JPH11179772A - Synthetic resin molded product with developing no weld line and molding method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a synthetic resin molded product, in which no weld line develops due to the minglement of front stocks held at optimum molding temperatures at the meeting of the flow fronts of molten stock to be filled in a cavity. SOLUTION: In a synthetic resin molding, in which a joining area is developed by meeting the flow fronts of a molten stock 4 at a molding performed by filling the molten stock 4 in the cavity 3 of molds, the flow fronts developing the joining area of this synthetic resin molding hold optimum molding temperature by heating until their meetings occur. At the meeting of the flow fronts, the flow fronts strike hard, resulting in developing the joining area, at which both the front stocks mingle with each other.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a synthetic resin molded article which does not generate a weld line and a molding method thereof.

[0002]

2. Description of the Related Art In molding a thermoplastic synthetic resin product, as the temperature of a mold is increased, moldability is improved, and a product of high precision and high quality can be obtained. However, on the other hand, the curing of the product takes time and the molding efficiency is reduced. Accordingly, the present inventor has proposed that a high-temperature gas is flowed into a cavity of a mold as a molding means having excellent moldability and a small decrease in molding efficiency, and the surface of the cavity is rapidly heated to an appropriate temperature for molding the raw material. When the temperature is increased, the molten raw material is filled while discharging the high-temperature gas into the cavity, and while the surface of the unfilled portion of the cavity is continuously heated by the high-temperature gas, the method of heating the flow front of the raw material is also invented. Flat 8-24
No. 4271, with high fidelity to the mold, high quality and uniform quality, good gloss, cold slug,
We succeeded in obtaining a product that is less likely to have defects such as weld lines and silver lines.

As described above, when the surface of the mold cavity and the flow front of the raw material are heated by the high-temperature gas, the flow front of the molten raw material can be formed in forming a molded product having a space or a molded product having two or more gates. In the case of a molded product that joins to form a joint, the joining point is maintained at an appropriate temperature for molding, so the condition of the joining part is improved compared to the conventional product in which the temperature at the joining point is lowered, and almost no weld line is observed. It will not be possible. Therefore, there is no problem at all for products that do not require strength or opaque products. However, even if the temperature of the flow tip is maintained at a suitable temperature for molding, simply pressing both ends at a normal flow rate only causes the surface layer of the flow tip to be butt-joined, so that a boundary exists, This part of the border is less strong than the other parts,
In the case of a transparent molded product, this portion tends to be cloudy. For this reason, in a molded article or a transparent molded article in which the same strength is required for the entire molded article, it is strongly desired to realize a seamless joint.

[0004]

The problem to be solved by the present invention is to maintain a suitable temperature for molding until the flowing tip of the molten raw material to be filled into the cavity merges to form a joint where the leading raw material is interlaced. That is not possible.

[0005]

Means for Solving the Problems To solve the above-mentioned problems, a synthetic resin molded article which does not generate a weld line and a molding method according to the present invention are characterized by adopting the following constitution and method. (1) When molding is performed by filling the molten material into the cavity of the mold, the flow ends of the molten material are merged to form a joint, and the joint of the synthetic resin molded product is formed. The flowing tips maintain the proper molding temperature by heating until they merge, and at the time of joining, they violently collide with each other to form a joint where both tip materials are interlaced. (2) A high-temperature gas is caused to flow through the cavity of the mold, and the surface of the cavity and the flowing tip of the molten raw material to be filled are heated so that the flowing tip is maintained at a suitable temperature for molding until the merging. The flow velocity in this section is accelerated so that a sharp discharge of the hot gas causes a violent collision. (3) Counter pressure is applied to the high-temperature gas sent into the mold cavity.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of a synthetic resin molded article according to the present invention which does not generate weld lines and a molding method thereof will be described with reference to the drawings.

In FIGS. 1 to 3, reference numeral 1 denotes ABS, P
This shows an example of a mold suitable for forming a synthetic resin molded product 2 (see FIG. 6) according to the present invention, which does not generate weld lines, using S, PP, PE, and other synthetic resins as raw materials. The mold 1 is divided into a fixed mold 1a and a movable mold 1b. On the other hand, for example, a space forming portion 1c is provided on the movable mold 1b side, and the movable mold 1b is brought into close contact with the fixed mold 1a. When the mold is clamped, a cavity 3 surrounding the space forming portion 1c is formed therein. If the cavity 3 is filled with, for example, an ABS resin melted at a suitable molding temperature as a raw material 4 from a nozzle 5 through a sprue 6 and a gate 7, a molded product 2 similar to the cavity 3 is molded. Same as mold. However, prior to filling the molten raw material 4, a high-temperature gas is circulated in the cavity 3, and the surface of the cavity 3 is rapidly heated in a short time within a few seconds as much as possible. The molten raw material 4 is filled while
Is different from the general mold 1 in that the surface of the unfilled portion is continuously heated by the high-temperature gas from the beginning to the end (from the start to the end of the filling), and the leading end of the molten raw material 4 in contact with the high-temperature gas is also heated by the high-temperature gas. doing. For this reason, the air supply path 8 is communicated with the fixed mold 1a side (movable mold 1b side) of the mold 1 on the opposite side of the sprue 6 of the cavity 3, that is, the portion where the molten raw material 4 is finally filled. A valve body 9 for opening and closing an opening 8 a is provided at a portion of the air supply passage 8 facing the cavity 3, and a pipe 11 to which high-temperature gas is supplied from a high-temperature gas generator 10 is connected to an outer end of the air supply passage 8. And this piping 1
1, a switching valve 12 is provided.

When molding the synthetic resin molded product 2 in which no weld line is generated by the mold 1, the movable mold 1b of the mold 1 is brought close to the fixed mold 1a and the temporary mold clamping is performed so that an exhaust gap g is formed. After that, as shown in FIG. 1, the valve body 9 provided in the air supply passage 8 is opened, and the switching valve 12 provided in the pipe 11 is brought into the air supply state. Then, the high-temperature gas of the high-temperature gas generator 10 is sent to the cavity 3 from the opening 8a through the air supply path 8, and this high-temperature gas is discharged from the gap g between the fixed mold 1a and the movable mold 1b, and passes through the cavity 3 Due to the circulation, the surface temperature of the cavity 3 increases quickly. Therefore, the temperature and flow rate of the high-temperature gas are set so that the surface temperature of the cavity 3 becomes a suitable temperature for molding the raw material within several seconds, the flow is continued, and when the surface of the cavity 3 reaches the proper molding temperature, as shown in FIG. The valve body 9 is closed, the switching valve 12 is stopped to supply air, the supply of high-temperature gas is stopped, and the fixed mold 1a and the movable mold 1b are fully closed so that the exhaust gap g is eliminated.

If the nozzle 5 is separated from the sprue 6 after the mold 1 has been fully tightened in order to heat the sprue 6 with a high-temperature gas, the nozzle 5 is connected to the sprue 6 and the molten raw material 4 is supplied to the nozzle 5. And into the cavity 3 through the sprue 6. Then, the molten raw material 4 fills the cavity 3 from the gate 7 side to the opposite side while discharging the high-temperature gas from the fine gap between the fixed mold 1a and the movable mold 1b. For this reason, the portion of the cavity 3 filled with the molten raw material 4 eliminates the high-temperature gas and has no heat source, and is immediately cooled by the cooling means provided in the mold 1. However, the portion where the raw material is not filled contains the high-temperature gas and continues to heat the surface of the cavity 3, and the temperature decreases with time due to heat conduction to the mold. However, on the other hand, since the high-temperature gas is compressed by the volume reduction of the cavity 3 accompanying the filling of the raw material and the temperature rises, the discharge amount of the high-temperature gas is adjusted to raise the temperature by the compression and the heat conduction to the mold. By equilibrating the temperature drop with the temperature, the temperature of the high-temperature gas existing in the cavity 3 can be kept constant from the start of filling of the raw material to the end of filling. Also, if necessary, adjust the discharge amount so that the temperature rise due to the compression of the high-temperature gas exceeds the temperature decrease due to heat conduction, and set the temperature higher at the end than at the start of material filling. It is also possible.

The high-temperature gas whose temperature has been adjusted as described above,
It keeps heating not only the surface of the cavity 3 but also the flow front of the molten raw material 4 filled in the cavity 3 and keeps this portion at an appropriate molding temperature from the start to the end of filling to maintain good fluidity. At the same time, a temperature suitable for complete welding when the flow tips merge is maintained. Therefore, when the filling of the molten raw material into the cavity 3 reaches 80 to 90% as shown in FIG. 4, the valve body 9 is opened and the switching valve 12 is evacuated as shown in FIG. Is immediately discharged to bring the inside of the cavity 3 to atmospheric pressure. For this reason, the tip of the molten raw material to which the filling pressure is applied is accelerated, and the two flowing tips separated by the space forming part 1c collide violently. Therefore, the raw materials at both ends are mixed by this impact, and if fibers or the like are mixed in the raw materials, these entanglements also occur, so that the raw materials at the front end form a joined portion so as not to generate a boundary, This joint has the same composition as the other parts. Therefore, in the conventional molded product, the weld line 13 unavoidably generated at the junction of the two flow fronts as shown by the chain line in FIG. 5 does not occur in the molded product 2 of the present invention. In addition, since the molded product 2 is fully filled by heating the surface of the cavity 3 and the flow front of the molten raw material 4 to the end of the cavity 3 easily, the fidelity to the mold 1 is improved. It is high in quality, uniform in density, excellent in surface gloss, and can provide a high-precision and high-quality molded product 13 which does not cause defects such as cold slug, silver line, and jetting. The molded article 2 is also effective in shortening the molding cycle because the heating of the cavity by the high-temperature gas is stopped with the filling of the raw material, and the process immediately shifts to cooling by the mold cooling means.

FIG. 5 shows a mold 1 suitable for molding a joint molded product 2 in which a joining portion formed by merging of flow fronts of a molten raw material is formed at two or more places. This mold 1 has a fixed mold 1a and a movable mold 1 similar to the mold 1 shown in FIGS.
b (omitted from the drawing), there is a space forming portion 1 c inside the cavity 3, and two gates 7 are provided on one of the long sides of the cavity 3 and communicate with the sprue 6. Therefore, in the molded article 2 molded by the mold 1, the molten raw material is diverted to one and the other of the space forming portion 1c at the time of molding and merges at two places. 8a is provided with an air supply passage 8 opened and closed by a valve body 9 so that the heating of the flow front by the high-temperature gas and the rapid discharge of the high-temperature gas are performed in both air supply passages 8 in the same manner. When the part where the flow front joins increases to two places due to the molded article 2, the number of the air supply passages 8 is increased accordingly so that the same action is performed at each joint.

When molding a synthetic resin molded article 2 in which no weld line is generated by the mold 1, a temporary mold is formed so as to form an exhaust gap g between the movable mold 1b and the fixed mold 1a as shown in FIG. The valve body 9 provided in the air supply passage 8 is opened, and the switching valve 12 provided in the pipe 11 is brought into the air supply state. Then
Since the high-temperature gas is sent from the generator 10 to the cavity 3 and is discharged from the exhaust gap g and flows through the cavity 3,
Since the surface temperature of the cavity 3 quickly rises to reach the optimum molding temperature, the valve element 9 is closed as shown in FIG.
Then, the supply of the high-temperature gas is stopped with the air supply stopped, and the fixed mold 1a and the movable mold 1b are tightly closed so that the exhaust gap g is eliminated. Then, when the molten raw material 4 is filled into the cavity 3 from the two gates 7, the molten raw material 4 moves one and the other of the cavity 3 divided by the space forming portion 1c toward the center in the longitudinal direction as shown in FIG. It flows and fills the cavity 3. For this reason, the portion of the cavity 3 filled with the molten raw material 4 is free of high-temperature gas, and is immediately cooled by the cooling means provided in the mold 1. However, the portion where the raw material is not filled is heated due to the presence of high-temperature gas, and the heating state is to compensate for the decrease in temperature due to heat conduction of the high-temperature gas to the mold by the heat generation of the gas by gas compression by the charged raw material. , It can be kept constant from the start to the end
It can be set to increase gradually as needed. The heating by the high-temperature gas extends not only to the surface of the cavity 3 but also to the leading edge of the flow of the molten raw material 4 to be filled in the cavity 3, and this portion is kept at an appropriate molding temperature from the start to the end of filling. Then, when the filling of the raw material into the cavity 3 reaches 80 to 90% as shown in FIG.
When the switching element 12 is evacuated by opening the valve body 9 as shown in FIG. 3, the high-temperature gas in the cavity 3 is immediately discharged, and the inside of the cavity 3 is brought to the atmospheric pressure. For this reason, the two sets of flowing tips of the molten raw material to which the filling pressure is applied are accelerated and collide violently. Therefore, the raw materials at both ends are mixed by this impact, and if fibers or the like are mixed in the raw materials, these entanglements also occur. As a result, these joints have the same composition as the other parts. Therefore, even in the case of the molded article 2 requiring a plurality of joints, the weld line 13 inevitably generated as shown by a chain line in FIG. A molded article 2 having the same characteristics as described above is obtained.

In the mold shown in FIGS. 1 to 4, a valve element 9 is provided at an opening 8a of an air supply path 8 for supplying a high-temperature gas into the cavity 3, and when the valve element 9 is opened, the air supply path is opened. 8 and opening 8
The high-temperature gas sent to the cavity 3 is stopped because the high-temperature gas is sent to the cavity 3 by communicating with the a. However, as shown in FIGS. 8 and 9, a member 13 such as a sintered metal, which allows high-temperature gas to pass through the opening 8 a to the cavity 3 of the air supply passage 8 but does not allow the molten raw material 4 to pass through, is installed. In this case, the valve element 9 can be omitted.
The mold 1 shown in FIGS. 8 and 9 is a sprue 6 of the fixed mold 1a.
As shown in FIG. 3, an exhaust passage 14 is provided in a portion close to the above, and a member 13 such as a sintered metal, which allows high-temperature gas to pass through the opening 14 a to the cavity 2 of the exhaust passage 14 but does not allow molten material 4 to pass If mounted, the high-temperature gas can be discharged from the exhaust path 14 and the high-temperature gas can flow through the cavity 3, so that the fixed die 1a and the movable die This eliminates the need to perform a temporary mold clamping operation for forming an exhaust gap g between the first mold 1b and the second mold 1b.

FIGS. 9 and 10 show that when filling the cavity 3 with the molten raw material 4, the discharge of high-temperature gas is suppressed to generate a counter pressure in the cavity 3 against the filling pressure of the molten raw material. 1 suitable for improving formability by acting on the filling material
It shows. The basic configuration of the mold 1 is the same as that shown in FIGS. However, the means for supplying and discharging the hot gas to and from the cavity 3 is different. That is, when a high-temperature gas is supplied to the cavity 3 of the mold 1 and flows therein to rapidly raise the temperature of the surface of the cavity 3, the supply of the high-temperature gas is stopped, and the high-temperature gas is discharged to the cavity 3 accordingly. While filling the molten raw material while
In order to apply a counter pressure to the charged raw material, the amount of discharged high-temperature gas is suppressed so that a pressure suitable for the counter pressure is left in the cavity 3. The high-temperature gas remaining is forcibly discharged, and the cavity 3 is made to have a negative pressure to increase the flow velocity of the molten material 4 at the leading end of the flow, thereby causing a more severe collision. Therefore, the gap between the fixed side 1a and the movable side 1b of the mold 1 is sealed by the sealing member 15, and the high-temperature gas passes through the opening 8a of the air supply passage 8 but does not allow the molten raw material 4 to pass. Is connected to the cavity 3 through a member 13 of
The exhaust port 12a is provided with a relief valve 16 as a counter pressure applying means, and a timer 1
7 is connected to a vacuum tank 19 provided with a valve 18 which is opened and closed by the valve 7. When filling the molten raw material, counter pressure is generated in the cavity 3 by the relief valve 16, and the cavity 3 is forced by the vacuum tank 19 at the end of filling. The pressure is reduced to a negative pressure.

When the synthetic resin molded article 2 is molded by the mold 1, the mold 1 is temporarily clamped so as to form an exhaust gap g, and the switching valve 12 is brought into an air supply state. Flows into the cavity 3 from the generator 10 and the fixed mold 1a
The air is discharged from the exhaust gap g between the mold and the movable mold 1b and flows through the cavity 3. For this reason, since the surface of the cavity 3 is rapidly heated to a temperature suitable for forming the raw material, the switching valve 12 is turned off to stop the supply of the high-temperature gas when the material is heated to the appropriate temperature, and the mold 1 is moved to the main mold. By tightening, the cavity 3 is sealed by the seal member 15. Then, the filling of the molten raw material 4 into the cavity 3 through the nozzle 5 and the sprue 6 is started, and the switching valve 12 is evacuated as shown in FIG. In this exhaust, the filling of the molten raw material 4 into the cavity 3 is 80% or more.
Since the timer 17 closes the valve 18 of the vacuum tank 19 until the pressure reaches 90%, the hot gas in the cavity 3 is exhausted through the relief valve 16. Therefore, if the relief pressure is set to be equal to the required counter pressure, the filling material is filled while receiving the counter pressure, but when the filling amount reaches 80% to 90% or more, the timer 17 activates the valve 18. To open, the hot gas in the cavity 3 is sucked into the vacuum tank 19 and
Negative pressure inside. Therefore, the flow front of the molten raw material 4 is greatly accelerated, and the impact at the time of merging causes a more intense collision than in the case of the mold 1 shown in FIGS. In addition to being promoted by the increase in impact, if fibers etc. are mixed, these entanglements are also promoted and seamless joining is performed, the strength of the joint is comparable to other parts, transparent products No clouding occurs at the joint. Therefore, a molded product that requires an average strength as a whole and a product that requires high transparency can be a molded product that can sufficiently satisfy the requirements. Moreover, in this counter pressure type, since a suitable resistance is given to filling of the molten raw material, the molten synthetic resin is completely pressed to the surface of each part of the cavity 2 to be completely filled to completely fill the cavity 2 and the mold transferability is improved. Good, uniform, dense and glossy products with no defects such as cold slug, silver line and jetting are formed.

Further, in the synthetic resin molded article according to the present invention which does not generate a weld line, when heat-resistant fibers are mixed into the synthetic resin of the raw material, the appropriate temperature for welding is maintained when the flow front of the molten raw material joins, and the pressure is reduced by reducing the pressure. If a collision of the tip is caused by acceleration, the heat-resistant fiber mixed in with the crossing of the tip material causes entanglement, thereby acting to further increase the strength of the welded portion.
Furthermore, when a foaming agent is mixed into the molten raw material, apply a counter pressure to the high-temperature gas, and the blowing agent mixed into the raw material is pressed down by the counter pressure so that it does not come out to the surface of the molded product and foams on the surface. Form a thin skin layer that is dense and glossy without the influence of the agent and has a good appearance with this part being sufficiently porous to concentrate the foaming agent inside and foam this part well. A product excellent in weight reduction, sound insulation, heat insulation, cushioning, etc. can be obtained on the top, and the synthetic resin molded product according to the present invention is a foaming agent, heat-resistant fiber, calcium carbonate powder, a flame retardant, etc. Similarly, a good molded product can be obtained when the characteristic improver is mixed.

[0017]

According to the first aspect of the present invention, (1) the molten material to be filled into the cavity is violently collided with the leading edge of the flow where the molten material joins at an appropriate temperature for molding. Therefore, we have realized molded products that do not generate weld lines that could not be realized despite the demands of the industry for many years, and also for molded products that require average strength as a whole and molded products that require high transparency. It is possible to provide a product that can fully satisfy the requirements. (2) When reinforcing materials such as heat-resistant fibers are mixed in the molten raw material,
These occur when the tip of the flow collides and mixes the raw materials.
This is particularly effective for products whose strength is essential, since they cause entanglement with each other to further enhance welding. (3) Since the high-temperature gas supplied to the cavity heats the surface of the cavity and the tip of the flow of the molten raw material and maintains a proper molding temperature until the completion of molding, the moldability is significantly improved, and the fidelity to the mold is high. It is also possible to obtain a molded article which is dense and uniform, has good gloss, and does not cause any defects such as cold slug, silver line and jetting. Advantageous Effects of Claim 2 (1) Since the heating of the cavity surface, the heat retention of the molten raw material, and the collision at the time of merging of the flow fronts can be reliably performed, a molded product that does not generate a weld line can be easily and stably molded. . (2) If the cavity surface is heated by the high-temperature gas and the flow front of the molten raw material is kept warm, the molten raw material is maintained at an appropriate temperature for molding, so that the formability is improved, the fidelity to the mold is high, and the quality is dense and uniform. In addition, it is possible to easily form a molded article having good gloss and free from various defects such as cold slug, silver line and jetting. (3) Since a high-temperature gas is supplied into the cavity and discharged along with the filling of the molten raw material, when the discharge is suppressed, the gas is compressed, the temperature drop due to heat conduction to the mold is corrected, and the constant temperature can be maintained. The temperature can be increased if necessary. (4) Since the raw material is heated in the cavity to improve the fluidity, the temperature and injection pressure of the filled raw material can be reduced, and the mold clamping pressure can be reduced. (5) The portion of the cavity filled with the raw material has no heat source and can be cooled immediately by the cooling means of the mold, so that the hardening of the molded article is promoted and the molding cycle is also improved. Advantageous Effects of Claim 3 (1) When counter pressure is applied to the molten raw material while suppressing the discharge of high-temperature gas, the pressure difference when the cavity is depressurized by the vacuum tank becomes large, and the acceleration of the raw material flow is increased. Therefore, the collision of the leading raw materials becomes intensified, which promotes the crossing of the raw materials and contributes to the realization of seamless welding. (2) If the discharge of high-temperature gas is suppressed, the counter pressure acts on the raw material in the cavity. Therefore, in the case of non-foamed synthetic resin raw material, the cavity is filled while being pressed against the mold surface by the counter pressure, and the mold transferability is improved. As a result, it is possible to obtain a product which is more dense and uniform in quality, has excellent gloss, and has an effect of preventing cold slug, weld line, silver line, jetting and other defects. (3) In the case of a foamed synthetic resin raw material, when a counter pressure is applied thereto, the foaming agent is pressed down below the surface layer, so that a skin layer as thin and good as possible is formed on the surface and the inside of the foaming agent is Since foaming is promoted by concentration, the product is sufficiently porous, and a product excellent in measurement, heat insulation, sound insulation, cushioning, and the like can be obtained. (4) Even in the case of synthetic resin mixed with glass fiber, calcium carbonate powder, flame retardant, etc., the mixture is pressed down below the surface layer, the surface is a smooth surface that is not affected by the mixture, and the inside is reinforced with the mixture. A product with sufficient flame retardancy and other effects can be obtained.

[Brief description of the drawings]

FIG. 1 is an explanatory view showing a state in which a high-temperature gas is fed into a cavity of a mold for molding a synthetic resin molded product that does not generate a weld line according to the present invention, and the cavity surface is heated.

FIG. 2 is an explanatory view showing a state in which a molten raw material is filled while discharging a high-temperature gas into a cavity of the mold.

FIG. 3 is an explanatory view showing a state in which a high-temperature gas is discharged from a cavity of the mold at the end of filling a molten raw material to depressurize the cavity.

FIG. 4 is an explanatory view showing the state shown in FIG. 3 except for a movable side of a mold.

FIG. 5 is a perspective view showing an example of a synthetic resin molded product according to the present invention that does not generate a weld line.

FIG. 6 is a perspective view showing another example of the same molded article.

FIG. 7 is an explanatory view showing a state in which the cavity is heated by feeding the high-temperature gas in the example shown in FIGS.

FIG. 8 is an explanatory diagram showing a state in which a high-temperature gas is discharged from a cavity of the mold and the pressure is reduced.

FIG. 9 is an explanatory view showing a state in which a high-temperature gas is fed into the cavity to heat the cavity in a mold for applying counter pressure to the molten raw material in the cavity.

FIG. 10 is an explanatory diagram showing a state in which a high-temperature gas is discharged from the cavity of the mold and the pressure is reduced.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Die 1a Fixed mold 1b Movable mold 2 Synthetic resin molded product 3 Cavity 4 Molten raw material 8 Air supply path 10 High temperature gas generator 12 Switching valve 15 Counter pressure applying means 19 Vacuum tank

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[Procedure amendment]

[Submission date] February 23, 1998

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] Brief description of drawings

[Correction method] Change

[Correction contents]

[Brief description of the drawings]

FIG. 1 is an explanatory view showing a state in which a high-temperature gas is fed into a cavity of a mold for molding a synthetic resin molded product that does not generate a weld line according to the present invention, and the cavity surface is heated.

FIG. 2 is an explanatory view showing a state in which a molten raw material is filled while discharging a high-temperature gas into a cavity of the mold.

FIG. 3 is an explanatory view showing a state in which a high-temperature gas is discharged from a cavity of the mold at the end of filling a molten raw material to depressurize the cavity.

FIG. 4 is an explanatory view showing the state shown in FIG. 3 except for a movable side of a mold.

FIG. 5 is an explanatory view showing the state shown in FIG. 3 except for the movable side of another mold.

FIG. 6 is a perspective view showing an example of a synthetic resin molded product according to the present invention which does not generate a weld line.

FIG. 7 is a perspective view showing another example of the molded product.

FIG. 8 is an explanatory view showing a state in which a cavity is heated by feeding a high-temperature gas in an example in which a high-temperature gas feeding portion and a discharging portion of a mold shown in FIGS. 1 to 3 are changed.

FIG. 9 is an explanatory view showing a state in which a high-temperature gas is discharged from the cavity of the mold and the pressure is reduced.

FIG. 10 is an explanatory view showing a state in which a high-temperature gas is fed into the cavity and the cavity is heated in a mold for applying counter pressure to the molten raw material in the cavity.

[Fig. 11] The hot gas is discharged from the cavity of the mold.
FIG. 4 is an explanatory diagram showing a state in which the pressure is reduced.

[Description of Signs] 1 Mold 1a Fixed mold 1b Movable mold 2 Synthetic resin molded product 3 Cavity 4 Molten raw material 8 Air supply path 10 Hot gas generator 12 Switching valve 15 Counter pressure applying means 19 Vacuum tank

Claims (3)

[Claims] 1. A synthetic resin molded product in which a molten material is filled into a cavity of a mold and molded to form a joint when flow points of the molten material join to form a joint. The leading edge of the flow is maintained at an appropriate temperature for molding by heating until it joins, and at the time of joining, a weld line is produced, characterized by violently colliding to form a joint where both tip materials intersect. Not synthetic resin molded products. 2. A high-temperature gas is caused to flow in the cavity of the mold, and the surface of the cavity and the flow tip of the molten material to be filled are heated, so that the flow tip is maintained at a suitable temperature for molding until the flow merges, and the flow tips merge. A method for molding a synthetic resin molded article free of weld lines, characterized in that the flow velocity in this portion is accelerated so as to cause a violent collision due to rapid discharge of high-temperature gas. 3. The molding method for a synthetic resin molded article free of weld lines according to claim 2, wherein a counter pressure is applied to the high-temperature gas fed into the cavity of the mold.