JPH07178765A - Insert molding method - Google Patents

Abstract

PURPOSE:To make the fixing of an insert part stronger without raising the temperature of a die by a method wherein the wall surfaces of a main die made of a metal, in which an insert part is set, are coated with a heat-insulating layer made of a heat-resistant polymer of a specified heat-conductivity, by a specified thickness. CONSTITUTION:The surfaces of a die around a depressed part 8 in which an insert part 10 is set, of a main die 7 are coated with a specified heat-insulating layer 9. This heat-insulating layer 9 is formed of a heat-resistant polymer of which the heat-conductivity is 0.002cal/cm.sec. deg.C or less, e.g., a non-crystal heat- resistant polymer such as polyimide, etc., and the thickness is set at 0.01-2mm. Also, it is preferable that the polymer is a tough polymer of which the rupture ductility is 10% or higher. The insert part 10 which is heated in advance is set in the depressed part 8 of the cooled die 7, and an article is injection-molded by closing the die.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is insert molding in which thermoplastic resin injection molding, blow molding, etc., in which a metal or other material part is set in advance in a mold and the part is embedded in the molded product. Pertaining to the law.

[0002]

2. Description of the Related Art Insert molding in which parts such as bolts and nuts are embedded in a molded product during molding is widely used in injection molding, extrusion blow molding and the like. It is necessary that the insert part be firmly embedded in the molded part, after which the insert part is not separated from the molded part during assembly and use.
The molding conditions are changed so that the insert part is sufficiently embedded in the molded product and firmly fixed to the molded product. The injection pressure is increased, the resin temperature is increased, or the mold temperature is increased.

The mold temperature has the greatest effect among these factors, and the higher the mold temperature, the better.
However, if the mold temperature is increased, the cooling time required for the cooling and solidification of the plasticized resin becomes longer, and the molding efficiency is lowered.
For this reason, there is a demand for a method that enables good insert molding without raising the mold temperature, and that does not lengthen the required cooling time even if the mold temperature is raised. For heating the mold,
Although a method of repeating heating and cooling of a mold by alternately mounting a cooling medium and alternately flowing a heating medium and a cooling hole is also performed, this method consumes a large amount of heat and requires a long cooling time.

A method for improving mold surface reproducibility by coating a mold wall forming a mold cavity with a substance having a low thermal conductivity is disclosed in US Pat. No. 3,544,518 for injection molding. Also in extrusion blow molding, a method of coating the mold wall surface with a substance having a small thermal conductivity is disclosed in US Pat. No. 5,041,247. The object of the present invention is to increase the mold temperature without increasing
An object of the present invention is to provide an insert molding method capable of firmly fixing an insert part to a molded product.

[0005]

That is, according to the present invention, in insert molding of a thermoplastic resin, the main mold wall surface made of metal for setting an insert part such as a metal part to be inserted has a thermal conductivity of 0. .002cal /
An insert molding method, characterized in that a heat-insulating layer made of a heat-resistant polymer having a temperature of cm · sec · ° C or less is coated to a thickness of 0.01 to 2 mm for molding.

The present invention will be described in detail below. The synthetic resin that can be used in the insert molding method of the present invention is not particularly limited as long as it is a thermoplastic resin that can be used in general injection molding, extrusion blow molding and the like. For example, styrene polymer, ABS resin or copolymer thereof, olefin polymer such as polyethylene and polypropylene, modified polyphenylene ether resin, vinyl chloride polymer or copolymer thereof, polycarbonate, polyamide, polyester,
Thermoplastic resins generally used for injection molding or extrusion blow molding such as polyacetal can be used.

Even when these resins are blended with various reinforcing materials or various fillers, or when polymer alloys are used, they can be similarly favorably used. For example, one or more kinds of rubber, glass fiber, asbestos, calcium carbonate, talc, calcium sulfate, wood powder and the like can be blended with the above resin. The main mold material made of the metal described in the present invention is generally used for molding synthetic resins such as iron or steel containing iron as a main component, aluminum or an alloy containing aluminum as a main component, zinc alloy, and beryllium-copper alloy. Including metal molds. Particularly, steel materials can be used favorably.

The heat-resistant polymer used for the heat insulating layer in the insert molding method of the present invention preferably has a glass transition temperature of 150 ° C. or higher, more preferably 190 ° C. or higher, and / or a melting point of 250 ° C. or higher. It is preferably a heat-resistant polymer having a temperature of 280 ° C. or higher. The heat conductivity of the heat resistant polymer is 0.002 cal / cm · sec ·
C. or less, and general polymers have a thermal conductivity of less than this. A tough polymer having a breaking elongation of 10% or more is preferable. The method of measuring elongation at break is ASTM D6
The tensile speed at the time of measurement is 5 mm / min.

Polymers which can be favorably used as the heat insulating layer in the present invention are heat resistant polymers having an aromatic ring in the main chain, and various amorphous heat resistant polymers soluble in organic solvents, various polyimides and the like are favorably used. Can be used. Examples of the non-crystalline heat resistant polymer include polysulfone, polyether sulfone, polyallyl sulfone, polyarylate, polyphenylene ether, polybenzimidazole and the like. The repeating units of these typical heat resistant polymers are shown below.

[0010]

[Chemical 1]

[0011]

[Chemical 2]

[0012]

[Chemical 3]

[0013]

[Chemical 4]

[0014]

[Chemical 5]

There are various kinds of polyimides, but linear high molecular weight polyimides can be preferably used. Generally, a straight chain type high molecular weight polyimide has a large breaking elongation and excellent durability.
Examples of linear high molecular weight polyimides that can be favorably used in the present invention are shown in Table 1. In addition, Tg is a glass transition temperature,
Also, n represents the number of repeating units.

[0016]

[Table 1]

The Tg of the straight-chain polyimide differs depending on the constituents, examples of which are shown in Tables 2 and 3. Tg is 15
A polymer of 0 ° C. or higher is preferably used, more preferably 190 ° C. or higher, particularly preferably 230 ° C. or higher.

[0018]

[Table 2]

[0019]

[Table 3]

Table 4 shows various soluble polyimides which can be favorably used in the present invention and can be dissolved in a solvent.

[0021]

[Table 4]

Injection molding has an economic value in that a molded product having a complicated shape can be obtained by molding once. In order to coat the surface of this complicated mold with a heat resistant polymer and firmly adhere it, a heat resistant polymer solution or / and a heat resistant polymer precursor solution is applied and then heated to obtain a heat resistant polymer. Most preferably, a coalescence is formed. Therefore, the heat resistant polymer or the heat resistant polymer precursor used in the present invention is preferably soluble in a solvent.

The above amorphous heat-resistant polymer, soluble polyimide or polyimide precursor is used by dissolving it in various solvents such as tetrahydrofuran, dimethylformamide, dimethylacetamide, N-methylpyrrolidone and the like. The linear polyimide precursor is synthesized, for example, by subjecting an aromatic diamine and an aromatic tetracarboxylic dianhydride to a ring-opening polyaddition reaction.

[0024]

[Chemical 6]

These polyimide precursors are heated to undergo a dehydration cyclization reaction to form a polyimide. The most preferable linear polyimide precursor is polyamic acid, and the repeating unit of a typical example thereof and the repeating unit of polyimide obtained by imidizing the same are shown below.

[0026]

[Chemical 7]

[0027]

[Chemical 8]

[0028]

[Chemical 9]

[0029]

[Chemical 10]

The above polyimide precursor polymer is N-
It is dissolved in a solvent such as methylpyrrolidone and applied on the wall surface of the mold. These heat-resistant polymer solution, or heat-resistant polymer precursor solution, to adjust the viscosity at the time of coating,
Additives for adjusting the surface tension of the solution and thixotropy can be added, and / or a small amount of additives for improving the adhesion to the mold can be added.

Regarding the heat resistant polymer used for the heat insulating layer,
Although the non-crystalline heat-resistant polymer and polyimide have been described, the present invention is basically not limited to these. Epoxy resin, silicone resin and the like having flexibility are usable depending on molding conditions. In the insert molding method of the present invention, it is necessary that the heat-insulating layer of the film made of a heat-resistant polymer and the main mold have a large adhesive force, and 0.5 k at room temperature.
g / 10 mm width or more, more preferably 0.8 kg / 10 mm width or more, particularly preferably 1 k
g / 10 mm width or more. This adhesion means cutting the adhered heat insulating layer into a width of 10 mm, and 20 m in the direction perpendicular to the adhesive surface.
The peeling force when pulled at a speed of m / min. Although the peeling force varies considerably depending on the measurement place and the number of times of measurement, it is important that the minimum value is large, and it is preferable that the peeling force is stable and large. The adhesion force described in the present invention is the minimum value of the adhesion force of the main part of the mold.

The insert molding method of the present invention further improves the smoothness of the surface of a thin layer of a heat insulating material such as polyimide, further improves the scratch resistance of the surface, or improves the releasability. Therefore, another material thinner than about 1/10 of the thickness of the polyimide layer or the like can be applied to the polyimide surface or the like as necessary. It is also possible to coat the surface of a synthetic resin sheet or mold with a coating generally used as a hard coat for improving scratch resistance. For example, a thermosetting silicone-based hard coating agent, particularly a hard coating agent having excellent adhesion, which is obtained by blending a silicone-based hard coating agent with an epoxy-based substance, can be favorably used and is preferable for the present invention. It is also possible to apply a fluororesin or a silicone-based polymer in order to improve the releasability.

In the insert molding method of the present invention, at least the wall surface of the main mold for setting the insert parts is covered with the heat insulating layer. Widely covering other mold wall surfaces with a heat insulating layer is appropriately selected as needed. In the present invention, the insert part refers to a general insert part that is insert-molded when a variety of other articles are attached to the molded article, or when the molded article is combined with other articles and used, and is made of metal. Examples include bolts, nuts, round bars, square bars, and hooks. It is preferable that the insert part is heated during molding and then set in the mold. 50 to 1 insert parts
It is particularly preferable to set the temperature after heating to 50 ° C.

The thickness of the heat insulating layer is appropriately selected within the range of 0.01 to 2.0 mm. Preferably 0.1 to 0.5
mm. If it is less than 0.01 mm, the effect is low and 2.0
It is not necessary to exceed mm. A thickness (cm) / thermal conductivity (cal / cm · sec · ° C) value of 5 to 100 is particularly well suited for use in the present invention, and such a very narrow range is particularly effective. If it is smaller than the range of 5 to 100, the mold surface reproducibility tends to be poor, and if it is larger than this range, the cooling time inside the mold tends to be long, or the mirror-like coating of the low thermal conductive material tends to be difficult. Often occurs.

In the present invention, the main mold temperature is cooled to 80 ° C. or lower, and the mold surface temperature is 100 ° C. or higher for at least 0.1 second after the injected synthetic resin comes into contact with the mold surface. It is preferably molded in the state. The main mold temperature is more preferably 80 ° C. or lower and room temperature or higher. Generally, the mold temperature is 80 ° C. or less for injection molding, and if the mold temperature is higher than 80 ° C., the molding cycle time becomes long and the molding efficiency decreases. If the temperature is lower than room temperature, dew condensation is likely to occur on the surface of the mold. The change in mold surface temperature during injection molding can be calculated from the temperature of the synthetic resin, the main mold, the heat insulating layer, the specific thermoplastic resin, the thermal conductivity, the density, the latent heat of crystallization, and the like. For example, ADINA and ADINAT (software developed at the Massachusetts Institute of Technology) can be used to perform unsteady heat conduction analysis by the nonlinear finite element method.

The present invention will be described with reference to the drawings. Figure 1
The cross-sectional view of the process of insert injection-molding a metal bolt by the method of the present invention is shown. FIG. 2 shows a cross-sectional view of a process of insert injection molding a metal nut by the method of the present invention. FIG. 3 shows a sectional view of a molding process of insert injection molding a metal bolt by a conventional method. 4 is a cross-sectional view of a metal nut insert molded product injection-molded by a conventional method. In FIG. 3, the cooled mold 1 is provided with a recess 2 for installing a bolt to be inserted (3-
1). A bolt 3 to be inserted into the recess 2 is installed (3-2). The mold is closed to form a mold cavity, and the heat-plasticized synthetic resin 4 is injected (3-3). The injected synthetic resin is cooled by the mold, and the bolt 3 and the mold 1
Cannot enter the back of the corner 5 formed by
The insert molded product 6 in which is unstablely fixed is obtained (3-4).

In FIG. 1, the cooled main mold 7 is covered with a heat insulating layer 9 on the mold surface around the recess in which a bolt to be inserted is installed (1-1). A preheated bolt 10 is installed in the recess 8 (1-
2). The mold is closed to form a mold cavity, and the synthetic resin 11 that has been heat-thermoplasticized is injected (1-3). Due to the function of the heat insulating layer 9, the injected synthetic resin sufficiently penetrates the bolt 10 into the inner part of the corner formed by the mold 7, and the bolt 10 is stably fixed.
Is obtained (1-4).

In FIG. 2, the cooled main mold 13 is provided with a convex portion 14 for mounting a nut to be inserted. A heat insulating layer 15 is coated on the mold surface around the convex portion 14 (2-1). The nut 16 which has been heated in advance is installed on the convex portion 14 (2-2). The mold is closed to form a mold cavity, and the heat-plasticized synthetic resin 17 is injected (2-3). The injected synthetic resin 17 is a heat insulating layer 1
By the function of 5, the deep insert of the corner formed by the nut 16 and the mold 13 is sufficiently obtained, and a good insert molded product 18 in which the nut 16 is stably fixed can be obtained (2-
4).

FIG. 4 shows an insert-molded product obtained by insert-molding the nut shown in FIG. 2 by the conventional method without covering the heat insulating layer. In FIG. 4, the synthetic resin 20 does not sufficiently enter the corners formed by the nut 19 and the mold, and the nut 19 is unstablely fixed, resulting in an insert-molded product. In the present invention, the wall surface of the main mold on which the insert part is set is covered with a heat insulating layer. In the case of the mold shown in the figure, the wall surface of the main mold near the corner formed by the bolt or nut and the mold is covered with a heat insulating layer. Although the present invention has been described in terms of injection molding, blow molding can be used as well. When a bolt is insert-molded by extrusion blow molding, a molded product similar to that shown in (3-4) of the figure by the conventional method and (1-4) in the present invention can be obtained. Generally, extrusion blow molding has a lower temperature during molding of synthetic resin than injection molding,
The pressure to press the synthetic resin against the mold wall is extremely low. Therefore, in insert molding of extrusion blow molding, the fixation of the insert part to the molded product is often insufficient, and the method of the present invention can be used particularly well.

[0040]

[Example] Insert extrusion blow molding of a copper bolt is performed using the following molds and materials. Main mold: Made of steel (S55C), 300 × 95
It has a rectangular parallelepiped mold cavity of 20 mm (300 mm in the direction of extrusion of the parison), the mold surface is mirror-like, and hard chrome plating is applied. The mold wall surface is provided with a recess for setting the bolt of the insert part. The main mold temperature is 60 ° C.

Polyimide Precursor and Polyimide After Curing: Linear high molecular weight polyimide precursor solution "Trenice # 3000" (trade name, manufactured by Toray Industries, Inc.). The performance of the polyimide after curing is Tg of 300 ° C. and thermal conductivity of 0.0.
005 cal / cm · sec · ° C, breaking elongation 60%. Polyimide-coated mold: A polyimide precursor solution is applied to the mold surface near the recess where the bolt of the main mold is set,
Partial imidization by heating to 0 ° C., then applying the coating, 160
The heating at 0 ° C. is repeated 10 times, and finally heating up to 290 ° C. is performed to perform 100% imidization to prepare a polyimide-coated mold in which the vicinity of the recess is covered with 0.3 mm thick polyimide. Thermoplastic resin: ABS resin, Stylak ABS, A
4593 (trade name, manufactured by Asahi Kasei Corporation).

[0042]

Example 1 A steel bolt was heated to 100 ° C., set in a recess of a polyimide-coated main mold as shown in (1-2) of FIG. 1, and ABS resin at 220 ° C. was immediately extrusion blow-molded. . The blow gas pressure is 6 kg / cm @ 2. ABS
The resin sufficiently penetrates into the corners formed by the mold wall surface, and an insert molded product in which the bolt is firmly fixed to the molded product as shown in (1-4) of FIG. 1 is obtained.

[0043]

[Comparative Example 1] A steel bolt was set in the concave portion of the main mold not coated with polyimide, and ABS was used in the same manner as in Example 1.
When the resin is extrusion blow-molded, the ABS resin cannot sufficiently enter the corners, and a molded product as shown in (3-4) of FIG. 3 is obtained, which is a molded product with insufficient bolt fixing.

[0044]

As compared with the conventional method, the insert molding method of the present invention can satisfactorily embed an insert part in a molded product without raising the mold temperature to obtain a sufficiently fixed insert molded product. be able to.

[Brief description of drawings]

FIG. 1 is a sectional view showing a process of insert injection molding a metal bolt by the method of the present invention.

FIG. 2 is a sectional view showing a process of insert injection molding a metallic nut by the method of the present invention.

FIG. 3 is a sectional view showing a molding process of insert injection molding a metal bolt by a conventional method.

FIG. 4 shows a cross section of an insert molded product of a metal nut injection-molded by a conventional method.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Mold 2 ... Recess 3 ... Metal bolt 4 ... Synthetic resin 5 ... Corner 6 ... Insert molding 7 ... Main mold 8 ... Convex 9 ... Heat insulation layer 10 ... Bolt 11 ... Synthetic resin 12 ... Insert molding 13 ... Main mold 14 ... Convex part 15 ... Thermal insulation layer 16 ... Metal nut 17 ... Synthetic resin 18 ... Insert molded product 19 ... Metal nut 20 ... Synthetic resin

Claims (1)

[Claims] 1. In insert molding of a thermoplastic resin, a main mold wall surface made of metal for setting an insert part such as a metal part to be inserted has a thermal conductivity of 0.00
An insert molding method characterized in that a heat-insulating layer made of a heat-resistant polymer of 2 cal / cm · sec · ° C. or less is coated in a thickness of 0.01 to 2 mm to be molded.