JP2002283424A - Hollow resin injection-molded product and molding method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a hollow resin injection-molded product having a hollow part formed as scheduled and having enhanced appearance having no sink. SOLUTION: A hollow part 13 is linearly formed to the base part 11 of the intermediate rib 7 provided to the back surface of a bamper face 3 in a projected state and a solid projected part 15 is provided to the back surface of the bamper face 3 adjacent to the hollow part 13 on the gas flowing downstream side of a gas injection part 19. The hollow projected part 17 having a communication hollow part 13b communicating with the hollow part 13 is provided to the back surface of the bamper face 3 adjacently in the vicinity of the terminal of the gas injection part 19 on the gas flowing downstream side of the solid projected part 15.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hollow resin injection-molded article having a hollow portion formed therein and a method for molding the same.

[0002]

2. Description of the Related Art As a method for performing gas injection molding of a hollow resin injection molded product, for example, Japanese Patent Application Laid-Open No. 10-291 is disclosed.
There are methods as disclosed in Japanese Patent No. 226 and Patent No. 25554529.

[0003] The hollow resin injection molded product obtained in the former publication is a bumper for an automobile in which two lateral ribs extending parallel to the vehicle width direction are provided on the back surface of the bumper face.
Hollow portions for preventing sink marks are formed at the bases of these lateral ribs. An X-shaped rib is formed between the horizontal ribs for the purpose of increasing the strength, and a hollow portion communicating with the hollow portion of each of the horizontal ribs is also formed in the X-shaped rib. In the case of having such X-shaped ribs, when the pressurized gas forming the hollow portion is injected from the intersection of the X-shaped ribs, the pressurized gas tends to merge from both ends of the X-shaped rib through the respective lateral ribs. In addition, a resin pool is formed at the confluence portion, and the condensed portion becomes thick, and the heat shrinkage difference between the thick portion and the periphery thereof causes sink marks on the surface of the bumper face of the thick portion, resulting in poor appearance. The movable pin provided corresponding to the portion is retracted to form a resin escape portion, and the molten resin at the pressurized gas merging portion is allowed to escape to the resin escape portion and the pressurized gas merges to form a thickness that causes sink marks. We try to eliminate the resin pool of meat.

In the latter publication, after a hollow resin injection molded article is molded, a movable pin provided in a hollow portion forming region is advanced in order to discharge a pressurized gas in the hollow portion to the outside. After forming a hollow resin injection molded product,
By retracting the movable pin, the hollow wall at that location is opened.

[0005]

By the way, in order to form the hollow portion of the hollow resin injection molded product as intended, it is necessary to spread the pressurized gas to every corner of the preset hollow portion forming region. .

However, since the temperature of the molten resin decreases as the pressurized gas moves away from the gas injection portion, that is, as it approaches the end of the molten resin, the resin resistance increases, and the pressurized gas is supplied to a predetermined hollow portion. It becomes difficult to reach every corner of the area. In this case, the hollow portion cannot be formed as intended, and the portion of the hollow portion forming region where the hollow portion is not formed becomes thick, and the surface of the hollow resin injection molded product has sink marks and looks good. Gets worse.
Regarding this, neither of the above two publications takes any measures.

The present invention has been made in view of the foregoing, and an object of the present invention is to provide a hollow resin injection molded article having a hollow portion formed as intended and having an improved appearance without sink marks. is there.

[0008]

In order to achieve the above object, the present invention is characterized in that means for inducing a pressurized gas is provided.

More specifically, the present invention relates to a hollow resin injection molded article having a hollow portion formed by injecting a pressurized gas into a molten resin injected into a cavity of a closed mold. The following solution was taken for the molding method.

That is, claims 1 to 3 relate to the former hollow resin injection-molded product, and the invention according to claim 1 includes a gas injection section on the back surface of the hollow resin injection-molded product. A solid projection adjacent to the hollow portion downstream of the flow, and a hollow projection having a communication hollow portion adjacent to the end of the hollow portion downstream of the gas flow and communicating with the hollow portion protrude from the solid projection. It is characterized by having been done.

According to a second aspect of the present invention, in the first aspect of the present invention, the hollow resin injection-molded article is provided with a rib protruding from a back surface of a molded article body, and the hollow portion is formed at a base of the rib. And a solid projection and a hollow projection are projected from the back surface of the molded article main body.

According to a third aspect of the present invention, in the second aspect, a fitting groove is formed in at least one of the solid projection and the hollow projection, and a rib is fitted in the fitting groove. It is characterized by being matched.

[0013] Claims 4 to 6 relate to the latter method of molding a hollow resin injection-molded article. Among them, the invention according to claim 4 injects a molten resin into a cavity of a closed mold. Then, the first slider disposed so as to be able to advance and retreat to the first slide hole of the molding die downstream of the gas injection portion from the gas flow is retracted, and the molten resin is introduced into the first slide hole to inject the hollow resin. A solid projection is projected from the back surface of the molded product, and then a pressurized gas is injected into the molten resin from the gas injection portion to form a hollow portion, and a gas flow downstream from the first slide hole is formed. A communication hollow that retreats a second slider disposed so as to advance and retreat in the second slide hole of the molding die, introduces the molten resin and pressurized gas into the second slide hole, and communicates with the vicinity of the end of the hollow portion. Hollow with part Characterized by projecting a raised portion on the back surface of the hollow resin injection molded article.

According to a fifth aspect of the present invention, in the invention of the fourth aspect, the hollow resin injection-molded article is formed by projecting a rib on the back surface of the molded article main body, and the hollow portion is formed at the base of the rib. And a solid projection and a hollow projection are provided on the back surface of the molded article main body.

The invention according to claim 6 is the invention according to claim 4 or 5.
In the invention described in (1), a gas guiding projection is provided at the tip of the second slider so as to protrude in the forward direction of the second slider.

With the above arrangement, according to the first and fourth aspects of the present invention, the molten resin is introduced into the first slide hole by the retreat of the first slider to form a solid projection. Thereafter, a pressurized gas is injected into the molten resin to form a hollow portion, and the retreat of the second slider introduces the molten resin and the pressurized gas into the second slide hole to communicate with the hollow portion. A hollow projection having a communicating hollow is formed.

At this time, since the inside of the cavity is depressurized by the retreat of the first and second sliders, the pressurized gas easily enters the molten resin. Further, on the downstream side of the gas flow from the solid projection, the pressurized gas is introduced together with the molten resin into the second slide hole near the end of the hollow downstream of the gas flow.
Accordingly, the pressurized gas spreads to every corner of the preset hollow portion forming region, and the hollow portion is formed as intended, so that a hollow resin injection-molded product with improved appearance without sink marks can be obtained.

According to the second and fifth aspects of the present invention, the hollow portion is a line and the formed portion is a base of a rib protruding from the back surface of the molded article main body, and corresponds to the rib of the molded article main body. By forming the hollow portion in the thick portion, the occurrence of sink marks on the thick portion is eliminated.

According to the third aspect of the present invention, the rib is reinforced by the protrusion by the fitting structure of the protrusion and the rib, and the rigidity of the rib is increased.

According to the sixth aspect of the present invention, the pressurized gas is guided by the gas guiding projections, so that it can more easily enter the molten resin in the second slide hole, and the pressurized gas is set in the predetermined hollow portion. The hollow portion smoothly spreads to every corner of the formation region, and is reliably formed as intended.

[0021]

Embodiments of the present invention will be described below with reference to the drawings.

FIGS. 1 to 4 show an automobile resin rear bumper 1 as an example of a hollow resin injection-molded product according to an embodiment of the present invention. What can be applied. The rear bumper 1 includes a bumper face 3 as a molded product main body having a substantially U-shaped vertical cross section, and the rear surface of the upper end edge of the bumper face 3 has a vehicle width over substantially the entire width except for both ends in the vehicle width direction. The upper ribs 5 extending in the vehicle direction are integrally protruded, and the intermediate ribs 7 extending in the vehicle width direction over substantially the entire surface except both ends in the vehicle width direction are also provided on the rear surface of the bumper face 3 in the middle in the vertical direction. It protrudes integrally and in parallel with the upper rib 5. The intermediate rib 7 protrudes longer than the upper rib 5 (see the shape of the cavity 31 of the molding die 25 in FIG. 5. In the figure, 31b is an upper rib cavity portion forming the upper rib 5, and 31d is an intermediate rib. 7 is an intermediate rib cavity portion.) Further, mounting holes 9a for mounting the rear bumper 1 to a vehicle body panel (not shown) are formed in upper end edges of both ends of the bumper face 3 in the vehicle width direction.
Each of the mounting pieces 9 has two pieces.

The base portion 11 of the intermediate rib 7 which is continuous with the back surface of the bumper face 3 is bulged out from other portions, and a hollow portion 13 is formed in a linear shape inside the base portion 11 so that the hollow portion 13 is formed. The surface of the bumper face 3 having a large thickness due to the presence of the intermediate rib 7 prevents sink marks due to a difference in heat shrinkage.

On the back surface of the bumper face 3, a pin-shaped solid projection 15 is integrally provided so as to correspond to both ends of the intermediate rib 7 in the vehicle width direction, and outwardly in the vehicle width direction. In the same manner, the pin-shaped hollow projections 17 are integrally provided so as to correspond to both ends in the vehicle width direction of the intermediate rib 7. Is also protruding. A gas injection part 19 having a gas injection port 19a corresponding to a gas injection part (not shown) of the molding die 25 is formed in the middle of the intermediate rib 7 in the vehicle width direction. (Not shown) to the gas injection portion of the molding die 25 (the gas injection portion 1 of the rear bumper 1).
The cavity 13 is formed by injecting into the molten resin in the cavity 31 through the gas injection port 19a). That is, the solid projection 15 is formed by the gas injection portion 19.
The hollow projection 17 is adjacent to the hollow portion 13 further downstream of the gas flow, and the hollow projection 17 is adjacent to the end of the hollow portion 13 downstream of the solid projection 15 downstream of the gas flow. The gas injection portion 19 of the rear bumper 1 is a trace of the gas injection portion remaining when the pressurized gas is injected into the molten resin from the gas injection portion of the molding die 25. Hereinafter, both are referred to as the same. . The intermediate rib 7 is provided between the gas injection portion 19 and the solid projection 15.
, And a narrow rib 7b between the solid projection 15 and the hollow projection 17. The wide rib 7a and the narrow rib 7b are interposed through the solid projection 15. Connected. However, since the wide ribs 7a and the narrow ribs 7b are formed one step earlier than the solid protrusions 15 and the hollow protrusions 17 and cooling is progressing, the wide ribs 7a and the narrow ribs 7b and the solid protrusions 15a are formed. And the hollow projections 17 are not completely melted and integrated, but in particular, their respective tip sides are in contact with each other.

At the time of forming the hollow portion 13, the pressurized gas slightly enters the molten resin in a first slide hole 27 b of the molding die 25 at the base end of the solid projection 15. As a result, the hollow recess 13a is formed shallow (FIG. 1).
1).

On the other hand, a hole 17a formed by a gas guiding projection 45a of the second slider 45, which will be described later, is formed at the tip of the hollow projection 17, and a base end of the hollow projection 17 is formed at the base end. The communicating hollow portion 13b communicating with the hollow portion 13 is formed at a depth substantially equal to the projecting dimension of the narrow rib 7b.

The rear bumper 1 configured as described above is
Injection molding is performed using a molding device 23 as shown in FIG. The molding device 23 includes a molding die 25 including a fixed die 27 and a movable die 29.
With the mold closed, a cavity 31 is formed therebetween. The cavity 31 includes a bumper face cavity 31a that forms the bumper face 3 of the rear bumper 1, an upper rib cavity 31b that forms the upper rib 5, and a wide rib cavity 31c that forms the wide rib 7a (see FIG. 7). ) And a narrow rib cavity portion 31d forming the narrow rib 7b.

An injection nozzle 35 of an injection molding machine is connected to the back side of the end of the movable mold 29.
A needle valve 33 is arranged to be able to move forward and backward. On the other hand, on the rear side of the end of the fixed mold 27, a runner valve 37 is disposed with its rod-shaped valve body 37a inserted into the through hole 27a of the fixed mold 27 so as to be able to advance and retreat. The valve body 37a is connected to the injection nozzle 35 and the cavity 31.
The front end faces a resin supply path 39 that communicates with the resin supply path 39. The resin supply path 39 is provided between the injection nozzle 35 and the cavity 3.
Sprue 39a, runner 39b arranged side by side on one side
And the gate 39c, and the sprue 39a
Are opened and closed by the reciprocating operation of the needle valve 33 of the injection nozzle 35, and the runner 39b of the resin supply path 39 is opened and closed by the reciprocating operation of the valve body 37a of the runner valve 37. Then, as shown in FIG. 5, the needle valve 33 is retracted in a state where the mold 25 is closed and the valve body 37a of the runner valve 37 is retracted to open the runner 39b of the resin supply path 39. Open the sprue 39a and set the injection nozzle 35
Is injected into the cavity 31 through the resin supply path 39, and pressurized gas is injected into the molten resin to form the rear bumper 1 in which the hollow portion 13 is formed. . Cavity 3 of the injected molten resin
Although not shown, the injection point of the pressurized gas into the first bumper 1 is on the upper end side of the bumper face 3 facing the gas injection portion 19 in the middle of the rear bumper 1 in the vehicle width direction in FIG.

As shown in FIG. 7, the gas injection portion of the molding die 25, that is, the fixed die 27 downstream of the gas injection portion 19 of the rear bumper 1 has a first slide hole 27b.
Are formed through the wide rib cavity portion 31c and the narrow rib cavity portion 31d of the cavity 31, and the first
A pin-shaped first slider 41 for forming the solid projection 15 of the rear bumper 1 is arranged in the slide hole 27 b so as to be able to advance and retreat by the contraction operation of the first hydraulic cylinder 43.

A second slide hole 27c is formed in the fixed die 27 downstream of the first slide hole 27b in the gas flow through the narrow rib cavity portion 31d of the cavity 31, and the second slide hole 27c is formed in the second slide hole 27c. , The rear bumper 1
A pin-shaped second slider 45 for forming the hollow projection 17 is arranged so as to be able to advance and retreat by the expansion and contraction operation of the second hydraulic cylinder 47. At the tip of the second slider 45, a gas guiding projection 45a is provided.
5 are provided coaxially in the forward and backward directions.

Next, the molding apparatus 23 constructed as described above
Of molding rear bumper 1 using
This will be described with reference to FIG.

(1) The molding die 25 is closed. In this state, both the first slider 41 and the second slider 45 have been advanced to a position closer to the bumper face cavity 31a in the cavity 31 by the extension operation of the first hydraulic cylinder 43 and the second hydraulic cylinder 47 (FIG. 7). reference). Further, the valve body 37a of the runner valve 37 is retracted to open the runner 39b of the resin supply path 39 (see FIG. 5).

(2) The molten resin is injected into the cavity 31 of the closed mold 25 from the injection nozzle 35 through the resin supply path 39 (see FIG. 8), and the inside of the cavity 31 is maintained at a predetermined pressure. As a result, the cavity 31 is entirely filled with the molten resin.

(3) When the above-mentioned pressure-holding step of the molten resin in the cavity 31 is completed, the cooling of the mold 25 is started,
The valve body 37a of the runner valve 37 is advanced to close the runner 39b of the resin supply path 39. At about the same time, the first slider 41 is retracted by the contraction operation of the first hydraulic cylinder 43 (see FIG. 9). Thereby, the first
The molten resin is introduced into the slide hole 27b, and a solid projection 15 projects from the rear surface of the bumper face 3 of the rear bumper 1.

(4) Pressurized gas is injected into the molten resin from the gas injection portion of the molding die 25, that is, the gas injection portion 19 of the rear bumper 1, and the hollow portion 13 is linearly formed on the base 11 of the intermediate rib 7. At the same time, the second slider 45 downstream of the first slider 41 in the gas flow is retracted by the contraction operation of the second hydraulic cylinder 47 (see FIG. 10). As a result, the molten resin and the pressurized gas are introduced into the second slide hole 27c, and the hollow protrusion 17 having the communication hollow portion 13b communicating with the vicinity of the end of the hollow portion 13 is formed on the rear surface of the bumper face 3 of the rear bumper 1. It protrudes (see FIG. 11). The communication hollow portion 13b is formed at substantially the same depth as the projecting dimension of the narrow rib 7b of the intermediate rib 7. This is because the pressurized gas is introduced into the second slide hole 27c because it goes to the end of the hollow portion forming region and has no further destination. In contrast, the solid projection 15
The reason why the recess 13a is formed shallow at the base end is that the pressurized gas passes through the first slide hole 27b and flows into the second slide hole 27c.

(5) After the cooling step of the rear bumper 1 is completed, the molding die 25 is opened, the molded rear bumper 1 is released, and the resin solidified in the resin supply passage 39 corresponds to the gate 39c. Remove from the part.

The rear bumper 1 thus formed
As described above, the intermediate rib 7 includes the wide rib 7a between the gas injection portion 19 and the solid protrusion 15 and the narrow rib 7b between the solid protrusion 15 and the hollow protrusion 17 as described above. The wide ribs 7a and the narrow ribs 7b are non-integrally connected via solid projections 15. This is because the wide ribs 7a and the narrow ribs 7b are formed one step earlier than the solid protrusions 15 and the hollow protrusions 17 and cooling proceeds, and therefore the wide ribs 7a and the narrow ribs 7b and the solid protrusions 15a are formed. And the hollow projections 17 are not completely melted and integrated, and particularly, the respective tip ends are in contact with each other.

As described above, the first and second sliders 4
Since the inside of the cavity 31 is depressurized by the retreat of 1, 45, the pressurized gas can easily enter the molten resin. At this time, since the first and second sliders 41 and 45 are retracted with the runner valve 37 closed, the pressure in the cavity 31 can be further reduced, and the pressurized gas is introduced into the molten resin. Can be promoted. Further, on the downstream side of the gas flow from the solid projection 15, the pressurized gas is introduced together with the molten resin into the first slide hole 27b near the end of the hollow portion 13 downstream of the gas flow. A rear bumper 1 which can be extended to every corner of a preset hollow portion forming area, has a hollow portion formed as desired, and has an improved appearance without sink marks on the surface of the bumper face 3 corresponding to the intermediate rib 7. Can be obtained.

Further, since the pressurized gas is guided by the gas guiding projections 45a to make it easier to enter the molten resin in the second slide hole 27c, the pressurized gas is formed into a predetermined hollow portion. The hollow portion 13 can be reliably formed as intended by facilitating smooth distribution to every corner of the region.

FIGS. 12 and 13 show modifications of the molding die 25 in which the shapes of the first and second sliders 41 and 45 of the molding die 25 are different from those of the above-described embodiment. FIG.
Rib, solid projection 1 of rear bumper 1
It is sectional drawing of 5 and the hollow projection part 17. In this example, the first
Two long grooves 41a are formed on both sides on the tip side of the slider 41 so as to extend in the axial direction corresponding to the projecting dimension of the intermediate rib 7, and one long groove 45b is formed on one side on the tip side of the second slider 45 in the axial direction. (See FIGS. 12 and 13).

The rear bumper 1 thus formed is
In the portion of the solid projection 15 except for the portion protruding from the intermediate rib 7, the long groove 41a of the first slider 41 fits the fitting groove 15
a are formed on both sides, and the intermediate rib 7
Wide rib 7a and narrow rib 7b are fitted. The second slider 4 is provided on a portion of the hollow projection portion 17 excluding the portion projecting from the intermediate rib 7 and the gas guiding projection 45a.
The fitting groove 17b is formed on one side by the five long grooves 45b, and the narrow rib 7b of the intermediate rib 7 is fitted into the fitting groove 17b. The solid projection 15 and the wide rib 7
a and the fitting structure with the narrow rib 7b, the hollow projection 17
The intermediate ribs 7 are reinforced by the solid projections 15 and the hollow projections 17 against the load applied in the vertical direction of the rear bumper 1 by the fitting structure of the intermediate ribs 7 and the narrow ribs 7b. Can be increased.

[0042]

As described above, according to the present invention, the molten resin is filled in the first slide hole by retreating the first slider from the solid projection adjacent to the hollow portion downstream of the gas injection portion from the gas flow. By being introduced, the hollow protrusion projecting from the back surface of the hollow resin injection-molded product and having a communicating hollow portion communicating with the hollow portion is moved to the second position by retreating the second slider.
The molten resin and the pressurized gas were introduced into the slide holes to protrude adjacent to the vicinity of the end of the gas injection section downstream of the solid projections in the gas flow. Therefore, the pressurized gas can be spread to all corners of the preset hollow portion forming region in a state where the inside of the cavity is depressurized by the retreat of the first and second sliders, and the hollow portion is formed as intended. Thus, it is possible to obtain a hollow resin injection-molded article having an improved appearance without sink marks.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing a solid projection and a hollow projection on the right side in the vehicle width direction of a rear bumper.

FIG. 2 is a cross-sectional view taken along line AA of FIG.

FIG. 3 is a front view showing a right half of a rear bumper in a vehicle width direction.

FIG. 4 is a rear view showing the rear bumper excluding both ends in the vehicle width direction.

FIG. 5 is a longitudinal sectional view of a molding die.

FIG. 6 is a timing chart showing a molding procedure.

FIG. 7 is a longitudinal sectional view showing the molding die before injection of the molten resin.

FIG. 8 is a longitudinal sectional view showing the molding die in a state after the molten resin has been injected.

FIG. 9 is a longitudinal sectional view showing the molding die in a state where the first slider is retracted.

FIG. 10 is a longitudinal sectional view showing the molding die in a state where the second slider is retracted.

FIG. 11 is a longitudinal sectional view showing a molding die in a state where a rear bumper having a hollow portion and a communication hollow portion is molded.

FIG. 12 is a diagram corresponding to FIG. 7, showing a modification of the first and second sliders.

13A is a cross-sectional view taken along line BB of FIG.
FIG. 13B is a sectional view taken along line CC in FIG. 12.

14A is a cross-sectional view of an intermediate rib and a hollow portion corresponding to line BB of FIG. 12 of a modification, and FIG.
It is sectional drawing of the intermediate rib and hollow protrusion part corresponding to CC line 2 of FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Rear bumper (hollow resin injection molded product) 3 Bumper face (molded product main body) 7 Rib 11 Base 13 Hollow portion 13b Communication hollow portion 15 Solid projection 15a Fitting groove 17 Hollow projection 17b Fitting groove 19 Gas injection portion 25 Mold 27b First slide hole 27c Second slide hole 31 Cavity 41 First slider 45 Second slider 45a Gas projection

Claims (6)

[Claims] 1. A hollow resin injection molded article having a hollow portion formed by injecting a pressurized gas into a molten resin injected into a cavity of a closed mold, wherein the hollow resin injection molding is performed. On the back side of the molded article, a solid projection adjacent to the hollow portion downstream of the gas flow from the gas injection portion, and adjacent to the end of the hollow portion downstream of the gas flow downstream of the solid projection portion and communicating with the hollow portion. A hollow resin injection-molded article characterized in that a hollow projection having a communicating hollow portion is provided so as to project therefrom. 2. The hollow resin injection-molded article according to claim 1, wherein the hollow resin injection-molded article has a rib protruding from a back surface of a molded article main body, and the hollow portion has a wire inside a base of the rib. A hollow resin injection-molded article formed in a strip, wherein the solid projection and the hollow projection are projected from a back surface of the molded article body. 3. The hollow resin injection-molded article according to claim 2, wherein a fitting groove is formed in at least one of the solid projection and the hollow projection, and a rib is fitted in the fitting groove. A hollow resin injection-molded product. 4. A hollow resin injection-molded product having a hollow portion formed by injecting a pressurized gas from a gas injection portion of the mold into a molten resin injected into a cavity of the closed mold. A method of molding a hollow resin injection molded article, comprising: injecting a molten resin into a cavity of a closed mold, and then a first slide hole of the mold at a gas flow downstream from the gas injection section. The molten resin is introduced into the first slide hole by retreating a first slider disposed so as to be able to advance and retreat, and a solid projection is projected from the back surface of the hollow resin injection molded product. A pressurized gas is injected into the molten resin from above to form a hollow portion, and a second slider disposed so as to be able to advance and retreat to a second slide hole of the molding die downstream of the first slide hole in gas flow is retracted. Let's go to the second slide A hollow projection having a communicating hollow portion communicating with the vicinity of the end of the hollow portion by introducing the molten resin and the pressurized gas into the hole and projecting from the back surface of the hollow resin injection molded product; Molding method of molded article. 5. The method for molding a hollow resin injection molded product according to claim 4, wherein the hollow resin injection molded product has a rib protruding from a back surface of a molded product main body, and the hollow portion has a base portion of the rib. Wherein the solid projections and the hollow projections are provided on the back surface of the molded article main body. 6. The method of molding a hollow resin injection-molded product according to claim 4, wherein a gas guiding projection is provided at a tip of the second slider in a forward direction of the second slider. A method of molding a hollow resin injection molded product.