JP2007260928A - Manufacturing method of bathtub made of synthetic resin - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a manufacturing method of a bathtub made of a synthetic resin capable of simply and efficiently manufacturing a bathtub product comprising the synthetic resin alone. <P>SOLUTION: The bathtub made of the synthetic resin is manufactured using a mold 20 having the cavity 29 constituted of a fixed mold 21 and a movable mold 22 to form the bathtub made of the synthetic resin and an injection device 10 equipped with an injection cylinder 11. The synthetic resin is supplied into the cylinder 11 and melted while rotating the screw 12 arranged in the cylinder 11 while the molten synthetic resin is allowed to continuously flow in the cavity 29 of the mold 20 by rotating the screw 12 to fill the cavity 29. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method for manufacturing a bathtub made of synthetic resin, and more particularly to a method for manufacturing a bathtub product made of a synthetic resin alone.

  Examples of the material used for the bathtub include stainless steel, resin-made artificial marble, and enamel, but recently, synthetic resins such as acrylic resins have become widespread. For example, an acrylic resin bathtub (acrylic bathtub) is manufactured mainly by thermoforming as represented by vacuum forming.

As a general manufacturing method of an acrylic bathtub, for example, Patent Document 1 discloses the following steps.
(I) A cast plate made of acrylic resin and having a thickness of 4 to 5 mm obtained by cast polymerization is vacuum-formed to obtain a bathtub-shaped acrylic molded product having a thickness of about 0.8 to 5 mm.
(Ii) An acrylic molded product is annealed in order to reduce molding distortion, and then cleaned and primed on the back surface. The annealing conditions are a glass transition temperature of the cast plate of -20 to 25 ° C., and the standard is about 3 to 4 hours including temperature rise and temperature fall.
(Iii) After that, reinforced plastic (FRP) is laminated on the back side of the acrylic molded product and cured (backing). After drilling and trimming of unnecessary parts, metal fittings are attached and a predetermined inspection is performed. Get a bathtub.

However, in the manufacturing method as described in Patent Document 1, it is necessary to back up an expensive FRP resin on the back surface, and there are many processes, so that a bathtub cannot be easily and efficiently manufactured. There is. In addition, the cost per product is high and the FRP is backed and integrated, making it difficult to recycle.
JP-A-9-109287

  In order to solve the above problem, there has been a demand for a bathtub product that does not back FRP, that is, a synthetic resin alone. In order to manufacture a bathtub product with a single synthetic resin, the thickness of the product is required to be about 5 to 15 mm in order to prevent deformation, and the weight per product is about 20 to 40 kg.

  However, it is very difficult to obtain a bathtub having the thickness and weight as described above by a molding process with fewer steps. For this reason, there has been no practical use of a bathtub made of synthetic resin alone without backing.

  The subject of this invention is providing the manufacturing method of the bathtub made from a synthetic resin which can manufacture the bathtub product of a synthetic resin single-piece | unit easily and efficiently.

  As a result of intensive studies to solve the above problems, the present inventor fused the synthetic resin supplied in the injection cylinder while rotating the screw disposed in the cylinder, and at the same time, the molten synthetic resin The new finding that a bathtub product made of a simple synthetic resin can be obtained simply and efficiently is found when filling the resin by continuously flowing it into the mold cavity by rotating the screw. It came to be completed.

That is, the synthetic resin bathtub manufacturing method of the present invention has the following configuration.
(1) A method for producing a synthetic resin bathtub using a mold for forming a synthetic resin bathtub having a cavity constituted by a fixed mold and a movable mold, and an injection device having an injection cylinder. Synthetic resin is supplied into the injection cylinder, and the synthetic resin is melted while rotating a screw disposed in the injection cylinder. At the same time, the molten synthetic resin is continuously fed into the mold cavity by rotating the screw. A method of manufacturing a synthetic resin bathtub, wherein the filling is performed by flowing into the container.
(2) Filling the molten synthetic resin by continuously flowing it into the mold cavity by rotating the screw, and applying pressure from the screw side to the synthetic resin in the cavity during or after the filling. The method for producing a synthetic resin bathtub as described in (1) above, wherein the synthetic resin is solidified by cooling while maintaining the pressure, and the bathtub is removed from the mold to obtain a product.
(3) When the temperature of the cavity surface of the mold is the glass transition temperature of the synthetic resin −50 to the glass transition temperature + 20 ° C., the filling of the melted synthetic resin into the cavity is started and filled The temperature of the cavity surface at the time of completion is adjusted to the glass transition temperature + 10 to the glass transition temperature + 30 ° C. of the synthetic resin, and then cooled, so that the temperature of the cavity surface is the glass transition temperature of the synthetic resin−80 -The manufacturing method of the synthetic resin bathtub as described in said (1) or (2) which takes out a product when it is glass transition temperature-20 degreeC.
(4) The method for producing a synthetic resin bathtub according to any one of (1) to (3), wherein a fluid passage for alternately passing a heating medium and a refrigerant is provided near the cavity surface of the mold.
(5) Near the cavity surface of the mold, there is a cavity block made of a metal having a higher thermal conductivity than that of the metal constituting the mold body, and the cavity block has a heat medium and a refrigerant inside. The manufacturing method of the synthetic resin bathtub as described in any one of said (1)-(4) which has a fluid passage for letting go alternately.
(6) The synthetic resin bathtub manufacturing method according to (5), wherein the cavity block is made of beryllium copper.
(7) The method for producing a synthetic resin bathtub according to any one of (1) to (6), wherein the synthetic resin is an acrylic resin.
(8) The synthetic resin bathtub manufacturing method according to (7), wherein the acrylic resin is a methacrylic resin.
(9) The method for producing a synthetic resin bathtub according to any one of (1) to (8), wherein the product has a thickness of 5 to 15 mm.

  According to the present invention, the synthetic resin supplied into the injection cylinder is melted while rotating the screw disposed in the cylinder, and at the same time, the molten synthetic resin is continuously fed into the mold cavity by the rotation of the screw. Therefore, it is possible to easily and efficiently obtain a bathtub product made of a single synthetic resin. Moreover, the synthetic resin bathtub obtained in the present invention is excellent in processing cost per unit and high quality appearance.

  Hereinafter, an embodiment of a method for producing a synthetic resin bathtub according to the present invention will be described in detail with reference to the drawings. FIG. 1 is a perspective view showing a synthetic resin bathtub according to this embodiment. FIG. 2 is a schematic explanatory view showing a molding apparatus according to the present embodiment.

  The manufacturing method according to the present embodiment is a method for manufacturing a synthetic resin bathtub 1 as shown in FIG. The bathtub 1 has a thickness of about 5 to 15 mm and is made of a synthetic resin alone. The synthetic resin may be any resin that satisfies the required physical properties as a bathtub. Specific examples include acrylic resins such as methacrylic resin, polycarbonate, polystyrene, and a copolymer of methyl methacrylate and styrene (MS resin). ), Polypropylene, polyethylene, high-density polyethylene, copolymers of acrylonitrile, butadiene and styrene (ABS resin), polysulfone resins, thermoplastic polyester resins, and other thermoplastic resins that can be melt-molded. In addition, you may add a mold release agent, a ultraviolet absorber, dye, a pigment, a polymerization inhibitor, a chain transfer agent, antioxidant, a flame retardant, etc. to these resin as needed.

  In the present embodiment, the synthetic resin is preferably an acrylic resin, particularly a methacrylic resin, in order to give the bathtub 1 a high-class feeling due to the gloss and transparency of the surface and further enable recycling. Is preferred. The methacrylic resin is a polymer mainly composed of methyl methacrylate. Examples of the polymer include a homopolymer of methyl methacrylate and methyl methacrylate and a small amount (for example, up to about 10% by weight) of a monomer such as alkyl acrylates (for example, methyl acrylate or ethyl acrylate). A copolymer can be illustrated.

  Next, the manufacturing method of this embodiment for manufacturing the bathtub 1 will be described. The manufacturing method according to the present embodiment is a method in which molten resin is filled into a mold cavity at a very low speed. ), The molten resin is filled into the mold cavity by the forward driving force accompanying the rotation of the resin while the screw provided in the cylinder is rotated.

  That is, the molten synthetic resin is not injected as in a normal injection molding method, but continuously flows into the mold cavity at a low speed by the rotation of the screw in the cylinder. As a molding apparatus used for this manufacturing method, a ROM (read only memory) for driving a motor in a normal injection molding machine can be obtained by remodeling the specification suitable for the manufacturing method. Specifically, it is preferable to use a molding apparatus as shown in FIG. The molding apparatus includes an injection apparatus 10 and a mold 20.

  The injection apparatus 10 includes an injection cylinder 11, a screw 12 disposed in the injection cylinder 11, a motor 13 for rotationally driving the screw 12, a ram mechanism 14 for moving the screw 12 forward, and a synthetic resin injected into the injection cylinder 11. A hopper 15 for supplying the liquid to the injection cylinder, a heater 16 installed on the outer surface of the injection cylinder 11, and an injection nozzle 18 for injecting the molten resin at the tip of the injection cylinder 11.

  The mold 20 is for forming the synthetic resin bathtub 1 and includes a fixed mold 21 and a movable mold 22. On the fixed mold 21 side, a hot runner 25 provided in each of the heated cylinder 23 and the hot tip bushing 24 for allowing the molten resin injected from the injection nozzle 18 to pass therethrough is provided. A sprue 26 having a tapered cross section is formed at the distal end toward the movable mold 22 side. The structure of the hot chip bushing 24 may be a general open gate system, but preferably the gate is opened when necessary, such as a valve gate system, so that the resin does not flow backward from the gate, A structure in which the gate is closed when unnecessary is preferable.

  By combining the fixed mold 21 and the movable mold 22, a cavity 29 for the molded product (bathtub 1) is formed. That is, the shape of the cavity 29 corresponds to the shape of the bathtub 1. As shown in FIG. 2, the cavity 29 communicates with the cylinder 11 of the injection device 10 through the sprue 26 and the hot runner 25.

The surface of the cavity 29 is preferably a mirror surface plated so as to improve the appearance of the obtained bathtub 1 and improve mold separation. Examples of the material of the plating layer include titanium carbide (TiC), titanium nitride carbide (TiCN), titanium nitride (TiN), tungsten carbide (W ₂ C), chromium (Cr), nickel (Ni), and the like. The plating layer is preferably a polished layer.

  The fixed mold 21 is fixed to a fixed platen 31, and a fixed-side cavity block 32 is provided in the vicinity of the surface on the cavity 29 side. On the other hand, the movable mold 22 is fixed to a movable plate (not shown), and a movable-side cavity block 33 is provided in the vicinity of the surface on the cavity 29 side. The mold 20 opens and closes when the movable plate moves forward and backward.

  Here, since the heat insulation and cooling of the synthetic resin filled in the cavity 29 is performed via the surface of the cavity 29, the heat exchange of the bathtub 1 depends on the thermal conductivity in the vicinity of the surface of the cavity 29. To do. Since the filling speed of the molten resin in the present embodiment is much slower than that of the normal injection molding method, the molten resin is easily cooled and solidified during inflow due to the cooling effect due to contact with the mold, and in the case of a bathtub with a large area May stop flowing. Therefore, the temperature of the synthetic resin filled in the cavity 29 is set so that the surface temperature of the mold cavity 29 is close to the glass transition temperature of the resin (about −5 ° C. to + 25 ° C. centering on the glass transition temperature). At the heated temperature, the resin flows into the cavity 29 and is filled, and then the temperature of the surface of the cavity 29 is lowered to the glass transition temperature of the resin or lower (a temperature lower than the glass transition temperature by 50 ° C. or more). Is preferred.

  As the above temperature control method, a method (so-called heat medium / refrigerant) in which a heat medium and a refrigerant are alternately passed through a passage (fluid passage) for passing a heat medium provided near the inside of the mold cavity surface. The exchange method) can be exemplified. This molding method using the temperature control method is called a cold cycle molding method. Examples of the heat medium and the refrigerant include machine oil and water. Among these, water is preferable as the refrigerant, and pressurized water is preferable as the heat medium.

  Specifically, as shown in FIG. 2, fluid passages for the heat medium and the refrigerant are provided along the cavity 29 in the cavity block 32 of the fixed mold 21 and the cavity block 33 of the movable mold 22. 34 and 34 are buried. Then, the temperature control equipment provided with the control device allows the heating medium and the refrigerant to be alternately switched and circulated in the fluid passages 34 and 34 according to the purpose, thereby increasing the temperature of the mold during the molding cycle. Alternatively, the temperature is lowered. The fluid passages 34 and 34 are preferably provided in both the fixed-side cavity block 32 and the movable-side cavity block 33. However, the fluid passages 34 and 34 may be provided only in one and the heat medium and the refrigerant may be alternately passed therethrough. The corresponding effect is demonstrated.

  In the thermal cycle forming method, copper or copper having a higher thermal conductivity than the metal (for example, steel material) constituting the mold 20 main body (mold base) is formed near the surface of the mold cavity 29 (particularly, around the fluid passage). It is preferred to use a metal such as the alloy. In particular, beryllium copper (that is, a copper alloy containing about 0.3 to 3% by weight of beryllium) having a high thermal conductivity of about 3 to 6 times that of a general steel material is preferable. Specifically, the fixed-side cavity block 32 and the movable-side cavity block 33 are preferably made of a metal having a higher thermal conductivity than that of the metal constituting the mold bodies 21 and 22, such as beryllium copper. As a result, the temperature can be raised or lowered in about half the time required for a normal cavity surface made of steel.

  In the present embodiment, the resin material may be filled in a state in which the mold 20 is opened in advance and the clearance is taken, and after the filling, the movable mold 22 may be further advanced and compressed to be molded. In that case, in order to prevent a burr | flash, it is preferable that the mating surface of the fixed mold | type 21 and the movable mold | type 22 is a push-cut type of a stamping structure.

  Protruding pins 38 and 38 for projecting the molded product when the molded product is taken out are provided in the product peripheral portion of the movable mold 22. The protruding pin 38 is configured to move forward and backward by a hydraulic ejector device (not shown).

  In order to manufacture the bathtub 1 using the molding apparatus described above, first, the cavity 29 of the mold 20 that is composed of the fixed mold 21 and the movable mold 22 and forms the bathtub 1 is provided in the cylinder 11 of the injection apparatus 10. Communicate. Next, in the present embodiment in which the rotation of the screw is used at the time of injection of the molten resin, the screw 12 is driven to rotate by the motor 13 while the screw 12 is at the most advanced position, and the resin material is injected from the hopper 15. Supply into the cylinder 11.

  The supplied resin material is plasticized, melted and kneaded by the heat from the heater 16 and the heat generated by the shearing and frictional force received by the rotation of the screw 12, and at the same time, in the direction of the screw tip by the rotational transfer action of the screw 12. It is carried and continuously flows into the cavity 29 through the hot runner 25, the sprue 26, and the gate 28 to be filled. That is, the resin material is supplied into the cylinder 11 by the rotational drive of the screw 12 and the molten resin is injected and filled into the cavity 29 in the mold 20. Thereby, the bathtub 1 of a synthetic resin simple substance can be obtained simply and efficiently. Moreover, since the possibility that the flow of the melted synthetic resin is cut off is lessened, the pattern and smoothness of the surface of the mold 20, that is, the surface of the cavity 29, are shaped better. Further, since the inflow of the molten resin is performed by continuous pumping by the rotational drive of the screw 12, by continuing the rotational drive, a large-size having a volume larger than that of the cylinder, which is usually difficult by one measurement. Of bathtub products can be manufactured. As a result, regardless of the weight (capacity) of the bathtub product, molding can be performed with a relatively small cylinder unit.

  It should be noted that pressure (back pressure) is applied from the rear of the screw 12 so as to prevent the screw 12 from moving backward due to the pressure of the resin transferred to the front of the screw 12, that is, to hold the screw 12 in that position. It is desirable to do. Specifically, it is preferable to apply a back pressure so that the screw 12 does not move backward with the resin pressure during filling, but with the pressure of the filled resin, and the screw 12 is rotated in the cylinder 11 of the injection device. Therefore, a mode in which the molten resin continuously flows into the mold cavity 29, for example, a flow mold method is advantageously employed.

  When the molten resin is continuously flowed into the mold cavity 29 while rotating the screw 12 in the cylinder 11, the rotational speed of the screw 12 leads to the flow injection speed, and the higher the rotational speed of the screw 12, the higher the speed. Get faster. Accordingly, the number of rotations of the screw 12 depends on the thickness and size of the product, generally from a value of about 20 to 180 rpm, depending on the diameter of the screw 12, the thickness of the molded product (bathtub 1), the number of molds taken, etc. Are appropriately selected.

  In a state where the surface temperature of the cavity 29 is heated to the vicinity of the glass transition temperature of the synthetic resin, the molten synthetic resin is continuously flowed into the cavity 29. The temperature is preferably lowered to a temperature lower than the glass transition temperature. Thereby, (1) generation of sink marks is suppressed, (2) a thick product having a good appearance is obtained, (3) the surface is shaped well, (4) heat exchange efficiency is increased, (5) Molding can be performed with a low clamping force, and (6) production efficiency can be increased.

  Specifically, when the molten synthetic resin is continuously flowed into the cavity 29 with the surface temperature of the mold cavity 29 being heated to near the glass transition temperature of the synthetic resin, Since the applied pressure (in-mold pressure) may be about half that of a normal injection molding method, a large-area bathtub can be manufactured with a low clamping force. The surface temperature of the mold 20, that is, the temperature of the cavity 29 surface varies depending on the type of synthetic resin used, but is generally about 90 to 150 ° C. In the case of a methacrylic resin, the glass transition temperature is around 105 ° C., so that the temperature of the surface of the mold 20 is preferably about 105 to 130 ° C. The injection temperature of the molten resin (resin temperature in the injection cylinder 11) also varies depending on the type of synthetic resin used, but is generally about 170 to 300 ° C. In the case of methacrylic resin, for example, about 200 to 300 ° C. Preferably, it is about 220-270 degreeC. The back pressure at this time is about 20 to 45 MPa in terms of the resin pressure at the tip of the screw 12.

  The temperature of the mold 20 when the molten resin flows in is preferably set to be equal to or higher than the glass transition temperature of the resin material to be molded, but may be a temperature lower than that at the start of injection due to the cycle. It is necessary to make the mold surface temperature equal to or higher than the glass transition temperature of the resin material at least before entering the next pressure holding step described later. Furthermore, it is desirable to improve the temperature control system so that the temperature increase / decrease proceeds at an earlier time.

  In particular, in this embodiment, when the temperature of the surface of the cavity 29 of the mold 20 is a glass transition temperature of the synthetic resin −50 to a glass transition temperature + 20 ° C., preferably a glass transition temperature −20 to a glass transition temperature, melting occurs. The filling of the synthetic resin into the cavity 29 is started, and the temperature of the surface of the cavity 29 when the filling is completed is set to the glass transition temperature of the synthetic resin + 10 to the glass transition temperature + 30 ° C. The product (bathtub 1) is preferably taken out when the surface temperature of the cavity 29 is from the glass transition temperature of the synthetic resin to -80 to the glass transition temperature of -20 ° C. Thereby, it becomes possible to reduce the molding distortion of a product. This is because when the molten resin is molded in the cavity 29, the molding is performed at a temperature higher than the glass transition temperature of the synthetic resin, so that no excessive stress is applied to the intermolecular and molecular chains of the synthetic resin. In addition, rapid cooling immediately after molding means that the molecules are frozen in a relaxed state, so that residual stress is generated due to non-uniform density that occurs when gradually cooling, as in normal injection molding. It is guessed that this is because it can be suppressed. Therefore, the product (bathtub 1) formed by this method is less prone to problems such as thermal deformation and chemical cracking due to molding distortion.

  The temperature control of the mold 20 will be described. First, a heating medium is passed through the fluid passages 34 and 34 in the cavity block 32 of the fixed mold 21 and the cavity block 33 of the movable mold 22 so that the cavity surface temperature of the mold is changed. Heat until it is close to the glass transition temperature of the resin material. For example, in the case of methacrylic resin, a heat medium such as pressurized water heated to 100 ° C. or higher, specifically about 110 to 130 ° C. is passed through the fluid passages 34, 34, and the mold cavity 29 surface temperature is 100 Heat to about ℃. When this temperature is reached, resin filling (injection or screw rotation) is started. If the resin is filled in this state, the temperature of the resin flowing into the cavity 29 is higher than that, so that the mold surface temperature is higher than that before the start of filling, that is, a temperature higher than the glass transition temperature of the resin material, for example, methacrylic. If it is resin, it can maintain at about 105-130 degreeC. After filling is completed, by switching a valve installed in the middle of the fluid passages 34, 34, a coolant such as water of about 10 to 40 ° C. is passed through the same fluid passages 34, 34, and the cavity 29 is rapidly cooled. To do. After sufficiently cooling, by switching the valve again, the mold 20 is opened at an appropriate mold temperature while passing the heat medium through the fluid passages 34, 34, the molded product (bathtub 1) is projected, and the pin 38 is used. Stick out and take out. It waits for a while until the mold temperature reaches a temperature sufficient to fill the resin again, and when the mold temperature reaches a predetermined value, the next cycle is started.

  While rotating the screw 12 in the cylinder 11, the molten resin is continuously flowed into the mold cavity, and the cavity 29 is completely filled with the resin or not completely filled, that is, in a short shot state (during filling) ), The screw 12 is retracted by the pressure of the filled resin. Therefore, it is preferable to apply pressure (holding pressure) to the resin in the cavity 29 from the screw 12 side when the screw 12 retracts to a predetermined distance.

  Note that it is preferable to switch the medium flowing in the fluid passages 34 and 34 to the refrigerant by setting a timer, switching a switch valve, or the like before and after starting to hold pressure. Then, the pressure is maintained for a predetermined time while maintaining the holding pressure, and the refrigerant is caused to flow through the fluid passages 36 and 36 so that the surface temperature of the mold cavity becomes equal to or lower than the glass transition temperature of the resin material at the end of holding. After the pressure holding is finished, the fixed die 21 and the movable die 22 are kept closed, and the holding time is further maintained for the time required for cooling, although it depends on the thickness of the product.

  When a predetermined cooling time has passed and the molded product (bathtub 1) is cooled to a temperature that does not deform when the molded product (tub 1) is taken out, the movable mold 22 is opened, and the molded product is ejected by protruding pins 38. After taking out the molded product, the medium in the fluid passages 34, 34 is changed to a heat medium, and the temperature of the cavity 29 is raised again so that the surface temperature of the resin 29 is preferably equal to or higher than the glass transition temperature of the resin material. Is closed, and the cycle for taking the next molded product starts. After cooling to a temperature lower than the temperature at which the molded product is taken out, the medium in the fluid passages 34 and 34 is switched from the refrigerant to the heat medium while the molded product is in the cavity 29, and molding is performed in the middle of the temperature increase. You may make it take out goods.

  The bathtub 1 obtained as described above has high accuracy in thickness and outer dimensions and is stable. Compared to general injection molding methods, injection filling of molten resin into the mold cavity is extremely slow and continuous. Therefore, the resin is compensated for volume shrinkage caused by cooling of the molten resin as needed. It is because is filled. For this reason, the volume shrinkage rate is stabilized, and as a result, the product dimensions are stabilized and the thickness variation is reduced. In addition, in the case where the synthetic resin material is continuously flowed into the mold cavity while the screw 12 is rotated in the cylinder 11 and molding is performed, since the resin material supply process and the injection process proceed simultaneously, Compared with the injection molding method, the residence decomposition of the molten resin in the injection cylinder is extremely small, so that a product having higher dimensional stability and high transparency can be obtained.

  On the other hand, when a bathtub product is molded as in the present invention using a general injection molding method, for example, when the average thickness is 10 mm, the total weight per unit is about 25 kg, but 25 kg The injection molding cylinder capable of metering and injecting molten resin of the above capacity is a large-scale molding of 50,000 to 7000 tons class with a cylinder capacity of 30,000 ml or more and a clamping force (actual resin pressure in the projected area of the product). A machine is required. In such a large molding machine, plasticization and metering of the synthetic resin in the cylinder becomes unstable, and defects due to decomposition of the resin such as bubbles, yellowing, and burning frequently occur, resulting in poor appearance. If used, such a problem does not occur because the molten resin is continuously filled simultaneously with the measurement. The fact that the capacity of the molding machine cylinder can be reduced, the clamping force can be reduced, and the ability to make a bathtub with a synthetic resin without backing results in a lower overall cost per bathtub.

  EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated further in detail, this invention is not limited to a following example.

(1) Design of mold and molding apparatus A bathtub-shaped model mold was used. Specifically, the mold has a size that can be used by being attached to a molding apparatus having a clamping force of 450 tons, the cavity is a molded product having a length of 450 mm, a width of 250 mm, and a height of 250 mm. It was designed to be 5 mm. The molding equipment was modified from the ROM of the molding equipment "J450 EL III-890H" manufactured by Nippon Steel Works, so that molten resin can be injected into the mold by rotating the screw.

(2) Molding of synthetic resin bathtub Using the above-described mold and molding apparatus, a methacrylic resin was filled therein to produce a bathtub model molded article. Specifically, methyl methacrylate resin “SUMIPEX MHF” (transparent) manufactured by Sumitomo Chemical Co., Ltd. was used as the resin material, and the resin temperature in the injection cylinder was set to 270 ° C. Further, a heating medium heated to 95 ° C. with a temperature controller was passed through the fluid passage of the mold.

  The movable mold was moved to the fixed mold side to close the mold, and a predetermined amount of molten methyl methacrylate resin that had been weighed in advance was pre-injected into the cavity formed by both at an injection rate of about 50 ml / second. Then, when the tip of the screw reaches the vicinity of the most advanced position, the limiter shifts to the screw rotation operation, and while holding the tip of the screw in the vicinity of the most advanced position, the screw is rotated at 80 rpm and the resin is put into the mold. Injected.

  Next, when the resin is filled in the cavity, the screw is gradually retracted by the resin pressure from the inside of the cavity, and a holding pressure of 40 MPa is applied from the cylinder side at a position lower than a predetermined amount necessary for the next pre-injection, After holding in that state for 40 seconds, the holding pressure was released, and the resin was cooled in the mold for 90 seconds, and the molded product was taken out. As a result, the obtained bathtub molded article had a constant dimensional accuracy, a good appearance, and a small molding distortion.

It is a perspective view which shows the synthetic resin bathtub concerning one Embodiment of this invention. It is a schematic explanatory drawing which shows the shaping | molding apparatus concerning one Embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Synthetic resin bathtub 10 Injection device 11 Injection cylinder 12 Screw 13 Motor 14 Ram mechanism 15 Hopper 16 Heating heater 18 Injection nozzle 20 Mold 21 Fixed type 22 Movable type 23 Heating cylinder 24 Hot tip bushing 25 Hot runner 26 Sprue 29 Cavity 31 Fixed platen 32 Fixed side cavity block 33 Movable side cavity block 34 Fluid passage

Claims (9)

A method of manufacturing a synthetic resin bathtub using a mold for forming a synthetic resin bathtub having a cavity formed of a fixed mold and a movable mold and an injection cylinder,
Synthetic resin is supplied into the injection cylinder, and the synthetic resin is melted while rotating a screw arranged in the injection cylinder. At the same time, the molten synthetic resin is continuously fed into the mold cavity by rotating the screw. A method of manufacturing a synthetic resin bathtub, wherein the filling is performed by flowing into the container.   The molten synthetic resin is continuously flowed into the mold cavity by rotation of the screw to perform filling, and during or after the filling, pressure is applied to the synthetic resin in the cavity from the screw side, The method for producing a synthetic resin bathtub according to claim 1, wherein the synthetic resin is solidified by cooling while maintaining the pressure, and the bathtub is taken out of the mold to obtain a product.   When the temperature of the cavity surface of the mold is the glass transition temperature of the synthetic resin −50 to the glass transition temperature + 20 ° C., the filling of the molten synthetic resin into the cavity is started, and when the filling is completed The temperature of the cavity surface is made to be the glass transition temperature of the synthetic resin + 10 to the glass transition temperature + 30 ° C., and then cooled, and the temperature of the cavity surface is the glass transition temperature of the synthetic resin−80 to the glass transition. The method for producing a synthetic resin bathtub according to claim 1 or 2, wherein the product is taken out when the temperature is -20 ° C.   The method for producing a synthetic resin bathtub according to any one of claims 1 to 3, further comprising a fluid passage for alternately passing a heat medium and a refrigerant in the vicinity of the cavity surface of the mold.   In the vicinity of the cavity surface of the mold, there is a cavity block made of a metal having a higher thermal conductivity than that of the metal constituting the mold body, and the cavity block contains a heat medium and a refrigerant alternately. The manufacturing method of the synthetic resin bathtub as described in any one of Claims 1-4 which has a fluid channel | path for letting it pass to.   The method for producing a synthetic resin bathtub according to claim 5, wherein the cavity block is made of beryllium copper.   The method for producing a synthetic resin bathtub according to any one of claims 1 to 6, wherein the synthetic resin is an acrylic resin.   The method for producing a synthetic resin bathtub according to claim 7, wherein the acrylic resin is a methacrylic resin. The method of manufacturing a synthetic resin bathtub according to any one of claims 1 to 8, wherein the product has a thickness of 5 to 15 mm.

Images