JP6688968B2 - Molding method and molded body - Google Patents

Description

  The present invention relates to a foamed resin molding method, and further to a molded body molded by the molding method.

  BACKGROUND ART As foam blow-molded products, various air-conditioning ducts mounted in, for example, an instrument panel of an automobile are known. Foam ducts made of foamed resin materials are widely used for these air conditioning ducts. The foam duct is lightweight and can be easily manufactured by, for example, adding a foaming agent to a resin material such as a polyolefin resin, melt-kneading the mixture, and blow-molding a foam parison extruded from a die of an extruder.

  In recent years, various forms of air conditioning ducts have been required, and in response to this, various molding methods have been developed also in foam blow molding. For example, in the above-mentioned air conditioning duct, it is necessary to form the mounting portion for mounting and fixing with a higher strength than other portions, and the mounting portion is formed by so-called compression molding. ing.

  For example, in Patent Document 1, a foamed resin parison in a softened state is placed in a split mold that can be opened and closed, and the foamed resin parison is sandwiched between molds to blow a gas into the foamed resin parison to form a hollow foamed resin. In the method for producing a molded body, at least a part of a foamed resin parison is closed along with the closing of a split mold, and is projected outward from an outer wall surface of a foamed resin hollow molded body to be molded, and the projected portions are overlapped with each other. A method for manufacturing a foamed resin hollow molded article that forms a mounting member by crushing is disclosed.

  It has also been proposed by the applicant of the present application to further advance the molding by crushing and crush and mold the entire parison. For example, in Patent Document 2, an arrangement step in which a thermoplastic resin material containing a foaming agent in a molten state is extruded into a tubular shape or a pair of sheet shapes and placed between a plurality of divided forming dies, and This mold retraction is performed by closing the mold by compressing the laminate along the molding surface of the mold by retracting at least a part of the molding surface in the process of compression molding performed in the molding process. There is disclosed a method for manufacturing a vehicle duct member, which includes a depressurizing step of depressurizing the inside of the region.

JP, 2006-341514, A JP, 2005-189412, A

  By the way, when the thickness is increased by the core back foaming technique as in the technique described in Patent Document 2, the slide core retreats after completion of mold clamping. At this time, the foamed resin is brought into close contact with the slide core by vacuum suction from the fine holes provided in the slide core that cores back.

  As described above, in the molding method using the core back, the resin follows the slide core without problems in the vicinity of the center of the core back portion. On the other hand, at the end portion of the slide core that cores back, the shearing speed is high, and thus there is a problem that the resin is difficult to follow. If the resin does not follow the slide core, the mold shape will not be sufficiently transferred to the molded body, and there will be a problem that the end portion of the core back region of the molded body will largely drip.

  The present invention has been proposed in view of such a conventional situation, and an object thereof is to provide a molding method capable of causing the resin to follow the core back of the slide core even at the core back region end portion, Furthermore, it aims at providing the molded object by which the transferability was improved.

In order to achieve the above-mentioned object, the molding method of the present invention, a thermoplastic resin material containing a foaming agent in a molten state is extruded into a tubular shape or a pair of sheet shapes, and sandwiched by a mold to have a predetermined shape. A molding method of molding , wherein a movable mold is provided in at least one mold, and a hollow portion is formed along the entire circumference of the movable mold, and the movable mold is clamped after the movable mold is formed. When the mold is retracted and the movable mold is retracted, air is blown into the hollow part, and a pressing force is applied to the thermoplastic resin in the boundary region between the core back part and the hollow part where the movable mold retracts. It is characterized by

Further, the molded product of the present invention is a molded product of a foamed resin and has a portion formed by retreating the movable mold and having an enlarged thickness, and a hollow portion adjacent to the portion, and the thickness is enlarged. The formed part is composed of a skin layer having small air bubbles formed on the surface and an intermediate layer between these skin layers,
(1) The thickness of the skin layer on the side formed by the movable mold is thinner than the skin layer on the opposite side, and the thickness of the intermediate layer is thicker than any of the skin layers.
(2) The maximum bubble diameter included in the intermediate layer is larger than 2.5 times the bubble diameter in the thickness direction of the maximum bubble included in the skin layer on the surface side formed by the movable mold. To do.

  As described above, at the end of the movable mold (slide core) that cores back, the shearing speed is high, so that the resin is hard to follow, and the shape transferability becomes insufficient. When a hollow part is made adjacent to the installation position of the movable mold and air is blown into the hollow part at the time of core back, it passes through the bubbles contained in the resin and presses the resin to follow the movable mold. Is added. As a result, the shape transferability in the end region of the movable die that cores back is improved.

  According to the present invention, the resin can be made to follow the core back of the movable mold even at the end portion of the core back region, and thus it is possible to provide a molded body with improved transferability.

1A and 1B are schematic cross-sectional views showing an embodiment of a molding method, in which (A) is a parison supplying step, (B) is a mold clamping step, (C) is a core back step, and (D) is a molded body removing step. is there. It is an expanded sectional view near a movable metallic mold in a core back state. It is a schematic sectional drawing which shows the shaping | molding example which provided the hollow part, (A) shows the state before core back, (B) shows the state at the time of core back, respectively. (A) is a schematic diagram showing a state where internal pressure is applied in the core back end region, and (B) is a diagram showing how transferability is improved thereby. It is a figure which shows the cross-section of a molded object, and shows the thickness of a skin layer and an intermediate | middle layer. It is a figure which shows the cross-sectional structure of a molded object, the bubble diameter of the largest bubble contained in an intermediate | middle layer, the thickness of a wall part, the line segment which divides the thickness of the expanded part into 2: 1, and the bubble which intersects this. Shows the bubble diameter of.

  Hereinafter, embodiments of a molding method and a molded body to which the present invention is applied will be described in detail with reference to the drawings.

  1 (A) to 1 (D) show an example of a molding method using a core back. When molding a molded body, first, as shown in FIG. 1 (A), a thermoplastic resin material containing a foaming agent in a molten state is extruded into a cylindrical parison 1 and divided into molds 2 and 3. Place in between. Although the cylindrical parison 1 is taken as an example here, the material of the thermoplastic resin may be extruded into a pair of sheets. Further, a known method can be used for extruding the tubular parison 1, so that illustration thereof is omitted here.

  As the thermoplastic resin, any resin material can be used, and examples thereof include polyolefin resins such as polyethylene resin and polypropylene resin. The polypropylene resin is a propylene homopolymer, a random or block copolymer of propylene and another α-olefin, or the like. Other α-olefins copolymerized with propylene include ethylene, butene, pentene, hexene, octene and methylpentene. The amount of α-olefin copolymerized with propylene is arbitrary, but in order to maintain the excellent physical properties of polypropylene, it is preferably about 0.1 to 20% by mass.

  As the foaming agent, an inorganic foaming agent such as air, carbon dioxide gas, nitrogen gas or water, or an organic foaming agent such as butane, pentane, hexane, dichloromethane or dichloroethane can be used. Of these, air, carbon dioxide gas, or nitrogen gas is preferably used as the foaming agent. By using these, it is possible to prevent mixing of organic substances and suppress deterioration of durability and the like.

  The molding dies 2 and 3 are prepared as those which have been previously processed into a shape suitable for molding a molded body. Further, one molding die 2 has a slide core (movable mold) 4, and the slide core 4 is slidable so as to retract from the molding die 2.

  In the molding step, as shown in FIG. 1B, the two molding dies 2 and 3 are clamped. As a result, the tubular parison 1 that was the material is crushed to form the laminated body 5 of the foamed resin material. Further, by applying compression to the laminate 5 by clamping, the laminate 5 is compression-molded along the molding surfaces of the molding dies 2 and 3. At the start of compression molding, the slide core 4 is in the most advanced initial position (position where the molding surface is continuous with the surroundings).

  Next, as shown in FIG. 1C, the slide core 4 is retracted (so-called “core back”) in the process of compression-molding the laminated body 5. As a result, the pressure in the region corresponding to the slide core 4 is reduced in the molds 2 and 3 in the clamped state, and the thickness of the laminated body 5 increases as the slide core 4 retreats. As a result, the foaming ratio of the laminated body 5 can be increased in the region corresponding to the slide core 4 as compared with the other regions.

  In addition, it is preferable that a vacuum suction hole is provided on a surface of the slide core 4 that is in contact with the stacked body 5, and vacuum suction is performed from the vacuum suction hole when the slide core 4 is core-backed. By performing vacuum suction, the followability of the resin forming the laminated body 5 to the slide core 4 becomes good.

  After the molding step and the depressurization step, as shown in FIG. 1D, the molding dies 2 and 3 are opened to remove the burrs, whereby the molded body 10 is obtained. The obtained molded body 10 is composed of a laminate of foamed resin material layers, has a structure mainly including a compression molding region, and further includes a thickening molding region 11 corresponding to the core back by the slide core 4. It becomes a structure.

  Although the above is the basic molding method, when the slide core 4 is core-backed, in particular in the end region of the slide core 4, the following of the resin becomes insufficient and the phenomenon that the shape sags may occur. is there. In particular, this tendency becomes remarkable as the amount of core back increases.

  FIG. 2 is an enlarged view showing the vicinity of the slide core 4. At the time of compression molding, the slide core 4 is advanced to the position of the broken line, and the laminated body 5 obtained by crushing the cylindrical parison 1 is compressed. Next, the slide core 4 is retracted (core back) in the direction of the arrow to the position shown in the figure, but at this time, the resin forming the laminated body 5 cannot fully follow the slide core 4, and therefore the end region T of the slide core 4 At, the shape is drooping. Such a decrease in the shape transfer property becomes a factor that deteriorates the quality of the molded body 10.

  Therefore, in the present invention, a hollow portion is provided adjacent to the end portion of the slide core 4, and air is blown into the hollow portion to improve shape transferability.

  FIG. 3 is a diagram showing an embodiment in which a hollow portion is provided to perform core back. That is, as shown in FIG. 3 (A), when a portion of the molding die 3 adjacent to the position facing the slide core 4 is retracted and the cylindrical parison 1 is sandwiched between the molding dies 2 and 3, the crushing is not crushed. A hollow portion in which a space K is formed is provided between the resin layers of the cylindrical parison 1. The hollow portion is preferably formed along the outer circumference of the slide core 4 over the entire circumference thereof.

  By providing the hollow portion, the molding region is composed of a core back portion (a region where the slide core 4 is provided), a boundary region between the core back portion and the hollow portion, and a hollow portion forming region. Become. The blow molding part (hollow part) is composed of the resin layer (outer wall) of the cylindrical parison 1 which is not crushed and the space K.

  After the compression molding shown in FIG. 3 (A), as shown in FIG. 3 (B), the slide core 4 is retracted in the direction of the arrow to perform core back. At this time, by inserting an air supply needle into the space K in the hollow portion, positive pressure air is sent into the space K in the same manner as in ordinary blow molding, and a pressing force is applied to the resin in the boundary region. The compressed air supplied to the space K of the hollow portion passes through the bubbles contained in the resin and reaches the resin portion that follows the core back of the slide core 4. Since the molded product molded by the core back has open cells, compressed air easily propagates in the resin.

  FIG. 4 shows the behavior of the resin in the core back region (particularly the end region of the slide core 4) when compressed air is supplied into the space K. As shown in FIG. 4 (A), the resin material forming the laminated body 5 has an increased thickness so as to enter the space formed along with the core back of the slide core 4, but FIG. As shown in FIG. 4, by supplying compressed air into the space K, internal pressure is applied to the resin in the direction in which it contacts the slide core 4, and the resin is moved by the slide core 4 and the molding die 2 as shown in FIG. 4 (B). It is shaped along the shape of the formed recess with good shape transferability.

  As described above, according to the molding method of the present invention, the resin can be made to follow the core back of the movable mold (slide core 4) even at the end of the core back region, which improves the shape transfer property. It is possible to provide a quality molded body.

  The molded body 10 molded by the molding method of the present invention has a specific form in its cross-sectional structure. In the following, a specific form of the molded body 10 to be molded will be described.

  The molded body 10 to be molded has a thickened molding region 11 formed by a core back and a hollow portion 12 adjacent to the thickened molding region 11. When used as a product, the hollow portion side can be cut off in the boundary region between the core back portion and the hollow portion.

  FIGS. 5 and 6 are enlarged views showing the vicinity of the boundary region. The core back portion (thickening molding region 11) is a skin layer on the core back surface side (surface side in contact with the slide core), and Comprises a skin layer on the opposite side and an intermediate layer between these skin layers. The intermediate layer is a void layer having voids for improving transferability, and in particular, in the core back edge region, the resin is stretched as compared with other portions for shaping, and the cell is formed in the ventilation step. The walls are destroyed, creating larger voids than the rest.

  In order to identify the form, bubbles are observed on the cross section of the product. Specifically, the product is divided along a plane orthogonal to the surface of the product, and bubbles are observed in a cross section where the hollow portion (foamed resin double wall portion) and the foamed resin single wall portion can be photographed in a single image. In both the hollow portion and the foamed resin single wall portion, a cross section having a product thickness larger than the respective average value is set as a measurement target, and the following measurement is performed on a cross section capable of ensuring a large product thickness in a possible range. Further, when MD (parison supply direction) / TD (direction orthogonal to MD direction) of the resin is clear, priority is given to measurement in a cross section in the MD direction at a portion having a wall thickness above the average.

The morphological features of the molded article 10 of the present invention observed by the bubbles are as follows.
(1) In the product thickness direction, (1-1) comparing the thickness A of the skin layer on the core back surface side (the surface side in contact with the slide core) with the thickness C of the skin layer on the opposite side, The thickness A of the skin layer on the core back surface side (the surface side in contact with the slide core) is smaller than the thickness C of the skin layer on the opposite side. Further, the thickness B of the intermediate layer affected by blowing is the thickness A of the skin layer on the core back surface side (the surface side in contact with the slide core) and the thickness C of the skin layer on the opposite side. Thicker than. That is, it has the relationship of the following formula (1).
B>C> A (1)
(1-2) The maximum diameter B1R in the thickness direction of the continuous void B1 formed in the core back end region is such that the maximum bubbles B2 contained in the skin layer on the side opposite to the core back surface side (the surface side in contact with the slide core). Is larger than 2.5 times the bubble diameter B2R in the thickness direction. That is, it has the relationship of the following formula (2).
B1R> 2.5B2R (2)

(2) In the product longitudinal direction (parison supply direction), (2-1) the maximum diameter E in the longitudinal direction of the continuous void B1 formed in the core back end region is 1.5 of the thickness D of the boundary wall in the boundary region. Greater than twice. That is, it has the relationship of the following formula (3).
E> 1.5D (3)
(2-2) The thickness of the enlarged part of the product is set to 2: 1 (the thickness G on the surface side molded by the slide core is 2, the thickness H on the opposite side is 1). The length of the continuous void B1 is longer than twice the maximum diameter J in the longitudinal direction of the bubble excluding the continuous void B1 formed in the core back end region among the bubbles intersecting with the line segment I to be divided. The maximum directional diameter E is larger. That is, it has the relationship of the following formula (4).
E> 2J (4)

  Although the embodiments to which the present invention is applied have been described above, it goes without saying that the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the gist of the present invention. It is possible.

1 Cylindrical parison 2, 3 Mold 4 Slide core (movable mold)
5 Laminated body 10 Molded body 11 Thickening molded region 12 Hollow part

Claims (4)

A molding method in which a thermoplastic resin material containing a foaming agent in a molten state is extruded into a tubular shape or a pair of sheet shapes, sandwiched by a mold and molded into a predetermined shape,
A movable mold is provided in at least one mold, and a hollow portion is formed along the entire circumference of the movable mold along its outer circumference,
After the mold is clamped, the movable mold is retracted,
Molding, characterized in that, when the movable mold is retracted, air is blown into the hollow part to apply a pressing force to the thermoplastic resin in a boundary region between the core back part and the hollow part where the movable mold retracts. Method.   The molding method according to claim 1, wherein vacuum suction is performed in the movable mold. A molded body of foamed resin,
It has a portion where the thickness formed by retracting the movable mold is enlarged and a hollow portion adjacent to it,
The portion where the thickness is enlarged is composed of a skin layer in which bubbles formed on the surface are small and an intermediate layer between these skin layers,
(1) The thickness of the skin layer on the side formed by the movable mold is thinner than the skin layer on the opposite side, and the thickness of the intermediate layer is thicker than any of the skin layers.
(2) The maximum bubble diameter included in the intermediate layer is larger than 2.5 times the bubble diameter in the thickness direction of the maximum bubble included in the skin layer on the surface side formed by the movable mold. Molded body. The maximum diameter in the longitudinal direction of the maximum bubble included in the intermediate layer is larger than 1.5 times the thickness of the wall portion existing between the maximum bubble and the hollow portion,
Among the bubbles intersecting with the line segment that divides the thickness of the entire molded body in the portion where the thickness is enlarged into 2: 1 (the surface side molded by the movable mold is 2 and the opposite side is 1), The molded body according to claim 3, wherein the maximum diameter of the maximum bubbles in the longitudinal direction is larger than twice the maximum diameter of the bubbles excluding the maximum bubbles in the longitudinal direction.

Images