JPH1199541A - Injection mold, method for producing the same and apparatus therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an injection mold capable of preventing the generation of a sink or a weld line and a method and apparatus for simply producing the same. SOLUTION: A rigid film 3 of amorphous carbon is formed on the surface coming into contact with a molding resin of an injection mold 1 through a polymeric heat insulating membrane 2. The injection mold is prepared in a vacuum treatment chamber evacuated under vacuum and the atmosphere thereof is brought to a heating atmosphere to heat the injection mold and vapors of at least two kinds of polymeric film raw material monomers are allowed to be present in the vacuum treatment chamber to form a heat insulating membrane of a copolymer on the surface of the injection mold and, thereafter, inert gas is introduced into the vacuum treatment chamber and at least one of the polymeric film raw material monomers is allowed to be present in the vacuum treatment chamber and high frequency power is applied to the injection mold to decompose at least one of the monomers by plasma to form the rigid film on the heat insulating membrane.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an injection mold capable of preventing sink marks and weld lines from forming on the outer surface of a molded article of a thermoplastic resin, a method of manufacturing the same, and an apparatus for manufacturing the same.

[0002]

2. Description of the Related Art Conventionally, a thermoplastic resin injection molding method has advantages such as good productivity and easy molding of a complicated shape, so that it is widely used for various industrial products and daily necessities. in use. When molding a synthetic resin with a mold, a product with high mold fidelity is expected, but in actuality, the difference between the volume in the molten state and the volume in the solidified state during molding of the synthetic resin, or the molded product during cooling Due to the non-uniform temperature distribution, sink marks and weld lines are generated, and a molded product exactly as a mold cannot be obtained. The sink marks are liable to be concentrated on the rear surface or the front surface of the thick part in a molded product having a thick part partially. In addition, at a place where the molten resin flowing in the mold joins, fusion between the resins is incomplete and a weld line is likely to occur.

Since sink marks and weld lines generated on the surface of a molded article significantly lower the commercial value and sometimes reduce the required molding accuracy, various measures have conventionally been taken. For example, a device provided with a heating device and a cooling device corresponding to a location where a weld line is generated in a mold (Japanese Patent Laid-Open No.
-2759), a device that applies a shearing force to a part of the molten resin in a mold (Japanese Patent Application Laid-Open No. 3-274127), a device that transmits ultrasonic waves to a flowing resin (Japanese Patent Application Laid-Open No. 4-90309), and the like. I can do it. Each of these methods requires the installation of special auxiliary equipment and equipment, and is quite effective in preventing the occurrence of weld lines, but is still unsatisfactory.

In order to prevent the occurrence of sink marks,
Japanese Unexamined Patent Publication No. 56-167410 discloses a molded product in which sink is not generated on the surface by locally heating the back surface of a spot where a sink occurs to a temperature equal to or higher than a mold temperature with a heater and delaying the cooling temperature of that spot from other locations. Japanese Patent Publication No. 61-9126 discloses a method of forming a through-hole of a porous member on the back surface of a part of a molded product where sink is likely to occur, and introducing compressed air through the through-hole to form the molded article. There is disclosed a method of obtaining a molded product having no surface sink by pressing the back surface of the product. However, these methods have problems that the mold becomes complicated and the molding cycle becomes long.

On the other hand, there has been proposed a method of forming a heat insulating film on the inner surface of a mold instead of trying to solve the problem mechanically and apparatus as described above. Japanese Patent Application Laid-Open No. 4-219912 proposes a mold for simultaneously eliminating weld lines and flow marks. In this mold, the inner surface of the mold cavity is formed of a metal oxide, a silicate compound, a silicate composite compound, or a plastic having a thermal conductivity of 0.1 cal / cm · sec · ° C. or less and a thickness of 0.1 to 50 μm. The coating process is performed with a thin film.

Japanese Patent Application Laid-Open No. 6-143294 discloses a mold which has a fine uneven surface such as a satin-like surface, gives a faithful molding to the mold, and withstands repeated molding.
Thermal conductivity of 0.002 cal / cm · sec on the inner surface of the mold cavity
-The temperature is below ℃, the glass transition point is above 200 ℃, and the thickness is 0.
A structure in which a polyimide layer having a thickness of 02 to 2 mm is provided and the surface of the polyimide layer has a fine unevenness has been proposed.

Furthermore, since the sink is not eliminated simply by forming a heat insulating film, Japanese Patent Application Laid-Open No. Hei 6-246797 discloses that the contact angle with water is 40 ° at the inner surface of the mold cavity corresponding to the outer surface of the molded product. A heat-insulating thin film of an aromatic polyimide or the like having a thermal conductivity of 0.03 to 90 degrees is used.
A mold for injection molding formed to a thickness of 5 cal / cm · sec · ° C. is disclosed, and it is stated that this mold can prevent sink marks and weld lines on the outer surface of a molded product. That is, in this mold, in the mold, the cooling of the side that becomes the outer surface of the molded article is delayed, the side that becomes the back side of the molded article is rapidly cooled, and the mold is peeled off from the inner surface of the mold cavity by volume shrinkage. It is intended to prevent sink marks from appearing on the outer surface in order to cause sink marks.

In addition, Japanese Patent Application Laid-Open No. 6-45382 discloses a mold in which a titanium compound, particularly titanium nitride, is coated on the inner surface for transfer molding to improve the mold accuracy and to increase the surface hardness to extend the life of the mold. However, there is no heat insulating film on the inner surface of the metal mold cavity.

[0009]

In order to prevent the occurrence of sink marks and weld lines on a molded article, it is effective to provide a heat insulating film on the injection mold. However, an aromatic resin such as polyimide is provided on the mold surface. When a polymer film is provided alone, if the resin is repeatedly injection-molded, the hardness of the polymer film itself is insufficient, so that the resin itself being injection-molded rubs or scratches the mold surface, and the heat-insulating film deteriorates in a short time. Progressive and impractical.
This deterioration can be prevented by forming a metal film on the heat insulation film,
In order to form the metal film, a separate device other than the heat-insulating film forming device is required, which increases the cost of mold production.

An object of the present invention is to provide a mold for injection molding which can prevent sink marks and weld lines from occurring, is durable and can be easily manufactured, and provides a method and apparatus for easily manufacturing the mold. It is intended for.

[0011]

According to the present invention, the above object is achieved by forming a hard film of amorphous carbon on a surface of an injection mold in contact with a molding resin through a heat insulating thin film of a polymer. To achieve. The hard film of amorphous carbon is preferably a film formed by decomposing a polymer monomer for forming the heat insulating thin film. In the mold of the present invention, an injection mold is prepared in a vacuum processing chamber evacuated, the atmosphere is set to a heating atmosphere, and the injection molding mold is heated. After forming a heat-insulating thin film of a copolymer polymer film on the surface of the injection mold by allowing vapor of the polymer film raw material monomer to exist, an inert gas is introduced into the vacuum processing chamber and the polymer A polymer film material monomer is decomposed by plasma generated by applying high-frequency power to the injection molding die in the presence of at least one kind of film material monomer to form an amorphous carbon hard film on the heat insulating thin film. By forming, it can be easily manufactured. The method for manufacturing a mold according to the present invention includes a vacuum processing chamber, a vacuum exhaust pipe for evacuating the vacuum processing chamber, and a polymer film raw material monomer for supplying vapor of the polymer film raw material monomer into the vacuum processing chamber. A heating heater for heating a surface in contact with the atmosphere in the vacuum processing chamber, and connecting a linear cathode wire extending from an outdoor high-frequency power supply to an injection mold prepared in the vacuum processing chamber. It can be carried out accurately by using the device.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a cross-sectional view in which a part of an injection mold is enlarged. The injection mold 2 is made of a heat-insulating copolymer such as pyromellitic anhydride (PMD) on the surface of the mold 1.
A) A heat-insulating thin film of a copolymer composed of polyimide or polyurea, and 3 is a hard film of amorphous carbon formed on the heat-insulating thin film 2. The heat insulating thin film 2 is formed to have a thickness of, for example, 100 μm, and the hard film 3 made of amorphous carbon has a thickness of, for example, 5 μm and a Vickers hardness of about 8 μm.
A 00Hv film is formed. The thickness of the heat insulating thin film 2 is
Determined in consideration of the film material and the molding temperature of the molding resin, when the melted polypropylene at 210 ° C. is injection-molded, the heat insulating coefficient of the polyimide heat-insulating thin film 3 is 0.03 to 0.5 cal / cm. Formed on the mold surface to a thickness of 100 μm so as to be less than sec · ° C. The thickness of the hard film 3 is determined by the glow discharge time.

The heat insulating thin film 2 and the hard film 3 are empirically formed on the surface of the mold facing the surface of the molded product where sink marks and weld lines are likely to occur due to the shape of the molded product.
It is desirable that these films 2 and 3 are formed in close contact with each other so as not to be separated from each other during the injection molding, and are easily formed in a series of steps. It is convenient to use the apparatus shown in FIG. is there.

The device will be described.
, A vacuum exhaust pipe 5 connected to a vacuum pump, and evaporating vessels 8, 9 connected via introduction pipes 6, 7, and Ar
In a vacuum processing chamber 11 having a gas introduction pipe 10 for introducing an inert gas such as a gas, an injection molding mold 1 heated to, for example, 200 ° C. is placed by a suitable means such as an insulator.
Suspended or installed in an electrically insulated state from 1,
A linear cathode 13 connected to a high-frequency power supply 12 outside the vacuum processing chamber 6 was connected to the mold 1. The evaporation vessels 8 and 9 are made of glass, stainless steel, Al, Al alloy, etc., and are provided with evaporation source heaters 15 and 16 around them to evaporate the polymer raw material monomers 17 and 18 filled in the evaporation sources. A heater 19 is provided in the vacuum exhaust pipe 5, the introduction pipes 6, 7 and the vacuum processing chamber 11, and the mold 1 prepared inside the processing chamber 11 is processed in a heating atmosphere. The illustrated evaporation vessels 8 and 9 have a diameter of 10
0 mm and length 265 mm.

When a PMDA-based polyimide film is formed on the mold 1 as a heat-insulating thin film 2 by using this apparatus, and an amorphous carbon hard film 3 is formed thereon, one of the evaporation vessels 8 is provided with a PMDA-based film. 20 high polymer raw material monomers
0 g and heated to 206 ° C., and the other evaporating vessel 9 was charged with 200 g of 4,4 diaminodiphenyl ether (ODA).
g and heated to 186 ° C., and the heater 19 was operated to set the vacuum processing chamber 11 to a heating atmosphere of 200 ° C.
The mold 1 heated to 200 ° C. is installed therein, and the inside of the vacuum processing chamber 11 is evacuated to 10 ⁻² Pa. And both evaporation vessels 8,
Open the valves 20, 21 of the inlet pipes 6, 7 extending from 9,
After about 5 hours, the evaporated polymer is vapor-deposited and polymerized on the surface of the mold 1 to form a heat-insulating thin film 2 of 100 μm of PMDA-based polyimide. Thereafter, the valve 22 of the gas introduction pipe 10 is inserted into the vacuum processing chamber 11 while the valves 20 and 21 are opened.
And the pressure in the chamber 11 is reduced to 2P by introducing an inert gas.
a from the high frequency power supply 12 to the mold 1 at a frequency of 13.5.
Glow discharge is generated by applying high frequency power of 6 MHz and 200 W. When this plasma is maintained for 20 minutes, the polymer monomer introduced into the vacuum processing chamber 11 from the evaporation container is decomposed, and a hard carbon film (amorphous carbon) of about 5 μm is formed on the heat insulating thin film 2 of the polyimide. 3 is formed. After that, the valves 20, 21, and 22 are closed and the exhaust valve 4 is closed, the application of the high-frequency power is stopped, and the mold 1 is taken out of the vacuum processing chamber 11. The hard film 3 firmly adheres to the heat insulating thin film 2 thereunder, has a clear two-layer structure as shown in FIG. 1, and obtains a hard film 3 having a Vickers hardness (Hv) of 800 kg / mm ² or more. .

For comparison, at the stage when the heat-insulating thin film 2 of PMDA-based polyimide was formed on the mold 1, the valves 4, 2
When the molds 0, 21, and 22 were closed and the surface of the mold 1 taken out of the vacuum processing chamber 11 was observed, a single-layer polyimide film was confirmed, and the hardness of the film was about 20 k in Vickers hardness.
g / mm ² .

Although various kinds of polymers having heat insulation properties can be used for the heat-insulating thin film 2, it is advantageous to use one that is capable of forming a hard film of amorphous carbon by decomposing monomers of the polymer film by plasma. is there. That is,
The heat-insulating thin film 2 and the hard film 3 can be formed successively without exchanging the raw materials, and the loss of time and raw materials is eliminated. In addition to the above polyimide, polyurea or the like is used for the heat-insulating thin film.
(4,4'-diphenylmethane diisocyanate), M
DA (4,4'-diaminodiphenylmethane) and the like are used. The pressure of the vacuum processing chamber 11, the temperature of the mold 1, the type and number of the monomer for the polymer film, the heating temperature of the evaporation containers 8 and 9 depend on the type of the heat-insulating thin film 2 formed on the mold 1. The thickness is changed depending on the film thickness of the heat insulating thin film 2 to be formed. The film thickness varies depending on the molding temperature of the molding resin, but can be arbitrarily changed by adjusting the film forming time. Further, the magnitude of the high-frequency power is also changed depending on the kind of the polymer film raw material monomer so that an appropriate hard film 3 is formed.
Mold 1 that does not need to form heat insulating thin film 2 and hard film 3
The surface is coated with a paint or other masking, and after the film is formed, the masking is removed to form a heat insulating thin film and a hard film at desired locations.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS In order to mold an injection-molded article 23 having the shape shown in FIGS. 3 and 4 from a melt of polypropylene resin, a fixed-side cavity forming the surface side of the injection-molded article 23 is shown in FIG.
The injection mold 1 having the shape shown in FIG. The mold 1 is made of Playdon steel (manufactured by Daido Steel: NAK80). The dimensions of the injection molded product 23 are 60 mm wide, 150 mm long,
It has a substantially plate-shaped, square-shaped through hole 24 with a thickness of 2 mm, and three ribs 26, 27, 28 with a thickness of 4mm, a width of 5mm, and a length of 30mm on the back surface 25. The description of the mold for the moving-side cavity forming the back surface 25 is omitted. The mold 1
A gate 29 for introducing a resin in a molten state is provided on the side of the.

The fixed side cavity of the mold 1 is roughened by sand blasting, preheated to 200 ° C., and then put into a vacuum processing chamber 11 in a heating atmosphere of 200 ° C. in which a heating heater is operated, and the pressure is increased to 10 ⁻² Pa. Exhaust, PM of evaporation container 8
The DA was heated to 206 ° C. and 4,4 diaminodiphenyl ether (ODA) in the other
C., and the polymer vapor was introduced into the vacuum processing chamber 11 from the evaporation containers 8 and 9 for 5 hours.
A heat-insulating thin film 2 of PMDA-based polyimide having a thickness of 00 μm was formed. Thereafter, while the valves 20 and 21 are open, an inert gas is introduced into the vacuum processing chamber 11 to adjust the pressure in the chamber 11 to 2 Pa.
A high-frequency power of 13.56 MHz and 200 W is applied to generate glow discharge for 20 minutes to decompose the polymer monomer to form a hard film 3 of about 5 μm carbon film (amorphous carbon) on the polyimide heat insulating thin film 2. Formed. The hard film 3 of the mold 1 has a Vickers hardness (Hv) of 800 kg /
mm ² .

The mold 1 is mounted on an injection molding machine so as to face the mold in the movable cavity, the mold temperature is maintained at 50 ° C., and the cavity is filled with a polypropylene resin melt at 210 ° C. for 1.5 seconds. After cooling for 20 seconds, the mold was opened, and an injection molded product 35 having the shape shown in FIG. 3 was taken out.

In the normal molding, the injection molded article 23 having this shape is formed by the portions 31, 3 of the surface 30 opposite to the positions of the ribs.
2 and 33, marked sink marks are generated, and the through holes 24 in the surface 30 are formed.
A weld line is generated at positions 34 and 35 on the opposite side of the gate 29 through the mold. However, when the mold 1 of the present invention is used, sink marks and weld lines are generated on the surface of the injection molded product 23. Did not. In addition, the mold 1 was not deteriorated after 10,000 times of repetitive molding.

For comparison, a 100 μm heat-insulating thin film 2 of PMDA-based polyimide was formed in the mold 1 by the above-mentioned method using the above-mentioned apparatus, and was taken out of the vacuum processing chamber. The Vickers hardness of the heat insulating thin film 2 was 20 kg / mm ² . A fixed-side cavity is formed using this comparative mold, and the mold is mounted on an injection molding machine together with the movable-side cavity mold. The mold is maintained at 50 ° C. in the same manner as described above, and the polypropylene resin is melted at 210 ° C. in the cavity. 1.5 hours filling body
Injection filling was performed in seconds, and after cooling for 20 seconds, the mold was opened, and a comparative injection molded product having the shape shown in FIG. 3 was prototyped. No sink marks or weld lines were observed on the surface of the injection molded product for comparison, that is, on the surface without ribs. However, when this trial production was repeated 100 times, the heat-insulating thin film of PMDA polyimide on the mold surface was deformed and the film was deteriorated, so that further injection molding tests could not be continued.

[0023]

As described above, according to the present invention, a hard film made of amorphous carbon is formed on the surface of an injection molding die in contact with a molding resin via a heat insulating thin film of a polymer. A mold capable of withstanding the molding and preventing the sink and weld line from being generated on the surface of the molded article without deterioration of the heat insulating thin film is obtained. A hard film having good adhesion and no delamination can be formed by decomposing the molecular monomer, and this mold is placed in a vacuum processing chamber in a heated atmosphere in a heated atmosphere. After a vapor of the two types of polymer film raw monomers is present to form a heat insulating thin film of a copolymer film on the surface of the mold, the vapor and an inert gas are introduced into the vacuum processing chamber while introducing the vapor and an inert gas. High frequency for mold By forming a hard film of amorphous carbon on the heat-insulating thin film by applying a force to the plasma by plasma, it can be easily manufactured in a series of steps, and the manufacturing can be suitably performed by the apparatus of claim 5. is there.

[Brief description of the drawings]

FIG. 1 is a sectional view of a main part of an injection mold according to the present invention.

FIG. 2 is a sectional view showing an embodiment of an apparatus for manufacturing an injection mold according to the present invention.

FIG. 3 is a perspective view of an injection molded product.

FIG. 4 is a sectional view taken along a line 4-4 in FIG. 3;

FIG. 5 is a perspective view showing an embodiment of an injection mold according to the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Injection mold, 2 Insulating thin film, 3 Amorphous carbon hard film, 5 Vacuum exhaust pipe, 8.9 evaporation vessel, 10 Gas introduction pipe, 11 Vacuum processing chamber, 12 High frequency power supply, 13 Linear cathode,

Claims (5)

[Claims] 1. A mold for injection molding, wherein a hard film of amorphous carbon is formed on the surface of the mold for injection molding in contact with the molding resin via a heat insulating thin film of polymer. 2. The injection mold according to claim 1, wherein the amorphous carbon hard film is a film formed by decomposing a polymer monomer for forming the heat insulating thin film. . 3. An injection molding die is prepared in a vacuum-evacuated vacuum processing chamber, and the atmosphere is heated and the injection molding die is heated. After forming a heat-insulating thin film of a copolymer polymer film on the surface of the injection mold by allowing vapor of the monomer for the molecular film to exist, an inert gas is introduced into the vacuum processing chamber, and At least one of the monomers is present,
A high-frequency power is applied to the injection molding die to decompose the polymer film material monomer to form a hard amorphous carbon film on the heat insulating thin film. Mold manufacturing method. 4. The method according to claim 1, wherein pyromethylic anhydride and 4,4 diaminodiphenyl ether are used as the raw material monomers for the polymer film, and the vapors of these raw material monomers are present in the vacuum processing chamber to generate plasma. A method for producing an injection mold according to claim 3. 5. A vacuum processing chamber, a vacuum exhaust pipe for evacuating the vacuum processing chamber, and an evaporation source container containing a polymer film raw material monomer for supplying vapor of the polymer film raw material monomer into the vacuum processing chamber. A heating heater for heating a surface in contact with the atmosphere in the vacuum processing chamber, and a linear cathode wire extending from an outdoor high-frequency power supply connected to an injection mold prepared in the vacuum processing chamber. Manufacturing equipment for molding dies.