JP5888547B2 - Float manufacturing method - Google Patents

Description

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

  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, the float of Patent Document 1 is prepared by kneading and extruding a resin heated and melted by an extruder and a glass microballoon to produce a pellet in which these resin and glass microballoon are mixed, and then using this pellet to produce an injection molding machine. However, if the proportion of glass microballoons is increased in order to reduce the specific gravity, the molten resin does not reach between these glass microballoons. The balloons were rubbed and broken, and there was a problem that it was 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 high viscosity at the time of melting, the molten resin does not spread between the glass microballoons. Was more prominent.

  The present invention aims to solve the above problems. That is, the present invention provides a float manufacturing method capable of obtaining a float having a small specific gravity while suppressing breakage of the glass particles mixed with the resin, and a float having a small specific gravity manufactured by this float manufacturing method. The purpose is that.

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 powder and the hollow glass particles are respectively in a solid state. A mixing step for generating a mixture mixed in step (b), and a compression molding step for compressing the mixture generated in the mixing step by applying pressure while heating the mixture at a temperature equal to or higher than the melting temperature of the resin powder. In the compression molding step, after the mixture is divided into a plurality of times and put into the mold, the first pressure is applied every time the mixture is put into the mold, and after the entire amount has been put A method for producing a float, wherein the mixture is heated while being compressed by applying a second pressure larger than the first pressure .

  The invention described in claim 2 is the invention described in claim 1, wherein, in the mixing step, the resin powder and the glass are such that a ratio of the glass particles is 41% by volume to 73% by volume. In the production method, the mixture is produced by mixing with granules, and in the compression molding step, the mixture placed in the mold is compressed by applying a pressure of 5 MPa or less.

  According to the present invention, the thermoplastic resin powder and the hollow glass particles are mixed in the solid state to form a mixture, so that a particulate material such as a powder or particles is used. Thus, these materials can be mixed uniformly to disperse the glass particles in the resin powder, and the mixture is put into a mold and heated and molded by pressure, so that the glass particles are included. Only pressure is applied without the molten resin being kneaded. Therefore, even when the ratio of the glass particles is increased, the glass particles are not rubbed with each other and the pressure applied to the glass particles is relaxed by the resin, and the glass particles can be prevented from being broken and mixed. It is possible to obtain a float having a small specific gravity while suppressing breakage of the glass particles. 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.

(A), (b) is a figure explaining the mixing process of the manufacturing method of the float of this invention. (A)-(f) is a figure explaining the compression molding process of the manufacturing method of the float of this 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. 3, (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 the glass bead in a mixture, and the specific gravity (actual value, theoretical value) of a float.

  Hereinafter, an embodiment of the method for producing a float 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 in which glass microballoons as glass particles are mixed with molten resin. However, when the mixing ratio of glass microballoons increases, Since the glass microballoon breaks, the specific gravity cannot be made smaller than a certain value. Therefore, it is not suitable for the production of a float floated on a liquid having a low specific gravity such as dimethyl ether (DME), butane gas, or ammonia. It was appropriate. 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. 3) 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 an 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 P (Sunfine LH-411, manufactured by Asahi Kasei Chemicals Corporation) are used. Of course, regarding the type of resin, in addition to polyethylene, for example, a powdery resin material such as polypropylene (PP) or polyamide (PA) may be used. What is necessary is just to be a magnitude | size of the grade which is not extremely larger than a body and mixes with this glass grain uniformly. In general, there is a correlation between the molecular weight and the melt viscosity in the resin, and even if it is the same kind of resin, the melt viscosity tends to increase as the molecular weight increases, but since it is mixed with the glass particles in the powder state, The melt viscosity does not affect the degree of mixing of the mixture and can be uniformly mixed. 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 an average particle size of about 35 μm and a specific gravity of about 0.34 are used. In this embodiment, glass beads G for filler (Sphericel 34P30, manufactured by Potters Barotini) 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. Therefore, the average particle diameter of the glass beads G and the like are determined so as to balance the specific gravity and the pressure resistance according to 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.). .

  In manufacturing the float, first, after weighing a predetermined amount of high-density polyethylene resin particles P and glass beads G, as shown in FIGS. 1 (a) and 1 (b), they are put into a mixer M and mixed. A mixture R in which these raw materials are uniformly mixed is generated (mixing step).

In this mixing step, the ratio of the glass beads contained in the generated mixture R (hereinafter also referred to as filling rate) is 41 to 41 in accordance with the use of the float to be manufactured (that is, the liquid to be floated). The high density polyethylene resin particles P and the glass beads G are mixed so as to fall within the range of 73% by volume. The “volume%” here is a value about the volume occupied by the high density polyethylene resin particles P and the glass beads G themselves, which does not include spaces between powders and granules, and these volumes (volume%) are: Calculated from the specific gravity and weight of each raw material. For example, when the high density polyethylene resin particles P (specific gravity 0.95) is 26 g and the glass beads G (specific gravity 0.35) is 17 g, the volume of the high density polyethylene resin particles P is 27.4 cm ³ (= 26 / 0.95) and the glass beads G become 50.0 cm ³ (= 17 / 0.34). When these are mixed, the filling rate of the glass beads G is 65 vol% (= 50.0 / (27.4 + 50.0). )).

  Next, as shown in FIGS. 2A to 2F, the mixture R generated in the mixing step is filled in a mold and compressed while being heated to a melting temperature or higher of the high-density polyethylene resin particles P ( Compression molding process).

  The mold K used in the compression molding process is provided with a bottomed cylindrical cavity C having an open upper end. In the cavity C, for example, a silicon release agent, a fluorine release agent, etc. The mold release process which applies | coats is performed previously. The cavity R is filled with the mixture R and filled with the mixture R until the cavity C overflows by about 10%. Specifically, the mixture is filled into a plurality of times, and is poured into the cavity C from above in small portions (FIGS. 2 (a) and (c)), and the mixture filled in the cavity C is poured each time the mixture is poured. It compresses from the upper part by the pressure of about 1 MPa, and it is performed until it overflows from the upper part of the cavity C (FIG.2 (e)), making the space | gap produced in the mixture R small (FIG.2 (b), (d)). Then, when the mixture R is filled in the cavity C, the mold is heated to 180 ° C. by a heater (not shown), the pressure is gradually increased to 5 MPa at a rate of 1 MPa / min, and a pressure of 5 MPa is applied. Compress the mixture R for 10 minutes at (Fig. 2 (f)). At this time, since the resin flows out from the gap between the molds K, the pressure is adjusted so that the pressure applied to the mixture R is maintained at 5 MPa.

  Then, the heater is turned off while holding the mold K, natural cooling is performed until the mold temperature (that is, the temperature of the mixture R) reaches 100 ° C., and further, the mold K is held while holding the mold K. Cooling water is circulated through a pipe line (not shown) provided in the mold K to perform cooling until the mold temperature reaches 40 ° C. (cooling process).

  Then, the molded product is taken out from the mold K, and the float F shown in FIG. 3 is completed.

  As described above, according to the present invention, the mixture R is formed by mixing the high density polyethylene resin particles P as the thermoplastic resin powder and the glass beads G as the hollow glass particles in a solid state. Therefore, by using particulate materials such as powders or granules, these materials can be mixed uniformly to disperse the glass beads G in the high density polyethylene resin particles P, and the mixture R can be made of gold. Since molding is performed by applying pressure while heating in the mold K, only the pressure is applied without kneading the molten polyethylene resin containing the glass beads G. Therefore, even when the ratio of the glass beads G is increased, the glass beads G are not rubbed with each other, and the pressure applied to the glass beads G is relaxed by the polyethylene resin, so that the glass beads G can be prevented from being broken and mixed. Float F with a small specific gravity can be obtained while suppressing breakage of the glass beads G. Moreover, since the ratio of the glass beads G is increased, the amount of liquid permeation into the high density polyethylene resin particles P can be reduced, and therefore, a float F with little change in specific gravity with time can be obtained.

  The float manufactured by the above-described float manufacturing method is used in, for example, 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.5 (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 inventor produced floats as shown in the following Examples 1 to 3 and Comparative Examples 1 to 5 using the production method of the present invention described above, and compared the specific gravity of these floats. It was. Moreover, the float disclosed by patent document 1 was made into Comparative Examples 6-25, and the comparison with the specific gravity of these floats was also performed.

Example 1
High-density polyethylene resin particles P (Sunfine LH-411, manufactured by Asahi Kasei Chemicals Corporation) having an average particle size of 100 μm (particle size range of 80 to 150 μm), a specific gravity of 0.95 and a melting temperature of 128 ° C., and an average particle size of 35 μm (particle size range: 10 to 50 μm), specific gravity of 0.34, pressure resistance of 20 MPa glass beads G (Sphericel 34P30, manufactured by Potters Barotini) were mixed in a solid state, and glass beads G A mixture having a filling rate of 65% by volume was produced. The mixture was filled in a mold and compressed at a pressure of 5 MPa, then cooled and demolded to obtain a float molded product.

(Example 2)
A float F molded product was obtained in the same manner as in Example 1 except that a mixture in which the filling rate of the glass beads G was 70% by volume was generated.

(Example 3)
A float F molded product was obtained in the same manner as in Example 1 except that a mixture having a glass bead G filling ratio of 65% by volume was produced, and this mixture was filled in a mold and compressed at a pressure of 10 MPa. It was.

(Comparative Example 1)
A float F molded product was obtained in the same manner as in Example 1 except that a mixture in which the filling rate of the glass beads G was 35% by volume was generated.

(Comparative Example 2)
A float F molded product was obtained in the same manner as in Example 1 except that a mixture in which the filling rate of the glass beads G was 75% by volume was generated.

(Comparative Example 3)
A float F molded product was obtained in the same manner as in Example 1 except that a mixture in which the filling rate of the glass beads G was 80% by volume was generated.

(Comparative Example 4)
A molded product of Float F was obtained in the same manner as in Example 1 except that a mixture in which the filling rate of the glass beads G was 35% by volume was produced, and this mixture was filled in a mold and compressed at a pressure of 10 MPa. It was.

(Comparative Example 5)
A molded product of Float F was obtained in the same manner as in Example 1 except that a mixture in which the filling rate of the glass beads G was 80% by volume was generated, and this mixture was filled in a mold and compressed at a pressure of 10 MPa. It was.

  About Comparative Examples 6-25, it respond | corresponds to Examples 1-20 in patent document 1, and refer patent document 1 for details, such as a manufacturing method.

  About these Examples 1-3 and Comparative Examples 6-25, it determined by the following determination criteria.

For chemical resistance,
○ ... (1) Dimethyl ether (DME), (2) Ammonia, (3) Liquefied butane gas, each of which is resistant to x. At least one of the above (1) to (3). It was judged as having no resistance or not suitable in nature.

For specific gravity determination,
O ... The specific gravity is less than 0.67, which is the liquid specific gravity of DME. X ... The specific gravity was determined to be 0.67 or more.

For general judgment,
○: Both chemical resistance and specific gravity determination are good (◯) ×: At least one of chemical resistance and specific gravity determination is defective (×).
Judged as.

Tables 1 and 2 show configurations and determination results of Examples 1 to 3 and Comparative Examples 6 to 25. In Table 2, for comparison with the present invention, items (the glass particle filling rate, the theoretical value of the molded product specific gravity) are added based on the description in Patent Document 1 and the like. The theoretical value of the specific gravity of the molded product in each table is the specific gravity when the glass beads G are not damaged at all in the molded product. The specific gravity of the high density polyethylene resin particles P is Hp, and the glass beads G When the specific gravity is Hg and the filling rate of the glass beads G is Jg, the theoretical value H of the molded product specific gravity is calculated by the following equation.
H = (Hp × (1− (Jg / 100))) + (Hg × (Jg / 100))

  From the judgment results in Table 1, the following was found. In Examples 1 to 3, float F having a specific gravity smaller than the liquid specific gravity of dimethyl ether could be obtained using high-density polyethylene resin P having high chemical resistance. In particular, in Example 1, a float having a specific gravity (specific gravity 0.57) lower than the liquefied butane gas (specific gravity 0.58) having a very low liquid specific gravity could be obtained. Further, in Comparative Examples 1 and 4, the amount of glass beads G filled is too small, and a float having a specific gravity smaller than the liquid specific gravity of dimethyl ether cannot be molded actually and theoretically. Theoretically, a float with a smaller specific gravity can be formed as the filling amount of the glass particles is increased. However, in Comparative Examples 2, 3, and 5, the filling amount of the glass particles is too large. Therefore, it is considered that the high density polyethylene resin particles are not sufficiently distributed between them, and therefore, even if the production method of the present invention is used, breakage of the glass particles cannot be prevented, and the specific gravity of the float is increased.

  In addition, from the determination results in Table 2, a float having a small specific gravity can be manufactured by the conventional manufacturing method shown in Patent Document 1 (for example, Comparative Examples 6, 8, 19, 20, and 23). Since the resin used is nylon 6 (PA6) or polypropylene (PP), it is inferior in chemical resistance or the like as compared with the high-density polyethylene resin (HDPE) used in Examples 1 to 3 and the like. In particular, nylon 6 has a certain degree of chemical resistance, but is weak against acid, and generally has high water absorption, so that the weight change easily occurs due to the moisture contained in the tank. 6 is not suitable as a float material. Polypropylene is known to be brittle at 0 ° C. or lower, and high-pressure liquefied gas generally has a large heat of vaporization, and may be cooled to 0 ° C. or lower when taking out the liquefied gas. Therefore, polypropylene is not suitable as a float material for high-pressure liquefied gas.

  Further, as shown in Comparative Examples 12 to 25, even when the filling rate of the glass particles was increased to 60% by volume or more, the specific gravity was significantly larger than the theoretical specific gravity, and a considerable amount was produced during production. It is considered that the glass particles are broken. If high-density polyethylene resin P having high chemical resistance is used instead of nylon 6 or polypropylene, this high-density polyethylene has a molecular weight higher than that of PA6 or PP. Therefore, it is expected that the glass particles will be damaged more than the conventionally used resin, and the chemical resistance is increased by using a high-density polyethylene resin having a large molecular weight. However, it is considered that a float with a small specific gravity cannot be obtained.

  As described above, according to the present invention, it is possible to obtain a float F having a small specific gravity while suppressing breakage of the mixed glass beads G. In particular, even if a high-molecular weight resin having high chemical resistance is used, the specific gravity is small. It became clear from the said Example and comparative example that the float F can be obtained.

  FIG. 6 is a graph showing the relationship between the filling rate of the glass beads G and the specific gravity (actual value, theoretical value) of the molded float F with respect to Examples 1 to 3 and Comparative Examples 1 to 5. As shown in FIG. 6, as for the theoretical value of the specific gravity of the float F, the specific gravity decreases as the filling rate increases. On the other hand, as for the measured value of the specific gravity of the float F, the specific gravity decreases approximately along the theoretical value as the filling rate increases, but the specific gravity increases at a certain filling rate. This is because if the filling rate is low, the high density polyethylene resin P is sufficiently distributed between the glass beads G, or the resin P acts as a cushion when compression molding to reduce the pressure and prevent the glass beads G from being damaged. It is considered that the specific gravity is almost as the theoretical value, and if the filling rate is high, the resin P does not sufficiently reach between the glass beads G, and the glass beads G are damaged by the pressure of compression molding. It is considered that the specific gravity is greater than the value. In the graph of FIG. 6, the measured value when the filling rate of the glass beads G is low (35% to 50%) is lower than the theoretical value. From the viewpoint of adhesion, it is considered that a slight pore exists at the interface between them. And, when liquid enters such pores, the weight change of the float F occurs. However, since the liquid used above has a specific gravity lower than that of the high density polyethylene resin P, even if the liquid enters the pores, If the beads G are not damaged, the specific gravity of the float F does not exceed the theoretical value.

  Further, from the graph of FIG. 6, the high-density polyethylene resin particles P having an average particle size of 100 μm (particle size range of 80 to 150 μm), a specific gravity of 0.95 and a melting temperature of 128 ° C., and an average particle size of 35 μm (particle size) These raw materials are mixed in a solid state using glass beads G having a diameter range of 10 to 50 μm), a specific gravity of 0.34 and a pressure resistance of 20 MPa, and (A) the filling rate of the glass beads G is 41 to 41 A mixture having a volume of 73% by volume was formed, and this mixture was filled in a mold and compression molded at a pressure of 5 MPa, so that (1) dimethyl ether (liquid specific gravity 0.67), (2) ammonia (liquid specific gravity 0. 64), (3) Float F suitable for each of liquefied butane gas (liquid specific gravity 0.58), or (B) a mixture in which the filling rate of glass beads G is 51 to 71% by volume Produces this Float F suitable for each of the above (2) and (3) can be produced by filling the mixture into a mold and compression molding at a pressure of 5 MPa, or (C) filling of glass beads G It is found that a float F suitable for the above (3) can be produced by producing a mixture having a rate of 64 to 66% by volume, filling the mixture in a mold, and compression molding at a pressure of 5 MPa. It was. The upper limit value and the lower limit value of the range of the filling rate of the glass beads G described above are derived from the measured value graph of the pressure of 5 MPa in FIG. In particular, by setting the filling rate of the glass beads G to 65%, 0.55 to 0.57 (the lower limit is a theoretical value) that could not be manufactured by the conventional manufacturing method shown in Patent Document 1. A specific gravity float can be produced.

  The embodiment described above describes, for example, a method for manufacturing a float floated on a liquid such as dimethyl ether (DME), butane gas, or ammonia, and a liquid level sensor to which the float manufactured by this manufacturing method is applied. However, the present invention 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, 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.

10, 20 Liquid level sensor F Float P High density polyethylene resin particles (resin powder)
G Glass beads (glass particles)
R mixture K mold C cavity

Claims (2)

A method for producing a float floating in a liquid,
A mixing step for producing a mixture in which the thermoplastic resin powder and the hollow glass particles are mixed in a solid state, and
A compression molding step in which the mixture produced in the mixing step is put into a mold and compressed by applying pressure while heating to a temperature equal to or higher than the melting temperature of the resin powder ,
In the compression molding step, the mixture is divided into a plurality of times and placed in the mold. Each time the mixture is placed in the mold, the first pressure is applied to compress the mixture. A method for producing a float, wherein the mixture is heated while being compressed by applying a larger second pressure . In the mixing step, the resin powder and the glass particles are mixed so that the ratio of the glass particles is 41% by volume to 73% by volume to generate the mixture,
In the compression molding step, the mixture put in the mold is compressed by applying a pressure of 5 MPa or less,
The method for producing a float according to claim 1.

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