WO1996012599A1 - Synthetic resin molding method - Google Patents

Abstract

A synthetic resin molding method in which the molding is done by using a metal mold which is obtained by covering a cavity-forming wall surface of a metal mold body with one or not less than two insulating layers of a heat resisting polymer, and which has a difference between a thermal expansion coefficient of the metal mold body-contacting insulating layer and that of the metal mold body of less than 2 x 10-5/°C. When the method according to the present invention is used for the injection molding or blow molding of a synthetic resin using a metal mold coated with a special insulating layer, the separation of the insulating layer from the metal mold does not occur, and the metal mold comes to have a durability. This method also enables a molded product having a good external appearance to be obtained. The method according to the present invention therefore enables an injection molded product, such as a housing for a light electric appliance, which has heretofore required a posterior process, such as painting due to many weld lines occurring thereon, to be obtained without carrying out a painting step.

Description

 Ming glue Synthetic resin molding method

<Technology field>

 The present invention relates to a method for molding a synthetic resin. More particularly, the present invention relates to a synthetic resin molding method such as an injection molding method and a blow molding method using a mold covered with a heat insulating layer and having durability.

 <Background technology>

 When a thermoplastic resin is injected into a mold cavity and molded, improving the reproducibility in imparting the shape of the mold surface to the molded product and improving the gloss of the molded product usually require a resin. This can be achieved to some extent by selecting molding conditions such as raising the resin temperature and increasing the injection pressure.

The most significant of these conditions is the mold temperature, with higher mold temperatures being preferred. However, if the mold temperature is increased, the cooling time required for cooling and solidifying the plasticized resin is prolonged and the molding efficiency is reduced, so that the mold temperature is not increased. There is a need for a method that improves the reproducibility of the mold surface and does not increase the required cooling time even if the mold temperature is increased. As an example of the latter, there is a method in which holes for heating and cooling are provided in the mold, and heating and cooling of the mold are repeated by alternately flowing a heating medium and a cooling medium. Consumes a lot of heat and has a long cooling time There is a disadvantage.

 On the other hand, in conventional injection molding, a method to improve the mold surface reproducibility by coating the mold wall forming the mold cavity with a substance having low thermal conductivity, that is, a heat insulating layer The present inventors have proposed in European Patent Publication No. 0 559 098 A1, for example. In this case, if a tough heat-resistant polymer with a large adhesion to the die body and a large elongation at break is selected as the heat insulating layer, the die can withstand tens of thousands of moldings. It is shown. However, depending on the shape of the mold and the thickness of the heat-insulating layer, there is a problem that the heat-insulating layer is separated from the mold body during molding. Furthermore, USP3, 7334 and 449 show molds in which a metal mold wall is coated with a heat insulating layer, and the heat insulating layer surface is coated with a thin metal layer. However, there is a problem that separation between the thin metal layer and the heat insulating layer occurs during molding.

In recent years, the painting process has been required to omit post-processing such as painting of injection molded products and blow molded products, that is, to reduce manufacturing costs and reduce environmental destruction due to solvent evaporation during painting. The demand for elimination has become extremely strong. There is an extremely strong demand for the elimination of post-processing for housing of electrical equipment and electronic equipment. Generally, these housings have a complicated shape, and many molded products have a shape having a substantially right-angled corner. Also, due to its complex shape, it is molded by multipoint gate injection molding. As a result, a large number of well lines are generated in the molded product, and this poor appearance dry line is eliminated. For this reason, it has required a paint finish. Many attempts have been made to obtain molded products that can be used practically without painting.

 The present inventors have studied various methods for covering the wall surface of the mold cavity with a heat insulating layer, improving the reproducibility of the mold surface, and reducing well-dwelling. As a result, uniformly covering the heat-insulating layer made of the heat-resistant polymer on the wall constituting the cavity of the mold for forming a molded article having a complicated shape is extremely effective for the above purpose. I knew it. However, there are various problems in applying this method to practical dies as follows.

 (1) If the heat insulating layer is coated on the almost right-angled sharp corners of the mold wall, the heat-insulating layer applied to the corners is likely to be separated, so that the shape of the molded product should be a shape avoiding the right-angled portions. There is a need to.

 (2) The present inventors have studied the application of a mold covered with a heat insulating layer to blow molding, and found that it is necessary to make the heat insulating layer thicker in blow molding. However, there is a problem that the separation is likely to occur as the thickness of the thermal insulation layer is increased.

 (3) When a polymer is used as the heat-insulating layer, the heat-insulating layer is easily damaged during use and needs to be improved.

(4) In molding using a mold covered with a heat-insulating layer made of a polymer, if the synthetic resin to be molded has polarity such as polyamide, it is released from the mold during molding. May be difficult, and improvement is needed. (5) By attaching a metal layer to the surface of the heat insulating layer made of a polymer by metal plating, etc., to prevent the heat insulating layer from releasing or being damaged, a synthetic resin Heating and cooling are repeated on the mold surface during molding, and the metal layer on the surface is easily peeled off in this cooling / heating cycle, and it is necessary to prevent this.

 Disclosure of the invention

 In order to solve these problems, the present inventors studied a mold covered with a heat insulating layer, and more specifically, a material of the heat insulating layer covering the surface of the mold body, its coating state, and heat insulation. When the layer material is combined with the material of the mold body, and when the outermost surface of the heat insulation layer is covered with a metal layer, the metal layer is examined and the heat insulation layer is combined with the mold body and the metal layer. The present inventors have discovered that it is extremely important that the difference between the coefficients of thermal expansion is small, and have led to the present invention.

 That is, the present invention is obtained by coating one or more heat-insulating layers made of a heat-resistant polymer on a wall constituting a cavity of a metal mold body, and The present invention relates to a synthetic resin molding method in which molding is performed using a mold in which a difference between a coefficient of thermal expansion of a heat insulating layer in contact with the main body and a coefficient of thermal expansion of the mold main body is less than 2 × 10 Z ° C.

 <Simple explanation of the drawing>

 Figure 1 shows the change (calculated value) in the temperature distribution near the mold surface when the heated synthetic resin comes into contact with the steel mold body.

Figure 2 shows a 0.1 mm polish on the surface of the steel mold body. The change (calculated value) of the temperature distribution near the mold surface when the heated synthetic resin comes into contact with the mold coated with the limit is shown.

 Figure 3 shows the temperature distribution near the mold surface when heated synthetic resin comes into contact with a mold in which 0.5 mm of polyimide is coated on the mold surface of a steel mold body. Changes (calculated values) are shown.

 FIG. 4 is an explanatory diagram for blow molding a synthetic resin using the mold of the present invention.

 FIG. 5 is an explanatory diagram of a molded product obtained by blow molding a synthetic resin with the mold of the present invention.

 Figure 6 shows the temperature change of the mold surface (polyimide surface) when blow molding at a steel mold body temperature of 70 ° C and an ABS resin temperature of 220 ° C. (Calculated value).

 FIGS. 7A and 7B show the separation of the heat insulating layer at the corners of the mold, which occurs when the heat insulating material is applied to the wall of the mold cavity at a right angle.

 FIGS. 8A, 8B, 8C and 8D show an example of a method of coating a heat insulating layer on the surface of the mold body.

 FIG. 9 is a diagram showing a general polyimide having a bent structure.

 FIG. 10 is a view showing a low thermal expansion type polyimide having a rigid structure.

 Explanation of reference numerals

1 Mold body 2 Thermal insulation layer

 Type 3 key bit

4 no, ⁰ ri

 5 Metal layer

 6 Blow molded product

 7 Mold body

 8 Insulation solution

 9 Insulation layer

 1 0 corner

 1 1 Mold body

 1 2 pore

 1 3 conduit

 1 Suction port

 1 5 Heat-resistant polymer sheet

 16 Pore for gas removal

 1 7 Metal layer

 <Best Mode for Carrying Out the Invention> The synthetic resin used in the present invention is a thermoplastic resin that can be used for general injection molding and blow molding. Examples thereof include polyethylene, polystyrene, and the like. Polyolefins such as propylene, polystyrene, polystyrene-acrylonitrile copolymer, rubber-reinforced polystyrene, ABS Examples include polystyrene resins such as resins, polyamides, polyesters, polycarbonates, metal acrylate resins, and vinyl chloride resins.

Synthetic resin contains 1 to 60% resin reinforcement Is preferred. Examples of the resin-reinforced material include various types of rubber, glass fibers, various types of fibers such as carbon fiber, and inorganic powders such as talc, carbonated calcium carbonate, and kaolin.

 A synthetic resin that can be used favorably is a rubber-reinforced synthetic resin. Of these, a rubber-reinforced polystyrene resin is particularly favorably used. The rubber-reinforced polystyrene-based synthetic resin described here is a resin phase in which the rubber phase is distributed in the form of islands, for example, rubber-reinforced polystyrene, ABS resin, AAS resin, MBS resin, etc. Say .

 Rubber-reinforced polystyrene is a resin in which a rubber phase such as polybutadiene or SBR is dispersed in an island shape in a resin phase of a polymer mainly composed of styrene. ABS resin is a resin in which a rubber phase such as polybutadiene and SBR is dispersed in the form of islands in a resin phase of a copolymer mainly composed of styrene and acrylonitrile. AAS resin is a resin in which the rubber phase of acrylic rubber is dispersed in the form of islands in the resin phase of a copolymer mainly composed of styrene and acrylonitrile.MBS resin is It is a resin in which the rubber phase is dispersed in the form of islands in a resin phase composed of a copolymer mainly composed of styrene and methyl methacrylate.

In addition, blends mainly composed of these resins can also be used in the present invention. For example, a blend with a rubber-reinforced polystyrene resin blended with poly (vinylene ether) can be used favorably. Injection molded products of these resins molded according to the present invention have extremely low performance and economical balance. It is suitable for use as a housing for light electrical equipment ^)

 Good molded articles molded by the molding method of the present invention are generally used as housings for light electric appliances and electronic appliances, as well as various automobile parts, various daily necessities, various industrial parts and the like.

 The molded article is preferably an injection molded article having a large number of well-lines and having sharp corners, or having a multipoint gate and having a sharp corner having a radius of curvature of less than lmm. It is suitably used as a housing for electronic devices and electric devices having the above. Further, a good molded product molded by the present invention is a blow molding metal coated with a heat insulating layer having a thickness of 0.2 mm or more, more preferably 0.3 to 0.5 mm. It is suitably used as various blow-molded products molded in a mold.

The mold body specified in the present invention includes, for example, iron or a steel mainly composed of iron, an alloy mainly composed of aluminum or aluminum, a zinc alloy, It means a metal mold generally used for molding synthetic resins such as copper-copper alloy. In particular, molds made of steel can be used favorably. The surfaces of the cavities of these metal mold bodies are preferably plated with hard chrome, nickel, or the like. The heat-resistant polymer used for the heat-insulating layer in the present invention is a polymer having a softening temperature higher than the molding temperature of the synthetic resin to be molded, and usually has a glass transition temperature of 140 ° C or more, It is preferably a heat-resistant polymer having a temperature of 160 ° C. or higher, a melting point of 200 ° C. or higher, and preferably 250 ° C. or higher. Heat resistant The thermal conductivity of the coalesced is generally 0.001 to 0.02 ca 1 / cm · sec * ° C, which is much smaller than metal. Further, the heat-resistant polymer preferably has a tensile elongation at break of 5% or more, more preferably a polymer having a toughness of 10% or more. The tensile elongation at break is measured according to ASTMD 638, and the tensile speed at the time of measurement is 5 mm / min.

 The heat-resistant polymer that can be favorably used as an insulating brow in the present invention is a heat-resistant polymer having an aromatic ring in the main chain, for example, various amorphous heat-resistant polymers soluble in organic solvents, various heat-resistant polymers. Polyimide can be used satisfactorily.

 Examples of the amorphous heat-resistant polymer include polysulfone, polyethersulfone, and polyetherimide. By blending carbon fibers or the like with these amorphous heat-resistant polymers, they can be used as the heat-insulating layer of the present invention by lowering the coefficient of thermal expansion. Although there are various types of polyimides, linear high molecular weight polyimides, polyimidimides, and partially crosslinked polyimides can be used favorably. In general, a linear high molecular weight polyimide has a large tensile elongation at break, is strong, has excellent durability, and can be used particularly well.

Further, in the present invention, an epoxy resin having a small coefficient of thermal expansion, that is, an epoxy resin in which various fillers are mixed in appropriate amounts, and the like can be used. Epoxy resins generally have a large coefficient of thermal expansion and a large difference in coefficient of thermal expansion from a metal mold. However, glass, silica, talc, clay, An appropriate amount of powder or particles such as zirconium silicate, lithium silicate, calcium carbonate, aluminum, and my strength, glass fibers, whiskers, carbon fibers, and other appropriate amounts of epoxy resin. The epoxy resin mixed with a filler having a difference in thermal expansion coefficient from the mold body of less than 2 × 10 ⁵ Z ° C can be used as the heat insulating layer of the present invention. In addition to these filler-containing epoxy resins, various compounds that impart toughness, such as nylon and rubber, are added to reduce the thermal expansion coefficient and toughness. Can be used well. The amount of the filler compounded epoxy resin is appropriately selected within the range of 15 to Ί5% by weight based on the total amount of the epoxy resin compounded, and is preferably 20 to 70% by weight. The relationship between the blending amount and the thermal expansion coefficient varies depending on the type of filler. For example, the thermal expansion coefficient of an epoxy resin containing silica and lithium silicate is approximately the following value.

 Compounding amount Thermal expansion coefficient

Shi Li force 20 ^{wt% 4.5 X 10 - 5 / °} C

 "70" 2.5 〃

 Lithium silicate 20 〃 4.2 "

 70 2.0 〃

In the present invention, it is necessary that the thermal expansion coefficient of the heat-insulating layer made of a heat-resistant polymer in contact with the mold body and the thermal expansion coefficient of the mold body are close. That is, in the present invention, the thermal expansion of the thermal insulation layer in contact with the mold body is required. The difference between the coefficient and the coefficient of thermal expansion of the mold body is less than 2 X 10 — ⁵ Z ° C, preferably less than 1.5 X 10 — ⁵ Z ° C. Preferably, the difference is less than 1 X 10 — ⁵ Z ° c. In general, metals have a lower coefficient of thermal expansion than polymers, and therefore, it is necessary to select a heat-resistant polymer having a smaller coefficient of thermal expansion.

 The coefficient of thermal expansion in the present invention is a coefficient of linear expansion. The thermal expansion coefficient of the thermal insulation layer is the linear thermal expansion coefficient of the thermal insulation eyebrows in the plane direction.

Measured according to the method shown in JISK 7197-11991, the average value between 50 ° C and 250 ° C, or the glass transition temperature of the adiabatic eyebrow below 250 ° C In this case, the average value is shown between 50 ° C. and the glass transition temperature. That is, a heat insulating eyebrow is formed on a smooth plate-like metal, and then the heat insulating layer is separated and the heat insulating layer is heated to a temperature between 50 ° C and 250 ° C or 50 ° C and a glass. The average coefficient of thermal expansion during the transition temperature is measured.

In the present invention, a mold obtained by covering with two or more insulated eyebrows can also be used favorably. This difference between the thermal expansion coefficient of the thermal expansion coefficient and a mold body of heat-insulating layer in contact with the mold body also rather small, when the 2 X 1 0 - ⁵ ° is required and this is less than C. When the mold body is covered with the heat insulating layer, or when injection molding or the like is performed using a mold covered with the heat insulating layer, the most severe stress is generated at the interface between the mold body and the heat insulating layer. The stress generated can be reduced by selecting and using an object having a thermal expansion coefficient close to that of the mold body as a heat insulating layer that forms this interface.

When the mold wall is covered with a heat insulating layer, the heat insulating layer is required to have various performances. Polishing of toughness, surface hardness, and surface, in addition to adhesion to the mold body, which is one of the issues of the present invention It is also required to be able to easily produce a glossy surface. In addition to having a small coefficient of thermal expansion, it is difficult to obtain a polymer that satisfies all of these properties by itself, and it is preferable to use two or more heat insulating layers. That is, the object of the present invention is to use a polymer having a small coefficient of thermal expansion for the heat-insulating layer on the side in contact with the mold body and a polymer having excellent performance required for the surface layer on the outer layer side. Is achieved favorably. In this case, the two heat-insulating layers need to have adhesive properties to each other, and it is preferable to select the same type of polymer as the heat-insulating layer.

Moreover, if having two or more layers of insulation layers, the difference in the thermal expansion coefficient of the insulating layer to contact the mold body 2 X 1 0 - favored correct thickness of less than ⁵ in sectional thermal layer, the thickness of the entire heat insulating layer Not less than 1% and not more than 99%, or not less than 0.05 mm and not more than 0.4 mm, more preferably not less than 5% and not more than 95% of the thickness of the total heat insulating layer, Or / and 0.01 mm or more and 0.35 mm or less.

When the outermost surface of the heat insulating layer of the mold used in the present invention is covered with a metal layer, the metal used for the metal layer is a metal generally used for metal plating and the like. Or one or more of nickel, copper, zinc, iron, aluminum, titanium, tin-cobalt alloy, iron-nickel alloy, and the like. The metal layer is coated on the surface of the heat insulating layer, and its thickness is 1/3 or less of the total thickness of the heat insulating eyebrows, preferably 1/5 or less, 1Z200 or more, and more preferably It is less than 1/10 and greater than 1/100. Gold if metal layer is too thick The effect of covering the surface of the mold body with the heat insulating layer is lost, and if the metal layer is too thin, it is not possible to achieve the purpose of applying the metal layer, such as prevention of damage. However, for the purpose of improving the releasability during molding, the effect is exhibited even if the metal layer is extremely thin. Generally, the thickness of the heat insulating layer is particularly preferably 1 Z 100 or less, and 1 Z 100 or more.

The metal for the mold body, which can be favorably used in the present invention, the metal of the metal layer covering the outermost surface of the heat insulating layer, the heat-resistant polymer of the heat insulating layer, and the heat of the synthetic resin used in the molding of the present invention Table 1 shows examples of expansion coefficients.

Table 1 Material Thermal expansion coefficient Steel 1.1 X 1 o- ⁵ / ° c Gold

 Aluminum 2.2 2 type

 Aluminum alloy 2.4 pcs

 Copper 1.7 body

 Brass 1.9

 3.3 zinc

 Zinc alloy (ZAS) 2.8 me / gold

 Tin 2.0 metal

 Chrome 0.8 layer

 Nickel 1.3 〃 Low thermal expansion type polyimide 0.4 ~ 3 Cutting General polyimide 3 ~ D ポ リ Polybenzimidazole 2.3 〃 Thermal polyimide 3 ~. 〃 Polyethersulfone * 4 to 5 • 5 layer Polysulfone * 4 to 5.6 〃 Polyetherimide * 4 to 5 • 6 〃 Polypropylene resin 6 to 9 Port Polyethylene resin 3 to 1 2 Composition Polyester resin 5 ~ Ten

 エ ポ キ シ Epoxy resin 6 to 10 〃 Resin Nylon resin 8 to 13

 Polyethylene resin 8 to 18 〃

[Note] ※ These are the resin can be reduced to around 4 X 1 0- ⁵ Z ° C the Netsu膨expansion coefficient by compounding the carbon fibers. As the coefficient of thermal expansion of the mold body increases, a heat insulating layer having a relatively large coefficient of thermal expansion can be used. Steel is the most commonly used mold material, but recently aluminum and zinc alloys have also been used. Aluminum alloys and zinc alloys have a higher coefficient of thermal expansion than steel, so that general polyimides can be used in the present invention if they are combined with aluminum alloys or zinc alloys. . However, the closer the coefficient of thermal expansion is, the more preferable. If steel is used for the mold body, a low thermal expansion type polyimide having an extremely small coefficient of thermal expansion can be used favorably. Table 2 shows the thermal expansion coefficients of various low thermal expansion type polyimides.

 In the table, B ifix and Free are each capable of freely shrinking the finolem when imidizing the polyimid precursor to form a polyimid film. The fixed force is fixed to a (Free) square frame, and the shrinkage that occurs during imidization is suppressed, and the polymer chains are oriented in-plane by the stress (Bifix). After applying the polyimide precursor solution to the mold body, the thermal expansion coefficient of the polyimide formed by heating is close to Bifix. Low thermal expansion polymer is a polymer with a polymer chain structure in which the polymer chain is rigid and extends straight. For example, in the polymer shown in Fig. 9, the polymer chain is bent, whereas in the polymer shown in Fig. 10, the polymer chain extends straight. It becomes a low thermal expansion type polyimide.

Table 3 shows the repeatability of heat-resistant polymers that can be used well in the present invention. The structure of the return unit and the glass transition temperature (T g) are shown.

Table 2 Thermal expansion coefficient of the low thermal expansion Boriimi de [10- ^S K one ']

Table 3

一般に、 射出成形は複雑な形状の成形品を一度の成形 で得られる と ころに経済的価値がある。 この複雑な金型 表面を耐熱性重合体で被覆し、 且つ強固に密着させるに は、 耐熱性重合体溶液及び Zまたは耐熱性重合体前駆体 溶液を塗布し、 次いで加熱して耐熱性重合体の断熱層を 形成させる こ とが最も好ま しい。 従って、 本発明の上記 耐熱性重合体、 あるいは耐熱性重合体の前駆体は溶剤に 溶解でき る こ とが好ま しい。

In general, injection molding has economic value where a molded article having a complicated shape can be obtained by one molding. In order to coat the complex mold surface with a heat-resistant polymer and to make it adhere tightly, a heat-resistant polymer solution and a solution of Z or a heat-resistant polymer precursor are applied, and then heated to heat-resistant polymer. It is most preferable to form a thermal insulation layer. Therefore, it is preferable that the heat-resistant polymer or the precursor of the heat-resistant polymer of the present invention can be dissolved in a solvent.

 A method in which a solution of polyamic acid, which is a precursor of polyimide, is applied to the mold wall surface and then cured by heating to form a polyimide on the mold wall surface can be used favorably. The formula for forming polyimid from polyamic acid is shown below.

ポ リ イ ミ ドの前駆体のポ リ ア ミ ド酸溶液を型壁面に塗 布 し、 次いで加熱キュアを行いポ リ イ ミ ドを形成した場 合、 加熱キュア温度及び/又は加熱キュア雰囲気によ り ポ リ イ ミ ドのガラ ス転移温度や熱膨張係数が異なる。 一 般に加熱キュア温度が高い程ガラ ス転移温度が高 く な り 又熱膨張係数が小さ く なる。 ポ リ ア ミ ド酸は一般に 2 5 0 °C以上にすればィ ミ ド化がほとんど 1 0 0 %進行 しポ リ イ ミ ドが形成されるが、 ポ リ イ ミ ドにな ってからの分 子の動きが熱膨張係数に影響を与える と考え られている。

When a polyimide precursor solution is applied to the mold wall surface and then cured by heating to form a polyimide, the heating cure temperature and / or heating cure atmosphere is reduced. The glass transition temperature and coefficient of thermal expansion of the polyimide are different. In general, the higher the heating cure temperature, the higher the glass transition temperature Also, the coefficient of thermal expansion becomes small. In general, when the temperature of the polyamic acid is raised to 250 ° C or higher, the imidization proceeds almost 100% and polyimid is formed. It is thought that the movement of the molecule affects the coefficient of thermal expansion.

 The adhesion between the heat-insulating layer of the present invention and the mold body needs to be large, and is preferably not less than 0.5 kg / 10 mm width at room temperature, more preferably. At least 0.8 kg / 10 mm width, particularly preferably at least 10 kg width. Here, the adhesion force is a separation force when the closely adhered heat insulating layer is cut into a width of 10 mm and the cut width is pulled at a speed of 2 Om mZ in a direction perpendicular to the bonding surface. Although there is considerable variation in this separation power 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 separation force be stable and large. Yes. The adhesion described in the present invention is the minimum value of the adhesion of the main part of the mold. In order to improve the adhesion, it is possible to make the surface of the mold body fine and irregular, make various platings, and perform primer treatment as appropriate.o

 Injection molding has the greatest advantage that a mold having a complicated shape can be formed at one time, and therefore, the mold cavity generally has a complicated shape. However, it is extremely difficult to apply a coating material to the surface of the mold cavity having such a complicated shape in a mirror-like manner, so that the applied coating layer is later polished to a mirror-like surface. Finishing is a good method.

The total thickness of the heat insulation layer is moderate in the range of 0.05 mm to lmm Is selected. Particularly preferably, in injection molding, the force is 0.05 mm, 0.2 mm, and in blow molding, 0.2 mm force, 0.5 mm. With a thin heat-insulating layer of less than 0.05 mm, the effect of improving the appearance of the molded product is small. If the thickness of the heat insulating layer exceeds lmm, the cooling time in the mold becomes longer, which is not preferable from an economic viewpoint.

 The surface of the mold body is covered with a heat-insulating layer made of a heat-resistant resin, and when the injected heated resin comes into contact with the surface of the heat-insulating layer, the surface of the mold is heated by the heat of the resin. The lower the thermal conductivity of the heat insulating layer and the thicker the heat insulating layer, the higher the mold surface temperature. In the injection molding of the present invention, after the injected synthetic resin comes into contact with the cooled mold surface, the mold surface temperature is at least equal to or higher than the softening temperature of the resin for at least 0.1 second. It is preferable that the state is maintained, and more preferable that the state be maintained for 0.2 seconds or more. If there is no heat-insulating layer on the surface of a commonly used metal mold body, the mold surface temperature will be almost the same as the mold body temperature after 1 second, but the mold surface will remain at 0.0. By coating with a heat insulating layer with a thickness of 5 mm to 1 mm, the mold surface can be kept at the softening temperature or higher for 0.1 seconds or more.

The change in the mold surface temperature during injection molding can be calculated from the respective temperatures, specific heat, thermal conductivity, density, latent heat of crystallization, etc. of the synthetic resin, the mold body, and the heat insulating layer. For example, using ADINA and ADINAT (software developed by the Massachusetts Institute of Technology), etc. It can be calculated by normal heat conduction analysis.

 The softening temperature of the resin described here is the temperature at which the synthetic resin can be easily deformed. The non-crystalline resin has a vicat softening temperature (ASTMD155), and the hard crystalline resin has a thermal deformation temperature. The molding temperature (ASTMD 648 load 18.6 kg / cnf) and the heat distortion temperature (ASTMD 648 load 4.6 kg Zcrf) for soft crystalline resin. Hard crystalline resins include, for example, polyoxymethylene, Nylon 6, Nylon 66, and the like, and soft crystalline resins include, for example, various types of polyethylene, polystyrene, and the like. And propylene.

In a further embodiment of the present invention, in order to further improve the smoothness or the like of the surface of the thin layer of the heat insulating material, or to further improve the scratch resistance of the surface, or to improve the release property. In order to improve the quality, it is possible to cover the surface of the heat insulating layer with another material having a thickness of less than half the thickness of the heat insulating layer. For example, it is possible to apply a coating generally used as a hard coat, which is used for improving abrasion resistance, to the surface of a synthetic resin or a mold. However, in the present invention, as described above, the above object can be favorably achieved by coating a thin metal layer on the heat insulating layer surface. The thickness of the metal layer is 1 Z 3 or less of the total thickness of the heat insulating layer. The metal layer can be coated by various methods, but can be coated by plating or the like. The plating described here is to adhere a thin layer of a hard metal to the surface of the heat insulating layer. In particular, the present invention has a high hardness and is hard to be damaged by chromium and nickel. However, it is preferable that the plating be present on the outermost surface. The plating method may be any of chemical plating and electric plating. For example, a method in which the surface of the heat insulating layer is first made moderately rough, a conductor such as copper is deposited on the surface to impart electrical conductivity, and then various metals such as nickel and chrome are plated. For example, a method of coating nickel with chemical plating can be used. Generally, the plating is performed through some of the following steps.

 Chemical corrosion (chemical etching with acid: making the surface moderately uneven) → Neutralization—Pretreatment for activation (Synthetic resin surface adsorbs metal salts with reducing power to activate ) → Activation treatment (a catalytic noble metal is applied to the resin surface) → Chemical nickel plating (nickel chemical plating) → Electric copper plating (copper plating) → Electric nickel plating (nickel electric plating) → Electric chrome plating (chromic electric plating) (For details, see "Plastic metallizing" by Rihei Tomono. (Refer to Ohmsha, etc. in 1983).

 When a metal layer is provided on the outermost surface of the heat insulating layer, the adhesion between the outermost surface of the heat insulating layer and the metal layer also needs to be large, and the adhesion between the mold body and the heat insulating layer must also be large. A similar level of adhesion is required.

In injection molding, blow molding, etc., the mold surface in contact with the heated resin to be molded is subjected to a severe cooling / heating cycle for each molding. In the prior art, the metal layer formed on the surface of the heat insulating layer by a method such as plating generally has a smaller coefficient of thermal expansion than the heat insulating layer made of a polymer, and the coefficient of thermal expansion between the heat insulating layer and the metal layer is large. Therefore, stress is repeatedly generated at the interface, and if molding is performed 10,000 times, stress is repeatedly generated 10,000 times, and finally, delamination occurs at the interface. The present invention in the heat insulation layer thermal expansion coefficient and the difference in thermal expansion coefficient of the metal brow 2 X 1 0 one ⁵ Z ° under C in contact with the metal layer is preferable to rather ^{1 5 X 1 0 -. 5} / ° C or less , 1 X 1 0 is rather to favored the al - ⁵ hand below, is intended to select the extremely thermal expansion coefficient is close, you reduce the stress caused can pull the剝離.

 Conventionally, among metals, copper, which is highly flexible, is first coated on a heat insulating layer, and then nickel and / or chromium, which is rich in hardness, is coated on the heat insulating layer. By doing so, we have avoided problems caused by differences in thermal expansion coefficients. For example, plating has been performed in the order of copper, nickel, and chromium, and copper has been made to have a total plating thickness of 34 or more.However, the problem of peeling has not been sufficiently solved. . By using a material having a very small difference in thermal expansion coefficient between the heat insulating layer and the metal layer as described in the present invention, it is not necessary to make the plating layer thicker than necessary. A good mold that can withstand long-term molding can be obtained.

The cause of separation between the heat insulating layer and the mold body is not limited to the difference in thermal expansion coefficient. However, the difference in coefficient of thermal expansion is a very significant factor. If the thermal insulation layer has a high adhesion between the mold body and the thermal insulation layer, the tensile elasticity of the thermal insulation layer is small, and the breaking elongation is large. No separation occurs even if the difference between the coefficients is slightly large. But the insulation layer Insulation materials that meet the requirements of high heat resistance, high hardness, and are easily mirror-polished by polishing are generally heat-resistant hard synthetic resins having an aromatic ring in the main chain with a large elastic modulus. In order to adhere the heat-resistant hard synthetic resin layer to the mold body so as not to cause separation, it is necessary that the difference in thermal expansion coefficient is small.

 Although the present invention has mainly been described with respect to injection molding and blow molding, it can be used in other molding methods using a mold. For example, it can be used for vacuum forming of a sheet, and a method of forming a corrugated pipe by using a corrugated mold for an extruded tube.

 The present invention will be described with reference to the drawings.

 Fig. 1, Fig. 2 and Fig. 3 show the temperature of the steel mold body at '50 ° C and the temperature of the rubber reinforced polystyrene when it was injection molded at 240 ° C. Changes in the temperature distribution (calculated values) of the synthetic resin layer near the mold wall surface, or the synthetic resin layer and the heat insulating layer are shown. The numerical value of each curve in the figure indicates the time (second) after the heated synthetic resin comes into contact with the cooled mold wall. The heated synthetic resin comes into contact with the mold wall surface and is rapidly cooled, while the mold surface receives heat from the heated synthetic resin and rises in temperature. As shown in the figure, when the mold surface is covered with 0.1 mm and 0.5 mm insulated eyebrows (Polyimide) (Figs. 2 and 3), the surface of the insulating layer that comes into contact with the synthetic resin The temperature rise increases and the rate of temperature decrease decreases.

Figures 2 and 3 show the calculated values when there is no metal layer on the outermost surface of the heat insulating layer. When a very thin metal layer of about 0 exists, the temperature distribution becomes almost the same. When the thickness of the metal layer is increased, the heat capacity of the metal is generally larger than the heat capacity of the heat insulating eyebrows, so that the mold surface is cooled and the heat insulating layer coating effect is reduced. Therefore, it is necessary that the metal layer on the outermost surface be thin, and it is preferable that the thickness of the heat insulating layer be 1 to 10 or less.

 In a mold covered with a heat-insulating layer, the shorter the time after the synthetic resin comes into contact with the mold wall, the higher the mold surface temperature. The same effect as increasing the width can be obtained, and the increase in molding cycle time is small. The numerical value shown on each curve in the figure indicates the number of seconds elapsed since the synthetic resin came into contact with the mold surface. From this figure, the mold surface temperature after a very short time from when the synthetic resin comes into contact with the mold surface and when the injection pressure is applied to the resin and the mold surface is pressed can be read from this curve.

 In FIGS. 4 and 5, the mold wall forming the mold cavity 3 of the metal mold body 1 is covered with a heat insulating layer 2, and a thin metal layer 5 is formed on the surface thereof if necessary. Is coated.

When the plastic 4 extruded by heating and plasticizing is clamped by a mold, the portions A and B of the plastic 4 contact the mold wall. Next, the pressurized gas body is blown into the balloon and blow-molded to obtain a blow-molded product 6 shown in FIG. The A 'and B' portions of the blow-molded product 6 take a long time to come into contact with the mold wall surface, and if the thickness of the heat insulating layer is not sufficient, the mold surface reproducibility deteriorates. Figure 6 shows the temperature change on the mold surface (polyimide surface) when the steel mold body was covered with polyimide. As explained in the previous figure, the longer the extruded heating pallet comes into contact with the mold wall surface, the faster the mold surface temperature drops. In order to improve mold surface reproducibility during molding, the mold surface temperature when blow pressure is applied must be equal to or higher than the softening temperature of the synthetic resin. Needs to be considerably thicker. Generally, it takes 3 to 5 seconds from the time of contact until the blow gas pressure is applied, so that the thickness of the heat insulating layer is generally required to be 0.3 mm or more.

 When the thickness of the heat insulating layer is increased, stress is generated between the eyebrows at the time of coating the heat insulating layer and at the time of Z or molding due to the difference between the thermal expansion coefficient of the heat insulating layer and the thermal expansion coefficient of the mold body and the metal layer. Separation is likely to occur at each interface. In the present invention, the stress generated by reducing the difference between the coefficient of thermal expansion of the heat insulating layer and the coefficient of thermal expansion of the mold body is reduced, and even if the heat insulating layer is thickened, it does not separate and is practical. You can get a mold. As described in the separation at the interface between the mold body and the heat insulation layer, also at the interface between the heat insulation layer and the metal layer when the surface of the heat insulation layer is coated with a metal layer, the similar thermal expansion coefficient is generated in the same way. The resulting stress is reduced and separation is less likely to occur.

Fig. 7 is a diagram for explaining the case where the heat insulating layer is applied to the mold wall surface of an injection mold having a corner part near a right angle, and general electronic equipment and electric equipment housings have such sharp edges. Corner It has A precursor solution of the heat insulating material or a solution 8 of the heat insulating material is applied to the mold body 7 (FIG. 7A), and then the applied mold body is put into a heating oven and heated to a high temperature to cut off heat. When the eyebrows 9 are formed, the heat-insulating layer 9 is generally stretched when cooled to room temperature because of its larger thermal expansion coefficient than the metal mold body, and the corners 10 are separated (FIG. 7B). . Peeling is likely to occur when the corner has a radius of curvature of lmm or less, particularly 0.5 mm or less, and a sharp corner close to a right angle.

 In order to prevent the occurrence of the separation of the corners 10, in the present invention, a material having a similar thermal expansion coefficient to the thermal insulation layer and the thermal expansion coefficient to the mold body is selected. By selecting such a combination of a heat insulating layer and a mold body, the material is hardened by heating at a high temperature before molding, and the stress generated even when cooled to room temperature is suppressed to a very small level. Further, even when molding with a mold covered with the heat insulating layer, the generated stress is suppressed to a small extent, and separation does not occur.

 There are various methods for coating the heat insulating layer on the metal mold body. As described above, a method in which a heat insulating material solution or a precursor solution of a heat insulating material is applied to a mold body and then heat-cured to form a heat insulating layer can be used favorably. However, methods other than the solution application method can be used. Figures 8A, 8B, 8C and 8D show another method of coating a thermal barrier with a blow mold.

In these figures, the mold wall of the metal mold body 11 is provided with pores 12 for suctioning into a vacuum. The small hole 12 is connected to the suction port 14 via the conduit 13 (see FIG. 8 A). A sheet 15 of a heat-resistant polymer having an adhesive layer on the mold body 11 side is placed on the mold cavity surface (FIG. 8B). The mold body 11 and the heat-resistant polymer sheet 15 are placed in a heating oven, heated to a temperature equal to or higher than the softening temperature of the heat-resistant polymer sheet, and evacuated from the suction port 14 in a heated state. Then, the heat-resistant polymer sheet is formed into a mold wall shape, and the mold wall is covered with the heat-resistant polymer (FIG. 8C). The whole is cooled down to room temperature while continuing to apply a vacuum, and then the heat-insulating layer other than the mold cavity surface is removed. Further, if necessary, a thin metal layer 17 is formed on the surface of the heat insulating layer by a plating process, and finally, pores 16 for degassing are opened to provide a heat insulating layer for blow molding according to the present invention. The mold is covered with a layer (Fig. 8D).

 When a mold covered with a heat insulating layer is made by the method shown in Figs. 8A, 8B, 8C, and 8D, if the coefficient of thermal expansion of the mold body and metal layer is close to that of the heat-resistant polymer. The stress generated is extremely small, and a mold covered with a good heat insulating layer can be obtained. The method of coating with this heat-insulating layer requires a heat-insulating layer having a thickness of 0.3 mm or more and is used for blow molding having a relatively gentle curved mold cavity shape. It can be used well for molds covered with a heat insulating layer.

By performing injection molding or blow molding of synthetic resin using a mold covered with a specific heat insulating layer in the method of the present invention, the mold eliminates peeling of the heat insulating layer, It becomes durable. In addition, a molding with good appearance can be obtained by the method. Therefore, a large number of conventional X-ray Injection molded products, such as housings of light electrical equipment, which have been produced and required post-processing such as painting, can be made unpainted by the method of the present invention.

【Example】

 Next, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples.

 The following is used for each mold body and each heat insulating layer.

 Die body 1: Blow mold for the boiler in the tail of a passenger car made of steel (S55C). The mold surface has a hard chrome finish. The thermal expansion coefficient of the mold body is 1.1 X 10 Z ° C.

 Die body 2: Blow mold for air spoiler in the tail of a passenger car, made of zinc alloy (ZAS). The mold surface has a hard chrome finish. The coefficient of thermal expansion of the mold body is 2.8 X 10 Z ° C.

Die body 3: Mold for the front panel of a portable radio cassette (radio cassette tape recorder) made of steel (S55C). The mold has a five-point gate and has a sharp corner that is almost perpendicular to the mold cavity wall. The mold surface has a hard chrome finish. The thermal expansion coefficient of the mold body ^{1 1 X 1 0 -. 5} ° C

Thermal insulation layer 1: Low thermal expansion type polyimide precursor solution U-Penix S (manufactured by Ube Industries, Ltd.) is applied, heated at 160 ° C, and this application and heating are repeated. The thickness is set to a predetermined value, and finally, it is heated to 290 ° C. to form a low thermal expansion type polyimide layer, and then the surface is polished to a mirror surface. The thermal expansion coefficient of the cured polyimide after heating is 0.6 X 10 Z ° C. Insulation layer 2: Apply a linear high molecular weight polyimide precursor solution # 300 (manufactured by Toray Industries, Inc.), heat at 160 ° C, and then apply Then, heating is repeated to obtain a predetermined thickness, and finally, heating is performed at 290 ° C. to form a polyimide layer, and then the surface is polished to a mirror surface. Thermal expansion coefficient of the Po Li Lee Mi de heat cured is 3. 2 X 1 0 _ ⁵ Bruno. C.

Insulation layer 3: Sheet made of carbon fiber mixed with polyetherimide. Thermal expansion coefficient of the mosquito Bon fibers blended Po Li Eterui Mi de is ^{4. 6 X 1 0 5 ZT} :.

Metal layer: Chemical nickel plating. Thermal expansion coefficient of the該Ni Tsu Kell is ^{1. 3 X 1 0 5 /} ° C.

 Example 1 and Comparative Example 1

 A heat insulating eyebrow 2 is coated on the mold body 1 and the mold body 2 to a thickness of 0.35 mm. The ABS resin is extruded and blow-molded using the heat-insulating layer-coated mold. Table 4 shows the results.

 Table 4

断熱層の熱膨張係数 と金型本体の熱膨張係数の差が

The difference between the thermal expansion coefficient of the heat insulation layer and the

0.4 X 10 ⁵ . In Example 1 of the present invention, which is C, separation of the heat insulating layer does not occur even after coating the heat insulating layer and further after blow molding. Difference is ^{2. 1 X 1 0 5 /} ° C der Ru Comparative Example In Example 1, separation occurred in some heat insulating layers immediately after coating with heat insulating layers. Example 2 and Comparative Example 2

 The heat insulating layer 1 and the heat insulating layer 2 are coated on the mold body 3 to a thickness of 0.15 mm. Using the heat-insulating layer-coated mold, a rubber-reinforced polystyrene resin is injection-molded. Table 5 shows the results.

 Table 5

 The difference between the thermal expansion coefficient of the heat insulation layer and the

In Example 2 where 0.5 X 10 — ⁵ Z ° C, the insulation of the almost right-angled sharp corners of the mold was obtained both after the mold body was covered with the thermal insulation layer and after injection molding. No layer separation occurs. However, the difference is 2.剝離occurs sharp corners in 1 X 1 0- ⁵ Z ° immediately after C a is Comparative Example 2, thermal barrier coating. Using the mold of Example 2, rubber-reinforced polystyrene resin is injection-molded to obtain a good injection-molded product in which the molded article is less noticeable. By this molding method, post-processing such as painting of the molded article can be omitted.

 Example 3

After the surface of the heat insulating layer of the mold of Example 2 was made fine and rough, a metal layer having a thickness of 0.05 mm was plated, and the acrylonitrile content was determined using the mold. Inject many ABS resins. Good mold releasability during molding is obtained, and a good molded product with less noticeable well drain is obtained. On the other hand, when injection molding is performed using the mold of Example 2 having no metal layer, the mold releasability during molding is poor.

 Example 4

 The mold body 2 is covered with the insulating eyebrows 3 by the method described in FIGS. 8A, 8B, 8C, and 8D. The mold wall of the mold body is coated with a rubber adhesive beforehand and bonded by vacuum forming. Cooling to room temperature is performed while maintaining the vacuum state, to obtain a mold covered with the heat insulating layer 3. Using this mold, an ABS resin is blow molded to obtain a boiler having a good appearance.

 Example 5

 The heat insulation layer 1 was coated on the mold body 3 to a thickness of 0.13 mm, and the heat insulation layer 2 was coated on the surface of the mold body 3 to a thickness of 0.02 mm. A mold covered with a heat insulating layer was obtained. The mold covered by the heat insulating layer has a sharp right-angled corner, but the heat insulating layer does not separate at the corner. Moreover, the outermost heat-insulating layer 2 is stronger than the heat-insulating layer 1, and by using two heat-insulating layers, a mold covered with a better heat-insulating layer can be obtained. Can be

Using this mold, rubber-reinforced polystyrene resin is injection-molded, and an injection-molded product with less noticeable well-drain in the molded product can be obtained. Industrial Applicability> According to the method of the present invention, injection molding or blow molding of synthetic resin is performed by using a mold covered with a specific heat insulating layer. The mold becomes durable by eliminating separation of the heat insulating layer. In addition, a molded article having a good appearance can be obtained by the method. Therefore, injection moldings such as housings for light electric appliances, which conventionally require many post-processing and require post-processing such as painting, can be made unpainted by the method of the present invention. You.

Claims

Scope of the request Obtained by covering one or two or more heat-insulating layers made of a heat-resistant polymer on the wall constituting the cavity of the metal mold body, and coming into contact with the mold body Molding method for synthetic resin using a mold whose difference between the thermal expansion coefficient of the heat insulating layer and the thermal expansion coefficient of the mold body is less than 2 X 10 — ⁵ Z ° C The method for molding a synthetic resin according to claim 1, wherein the heat insulating layer is at least two heat insulating layers. . The difference in thermal expansion coefficient between the mold body of heat-insulating layer in contact with the mold body ^{1 5 X 1 0 -. 5} / ° molding of synthetic resin according to claim 1 C or less. . Molding of synthetic resin according to claim 1 ⁵ / ° is C or less - the difference in thermal expansion coefficient between the mold body of heat-insulating layer in contact with the mold body 1 X 1 0. . Molding of synthetic resin according to claim 2 ⁵ / ° is C or less - the difference in thermal expansion coefficient between the mold body of heat-insulating layer in contact with the mold body 1 X 1 0. The outermost surface of the heat-insulating layer is further covered with a metal layer having a thickness of 13 or less of the total thickness of the heat-insulating layer, and the thermal expansion coefficient of the heat-insulating layer in contact with the metal layer and the thermal expansion coefficient of the metal layer are reduced. molding of synthetic resin according to claim 1 difference is that 2 X 1 0 less than ⁵ Z ° C. The outermost surface of the heat insulation layer is less than 1 3 of the total thickness of the heat insulation layer Of being coated to be al in metal eyebrow thickness, the difference in thermal expansion coefficient of the metal brow of the heat insulating layer to contact the metal layer 2 X 1 0 - ⁵ is Z ° less than C claim 2 Molding method of synthetic resin 8. The method for molding a synthetic resin according to claim 6, wherein a difference between a thermal expansion coefficient of the heat insulating layer in contact with the metal layer and a thermal expansion coefficient of the metal layer is 1.5 X 10 — ⁵ Z ° C or less. . 9 difference Netsu膨expansion coefficient of the thermal expansion coefficient and a metal layer of insulation debris in contact with the metal layer ^{1 X 1 0 - 5 / °} C or less molding process of synthetic resin according to claim 6. Molding process of synthetic resin according to claim 7 is ⁵ Z ° C or less - 10. difference Netsu膨expansion coefficient of the thermal expansion coefficient and the metal layer of the heat insulating layer in contact with the metal layer 1 X 1 0.  11. The method for molding a synthetic resin according to claim 1, wherein at least one layer of the heat insulating eyebrows is made of an amorphous heat-resistant polymer.  12. The method for molding a synthetic resin according to claim 1, wherein at least one layer of the heat-insulating eyebrows is made of low thermal expansion polyimide.  13. The method for molding a synthetic resin according to claim 1, wherein the molding method is an injection molding method.  14. The synthetic resin molding method according to claim 13, wherein the cavity has a multi-point gate, and the cavity is injection-molded with a mold having a sharp corner having a radius of curvature of less than 1 mm on the wall surface.  15. The method for molding a synthetic resin according to claim 1, wherein the molding method is a blow molding method.