination angle is greater than 60 °, high pressure is required for press-fitting the billet, making press-fitting and filling work difficult, and even if press-fitting, the molecular chain orientation becomes non-uniform due to the stick slip phenomenon. It is not easy to obtain a satisfactory compression-oriented molded article because cracks and the like due to poor filling and the like tend to occur.

On the other hand, when the area of the cross section of the billet accommodating cavity is smaller than 1.5 times the area of the cross section of the molding cavity, the deformation ratio R = So / S (where So is the billet) (S is the cross-sectional area of the compression-oriented molded body) is substantially smaller than 1.5, and the orientation of molecular chains (crystals) and the compressibility of the material are low. It becomes difficult to improve. Conversely, even if it is larger than 6 times, the flow of the resin is not good enough to match it, so it is difficult to press-fit and fill the billet, and the orientation of the molecular chains becomes excessive, causing a fibrillation phenomenon, The molded product is easily torn between fibrils.

In particular, when the inclination angle of the tapered surface or the inclined surface of the narrowed portion is set to 15 to 45 ° and the area of the cross section of the billet accommodating cavity is set to 2 to 3.5 times the area of the cross section of the molding cavity, The press-filling is effective, and the molecular chains (crystals) having good compression orientation, orientation angle, and degree of compression are obtained, and MD and TD have little anisotropy and mechanical strength is excellent overall. A compression-oriented molded article can be obtained.

In addition, when a molding die in which the inclination angle of the tapered surface of the narrowed portion gradually changes over the entire circumference of the tapered surface or at an arbitrary portion is used, the molecular chain ( (Crystal) is obtained in the form of a columnar compression-formed body that is obliquely oriented, and the use of a mold in which the slope angle of at least one slope of the drawn portion is different from the slope angle of the other slopes results in the center of the formed body. Thus, a prism-shaped compression-orientation molded body in which molecular chains (crystals) are obliquely oriented toward an axis at a position deviated from the above. In particular, when using a mold in which one inclined angle of the opposed slopes of the narrowed portion is different from the other inclined angle, the orientation angle of the molecular chains (crystals) and the Accordingly, it is possible to obtain a compression-oriented molded article having different mechanical properties.

Furthermore, in the production method of the present invention, even if a billet obtained by melt-molding a crystalline thermoplastic polymer material containing a powder filler is used, the billet can be compressed as described above. It is possible to obtain a compression-oriented molded article without voids.

In the case of a method in which a billet is coldly extruded from a squeeze port as in the conventional solid extrusion method, the billet is compressed and molecular chains are oriented when passing through the squeeze port. At this point, the pressure from around the material is released, so that a so-called return phenomenon occurs in which the restraining force due to the compression is relaxed due to the effect of the ballast effect and the like, and the compression ratio of the extruded product is reduced, and the molecular orientation is disturbed. Therefore, a molded article oriented similarly to the compression-oriented molded article of the present invention cannot be obtained, and an extruded article having high mechanical strength cannot be obtained.

As is apparent from the above description, in the compression-oriented molded article of the present invention, since the molecular chains (crystals) are substantially obliquely oriented toward the axis of the molded article or a plane including the axis, the axial orientation And low transverse anisotropy of the molecular chain (crystal) orientation to the transverse direction perpendicular to this, so that the overall mechanical strength against forces in various directions such as bending strength, tensile strength, tear strength, shear strength and torsional strength In addition, it has an excellent effect of being densely improved and having a high surface hardness.

Further, the production method of the present invention can easily produce a compression-oriented molded article having excellent mechanical strength as described above, and can adjust the orientation angle of molecular chains (crystals) and perform mechanical This has a remarkable effect that physical properties can be easily adjusted.

Hereinafter, specific embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a conceptual diagram showing an orientation state of molecular chains (crystals) in a longitudinal section of a cylindrical compression-oriented molded product according to an embodiment of the present invention, and FIG. It is a conceptual diagram which shows the orientation state of the molecular chain (crystal) in the cross section.

The compression-oriented molded body 1 is a compressed cylindrical molded body made of a crystalline thermoplastic polymer material, and the molecular chain M is substantially at the center from the outer peripheral surface of the molded body 1 as shown in the figure. The crystal is oriented obliquely downward toward the axis L, and the crystal is similarly oriented along with the molecular chain orientation. In other words, the molded body 1 forms a substantially conical surface by connecting a number of reference axes of molecular chains (crystals) M having a radial arrangement around the central axis L. The substantially conical surface is oriented in the direction of the axis L at the center of the compact, and such crystals can also be seen to be aligned in the direction of the length of the column (TD).

As described above, the columnar compression-oriented molded body 1 in which the molecular chains (crystals) are oriented obliquely downward with respect to the axis L is dense, has a high density and a high surface hardness, and has an axis L direction and a lateral direction perpendicular thereto. The anisotropy of the molecular chain (crystal) orientation between them is small, so not only the bending strength and tensile strength but also the mechanical strength in various directions such as tear strength and shear strength are generally improved. Since the molecular chains (crystals) M take a radial arrangement around the axis L, the torsional strength is also improved.

配 向 It is important to adjust the orientation angle of the molecular chain (crystal) M with respect to the center axis L of the compression-orientation molded product 1 to about 10 to 60 °. When the tilt angle is smaller than 10 °, the molecular chain (crystal) orientation is nearly uniaxial orientation parallel to the central axis L, and the molecular chain (crystal) orientation is anisotropic in the direction of the axis L and in the lateral direction perpendicular thereto. Therefore, it is difficult to generally improve the mechanical strength in various directions. In addition, a molded product having an orientation angle of the molecular chain (crystal) M of more than 60 ° is difficult to press-fit as described below, so that it is not easy to manufacture and a crack or the like is generated, so that it is difficult to obtain a uniform molded product. In particular, in the molded article 1 in which the orientation angle of the molecular chain (crystal) M is adjusted to about 10 to 35 °, the anisotropy of the molecular chain (crystal) orientation is small, and the mechanical strength in various directions is generally remarkable. It is very preferable because it improves. The orientation angle of the molecular chain (crystal) M can be easily adjusted by changing the inclination angle of the tapered surface of the narrowed portion of the mold and the area ratio of the cross section of the billet housing cavity and the mold cavity as described later. .

As the thermoplastic polymer material as the raw material of the compression-orientation molded product 1, any crystalline and linear polymer can be used, and various types are selected and used depending on the use of the molded product. For example, when the application is a pin, rod, screw or the like for osteosynthesis, a biodegradable and absorbable polymer having an initial viscosity average molecular weight of about 100,000 to 700,000, preferably about 150,000 to 600,000. Lactic acid and various polylactic acid copolymers (eg, lactic acid-glycolic acid copolymer) are preferably used, and when the application is an industrial screw or the like, ultrahigh molecular weight polyethylene is preferably used. You. In addition, polyethylene terephthalate (Tg: 69 ° C., Tm: 230 ° C.), polyamide (Tg: 40 to 50 ° C., Tm: 225 to 265 ° C.), crystal phase and rubber phase Polypropylene (Tg: −20 ° C., Tm: 165 ° C.), poly-4-methylpentene-1 (Tg: 29 ° C., Tm: 250 ° C.).

Resins to which compression orientation processing can be applied are basically those in which the polymer phase at normal temperature is composed of a crystal phase and a rubber phase, and a crystal phase and a glass phase, and the processing temperature is lower than that of ordinary melt molding. The temperature can be selected by selecting a temperature slightly lower than the softening temperature (Ts) between the transition point (Tg) and the melting point (Tm). A resin having such a phase at room temperature can form each of the phases by an appropriate intermolecular force after being molded by the present molding method, and can maintain the shape. However, this method cannot be applied to a polymer consisting of only a crystal phase or a glass phase. However, a molded product is hard (hard) but lacks viscoelasticity and is brittle against deformation. Has the disadvantage of cracking and is often undesirable in some applications. In order to impart toughness to the compression-oriented molded body 1 or to facilitate plastic deformation at the time of production, an appropriate amount of an amorphous thermoplastic polymer material may be mixed and used.

圧 縮 The compression-oriented molded product 1 may contain a powder filler (not shown) uniformly depending on the use. Even if the powder filler is contained in this way, since the compact 1 is compressed, no voids (voids) exist around the powder filler, and the mechanical strength does not decrease. As the powder filler, those having a size of the particles or aggregates of the particles of about 0.1 to 300 μm can be used. It is necessary to select and use fine particles of about 0.1 to 50 μm or aggregates when it is required to have a high mechanical strength. There is. However, in the case of a compact having no details and not requiring extremely high strength, particles of about 50 to 300 μm or aggregates thereof can be uniformly dispersed and used.

(4) The content of the powder filler is desirably about 10 to 70 wt%. If it is less than 10 wt%, the effect of adding the powder filler is small, and if it exceeds 70 wt%, the amount is too large, and the obtained molded body is brittle.

What is necessary is just to select and contain a powder filler suitable for the use of the compression-orientation molded product 1. For example, when the use is an osteosynthesis material or other implant material, a bio-bonding material having a binding property to bone is used. It is desirable to include ceramic powder. For applications requiring improved heat resistance, use silica, bentonite, calcium carbonate, etc., for applications requiring conductivity, use carbon black, polyaniline, etc., and for applications requiring thermal conductivity, use alumina, etc. For applications requiring abrasion resistance, graphite or the like is preferably contained.

The above-mentioned cylindrical compression-oriented molded body 1 is provided between a molding die 2 as shown in FIG. 7, that is, a large-diameter cylindrical billet accommodating cavity 2a and a small-diameter cylindrical molding cavity 2c with a bottom. A molding die 2 having a constricted portion 2b whose peripheral surface is formed in a tapered surface with a constriction provided coaxially, and a male mold 2d for pressurization inserted into a billet accommodating cavity 2a (hereinafter referred to as an accommodating cavity). Used and manufactured in the following manner.

First, a crystalline thermoplastic polymer material is melt-molded to form a cylindrical billet 10 having a diameter substantially equal to the inner diameter of the housing cavity 2a, and the billet 10 is placed in the housing cavity 2a as shown in FIG. To accommodate. As a method for producing the billet 10, a melt extrusion molding method is preferably employed, but another molding method such as an injection molding method or a compression molding method may be employed. However, these preforms must be formed under conditions that are basically amorphous so that they can be easily processed at temperatures of Tm or lower and Tg or higher. In the case of these biodegradable and absorbable thermoplastic polymer materials, it is important to adopt a temperature condition slightly higher than their melting point and a minimum extrudable pressure condition in order to suppress molecular weight reduction. It is. For example, when a polylactic acid (PLLA) having a viscosity-average molecular weight of about 100,000 to 700,000 as described above as a polymer material is melt-extruded to form a billet, a billet is formed at a melting point or higher and 220 ° C. or lower, preferably 200 ° C. or lower. It is preferable to employ the following temperature conditions and pressure conditions of 260 kg / cm ^ 2 or less, preferably about 170 to 210 kg / cm ^ 2. In the case of manufacturing a compression-oriented molded body containing a powder filler, a thermoplastic polymer material in which the powder filler is uniformly blended is similarly melt-molded to produce a billet 10 which is a pre-molded body. May be accommodated in the accommodation cavity 2a.

Next, the billet 10 is pressed at a crystallization temperature higher than the glass transition point of the thermoplastic polymer material and lower than the melting temperature by press-fitting the male mold 2d into the receiving cavity 2a while continuously or intermittently applying pressure. As shown, the molding cavity 2c with the bottom is continuously and intermittently press-filled through the narrowing portion 2b. At this time, the air inside the molding cavity 2c is naturally drawn out from a minute hole (not shown) formed at the bottom of the molding cavity 2c.

When press-fitting is performed in this manner, when the billet 10 passes through the constricted portion 2b, a large shearing force is generated between the billet 10 and the tapered surface of the constricted portion 2b due to frictional resistance. Since it acts as an external force in the TD direction, the molecular chains (crystals) are compressed while being oriented obliquely downward toward the axis Lc at the center of the mold 2, and crystallization proceeds. After being filled in the molding cavity 2c, the molding 1 is fixed while receiving the back pressure from the inner surface and the bottom surface of the molding cavity 2c and maintaining the molecular chain (crystal) orientation and the compressed state. Accordingly, the obtained columnar molded body 1 is compressed to be dense, and the molecular chains (crystals) M are oriented obliquely downward from the outer peripheral surface toward the center axis L of the molded body as described above. become.

In this case, the orientation angle of the molecular chain (crystal) (the angle of the orientation axis of the molecular chain (crystal) with respect to the axis serving as the mechanical center of the molded body) is determined by the inclination angle of the tapered surface of the narrowed portion 2b (the inclination angle of the mold 2). (The inclination angle with respect to the center axis) and the area ratio of the cross section of both cavities 2a and 2c. That is, as shown in FIG. 9, the radius of the receiving cavity 2a is R, the radius of the molding cavity 2c is r, the inclination angle of the tapered surface of the narrowed portion 2b with respect to the center axis Lc of the molding die is θ, and both cavities 2a, The area ratio of the cross section of 2b is A = R ^ 2 / r ^ 2, and the point X on the outer peripheral portion of the billet is pressed along the tapered surface in the direction of the axis Lc by the distance d while the center X is on the center axis Lc. Assuming that the distance at which the point Y is pressed is D, the molecular chains (crystals) are oriented in the direction of the line segment lm. Assuming that the orientation angle (the orientation angle with respect to the axis Lc) of the molecular chain (crystal) oriented in the direction of the line segment lm is θm, tan θm = r / D−d, and since D−d = A · d, tan θm = R / A · d [Equation 1]. d = (R−r) / tan
Since θ is substituted into [Equation 1], tan θm = rtan θ / A (R−r) [Equation 2], and R = r · A0.50.5. Substituting into
tan θm = tan θ / A (A ^ 0.5 -1) [Equation 3].

That is, the molecular chains (crystals) are oriented obliquely with respect to the axis at the orientation angle θm that satisfies the above [Equation 3]. As the inclination angle θ of the tapered surface increases, the orientation of the molecular chains (crystals) increases. As the angle θm increases and the area ratio A of the cross section of both cavities increases, the orientation angle of the molecular chain (crystal) decreases. Therefore, by changing the inclination angle θ of the tapered surface and the area ratio A, the molecular chain (crystal) can be adjusted to a desired orientation angle θm.

However, considering the ease of press-fitting work of the billet 10 and the orientation of molecular chains (crystals), the inclination angle θ of the tapered surface of the narrowed portion 2b is set to 10 to 60 °, and the accommodation cavity 2a Is set to 1.5 to 6 times the area of the cross section of the molding cavity 2c, and the deformation ratio R of the obtained compression-oriented molded product 1 is R = So / S (where So is the billet 10 It is desirable that the cross-sectional area, S, is substantially 1.5 to 6.0. When the inclination angle θ of the tapered surface is less than 10 °, a large shearing force due to the frictional resistance between the billet 10 and the tapered surface is less likely to occur, the outer peripheral portion of the billet 10 is easily slid, and the molecules can efficiently reach the inside of the molded body 1. It is difficult to orient the chains (crystals). On the other hand, if the inclination angle θ is larger than 60 °, high pressure is required for press-fitting the billet 10 and press-fitting work becomes difficult. ) It is not easy to obtain a satisfactory compression-oriented molded product 1 because the orientation tends to be inhomogeneous and cracks are likely to occur. If the area of the cross section of the housing cavity 2a is smaller than 1.5 times the area of the cross section of the molding cavity 2c, the orientation of molecular chains (crystals) is poor due to low compressibility, and mechanical It becomes difficult to greatly improve the strength. Conversely, if it is larger than 6 times, it becomes difficult to press-fit and fill the billet 10, and the orientation becomes excessive and fibrillates, so that the molded article 1 is easily torn between fibrils.

In particular, the inclination angle θ of the tapered surface of the narrowed portion 2b is set to 15 to 45 °, and the area of the cross section of the receiving cavity 2a is set to 2 to 3.5 times the area of the cross section of the molding cavity 2c. In the case of setting, the press-fitting fillability of the billet 10, the orientation and orientation angle of the molecular chains (crystals), the compressibility, and the like are improved, and the compression-oriented molded body 1 having less anisotropy and excellent mechanical strength can be easily obtained. It is very preferable because it can be obtained.

Depending on the type of the thermoplastic polymer material, the billet 1 can be press-filled at room temperature lower than the glass transition point (Tg) (when the polymer has a Tg higher than room temperature). In order to achieve the effect of molecular chain (crystal) orientation and the adjustment of the degree of crystallinity, the crystallization temperature of the billet 1 in the accommodation cavity 2a from the glass transition temperature (Tg) to the melting temperature (Tm). It is important to select (Tc), heat, and press-fit the cavity 2b. Therefore, when the thermoplastic polymer material is a crystalline polymer such as polylactic acid or a copolymer of lactic acid and glycolic acid, any temperature within the effective crystallization temperature range of 80 to 110 ° C. It is appropriate to select and press-fit.

In this case, the pressure for press-fitting the billet 1 varies depending on the polymer, but is usually 4000 kgf / cm ^ 2 or less, preferably 2000 kgf / cm ^ 2 or less. 4000kgf / cm ^ 2
If the pressure is excessively exceeded, the shear force and the resulting heat will cause a significant decrease in the molecular weight, crystallization will not be performed sufficiently, and the oriented phase will not form a stable system. It becomes difficult to obtain the oriented molded body 1.

The press-fitting speed is suitably from 8 to 80 mm / min when a special surface treatment for improving the slip is not applied to the inner surface of the mold. If the press-fitting is performed at a lower speed than this, the portion of the billet 10 that has not yet been press-fitted into the molding cavity 2c is hardened by the progress of crystallization, making it difficult to press-fit. On the other hand, if the press-fitting is performed at a speed higher than the above, stick-slip occurs and an inhomogeneous molded body 1 is obtained, which is not good.

The degree of crystallinity of the obtained compression-oriented molded product 1 varies depending on the deformation ratio R of the molded product 1, the temperature, pressure, time (pressing speed) at the time of press-fitting, and generally, the deformation ratio R is large and the temperature is high. The higher the pressure and the longer the time, the higher the crystallinity. The degree of crystallinity of the compression-oriented molded body 1 in the case of polylactic acid and its copolymer is desirably in the range of 30 to 60%. The balance between the ratio of the phase and the amorphous phase is good, and the improvement in strength and hardness by the crystalline phase and the flexibility by the amorphous phase are well harmonized, so that there is no brittleness as in the case of only the crystalline phase, A weak property without strength as in the case of only an amorphous phase does not appear. Therefore, a molded article having toughness and sufficiently high strength overall is obtained. When the degree of crystallinity is less than 30%, improvement in strength due to crystals cannot generally be expected. On the other hand, if the degree of crystallinity increases, the strength increases accordingly, but if the degree of crystallinity exceeds 60%, the brittle property of easily breaking when subjected to an impact or the like due to lack of toughness is remarkably exhibited. In addition, the degradation in the living body is slow, which is not preferable as the degradation characteristics of the implant. For this reason, in the case of a biodegradable and absorbable thermoplastic polymer such as polylactic acid and a copolymer thereof, the deformation ratio R of the compression-orientation molded product 1 and the temperature, pressure, time and the like at the time of press-fitting are set as described above. It is desirable to control the crystallinity of the compression-oriented molded product 1 to 30 to 60% by controlling the temperature within the range described above or performing a short-time heat treatment at the crystallization temperature after press-fitting. And the range of the more desirable crystallinity of those compression-orientation molded objects 1 is 40 to 50%.

{Circle around (4)} The columnar compression-oriented molded body 1 molded as described above is removed from the mold 2 after cooling, and the blank material portion 1a that is not compression-oriented is cut off. Then, it is used in various applications as it is without processing, or after being cut into a desired shape such as a screw, a nail, or a cylindrical object.

FIG. 3 is a conceptual diagram showing an orientation state of molecular chains (crystals) in a longitudinal section of a plate-shaped compression-oriented molded product according to another embodiment of the present invention, and FIG. FIG. 3 is a conceptual diagram showing an orientation state of a molecular chain (crystal) in the cross section.

As shown in the figure, the plate-shaped compression-oriented molded body 1 has molecular chains (crystals) M of a crystalline thermoplastic polymer material obliquely downwardly from both sides of the molded body 1 toward a plane P including a central axis. Is oriented. This plane P is located at a position parallel to both surfaces of the plate-shaped molded body 1 and bisecting the plate-shaped molded body 1 in the thickness direction, and the orientation angles of the molecules M on both sides of the plane P are equal to each other. This plate-shaped compression-oriented molded product 1 also has small anisotropy in molecular orientation in the direction of the plane P and the transverse direction perpendicular thereto, and has a high density due to compression. Is generally better. The plate-shaped molded body 1 may of course contain a powder filler.

Such a plate-shaped compression-oriented molded body 1 has inner surfaces on both sides between a wide rectangular receiving cavity 2a having a large cross-sectional area and a narrow rectangular forming cavity 2c having a small cross-sectional area. A thick plate-shaped billet 10 obtained by melt-molding a crystalline thermoplastic polymer material using a molding die 2 having a narrowed portion 2b having inclined surfaces having the same inclined angle at both long sides facing each other. Is housed in the housing cavity 2a, and the billet 10 is continuously or intermittently press-fitted into the molding cavity 2c through the narrowed portion 2b at the crystallization temperature by the male mold 2d. In the compact 1 oriented in such a compression manner, the material is subjected to a force directed obliquely downward and inward by the slopes on both sides of the narrowed portion 2b, and the portions where the forces from both sides are balanced are parallel to the both faces of the compact. It becomes P.

The above embodiment is about manufacturing a columnar and plate-shaped compression-oriented molded body, but when manufacturing a prism-shaped compression-oriented molded body, a rectangular cylindrical shape having a large cross-sectional area is used. A molding die 2 is used which is coaxially provided with a narrowed portion 2b whose side surface is formed on a slope having a downward constriction, between a housing cavity 2a and a molding cavity 2c having a rectangular cross section with a small cross section. Then, the prismatic billet 10 is housed in the housing cavity 2a, and the male mold 2d is similarly press-fitted, so that the billet 10 is continuously or intermittently press-filled into the molding cavity 2c through the drawing portion 2b at the crystallization temperature. Just do it. When pressed and filled in this manner, the molecules are substantially prism-shaped compression orientations in which molecules are oriented obliquely from each side surface of the molded body toward the center axis or the plane including the axis, which forms the mechanical center of the molded body. A molded article is obtained. It is needless to say that the prism-shaped molded body is not limited to a quadrangular prism, but may be a triangular prism or a pentagon or more polygonal prism.

FIG. 5 is a conceptual diagram showing a molecular orientation state in a longitudinal section of a plate-shaped compression-oriented molded product according to still another embodiment of the present invention, and FIG. It is a conceptual diagram which shows the orientation state of the molecule | numerator in a surface.

As shown in the figure, the plate-shaped compression-oriented molded body 1 has a molecular chain (crystal) M of a crystalline thermoplastic polymer material on both sides of the molded body 1 and on a plane P deviated from the center to one side. It is oriented obliquely downward. This plane P is a plane that includes an axis at a position off the center of the molded body 1 and is parallel to both surfaces of the plate-shaped molded body 1. The orientation angles of the molecular chains (crystals) M on both sides of the plane P are Different from each other.

Such a plate-like compression-oriented molded product 1 has a small anisotropy of molecular chain (crystal) orientation in the plane P direction and the transverse direction perpendicular thereto, and is dense by compression. Of course, the mechanical strength in the direction is excellent in general, but furthermore, since the orientation angles of the molecular chains (crystals) M on both sides of the plane P are different, the mechanical properties are different on both sides. Since the plate-like molded body is obtained as if two sheets having different physical properties are laminated, the overall mechanical physical properties of the plate-like molded body 1 can be changed according to the application by changing the position of the deviation of the plane P. Various adjustments are possible. The plate-shaped molded body 1 may of course contain a powder filler.

Such a plate-shaped compression-oriented molded body 1 has a pair of inner surfaces (opposite to each other) between a rectangular housing cavity 2a having a large cross-sectional area and a narrow rectangular molding cavity 2c having a small cross-sectional area. Using a forming die 2 having a narrowed portion 2b whose inner surfaces on both long sides are inclined at different inclination angles, and a thick plate-shaped billet is formed in the same manner as in the case of the plate-shaped compression-oriented molded body. 10 can be manufactured by press-fitting into the molding cavity 2c through the drawing portion 2b at the crystallization temperature. By changing the inclination angles of the inclined surfaces on both sides of the narrowed portion 2b, the position of the deviation of the plane P and the orientation angle of the molecular chain (crystal) M can be arbitrarily adjusted.

Similarly, as the forming die, a forming die in which the inclination angle of the tapered surface of the drawn portion 2b of the forming die 2 shown in FIGS. 7 and 8 gradually changes over the entire circumference of the tapered surface or at an arbitrary portion is used. When a columnar compression-oriented molded article is manufactured, the molecular chains (crystals) are oriented obliquely downward toward an axis located at a position off the center of the molded article, and the orientation angle is set over the entire circumference of the molded article or in part. As a result, a columnar molded body that gradually changes is obtained. Then, when a prismatic compression-oriented molded body is manufactured by using a molding mold in which at least one slope of the drawn portion has a different inclination angle from the other slopes, the molecular chains (crystals) of the molded body are reduced. Each of the side surfaces is obliquely oriented toward an axis located at an off-center position or a plane including the axis (in the case of a prism-shaped molded body having a horizontally long polygonal cross section), and the orientation angle of the drawn portion is A different prism-shaped compression-orientation molded product is obtained according to the inclination angle of each slope.

Hereinafter, more specific examples of the present invention will be described.

Poly-L-lactic acid having a viscosity average molecular weight of 400,000 was melt-extruded at 190 ° C. using an extruder to obtain a cylindrical billet having a diameter of 13 mm, a length of 50 mm, and a viscosity average molecular weight of 300,000.

This billet is placed in a cylindrical receiving cavity of a molding die having a diameter of 13 mm, heated to 110 ° C., and passed through a narrowed portion having a taper surface inclination angle of 45 °, a cylinder having a diameter of 8.5 mm and a length of 92 mm. By press-fitting and filling into a cylindrical molding cavity, a cylindrical compression-oriented molded body (deformation ratio R = 2.3) having the same size as the molding cavity was obtained.

Then, the compression-oriented molded product was cut to produce an osteosynthesis pin having a diameter of 3.2 mm and a length of 40 mm, and the bending strength, density, crystallinity, and fracture torque value were measured. The results are shown in Table 1 below. The bending strength was measured by a three-point bending test method [JIS K 7203 (1982)], the density was calculated from the size and weight of the compact, and the crystallinity was determined from the results of analysis by a differential scanning calorimeter (DSC). The calculated and the breaking torque values were measured with a torque tester (Screw Tester, manufactured by Shinpo Kogyo Co., Ltd.).

For comparison, the same physical properties were measured for osteosynthesis pins of the same shape made of poly-L-lactic acid having a draw ratio of 2.3 times and stretched in the major axis direction, and the results are also shown in Table 1.

As shown in Table 1, the compression-oriented osteosynthesis pin of the present invention had a higher bending strength and a higher density than the osteosynthesis pin formed by stretching. In addition, the fracture torque value of the osteosynthesis pin of the present invention is larger than that of the osteosynthesis pin of the present invention, which indicates that the osteosynthesis pin of the present invention has improved torsional strength.

In order to examine the orientation state of the molecules, as shown in FIG. 10, a through hole perpendicular to the center axis of the cylindrical billet 10 melt-formed in Example 1 was drilled, and a thin wire 11 of the same polylactic acid was colored. It was inserted into the through hole. Then, the billet 10 is heated at 110 ° C. in the cavity of the molding die, and is passed through a narrowed portion having a taper surface inclination angle of 45 ° into a cylindrical molding cavity having a diameter of 7.8 mm and a length of 95 mm. By press-fitting, a columnar compression-oriented molded body (deformation ratio R = 2.8) having the same size as the molding cavity was obtained.

は As shown in FIG. 11, in the obtained compression-oriented molded body 1, the wire 11 was bent in a substantially V shape, and the width of the wire was expanded in the axis L direction. This confirmed that the molecular chains (crystals) were obliquely oriented from the outer peripheral surface side of the molded body toward the central axis L.

Next, the orientation angle of the molecules of the compression-orientation molded product 1 was calculated using the above-mentioned [Equation 3], assuming that the area ratio A = 2.8 and the inclination angle θ of the tapered surface = 45 °. The calculated value was about 28 ° and the measured value was about 30 °, as compared with the actually measured value of the inclination angle θ of the wire 11 of the compression-orientation molded body 1, which was almost the same.

A poly-L-lactic acid having a viscosity average molecular weight of 400,000 was extruded at 190 ° C. by an extruder to obtain a plate-shaped billet having a width of 10 mm, a thickness of 4 mm and a length of 50 mm.

This billet is placed in a rectangular cylindrical receiving cavity having a width of 10 mm and a thickness of 4 mm of a molding die and heated to 110 ° C., and one of two opposite slopes (both long sides) has a slope angle of 45 ° and the other slope angle is 45 °. Is press-fitted into a rectangular cylindrical molding cavity having a width of 10 mm, a thickness of 1.6 mm, and a length of 110 mm through a narrowed portion having an inclination angle of 15 °, thereby forming a plate-shaped member having the same size as the molding cavity. A compression-oriented molded product (deformation ratio R = 2.5) was obtained.

Then, the compression-oriented molded body is cut into a length of 50 mm to produce an osteosynthesis plate having a width of 10 mm and a thickness of 1.6 mm, and the bending strength of the plate is reduced from the slope having the inclination angle of 15 °. The force was applied to a surface narrowed from the inclined surface having an inclination angle of 45 °, and the measurement was performed. As a result, when a force was applied to a surface narrowed from a slope having a tilt angle of 15 °, the bending strength was 234 MPa, whereas a force applied to a surface narrowed from a slope having a tilt angle of 45 ° was measured. In this case, it was 248 MPa.

This is because, due to the difference in the inclination angle of the slope, the shear force received by friction at the time of press-fitting is different, so that the molecular chain orientation of the polymer inside the plate is different between the 15 ° side and the 45 ° side, as if the physical properties are different. It is considered that the two types of plates have a laminated structure. In other words, it is considered that the 45 ° side is denser than the 15 ° side because the shearing force and the press-in pressure received during press-fitting and filling are large. Such a plate having different physical properties on both sides is deformed into a curve at a temperature higher than the glass transition temperature of poly-L-lactic acid (for example, hot water of 80 ° C.) to form a shape suitable for an arbitrary living body part. It is effective to select a side to facilitate more elaborate processing.

Next, a plate for osteosynthesis having the same degree of deformation and size was manufactured using a molding die in which the inclination angles of the inclined surfaces of the drawn portions were both 45 °, and the bending strength was measured. As a result, the bending strength was 256 MPa, which exceeded the strength of the plate. Accordingly, the plate is uniformly oriented from both sides of the plate, and is a dense compression-oriented molded body.

A high-density polyethylene having a viscosity-average molecular weight of 85,000 (manufactured by Mitsubishi Yuka Co., Ltd.) is melt-extruded at 230 ° C. using an extruder, and has a square cross section of 10 mm square and 50 mm length. A crystallized billet was obtained.

Next, this billet was placed in a square cylindrical receiving cavity having a side of 10 mm, heated to 95 ° C., and passed through a narrowed portion having a slope of 15 ° with a slope of 15 °. By press-fitting into a 120 mm square cylindrical molding cavity, a prismatic compression-oriented molded body (deformation ratio R = 3.0) having the same size as the molding cavity was obtained.

Then, the tensile strength of this compression-oriented molded product was measured. However, the tensile test method was performed according to JIS K 7113 (1981).

Further, the billet was cut into a prism having the same size as that of the compression-orientation molded product, and the tensile strength was measured in the same manner.

As a result, the billet after cutting was 19.6 MPa, whereas the compression-oriented molded product was improved to 32.4 MPa.

PLLA having a viscosity average molecular weight of 400,000 was extruded by the same method and under the same conditions as in Example 1 to obtain a billet having a viscosity average molecular weight of 300,000. Next, this billet was put into a cylindrical receiving cavity of a molding die having a diameter of 13 mm, and was passed through a narrowed portion having a taper surface inclination angle of 45 ° to a cylindrical molding cavity having a diameter of 10.6 mm and a length of 60 mm. Under the same conditions as described above, press-fitting was performed to obtain a columnar compression-oriented molded body having a deformation ratio R of 1.5. A pin having a diameter of 3.2 mm and a length of 40 mm was prepared from this molded body by cutting, and subjected to the same physical property test (excluding the fracture torque test) as in Example 1. As a result, the flexural strength was 168 MPa, the density was 1.250 g / cm ^ 2, the crystallinity was 44.7%, and the flexural strength and density were higher than those of the uniaxially stretched product at the same stretching ratio as the deformation ratio R. Was.

The billet of PLLA obtained in Example 5 was put into a cylindrical accommodation cavity having a diameter of 13.0 mm of a molding die, and was formed into a 5.3 mm diameter, 220 mm length molding through a narrowed portion having a taper surface with a tilt angle of 15 °. The cavity was press-filled under the same conditions as in Example 1, and an attempt was made to obtain a PLLA compression-oriented molded body having a deformation ratio R of 6.0. However, press-fitting required a very high pressure of 10,000 kgf / cm ^ 2, and the resulting molded article had cracks.

Similarly, a trial production was conducted when the degree of processing R was 5.5, but cracks were only partially present. However, when a treatment for making the surface of the mold slippery was performed, a high-quality compression-oriented molded product was obtained.

Polya-L-lactic acid having a viscosity average molecular weight of 400,000 in which hydroxyapatite (calcined at 900 ° C.) having an average particle size of 1.84 μm (dispersed at 900 ° C.) is uniformly dispersed is melt-extruded at 185 ° C. by an extruder to obtain a diameter of 13.0 mm. A cylindrical billet having a length of 40 mm and a viscosity average molecular weight of 250,000 was obtained.

This billet is put into a cylindrical receiving cavity having a diameter of 13.0 mm of a mold, heated to 107 ° C., and passed through a narrowed portion having a taper surface with a tilt angle of 15 °, and has a diameter of 7.8 mm and a length of 90 mm. By press-fitting into the cylindrical molding cavity, a cylindrical compression-oriented molded body (deformation ratio R = 2.8) containing a powder filler and having the same size as the molding cavity was obtained. When the bending strength, density and crystallinity of this molded body were measured in the same manner as in Example 1, the bending strength was 280 MPa, the density was 1.50 g / cm ^ 3, and the crystallinity was 42.5%. It had excellent bending strength.

FIG. 3 is a conceptual diagram showing an orientation state of molecular chains (crystals) in a vertical cross section of a columnar compression molded body according to one embodiment of the present invention. FIG. 3 is a conceptual diagram showing an orientation state of molecular chains (crystals) in a cross section of the columnar compression molded body of the embodiment. FIG. 4 is a conceptual diagram showing an orientation state of molecular chains (crystals) in a longitudinal section of a plate-shaped compression molded body according to another embodiment of the present invention. FIG. 3 is a conceptual diagram showing an orientation state of molecular chains (crystals) in a cross section of the plate-shaped compression molded body of the embodiment. It is a key map showing the orientation state of the molecular chain (crystal) in the longitudinal section in the plate-shaped compression molding concerning other embodiments of the present invention. FIG. 3 is a conceptual diagram showing an orientation state of molecular chains (crystals) in a cross section of the plate-shaped compression molded body of the embodiment. FIG. 3 is a cross-sectional view showing a state before press-fitting and filling a billet into a molding cavity of a mold in one embodiment of the production method of the present invention. FIG. 4 is a cross-sectional view showing a state after the billet is press-fitted into a molding cavity of a molding die in the same embodiment. FIG. 3 is an explanatory diagram for obtaining an orientation angle of a molecular chain (crystal). It is sectional drawing of the column-shaped billet manufactured in order to investigate the orientation state of a molecular chain (crystal). It is sectional drawing of the columnar compression molding obtained using the same billet.

Explanation of reference numerals

Reference Signs List 1 compression-oriented molded body 2 molding die 2a receiving cavity 2b drawing part 2c, molding cavity 2d male die 10 billet θm orientation angle of molecular chain (crystal) θ inclination angle of tapered surface or inclined surface of drawing part L axis of molding (center Axis)
Lc Center axis of mold M Molecular chain (crystal)
P Surface including the axis of the mold

Claims (13)

A compressed molded body made of a crystalline thermoplastic polymer material, wherein molecular chains or crystals are substantially obliquely oriented toward an axis of the molded body or a plane including the axis. Compression-oriented moldings. The compression-oriented molded body according to claim 1, wherein the axis of the molded body is an axis serving as a mechanical core of the molded body, and is located at the center or at a position off the center of the molded body. 3. The compression-oriented molding according to claim 2, wherein the molecular chains or crystals are obliquely oriented toward an axis located at a center or an off-center position from the outer peripheral surface of the substantially columnar molded body. body. 3. The method according to claim 2, wherein the molecular chains or crystals are oriented obliquely toward an axis or a plane containing the axis at a center or off-center from each side face of the substantially prismatic shaped body. 3. The compression-oriented molded product according to item 1. The molecular chains or crystals are oriented obliquely from both sides of the substantially plate-like molded body toward a plane including an axis at the center or an off-center position of the molded body and parallel to both surfaces of the molded body. The compression-oriented molded product according to claim 2, wherein: The compression-oriented molded product according to any one of claims 1 to 5, wherein the molded product contains a powder filler. The compression-oriented molded product according to claim 6, wherein the powder filler is a bioceramic powder. Between the billet accommodating cavity having a large cross-sectional area and a molding cavity having a bottom having a small cross-sectional area, there is a constricted portion whose inner peripheral surface is a tapered surface or a constricted portion in which at least both inner surfaces are inclined surfaces. Using a mold, an essentially amorphous billet obtained by melt-molding a crystalline thermoplastic polymer material is accommodated in a billet accommodating cavity of the mold, and a glass transition point of the thermoplastic polymer material is stored. A method of press-fitting the billet into a molding cavity having a bottom through a drawing portion at a crystallization temperature higher than the melting temperature. The inclination angle of the tapered surface or the inclined surface of the narrowed portion is 10 to 60 °, and the area of the cross section of the billet accommodating cavity is 1.5 to 6 times the area of the cross section of the molding cavity. 9. The production method according to 8. The tapered surface or the inclined surface of the narrowed portion has an inclination angle of 15 to 45 degrees, and the area of the cross section of the billet receiving cavity is 2 to 3.5 times the area of the cross section of the molding cavity. 9. The production method according to 8. The inclination angle of the tapered surface of the constricted portion changes gradually over the entire circumference of the tapered surface or at an arbitrary portion, or the inclination angle of at least one inclined surface of the constricted portion is different from the inclination angles of the other inclined surfaces. The method according to any one of claims 8 to 10, wherein: The method according to any one of claims 8 to 11, wherein the billet is obtained by melt-molding a crystalline thermoplastic polymer material containing a powder filler. The method according to claim 12, wherein the powder filler is a bioceramic powder.