JPH0780187B2 - 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. More specifically, it relates to a mold for injection molding or blow molding that can endure molding of tens of thousands of times.

[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, and a substance having a small thermal conductivity is disclosed. As such, polyethylene terephthalate, polyphenylene sulfide, etc. are shown. 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, the mold re-surface is made of a metal such as aluminum or nickel, and the next layer is a heat insulating layer The mold structure is shown as the mold body. The purpose of providing the heat-insulating layer is to significantly reduce the cooling rate of the injected heating resin, and as the heat-insulating layer, a plate of liquid crystal polymer having a thickness of several mm, Vespel (molded polyimide, Du Pon)
A plate (trade name of company t) 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. There is a description of polyimide in the heat insulation layer, but there is no further description.
Further, US Pat. No. 5,004,627 discloses a method of coating the surface of a mold with a fluorinated polyimide in order to improve the mold releasability at the time of injection molding. It works as an agent. Fluorine compounds are generally remarkably excellent in slipperiness and releasability with the same substance or other substances, and are widely used as a lubricant, a release agent and a release agent.

In US Pat. No. 5,004,627, this property of fluorinated polyimide is used to make a release agent, and the fluorinated polyimide cannot firmly adhere to a mold.

[0007]

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.

INDUSTRIAL APPLICABILITY The present invention can be applied to a mold in which the mold surface is covered with a heat insulating layer, and can be applied to a mold having a mold cavity with a complicated shape. It is to provide a mold capable of achieving high durability and durability of mold surface reproducibility, for example, a high-gloss molded product can be obtained.

[0009]

In order to achieve this object, the inventors of the present invention have investigated a mold covered with a heat insulating layer, and have investigated the heat insulating substance for covering the surface of the main mold, its coating state,
We have found that the following are very important for the coating method. That is, regarding the heat insulating layer, it is substantially a thin layer on the outermost surface of the mold, and regarding the heat insulating material, it has low thermal conductivity, excellent heat resistance, high tensile strength, high elongation and cold heat. Cycle-resistant, high surface hardness, excellent wear resistance, good adhesion to the mold body, surface polishing, further when forming a heat insulating layer or using synthetic resin using this mold It is excellent in corrosion resistance during molding.

Therefore, the inventors of the present invention have conducted further researches on a heat insulating material, a coating state and a coating method which satisfy these matters, and as a result, have reached the present invention for the first time. That is, the present invention has a thermal conductivity of 0.05 cal at room temperature.
Is a mold in which a polyimide layer is provided on a mold wall surface forming a mold cavity of a main mold made of a metal having a temperature of at least 1 / cm · sec · ° C., and the polyimide layer is (1) 0.02 to 2 m.
m thickness, (2) thermal conductivity is 0.002 cal / cm
・ Sec · ° C or less, (3) glass transition temperature is 20
A polyimide having a high heat resistance of 0 ° C. or higher and (4) applying a precursor solution of a straight-chain high-molecular-weight polyimide containing no fluorine to a mold wall surface and then heating the same.
(5) The synthetic resin molding die is characterized in that its breaking elongation is 10% or more, and (5) the adhesion to the mold wall surface is 500 g / 10 mm width or more.

The present invention will be described in detail below. As described above, there are many known documents about a method of improving the mold surface reproducibility of a molded product by coating the surface of a main mold made of metal with a thin heat insulating layer made of synthetic resin. However, although these molds are conventionally simple molds and can be used for molding with a small number of molding times, it is possible to form a mold cavity with a strong material such as steel in a full-scale mold that can withstand tens of thousands of moldings. It is common sense so far. In injection molding, a synthetic resin is injected into a thin mold cavity of about 2 mm at high speed, so it is essential to form a mold cavity with a strong material such as steel for a full-scale mold that performs tens of thousands of times. It is believed that.

We have conducted a deeper study on this, and even if the surface of the main mold is covered with a thin synthetic resin, if a heat insulating layer made of a synthetic resin satisfying certain conditions is used, tens of thousands of injections are performed. The present invention was discovered by discovering that it withstands 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 resin subsequently injected is between the solidified layer and the solidified layer. When it reaches the flow front, it moves 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. .

The main mold material used in the present invention has a thermal conductivity of 0.05 cal / cm.sec..degree. C. or more, and iron or a steel material containing 50 wt% or more of iron, aluminum or 50 wt% of aluminum. Metals generally used for synthetic resin molds such as alloys, zinc alloys, copper alloys, such as beryllium copper alloys, contained above are included. In particular, steel materials can be used most preferably.

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

[0016]

[Table 1]

In the injection molding, the heated and plasticized synthetic resin is injected into the cooled mold and is cooled and molded in the mold. Therefore, for each molding, one mold surface is used.
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 that can withstand this stress for tens of thousands of times, both breaking strength and breaking elongation are large, and it is necessary that the adhesive force with the mold is large, and a substance such as fluorine that inhibits the adhesiveness with the mold is used. It has been discovered that tough, straight chain, high molecular weight polyimides that do not contain are most preferred.

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.

[0019]

[Table 2]

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

[0021]

[Table 3]

[0022]

[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 complicated mold surface with polyimide and firmly adhere it, it was found that it is most preferable to apply a polyimide precursor solution and then heat to form the polyimide, and arrived at the present invention. . The polyimide of the present invention does not substantially contain fluorine or the like which hinders the adhesion to the mold. It is formed by coating a precursor solution of a straight-chain high-molecular-weight polyimide on the wall surface of a mold and then heating it. The polyimide is a highly heat resistant resin having a glass transition temperature (hereinafter abbreviated as Tg) of 200 ° C. or higher, is excellent in strength and elongation, and has a breaking elongation of 1
0% or more, the adhesion to the mold wall is 500g / 10m
m 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.

[0025]

[Chemical 1]

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

[0027]

[Chemical 2]

[0028]

[Chemical 3]

[0029]

[Chemical 4]

[0030]

[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 adhesion with the mold. Minor additives can be added. Among these polyimides, pyromellitic dianhydride (PMDA) -based polyimides are most preferable because of their excellent heat resistance and mechanical properties. In particular, a varnish modified for coating can be favorably used. 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 polyimide of the present invention does not contain fluorine. This means that the polyimide does not contain fluorine that greatly reduces the adhesion to the main mold, and fluorine that does not substantially affect the adhesion is irrelevant. Generally, when the fluorine content in the polyimide exceeds 10% by weight, the adhesive force and the peeling force increase. In the present invention, fluorine is 10% by weight or less, preferably 5% by weight or less, more preferably 1% by weight.
It is the case where the following is not contained.

The smaller the thermal conductivity of polyimide is, the more preferable it is, but the thermal conductivity of polyimide is 0.002 cal / cm.multidot.
Those having a temperature of sec · ° C. or less can be preferably used. The thickness of the polyimide layer is appropriately selected within the range of 0.02 to 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. Also, the preferable thickness of the polyimide layer varies depending on the molding method in which the mold of the present invention is used.
In injection molding in which the mold of the present invention can be best used,
The thickness is preferably 0.02 to 0.5 mm, more preferably 0.05 to 0.2 mm. On the contrary,
In extrusion blow molding, a thickness of 0.1 to 1 mm is preferable.

The strength and elongation of the linear high-molecular-weight polyimide used in the present invention must be high, and in particular, the high elongation at break is essential for the heat and cold resistance cycle.
The required breaking elongation is 10% or more, preferably 20% 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, and therefore it is the best method to polish the applied coating layer to a mirror-like 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 breaking elongation 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 and the like 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 blended with various reinforcing materials and various fillers, or when they are polymer alloys or the like, 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 described mainly by injection molding, the mold of the present invention can be used in blow molding as well.

[0042]

EXAMPLES Each mold and each polyimide used in the examples are as follows. (1) Mold Main mold: Steel (S55C) (thermal conductivity of about 0.2 cal /
cm / sec / ° C. ), 100mm x 100
mm square, with side gates on the sides of the square, and with a flat mold cavity with a thickness of 2 mm. (2) Polyimide Polyimide (A): Linear polyimide precursor, polyimide varnish "Trenis # 3000" (Toray brand name).
Tg after curing is 300 ° C, thermal conductivity is 0.0005ca
It was 1 / cm · sec · ° C and the elongation at break was 60%.

Polyimide (B): Linear polyimide precursor, polyimide varnish "Larc-TPI" (trade name of Mitsui Toatsu). Tg after curing is 256 ° C., thermal conductivity is 0.00
It was 05 cal / cm · sec · ° C and the elongation at break was 25%. Polyimide (C): Linear polyimide precursor, polyamideimide "AI-10" (Amoco Japan Limited product) solution. Tg after curing is 230 ° C, thermal conductivity is 0.0
It was 005 cal / cm · sec · ° C. and the elongation at break was 40%.

[0044]

Example 1 Three main molds are prepared, and the mold surfaces of the molds are polished with sandpaper or the like to form molds having various surface roughnesses. The mold surface is thoroughly degreased, then polyimide (A) 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. Form. Next, a diamond paste is applied to the buff and polished with an electric grinder to form a 0.05 mm thick mirror-like linear polyimide coating layer.

The coating layer is cut into a width of 10 mm and pulled at a rate of 20 mm / min in the direction perpendicular to the coated surface to measure the adhesive force. The results are shown in Table 5. The adhesion between the main mold and the polyimide is 0.6 kg / 10 mm width or more, and the adhesion between the buffed main mold and the polyimide (A) is 1 kg.
The width is as large as / 10 mm and the variation is small, which is very preferable. It is important that the adhesive force has a large minimum value.

[0046]

[Table 5]

[0047]

Example 2 Four main molds were prepared, and each buff-finished mirror-like mold was thoroughly degreased, then polyimide (A),
(B) and (C) are respectively applied, and a mirror-like linear polyimide coating layer having a thickness of 0.04 mm and 0.1 mm is formed in the same manner as in Example 1. Using the linear polyimide-coated mold and the main mold, rubber-reinforced polystyrene # 495 (manufactured by Asahi Kasei Corporation) was injection-molded, and the glossiness of the molded product was measured.
The results are shown in Table 6. Polyimide (A), (B), (C)
So you get exactly the same result. When coated with polyimide, the gloss of the molded product is remarkably improved, and even after injection molding is performed 10,000 times, no abnormality on the mold surface and no decrease in the gloss of the molded product are observed.

The injection molding conditions and the glossiness measurement conditions are 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 K7
105, reflection angle 60 degrees

[0049]

[Table 6]

[0050]

Example 3 A silane coupling agent KBE903 (produced by Shin-Etsu Chemical Co., Ltd.) is applied to the surface of a 0.04 mm-thick and 0.1 mm-thick specular linear polyimide layer formed on the surface of a mold by the method shown in Example 2. Is 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 is applied.

Using this mold, injection molding is carried out in the same manner as in Example 2 to obtain an injection molded product having substantially the same high gloss.
By applying the silicone hard coat layer on the outermost surface, it is possible to prevent scratches during handling of the mold.

[0052]

[Comparative Example] A fluorinated polyimide precursor solution having a repeating unit represented by the following formula was applied to a main mold, and heated to 0.
05mm thick fluorinated polyimide (fluorine content is 17
%) To obtain a mold coated with

[0053]

[Chemical 6]

The adhesion between the polyimide and the mold is 0 to 0.5.
With a width of kg / 10 mm, there is a large variation in the adhesion force depending on the measurement location, and there is zero at some locations. Such a heat-insulating layer having a low adhesive force cannot withstand injection molding accompanied by tens of thousands of severe cooling and heating cycles.

[0055]

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. .

Claims (1)

[Claims] 1. The thermal conductivity at room temperature is 0.05 cal.
Is a mold in which a polyimide layer is provided on a mold wall surface forming a mold cavity of a main mold made of a metal having a temperature of at least 1 / cm · sec · ° C., and the polyimide layer is (1) 0.02 to 2 m.
m thickness, (2) thermal conductivity is 0.002 cal / cm
・ Sec · ° C or less, (3) glass transition temperature is 20
A polyimide having a high heat resistance of 0 ° C. or higher and (4) applying a precursor solution of a straight-chain high-molecular-weight polyimide containing no fluorine to a mold wall surface and then heating the same.
(5) A synthetic resin molding die characterized by having a breaking elongation of 10% or more and (6) an adhesive force with a mold wall surface of 500 g / 10 mm width or more.