JPH0538721A - Molding die and molding method using the same - Google Patents

Abstract

PURPOSE:To mold in the state that surface layer only is at a high temperature and make the reproducibility of mold surface good by forming a wall surface of a mold cavity with ceramic of small heat conductivity or the like. CONSTITUTION:A ceramic or a cermet thin layer is formed on a surface 9 of a mold constituting a mold cavity, and the thickness of the thin layer is 0.05-2mm and the heat conductivity of the thin layer is 0.04cal/cm.sec. deg.C or less. Otherwise, a material of low heat conductivity such as synthetic resin of 0.001cal/cm.sec. deg.C or less heat conductivity or the like is formed on the surface of said thin layer of ceramic or the like in the thickness of 0.001mm or over to 0.05mm. When heated and plasticized resin is injected into a mold cavity, the thin layer is heated by the heated resin and its temperature is risen and molded in the state that its surface layer only is at a high temperature, and the reproducibility of mold surface becomes favorable. Further, when the heated gas is introduced from a duct 8, gas is passed through a circumferential channel 7 and exhausted outside from a gate 4. The temperature of gas should be higher than the mold temperature, preferably by 100 deg.C or over.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a synthetic resin mold and a molding method using the mold.

[0002]

2. Description of the Related Art A thermoplastic resin is usually injected into a mold cavity for molding to improve reproducibility in imparting a shape condition of a mold surface to a molded product and to improve the gloss of the molded product. It can be achieved to some extent by selecting molding conditions such as increasing the pressure or increasing the injection pressure.

The mold temperature has the greatest effect among these factors, and the higher the mold temperature, the better.
However, when the mold temperature is increased, the cooling time required for cooling and solidifying the plasticized resin becomes longer, and the molding efficiency is lowered. There is a demand for a method that improves the reproducibility of the mold surface without increasing the mold temperature, and that does not increase the required cooling time even if the mold temperature is increased. There is also a method in which a heating hole and a cooling hole are attached to the mold and heating and cooling of the mold are repeated by alternately flowing a heat medium and a refrigerant, but this method also consumes heat. Many, cooling time becomes long.
Also, it is said that the reproducibility of the mold surface is improved when injection molding is performed using a mold in which the mold wall surface forming the mold cavity is coated with polytetrafluoroethylene or the like. It is necessary to coat with a heat-resistant polymer such as tetrafluoroethylene to obtain the effect, and it is necessary to coat the polymer with a considerable thickness. There was a problem.

On the other hand, a method has been proposed in which only the mold wall surface of an iron mold cavity is rapidly heated by high-frequency induction heating, and injection molding is immediately performed with only the mold surface being heated (Japanese Patent Publication No. 58-40504). 57-4748, etc.). However, this method is uncommon because the high frequency induction heating device is very expensive.

[0005]

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems. INDUSTRIAL APPLICABILITY The present invention improves reproducibility of imparting mold surface properties to a molded product when molding a molded product by a method such as injection molding, compression molding, and hollow molding of a thermoplastic resin. If so, it relates to a method of making the surface of the molded product a mirror surface as close as possible. In particular, when the synthetic resin contains a filler such as glass fiber or asbestos, the surface of the mold is rough and a smooth surface cannot be obtained. The present invention ameliorates these problems.

[0006]

According to the present invention, the main mold material is made of iron or a metal having a thermal conductivity equal to or higher than that of iron, and only on the surface of the mold wall surface forming the mold cavity. There is a thin layer of ceramics or cermet,
The thin layer has a thickness of 0.05 to 2 mm, and the thermal conductivity of the thin layer is 0.04 cal / cm · sec · ° C. or less. Thermal conductivity of ceramics or cermet thin layer is 0.001-
It is 0.04 cal / cm · sec · ° C., and is a synthetic resin molding die in which a thin layer having a low thermal conductivity of less than 0.001 cal / cm · sec · ° C. is present on the surface of the thin layer.

Further, the above-mentioned mold cavity is characterized in that a fluid heated to a temperature higher than 100 ° C. is introduced into the mold cavity to heat only the mold surface and then a synthetic resin is injected. This is a synthetic resin molding method. The present invention will be described below. The synthetic resin used in the present invention is generally a thermoplastic resin that can be used for injection molding and the like. For example, styrene polymers and copolymers thereof, olefin polymers such as polyethylene and polypropylene and copolymers thereof, vinyl chloride polymers and copolymers, and general thermoplastic resins such as polyamide and polyester can be used.

Various fillers can be added to these resins.
For example, one kind or two or more kinds of glass fiber, asbestos, calcium carbonate, talc, calcium sulfate, foaming agent, wood powder and the like are used. The iron or a metal having a thermal conductivity equal to or higher than that of iron described in the present invention is iron or an alloy mainly composed of iron, and the thermal conductivity of iron is 0.12 cal /
It is a metal having a thermal conductivity almost equal to or higher than cm · sec · ° C.

The thermal conductivity described in the present invention is 0.04 cal.
As the ceramics or cermet having a heat conductivity of / cm · sec · ° C or less, a ceramic or a cermet having a thermal conductivity of the above value or less may be selected and used. Thermal conductivity is 0.04
cal / cm · sec · ° C or less, preferably 0.01c
al / cm · sec · ° C or less, and the thickness of the thin layer is 0.05 to 2 mm, preferably 0.1 to 1 mm,
More preferably, it is 0.2 to 1 mm.

This thermal conductivity indicates the thermal conductivity of the thin layer, and includes a thin layer having a small thermal conductivity because a large number of bubbles are contained in the thin layer. This may be a thin layer containing a large number of bubbles depending on the method of forming the thin layer, and such a thin layer has small thermal conductivity due to the bubbles. Such a thin layer having an apparently low thermal conductivity can be favorably used in the present invention.

Particularly in the present invention, various ceramics or cermets which are alloys of ceramics and metals can be favorably used. For example, ZrO ₂ , ZrO ₂ —CaO, Zr
_{O 2 -Y 2 O 3, ZrO} 2 -MgO, K 2 O-Ti
_{O 2, CaO-SiO 2,} ZnO 2 -SiO 2 and the like can be used satisfactorily. ZrO ₂ or a compound containing ZrO ₂ has a low thermal conductivity and is preferable for the present invention. Further, those containing a large number of bubbles at the time of thermal spraying have a remarkably low thermal conductivity and are particularly preferable. Z among the ZrO ₂ series
rO ₂ —Y ₂ O ₃ is more preferred. In addition, NaZr ₂ (P
O ₄ ) ₃ and (Ca _1-x , Mgx) Zr ₄ (PO ₄ ) ₆ (x
= 0 to 0.5) and other ceramics or cermets containing Zr can be favorably used. Also, 2CaO / Si
O ₂ also has a small thermal conductivity and can be used favorably. In particular, since there is a case where the distinction between ceramics and cermet may be unclear, hereinafter, ceramics or cermet will be referred to as ceramics and the like.

According to the present invention, by forming the wall surface of the mold cavity with a thin layer of ceramics or the like having a small thermal conductivity,
When the heat-plasticized synthetic resin is injected into the mold cavity, the thin layer is heated by the heating resin to raise the temperature and is molded in a state where only the surface layer has a high temperature. Become. If the thin layer of ceramics or the like is too thick, there is a drawback that the cooling time becomes long, and if it is too thin, the effect of improving the mold surface reproducibility becomes small. The smaller the thermal conductivity of ceramics, the larger the effect of improving the reproducibility of the mold surface, which is preferable.

There are various methods for forming a thin layer of ceramics or the like according to the present invention. Coating treatment using a special solution, plasma spraying,
Combustion gas spraying, physical and chemical vapor deposition (PVD, CV
D) etc. Plasma spraying will be described as a typical example. When a positive and negative current difference is applied to the counter electrode and an electric current is applied, an arc is generated, resulting in a very high temperature. When a gas is made to flow in this arc, the gas dissociates and electrons are taken off,
That is, they are released in the form of atomic nuclei to generate plasma. Plasma spraying is a method in which a substance of the type to be melt-coated is powdered or rod-shaped and inserted into plasma.

The droplet flying in the plasma needs to obtain sufficient energy and momentum from the plasma, and controls the plasma temperature, velocity, atom density in excited state, and electron density. Details of coating such as ceramics by thermal spraying are shown in Industrial Materials, Vol. 35, No. 9, pages 26 to 60, and Industrial Materials, Vol. 37, No. 16, pages 9 to 80. And select and use these methods.

Further, according to the present invention, the thermal conductivity of the above-mentioned ceramic or cermet thin layer is 0.001 to 0.04 ca.
A synthetic resin molding die in which a thin layer of an object having a low thermal conductivity of less than 0.001 cal / cm · sec · ° C. is formed on the surface of the thin layer. .
The thermal conductivity of general ceramics or cermet is 0.0
01 cal / cm · sec · ° C or higher.

ZrO ₂ --Y which can be preferably used in the present invention
The thermal conductivity of ₂ O ₃ is 0.004 cal / cm · sec ·
℃. If fine bubbles are added to this, the thermal conductivity further decreases. However, 0.001 cal / cm ・ sec ・ ° C
If it is less than the above range, problems occur in strength and surface smoothness. For the purpose of further lowering the thermal conductivity and smoothing the surface, it is effective to apply a thin layer of an object such as a synthetic resin having a small thermal conductivity on the ceramics or the like so that the ceramics and the like are made to exist. The thermal conductivity of synthetic resins is generally 0.0
If it is less than 01 cal / cm · sec · ° C. and the synthetic resin layer is thin, there are few problems peculiar to the synthetic resin layer.
It can also solve the problem of mirror surface and durability.

As the object for forming the thin layer having a low thermal conductivity described in the present invention, the synthetic resin is preferable as described above,
It is a thermoplastic resin or a thermosetting resin, and an epoxy resin, a polyimide resin, a fluorine resin, or the like is preferable. The thin layer of synthetic resin or the like is preferably less than 0.05 mm, more preferably 0.005 mm or more and 0.04 mm or less. 0.00
If it is less than 1 mm, the heat insulating effect is difficult to appear. The synthetic resin also has a function of smoothing the irregularities on the surface of a thin layer of ceramics or the like, and the synthetic resin enters into the recesses of the surface of the ceramics or the like to smooth the surface. The thickness of the thin layer in this case is expressed as an average thickness.

In order to smooth the surface of ceramics or the like, a very thin (several μm) silicone coating material can be applied to the outermost surface. Such very thin surface coatings can be carried out as needed and are included in the present invention. Further, in the present invention, a better surface of the molded product can be obtained by introducing a heated gas body or the like into the mold cavity. By introducing a fluid such as a heated gas body into the mold cavity, the mold wall surface forming the mold cavity can be selectively heated.

The temperature of the heating gas introduced into the mold cavity may be higher than the mold temperature, but it is more effective to introduce the high temperature gas for a short time, and the gas temperature is 100% higher than the mold temperature.
℃ or more, preferably 200 ℃ or more, more preferably 30
A gas having a temperature of 0 ° C. or higher is preferable. There are various possible methods for introducing the heating gas into the mold cavity,
As one example, a pore having a size that allows gas to pass but not molten resin can be opened in the mold cavity, and the heating gas is introduced through the pore.

Therefore, it is necessary to provide pores at positions suitable for the inlet and outlet of the heating gas. The size of pores through which gas can pass but molten resin cannot pass varies depending on the type of resin, molding conditions, etc.
Elongated pores with 0.2 mm voids are suitable. However, the usual mold is not airtight, and the parting surface satisfies the condition of this void. Particularly, in the mold having a hermetically-sealed parting surface, the holes are specially provided to introduce the gas.

A method in which the heated gas is blown into the mold cavity from the nozzle of the injection molding machine can also be used favorably. The present invention is characterized in that the heating gas is introduced into the mold cavity just before the injection of the plasticized resin to heat only the surface of the mold, but the heating gas introduced into the mold cavity causes the heating of the mold cavity. It is also possible to mold the resin while keeping it under pressure.

The effect is high when high-speed injection molding is performed using the mold of the present invention. That is, in order to obtain the effect of the present invention, the heat-melted synthetic resin injected into the mold cavity is
It is necessary to press the mold wall surface with a high pressure in a state of being above the softening temperature. High speed injection molding using the mold of the present invention is the most preferred method of the present invention. The high-speed injection molding described here is a molding in which the injection is completed in less than 1 second and a high injection pressure is applied to the mold wall surface, preferably 0.5 seconds or less, more preferably 0.3 seconds or less. ..

The present invention will be described with reference to the drawings. FIG. 1 schematically shows only the portion of the mold section according to the present invention,
Fixed mold 1, moving mold 2, mold cavity 3, central direct gate 4, cooling water hole 5 for cooling the mold, O-ring 6 for holding the mold cavity under pressure, the periphery of the mold cavity And a conduit 8 for introducing a pressurized gas body or a heated gas body into the mold cavity.

When the heated gas body is introduced through the conduit 8, the gas body passes through the circumferential groove 7 and exits from the mold through the gate 4. The mold wall surface 9 forming the mold cavity has a thin layer of ceramics or the like, which is a feature of the present invention, and the thickness of the thin layer is 0.
005-2 mm, and the thermal conductivity of the thin layer is 0.04c
Al / cm · sec · ° C or less. Alternatively, the surface of the thin layer of the ceramic or the like has a thermal conductivity of 0.001 ca.
An object having a low thermal conductivity such as a synthetic resin of less than 1 / cm · sec · ° C. is formed in a thickness of 0.001 mm or more and less than 0.05 mm.

Although the present invention has been described with reference to the injection molding method, it can be used not only in the injection molding method but also in the extrusion hollow molding method, the compression molding method and the like.

[0026]

EXAMPLES The following experiments (1), (2) and (3) were carried out using a mold using the following items. Main mold: made of steel (S55C), having a 2 mm-thick flat plate mold cavity, and the mold surface forming the mold cavity is a mirror surface. The thermal conductivity of the steel material (S55C) is 0.12 cal / cm · sec · ° C. Thin-layer ceramics: Y ₂ O ₃ · ZrO ₂ is used as the ceramic forming the mold surface of the mold cavity, Y ₂
The thermal conductivity of O ₃ · ZrO ₂ is 0.004 cal / cm ·
sec / ° C. Thin-layer polyimide: Toray Industries, Inc., heat-resistant insulation varnish "Trenis # 3000" Injection molding synthetic resin: Asahi Kasei Corporation rubber-reinforced polystyrene "Styron # 49"
5 "(black colored product) When only the above-mentioned main mold is used (Comparative example) (1), when a ceramic is sprayed on the above-mentioned main mold and the surface of which is mirror-polished is used ( 2) A ceramic reinforced polystyrene is sprayed on the main mold, and polyimide is applied on the surface of the main mold in a mirror-like manner. Using the mold in each case, rubber-reinforced polystyrene as a synthetic resin {Asahi Kasei Co., Ltd. , Stylon 495 (black colored product)} was used for injection molding, and the glossiness of the molded product was measured. The results are shown in Table 1. The gloss of the molded product was remarkably improved by coating the mold surface with ceramics or with ceramics and polyimide.

[0027]

[Table 1]

[0028]

According to the present invention, a molded article having excellent mold surface reproducibility can be economically obtained.

[Brief description of drawings]

FIG. 1 is a sectional view showing an example of an injection molding die used for carrying out the method of the present invention.

[Explanation of symbols]

1 Fixed Side Mold 2 Moving Side Mold 3 Mold Cavity 4 Central Direct Gate 5 Cooling Water Hole 6 O Ring 7 Circumferential Groove 8 Gas Conduit 9 Thin Layer with Low Thermal Conductivity on Mold Wall Surface or Ceramics A thin layer of low thermal conductivity such as synthetic resin formed on the surface of the layer.

Claims (3)

[Claims] 1. The main mold material is made of iron or a metal having a thermal conductivity equal to or higher than that of iron, and a thin layer of ceramics or cermet is present only on the surface of the mold wall forming the mold cavity. The thickness of the thin layer is 0.05 to
2 mm, and the thermal conductivity of the thin layer is 0.04 cal /
Mold for synthetic resin molding with cm / sec / ° C or less. 2. A ceramic or cermet thin layer having a thermal conductivity of 0.001 to 0.04 cal / cm.sec.
C. and 0.001 cal / cm on the surface of the thin layer.
The mold according to claim 1, wherein there is a thin layer having a low thermal conductivity of less than sec · ° C. 3. Injecting a fluid heated to a temperature of 100 ° C. or higher from the mold temperature into the mold cavity according to claim 1 or 2 to heat only the mold surface and then injecting a synthetic resin. A method for molding a synthetic resin characterized by: