JP2001246657A - Method for manufacturing injection molding and injection die - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an injection molding method by which an inverted blister is prevented from being generated in a large thickness part while dimensional accuracy is securely maintained at an important region of the injection molding and which is appliable to mass production. SOLUTION: The method for manufacturing an injection molding is to melt a thermoplastic material containing a foamed material previously and fill the cavity 13 of a injection molding die 10 with the molten material and further, cool the thermoplastic material in the cavity 13 below a softening temperature by lowering the wall face temperature of the cavity 13 to be followed by the step to release the injection molding from the mold. In this method, a coolant at a different temperature from other coolant flow channels is made to flow through at least one of a plurality of independent coolant flow channels 21, 22, 23, 24 and thus the foaming extent of the foamed material is locally varied under localized control.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an injection molding method for injection molding of a molded article whose thickness is locally changed, while ensuring the dimensional accuracy of the molded article and preventing sink marks which are likely to occur in a thick portion. And an injection mold used for the same.

[0002]

2. Description of the Related Art There are many molded products formed by injection molding, which have locally different thicknesses. For example, a base 1 of a toothbrush whose one example is shown in FIG. 2 is a flocked portion 3 in which a plurality of flocked holes 2...
And a handle portion 4 continuous with the flocked portion via a neck portion 5 are integrally formed by injection molding of a thermoplastic resin. The handle portion 4 is at least partially formed to be thicker than the flocked portion 3. There are many things that have been done.

When an injection-molded product having a locally different thickness such as the toothbrush substrate 1 is injection-molded by an injection molding die and an injection molding method which are conventionally generally used,
In the thick part of the molded product inside or out of the mold,
There is a problem that the designed shape cannot be obtained due to volume shrinkage called “sinking”. Although sink marks are caused by thermal shrinkage of the molding material, they occur in all parts of the molded product.However, especially in the thick part, the linear shrinkage is large, impairing the appearance, and causing the entire molded product to have warpage or warping. Induce deformation.

Conventionally, in order to prevent sink marks when a product having a locally different thickness is formed, the product is gradually cooled under pressure in a mold, and the molded product is put into a water tank immediately after the mold is released from the mold. Measures such as rapid cooling and foaming of a foamed material in a mold have been implemented or proposed.

[0005]

However, conventional measures for preventing sink marks each have problems. In other words, the method of gradually cooling under pressure in the mold reduces the production efficiency because the injection molding material injected into the mold cavity is gradually cooled while maintaining the injection pressure until the material is sufficiently solidified. I do.
The method of putting the product into a water tank immediately after taking it out of the mold for injection molding requires extra facilities and steps such as drying because the product gets wet. For example, when a foam is added to a material for injection molding, the foam is foamed in the mold to generate an internal pressure, and the skin of the molded article is solidified until it is solidified. Pressing against the cavity wall of the mold can prevent sink marks.However, in the thin part of the molded product or in the part having a complicated shape, deformation and dimensional accuracy decrease due to foaming, and strength decreases. Problems arise.

To solve this problem, Japanese Patent Application Laid-Open No.
Japanese Patent Application Laid-Open No. 11-90962 and Japanese Patent Application Laid-Open No. H11-90962 disclose injection molding with a material for injection molding in a cavity after placing a foaming material in advance in a thick portion or the like in the cavity where mold sinks are likely to occur. Alternatively, it discloses a method of manufacturing a resin molded product in which a foam is introduced into a specific portion of a cavity after the material for injection molding is injected into the cavity. According to these methods, it is only necessary to dispose a foam material in a thin portion where dimensional accuracy is required, so that the dimensional shape of the thin portion can be maintained, but the foam material is accurately placed at a predetermined position in the cavity for each shot. It is extremely difficult in practice to fix and fix the work, and even if it is possible, the work efficiency is greatly reduced, so that it cannot be applied at least to mass production. The present invention has been made in order to solve the above-mentioned problems, and therefore, an object of the present invention is to prevent sink marks in a thick part while securing dimensional accuracy of a necessary part, and to apply the present invention to mass production. An object of the present invention is to provide an injection molding method that can be used and an injection molding die used for the injection molding method.

[0007]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention relates to a method of melting a thermoplastic material containing a foaming material in advance, filling the molten material into a cavity of an injection mold, and forming a wall of the cavity. In the method for producing an injection-molded product in which the temperature is lowered and the thermoplastic material in the cavity is cooled to a softening temperature or lower and then released from the mold, the degree of foaming of the foamed material is controlled by locally controlling the wall surface temperature of the cavity. Provided is a method of manufacturing an injection molded article which is locally changed.

[0008] In general, the degree of foaming of a foamed material in a thermoplastic material varies depending on the temperature of the system and its duration. The degree of foaming increases when maintained at a relatively high temperature for a long time. According to the method of manufacturing an injection-molded product of the present invention, since the wall surface temperature of the cavity is locally controlled, the foam material in the thermoplastic material that comes into contact with the cavity wall surface corresponding to the local wall surface temperature is controlled. The degree of foaming changes. As a result, the degree of foaming at a specific portion of the molded injection molded product is adjusted according to the required characteristics, and an injection molded product without sink marks can be manufactured while ensuring dimensional accuracy.

In the above, when an injection mold having a locally different thickness of the cavity is used, a cooling rate of the wall surface is higher at a portion where the thickness of the cavity is relatively thinner than at a portion where the thickness of the cavity is relatively thicker. Is preferably faster. By suppressing foaming in a portion where the thickness of the cavity is relatively thin, high dimensional accuracy can be obtained in the portion of the thermoplastic material which is cooled by contacting the portion of the cavity wall. Also, in a portion where the thickness of the cavity is relatively thick, foaming is promoted to prevent sink marks. From this point of view, it is preferable to rapidly cool the wall surface in a portion where the cavity is thin, and to reduce the cooling rate so as to maintain the temperature as high as possible within the allowable limit of the holding time in the portion where the cavity is thick.

[0010] The injection molded article may be a brush base having a flocked portion having a plurality of flocked holes for flocking a bristle bundle, and a handle portion formed continuously with the flocked portion. . A plurality of densely arranged flocking holes need to be formed with high dimensional accuracy in the flocking portion of the brush base, and in the handle portion, sink must be prevented so as not to impair the appearance. Even if a foam material is used by the conventional method, it is extremely difficult to realize the conflicting requirements of dimensional accuracy and sink prevention by uniform cooling,
According to the injection molding method of the present invention, the above conflicting requirements can be satisfied together, and a brush with high commercial value can be obtained.

The present invention also provides an injection molding die having a cavity filled with a molten thermoplastic material and wall surface temperature control means for lowering the wall surface temperature of the cavity. Provided is an injection molding die capable of locally changing the temperature of a filled thermoplastic material. Further, the wall surface temperature control means has a plurality of independent refrigerant passages for circulating the refrigerant inside the mold, and at least one of the refrigerant passages circulates a refrigerant having a different temperature from the other refrigerant passages. Is preferred.

If the cavity is filled with a thermoplastic material containing a foam material in advance using the injection mold of the present invention, the cooling temperature of the cavity wall surface can be locally controlled. It is possible to change the degree of foaming of the foam material in the thermoplastic material in contact with the cavity wall surface in accordance with the above, whereby the degree of foaming at a specific portion of the molded injection molded product can be changed according to the required characteristics. It is possible to manufacture an injection-molded product that is adjusted by adjusting the dimensional accuracy and is free from sink marks while ensuring dimensional accuracy.

[0013]

Embodiments of the present invention will now be described specifically with reference to the drawings, but the following embodiments do not limit the present invention in any way. 1 (a), 1 (b) and 1 (c) show an example of an injection molding die block (hereinafter simply referred to as “die”) according to an embodiment of the present invention and an injection molded product molded in this die. Is shown. The mold 10 has a split surface 10A
Accordingly, the mold is divided into a fixed mold 11 and a movable mold 12. FIG. 1A shows that the fixed mold 11 is divided into the divided surfaces 10.
FIG. 1B is a plan view seen from the A side, and FIG.
FIG. 1C is a cross-sectional view illustrating a state in which the movable mold 1 and the movable mold 12 are combined, and FIG. 1C is a plan view of the movable mold 12 as viewed from the division surface 10A side. Fixed mold 11 and movable mold 12
A concave portion is formed on each of the divided surfaces 10A, and when the fixed mold 11 and the movable mold 12 are fitted together, these concave portions are combined to form a cavity 13 which is a space for molding an injection molded product. I do.

The injection molded product molded in the cavity 13 of the mold 10 is a base of the toothbrush. The toothbrush substrate 1 is made of polypropylene and has a flocked portion 3 having a plurality of flocked holes 2 for flocking a bristle bundle, a neck portion 5 extending from the flocked portion 3 along an axis, and a neck portion. 5, a handle portion 4 further extending from
The handle portion 4 is formed to have a thickness greater than the thickness of the flocking portion 3. Accordingly, the space thickness of the cavity 13 for molding the toothbrush base 1 is relatively thin at the portion where the flocked portion 3 is formed, and relatively thick at the portion where the handle portion 4 is formed.

In each block of the fixed mold 11 and the movable mold 12, there is provided a dividing surface 1 for forming a cavity 13.
The coolant passages 21, 22, 23, and 24 through which the cooling water flows are located on the back side of the concave surface (hereinafter, referred to as the “cavity wall 14”) of 0 A.
Are formed respectively. Flocked part 3 of fixed side mold 11
Passage 21 formed at the back of the cavity wall for molding
Are arranged along the axis of the toothbrush base 1 to be formed.
The pipe is arranged so that cooling water is introduced from the top of the mold, bent in an L-shape at the neck 5, and discharged from the side of the mold. The coolant passage 22 formed at the back of the cavity wall for molding the handle portion 4 of the stationary mold 11 introduces cooling water from the terminal end of the handle portion 4 along the axis of the toothbrush base 1 to be molded, and forms a neck. The pipe is bent so as to be bent in an L-shape at the portion 5 and discharged from the side of the mold. The coolant passage 21 formed at the back of the cavity wall for molding the flocking portion 3 of the moving mold 12 has a nest fitted in the moving mold 12 to form the flocking holes 2 of the flocking portion 3. Pin block 1
The cooling water is introduced parallel to the axis of the toothbrush base 1 from the top side of the flocked portion 3 while avoiding the pipe 5, bent in a U-shape at the neck portion 5, and discharged again from the top side of the flocked portion 3. Have been. The coolant passage 24 formed at the back of the cavity wall for molding the handle portion 4 of the moving mold 12 introduces cooling water from the terminal end of the handle portion 4 along the axis of the toothbrush base 1 to be molded, and forms a neck. The pipe is bent so as to be bent in an L-shape at the portion 5 and discharged from the side of the mold.

In molding the toothbrush substrate 1 using the above-described mold according to one embodiment of the present invention, a thermoplastic material obtained by mixing a foaming material with polypropylene is used. The fixed-side mold 11 and the movable-side mold 12 are aligned at the dividing surface 10A, and the melted thermoplastic material is pressure-filled into the cavity 13 through a resin passage (not shown). Next, cooling water flows through the refrigerant passages 21, 22, 23, and 24. At this time, the temperature of the coolant flowing through the coolant passages 21 and 23 formed on the flocking portion 3 side is set lower than the temperature of the coolant flowing through the coolant passages 22 and 24 formed on the handle portion 4 side. It is also effective to set the water temperature low and increase the flow velocity. Thereby, the portion of the thermoplastic material that contacts the cavity wall on the flocking portion 3 side is cooled more quickly than the portion of the thermoplastic material that contacts the cavity wall on the handle portion 4 side.

When the thermoplastic material is filled into the cavity 13, the foam material starts foaming at the filling temperature.
The degree of this foaming increases at sites where the high temperature lasts for a long time. That is, since the bristles 3 are rapidly cooled on the flocked portion side, the degree of foaming can be suppressed to a small level. Therefore, the periphery of the bristled holes 2 is a molded portion having high density and high dimensional accuracy. Further, the degree of foaming on the handle portion 4 side becomes large, and the skin of the handle portion 4 is strongly pressed against the cavity wall by the foaming internal pressure of the foam material in the process of cooling to a temperature lower than the softening temperature of the thermoplastic material, and solidifies in this state. Sinking is prevented.

When the movable mold 12 is separated from the fixed mold 11 after the injection molded product is cooled to the softening temperature or lower, the molded toothbrush base 1 adheres to the movable mold 12 and the fixed mold 12 is attached. 11 from the cavity wall. Next, when a plurality of ejection pins (not shown) provided on the movable mold 12 are ejected, the toothbrush base 1 is detached from the movable mold 12 and removed. In the obtained toothbrush base 1, the flocked portion 3 is dense and has high dimensional accuracy, and the handle portion 4 does not have sink marks even in a particularly thick portion, and is a product excellent in shape stability as a whole. Further, there is no variation in shape between products due to sink marks and warpage.

The thermoplastic material used in the method for producing an injection-molded article of the present invention is not particularly limited. Examples of preferred thermoplastic materials include, for example, polyolefin resins, such as polypropylene, low density polyethylene, linear low density polyethylene, high density polyethylene, or polyester resins, such as polyethylene terephthalate.

The method for producing an injection molded article of the present invention is used.
The foam material is not particularly limited, but for example, a pen
Tan, neopentane, hexane, isohexane, hepta
Hydrocarbons such as methane, isoheptane or halogenated carbon
Volatile foaming material containing hydrogen fluoride, sodium hydrogen carbonate
CO by chemical reaction such as mixed paste of water and water_Two,
N _Two, H_TwoReactive foaming that generates inert gas such as O
Material, azodicarbonamide, dinitrosopentamethylene
All decomposable foaming materials containing tetramine etc.
Or mixed. In addition to foaming material, foaming aid
Agents, such as metal oxides, calcium silicates, etc.
May be.

The shape of the refrigerant passage provided in the injection mold is not particularly limited, and may be any of a single tube, a double tube, a flat shape, a mesh shape, and the like. The refrigerant is not limited to water, but may be an organic refrigerant such as di- or poly-ethylene glycol, or a Freon-based refrigerant. The temperature and flow rate of the refrigerant flowing through each refrigerant passage may be constant temperature and constant speed, depending on the degree of foaming required at the corresponding portion of the injection molded product, or the temperature and flow rate may be adjusted according to a preset program. It may be controlled to change.

The method for producing an injection-molded article and the mold for injection molding according to the present invention are not limited to the production of the toothbrush base of the above-described embodiment. In addition, the present invention can be widely applied to the production of injection-molded products that are required to achieve both the dimensional accuracy of a thin portion and the prevention of sink marks on a thick portion.

[0023]

The method for producing an injection-molded article of the present invention is characterized in that the foam material is foamed by locally controlling the wall surface temperature of the cavity in a state where the thermoplastic material containing the foam material is filled in the cavity in advance. Since the degree is locally changed, it is possible to manufacture an injection-molded product in which sinks, which are likely to occur in a thick portion, are prevented while securing dimensional accuracy of a necessary portion. Since the injection mold of the present invention has wall temperature control means for locally changing the temperature of the thermoplastic material filled in the cavity, the thermoplastic material containing a foaming material in advance is used for this mold. When filling, the degree of foaming of the foamed material can be locally changed, and it is possible to manufacture an injection-molded product in which sinks, which are likely to occur in a thick portion, are prevented while ensuring dimensional accuracy at a necessary portion. it can.

[Brief description of the drawings]

FIG. 1 shows an embodiment of the present invention, and FIG.
FIG. 1 is a plan view of a fixed mold as viewed from a dividing surface side, and FIG.
FIG. 1B is a cross-sectional view showing a state in which the fixed mold and the movable mold are combined, and FIG. 1C is a plan view of the movable mold as viewed from the division surface side.

FIG. 2 is a cross-sectional view showing an example of a toothbrush base.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Toothbrush base 2 ... Flocked hole 3 ... Flocked part 4 ... Handle part 5 ... Neck part 10 ... Mold 10A ... Dividing surface 11 ... Fixed side mold 12 ... Moving side mold 13 ... Cavity 14 ... Cavity wall 21,22 , 23,24 ... refrigerant passage

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Teru Matsumoto 1-3-7 Honjo, Sumida-ku, Tokyo F-term (reference) in Lion Corporation 4F202 AB02 AG20 AH72 AM34 AM35 AR06 CA11 CB01 CN05 CN21 4F206 AA11 AA24 AB02 AG20 AH72 AM34 AM35 AR065 JA07 JN44 JP18 JQ81

Claims (5)

[Claims] 1. A thermoplastic material containing a foaming material previously melted and filled into a cavity of an injection molding die, the wall surface temperature of the cavity is lowered, and the thermoplastic material in the cavity is cooled to a softening temperature or lower. A method of manufacturing an injection-molded article, which is demolded after being cooled, wherein the wall surface temperature of the cavity is locally controlled to locally change the degree of foaming of the foamed material. . 2. An injection mold having locally different thicknesses of cavities is used, and a cooling rate of the wall surface is made faster at a portion where the thickness of the cavity is relatively thinner than at a portion where the thickness of the cavity is relatively thicker. 2. The method according to claim 1, wherein
3. The method for producing an injection-molded product according to item 1. 3. The brush molded body having a flocked portion having a plurality of flocked holes for flocking a bristle bundle, and a handle portion formed continuously with the flocked portion. The method for producing an injection-molded product according to claim 1, wherein: 4. An injection molding die having a cavity filled with a molten thermoplastic material and wall surface temperature control means for lowering the wall surface temperature of the cavity, wherein the wall surface temperature control means is filled in the cavity. A mold for injection molding characterized in that the temperature of a thermoplastic material can be locally changed. 5. The wall surface temperature control means has a plurality of independent refrigerant passages for circulating a refrigerant inside the mold, and at least one of the refrigerant passages circulates a refrigerant having a different temperature from the other refrigerant passages. 5. The method according to claim 4, wherein
The mold for injection molding according to 1.