JP3396254B2 - Mold and its manufacturing method - 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. More specifically, it relates to a mold for injection molding or blow molding that can withstand molding of tens of thousands of times, and a manufacturing method thereof.

[0002]

2. Description of the Related Art In order to improve the reproducibility in imparting the shape condition of the mold surface to a molded product and to improve the gloss of the molded product, it is usually necessary to inject a thermoplastic resin into a mold cavity for molding. Can be achieved to some extent by selecting molding conditions such as higher injection pressure and injection pressure.

The mold temperature has the greatest influence among these factors, and the higher the mold temperature, the more preferable.
However, if the mold temperature is increased, the cooling time required for cooling and solidifying the plasticized resin becomes longer, and the molding efficiency decreases.
Improves mold surface reproducibility without raising mold temperature,
There is also a demand for a method which does not lengthen the required cooling time even if the mold temperature is raised. There is also a method in which heating and cooling holes 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 a lot of heat, Cooling time becomes longer.

A method for improving mold surface reproducibility by coating a mold wall forming a mold cavity with a substance having a small thermal conductivity is disclosed in US Pat. No. 3,544,518 and the like. Polyethylene terephthalate, polyphenylene sulfide, etc. are shown as substances having a low rate. Further, there is WO89 / 10823 as a method of providing a heat insulating layer near the surface of the mold. In this specification, when the injected resin is cooled in the mold,
As a means for slowly cooling, a mold structure is shown in which the outermost surface of the mold is made of metal such as aluminum or nickel, the next layer is a heat insulating layer, and the lower part is a mold body. The purpose of providing the heat-insulating layer is to greatly reduce the cooling rate of the injected heating resin. As a heat-insulating layer, a liquid crystal polymer plate having a thickness of several mm, Vespel (molded polyimide, Du P
The board of the Ont company brand name) is shown.

Japanese Unexamined Patent Publication No. 62-37107 discloses a method of preventing the occurrence of silver streaks by providing a heat insulating layer having air permeability on the mold surface.

[0006]

It is generally difficult to bring a metal and a polyimide having a coefficient of thermal expansion different by one digit into close contact with each other, and to maintain the close contact in a thermal cycle test of tens of thousands of times.
Injection molding has the greatest advantage that a molded product with a complicated shape can be obtained by one-time molding. While maintaining this advantage, cooling time in the mold does not become long, and mold surface reproducibility is improved. There is a demand for molding improved mirror-like molded products.

The present invention is a mold that meets these requirements. The object of the present invention is a mold having a mold surface coated with a heat insulating layer, which can be applied to a mold having a mold cavity with a complicated shape, 2) a small increase in cooling time, and 3) The object of the present invention is to provide a mold and a manufacturing method thereof, which can endure tens of thousands of repeated moldings and 4) have excellent mold surface reproducibility. As a result, for example, the inventors of the present invention, which can obtain a high-gloss molded article, have studied a mold covered with a heat-insulating layer, and have investigated the main mold surface, a heat-insulating substance that coats it, and its coating. It has been found that the following is very important for the condition and the coating method.

That is, the heat insulating layer is a thin layer substantially on the outermost surface of the mold, and the heat insulating material has low thermal conductivity, excellent heat resistance, tensile strength and elongation. Large and resistant to cooling / heating cycles, large surface hardness, excellent abrasion resistance, good adhesion to the mold body, surface polishing, and when forming a heat insulating layer or using this mold It is excellent in corrosion resistance when molding a synthetic resin.

The present inventors plated the surface of the mold with nickel and / or nickel and covered the surface with a high molecular weight polyimide to improve the adhesion of the polyimide, withstand long-term molding, and reproduce the surface of the mold. A mold for improving the property has been proposed in Japanese Patent Application No. 4-145541. However, even better molds are required. As mentioned above,
There are many known documents about a method for improving the mold surface reproducibility of a molded article by coating the surface of a main mold made of metal with a thin heat insulating layer made of synthetic resin. But,
Conventionally, these molds can be used as simple molds for molding that requires a small number of moldings, but for full-scale molds that can withstand molding of tens of thousands of times, mold cavities have been formed with a strong material such as steel. Is common sense. In injection molding, synthetic resin is injected into a thin mold cavity of about 2 mm at high speed, so forming a mold cavity with a strong material such as steel is indispensable for full-scale molds that perform tens of thousands of moldings. It is believed that.

We have conducted a deeper study on this, and even if the surface of the main mold is coated with a thin synthetic resin, if a heat insulating layer made of a synthetic resin satisfying certain conditions is used, injection can be performed tens of thousands of times. We have found that it can withstand molding. That is,
In injection molding, the heat-plasticized resin injected into the mold contacts the cooled mold wall surface to immediately form a solidified layer on the contact surface, and the subsequently injected resin proceeds between the solidified layer and the solidified layer. Then, when it reaches the flow front, it turns toward the mold wall surface and comes into contact with the mold wall surface to form a solidified layer.

That is, the injected resin flows so as to press the mold wall surface from above, and does not flow like dragging the mold wall surface. Therefore, it has been found that if the mold surface is coated with a thin heat insulating layer made of a selected synthetic resin, the heat insulating layer is not directly worn by the injected resin and can withstand tens of thousands of injection moldings. .

[0012]

That is, the present invention is
Thermal conductivity at room temperature is 0.05 cal / cm · sec
The mold wall surface that forms the mold cavity of the main mold made of a metal having a temperature of ℃ or higher is a rough surface with fine irregularities, and the surface is coated with nickel plating and / or chrome plating,
Further, it is a synthetic resin molding die whose surface is covered with polyimide. More preferably, the mold is one in which the polyimide is a linear high molecular weight polyimide. Furthermore, the thermal conductivity at room temperature is 0.05 cal / cm · sec ·
After roughening the mold wall surface that forms the mold cavity of the main mold made of a metal having a temperature of ℃ or more, it is coated with nickel plating and / or chrome plating, and the surface is coated with a polyimide precursor solution, and then This is a method for producing the above-mentioned mold in which it is imidized by heating.

The present invention will be described in detail below. The main mold material used in the present invention has a thermal conductivity of 0.05 cal.
/ Cm · sec · ° C or higher, iron or a steel material containing 50% by weight or more of iron, aluminum or an alloy containing 50% by weight or more of aluminum, a zinc alloy, a copper alloy, for example, a general synthetic resin such as beryllium copper alloy Includes the metals used in the mold. In particular, steel materials can be used most preferably.

The finely roughened surface of the present invention can be formed by operations such as sandblasting, chemical etching, and rubbing with a coarse-grained abrasive. The irregularities are preferably fine and uniform. The roughness of the center line average roughness (Ra) is preferably about 0.1 μm to 5 μm. In addition, irregularities without a sharp angle are preferable. The center line average roughness is measured according to JIS B0601-1982.

The surface of the fine irregularities is plated with nickel and / or
Alternatively, by coating with chrome plating, adhesion with polyimide is improved and durability of the mold is improved. The nickel plating and / or chrome plating of the present invention has an average thickness of about 0.1 μm to 20 μm, which is a thickness that does not erase fine irregularities on the surface of the main mold, and the plating surface also has fine irregularities.

The plating is formed by chemical plating, electroplating or the like. Chemical plating is preferable because it can reproduce the irregularities on the surface of the main mold (electroless plating and chemical plating have the same meaning here). In the present invention, thin-walled chemical plating of nickel can be used particularly well. In this case, nickel also includes nickel containing small amounts of other elements. For example, nickel containing 4-14% phosphorus in nickel can be used successfully. As the nickel chemical plating method, a method using a reducing agent is preferable. The plating can be performed by an autocatalytic reaction or the like, and the feature thereof is that the metal to be reduced itself acts as a catalyst. As a result, the plating reaction is self-sustaining and the plated film grows as long as the liquid composition is kept constant. In chemical nickel plating, nickel acts as a catalyst for the oxidation reaction of hypophosphite, hydrazine, boron hydride compounds and the like. Chemical plating is a method widely used for metal molds under the name of Kanisen nickel plating, but this Kanisen nickel plating and similar plating can be used favorably.

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 likely to be deteriorated in the coating step, the adhesion with the polyimide becomes unstable, and peeling is likely to occur. The surface of nickel plating or the like is unlikely to be deteriorated and has a strong adhesion with polyimide, so that the surface is stable. Further, it was found that the contact area was increased by making the nickel-plated and / or chrome-plated surface rough so that the effect was remarkable.

Generally, polyimide is classified into a linear type and a thermosetting type, and there are various types of polyimide precursors thereof, which are classified as shown in Table 1 below.

[0019]

[Table 1]

In injection molding, a heated and plasticized synthetic resin is injected into a cooled mold and cooled in the mold for molding.
Every time heating and cooling up to 00 ° C. are repeated, severe stress is generated at the interface between the metal and the polyimide. As a polyimide capable of withstanding this stress for tens of thousands of times, it is particularly preferable that the breaking strength and the breaking elongation are large and the adhesion with the mold is large. A mold with nickel and / or chrome plating on the rough surface of fine unevenness,
Most preferably, it is coated with a tough linear high molecular weight polyimide.

Table 2 shows examples of linear type high molecular weight polyimides which can be favorably used in the present invention. In addition, Tg represents a glass transition temperature, and n represents the number of repeating units.

[0022]

[Table 2]

The glass transition temperature (hereinafter abbreviated as Tg) of the linear polyimide differs depending on the constituents, and examples are shown in Tables 3 and 4. Tg is preferably 200 ° C or higher, more preferably 230 ° C or higher.

[0024]

[Table 3]

[0025]

[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 this complex mold surface with polyimide and firmly adhere it, it is most preferable to apply a polyimide precursor solution and then heat to form the polyimide. It is preferable that the polyimide of the present invention does not substantially contain a substance that inhibits the adhesion to the mold, but the rough surface mold surface is coated with nickel or the like to form rough surface nickel to improve the adhesion force. It is good, within the range that does not significantly reduce the adhesion,
Blends of modified polyimides and various additives can also be used.

The polyimide coating is formed by applying a polyimide precursor solution on the wall surface of the mold and then heating. The polyimide is a high heat resistant resin having a Tg of 200 ° C. or higher, is excellent in strength and elongation, and has a breaking elongation of 10% or more,
The adhesion with the mold wall surface is preferably 500 g / 10 mm width or more. The linear polyimide precursor is synthesized, for example, by subjecting an aromatic diamine and an aromatic tetracarboxylic dianhydride to a ring-opening polyaddition reaction.

[0028]

[Chemical 1]

These polyimide precursors are heated to undergo a dehydration cyclization reaction to form a polyimide. The most preferable linear polyimide precursor for the present invention is polyamic acid, and a repeating unit of a typical example thereof and a repeating unit of a polyimide obtained by imidizing the same are represented by Chemical formula 2, Chemical formula 3, Chemical formula 4, and Chemical formula 5
Shown in.

[0030]

[Chemical 2]

[0031]

[Chemical 3]

[0032]

[Chemical 4]

[0033]

[Chemical 5]

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. To the polyimide precursor solution, for adjusting the viscosity at the time of coating, adjusting the surface tension of the solution, adding an additive for adjusting the thixotropic property, and / or for increasing the adhesiveness with the mold. Minor additives can be added. The varnish modified for coating can be used well. However, additives that greatly increase the thermal conductivity of polyimide are not preferred.

Since the polymer of the polyimide precursor contains a carboxyl group and 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. The adhesion between the polyimide of the present invention and the main mold is 500 g / 10 mm width or more at room temperature, preferably 0.8 kg / 10 mm width or more,
More preferably, it is 1 kg / 10 mm or more. This is the peeling force when the adhered polyimide was cut into a width of 10 mm and pulled at a speed of 20 mm / min in the direction perpendicular to the adhesive surface.
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 smaller the thermal conductivity of the polyimide is, the more preferable it is, and the thermal conductivity is preferably 0.002 cal / cm · sec · ° C. or less. The thickness of the polyimide layer is 0.02
It is appropriately selected within the range of 2 mm. If the thickness is less than 0.02 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.
It is necessary to reduce the thickness of the polyimide layer as the mold temperature is higher, and to increase the thickness of the polyimide layer as the mold temperature is lower, and the thickness is appropriately selected within the range of 0.02 to 2 mm. or,
The preferable thickness of the polyimide layer also varies 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 used most preferably, the thickness is preferably 0.02 to 0.5 mm, more preferably 0.05 to 0.2 mm. On the other hand, in extrusion blow molding,
A thickness of 1 mm is preferred.

The linear high-molecular-weight polyimide used in the present invention preferably has high strength and elongation, and in particular, high elongation at break is necessary for long-term molding which is repeatedly exposed to the heat and cold cycle. The breaking elongation is preferably 10% or more, more preferably 15% or more. The method of measuring the elongation at break is according to ASTM D638. Injection molding has the greatest merit that a mold having a complicated shape can be formed by one molding, and therefore, a mold cavity generally has a complicated shape. It is extremely difficult to apply a coating material to the surface of this complicated mold cavity in a mirror-like manner.
Therefore, the best method is to polish the applied coating layer to give a mirror finish. Therefore, the coating material is required to be capable of being polished and mirror-finished.

Polishing a synthetic resin to grind unnecessary portions to give a mirror surface is a method used when polishing a plastic lens or the like. In order to polish a synthetic resin with polishing powder or the like, it is necessary to use a synthetic resin suitable for polishing, and a well-known CR-39 (diethylene glycol bisallyl carbonate) polymer or the like is suitable.
That is, it is generally said that a resin that is highly crosslinked, hard, has a small elongation, and has a high glass transition temperature is suitable. On the other hand, a linear high molecular weight compound,
It has been considered that a resin having a large elongation at break and a toughness is not suitable for polishing.

According to this conventional idea, the straight-chain high-molecular-weight polyimide has a large elongation at break and is tough, and therefore is not suitable for polishing. However, it was revealed for the first time by the present invention that such a straight-chain high-molecular-weight polyimide as well as the thermosetting polyimide having a high degree of cross-linking have a good polishing property, and can be favorably used in the present invention.

In order to further improve the smoothness of the surface of the thin layer of polyimide, or to further improve the scratch resistance of the surface, the thickness of the polyimide layer is 1/10 or less, preferably 1/20 or less. It is also possible to apply another substance to the surface of the polyimide, which is included in the present invention. The surface of a synthetic resin sheet or mold may be coated with a paint generally called a hard coat agent, which is used for improving scratch resistance. For example, a thermosetting type silicone hard coat agent can be favorably used and is preferable for the present invention.

The synthetic resin that can be molded with the mold of the present invention is generally a thermoplastic resin that can be used 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 polyacetal, a polyamide, a polyester, or the like can be used. .

When these resins are mixed with various reinforcing materials and various fillers, or when they are polymer alloys, a particularly great effect is obtained. For example, resin, 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. Recycled resin containing foreign matter such as dust and paint powder can also be favorably used in the present invention.

Although the present invention has been mainly described by injection molding, the mold of the present invention can be used in blow molding as well.

[0044]

EXAMPLES The following mold and polyimide are used. Main mold: Steel material (S55C) (heat conductivity about 0.2cal /
cm ・ sec ・ ℃), 100mm × 100m
It has a square mold cavity of m and a flat mold cavity with a thickness of 2 mm. It has side gates on the sides of the square.

Polyimide: Linear polyimide precursor, polyimide varnish “Trenis # 3000” (Toray brand name). Tg of the cured polyimide is 300 ° C., thermal conductivity is 0.0005 cal / cm · sec · ° C., elongation at break is 60.
%. Two main molds were prepared, and the mold surfaces were (A) the main mold surface was mirror-polished, (B) the main mold surface was sandblasted, and the center line average roughness (Ra) was 0. After roughening to a surface of 0.5 μm, it was processed to have a thickness of 0.5 μm by chemical nickel plating.

The above mold surface was thoroughly degreased, and then
Polyimide is applied and heated in the order of 120 ° C. to 210 ° C. This application and heating are repeated 3 times, and finally heated to 290 ° C. to form a polyimide layer. Next, a diamond paste was applied to the buff and polished to form a 0.05 mm thick mirror-like linear polyimide coating layer. The adhesive force between the mold and the polyimide is 1.1 to 2.0 kg / 1 in (A).
The width of 0 mm was 2.3 kg / 10 mm in (B). By making the surface of the main mold rough and then plating the surface with nickel, the adhesion of the polyimide is obviously improved. Using the mold (B) coated with polyimide, injection molding was performed 20,000 times with a rubber-reinforced polystyrene resin, and a good molded product was obtained.

[0047]

By performing injection molding or blow molding of synthetic resin using the mold of the present invention, the increase in molding cycle time can be slightly increased and the appearance of the molded product can be remarkably improved. .

─────────────────────────────────────────────────── ─── Continuation of the front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) B29C 33/00-33/76 B29C 39/26-39/34 B29C 41/38-41/40 B29C 43 / 36-43/42 B29C 45/26-45/37 B29C 49/48-49/54 B29C 51/30-51/40

Claims (3)

(57) [Claims] 1. The thermal conductivity at room temperature is 0.05 cal.
/ Cm · sec · ° C. or more The mold wall of the main mold made of metal is a rough surface with fine irregularities,
A synthetic resin molding die whose surface is coated with nickel plating and / or chrome plating, and whose surface is further coated with polyimide. 2. The mold according to claim 1, wherein the polyimide is a linear high molecular weight polyimide. 3. The thermal conductivity at room temperature is 0.05 cal.
/ Cm · sec · ° C or higher After making the mold wall forming the mold cavity of the main mold rough, it is coated with nickel plating and / or chrome plating, and further the surface thereof is a polyimide precursor solution. The method for producing a mold according to claim 1 or 2, wherein is applied and then heated to imidize.