JP3268067B2 - 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 particularly, it relates to a mold for injection molding or blow molding that can withstand tens of thousands of moldings.

[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 becomes longer, 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 respectively, and a heating medium and a coolant are alternately flowed to repeat 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 the mold, the surface of the mold is made of a metal such as aluminum or nickel. A mold structure as a mold body is shown. The purpose of providing the heat insulating layer is to greatly reduce the cooling rate of the injected heated resin, and as the heat insulating layer, a liquid crystal polymer plate having a thickness of several mm, Vespel (a molded polyimide, DuPont
(T company name) is shown. JP-A-62-371
No. 07 describes a method of attaching a heat-insulating layer having air permeability to the mold surface to prevent the occurrence of silver streaks and the like.

[0005] It has generally been considered difficult to adhere a metal and a heat-resistant resin that differ in thermal expansion coefficient by almost an order of magnitude and maintain the adhesion in tens of thousands of molding cycles. Injection molding has the greatest advantage in that a molded article with a complicated shape can be obtained by one molding, and while maintaining this advantage, the cooling time in the mold does not increase and the reproducibility of the mold surface is improved. There is a demand for molding an improved mirror-like molded article.

An object of the present invention is to provide a mold having a mold surface covered with a heat insulating layer, which can be applied to a mold having a complex-shaped mold cavity, and a small increase in cooling time.
3) A mold capable of withstanding tens of thousands of repeated moldings and 4) having excellent mold surface reproducibility, for example, a high gloss molded product can be obtained. 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,
It should have good adhesion to the mold body and be excellent in corrosion resistance when forming the heat insulating layer or when molding the synthetic resin using the present mold.

The inventors of the present invention have disclosed a mold capable of withstanding long-term molding and improving mold surface reproducibility by coating the surface of the mold with a linear high molecular weight polyimide.
74 mag.

[0008]

The present invention is based on the above and is a further improvement. That is, the mold of the present invention is used for injection molding and blow molding of synthetic resin.
It is to provide a molded article having an excellent appearance.

[0009]

That is, the present invention provides:
Thermal conductivity at room temperature is 0.05 cal / cm · sec
The mold wall forming the mold cavity of the main mold made of a metal having a temperature of not less than ° C has a thermal conductivity of 0.002 cal / cm · s.
a mold covered with a heat insulating layer of ec · ° C or less; (1)
(2) the heat insulating layer is a heat-resistant polymer having a glass transition temperature of 150 ° C. or more,
(3) The present invention relates to a synthetic resin molding die in which the surface of the heat insulating layer is covered with a hard thin film made of a polymer mainly composed of polysiloxane and epoxy resin.

Further, it is preferable that the hard thin film is a mold made of a polymer containing polydiphenylsiloxane and a bisphenol A epoxy resin as main components. A mold having a breaking elongation of 10% or more and / or a coefficient of thermal expansion of the heat-resistant polymer of 3 times or less and 0.5 times or more of the thermal expansion coefficient of the main mold. It is. Further, it is preferable that the heat-resistant polymer is a mold made of polyimide.

Hereinafter, the present invention will be described in detail. It has been found that even if the surface of the main mold is coated with a thin synthetic resin, it can withstand tens of thousands of injection moldings if a heat insulating layer made of a synthetic resin meeting certain conditions is used. That is, in injection molding, the heat plasticized resin injected into the mold comes into contact with the cooled mold wall surface and immediately forms a solidified layer on the contact surface, and the subsequently injected resin flows between the solidified layer and the solidified layer. When it reaches the flow front, it is directed 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, if the mold surface is covered with a thin heat-insulating layer made of the selected synthetic resin, the heat-insulating layer will not be 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, iron or a steel material containing 50% by weight or more of iron, or aluminum or 50% by weight of aluminum. Metals generally used in synthetic resin molds, such as alloys, zinc alloys, copper alloys such as beryllium copper alloys, are included. In the case where the surface of the main mold made of steel or the like is directly coated with the heat insulating layer, the surface of the main mold is easily deteriorated in the coating process, the adhesiveness with the heat insulating layer becomes unstable, and the peeling easily occurs. In order to improve this, it is very preferable to coat the heat insulating layer after chromium plating and / or nickel plating on the main mold surface.
By performing chrome plating and / or nickel plating, surface deterioration is unlikely to occur and the surface is stabilized. Further, it is possible to increase the contact area by making the nickel plating and / or chromium plating surface rough, if necessary.

The heat insulating layer has a glass transition temperature of 150 ° C. or more,
Preferably a heat-resistant polymer of 200 ° C. or higher,
Preferably, the heat-resistant polymer has a breaking elongation of 10% or more, and / or the thermal expansion coefficient of the heat-resistant polymer is 3 times or less, 0.5 times or more of the thermal expansion coefficient of the main mold. The elongation at break is measured according to ASTM D638. The coefficient of thermal expansion is a coefficient of linear expansion measured according to ASTM D696.

In the injection molding, a heated and plasticized synthetic resin is injected into a cooled mold, and the synthetic resin is cooled and molded in the mold.
Every time heating and cooling up to 00 ° C. are repeated, severe stress is generated at the interface between the main metal and the heat insulating layer.
As a heat insulating layer that can withstand this stress tens of thousands of times, whether the breaking strength and the breaking elongation are large and the adhesion to the mold is large, and / or the coefficient of thermal expansion of the heat insulating layer is the coefficient of thermal expansion of the main mold It is preferably 3 times or less and 0.5 times or more.

The polymer which can be favorably used as the heat-insulating layer in the present invention is a heat-resistant polymer having an aromatic ring in its main chain, and various heat-resistant polymers such as polyimide and polybenzimidazole can be favorably used. There are various types of polyimides, and linear high molecular weight polyimides can be used favorably. Generally, linear high molecular weight polyimide has a large elongation at break and is excellent in durability.

Table 1 shows examples of straight-chain high molecular weight polyimides which can be favorably used in the present invention. Here, Tg represents a glass transition temperature, and n represents the number of repeating units.

[0018]

[Table 1]

The Tg of the linear polyimide differs depending on the constituent components, and examples thereof are shown in Tables 2 and 3. Tg is 15
A polymer at 0 ° C. or higher is used, preferably at 200 ° C. or higher, more preferably at 230 ° C. or higher.

[0020]

[Table 2]

[0021]

[Table 3]

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. It is preferable that the polyimide of the present invention does not substantially contain a substance that inhibits adhesion to a mold, but the adhesion is improved by coating a rough mold surface with nickel or the like to form a rough nickel. Compounds of modified polyimides and various additives can be used within a range that improves the adhesion and does not significantly reduce the adhesion. The polyimide coating is formed by applying a polyimide precursor solution to a mold wall surface and then heating.

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]

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These polyimide precursors are heated to cause a dehydration cyclization reaction to form a polyimide. The most preferable straight-chain polyimide precursor 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),
(Formula 5)

[0026]

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[0027]

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[0028]

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[0029]

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The polymer of the above polyimide precursor is N-
It is dissolved in a solvent such as methylpyrrolidone and applied to the mold wall. 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 thixotropic property, and / or to increase the adhesion with the mold Minor additives can be added. Varnishes modified for application can be used successfully. However, additives that greatly increase the thermal conductivity of polyimide are not preferred.

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. Further, the polymer which can be used in the present invention is a heat-resistant polymer having a small coefficient of thermal expansion having a coefficient of thermal expansion of 5 × 10 ⁻⁵ or less, more preferably 4 × 10 ⁻⁵ or less. The closer the coefficient of thermal expansion between the polymer and the main mold, the better. The thermal expansion coefficient of the polymer is preferably 3 times or less, 0.5 times or more, more preferably 2 times or less, of the thermal expansion coefficient of the main mold.
It is 0.6 times or more at times or less. The coefficient of thermal expansion used here is a coefficient of thermal expansion between room temperature and 100 ° C.

In the present invention, if a polymer and a mold having a similar thermal expansion coefficient are combined, even a polymer having a breaking elongation of less than 10% can withstand a thermal cycle. The following table shows various metals generally used in molds and approximate values of thermal expansion coefficients of various resins.

[0033]

[Table 4]

Among them, a combination of a metal having a large thermal expansion coefficient and a resin having a small thermal expansion coefficient, that is, a combination having a metal and a resin having similar thermal expansion coefficients is suitably used in the present invention. As the polymer having a small coefficient of thermal expansion, polybenzimidazole (hereinafter abbreviated as PBI), low-thermal-expansion-type polyimide and the like can be used favorably. PB shown in (Chem. 6)
I: Poly- [2,2 ′-(m-phenylen
e) -5,5'-bibenzimidazole] easily turns into a solution, so that it can be applied to the mold wall surface and has good adhesion to the mold wall surface, and can be used favorably in the present invention. This PBI has a small coefficient of thermal expansion, a coefficient of thermal expansion substantially equal to that of aluminum, and a glass transition temperature of 40.
It is close to 0 ° C. and can be favorably used in the present invention.

[0035]

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As the polymer, a low thermal expansion type polyimide can be favorably used in the present invention. Table 2 shows the thermal expansion coefficients of various low thermal expansion polyimides. In the table, Bifix and Fr
ee means that when the polyimide precursor is imidized to form a polyimide film, the film can be freely shrunk (Free) or fixed to a square frame,
The difference is whether the polymer chains are oriented in-plane by the stress while suppressing the shrinkage that occurs during imidization (Bixix). After the polyimide precursor solution is applied to the main mold, the polyimide formed by heating has a coefficient of thermal expansion intermediate between Free and Bifix. Among these, the biphenyltetracarboxylic acid type polyimide is soluble in a solvent and can be easily applied to the mold wall surface, so that it can be favorably used in the present invention.

[0037]

[Table 5]

The adhesive strength between the heat insulating layer of the present invention and the main mold is 0.5 kg / 10 mm width or more at room temperature, preferably 0.8 kg / 10 mm width or more, more preferably 1 kg / mm.
The width is 10 mm or more. This is a 10m
This is the peeling force when cut into m widths and pulled at a speed of 20 mm / min in a direction perpendicular to the adhesive surface. Although this peeling force varies considerably depending on the measurement location and the number of measurements, it is important that the minimum value is large, and it is preferable that the peeling force be stably large. The adhesion described in the present invention is the minimum value of the adhesion of the main part of the mold.

Although the heat conductivity of the heat insulating layer is preferably as small as possible,
Generally, the thermal conductivity of the polymer is 0.002 cal / cm · s
ec · ° C. or less. The thickness of the heat insulating layer is 0.02 to 2 m
m is selected appropriately. When the thickness is less than 0.02 mm, the effect of improving the surface of the molded product is small, and when 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 heat insulating layer as the mold temperature increases, and to increase the thickness of the heat insulating layer as the mold temperature decreases.
It is appropriately selected in the range of mm. The preferred 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 from 0.02 to 0.5 mm, and more preferably from 0.05 to 0.2 mm. On the other hand, in extrusion blow molding, a thickness of 0.1 to 1 mm is preferable.

The biggest advantage of injection molding is that a mold having a complicated shape can be formed in a single molding operation. Therefore, the mold cavity generally has a complicated shape. It is extremely difficult to apply the coating substance to the surface of the complicated mold cavity in a mirror-like manner, and therefore, the best method is to polish the surface of the applied coating layer to finish the mirror-like shape. Therefore, it is preferable that the coating material can be polished and mirror-finished. However, it is not easy to make the mirror surface almost the same as the polished surface of the metal mold.

In the present invention, in order to further improve the smoothness and the like of the surface of the heat insulating layer or to further improve the scratch resistance of the surface, polysiloxane and epoxy resin having a thickness of 1/10 or less of the thickness of the heat insulating layer are used. It has been found that it is extremely effective to apply a polymer thin film as a main component to the surface of the heat insulating layer. It is common practice to apply a coating generally used as a hard coat agent, which is used for improving scratch resistance, to the surface of a synthetic resin sheet or mold. When used in the present invention, good adhesion to the heat insulating layer, hard,
It is necessary to have durability enough to withstand tens of thousands of moldings, and it has been found that a polymer mainly composed of polysiloxane and an epoxy resin is effective for this purpose. In particular, they have found that a polymer mainly composed of polydiphenylsiloxane and a bisphenol A epoxy resin is preferable. That is, a composition in which the polysiloxane and the epoxy resin are compatible with each other, and which is hard, durable, and has good adhesion to the heat insulating layer is required. The obtained polymer proved to be very favorable. When the terminal of the polysiloxane has reactivity with the epoxy group, the polysiloxane and the epoxy resin are more integrated, which is preferable in the present invention. The bisphenol A epoxy resin is synthesized from bisphenol A and epichlorohydrin and generally has the following structural formula. N in the formula is used in the range of 0 to 20, preferably 0 to 5.

[0042]

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In the present invention, a polysiloxane and an epoxy resin are mainly used.
The polymer is contained in an amount of at least 60% by weight, preferably at least 60% by weight, more preferably at least 80% by weight. The polysiloxane and the epoxy resin are used in a weight ratio of 1: 5 to 5: 1. A composition comprising polysiloxane and epoxy resin diluted with a solvent is blended with various curing agents and the like, applied to a heat insulating layer, and then cured by heating to form a polymer thin film of the present invention.

The thickness of the polymer mainly composed of polysiloxane and epoxy resin is preferably 1/10 or less of the thickness of the heat insulating layer, more preferably 1/20 or less, and it is a thin layer having a thickness of 0.1 μm or more and 10 μm or less. . If it is a thin layer, it can withstand a thermal cycle even if the elongation at break of the thin layer is relatively small.
The synthetic resin which can be molded by the mold of the present invention is a thermoplastic resin which can be generally used for injection molding, blow molding and the like. For example, a styrene polymer or a copolymer thereof, polyethylene,
Olefin polymers such as polypropylene or copolymers thereof,
General thermoplastic resins such as vinyl chloride polymers or copolymers thereof, polyacetals, polyamides and polyesters can be used.

Particularly when these resins are mixed with various reinforcing materials and various fillers, or when a polymer alloy or the like is used, a particularly great effect can be obtained. 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. In addition, recycled resin containing foreign matter such as dust and paint powder can 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 similarly used in blow molding.

[0047]

EXAMPLES The following various substances are used. The main die is made of steel (S55C) (thermal conductivity about 0.2 cal / cm · sec)
.Degree. C.), has a side gate on the side of a 100 mm.times.100 mm square, and has a 2 mm thick plate-shaped cavity. The mold surface is mirror-polished and hard chrome plated.

The polyimide cures a straight-chain polyimide precursor, polyimide varnish “Trenice # 3000” (trade name of Toray). The Tg of the cured polyimide is 300
° C, thermal conductivity 0.0005 cal / cm · sec · ° C Elongation at break is 60%. Polymer composed mainly of polysiloxane and epoxy resin: YP-932 composed mainly of polydiphenylsiloxane and bisphenol A epoxy resin
7 (manufactured by Toshiba Silicon Corporation).

The synthetic resin is rubber-reinforced polystyrene, Asahi Kasei Polystyrene 495 (manufactured by Asahi Kasei Kogyo Co., Ltd.). Two main dies are prepared, and the surfaces of the dies are processed as follows. (A): The above mold surface is sufficiently degreased, and then polyimide is applied and heated in the order of 120 ° C. to 210 ° C.
This coating and heating are repeated three times and finally heated to 290 ° C. to form a polyimide layer. Next, a diamond paste is applied to the buff and polished to form a smooth linear polyimide coating layer having a thickness of 0.05 mm. (B): A solution mainly composed of polysiloxane and epoxy resin, YP-9327, is applied to the surface of the polyimide layer formed in the same manner as in (A), and cured by heating at 150 ° C. to a 2 μm-thick polymer thin film. Is mirror-finished.

Using two molds (A) and (B), injection molding of synthetic resin was performed. The molded product molded by the mold of (B) is clearly superior in gloss to the molded product of (A).

[0051]

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

Continuation of front page (56) References JP-A-55-55839 (JP, A) JP-A-54-142266 (JP, A) JP-A-62-37107 (JP, A) JP-A-62-208919 (JP) JP-A-61-222708 (JP, A) JP-A-5-131456 (JP, A) JP-A-6-34927 (JP, A) JP-A-6-315955 (JP, A) 6-15776 (JP, A) JP-A-4-62125 (JP, A) JP-A-4-211912 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B29C 33/38 B29C 45/37 B29C 49/48

Claims (3)

(57) [Claims] 1. The thermal conductivity at room temperature is 0.05 cal.
/Cm.sec..degree. C. or higher, the mold wall forming the mold cavity of the main mold made of metal having a thermal conductivity of 0.002c
a mold covered with a heat insulating layer of al / cm · sec · ° C. or less; (1) the heat insulating layer is 0.02 to 2 mm thick;
(2) The heat insulating layer is a heat-resistant polymer having a glass transition temperature of 150 ° C. or higher. (3) The surface of the heat insulating layer is covered with a hard thin film made of a polymer mainly composed of polysiloxane and epoxy resin. There is a synthetic resin mold. 2. The mold according to claim 1, wherein the polymer thin film comprises a polymer containing polydiphenylsiloxane and bisphenol A epoxy resin as main components. 3. The heat-resistant polymer has an elongation at break of 10% or more,
The mold according to claim 1 or 2, wherein the thermal expansion coefficient of the heat-resistant polymer is 3 times or less and 0.5 times or more of the thermal expansion coefficient of the main mold.