JP2011245298A - Core-back molding die for game board made of resin - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a core-back molding die that can mold a game board made of resin, excelling in moldability, nailing property, nail holding property, dimensional stability, cutting property, etc.SOLUTION: A core-back injection molding method which is a method for molding the game board by resin using the core-back molding die formed with air vents for ejecting air in a cavity, at all of four sides of an anti-bottom part on the fixed die Mside of the cavity facing a bottom part on the movable die Mside of the cavity formed by the core-back molding die, includes injection-filling a molten resin material K containing a foaming agent, into the cavity with no clearance and then retreating the movable die Mconstituting the core-back molding die. Using this core-back injection molding method, a void part is formed in a portion that faces the bottom part of the cavity to increase the foaming degree of the resin by the presence of the void part, and gas generated in foaming is ejected from the air vents to mold the game board made of resin with a plate thickness corresponding to the thickness of a molding space after the retreat of the movable die M.

Description

  The present invention relates to a core back mold for molding a resin game board constituting a gaming machine to which a game nail is pierced or an accessory is attached, and more specifically, excellent moldability, nailing performance, The present invention relates to a core back mold that can mold a resin game board having nail retention, dimensional stability, machinability and the like. In this specification, the term “resin veneer” is used, but the “resin veneer” means a “veneer substitute” in which a wooden veneer is replaced with a resin, Synonymous with “game board”.

  The gaming board of the gaming machine has a substantially rectangular shape and is provided with a large opening for placing a center accessory in the center, and another accessory is placed below the large opening. Alternatively, a plurality of small openings are formed to form an out opening. In the game board, in addition to a plurality of functions mainly including a center character in combination with the opening, another small character is attached by screwing, and the characters in the game board are A lot of game nails are pierced in the part other than the arrangement.

  As a conventional game board, a veneer board is used, and as the veneer board, a beech plywood that is harder than a lauan plywood and has a high nail pulling strength is used frequently. In order to be able to be finally built into the frame of the gaming machine by hitting a nail, it goes through the following steps, and since it has significance in the comparison of the effects of the present invention and the prior art, it is easy Explained. In the first step, a cell, which is a thin resin plate, is attached to the surface of the plywood plate, and in the second step after this cell is attached, a reference pin hole serving as a reference for the position of the objects on the plywood plate and the plywood plate. A plurality of rail nail holes, which are pilot holes for fixing the rail, are respectively opened. In the third step, the above-mentioned accessories are arranged, or a plurality of holes serving as out ports are opened using a punch called a router. In the fourth step, a large number of game nails are hit against the plywood board, an accessory is arranged at a set position of the game board and fixed by screw tightening, or a launch rail is fixed using a rail nail.

  On the other hand, wood plywood uses natural wood, so in the gaming machine manufacturing industry, not only has the material cost increased due to depletion of wood resources, but also the use of gaming machines over the last few years. There has also been a problem that the cost of disposal of wooden plywood later increased, and there is a need for the development of game boards using alternative materials other than wood.

  The elements required as substitutes for wooden plywood are as follows. As the accuracy of the game board which is the most important element, there are nailability related to game nail driving, holding power of the game nail after driving, dimensional stability as a game board against thermal change and aging, etc. It is required to be equivalent to or better than wooden plywood. Further, from the viewpoint of resource reuse required in various fields in recent years, it is also required that reusability (recyclability) is easy. In addition, many parts manufacturers that make up gaming machines have equipment for manufacturing wooden plywood boards, and it is possible to process substitute materials using the manufacturing equipment. Required from the standpoint of reducing manufacturing costs.

  Resin has attracted attention as an alternative to wooden plywood, and Patent Document 1 discloses a resin game board using an injection molding technique called “counter pressure method”. This “counter pressure method” is an injection molding method in which a gas pressure that opposes resin foaming is applied to a cavity (molding space) of a mold, and a molten resin containing a foaming agent is injected into the cavity. In this molding technique, the molded product is cured while the foaming gas is ejected on the surface of the molded product, thereby preventing the surface accuracy of the molded product from being deteriorated and increasing the surface accuracy of the molded product. In Patent Document 1, a game board is molded by the above-described “counter pressure method” to prevent surface defects such as surface sinks and surface roughness, as in a general molded product.

  In the resin game board of Patent Document 1, the hardness of the unfoamed part molded on the surface layer part by applying a gas pressure to the surface layer part of the molding resin raw material containing the foaming agent injected into the mold. To increase the holding power of the game nail against the game board by making the tip side of the game nail driven from the front side of the resin plate reach the unfoamed portion with high hardness on the back side. It is a summary. For this reason, it is indispensable to make the length of the game nail longer than necessary, and it is difficult to make the thickness of the unfoamed portion uniform over the entire surface. It is difficult to keep the holding force constant.

  In addition to the game nails, the members fixed to the game board include an accessory. The accessory is fixed using a screw, and the game board formed by the above-described “counter pressure method”. In order to increase the fixing force of the screw, as with the fixing nail, in order to screw the screw so that it reaches the back side of the game board, it is necessary to lengthen the screw length and rotate the screw for fixing. The number increases, the work time becomes long, and it is difficult to deal with reality.

  However, including the above-mentioned “counter pressure method”, when a molten resin containing a foaming agent is injected into a mold and cured as it is, a portion close to the inner peripheral surface of the mold (injection molding) From the viewpoint of the product, since the entire surface layer part) is not sufficiently foamed, the hardness of the surface layer part is larger than that of the central part where foaming is sufficiently performed, but bubbles remain inside. The so-called “nest” is generated. Regarding the “counter pressure method”, the occurrence of “sink” on the molding surface can be prevented, but the occurrence of “nest” on the surface layer cannot be prevented. Therefore, even if the hardness of the surface layer part where the unfoamed part remains is high, when the game nail accidentally reaches the internal bubble part when hitting the game nail, the holding force of the game nail is Since this situation is not sufficient and such a situation occurs at a certain frequency, a veneer board cannot be substituted for a game board molded by a normal injection molding method including the “counter pressure method”.

  In addition, the present applicant made an injection molding of a molten resin containing a foaming agent by the following method, but a resin game board satisfying various physical properties could not be obtained. That is, about (2/3) of the molten resin is injected and injected with respect to the capacity of the mold cavity, and the molten resin material is foamed with the remaining space (about 1/3) as the foaming space. A molded product was obtained. However, in this molding method, sufficient injection pressure does not act on the entire molten resin injected into the cavity, so that even in the molded product after foaming, many voids are generated in the surface layer part, particularly at the four corners. As a result, it was found that the necessary holding power of the game nail could not be obtained.

JP 2006-94879 A

  In the present invention, a molten resin containing a foaming agent is injection-molded by a “core back method” to form a resin game board excellent in moldability, nailing performance, nail retention, dimensional stability, machinability, etc. The goal is to provide a core back mold that has been made possible.

  The invention according to claim 1 for solving the above-described problem is a movable mold in which a cavity is formed by fitting a cavity forming convex portion of the stationary mold to a stationary mold having a cavity forming convex portion and the cavity forming portion. After the molten resin raw material containing a foaming agent is injected and filled in the cavity without gaps, the movable mold is moved backward with respect to the fixed mold, and the movable mold side of the cavity is moved to the movable mold side. A core back used for forming a rectangular thick plate-like resin game board by a core back injection molding method in which a gap is formed in a portion facing the bottom and the molten resin is foamed by the presence of the gap. Each of the four sides of the bottom part which is the movable mold side of the cavity formed by the fixed mold and the movable mold, and the opposite bottom part of the cavity facing the fixed mold side. All Air vents in the bitty are possible, but air vents on the bottom side and the bottom side that prevent the molten resin from entering are formed, and each air vent is inside the movable mold or the movable mold. The gas vents and the air vents are connected to the outside of the mold through a plurality of air vent holes formed in the close contact portion between the mold and the stationary mold, and the gas generated at the time of foam molding of the molten resin material. A game board having a thickness corresponding to the depth of the cavity after the movable mold is retracted is formed by discharging from the hole.

  According to the first aspect of the present invention, when the molten resin containing the foaming agent is injected and filled in the initial cavity formed by the fixed and movable molds, the air in the initial cavity is Since air is effectively discharged from the air vents formed on the four sides on the movable mold side, which is the bottom of the cavity, and the air vent holes connected to the air vents, air is entrained on the bottom side of the initial cavity. Instead, if the molten resin is filled to every corner and left as it is without applying pressure, the molten resin tends to expand due to the action of the foaming agent. Since air vents are formed on each of the four sides of the bottom part of the cavity formed by the mold, which is the movable mold side, and the bottom part of the cavity opposite to the fixed mold side, the air in the cavity is formed. As described above, the gas generated by foaming of the foaming agent is discharged out of the cavity through the air vents and the air vent holes. Since the volume of the molten resin in the cavity tends to increase due to the action of the foaming agent, if the movable die is retracted (core back) in accordance with this and the volume of the cavity is increased, the volume is finally expanded. In the cavity, the foaming agent is easily foamed, and the air in the final cavity and the gas generated at the time of foaming are the air vents and the air vents formed on the four sides of the bottom and the bottom of the final cavity. In order to be effectively discharged from the air vent hole to the outside of the molding die, the molten resin is filled into every corner of the expanded final cavity and foam-molded. In this case, the molten resin in the surface layer portion close to the inner wall surface of the final cavity is in contact with the inner wall surface, so that the foaming is limited in order to start curing earlier than the molten resin in the central portion, and the foaming ratio becomes lower. Therefore, although an unfoamed portion exists, the molten resin in the central portion foams at a higher rate than the surface layer portion because there are few portions that suppress foaming. As described above, even when the movable mold is core-backed, the air in the final cavity and the gas generated by foaming of the foaming agent are passed through the air vents and the air vent holes from the inside of the final cavity to the outside of the mold. Therefore, the ratio of the air entrained in the foamed resin game board or the remaining gas is remarkably reduced, which contributes to increasing the holding power of the game nail.

  According to a second aspect of the present invention, in the first aspect of the present invention, an air vent forming frame member is fitted into each inner side surface of the cavity forming portion formed in the movable mold to form a cavity forming space. Each air vent is formed by notching each corner portion on the inner surface side of each air vent forming frame member into a stepped shape.

  According to the second aspect of the present invention, the air vent formed on each of the four sides of the bottom portion of the cavity formed in the mold that is on the movable mold side and the opposite bottom portion facing the bottom portion is the cavity of the movable mold. Since each air vent forming frame member fitted to each inner side surface of the forming portion is formed by notching each corner portion on the inner surface side in a stepped shape, each air vent can be easily formed, and the air vent opening The width and depth can be easily formed as designed.

  The invention of claim 3 is characterized in that, in the invention of claim 1 or 2, each of the air vents is formed continuously over the entire circumference of each of the four sides.

  According to invention of Claim 3, since it forms continuously over the perimeter of each bottom part of the cavity of a shaping | molding die, and each anti-bottom part, it generate | occur | produces at the time of the air in the said cavity, and foaming Gas discharge is further ensured, and it becomes possible to mold a high-quality foamed resin molded product (resin game board) without air entrainment. Further, there is no restriction on the formation position of the air vent hole arranged so as to communicate with each air vent.

  According to a fourth aspect of the present invention, in the second or third aspect of the present invention, the air vent holes except for the external communication air vent holes that communicate directly with the outside of the molding die are the air vent forming frame members. A groove communicating with each air vent is formed on the outer side surface and both opposing side surfaces, and the outer communication air vent hole is formed on a contact surface between the fixed mold and the movable mold.

  According to the fourth aspect of the present invention, the remaining air vent holes excluding the external air vent holes are formed by the grooves formed on the outer side surface and the opposite side surfaces of the air vent forming frame member so as to communicate with the air vent. Therefore, it is easy to form an air vent hole provided inside the movable mold.

  According to a fifth aspect of the present invention, in any one of the first to fourth aspects of the present invention, in each of the four corners of the cavity in the movable mold or in the contact portion between the movable mold and the fixed mold. Each of the corresponding portions is characterized in that an air vent hole is formed.

  According to the invention of claim 5, in the “core back type” injection molding, the molten resin containing the foaming agent is injected into the cavity and filled, and at the time of foam molding of the molten resin. In both of the above, the air in the cavity and the gas generated by foaming of the foaming agent are likely to be collected in each of the four corners of the cavity. Inside air and foaming gas are surely discharged. As a result, air or foaming gas is caught in the portion that becomes the corner of the resin game board to be molded, and the holding power of the game nail is reduced, and further, the air or It is possible to prevent the formation of a defective resin game board in which the foaming gas remains and the corner portion is partially missing, thereby increasing the molding yield.

  According to a sixth aspect of the present invention, in the invention according to any one of the first to fifth aspects, an insert piece mold for forming an accessory attachment hole is disposed in a cavity formed by the fixed mold and the movable mold. It is characterized by that.

  According to the sixth aspect of the present invention, by providing a top die in the cavity, it is possible to form a space for placing an accessory or the like on the game board to be formed, and to empty in a later process. Cutting processing (router processing) is not required for forming the place.

  According to the present invention, each air vent is formed on each of the four sides of the bottom part which is the movable mold side of the cavity formed by the mold and the opposite bottom part of the cavity facing the fixed mold side of the cavity. Therefore, the air in the cavity and the gas generated by the foaming of the foaming agent are discharged out of the cavity through the air vents and the air vent holes communicating with the air vents. In order to increase the volume of the molten resin, if the volume of the cavity is increased by retracting the movable mold in accordance with this (core back), the foaming agent easily foams in the cavity with the increased volume. Therefore, in the enlarged cavity, the molten resin is filled to every corner of the cavity and foamed. For this reason, unfoamed portions exist in the front and back surface portions of the resin game board to be molded, but no air is trapped inside or no gas remains. As a result, the resin game board molded by the core back mold of the present invention has a high game nail holding force.

It is typical sectional drawing (WW sectional view taken on the line of FIG. 5) of the core back shaping | molding die M used for shaping | molding of the resin-made game boards P based on this invention. (A), (b) is the enlarged view of the part shown by code | symbol "D" and "E" of FIG. 1, respectively. It is the XX line partial expanded sectional view of FIG. It is the YY line | wire partial expanded sectional view of FIG. FIG. 2 is a partial enlarged cross-sectional view taken along line ZZ in FIG. (A) to (c) show the state in which the molten resin raw material K is injected and filled into the initial cavity C ₁ of the core back mold M, and the movable mold M ₂ is retracted immediately after the injection and filling. FIG. 3 is a schematic cross-sectional view of a state in which a final cavity C ₂ having increased is formed, and a state in which the volume of a molten resin raw material K is increased by foaming to fill the final cavity C ₂ after the increase. 1 is a perspective view of a resin game board P. FIG. “AE850S27” (hereinafter referred to as “AE850”), “AE321S27” (hereinafter referred to as “AE321”), and “AE191S27” of Stylac TM-ABS manufactured by Asahi Kasei Chemicals Corporation, which are three types of ABS resin raw materials. (Hereinafter abbreviated as “AE191”) and the coefficient of linear expansion. It is a figure which shows the various characteristics of "AE850", "AE321", and "AE191" which are three types of ABS resin raw materials. It is a figure which shows processability evaluation with respect to each item of "AE850", "AE321", and "AE191" which are three types of ABS resin raw materials. It is a typical sectional view of resin game board P concerning the present invention. It is a figure which shows the "nail pulling strength" and the "nail bending strength" of a game nail with respect to each resin game board P shape | molded by three types of different ABS resin raw materials. It is a graph which shows the temperature change and displacement with respect to time of the resin veneer shape | molded with three types of ABS resin raw materials from which a composition differs, and a wooden veneer. It is a figure which shows the thermal displacement test result of the resin veneer and the wood veneer in two different temperatures.

Hereinafter, the present invention will be described in more detail with reference to the best examples. First, referring to FIGS. 1 to 5, after describing a core back mold M for molding a resin game board P according to the present invention, a resin game board using the core back mold M is described. The molding of P will be described, and thereafter, the effects of the present invention will be examined by comparing various characteristics of the molded resin gaming board P with the veneer gaming board. FIG. 1 is a schematic cross-sectional view (a cross-sectional view taken along line WW in FIG. 5) of a core back mold M used for molding a resin game board P according to the present invention. ) Are enlarged views of portions indicated by reference numerals “D” and “E” in FIG. 1, respectively, and FIGS. 3 to 5 are respectively an XX line, a YY line, and a ZZ line in FIG. FIG. 1 to 5 are intended to explain the molding principle, the ratio of the longitudinal and lateral lengths of the initial and final cavities C ₁ and C ₂ corresponds to the resin game board P that is a molded product. However, it is schematically shown by ignoring the ratio of the portrait or landscape and the depth.

1 to 5, the core back mold M includes a fixed mold M ₁ and a movable mold M _2, and further, the bottom surface of the cavity forming portion 1 formed in a rectangular concave shape of the movable mold M _2. A rectangular frame-shaped air vent forming frame member 2 is fitted on all inner surfaces except the inner surface. The air vent forming frame member 2 is fitted into the cavity forming portion 1 of the movable mold M ₂ in a form in close contact with the bottom surface 3 of the cavity forming portion 1 of the movable mold M ₂ and all the inner side surfaces 4 of the four sides. In the air vent forming frame member 2, another opposing side surface 6 facing the bottom surface 3 of the cavity forming portion 1 of the movable mold M ₂ is opposed to the fixed mold M ₁ in the movable mold M ₂ . It is the same surface as the contact surface 8 that is in close contact with the surface 7. Cavity forming the protrusions 9 in the form towards the movable mold M ₂ is being fitted to the inner surface 11 of the four sides of the air vent formed frame member 2 fitted in the movable mold M _2, the movable mold M ₂ a bottom surface 3, an inner surface 11 of the four sides of the air vent formed frame member 2, with the front end surface 12 of the cavity forming the protrusions 9 of the stationary mold M _1, the cavity C the molten resin is injected and filling is formed. A sprue 13 is formed by a sprue bush (not shown) at the center of the fixed mold M ₁ , and a nozzle 14 of an injection molding machine is pressed to the outside of the sprue 13. “Cavity C” refers to a general cavity. As will be described later, when the height of the cavity changes due to the retreat (core back) of the movable mold M ₂ , the cavities before and after the change are initially set. Called cavity C ₁ and final cavity C ₂ .

Moreover, as shown in FIGS. 1 to 5, a step for forming a first air vent V ₁ inside the opposed side surface 5 of the air vent forming frame member 2 and the bottom surface 3 of the movable mold M _2. The concave portions are formed over the entire circumference of the four sides and face the inner side surface 11, and the contact surface 7 of the fixed mold M _{1 and} the contact surface 8 of the movable mold M ₂ are in close contact with each other. In this state, a step-shaped recess for forming the second air vent V ₂ is formed in the same form as described above between the contact surface 7 of the fixed mold M ₁ . Further, at the same position along the circumferential direction of the opposite side surfaces 5 and 6 of the air vent forming frame member 2, a plurality of first and second air vent holes H ₁ , a predetermined distance along the circumferential direction, H ₂ is formed in the plate thickness direction of the air vent forming frame member 2. The outer surface 15 of the air vent formed frame member 2, the third air vent holes H ₃ of the same number of communicating with a plurality of said first and second respective air vent holes H _1, H _2, the air vent formed frame member 2 The contact surface 8 of the movable mold M ₂ is communicated with the plurality of second and third air vent holes H ₂ , H ₃ and outside the mold M. A plurality of external communication air vent holes H ₄ communicating with each other are formed. The second air vent V ₂ and the second air vent hole H ₂ can also be provided in the fixed mold M ₁ . Further, a gap between the inner side surface of the air vent forming frame member 2 and the outer side surface of the cavity forming convex portion 9 of the fixed mold M ₁ fitted to the air vent forming frame member 2 is defined as a third air vent V _3. It is functioning. As a result, the first and second air vent holes H ₁ and H ₂ face the first and second air vents V ₁ and V ₂ , respectively. The first to fourth air vent holes H _{1 to} H ₄ communicate with each other, and the air and the generated gas in the cavity C are the first to fourth at the bottom portion and the opposite bottom portion of the cavity C. The third air vents V _{1 to} V ₃ and the first to fourth air vent holes H _{1 to} H ₄ are discharged out of the mold. Here, in order to ensure the discharge of the internal residual air gathered to each corner portion of the cavity C at the time of injection / filling of the molten resin, each corner portion of the cavity C having a square shape in a plan view is provided. The first to fourth air vent holes H _{1 to} H ₄ are provided, respectively. The depth or spacing of the first to third air vent V ₁ ~V _3, because of the order of 0.05 to 0.1 mm, will not enter the injection and filling molten resin into the cavity C . Moreover, the depth of each of the first to fourth air vent holes H _{1 to} H ₄ is about 0.5 to 1 mm.

Next, referring to FIGS. 1 to 6, the core back molding die M having the above-described configuration is retreated ("core back") while the movable mold M ₂ is retracted, thereby containing a foaming agent at a predetermined ratio. The principle of molding the resin game board P with molten resin will be described. FIG 6 (a) ~ (c) is a state of being injected, the molten resin material K in the initial cavity C ₁ core back molding die M, respectively, to retract the movable mold M ₂ immediately after the injection and filling FIG. 5 is a schematic cross-sectional view of a state in which a final cavity C ₂ having an increased volume is formed and a state in which the volume of a molten resin raw material K is increased by foaming and the final cavity C ₂ after the increase is filled. First, in FIG. 6A, the height (J ₁ ) of the initial cavity C ₁ having a rectangular shape in which the fixed mold M ₁ and the movable mold M ₂ are formed in close contact with each other is a molded product. It is smaller than the thickness (T) of the resin game board P (J ₁ <T). The sprue 13 of the fixed mold M ₁ is pressed against the nozzle 14, the molten resin material K so that a gap in the initial cavity C ₁ formed by the fixed mold M ₁ and the movable mold M ₂ is not formed The injection of the molten resin material K is stopped in a state where it is injected and filled. Immediately after the initial cavity C ₁ is filled with the molten resin material K, the movable mold M ₂ is retracted (“core back”), and the height (J ₂ ) of the final cavity C ₂ is The final cavity C ₂ having an increased volume is formed by making it equal to the thickness (T) of the resin game board P that is a molded product. Here, the injection pressure of the molten resin raw material K is the same as the injection pressure of a normal molten resin not containing a foaming agent, but the molten resin raw material K is contained in the initial cavity C _{1 having a} volume smaller than the original volume. In order to promote foaming of the molten resin raw material K injected and filled in the initial cavity C ₁ , including the time when the movable mold M ₂ is “core back”, Unlike injection molding, no holding pressure is applied to the injected molten resin material K.

The height of the initial cavity C ₁ and (J _1), and the height of the final cavity C ₂ (J _2), the resin used, and the kind of the foaming agent, but is determined by the mixing ratio or the like of the blowing agent In the case where the resin is an ABS resin and the mixing ratio of the foaming agent to the entire molten resin raw material is 5% by weight as in the examples described later, the height of the initial cavity C ₁ (J ₁ = 11 mm), the characteristics of the “nail pulling strength” and “nail bending strength” and further “thermal displacement” are obtained by performing at the height of the final cavity C ₂ (J ₂ = 15 mm). A “resin game board” with a value close to “wooden veneer” was obtained. In the above example, the ratio of the increased cavity Ca to the initial cavity C ₁ is about 36%, and the foaming ratio of the resin is 1.36.

Here, the cavity C of the core back mold M communicates with the outside of the cavity C through the _first to _third air vents V _{1 to} V ₃ and the first to fourth air vent holes H _{1 to} H _4. The air and the generated gas in the cavity C do not remain in the cavity C or enter the molten resin to form voids that cause nests, so that the first to third air vents are formed. It is discharged to the outside through the V ₁ ~V ₃ and the air vent of the first to fourth holes H ₁ to H _4. That is, the first air vent V ₁ and the second and third air vents V ₂ and V ₃ are formed on the bottom and the opposite bottom of the cavity C, respectively, over the entire circumference (over the entire length of the four sides). Therefore, the first air vent V ₁ is formed not only on the side of the bottom of the cavity C where the fixed mold M ₁ and the movable mold M ₂ are fitted, but also on the side of the bottom of the cavity C. In addition, since the first to third air vents V _{1 to} V ₃ are provided over the entire circumference (over the entire length of the four sides), the remaining air and the generated gas in the cavity C are effectively generated. Since it is discharged to the outside and no gap is generated in the resin game board P that is a molded product, the quality of the resin game board P is improved.

Further, as shown in FIGS. 6A and 6B, in the state where the molten resin raw material K is injected and filled in the initial cavity C ₁ , the injection of the molten resin raw material K is stopped. Since the movable mold M ₂ is core-backed, the increased cavity Ca newly formed by the core back functions to assist foaming of the molten resin material K. That is, the increased cavity Ca communicates outside the mold through the _first to _third air vents V _{1 to} V ₃ and the first to fourth air vent holes H _{1 to} H _4. Unlike the “pressure method”, a large pressure is not applied to the molten resin raw material K whose volume is increased by foaming (the pressure acting on the molten resin raw material K is atmospheric pressure). The part is allowed to be freely foamed. For this reason, the portion of the molten resin raw material K in the vicinity of the inner peripheral surface of the core back mold M that is the outer peripheral portion of the final cavity C ₂ starts to be hardened earlier than the central portion. Although there is an unfoamed part that is constrained compared to the foaming of the central part, the degree of foaming is increased compared to the above-mentioned “counter pressure method”, so that the mechanical rigidity is high while having a low specific gravity. This makes it possible to mold resin game boards. In addition, the unfoamed portion of the outer peripheral portion of the molded resin game board is not completely foamed, but compared with the “counter pressure method”, the degree of foaming is increased. This means that the “nailability”, which is the ease of nailing, is good. In addition, at the time of foaming, the cavity C ₁ (C ₂ ) in the outer peripheral portion of the molten resin raw material K, that is, both the initial cavity C ₁ and the final cavity C ₂ , has a low pressure that is almost the same as the atmospheric pressure. In addition, the gas generated by foaming is immediately ejected to the outside of the molten resin raw material K, and the first to _third air vents V _{1 to} V ₃ and the first to fourth air vent holes H _{1 to} H _4. Since there is no generation of large voids (so-called “nests”) due to foaming gas inside the resin game board P, this structure provides good “nailing”. While being held, as shown in the examples described later, by selecting a specific resin, the “nail pulling strength” which is a resistance force against the pulling force of the game nail driven into the resin game board is also increased. In the cross-sectional view of the resin game board P in FIG. 11, it is schematically illustrated that the foamed state of the resin is different between the center portion and the front and back surface layer portions.

Next, as an ABS resin raw material which is a ternary copolymer of butadiene, acrylonitrile and styrene, the above-mentioned ABS resins (95% by weight) of “AE850”, “AE321”, “AE191” By using the core back mold M described above, the “core back method” is performed using the foamed resin raw material in which only (5% by weight) of “EB207” which is an organic acid chemical foaming agent manufactured by Kasei Kogyo Co., Ltd. An injection molded resin game board P (see FIG. 7) was obtained. In FIG. 7, the length (L ₁ ), the width (L ₂ ), and the plate thickness (T) of the resin game board P are 480 mm, 438 mm, and 15 mm, respectively. Here, the composition of the three components “AE850”, “AE321”, and “AE191”, which are the ABS resin raw materials, is as shown in FIG. FIG. 8 shows the composition and linear expansion coefficient of the “ABS resin” constituting the three types of ABS resin raw materials. When the “ABS resin raw material” is referred to, a certain percentage of foaming is produced in the ABS resin. It refers to those containing a drug.

  FIG. 9 shows the vertical and horizontal dimensions, plate thickness, weight, density, and presence / absence of bubbles by X-ray inspection of each resin game board P using the above-mentioned three types of foamed resin raw materials. . The data of each item shown in FIG. 9 shows the average value obtained by conducting a plurality of tests for each foamed resin raw material. As for “plate thickness”, the “plate thickness” of each of the four corner portions is measured, and the average is shown. Regarding the “presence / absence of bubbles by X-ray inspection”, each foamed resin raw material has the most difference in the fluidity of the resin in the molten state depending on the weight ratio (composition) of the three components, and contains the most butadiene. In “AE850”, before the molten resin raw material spreads (completely fills) in the mold, bubbles grew at the end of the molten resin that was flowing, and bubbles existed inside the molded product. Bubbles were not generated in the molded products of “AE321” and “AE191” having a butadiene composition smaller than that of “AE850”.

  FIG. 10 shows the evaluation regarding each processing of “cell pasting”, “cutting”, “screw fastening” and “nailing” of the resin game board P molded from the above-mentioned three kinds of foamed resin raw materials. It is shown. Regarding “cell pasting”, “resin veneer” is inferior in heat resistance to “wood veneer”, so it is necessary to lower the set temperature of the hot press, which results in longer processing time. Cell pasting using a “cell pasting machine” for mass production used in “resin veneer” is possible. Regarding “cutting”, the “resin veneer” is inferior in heat resistance compared to “wooden veneer”, so it is necessary to lower the rotation speed of the tool spindle, resulting in longer machining time. This is the same as “cell pasting”. In addition, in “AE850” and “AE321”, complex machining is possible, and there is no “hammer chipping” in which the corner portion is chipped by receiving external force during processing, but in “AE191”, the processing surface is not processed. A melted portion may occur, which is considered to be due to heat generation during processing.

  In addition, with regard to “screw tightening”, it is possible to use a dedicated “screw tightening machine” used for “wood veneer”, and the appearance is not inferior to “wood veneer” and “hold” Regarding “force”, “resin veneer” seems to be higher than “wood veneer” because it is “dense” than “wood veneer”. In addition, as for “nailing”, it is possible to nail with a “nailing machine” dedicated to “wooden veneer”, and regarding “holding force”, as shown in the experimental results described later, Although it was slightly inferior to “wood veneer”, it was found that “AE191” was almost inferior to “wood veneer”. In addition, regarding the appearance of the part where the nail is driven, the “resin veneer” is “dense” compared to the “wooden veneer”, so a slight bulge is generated, but the tip shape of the nail is changed. Therefore, it seems that the “bulge” can be eliminated.

  FIG. 11 shows a schematic cross-sectional view of a resin game board P injection-molded by the above-described “core back system”. FIG. 12 shows the above-described three different ABS resin raw materials. In a state where game nails are driven into the molded resin game boards P, “nail pulling strength” and “nail bending strength” are shown in comparison with “wooden veneer”. Here, “nail pulling strength” and “nail bending strength” indicate average values of the results of a plurality of tests (average of 8 times). The length and outer diameter of the game nail N are 33 mm and 1.9 mm, respectively. Further, the board thickness of each of the wooden and resin game boards P is about 15 mm, and the nail driving depth is about 14 mm. “Nail pullout strength” is the maximum value when the nail head is gripped and pulled out, and “nail bending strength” is the nail bending strength placed almost horizontally, This is the maximum value at which the game nail starts to bend in a state where a force is applied to the head from above to below.

  As described above, the unfoamed layer A on the front and back surfaces of the resin game board P has a lower degree of resin foaming than the foamed layer B in the center, but includes the “counter pressure method”. In comparison with the conventional injection molding method, the degree of foaming of the unfoamed layer A is increased, so-called “nest” is not generated, and the ratio of the three components of the ABS resin is set to a specific ratio. Although the density of the resin game board P is small, both “nail pulling strength” and “nail bending strength” can be increased. That is, as shown in FIG. 12, the “nail pullout strength” of “AE191” with a small proportion of butadiene is similar to the “nail pullout strength” of wooden veneer (489.3N) (424.8N). was gotten. In addition, each of “AE850” and “AE321” “nail pulling strength” is smaller than that of wooden veneer, both of which have a higher proportion of butadiene than “AE191”, and are rubbery (sticky) It seems that the pull-out force is reduced as the value increases. In addition, regarding the “nail bending strength”, a value slightly larger than that of the wooden veneer was obtained almost regardless of the proportion of butadiene. This is because the density of the resin game board (resin veneer) is higher than that of the wooden veneer, and therefore when the game nail is driven into the resin game board (resin veneer), the resin veneer is more of a wooden veneer. It seems that the “nail bending strength” is larger than In FIG. 11, the sum of the thicknesses of the front and back unfoamed layers A is (3.5 to 8.5) mm while the thickness T of the resin game board P is about 15 mm. .

  The ratio of butadiene, acrylonitrile and styrene constituting the ABS resin is selected from the ranges of butadiene: (15-25) wt%, acrylonitrile: (21-24) wt%, and styrene: (51-60) wt%. Need to be done. The ratio of butadiene is (15-25) wt%. If the ratio is 15 wt% or less, the ratio is too small, the resin veneer becomes too hard, and cracks are easily generated when nailing, This is because if it is 25% by weight or more, the rubber property is increased and the necessary “nailing strength” is not ensured.

  Next, referring to FIG. 13 and FIG. 14, the displacement of the resin veneer molded with the above-mentioned three types of ABS resin raw materials “AE850”, “AE321”, and “AE191” with respect to the temperature change is compared with the wooden veneer. To consider in the comparison. FIG. 13 is a graph showing temperature change and displacement with respect to time of a resin veneer and a wood veneer formed from three types of ABS resin raw materials having different compositions, and FIG. 14 is a graph showing resin veneer at two different specific temperatures. The thermal displacement test result of the wooden veneer is shown. That is, FIG. 13 shows the result of measuring three types of resin veneers and wooden veneers in a humidity (60%) temperature and humidity chamber, and measuring the displacement with a laser displacement meter at regular intervals. On the other hand, FIG. 14 shows a state in which the temperature in the temperature / humidity tank is lowered from room temperature to 0 ° C. and this state is maintained for 5 hours, and the temperature in the tank is increased from 0 ° C. to 50 ° C. The displacement values of three types of resin veneer and wooden veneer when held for 5 hours are shown. The displacement (value) shown in FIGS. 13 and 14 is the displacement (value) with respect to the “vertically long (about 480 mm)” of the resin veneer and the wooden veneer.

  When the temperature in the temperature and humidity chamber is changed, the dimensional displacement of the resin veneer and the wooden veneer changes following the temperature. When the temperature in the temperature and humidity chamber is maintained at about (0 ° C.), the thermal displacement dimensions of the resin veneer and the wooden veneer both maintain about (−0.2 mm). When the temperature in the temperature and humidity chamber is raised to (50 ° C.), the thermal displacement dimension is (1.9 mm) in the resin veneer whose ABS resin raw material is “AE850” or “AE321”. However, the resin veneer with the ABS resin raw material “AE191” has a thermal displacement dimension (1.1 mm), and is found to have dimensional stability almost equal to the thermal displacement dimension (0.9 mm) of the wooden veneer. did.

  Also, in the above embodiment, the case where only the ABS resin is used as the resin raw material is shown, and the ABS resin has a good nailing property, nail retention property, dimensional stability, etc. Although it proved to be suitable for molding a resin game board as an alternative, for example, it is also possible to use “polymer alloy” in which the ABS resin is blended with other resin, for example, polycarbonate resin at a predetermined ratio. Is possible.

  As for the foaming agent for foaming the resin, in the above examples, “EB207” which is an organic acid chemical foaming agent manufactured by Eiwa Kasei Kogyo Co., Ltd. was used. The foaming agent is not particularly limited as long as the resin can be foamed inside.

A: Unfoamed layer of resin game board
B: Foam layer of resin game board
C: Cavity
C ₁ : Initial cavity
C ₂ : Final cavity
Ca: increasing cavity H ₁ to H _4: bleeding hole
K: Molten resin raw material
M: Core back mold
M ₁ : Fixed mold
M ₂ : Movable mold
P: Resin game board (resin veneer)
V ₁ ~V _3: air vents
1: Cavity forming part
2: Air vent forming frame material
5, 6: Opposite side surfaces of the air vent forming frame material
7: Contact surface of fixed mold
8: Adhering surface of movable mold
11: Inner side surface of air vent forming frame member
15: Outer surface of air vent forming frame member

Claims (6)

A fixed mold having a cavity forming convex part, and a movable mold in which a cavity is formed by fitting the cavity forming convex part of the fixed mold to the cavity forming part,
After the molten resin raw material containing the foaming agent is injected and filled into the cavity without any gap, the movable mold is moved backward with respect to the fixed mold, and the portion facing the bottom of the cavity on the movable mold side is placed. A core back mold used for forming a rectangular thick plate-like resin game board by a core back injection molding method in which a void is formed and the molten resin is foamed by the presence of the void,
The cavity formed by the fixed mold and the movable mold has a bottom that is on the movable mold side, and all four sides of the opposite side of the cavity that faces the bottom of the fixed mold side are in the cavity. The air vents on the bottom side and the bottom side making the infiltration of the molten resin impossible are formed,
Each of the air vents communicates with the outside of the mold through a plurality of air vent holes formed in the movable mold or the contact portion between the movable mold and the fixed mold,
A gas generated at the time of foam molding of the molten resin material is discharged from each air vent and each air vent hole to mold a game board having a thickness corresponding to the depth of the cavity after the movable mold retreats. Features a core back mold for resin game boards.   An air vent forming frame member is fitted into each inner side surface of the cavity forming portion formed in the movable mold to form a cavity forming space, and each air vent is formed on each inner surface side of each air vent forming frame member. 2. The core back mold for resin game board according to claim 1, wherein the corner portion is formed by cutting out the corner portion in a step shape.   3. The core back mold for resin game board according to claim 1, wherein each of the air vents is formed continuously over the entire circumference of each of the four sides.   Of the air vent holes, the air vent holes except for the external communication air vent holes that communicate directly with the outside of the mold are formed by grooves communicating with the air vents on the outer side surface and the opposite side surfaces of the air vent forming frame member. 4. The core back mold for a resin game board according to claim 2 or 3, wherein the external communication air vent hole is formed in a close contact surface between the fixed mold and the movable mold.   Air venting holes are formed in portions corresponding to the four corner portions of the cavity in the movable mold or in the contact portion between the movable mold and the fixed mold, respectively. The core back mold for resin game boards according to any one of claims 1 to 4.   The resin-made product according to any one of claims 1 to 5, wherein a insert piece mold for forming an accessory attachment hole is disposed in a cavity formed by the fixed mold and the movable mold. Core back mold for game board.

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