JP2006291048A - Surface-modified molded article of ultra-high-molecular-weight polyethylene and method for producing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a molded article of an ultra-high-molecular-weight polyethylene having improved friction resistance and abrasion resistance and a method for producing the article. <P>SOLUTION: The 1st invention comprises the bombardment of the surface of an ultra-high-molecular-weight polyethylene molded article with ions by an ion accelerator to carbonize the surface of the article to a depth of about 4μm and form a diamond-like carbon layer giving G band and D band by Raman spectroscopy and the 2nd invention comprises the ion bombardment with an ion accelerator at acceleration energy and ion exposure rate falling within respective specific ranges to obtain the surface-modified molded article of ultra-high-molecular-weight polyethylene. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

The present invention relates to a surface-modified ultra-high molecular weight polyethylene molded article and a method for producing the same. More specifically, the present invention relates to an ultra-high molecular weight polyethylene molded product whose surface has been modified from the surface of the molded product to a depth of about 4 μm by irradiating the ultra-high molecular weight polyethylene molded product with high-energy ions, and a method for producing the same. .

Ultra high molecular weight polyethylene molded products are used as sliding parts for artificial joints. The sliding portion of the artificial joint is composed of a metal or ceramic ball and an ultrahigh molecular weight polyethylene cup (or mortar). The life of an artificial joint is generally about 10 to 20 years because osteolysis and loosening occur. This is because the cup made of ultra high molecular weight polyethylene wears during use, and macrophages proliferate against the abrasion powder generated by the wear, thereby activating osteoclasts, causing osteolysis (bone resorption) This is because it is understood as one of the causes. In order to improve the life of the artificial joint, it is considered necessary to reduce the friction coefficient of the cup made of ultrahigh molecular weight polyethylene and improve the wear resistance.

As a method for improving the wear resistance of an ultra-high molecular weight polyethylene molded product, (1) a method of coating a diamond-like carbon (hereinafter sometimes referred to as DLC) thin film on the surface of the molded product (for example, patent literature) 1), (2) a method of irradiating the surface of the molded product with an electromagnetic wave such as gamma rays to crosslink (for example, see Patent Document 2 and Patent Document 3), and (3) irradiating the surface of the molded product with accelerated ions ( A method of injection) (see, for example, Patent Document 4).

However, in the coating method (1), the dimensions change by the thickness of the coating thin film. For products that require precision machining, including artificial joints, the dimensional change caused by the coating thin film is taken into account. It must be designed and processed. Furthermore, the most important issue is the adhesion between the coating thin film and the substrate, and the coating method in which the thin film is likely to peel off is not suitable for use as an artificial joint to be implanted in the body. In the coating method, it is necessary to provide an undercoat layer (undercoat layer) in advance for the purpose of improving the adhesion between the molded product and the coating thin film, which increases the number of work steps and is complicated.

The gamma ray irradiation method (electromagnetic wave irradiation method) of (2) above is a technique for improving the wear resistance by crosslinking the surface of a molded article made of ultrahigh molecular weight polyethylene. However, this method has a limit in improving wear resistance, and further improvement is desired. Moreover, when this method is used, there is a drawback that heat treatment is required after irradiation with electromagnetic waves, and the operation is complicated. The method (3) of irradiating the surface of the molded product with accelerated ions is a method of forming a DLC layer on the surface of the resin molded product. In the proposed method, the acceleration energy is a low level of several tens keV to 100 keV, so that the ion penetration (arrival) depth from the surface of the molded article is as shallow as about 0.1 μm, and the modified layer (DLC layer) is 0. The thickness is only 1 μm or less. If the thickness of the modified layer is 0.1 μm or less, there is a disadvantage that the modified layer is too thin, and the DLC layer cannot be formed unless the irradiation dose is set to 10 ¹⁷ ions / cm ² or more. On the other hand, if the ion irradiation amount is set to 10 ¹⁷ ions / cm ² or more and the DLC layer is formed, the processing time becomes long. When a large amount of accelerated ions are irradiated (implanted), the internal stress of the molded product increases, This causes deformation and breakage, and causes inconveniences such as roughness on the surface of the molded product.
Japanese Patent Laying-Open No. 2005-2377 JP 2004-27237 A JP-A-9-122222 JP 2000-182284 A

In view of this situation, the present inventor has intensively studied to provide an improved technique that eliminates the disadvantages of the prior art, and as a result, has completed the present invention. The object of the present invention is as follows.
1. To provide an ultra-high-molecular-weight polyethylene molded product that is surface-modified from the surface of the ultra-high-molecular-weight polyethylene molded product to a depth of about 4 μm and has greatly reduced friction and wear resistance.
2. To provide a method for producing a molded product whose surface has been modified from the surface of a molded product made of ultrahigh molecular weight polyethylene to a depth of about 4 μm.

In order to solve the above problems, in the first invention, the surface of the ultra-high molecular weight polyethylene molded product is irradiated with ions by an ion accelerator, and carbonized from the surface of the ultra-high molecular weight polyethylene molded product to a depth of about 4 μm, Provided is a surface-modified ultra-high molecular weight polyethylene molded article characterized in that a diamond-like carbon layer having a G band and a D band in a Raman spectroscopic spectrum is formed.

In the second invention, the ion acceleration energy is set to 3 MeV to 5 MeV and the ion irradiation amount is set to 5 × 10 ¹⁴ ions / cm ² to 1 × 10 ¹⁵ ions / cm on the surface of the ultra-high molecular weight polyethylene molded product by an ion accelerator. ^It is characterized in that it is irradiated with ions under the condition ² and carbonized from the surface of the ultra-high molecular weight polyethylene molded product to a depth of about 4 μm to form a diamond-like carbon layer in which G band and D band are recognized in the Raman spectrum. And a method for producing a surface-modified ultra-high molecular weight polyethylene molded article.

The present invention is as described in detail below, has the following particularly advantageous effects, and its industrial utility value is extremely great.
1. The ultra high molecular weight polyethylene molded article having a modified surface according to the present invention achieves low surface friction (low friction coefficient) and greatly improves the wear resistance of the molded article surface.
2. Since the ultra high molecular weight polyethylene molded product with a modified surface according to the present invention is modified to a depth of about 4 μm from the surface of the molded product, the modified layer is peeled off as in the DLC coating method. The product can be designed without taking into account the dimensional change, and no post-processing is required.
3. According to the method for producing an ultra-high molecular weight polyethylene molded product having a modified surface according to the present invention, it can be modified to a depth of about 4 μm from the surface of the molded product in one step.
4). According to the method for producing an ultra-high molecular weight polyethylene molded article having a modified surface according to the present invention, ions are irradiated with high acceleration energy using an ion accelerator, so that the thickness is about 40 times that of the conventional method. A modified layer can be formed.
5. According to the method for producing a molded article of ultrahigh molecular weight polyethylene having a modified surface according to the present invention, ions are irradiated with high acceleration energy using an ion accelerator, so the irradiation amount is about 1/100 of that of the prior art. Can be.

Hereinafter, the present invention will be described in detail.
In the present invention, ultra high molecular weight polyethylene (hereinafter sometimes referred to as UHMWPE) refers to those produced by Ziegler polymerization technique and having an average molecular weight of 1,000,000 to 5,000,000 by viscosity method. UHMWPE is extremely large compared to the molecular weight of 20,000 to 200,000 of general high-density polyethylene (HDPE), and especially wear resistance, impact resistance, self-lubrication and chemical resistance compared to HDPE and other engineering plastics. Excellent in properties. Ultra high molecular weight polyethylene having such a molecular weight is available from Asahi Kasei Corporation (product name: Hymorer), Mitsui Chemicals Co., Ltd. (product name: Hi-Zex Million), German Hoechst (product name: HOSTALENGUR), American Hercules Corporation (HIFAX1000) is sold by four companies. UHMWPE preferably has a viscosity average molecular weight of 3.5 to 4.5 million.

In the present invention, the molded product refers to a flat plate, a rod, a box, a tube, a lens, a ring, a cup (mortar), a heel, a ball, a gear, an artificial joint (shoulder joint, elbow joint, wrist joint, finger joint, hip joint, knee). Joint, ankle joint, etc.). These molded products can be manufactured by an extrusion molding method, an injection molding method, a compression molding method, or the like.

In the method according to the present invention, a UHMWPE molded product is subjected to surface modification treatment by an ion accelerator. The ion accelerator functions to accelerate the irradiation speed of the ions irradiated to the UHMWPE molded article so that the ions penetrate (arrive) deep from the surface of the UHMWPE molded article. Examples of the ion accelerator that can be used for this purpose include an ion accelerator using a cesium sputter ion source and a tandem accelerator tube as shown in FIG.

  When the surface modification of the UHMWPE molded product is performed by the ion accelerator, the ion acceleration energy is preferably selected in the range of 3 MeV to 5 MeV. If the ion acceleration energy is less than 3 MeV, the ion penetration depth from the molded product surface is shallow, the wear resistance of the UHMWPE molded product is not improved, and if the acceleration energy exceeds 5 MeV, irradiation is in progress. In addition, the surface of the molded product may be melted, which is not preferable.

Examples of types of ions include ions of silicon, carbon, nitrogen, gold, and the like. In general, ions of an element having a low atomic number easily penetrate (arrive) deeply from the surface of the molded article when the molded article is irradiated, and a thick DLC layer is easily formed. Among these, silicon ions that are harmless to the human body and easily penetrate deeply from the surface of the molded product are preferable.

When the surface modification treatment of the UHMWPE molded product is performed by the ion accelerator, the ion acceleration energy is selected within the above range, and the ion irradiation amount is 5 × 10 ¹⁴ ions / cm ² to 1 × 10 ¹⁵ ions / cm ^2. It is preferable to select within the range. When the ion irradiation amount is less than 5 × 10 ¹⁴ ions / cm ² , the ion irradiation amount is insufficient and the DLC layer is not formed. When the ion irradiation amount exceeds 1 × 10 ¹⁵ ions / cm ² , the effect of improving the wear resistance of the surface of the molded product This is because there is no point in increasing the ion irradiation amount.

When the surface modification treatment of the UHMWPE molded product is performed, the acceleration spectrum of ions is selected within the above range, and the ion irradiation amount is selected within the above range. Formation of a layer having a band and a D band is observed (see FIG. 2 described later). The G band is a band near a wavelength of 1550 cm ⁻¹ due to carbon having a graphite structure, and the D band is a band near a wavelength of 1350 cm ⁻¹ due to carbon having an amorphous structure. When these G band and D band are observed, it can be said that a DLC layer is formed on the surface of the molded product. By selecting the acceleration energy of ions within the above range and the ion irradiation amount within the above range, the surface of the molded article made of UHMWPE can be carbonized to a depth of about 4 μm to form a DLC layer.

Next, an outline of a method for modifying the surface of a UHMWPE molded article according to the method of the present invention will be described. FIG. 1 is a schematic view of an example of an ion accelerator used in manufacturing a surface-modified molded article according to the present invention. The ion accelerator 1 includes a cesium sputtering ion source 2, an extraction electrode 3, a mass separation electromagnet 4, a tandem acceleration tube 5, an energy separation electromagnet 6, a scanning electrode 7, a neutral / ion separation electrode 8, and an irradiation chamber 9. , Composed of the substrate 10.

In FIG. 1, ions generated by the cesium sputter ion source 2 are negative ions. As the ion source 2, silicon powder is used when silicon ions are generated and irradiated on the surface of a molded product. In FIG. 1, the arrow indicates the direction of ion transport (transportation, travel). The negative ions are guided to the mass separation electromagnet 4 by the extraction electrode with an acceleration energy of about 20 keV. Among the introduced negative ions, there are other ions in addition to the negative ions to be irradiated. Therefore, only the monovalent ions of the negative ions to be irradiated are separated by the mass and the acceleration energy by the mass separation electromagnet 4. , And transferred to the tandem type acceleration tube 5.

The central part of the tandem type acceleration tube 5 is a positive electrode, and negative ions are accelerated to the central part. The voltage that can be applied at the center is in the range of 0.5 MV to 1.7 MV. A small amount of nitrogen gas flows in the center, and when monovalent negative ions arrive there, they are converted into positive ions by reaction with nitrogen gas. Since the potential at the end of the tandem accelerator tube 5 is ground, the ions converted into positive ions are further accelerated and transferred toward the end of the tandem accelerator tube 5. The positive ions include ions having various valences such as monovalent and divalent ions, and each has different acceleration energy. Therefore, the positive ions are separated into single acceleration energy by the energy separation electromagnet 6 and irradiated by the scanning electrode 7. On the other hand, the substrate 10 is scanned so as to have a uniform beam intensity, and is irradiated onto the substrate 10 installed in the irradiation chamber 9.

The atoms neutralized between the tandem type acceleration tube 5 and the scanning electrode 7 are separated by the neutral / ion separation electrode 8, and the substrate 10 is irradiated only with positive ions having a single acceleration energy. The acceleration energy added to the positive ions is 0.5 to 1.7 MeV on the negative ion side and 1.0 to 3.4 MeV on the negative ion side in the case of the divalent positive ion, so that the total is 1.5 MeV. -5.1 MeV.

EXAMPLES Hereinafter, although this invention is demonstrated further in detail based on an Example, this invention is not limited to the following description examples, unless the meaning is exceeded.

A round bar made of UHMWPE (made by Asahi Kasei Co., Ltd., trade name: Hi-Molar EX1300W, having a viscosity average molecular weight in the range of 3.5 million to 4.5 million) with a diameter of 30 mm and a thickness of 3 mm by extrusion molding And prepared by a cutting method. The disk surface was polished with diamond grains having a diameter of 1 μm, and ultrasonically cleaned with ethanol immediately before being placed on the substrate 10 portion of the irradiation chamber 9, and placed on the substrate 10 portion of the ion accelerator shown in FIG. The type of ions irradiated by the ion accelerator was silicon. The reason why silicon ions are selected in the embodiment is that, when using the cesium sputter ion source 2, it is an element that generates a large amount as negative ions and an element that does not adversely affect the living body. The acceleration energy was set to two levels of 1.5 MeV and 3.0 MeV, and the irradiation amount was changed within a range of 5 × 10 ¹³ to 1 × 10 ¹⁵ ions / cm ² .

FIG. 2 is an example of a spectrum taken by Raman spectroscopy on a disk surface after irradiating a UHMWPE disk with silicon ions at an acceleration energy of 3.0 MeV and an irradiation amount of 1 × 10 ¹⁵ ions / cm ^2. . In the spectrum by Raman spectroscopy, a G band near a wavelength of 1550 cm ⁻¹ due to carbon having a graphite structure and a D band near a wavelength of 1350 cm ⁻¹ due to carbon having an amorphous structure are recognized, and DLC is observed on the disk surface. It was confirmed that a layer was formed.

3 to 5 show that a UHMWPE disk is irradiated with silicon ions at an acceleration energy of 3.0 MeV and an irradiation amount of 1 × 10 ¹⁵ ions / cm ² , and then the disk surface is in the depth direction from the surface. It is an example of the result of having measured the element distribution to to by secondary ion mass spectrometry. 3 shows the element distribution of carbon atoms, FIG. 4 shows the element distribution of hydrogen atoms, and FIG. 5 shows the element distribution of silicon atoms. From FIG. 3 to FIG. 5, silicon ions penetrate (arrive) from the surface of the UHMWPE disk to a depth of about 3 μm to about 4 μm, and the depth position of the penetration concentration peak is about 3.8 μm ( (See FIG. 5). Since the strength of hydrogen atoms is lower on the surface side than the depth at which silicon ions have entered (about 3.8 μm) (see FIG. 4), in the region where silicon ions have entered, The chemical bonds of carbon atoms are broken and hydrogen atoms are released to the outside. As a result, it is presumed that a DLC layer is formed when recombining in a region where the number of hydrogen atoms decreases and carbon atoms exist (see FIG. 3). Further, it is apparent that the thickness of the modified layer is about 4 μm when irradiated with silicon ions having an acceleration energy of 3.0 MeV (see FIG. 5).

6 and 7 are graphs showing the results of measuring the friction coefficient of a UHMWPE disk using a ball-on-disk tester. In the ball-on-disk test, an alumina ball having a diameter of 6 mm was used, the friction diameter was 10 mm, the rotation speed was 1 rotation per second, and the pressing load was 10 N. The measurement was performed in air and in an unlubricated state. It is. During the test, the friction force is measured at intervals of 1 second, and can be converted into a coefficient of friction and stored in a memory by a control computer.

FIG. 6 shows a surface of an unirradiated UHMWPE disk irradiated with silicon ions under a condition where the acceleration energy is constant 1.5 MeV and the irradiation amount is 5 × 10 ¹³ to 1 × 10 ¹⁵ ions / cm ^2. It is a graph which shows the relationship between a friction coefficient and a friction rotation speed about a disk made from UHMWPE by a ball-on-disk test machine after a modification process. FIG. 7 shows an unirradiated UHMWPE disk irradiated with silicon ions at a constant acceleration energy of 3.0 MeV and an irradiation amount of 5 × 10 ¹³ to 1 × 10 ¹⁵ ions / cm ^2. It is a graph which shows the relationship between the friction coefficient about a UHMWPE disc, and a friction rotation speed by a ball-on-disk test machine after a modification process.

6 and 7 reveal the following.
1. An unirradiated UHMWPE disk is irradiated with silicon ions at a constant acceleration energy of 1.5 MeV and an irradiation dose of 2 levels of 5 × 10 ¹³ ions / cm ² and 1 × 10 ¹⁴ ions / cm ^2. However, the friction coefficient of the disk surface does not decrease (see FIG. 6).
2. An unirradiated UHMWPE disk is irradiated with silicon ions at a constant acceleration energy of 3.0 MeV and an irradiation dose of 2 levels of 5 × 10 ¹³ ions / cm ² and 1 × 10 ¹⁴ ions / cm ^2. However, the friction coefficient of the disk surface does not decrease (see FIG. 7).
3. When an unirradiated UHMWPE disk is irradiated with silicon ions at a constant acceleration energy of 1.5 MeV and an irradiation dose of 5 × 10 ¹⁴ ions / cm ² and 1 × 10 ¹⁵ ions / cm ² , The friction coefficient of the disk surface decreases (see FIG. 6).
4). When a non-irradiated UHMWPE disc is irradiated with a constant acceleration energy of silicon ions of 3.0 MeV and an irradiation amount of ² × 10 ¹⁴ ions / cm ² and 1 × 10 ¹⁵ ions / cm ² , The friction coefficient of the plate surface is greatly reduced (see FIG. 7).
5. When the irradiation energy of silicon ions is applied to an unirradiated UHMWPE disk, 3.0 MeV is more conspicuous in reducing the friction of the disk surface, and this reduced friction state is maintained. (See FIGS. 6 and 7).
6). From the above, in order to reduce the friction of the UHMWPE disk, the acceleration energy is preferably 3.0 MeV or more, and the ion irradiation amount is 5 × 10 ¹⁴ ions / cm ² to 1 × 10 ¹⁵ ions / cm ^2. It is clear that the range of is preferred.

Next, the wear resistance of the surface of the UHMWPE disk product according to the present invention was evaluated by a method different from the test method described above. UHMWPE discs prepared in the same manner as described above were irradiated with silicon ions at an acceleration energy of 3.0 MeV and ion irradiation doses of 5 × 10 ¹⁴ ions / cm ² and 1 × 10 ¹⁵ ions / cm ² . . The disc was rubbed at 200,000 revolutions under the test conditions described above using the above ball-on-disk tester. Then, the shape of the wear mark on the disk was measured with a stylus type surface roughness meter, and the results of calculating the wear volume are shown in Table 1. In addition, assuming that the shape of the wear scar was a trapezoid, the upper width, the lower width, and the depth of each were measured, and the volume was calculated.

From Table 1, the following becomes clear.
1. Compared to unirradiated ultra high molecular weight polyethylene discs, those irradiated with ions under the conditions of 5 × 10 ¹⁴ ions / cm ² and 1 × 10 ¹⁵ ions / cm ² have a smaller wear powder volume and improved wear resistance. Has been.
2. When the ion irradiation amount is increased, the wear resistance of the surface of the molded product is further improved.

Examples of the ultra-high molecular weight polyethylene molded product having a modified surface according to the present invention include artificial joints, industrial parts, industrial products, etc. that require low wear (low friction coefficient), wear resistance, and the like. It is done. Among them, artificial joints such as shoulder joints, elbow joints, carpal joints, finger joints, hip joints, knee joints, and foot joints are suitable.

It is the schematic of an example of the ion accelerator used for the surface modification method of this invention. It is an example of the Raman spectrum about the ultra high molecular weight polyethylene disk by which the surface modification process was carried out. It is an example of the result of having measured the depth direction distribution of carbon by the secondary ion mass spectrometry about the ultra high molecular weight polyethylene disk by which the surface modification process was carried out. It is an example of the result of having measured the depth direction distribution of hydrogen by the secondary ion mass spectrometry. It is an example of the result of having measured the depth direction distribution of silicon by secondary ion mass spectrometry. Relationship between friction coefficient and rotational speed of ultra high molecular weight polyethylene disk surface-modified with a constant acceleration energy of 1.5 MeV and an irradiation dose of 5 × 10 ¹³ to 1 × 10 ¹⁵ ions / cm ² It is. Relationship between friction coefficient and rotational speed of ultra high molecular weight polyethylene disk surface-modified by changing the irradiation energy from 5 × 10 ¹³ to 1 × 10 ¹⁵ ions / cm ² at a constant acceleration energy of 3.0 MeV. It is.

Explanation of symbols

1: ion accelerator 2: cesium sputter ion source 3: extraction electrode 4: electromagnet for mass separation 5: tandem acceleration tube 6: electromagnet for energy separation 7: scanning electrode 8: electrode for neutral / ion separation 9: irradiation chamber 10: Substrate

Claims (6)

The surface of the ultra high molecular weight polyethylene molded product is irradiated with ions by an ion accelerator to be carbonized to a depth of about 4 μm from the surface of the ultra high molecular weight polyethylene molded product, and G and D bands are observed in the Raman spectrum. A surface-modified ultra-high molecular weight polyethylene molded product characterized in that a diamond-like carbon layer is formed. The method for producing a surface-modified ultrahigh molecular weight polyethylene molded article according to claim 1, wherein the ultrahigh molecular weight polyethylene has a viscosity average molecular weight of 3.5 to 4.5 million. The surface-modified ultrahigh molecular weight polyethylene molded article according to claim 1 or 2, wherein the irradiation ions irradiated by the ion accelerator are silicon ions. The ultrahigh molecular weight polyethylene molded article whose surface is modified according to any one of claims 1 to 3, wherein the acceleration energy of ions is 3 MeV to 5 MeV. The ultra-high molecular weight polyethylene molding whose surface is modified according to any one of claims 1 to 4, wherein the ion irradiation amount is 5 x 10 ¹⁴ ions / cm ² to 1 x 10 ¹⁵ ions / cm ^2. Goods. On the surface of the ultra-high molecular weight polyethylene molded product, ions are accelerated by an ion accelerator under the conditions of an ion acceleration energy of 3 MeV to 5 MeV and an ion irradiation amount of 5 × 10 ¹⁴ ions / cm ² to 1 × 10 ¹⁵ ions / cm ^2. To form a diamond-like carbon layer in which the G band and D band are observed in the Raman spectroscopic spectrum, and carbonized to a depth of about 4 μm from the surface of the molded article made of ultrahigh molecular weight polyethylene. A method for producing a molded product of ultra-high molecular weight polyethylene.

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