Method for producing resin porous material

Abstract

To enable antistatic property without mixing a conductive agent or antistatic agent into a resin, and also without causing degradation of the performance of the porous material obtained by sintering a granular resin.SOLUTION: In a resin porous material, a conductive agent is applied to either a front or back surface, and after a predetermined time has elapsed but before the conductive agent has completely dried, a positive or negative pressure is applied to the entire surface from either the surface applied with the conductive agent or the reverse surface thereof.EFFECT: Since an electrically static material is not mixed into a resin, it is possible to perform electrostatic discharge while ensuring consistent sintering conditions and post-sintering porosity, with reliable retention of pore openings thereof.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a porous material obtained by sintering a resin. [Background technology]

[0002] Metal porous materials are expensive and heavy, so many resin porous materials are known, such as those disclosed in JP 2005-219985 A (Patent Document 1), which are made by sintering granular resin as the main material.Porous materials made by sintering granular resin as the main material are lighter than those made primarily from metal, and have the advantage of being cheaper due to the lower purchase price of the main material and the lower sintering temperature.

[0003] When porous materials made by sintering resin are used, for example as air ejection components in devices for levitating and transporting extremely small electronic components, the charging (static charge) of the resin inevitably becomes a problem.

[0004] Therefore, for example, Patent Document 1 above proposes mixing a conductive agent into the resin, which is the main material of the porous material, before sintering in order to form a conductive layer on the inner walls of the communicating holes. In addition to Patent Document 1, other well-known examples of antistatic methods include coating the surface of a sintered porous material with an antistatic agent, vapor-depositing a conductive agent, and impregnating a sintered porous material with an antistatic agent or a conductive agent.

[0005] However, in the method of Patent Document 1 and others in which a conductive agent is mixed into a resin before sintering, the sintering conditions for resin sintering alone may differ from the sintering conditions for the mixed resin, and there is a possibility that the intended porosity may not be obtained. In addition, in some cases, integral molding may not be possible, or other unnecessary conditions may arise, such as the need for another binder for integral molding. These other unnecessary conditions increase the possibility that the intended porosity (specifications and performance such as average pore size and porosity) may not be obtained, as described above.

[0006] Furthermore, in known methods of coating the surface of a sintered porous material with an antistatic agent, vapor-depositing a conductive agent, or impregnating a sintered porous material with an antistatic agent or a conductive agent, if the average pore size exceeds 10 μm, the conductive agent or antistatic agent may be unlikely to clog the pores. However, in the case of fine pores with an average particle size of 10 μm or less, the conductive agent or antistatic agent that has entered the pores may dry and harden, causing the openings or flow paths to be clogged. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Laid-Open No. 2005-219985 Summary of the Invention [Problem to be solved by the invention]

[0008] The problem to be solved is to make it possible to prevent static electricity without mixing conductive agents or antistatic agents into the resin and without degrading the performance of the porous material obtained by sintering granular resin. [Means for solving the problem]

[0009] In order to solve the above problem, the present invention provides a method for applying a conductive agent to either the front or back surface of a porous material made of a resin material, and then applying positive or negative pressure to the entire surface from either the surface to which the conductive agent is applied or the opposite surface after a certain period of time has passed and before the conductive agent has completely dried. [Effects of the Invention]

[0010] In the present invention, since a conductive agent is not mixed into the resin material, there is no change in, for example, the sintering conditions for integral molding, the porosity, and the resin characteristics. Furthermore, after the conductive agent is applied, the conductive agent is actively drawn into the pores to further ensure the pores are open, making it possible to maintain the intended porosity. DETAILED DESCRIPTION OF THE INVENTION

[0011] The present invention achieves the objective of making it possible to prevent static electricity without mixing a conductive agent or antistatic agent into the resin and without causing a decrease in the performance of the porous material obtained by sintering granular resin by applying a conductive agent to either the front or back surface, and then, after a certain period of time has passed and before the conductive agent dries, applying positive or negative pressure to the entire surface from either the surface to which the conductive agent has been applied or the opposite surface.

[0012] (Resin material) In the embodiment of the present invention, a synthetic resin that is generally classified as a plastic may be used as the resin that is the main component of the porous material, but in this example, it is desirable to use, for example, ultra-high molecular weight polyethylene (UHMWPE), because it has high impact resistance, abrasion resistance, lubricity, and chemical resistance, and is lightweight and has stable chemical and physical shape.

[0013] When this ultra-high molecular weight polyethylene is used to make plate- or sheet-shaped porous materials, it has the same performance as metal porous materials used up until now, but is lighter, which reduces the load on the drive unit and allows for the miniaturization and cost reduction of the entire industrial machinery.

[0014] (Plate-shaped porous material) The porous material obtained by sintering granular resin is curved with a depression in the center. In this example, for example, after sintering, the material is left to stand at room temperature to remove the heat generated during sintering and stabilize the curved shape. If this step is not performed and the material is immediately flattened after sintering, the internal air bubbles may be crushed.

[0015] In this example, the material is left to stand at room temperature, and then heated to 80 to 100°C. This heating is intended to plastically deform the porous material, which has still been curved up to this point, and is not intended to strengthen the bond by remelting or to modify the resin. Therefore, the heating temperature should be such that plastic deformation can occur.

[0016] Many thermoplastic resins, which are synthetic resins classified as plastics, can undergo plastic deformation at temperatures between 80°C and 100°C. If the temperature is lower than 80°C, plastic deformation (curvature correction) becomes difficult, and if the temperature exceeds 100°C, fluctuations in thickness and surface area may occur.

[0017] After heating to 80-100°C, the curved porous material is flattened by being sandwiched between highly flat plate members and plastically deforming it. The curvature is corrected by applying pressure between the highly flat plate members. The pressure (force) applied at this time varies depending on the resin material and the thickness of the porous material, but should be sufficient to correct the curvature by plastically deforming it, without causing thickness fluctuations (thinning) or cracking when pressed.

[0018] (sheet-shaped porous material) The above-mentioned manufacturing method for plate-shaped porous materials can also be applied to the production of sheet-shaped porous materials. When attempting to obtain sheet-shaped porous materials by sintering granular resin, it is extremely difficult to limit the thickness to, for example, 1 mm or less, because it is difficult to form internal air bubbles through heating and pressure.

[0019] Furthermore, even if granular resin were sintered to obtain a sheet-shaped porous material of a specified thickness (for example, 1 mm or less), it would be subject to severe curvature (rolling) for the same reason as the plate-shaped porous material described above, making it difficult to commercialize in a flat state.

[0020] Therefore, rather than producing a sheet-shaped porous material from the beginning, the inventors have considered first producing a flat plate-shaped porous material and then forming the plate-shaped porous material into a sheet. That is, in the present invention, a granular resin material is integrally formed into a plate of a predetermined thickness by sintering, left to stand at room temperature, heated at 80 to 100°C, sandwiched between highly flat plate members to cause plastic deformation and ensure the flatness of the plate-shaped porous material, and then the surface is shaved with a plane, and the sheet side shaved with the plane is heated again at 80 to 100°C and sandwiched between highly flat plate members to cause plastic deformation.

[0021] As described above, the process of sintering granular resin material into a plate of a predetermined thickness, leaving it at room temperature, heating it to 80°C to 100°C, and sandwiching it between highly flat plate members to cause plastic deformation is the same as the process of obtaining a flat, plate-shaped porous material, so explanations will be omitted.

[0022] After obtaining a flat plate-shaped porous material, the surface is shaved to a predetermined thickness (for example, 10 μm or less) using a plane. Here, the plane may be a manual sharp tool or an electric tool. When shaving the surface, there is a processing technique called surface cutting in mechanical processing, but in all of these, the base material is the main focus of finishing and processing, and the shape of the side cut from the base material (so-called cutting chips) is in the form of small pieces of chips. In contrast, when shaving the surface with a plane, although the main focus is of course finishing and processing the base material, the shape of the side cut from the base material is stable. In other words, in the present invention, the surface is shaved with a plane because the shape of the side cut from the base material is stable and sheet-like.

[0023] The surface of a flat, plate-shaped porous material is scraped with a plane to obtain a rolled, sheet-shaped porous material. This rolled, sheet-shaped porous material is heated to 80°C to 100°C, sandwiched between highly flat plate members, and plastically deformed to obtain a flat, sheet-shaped porous material. The heating temperature range and the pressure range required for plastic deformation are the same as those for the plate-shaped porous material described above, so they are not repeated here.

[0024] In this way, an extremely thin and flat sheet-shaped porous material can be obtained. In addition, since the sheet-shaped porous material in this example is obtained by scraping the surface of a porous material that is originally in the form of a plate with a plane, the porosity does not deteriorate.

[0025] (anti-static) A conductive agent is applied to either the front or back surface of the plate-shaped or sheet-shaped porous material (hereinafter, when the term "porous material" is used, it includes both plate-shaped and sheet-shaped materials) that has been completed as described above.

[0026] In this example, a low-viscosity, highly fluid emulsion containing dispersed carbon nanotubes is used as the conductive agent. The conductive agent is then applied thoroughly to the entire surface of the porous material. "Sufficiently" means that the conductive agent penetrates from the surface into the interior (pores) of the porous material, but does not necessarily need to be applied so that it seeps out to the back side.

[0027] It takes a considerable amount of time for the pressureless fluid to reach from the surface to the back of the porous material, during which time the conductive agent dries and hardens. When the conductive agent dries and hardens, it may clog the pores. Therefore, a conductive agent with low viscosity and high fluidity should be used, and the application conditions should be such that the conductive agent penetrates shallowly from the surface into the interior (pores) of the porous material.

[0028] After the above, after a certain time has passed but before the conductive agent has completely dried, a positive or negative pressure is applied to the entire surface from the side opposite to the side on which the conductive agent has been applied. Waiting for a certain time is a time to wait for the conductive agent to penetrate into the pores, and applying a positive or negative pressure to the entire surface from the side opposite to the side on which the conductive agent has been applied before the conductive agent has completely dried is to prevent the conductive agent from drying and hardening.

[0029] In the present invention, before the conductive agent dries completely, a positive or negative pressure is applied to the entire surface opposite to the surface to which the conductive agent is applied. The technical significance of applying this positive or negative pressure is to remove the conductive agent that has infiltrated into the pores during application or to promote application to the inner walls of the pores, thereby ensuring the opening of the pores.

[0030] In other words, the conductive agent only needs to be applied to the inner walls of the holes, and the hole opening is ensured by removing the excess. Positive and negative pressure can be applied from either the surface on which the conductive agent is applied or the surface opposite to the surface on which the conductive agent is applied.

[0031] When "positive pressure" is applied, the conductive agent can penetrate deep into the interior from the coated surface while ensuring the opening of holes if it is applied to the "coated surface," and can penetrate shallow into the interior from the coated surface while ensuring the opening of holes if it is applied from the "opposite surface" to the coated surface, which means that less conductive agent can be applied and completion is faster.

[0032] When applying "negative pressure," if the pressure is applied from the "opposite side" of the surface on which the conductive agent is applied, the conductive agent can penetrate deep into the interior while ensuring the opening of the holes, and if the pressure is applied from the "opposite side" of the surface on which the conductive agent is applied, the conductive agent can penetrate shallow into the interior from the surface on which the conductive agent is applied, which means that less conductive agent needs to be applied and completion is faster.

[0033] The present invention is suitable, for example, for use as an air blowing member for floating extremely small electronic components in industrial machinery that floats and transports the components, and for obtaining a porous material having fine pores with an average pore size of 10 μm or less. The resin porous material produced in this way retains its inherent porosity and can be used as is for ordinary purposes, such as filtration. However, it is possible to reliably remove static electricity by grounding the part of the porous material to which the conductive agent is applied, or by supporting the part of the porous material to which the conductive agent is applied on a metal frame and grounding the metal frame.

Claims

[Claim 1] A method for manufacturing a resin porous material in which a conductive agent is applied to either the front or back surface of a porous material made of a resin material, and after a certain period of time has passed and before the conductive agent has completely dried, positive or negative pressure is applied to the entire surface from either the side to which the conductive agent has been applied or the opposite side.