JP2014052283A - Manufacturing method of float - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a manufacturing method of a float that suppresses damage of a glass grain mixed to a resin to thereby obtain a float with small specific gravity.SOLUTION: A manufacturing method of a float used in a float manufacturing system 1 subsequently includes: a low viscosity step of making a high-density polyethylene resin particle PE1 with thermoplasticity into a low viscosity state; an admixture step of mixing a hollow glass bead G to a high-density polyethylene resin PE2 of the low viscosity state, and generating a mixture R of the high-density polyethylene resin PE2 and the glass bead G; and an extrusion molding step of extruding the mixture R in a predetermined cylindrical shape and molding it.

Description

  The present invention relates to a method for manufacturing a float used in, for example, a liquid level sensor that measures the liquid level of a liquid contained in a liquid tank.

  In the float type liquid level sensor, the liquid level is measured by detecting the vertical movement of the float floated on the liquid level. Such a float type liquid level sensor may be used, for example, for measurement with a high pressure liquefied gas such as petroleum liquefied gas (LPG), and the float is required to have pressure resistance and low liquid permeability. Furthermore, since the specific gravity of such a liquefied gas is small, a small specific gravity is required for the float to obtain buoyancy.

  For example, when a float is formed of a hollow metal body, the thickness of the metal increases to increase the weight and sufficient buoyancy cannot be obtained to ensure pressure resistance, and the shape is spherical from the point of pressure resistance. There was a problem of being constrained. Even when the float is made of a resin material having a specific gravity smaller than that of metal, the liquid penetrates the resin material in the high-pressure liquid regardless of whether it is a hollow body or foam, and the liquid enters the space in the float. There was a problem that buoyancy could not be obtained. And the technique which solves such a problem is disclosed by patent document 1. FIG.

  The float described in Patent Document 1 is made of a thermoplastic resin containing a minute hollow body such as a glass microballoon. According to such a float, it was possible to reduce the specific gravity and secure buoyancy without providing a space inside such as a hollow body or a foamed body.

Japanese Patent Laid-Open No. 1-212319

  However, in the float of Patent Document 1, resin pellets and glass microballoons are kneaded and extruded by an extruder to produce mixed pellets in which these resins and glass microballoons are mixed, and then an injection molding machine using the mixed pellets. In such an injection molding machine, since the mixed pellets in a molten state are injected at a high pressure, if the glass microballoons are highly filled to reduce the specific gravity of the float, the glass microballoons Sometimes rubbed and cracked.

  In addition, instead of the injection molding machine, it is conceivable to directly extrude the float by an extrusion molding machine. Since such an extrusion molding machine generally uses a uniaxial extrusion molding machine, In order to melt the resin pellet by increasing the temperature to a temperature near its melting point while applying pressure by screw rotation to the mixture with the glass microballoon, the viscosity of the resin is in a very high state, Therefore, if the ratio of the glass microballoons is increased in order to reduce the specific gravity, the resin does not sufficiently reach between these glass microballoons, and even when an extruder is used, the glass microballoons are rubbed with each other. Sometimes it broke. Therefore, there is a problem that it is difficult to obtain a float with a small specific gravity. In particular, when a high molecular weight resin having high chemical resistance and rigidity is used, since such a resin has a relatively high viscosity, the resin does not reach between the glass microballoons, and thus the above problem is more remarkable. Met.

  The present invention aims to solve the above problems. That is, an object of the present invention is to provide a method for producing a float that can obtain a float having a small specific gravity while suppressing breakage of glass particles mixed in a resin.

  In order to achieve the above object, the invention described in claim 1 is a method for producing a float floated on a liquid, wherein the thermoplastic resin is heated to a temperature equal to or higher than the melting point of the resin and melted in a liquid state. A mixture of the resin and the glass particles obtained by mixing a hollow glass particle with the resin having the viscosity reduced in the step of reducing the viscosity. The method for producing a float is characterized by sequentially including a mixing step of generating a mixture and an extrusion molding step of extruding the mixture generated in the mixing step into a predetermined shape.

  The invention described in claim 2 is the method according to claim 1, wherein the melt mass flow rate of the resin is in the range of 0.5 to 40 [g / 10 min]. is there.

  According to the invention described in claim 1, after the thermoplastic resin is heated to a temperature equal to or higher than the melting point of the resin to be melted into a liquid state, the resin in the low viscosity state is hollow. The glass particles are mixed to form a mixture of the resin and glass particles, and the mixture is extruded into a predetermined shape. When the glass particles are mixed with the resin, the resin quickly goes between the glass particles, and even when the proportion of the glass particles is increased, the glass particles are not rubbed with each other. The pressure applied to the granules can be relaxed by the resin, and the glass granules can be prevented from breaking, and the float of the mixed glass granules can be suppressed to obtain a float with a small specific gravity. Moreover, since the ratio of the glass particles increases, the amount of liquid permeation into the resin can be reduced, so that a float with little change in specific gravity with time can be obtained. Moreover, since the usage-amount of resin decreases because the ratio of a glass granule increases, manufacturing cost can be reduced.

  According to the invention described in claim 2, since the melt mass flow rate of the thermoplastic resin is in the range of 0.5 to 40 [g / 10 min], the thermoplastic resin is used as a glass particle. It can be in a low-viscosity state suitable for mixing and extrusion, so that it is possible to obtain a float with a small specific gravity by suppressing breakage of the mixed glass particles, and a mixture in which a resin and glass particles are mixed It is possible to obtain a float having a desired shape while preventing deformation immediately after extruding.

These are figures explaining an example of the float manufacturing system which manufactures a float using the manufacturing method of the float of the present invention. FIG. 2 is a front view (partially including an enlarged cross-sectional view) schematically showing a configuration of an embodiment of the float of the present invention. It is a figure explaining the structure of the liquid level sensor which has the float of FIG. (A) is sectional drawing of the float body which provided the metal foil in the outer peripheral surface of the float of FIG. 2, (b) demonstrates the structure of the other liquid level sensor which has the float body of (a). FIG. It is a graph which shows the relationship between the filling rate of a glass bead, and the specific gravity of a float.

  Hereinafter, an embodiment of the float manufacturing method of the present invention will be described with reference to FIGS. The float manufactured by the manufacturing method of the present invention is used for, for example, a liquid level sensor that measures the liquid level (that is, the liquid level and also the liquid level) of the liquid stored in the liquid tank. .

  Conventionally, such a float has been manufactured by injection molding using a pellet obtained by mixing a resin and glass microballoon as a glass particle. However, when the mixing ratio of the glass microballoon becomes high, the pellet is molded or injection molded. Since the glass microballoon breaks at times, the specific gravity cannot be made smaller than a certain value. Therefore, for example, a float that can float on a liquid with a low specific gravity such as dimethyl ether (DME), butane gas, ammonia, etc. It was inappropriate. And in the manufacturing method of this invention, the float which can float on the liquid with such a small specific gravity can be manufactured.

  In the float manufacturing method described below, a cylindrical float F (FIG. 2) is manufactured using thermoplastic resin powder and hollow glass particles as raw materials. Of course, such a shape is an example, and the shape of the float F is arbitrary as long as it does not contradict the object of the present invention.

  As the resin powder, for example, powdered polyethylene (PE) having a number average particle diameter of about 100 μm, a specific gravity of 0.95, and a melting temperature of 128 ° C. is used. In this embodiment, high-density polyethylene resin particles PE1 (Sunfine LH-411, manufactured by Asahi Kasei Chemicals Corporation) are used. Of course, as for the type of resin, in addition to polyethylene, for example, a powdery resin material such as polypropylene (PP) or polyamide (PA) may be used. Moreover, since the chemical resistance and rigidity become high when the molecular weight in the resin is large, it is advantageous for the production of a high pressure resistant float having excellent chemical resistance and low specific gravity.

  As the glass particles, for example, those formed in a hollow sphere having a number average particle size of about 25 μm and a specific gravity of about 0.4 are used. In this embodiment, glass beads G for filler (S42XHS (specific gravity 0.42, pressure resistance 55 MPa), manufactured by 3M Company) are used. The larger the particle size of the glass beads G, the smaller the specific gravity and the lower the pressure resistance. By reducing the specific gravity of the glass beads G, the specific gravity of the float F molded using the glass beads G can be reduced. However, since the glass beads G are easily broken during production, the float F having a desired specific gravity is obtained. In addition, since the pressure resistance of the float F itself is determined by the pressure resistance of the glass beads G, the necessary pressure resistance cannot be obtained if the specific gravity is too small. For this reason, the number average particle size of the glass beads G is determined in accordance with the pressure applied at the time of forming the float F and the properties of the liquid that floats the float F (specific gravity, pressure, etc.) so as to balance the specific gravity and pressure resistance. To do.

  FIG. 1 shows an example of a float manufacturing system 1 that manufactures a float F using the float manufacturing method of the present invention. The float manufacturing system 1 is provided with an extrusion molding machine 100, a cooling tank 200, and a cutting machine 300 arranged in order.

  The extrusion molding machine 100 has a cylinder 110 and a pair of screws 120. That is, although the extrusion molding machine 100 is a twin screw extrusion molding machine, it is not limited to this, and a single screw extrusion molding machine may be used.

  The cylinder 110 is made of, for example, a metal material, and is integrally provided with a main body 111 formed in a substantially elliptical cylinder shape and a bottom wall 112 that closes one end 111a of the main body 111. . In FIG. 1, the cylinder 110 is shown in a sectional view. The other end 111b of the main body 111 is formed in a tapered shape, and a nozzle die 113 is disposed so as to overlap the opening at the tip. The shape of the nozzle die 113 is determined so that an after-mentioned mixture R pushed out from the other end 111b of the cylinder 110 passes through the nozzle die 113 to obtain an intermediate molded product E having a desired shape. . In the present embodiment, the nozzle die 113 is formed so that the intermediate molded product E has a cylindrical shape.

  A first through hole 111 c and a second through hole 111 d that penetrate the main body 111 are provided in the upper part of the main body 111. The first through hole 111c is provided near the one end 111a of the main body 111, and the second through hole 111d is provided near the other end 111b of the main body 111. A first hopper 114 for introducing high-density polyethylene resin particles PE1 into the main body 111 is attached to the first through hole 111c. A second hopper 115 for introducing the glass beads G into the main body 111 is attached to the second through hole 111d.

  A heater (not shown) is provided on the outer peripheral surface of the main body 111, and the main body 111 is heated by the heater. Thereby, the high density polyethylene resin particle PE1 in the main body 111 is heated to a desired temperature. In the present embodiment, the main body 111 is heated to 230 ° C. by a heater. Thereby, the high density polyethylene resin particle PE1 in the main body 111 is heated to a temperature equal to or higher than its melting point (about 130 ° C.).

  The pair of screws 120 are accommodated in the cylinder 110 so as to be rotatable in parallel with the cylinder 110 in the axial direction. The pair of screws 120 are arranged in parallel to the front-back direction in FIG. 1 (only the screw on the front side of the pair of screws 120 is shown). The screw 120 is rotated around its axis by a driving means such as a motor (not shown). When the screw 120 is rotated, the high-density polyethylene resin or the mixture R stored in the cylinder 110 is moved from the one end 111a of the cylinder 110 to the other end 111b. In addition, the shape of the cylinder 110 and the shape of the screw 120, the direction of rotation, and the rotation are set so that the contents are moved at a predetermined speed in the cylinder 110 and a predetermined pressure is applied along with the movement. Numbers are determined.

  When the high-density polyethylene resin particles PE1 charged into the cylinder 110 through the first hopper 114 are heated by the heater and pressured by the rotation of the screw 120 and kneaded, the solid particles are transformed into a low viscosity state. It changes to high density polyethylene resin PE2. Then, by the rotation of the screw 120, it is mixed with the glass beads G introduced into the cylinder through the second hopper 115 to become a fluid mixture R, and this mixture R is pushed out through the other end 111b of the cylinder 110 and the nozzle die 113. .

  Here, the low-viscosity state is a state in which a high-density polyethylene resin is heated to a temperature equal to or higher than its melting point and melted into a liquid state, and indicates a state in which the viscosity is sufficiently low and the load when stirring is small. . Thermoplastic resin is in the form of a gel that does not drip into a thread form due to gravity because of its high viscosity near the melting point, but the viscosity decreases as the temperature is further raised from around the melting point, and the liquid state that droops in a thread form without interruption due to gravity. It becomes.

  When the high-density polyethylene resin particles PE1 heated and kneaded in the cylinder 110 are in such a liquid state (that is, in a low-viscosity state), when the glass beads G are put into the cylinder 110, they are rotating and flowing by the screw 120. Glass beads G bite into the liquefied high-density polyethylene resin PE2 and dragged by rotation, and are sufficiently evenly mixed with the resin PE2. On the other hand, if the high-density polyethylene resin particles PE1 in the cylinder 110 are not in a liquid state, such as a gel at a temperature near the melting point, for example, the glass beads G are not sufficiently bitten into the high-density polyethylene resin, and due to rotation. The glass beads G are repelled and cannot be evenly mixed with the high-density polyethylene resin.

  Moreover, it is preferable that the melt mass flow rate (MFR) which is a parameter | index prescribed | regulated by JISK7210 in a high density polyethylene resin is 0.5-40 [g / 10min]. If the MFR is less than 0.5, the viscosity is too high, and the glass beads G are not sufficiently evenly mixed with the high-density polyethylene resin, and the difficulty of mixing at a desired ratio increases. On the other hand, if the MFR is larger than 40, the viscosity is too low and it is difficult to maintain the shape when extruded from the nozzle die 113, and the degree of difficulty in forming the desired shape increases. The MFR in the high-density polyethylene resin is more preferably 1 to 18, and by using such a resin, the filling rate of the glass beads G is further increased, and the float F has a smaller specific gravity and higher shape accuracy. Can be obtained.

  The cooling tank 200 is a device for cooling the mixture R pushed out from the cylinder 110 with cold water, cold air, or the like. By passing the mixture R through the cooling bath 200, the mixture R is cooled and cured, and a solid intermediate molded product E is obtained. Note that the intermediate molded product E may be obtained by naturally cooling the mixture R without providing the cooling bath 200.

  The cutting machine 300 is a device that cuts the intermediate molded product E to a desired length. The float F is obtained by cutting the intermediate molded product E with the cutting machine 300.

  Next, a float manufacturing method using the above-described float manufacturing system 1 will be described.

  In manufacturing the float, first, heating of the heater and rotation of the screw 120 are started in the extruder 100. Then, the high-density polyethylene resin particles PE1 are put into the cylinder 110 through the first hopper 114, heated and kneaded to a temperature equal to or higher than the melting point thereof to form a liquid, and a high-density polyethylene resin PE2 having a low viscosity state is obtained ( (Low viscosity process).

  Then, the glass beads G are put into the cylinder 110 through the second hopper 115 and mixed with the liquid high-density polyethylene resin PE2 by the screw 120 (mixing step). Thereby, the mixture R in which the high-density polyethylene resin PE2 and the glass beads G are mixed is generated. It should be noted that the input amount of the glass beads G is adjusted in advance by, for example, preliminary measurement so that the glass beads G included in the float F finally have a desired ratio.

  In the present embodiment, in this mixing step, the ratio of the glass beads contained in the generated mixture R (hereinafter also referred to as filling rate) is used for the purpose of the float to be manufactured (that is, the liquid to be floated). In addition, the glass beads G are introduced so as to be included in the range of 20% by mass to 45% by mass. For example, when high density polyethylene resin particles PE1 (specific gravity 0.95) is 25 g and glass beads G (specific gravity 0.42) is 17 g, when these are mixed, the filling rate of glass beads G (ratio of mixing) is 40% by mass (= 17 / (17 + 25)).

  And this mixture R is extruded through the nozzle die 113 from the cylinder 110 with the screw 120 (extrusion molding process). The mixture R extruded from the cylinder 110 passes through the nozzle die 113 and is formed into a cylindrical shape.

  Then, the mixture R formed in a cylindrical shape through the nozzle die 113 is cooled in the cooling bath 200 and cured to obtain an intermediate molded product E (cooling step). Then, the intermediate molded product E is cut into a desired length by the cutting machine 300 (cutting step). In this way, the float F shown in FIG. 2 is completed.

  As described above, according to the present embodiment, after the thermoplastic high-density polyethylene resin particles PE1 are heated to a temperature equal to or higher than the melting point of the resin to be melted in a liquid state, the low-viscosity high-density polyethylene resin PE2 is obtained. Hollow glass beads G are mixed with this low-viscosity high-density polyethylene resin PE2 to produce a mixture R of high-density polyethylene resin PE2 and glass beads G, and this mixture R has a predetermined shape. Since the resin is extruded into a cylindrical shape, such a low-viscosity resin has good fluidity. Therefore, when the glass beads G are mixed with the high-density polyethylene resin PE2, the high-density polyethylene resin PE2 is interposed between the glass beads G. However, even when the ratio of the glass beads G is increased, the glass beads G are not rubbed. In addition, the pressure applied to the glass beads G is relaxed by the high-density polyethylene resin PE2, and the glass beads G can be prevented from breaking, and the mixed glass beads G can be prevented from being broken to obtain a float F having a small specific gravity. it can. Moreover, since the ratio of the glass beads G is increased, the amount of liquid permeation into the high-density polyethylene resin can be reduced, so that a float F with little change in specific gravity with time can be obtained. Moreover, since the usage-amount of a high-density polyethylene resin decreases because the ratio of the glass bead G increases, manufacturing cost can be reduced.

  Further, in the mixing step, the thermoplastic high-density polyethylene resin is mixed with the glass beads G by making the thermoplastic resin into a liquid state having a melt mass flow rate of 0.5 to 40 [g / 10 min]. It can be in a low-viscosity state suitable for extrusion molding, so that the high-density polyethylene resin is not too hard and not too soft, has an appropriate viscosity, can maintain fluidity, and has a shape immediately after being extruded. Can be maintained. Accordingly, it is possible to obtain a float F having a small specific gravity while suppressing breakage of the mixed glass beads, and to prevent deformation immediately after extrusion of the mixture R in which the high-density polyethylene resin PE2 and the glass beads G are mixed, and to achieve a desired value. An intermediate molded product E having a shape, that is, a float F can be obtained.

  In addition, since the resin can flow through the gaps between the glass beads G by making the high-density polyethylene resin into a low-viscosity state, a phase added to increase the adhesion between the high-density polyethylene resin and the glass beads G The adhesion between the high-density polyethylene resin and the glass beads G can be improved without adding a solubilizer.

  The float F manufactured by the above-described float manufacturing method is used, for example, in the liquid level sensor 10 schematically shown in FIG.

  The liquid level sensor 10 is provided, for example, in a fuel tank T that contains dimethyl ether (DME) as a liquid. When the float F moves up and down due to the change in the liquid level of the DME contained in the fuel tank T, the movement is changed to the rotational movement of the shaft 13 by the gear 12 arranged at the starting point of the float arm 11. A first magnet 14 is fixed to the upper end of the shaft 13 and rotates in accordance with the rotation of the shaft 13. The magnetic field of the first magnet 14 passes through the flange Ta and affects the second magnet 15, whereby the second magnet 15 also rotates in the same manner as the first magnet 14. Then, the rotation angle of the second magnet 15 is detected by the Hall IC 16, and the fuel level is detected from the change in the rotation angle.

  Or the float manufactured with the manufacturing method of the float mentioned above is used in the liquid level sensor 20 which shows schematic structure to Fig.4 (a), (b).

  The liquid level sensor 20 is provided, for example, in a fuel tank T that contains ammonia as a liquid. The liquid level sensor 20 includes a float body 22 in which the outer peripheral surface of the float F is covered with a metal foil 21, a cylindrical insulating guide 23 erected from the bottom wall to the upper wall of the fuel tank T, and an insulating property. And a pair of electrodes 24 provided densely on the outer peripheral surface of the guide 23. The insulating guide 23 has an inner diameter that is the same as the outer diameter of the float body 22, and the float body 22 is disposed inside the insulating guide 23 so as to be movable in the vertical direction. The pair of electrodes 24 are disposed so as to face the radial direction of the insulating guide 23. Further, the length (that is, the width) along the circumferential direction of the insulating guide 23 gradually increases (or narrows) along the circumferential direction of the insulating guide 23 as the pair of electrodes 24 moves from the lower end to the upper end of the insulating guide 23. It is formed as follows. When the float body 22 moves up and down due to a change in the liquid level of ammonia contained in the fuel tank T, the capacitance between the pair of electrodes 24 changes, and the liquid level is detected from the change in capacitance. Is done.

  The present inventor prepared a float as shown in Examples 1 to 6 below using the above-described manufacturing method of the present invention and a comparative manufacturing method as shown in Comparative Example 1 below using a conventional manufacturing method. The float was evaluated.

Example 1
In the extrusion molding machine 100 of the float manufacturing system 1 described above, the first hopper 114 has a number average particle size of 100 μm (particle size range 80 to 150 μm), a specific gravity of 0.95, a melting temperature (melting point) of 128 ° C., MFR. Is introduced into the second hopper 115, and the glass beads G having a number average particle size of 25 μm (particle size range of 10 to 50 μm), a specific gravity of 0.42, and a pressure resistance of 55 MPa. The high-density polyethylene resin particles PE1 are heated to a temperature equal to or higher than the melting point (target value 150 ° C.) in the cylinder 110 of the extrusion molding machine 100 to obtain a low-viscosity state melted in a liquid state. The beads G are mixed to form a mixture R. The mixture R is extruded from the nozzle die 113 and cooled, and then cut to a predetermined length to obtain the float F shown in FIG. It was. At this time, the filling rate (mixing ratio) of the glass beads G is adjusted so that the filling rate becomes 20% by mass, 25% by mass, 30% by mass, 35% by mass, 40% by mass, and 45% by mass. 6 types of float F were formed.

(Example 2)
Six types of floats F were molded in the same manner as in Example 1 except that the MFR of the high-density polyethylene resin particles PE1 was 1.

(Example 3)
Six types of floats F were molded in the same manner as in Example 1 except that the MFR of the high-density polyethylene resin particles PE1 was 8.

Example 4
Six types of floats F were molded in the same manner as in Example 1 except that the MFR of the high-density polyethylene resin particles PE1 was 18.

(Example 5)
Six types of floats F were molded in the same manner as in Example 1 except that the MFR of the high-density polyethylene resin particles PE1 was 40.

(Comparative Example 1)
Six types of floats F were molded in the same manner as in Example 1 except that the MFR of the high-density polyethylene resin particles PE1 was 50.

(Comparative Example 2)
By means of an extruder, high-density polyethylene resin particles PE1 having a number average particle size of 100 μm (particle size range of 80 to 150 μm), specific gravity of 0.95, melting temperature (melting point) of 128 ° C., and MFR of 18 are brought close to the melting temperature. It is heated to a temperature (target value 130 ° C.) to form a gel, kneaded with glass beads G having a number average particle size of 25 μm (particle size range: 10 to 50 μm), specific gravity of 0.42 and pressure resistance of 55 MPa, and then extruded. Then, after preparing a mixed pellet in which the high-density polyethylene resin and the glass beads G were mixed, a float having the same shape as the float F of FIG. 2 was formed by an injection molding machine using the mixed pellet. At this time, the filling rate of the glass beads G is adjusted so that the filling rate becomes 20% by mass, 25% by mass, 30% by mass, 35% by mass, 40% by mass, and 45% by mass, so that six kinds of floats F was molded.

  About these Examples 1-5 and Comparative Examples 1 and 2, it determined by the following criteria.

For specific gravity determination,
◎ ... Six types of floats with different filling rates include those with a specific gravity of 0.70 or less. ○ ... Six types of floats with different filling rates include those with a specific gravity of 0.72 or less. .. Six types of floats with different filling rates do not include those with a specific gravity of 0.72 or less.
◎ ・ ・ ・ Shape accuracy is ± 3% or less ○ ・ ・ ・ Shape accuracy is ± 5% or less × ・ ・ ・ Shape accuracy is more than ± 5%
◎ ・ ・ ・ The specific gravity judgment result and the molding judgment result are both very good (◎). ○ ・ ・ ・ The specific gravity judgment result and the molding judgment result are very good (◎) or good (○). It was determined that either the determination result or the molding determination result was defective (x).

  Table 1 shows configurations and determination results of Examples 1 to 5 and Comparative Examples 1 and 2 described above.

  From the results in Table 1, the following was found.

  In Examples 1 to 5, by using a high-density polyethylene resin with high chemical resistance, the float F having a specific gravity of 0.72 or less and a shape accuracy of ± 5% or less is obtained by adjusting the filling rate of the glass beads G. I was able to.

  In particular, in Examples 2 to 5, a float F having a specific gravity of 0.70 or less could be obtained, and the specific gravity determination was very good. Among them, in Example 5, the float F having a specific gravity of 0.6 can be obtained by increasing the filling amount of the glass beads G to 45% by mass, and dimethyl ether (liquid specific gravity 0.67) or ammonia (liquid specific gravity 0). .64) and the like can be formed.

  In particular, in Examples 1 to 4, the shape accuracy was ± 3% or less, and the molding determination was very good.

  From the results of Examples 1 to 5, good results can be obtained when the MFR in the high-density polyethylene resin is 0.5 to 40, and in particular, very good results are obtained when the MFR is 1 to 18. It became clear that it was possible.

  On the other hand, from the results of Comparative Example 1, it was confirmed that when the MFR is increased, the float F having a small specific gravity can be obtained, but the shape accuracy cannot be obtained. Further, from the result of Comparative Example 2, it was confirmed that when a conventional manufacturing method was used, a float having a specific gravity of 0.73 or less could not be molded even if the filling amount of the glass beads G was increased.

  As described above, according to the present invention, it was confirmed from the above Examples and Comparative Examples that the fracture F of the mixed glass beads G can be suppressed and a specific gravity and a desired shape F can be obtained. .

  FIG. 5 is a graph showing the relationship between the filling rate of the glass beads G and the specific gravity of the molded float F for Examples 1 to 5 and Comparative Examples 1 and 2. From the graph of FIG. 5, it can be seen that the float F having a small specific gravity can be obtained by increasing the filling rate of the glass beads G, and even if the filling rate is increased, the float depends on the MFR of the high-density polyethylene resin. It was found that the specific gravity of F was saturated at a predetermined value. Moreover, it turned out that the value which saturates becomes small, so that MFR is large.

  The embodiment described above describes, for example, a method for manufacturing a float floated on a liquid such as dimethyl ether (DME) or ammonia, and a liquid level sensor to which the float manufactured by this manufacturing method is applied. However, it is not limited to this. The liquid in which the float is floated is not limited to the above liquid, but may be, for example, a liquefied gas for industrial use such as nitrogen or oxygen, or a fuel (kerosene, gasoline, etc.) that becomes liquid at room temperature and normal pressure, or various chemicals. As long as the object of the present invention is not violated, the kind thereof is arbitrary. Also, the apparatus to which the float is applied is not limited to the liquid level sensor, and the apparatus and system to which the present invention is applied are arbitrary as long as the object of the present invention is not violated.

  In addition, embodiment mentioned above only showed the typical form of this invention, and this invention is not limited to embodiment. That is, various modifications can be made without departing from the scope of the present invention.

DESCRIPTION OF SYMBOLS 1 Float manufacturing system 100 Extruder 110 Cylinder 120 Screw 200 Cooling tank 300 Cutting machine F Float PE1 High density polyethylene resin particle PE2 Liquid high density polyethylene resin G Glass beads (glass granules)
R mixture E Intermediate molding

Claims (2)

A method for producing a float floating in a liquid,
A viscosity-reducing step in which a thermoplastic resin is heated to a temperature equal to or higher than the melting point of the resin and melted into a liquid state to obtain a low-viscosity state;
A mixing step of mixing a hollow glass particle with the resin in the low-viscosity state in the low-viscosity step to generate a mixture of the resin and the glass particle;
A method for producing a float, comprising: an extrusion molding step of sequentially extruding the mixture generated in the mixing step into a predetermined shape.   The method for producing a float according to claim 1, wherein a melt mass flow rate of the resin is in a range of 0.5 to 40 [g / 10 min].

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