JP2715357B2 - Mold for synthetic resin molding - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a synthetic resin molding die.

[0002]

2. Description of the Related Art In order to improve the reproducibility of imparting the shape state of the mold surface to a molded article by injecting a thermoplastic resin into a mold cavity and to improve the gloss of the molded article, it is usually necessary to use a resin temperature. It can be achieved to some extent by selecting molding conditions such as increasing the injection pressure and increasing the injection pressure.

[0003] Among these factors, the mold temperature has the greatest effect, and it is preferable to increase the mold temperature.
However, when the mold temperature is increased, the cooling time required for cooling and solidifying the plasticized resin increases, and the molding efficiency decreases.
Improves the reproducibility of the mold surface without increasing the mold temperature,
There is also a demand for a method in which the required cooling time is not prolonged even when the mold temperature is increased. Heating and cooling holes are attached to the mold, and the heating medium and the coolant are alternately flown to repeat the heating and cooling of the mold.However, this method consumes a large amount of heat, The cooling time becomes longer.

A method of improving the mold surface reproducibility by coating the mold wall surface forming the mold cavity with a substance having a low thermal conductivity is disclosed in US Pat. No. 3,544,518 and the like. Examples include polyethylene terephthalate and polyphenylene sulfide. Further, as a method of providing a heat insulating layer near the surface of a mold, there is WO 89/10823. In this specification, when the injected resin is cooled in a mold, it is cooled slowly, the temperature difference between the outer surface and the central portion of the resin is reduced, and a method of molding a lens or the like with a small distortion is used. Is shown. As a means for slowly cooling, a mold structure is shown in which the outermost surface of the mold is made of a metal such as aluminum or nickel, the next layer is a heat insulating layer, and the lower layer is a mold body.
The purpose of providing the heat insulating layer is to greatly reduce the cooling rate of the injected heated resin, and as a heat insulating layer, a liquid crystal polymer plate having a thickness of several mm, Vespel (a molded polyimide, D
u Pont).

Japanese Patent Application Laid-Open No. Sho 62-37107 discloses that
It discloses that a heat insulating layer is provided on the surface of a rubber vulcanizing mold, and ceramics, graphite, Teflon, polycarbonate and polyimide are described as heat insulating materials, but no further description is given.

[0006]

Injection molding has the greatest advantage that a molded article having a complicated shape can be obtained by a single molding. While maintaining this advantage, the cooling time in the mold does not become long. In addition, there is a demand for molding a mirror-like molded product with improved mold surface reproducibility. The present invention is a mold that meets these requirements.

The object of the present invention is to achieve 1) application to a mold having a mold cavity having a complicated shape, 2) a small increase in cooling time, 3) endurance of repetitive molding, and 4) obtaining a high gloss molded product. Is to provide a mold.

[0008] To achieve this object, the present inventors have
We examined the mold coated with the heat insulating layer, and found that the following matters are very important for the heat insulating material that coats the main mold surface, its coating state, and the coating method. That is, the heat insulating layer is substantially a thin layer on the outermost surface of the mold, and the heat insulating material is low in thermal conductivity, excellent in heat resistance, large in tensile strength, large in elongation and cold. High cycle resistance, high surface hardness, excellent wear resistance, good application to the mold body, good adhesion to the mold body, good surface polishing, and formation of a heat insulating layer It is excellent in corrosion resistance at the time of molding of a synthetic resin using the present mold.

Therefore, the present inventors have further studied on a heat insulating material, a coating state and a coating method satisfying these matters, and have reached the present invention for the first time.

[0010]

That is, the present invention is as described below.

The thermal conductivity at room temperature is 0.05 cal
/ Cm · sec · ° C or higher
Chrome walls and / or
Coated with a nickel plating, and the surface is covered with linear high molecular weight poly.
Apply imide precursor solution, then heat to mold surface
Form a high-chain high-molecular-weight polyimide with a thickness of 0.001 to 2 mm
And the adhesion between the polyimide and the main mold is 500 g / 10
A synthetic resin mold having a width of at least mm .

Hereinafter, the present invention will be described in detail.

The synthetic resin applicable to the mold of the present invention is a thermoplastic resin generally usable for injection molding, blow molding and the like. For example, a general thermoplastic resin such as a styrene polymer or a copolymer thereof, an olefin polymer such as polyethylene or polypropylene or a copolymer thereof, a vinyl chloride polymer or a copolymer thereof, a polyamide, or a polyester can be used.

Particularly great effects can be obtained when these resins are mixed with various reinforcing materials and various fillers, or when a polymer alloy or the like is used. For example, these resins include rubber, glass fiber, asbestos, calcium carbonate,
One or two of talc, calcium sulfate, foaming agent, wood flour, etc.
More than one species can be blended. The main mold material having a thermal conductivity of 0.05 cal / cm · sec · ° C. or more described in the present invention is iron or a steel material containing iron as a main component, aluminum or an alloy containing aluminum as a main component, a zinc alloy, or the like. And metals generally used in synthetic resin molds.
In particular, steel materials can be used most preferably.

In the present invention, the mold wall forming the mold cavity of the main mold is covered with chrome plating and / or nickel plating. Since chromium plating and nickel plating are excellent in adhesion to polyimide and also excellent in corrosion resistance, it has been found that the effect is particularly remarkable when employed in the mold of the present invention.

That is, when the surface of the main mold made of steel or the like is directly coated with polyimide, the surface of the main mold is liable to be deteriorated in the coating process, the adhesion to the polyimide becomes unstable, and peeling is apt to occur. Was. In the case of chrome plating or nickel plating, surface deterioration is unlikely to occur, and chromium and nickel have better adhesion with polyimide than iron,
In addition, it has been found to be very favorable for the present invention because the surface is stable. During molding of the synthetic resin, heating and cooling are repeatedly applied to the mold. Therefore, it is very important that the adhesion is stable and large. In order to withstand tens of thousands of moldings, chromium plating or / and It was also found that the effect of nickel plating was remarkably large. Among the hard chrome platings, the hard chrome plating was hard and had excellent scratch resistance, and was the most preferable.

The thickness of the chrome plating and / or nickel plating is preferably 0.001 to 0.1 mm. The plating method may be either electroplating or chemical plating. Electroplating is generally performed in the following operation steps, but the same operation steps can be applied to the present invention. Substrate finishing → surface cleaning → stop off → jig mounting → anodizing → plating operation → hydrogen removal → finishing.

The plating may be a single plating of chromium or nickel, but a multi-layer plating of copper-nickel-chromium, nickel-chromium, copper-chromium-copper-nickel or the like can be used if necessary. In the present invention, because it utilizes the good adhesion between nickel or chromium and polyimide,
It is necessary that nickel or chromium be present on the outermost surface of the plating, and a multilayer plating satisfying this condition is included in the present invention.

There are various types of polyimide, which are classified as shown in Table 1 below.

[0020]

[Table 1]

[0021] The mold of the present invention is coated with polyimide.
Can be used. The solvent of this solution is a solvent that evaporates prior to or concurrently with curing when applied to a mold and heated, and is a commonly used organic solvent.

The polyimide formed by applying the solution to a mold and then heating adheres very well to chromium or nickel on the mold surface. The surface of the polyimide thus obtained has high surface hardness, excellent abrasion resistance, and is hardly scratched during use. In injection molding, a heated and plasticized synthetic resin is injected into a cooled mold, which is cooled and molded in the mold. Extensive heating and cooling are repeated. Since metals such as polyimide and iron have a coefficient of thermal expansion that differs by an order of magnitude, each time heating and cooling up to 100 ° C. are repeated, severe stress is generated at the interface between the metal and the polyimide. The polyimide can withstand several thousand or tens of thousands to this stress, breaking strength, breaking elongation are large, a high molecular weight Po <br/> Riimi de of tough linear.

Thermosetting polyimides such as bismaleimide-based resins, acetylene-terminated polyimides, and nadic-modified polyimides are highly crosslinked, and are inferior to linear polyimides in withstanding severe cooling and heating cycles.

In particular, the polyimide used in the present invention comprises a high molecular weight closed body obtained by applying a linear high molecular weight soluble polyimide precursor to a mold surface and then heating to form an imide ring. It is a linear high molecular weight polyimide.
Table 2 shows examples of the linear high molecular weight polyimide used in the present invention. In addition, Tg represents a glass transition temperature.

[0025]

[Table 2]

The Tg of the linear polyimide differs depending on the constituent components, and examples thereof are shown in Tables 3 and 4. According to the findings of the present inventors, Tg is preferably 200 ° C. or higher, more preferably 230 ° C. or higher.

[0027]

[Table 3]

[0028]

[Table 4]

Injection molding has economic value in that a molded article having a complicated shape can be obtained by one molding. In order to coat the complex mold surface with polyimide and to make it tightly adhere, it is most preferable to apply a polyimide precursor solution and then heat to form polyimide. In the present invention, a polyimide solution is used as described above,
A repeating unit of a typical example of polyamic acid, which is the most preferred straight-chain polyimide precursor, is shown in Chemical formula 1.

[0030]

Embedded image

The polyimide precursor polymer has good adhesion to the mold due to carboxyl groups and the like, and a polyimide thin layer adhered to the mold surface can be obtained by reacting and forming polyimide on the mold surface. To the polyimide precursor solution, to adjust the viscosity at the time of coating, to adjust the surface tension of the solution, to add an additive to adjust the thixotropy, and / or to increase the adhesion with the mold Additives can be added. Among these polyimides, PMDA-based polyimides are excellent in heat resistance, mechanical properties and the like, and are most preferable. Particularly, a varnish modified for coating can be used favorably. However, additives that greatly increase the thermal conductivity of polyimide are not preferred. Further, an additive that significantly reduces the adhesion between the polyimide and the mold is not preferable.

Since the polymer of the polyimide precursor contains a carboxyl group or the like, it has good adhesion to the mold, and a polyimide thin layer adhered to the mold surface can be obtained by reacting and forming polyimide on the mold surface. Tight force application between the polyimide and the main mold of the present invention, 500 g / 10 mm at room temperature
The width is not less than the width, more preferably not less than 1 kg / 10 mm, most preferably not less than 1.5 kg / 10 mm. This is the peeling force when the adhered polyimide is cut into a width of 10 mm and pulled at a speed of 20 mm / min in a direction perpendicular to the adhesive surface. Although the peeling force varies considerably depending on the measurement place and the number of measurements, the minimum value of the dispersion is important, and it is preferable that the peeling force is stable and large. In the case of chrome plating and nickel plating, a stable peeling force is provided.

The smaller the thermal conductivity of the polyimide, the better, but the thermal conductivity of the polyimide is 0.002 cal / cm ·
Those having a temperature of not more than sec · ° C can be preferably used. The thickness of the polyimide is appropriately selected in the range of 0.001 to 2 mm. If the thickness is less than 0.001 mm, the effect of improving the surface of the molded product is small, and if it exceeds 2 mm, the cooling effect of the mold is reduced, and the molding efficiency is reduced. The higher the mold temperature, the thinner the polyimide thickness, and the lower the mold temperature, the thicker the polyimide thickness, which is appropriately selected in the range of 0.001 to 2 mm. The preferred thickness of the polyimide also differs depending on the molding method in which the mold of the present invention is used. In the injection molding in which the mold of the present invention can be best used, 0.0
The thickness is preferably 1 to 0.5 mm, more preferably 0.1 to 0.5 mm.
The thickness is from 0.1 to 0.1 mm. In contrast, in extrusion blow molding, a thickness of 0.2 to 1 mm is preferable.

Injection molded products, especially large injection molded products, generally have good mold surface reproducibility and good gloss near the resin injection port (hereinafter referred to as gate) where the injection pressure is easily transmitted. The surface reproducibility is poor, and the resin flow edge is the worst. The thickness of the molded product becomes thin,
Alternatively, especially when the viscosity of the injected resin is high or the molded product is large, the difference in appearance between the gate portion and the resin flowing end becomes large.

The present invention also provides a mold for improving these. That is, it is a mold in which the thickness of the polyimide increases from the vicinity of the resin injection port (gate) toward the resin flowing end. The vicinity of the gate described here is the vicinity of a generally used gate such as a direct gate, a pinpoint gate, and a side gate. Injection molded products have a part requiring an appearance and an unnecessary part. In general, a gate selects a part not requiring an appearance and determines its position. Therefore, the thickness of the polyimide closest to the gate where the appearance is required is defined as the polyimide thickness near the gate. The vicinity of the gate refers to a portion that enters the mold cavity from the gate, generally a mold wall surface that is about 1/10 of the distance from the gate to the resin flowing end.

There is no polyimide in the immediate vicinity of the mold cavity from the gate and in the vicinity thereof, and the polyimide may be coated from a place advanced by several tens of millimeters. In this case, the polyimide is fully coated. This portion is defined as the vicinity of the gate according to the present invention. Then, the thickness of the polyimide in this portion is used. The vicinity of the resin flowing end is the portion closest to the resin flowing end where appearance is required, that is, 1/10 of the distance from the resin flowing end to the gate.
Show the vicinity. In the present invention, the thickness of the polyimide near the resin flow end is 1.1 to 4 times, preferably 1.2 to 3 times, more preferably 1.3 to 2 times the thickness of the polyimide near the gate. 0.5 times.

Injection molding has the greatest advantage that a mold having a complicated shape can be formed at one time, so that the mold cavity generally has a complicated shape. It is extremely difficult to apply a coating substance to the surface of the complicated mold cavity in a mirror-like manner, and therefore, it is necessary to polish the surface of the applied coating layer to obtain a mirror-like finish. Therefore, it is required that the coating material can be polished and mirror-finished.

Polishing a synthetic resin to remove unnecessary portions to make it a mirror surface is a method used when polishing a plastic lens or the like. In order to polish a synthetic resin using an abrasive powder or the like, it is necessary to use a synthetic resin suitable for polishing, and a well-known CR-39 (gethylene glycol bisallyl carbonate) polymer or the like is suitable. .
That is, it is generally said that a resin that is highly crosslinked, hard, has low elongation, and has a high glass transition temperature is suitable. On the other hand, in the linear high molecular weight,
It has been observed that a tough resin having a large elongation at break is not suitable for polishing.

According to the conventional concept, straight-chain high molecular weight polyimide is not suitable for polishing because it has a large elongation at break and is tough. However, such straight-chain high-molecular-weight polyimides, together with thermosetting polyimides that are highly crosslinked, have good polishing properties for the first time according to the present invention, and can be favorably used in the present invention. I understood.

In order to further improve the smoothness and the like of the surface of the thin polyimide layer or to further improve the scratch resistance of the surface, another material thinner than about 1/10 of the thickness of the polyimide layer is applied to the polyimide surface. This can also be performed as needed and is included in the present invention. A coating generally used as a hard coat, which is used for improving scratch resistance, can be applied to the surface of a synthetic resin sheet or a mold.
For example, a thermosetting silicone hard coat agent can be used favorably and is preferred for the present invention.

The heat-melted synthetic resin injected into the mold cavity needs to be pressed at high pressure against the mold wall surface at a temperature not lower than its softening temperature. The mold of the present invention is particularly effective for high-speed injection molding. High-speed injection molding is a synthetic resin injection molding method for performing high-speed injection molding in which the injection time into the mold cavity is less than 1 second. Preferably, the high-speed injection time is 0.5 seconds or less, more preferably 0.3 seconds or less.

The above-described high-speed injection molding in which the injection time into the mold cavity is less than 1 second means that the synthetic resin, which has been plasticized by heating, enters the mold cavity from the gate of the mold cavity and reaches the end of the mold cavity. Is less than 1 second. If there are a large number of gates, this is the time from when synthetic resin first starts to enter until the mold cavity is filled. After the heat plasticized synthetic resin reaches the end of the mold cavity, the synthetic resin continues to
The high-pressure injection pressure is applied, the pressure becomes high, and the synthetic resin, which supplements the shrinkage due to the cooling of the synthetic resin, is continuously injected into the mold cavity.

Further, by introducing a fluid such as a heated gas into the mold cavity, a better molded product surface can be obtained. By introducing a fluid such as a heated gas 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 should be higher than the mold temperature,
Introducing a high-temperature gas for a short time has a greater effect, and a gas having a temperature 100 ° C. or higher, preferably 200 ° C. or higher, more preferably 300 ° C. or higher than the mold temperature is preferable.

[0044] Various methods as a method for introducing a heated gas into the mold cavity. However, the gas in the mold cavity can pass through but that leave only pores Oa size of the molten resin can not pass through as an example A heating gas is introduced through the pores. Therefore, pores must be provided at positions suitable for the inlet and outlet of the heating gas. The size of the pores that can pass gas but cannot pass the molten resin varies depending on the type of resin, molding conditions, and the like.
Elongated pores with a 0.2 mm void are suitable. However, conventional mold par tee ring surface not airtight To fill the conditions of the gap. Particularly par tee ring surface is to the introduction of gas provided such aforementioned special pores airtight mold.

[0045]

EXAMPLES Experiments were conducted using the following molds and polyimides. (1) Mold Main mold (A): made of steel (S55C), has a 2 mm thick flat mold cavity, and the mold surface is mirror-finished.
The thermal conductivity of steel is about 0.2 cal / cm · sec · ° C.

Main mold (B): Hard chromium plating by electrolysis is applied to the surface of main mold (A) in a mirror-like manner with a thickness of 0.02 mm.
Thing that went thick. (2) Polyimide Polyimide (A): straight-chain polyimide precursor, polyimide varnish “Trenice 3000” (trade name of Toray Industries, Inc.).

The Tg of the cured polyimide is 300 ° C., and the thermal conductivity is 0.0007 cal / cm · sec · ° C. Polyimide (B): linear type polyimide precursor, polyimide varnish “Larc-TPI” (trade name of Mitsui Toatsu Co., Ltd.). The Tg of the cured polyimide is 256 ° C.

Polyimide (C): a linear polyimide precursor, polyamideimide “AI-10” (Amoco Japan Limited) solution. The Tg of the cured polyimide is 2
30 ° C.

[0049]

Example 1 Four main molds (A) were prepared, and each mold was polished with sandpaper or the like to use each mold having a changed surface roughness and a main mold (B). . After the mold surface is sufficiently degreased, a coating material in which a slight thixotropic agent is mixed with the polyimide (A) is applied, and the coating is applied at 120 ° C. for 15 minutes.
Heating at 210 ° C. for 15 minutes and 290 ° C. for 30 minutes formed a linear polyimide. Next, a diamond paste was applied to the buff and polished with an electric grinder,
A mirror-like linear polyimide coating layer having a thickness of 5 mm was formed.

The coating layer was cut to a width of 10 mm,
The film was pulled in the direction perpendicular to the coated surface at a speed of one minute, and the adhesion was measured. Table 5 shows the results. The adhesion between the main mold and the polyimide was 0.3 kg / cm or more, but the adhesion between the hard chrome-plated main mold B and the polyimide (A) was as large as 1 kg / cm, and the variation was large. Was also very small. It is important that the minimum value of the adhesion is large.

[0051]

Example 2 Four main molds (B) were prepared, and after each mold was sufficiently degreased, polyimides (A), (B) and (C) were applied respectively, and the same as in Example 1 was carried out. To form a mirror-like linear polyimide coating layer having a thickness of 0.04 mm and 0.1 mm. Using the linear polyimide-coated mold and the main mold (B), rubber-reinforced polystyrene (trade name: Styron 495, trade name of Asahi Kasei Kogyo Co., Ltd.) is injection-molded, and the gloss of the molded article is measured. 6 shows the results. Polyimide (A),
In (B) and (C), exactly the same results were obtained. When the polyimide was coated on the chromium plating, the gloss of the molded article was significantly improved, and even after the injection molding was performed 10,000 times, no abnormality in the mold surface and no decrease in the gloss of the molded article were observed.

The injection molding conditions and gloss measurement conditions were as follows. Injection molding conditions: Injection cylinder temperature 220 ° C Mold temperature 60 ° C Injection speed X: Injection time 1.1 seconds Injection speed Y: Injection time 0.2 seconds Glossiness measurement conditions: JIS K7105, reflection angle 60
Every time

[0053]

Comparative Example 3 A silane coupling agent KBE903 (Shin-Etsu Chemical Co., Ltd.) was applied to the surface of a mirror-like linear polyimide layer having a thickness of 0.04 mm and a thickness of 0.1 mm formed on the surface of a mold by the method shown in Example 1. ) Product and heated at 120 ° C. for 10 minutes to form a thin film having a thickness of 0.1 μm or less, and a silicone hard coat agent X-12-2150A / B (Shin-Etsu Chemical Co., Ltd.) on the surface of the silane coupling agent thin film. (Product)
Was applied and heated at 120 ° C. for 10 minutes to form a thin film having a thickness of about 1 μm, and a silicone hard coat layer was formed thereon.

Using this mold, injection molding was performed in the same manner as in Example 3 to obtain an injection molded product having almost the same high gloss.
By applying the silicone hard coat layer on the outermost surface, it was possible to prevent damage such as during handling of the mold.

[0055]

[Table 5]

[0056]

[Table 6]

[0057]

According to the synthetic resin mold of the present invention, a molded article having extremely excellent mold surface reproducibility can be obtained. It can be a mold having a mold cavity of a complicated shape,
This is a synthetic resin molding die that is industrially very useful, such as a small increase in cooling time, durability against repeated molding, and a molded product with high gloss.

Claims (1)

(57) [Claims] 1. The thermal conductivity at room temperature is 0.05 cal.
/ Cm · sec · ° C. or higher is coated on the mold wall forming the mold cavity of the main mold with chrome plating and / or nickel plating, and the surface is covered with linear high molecular weight poly.
Apply imide precursor solution, then heat to mold surface
Form a linear high molecular weight polyimide with a thickness of 0.001 to 2 mm
And the adhesion between the polyimide and the main mold is 500 g / 10
A synthetic resin mold having a width of at least mm .