JPH08187731A - Mold for molding synthetic resin and manufacture thereof - Google Patents

Abstract

PURPOSE: To obtain a molded form having excellent external appearance by providing a specific heat insulation layer and a metal layer on the wall of a main mold, and forming the metal layer of a metal layer thin part having half or more of the wall and a metal layer thick part having less than the half in such a manner that the thickness of the thin part is a predetermined value or less of the insulation layer thickness. CONSTITUTION: A mold comprises a heat insulation layer 2 made of a heat resistant polymer and a thickness of 0.1 to 2mm and existed at a mold wall for forming the mold cavity of a main mold 1 made of a metal, a metal layer having an embossed surface on the front surface in such a manner that the metal layer has a thin part 3 of a recess for occupying the half or more of the wall and a thick part 4 of a protrusion for occupying less than half and the thickness of the part 3 is 1/3 or less of the thickness of the layer 2. As a result, the mold is used, the uppermost surface of the mold is reduced to damage on the surface during molding as compared with the mold having the embossed heat insulation layer on the uppermost surface of the mold, further mold releasability is improved, and the mold durability at the time of molding for a long period, or particularly the durability of the part having small pattern draft is improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a mold for synthetic resin and a method for producing the same. More specifically, the present invention relates to a heat-insulating layer-covering mold having a metal layer having a grain surface and used for injection molding or blow molding of a synthetic resin that can withstand molding of tens of thousands of times, and a manufacturing method thereof.

[0002]

2. Description of the Related Art In order to improve the reproducibility in giving the shape condition of the mold surface to the molded product and to improve the appearance of the molded product, it is usually necessary to inject the thermoplastic resin into the mold cavity for molding. It can be achieved to some extent by selecting molding conditions such as increasing the mold temperature or increasing the 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 mold in which the mold wall forming the mold cavity is coated with a substance having a small thermal conductivity, that is, a heat insulating layer is disclosed in WO 93/06980 and the like.

Further, in US Pat. No. 3,734,449 and JP-A-53-86754, a metal mold wall surface is coated with a heat insulating layer, and the surface of the heat insulating layer is further coated with a thin metal layer. The mold is shown.

[0006]

In recent years, there has been a strong demand for omitting post-processing such as coating on injection molded products and blow molded products of synthetic resins. There is a strong desire to eliminate painting because of reduction in manufacturing costs and reduction of environmental damage due to solvent evaporation during painting. There is a strong demand for omitting post-processing of synthetic resin housings for electrical equipment, electronic equipment, office equipment, etc. The surface of these synthetic resin housings is often grain-shaped. There is a demand for a molded product having such a grainy surface and having less conspicuous weld lines and requiring no post-processing such as painting.

Furthermore, when a polymer is used as the heat insulating layer on the outermost surface of the mold, the heat insulating layer is easily scratched during use, and depending on the type of synthetic resin to be molded, the heat insulating layer may be easily removed from the mold. Mold release may be difficult, and its improvement is required. As an improved method, it is possible to coat the surface of the heat insulating layer with a thin metal layer. However, a mold in which the surface of the heat insulating layer is coated with a thin metal layer also has various problems.
For example, if the relationship between the thickness of the metal layer and the thickness of the heat insulating layer is inappropriate, the reproducibility of the mold surface during molding will be poor.

Further, it has been a general practice to deposit the metal layer to a thickness of several μm by plating. Even when the mold surface is made to have a grain-shaped unevenness, the heat-insulating layer has been made to have a grain-shaped unevenness, and a metal layer having a uniform thickness of several μm is coated on the heat-insulating layer by plating to form the grain-shaped unevenness. It has been considered to make a state. That is, even when the mold surface had a concave-convex shape, the outermost metal layer had a substantially uniform thickness. However, in the case of the wrinkle-shaped surface having such a metal layer having a uniform thickness, there is a problem in forming the wrinkle-shaped surface having a good appearance, which is the object of the present invention, for a long period of time.

There are various types of creases formed on the surface of a synthetic resin housing or the like, such as leather grain and grain grain. Generally, the crevices of these housings have a large area of convex portions of surface irregularities and an area of concave portions. small. The reason for this is that, in addition to the appearance of irregularities being preferred, increasing the area of the convexes makes it difficult to scratch the grain surface. In the case of the grain having such a shape, on the contrary, the mold wall surface for molding the grain surface has a small area of the convex portion and a large area of the concave portion. When the mold surface is covered with a heat-insulating layer made of a heat-resistant polymer to form a grain-like surface, a convex portion made of a heat-insulating material has a shape protruding from the mold surface. A shape in which a heat insulating material, which is inferior in toughness compared to metal, pops out on the surface of the mold is likely to be scratched, and the durability of the surface of the mold during long-term molding is also poor. Even in the case of a grain-shaped mold in which the surface of the heat insulating layer is covered with a thin metal layer having a uniform thickness, there are almost the same problems, and the durability of the convex portions on the mold surface is a problem. Further, in the grain-shaped mold in which the surface of the heat insulating layer is covered with a thick metal layer having a uniform thickness, the thick metal layer reduces the effect of covering the heat insulating layer, resulting in poor mold surface reproducibility.

[0010]

In order to solve these problems, the present inventors have studied 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, The present invention was accomplished by studying the combination with the mold material and the metal layer covering the outermost surface. That is, the present invention provides a metal having a heat-insulating layer made of a heat-resistant polymer and having a thickness of 0.1 to 2 mm on a mold wall forming a mold cavity of a main mold made of metal, and further having a wrinkled surface on the surface thereof. There is a layer, and the metal layer is composed of a recessed metal layer thin-walled portion that occupies more than half of the mold wall surface, and a convex metal layer thick-walled portion that occupies less than half the thickness of the metal layer thin-walled portion 1
It is a synthetic resin molding die of / 3 or less.

Further, in the present invention, the mold wall surface of the mold cavity of the main mold made of metal is coated with a heat insulating layer made of a heat-resistant polymer, the surface thereof is further coated with a metal layer, and then the metal layer is coated. Is a method for producing a synthetic resin molding die in which the outermost surface of the is made a grain surface by an etching method.

The present invention will be described in detail below.

The synthetic resin molded using the mold of the present invention is a thermoplastic resin that can be used in general injection molding and blow molding, and includes polyolefins such as polyethylene and polypropylene, polystyrene, styrene-acrylonitrile copolymer, and rubber. Examples include reinforced polystyrene, styrene resins such as ABS resin, polyamide, polyester, polycarbonate, methacrylic resin, vinyl chloride resin, and the like. It is preferable that the synthetic resin contains 1 to 60% of a resin reinforcement. The resin reinforced material includes various rubbers, various fibers such as glass fibers and carbon fibers, and inorganic powders such as talc, calcium carbonate and kaolin. The rubber-reinforced synthetic resin is particularly preferably used, and the rubber-reinforced styrene resin is more preferably used. The rubber-reinforced styrene-based synthetic resin described here means rubber-reinforced polystyrene, ABS resin, in which the rubber phase is distributed in an island shape in the resin phase,
Refers to AAS resin, MBS resin and the like. In the rubber-reinforced polystyrene, a rubber phase such as polybutadiene and SBR is dispersed in an island shape in a resin phase of a polymer mainly containing styrene. A
The BS resin has a rubber phase such as polybutadiene and SBR dispersed in an island shape in a resin phase of a copolymer mainly composed of styrene and acrylonitrile. AAS resin is a resin in which a rubber phase of acrylic rubber is dispersed in an island shape in a resin phase of a copolymer mainly composed of styrene and acrylonitrile.
The resin is a resin in which rubber is dispersed in an island shape in a resin phase composed of a copolymer mainly composed of styrene and methyl methacrylate. Furthermore, blends and the like containing these resins as the main components can also be used in the present invention. For example, a rubber-reinforced polystyrene resin containing polyphenylene ether can be favorably used. Injection-molded products of these resins have a very good balance between performance and economy, and are suitable for housings of light electric appliances, office equipment and the like.

Good molded products molded by the mold of the present invention are generally used synthetic resin injection molded products such as housings for light electric appliances, electronic devices, office equipment, various automobile parts, various daily necessities, and various industrial parts. Is. Particularly preferred are housings of electronic equipment, electric equipment, office equipment, etc., which have many weld lines. Further, good molded products molded with the mold of the present invention are various blow-molded products required to have a grainy appearance.

The main mold made of metal described in the present invention is
It includes metal dies generally used for molding synthetic resins such as iron or steel materials containing iron as a main component, aluminum, alloys containing aluminum as a main component, zinc alloys such as ZAS, and beryllium-copper alloys. Particularly, a mold made of steel can be used favorably. The mold surface of the mold cavity of the main mold made of these metals is preferably plated with hard chromium, nickel or the like.

The metal used for the metal layer coated on the surface of the heat insulating layer of the mold used in the present invention is a metal generally used for metal plating, metal spraying and the like, and chromium, nickel, copper, zinc, One or more of iron, aluminum, titanium, alloys mainly containing these, tin-cobalt alloys, iron-nickel alloys, and the like. The metal layer is coated on the surface of the heat insulating layer, and the surface has a grain shape.

The thickness of the metal layer described in the present invention is the thickness of the metal layer on the wall surface of the mold for molding the portion of the molded product which is required to have a grainy appearance. The thin portion of the metal layer is more than half of the wall surface of the mold, preferably 60 to It accounts for 90%, and the others consist of thick metal layer portions.

The difference in thickness between the metal layer thick portion and the metal layer thin portion is preferably 0.01 mm or more, more preferably 0.02.
Is selected from the range of 0.1 mm.

The thickness of the thin portion of the metal layer is 1/3 of the thickness of the heat insulating layer.
Or less, preferably 1/4 or less, more preferably 1
/ 5 or less, and most preferably 1/20 to 1/5. The absolute value of the thickness is preferably 0 to 0.1 mm, more preferably 0.001 to 0.05 mm,
Most preferably, it is 0.005-0.03 mm. If the thin portion of the metal layer is too thick, the effect of coating the heat insulating layer on the surface of the main mold is lost and the reproducibility of the mold surface deteriorates. In the present invention, it is preferable that the metal layer thin portion has a metal layer of 0.001 mm or more because it has an effect of suppressing peeling of the metal layer thick portion, but the present invention also includes a case where there is almost no metal layer thin portion. Be done.

The heat-resistant polymer used in 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 preferably has a glass transition temperature of 1 or less.
It is a heat-resistant polymer having a temperature of 40 ° C. or higher, preferably 160 ° C. or higher, and / or a melting point of 200 ° C. or higher, more preferably 250 ° C. or higher. The thermal conductivity of heat resistant polymers is generally 0.0
001 to 0.002 cal / cm · sec · ° C.,
Significantly smaller than metal. Further, the elongation at break of the heat resistant polymer is 5% or more, preferably 10% or more, more preferably 1
A polymer having a toughness of 5% or more is preferable. The breaking elongation is measured according to ASTM D638, and the tensile speed at the time of measurement is 5 mm / min.

Polymers which can be favorably used as the heat insulating layer in the present invention are heat resistant polymers having an aromatic ring in the main chain, and examples thereof include various amorphous heat resistant polymers soluble in organic solvents and various polyimides. It can be used well. As the amorphous heat resistant polymer, polysulfone, polyether sulfone,
Polyetherimide and the like. By blending a filler such as carbon fiber with these non-crystalline heat-resistant polymers, the coefficient of thermal expansion can be lowered and used as the heat insulating layer of the present invention. There are various types of polyimide, but linear high-molecular-weight polyimide, polyamide-imide, and partially cross-linked polyimide can be favorably used. Generally, the straight chain type high molecular weight polyimide has a large breaking elongation and is tough, has excellent durability, and can be used particularly favorably.

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 can be used. Epoxy resin generally has a large coefficient of thermal expansion, and the difference in coefficient of thermal expansion with the metal mold is large.
However, glass, silica, talc, which has a small coefficient of thermal expansion,
Clay, zirconium silicate, lithium silicate, calcium carbonate, alumina, powder and particles of mica, glass fiber,
A filler-containing epoxy resin in which an appropriate amount of whiskers, carbon fibers or the like is mixed with an epoxy resin to reduce the difference in coefficient of thermal expansion from the metal mold can be favorably used as the heat insulating layer of the present invention. Further, to the epoxy resin or the filler-blended epoxy resin, various blends such as nylon and rubber which give the toughness are further added, and the blended epoxy resin to which the toughness is given can be favorably used. In particular, a polymer alloy obtained by blending an epoxy resin with polyether sulfone or polyether imide and curing it has excellent toughness and can be used favorably.

In injection molding, blow molding, etc., the mold surface that comes into contact with the heated resin to be molded is exposed to a severe cooling and heating cycle for each molding. Further, in the prior art, the metal layer formed on the surface of the heat insulating layer by plating or the like generally has a smaller coefficient of thermal expansion than the heat insulating layer made of a polymer, and the coefficient of thermal expansion of the heat insulating layer and that of the metal layer are largely different. The stress is repeatedly generated, and if the molding is performed 10,000 times, the stress is repeatedly generated 10,000 times, and finally peeling occurs at the interface. In the present invention,
By reducing the difference between the coefficient of thermal expansion of the main mold and / or the metal layer in contact with the heat insulating layer and the coefficient of thermal expansion of the heat insulating layer, the stress that causes peeling can be reduced. In the present invention, the difference between the coefficient of thermal expansion of the main mold and / or the metal layer in contact with the heat insulating layer and the coefficient of thermal expansion of the heat insulating layer is preferably less than 3 × 10 ⁻⁵ / ° C. More preferably, the difference is 2 × 10 ^-5
/ ° C. Generally, the metal has a smaller coefficient of thermal expansion than the polymer, and therefore it is preferable to select a heat resistant polymer having a smaller coefficient of thermal expansion.

The coefficient of thermal expansion described here is a coefficient of linear expansion. The thermal expansion coefficient of the heat insulating layer is a linear expansion coefficient in the surface direction of the heat insulating layer, and is measured by the method shown in JIS K7197-1991, and is the average value between the temperatures of 50 ° C. and 250 ° C., or the glass transition temperature of the heat insulating layer. If the temperature is below 250 ℃,
The average value between 50 ° C. and the glass transition temperature is shown. That is, a heat insulating layer is formed on a smooth flat metal, and then the heat insulating layer is peeled off, and the heat insulating layer is heated between 50 ° C. and 250 ° C.
Alternatively, the average coefficient of thermal expansion between 50 ° C and the glass transition temperature is measured.

In the present invention, a mold comprising two or more heat insulating layers can also be used favorably. In this case, it is preferable that at least the difference between the coefficient of thermal expansion of the main mold and / or the metal layer in contact with the heat insulating layer and the coefficient of thermal expansion of the heat insulating layer is small, 3 × 10 ⁻⁵ /
It is preferably lower than ° C. When the main mold is coated with the heat insulating layer and the metal, or when the mold of the present invention is used for injection molding, the most severe stress is applied to the interface between the main mold and the heat insulating layer and / or the interface between the metal layer and the heat insulating layer. Occurs. The stress generated can be reduced by selecting and using a material having a thermal expansion coefficient close to both layers forming the interface.

The cause of the peeling between the heat insulating layer and the main mold or between the heat insulating layer and the metal layer is not only the difference in the coefficient of thermal expansion.
However, the difference in the coefficient of thermal expansion is an extremely large factor. If the heat insulating layer is a so-called rubber-like heat insulating layer having a large adhesive force between the heat insulating layer and the main mold and / or the metal layer, a small tensile elastic modulus of the heat insulating layer, and a large breaking elongation, Peeling does not occur even if the difference is slightly large. However, a material suitable for the heat insulating layer, that is, a heat insulating material having high heat resistance, high hardness, and easily becoming a mirror surface by polishing,
Generally, it is a heat-resistant hard synthetic resin having an aromatic ring in the main chain, which has a large elastic modulus.
Alternatively, it is preferable that the difference in the coefficient of thermal expansion is small in order to bring the metal layer into close contact with the metal layer and prevent peeling.

When the wall surface of the mold is covered with a heat insulating layer, the heat insulating layer is required to have various performances. In addition to the adhesion to the main mold, toughness, surface hardness, and ease of gloss when the surface is polished are required. In addition to having a small coefficient of thermal expansion, it is difficult to obtain a polymer satisfying all of these properties, and thus it is preferable to use two or more heat insulating layers.

A metal of the main mold which can be favorably used in the present invention,
Table 1 shows the coefficients of thermal expansion of the metal of the metal layer coated on the outermost surface, the heat-resistant polymer of the heat insulating layer, and general synthetic resins.

[0029]

[Table 1] * The coefficient of thermal expansion by blending carbon fibers into these resins can be reduced to around 4 × 10 ^-5 / ° C.

If the coefficient of thermal expansion of the main mold and / or the metal layer is increased, a heat insulating layer having a relatively large coefficient of thermal expansion can be used. Steel is most often used as the mold material, but recently aluminum alloys and zinc alloys have also been used. In the present invention, the closer the coefficient of thermal expansion is, the more preferable, and when steel is used for the main mold, a low coefficient of thermal expansion polyimide having an extremely small coefficient of thermal expansion can be favorably used. Table 2 shows the thermal expansion coefficient of various low thermal expansion polyimides.

[0031]

[Table 2]

In the table, Bifix and Free did not allow the film to shrink freely when the polyimide precursor was imidized to form a polyimide film.
e) Is the polymer chain fixed in a square frame to suppress the shrinkage that occurs during imidization and to cause the polymer chains to be in-plane oriented by the stress (Bi
fix). After the polyimide precursor solution is applied to the main mold, the polyimide formed by heating has a thermal expansion coefficient close to that of Bifix. The low thermal expansion type polyimide is a polymer having a polymer chain structure in which the polymer chain is rigid and extends straight.

Table 3 shows the structure and glass transition temperature (Tg) of the heat resistant polymer which can be favorably used in the present invention.

[0034]

[Table 3]

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 the surface of this complicated mold with the heat-resistant polymer and firmly adhere it, the heat-resistant polymer solution and / or the heat-resistant polymer precursor solution is applied and then heated to heat-resistant polymer. Most preferably, a coalescing heat insulating layer is formed. Therefore, the heat-resistant polymer of the present invention or the precursor of the heat-resistant polymer is preferably soluble in a solvent. A method of applying a solution of a polyamic acid, which is a precursor of polyimide, to a mold wall surface and then performing heat curing to form a polyimide on the mold wall surface can be favorably used. Formula 1 shows a formula for forming a polyimide from a polyamic acid.

[0036]

Embedded image

When a polyamic acid solution of a polyimide precursor is applied to the mold wall surface and then heated and cured to form a polyimide, the glass transition temperature and the coefficient of thermal expansion of the polyimide may vary depending on the heating and curing temperature and / or the heating and curing atmosphere. different. Generally, the higher the heating and curing temperature, the higher the glass transition temperature and the smaller the coefficient of thermal expansion. Generally, polyamic acid shows almost 1 imidization at 250 ° C or higher.
Although it progresses by 100% to form a polyimide, it is considered that the movement of molecules after becoming a polyimide affects the thermal expansion coefficient.

It is necessary that the heat-insulating layer of the present invention and the main mold and / or the heat-insulating layer and the metal layer have a high adhesion, and the width at room temperature is preferably 0.5 kg / 10 mm or more, more preferably 0. 8kg / 10mm width or more, most preferably 1k
g / 10 mm width or more. This is the peeling force when the adhered metal layer or the metal layer and the heat insulating layer are cut into a width of 10 mm and pulled at a speed of 20 mm / min in the direction perpendicular to the adhesive surface. This peeling force varies considerably depending on the measurement location and the number of measurements, but it is important that the minimum value is large.
A stable and large peeling force is preferable. The adhesion force described in the present invention is the minimum value of the adhesion force of the main part of the mold.
In order to improve the adhesion, it is possible to appropriately form the surface of the main mold into fine irregularities, perform various kinds of plating, and perform a primer treatment. 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. However, it is extremely difficult to apply the coating material to the surface of the mold cavity of this complicated shape in a mirror surface, and therefore it is the best method to polish the applied coating layer afterwards to make it a mirror surface. Is.

The total thickness of the heat insulating layer is appropriately selected within the range of 0.1 mm to 2 mm. It is preferably 0.1 mm to 0.5 mm in injection molding, 0.3 mm to 1.0 mm in blow molding, and more preferably 0.12 mm to 0.4 mm in injection molding and 0.1 mm in blow molding. It is 3 mm to 0.6 mm. With a thin heat insulating layer of less than 0.1 mm, the effect of improving the appearance of the molded product is small. 2m
If the thickness of the heat insulation layer exceeds m, the cooling time in the mold will increase,
Not preferable from an economic point of view. The surface of the heat insulating layer described in the present invention is almost smooth or has fine irregularities for increasing the adhesion with the metal layer, which is excellent in the appearance to be formed on the outermost metal layer surface in the present invention. It is not as big as a grain.

The term "crimped" as used in the present invention means that the surface of a molded article molded with the mold of the present invention is generally given to the surface of a synthetic resin housing or the like of general household appliances, office equipment and the like. It is an uneven shape such as a wrinkle pattern of leather, a cloth pattern, a wood grain pattern, and a hairline pattern. The area of the convex portion of the grain surface of the mold of the present invention is smaller than the area of the concave portion.

The metal layer of the present invention can be coated by various methods, but it is coated by plating, thermal spraying or the like. The plating described here may be either chemical plating or electroplating. For example, first the surface of the heat insulating layer is made a moderately rough surface, a conductor such as copper is deposited on the surface to impart electrical conductivity, and then various metals such as nickel are electroplated, and nickel is coated by chemical plating. Etc. can be used. Generally, plating is performed through some of the following steps.

Pretreatment (deburring, resin) → Chemical corrosion (chemical etching with acid or alkali: making the surface have a suitable unevenness) → Neutralization → Sensitization treatment (adsorption of reducing metal salts on the surface of synthetic resin) The activation effect) → Activation treatment (providing a noble metal with a catalytic action on the resin surface)
→ Chemical nickel plating (chemical plating of nickel) → Electrolytic nickel plating (electroplating of nickel) (For details, refer to "Plastic plating", written by Tatsumu Romo, published in Nikkan Kogyo Shimbun, etc.)

The most preferable method is to apply a chemical plating of a nickel alloy (nickel-phosphorus alloy) to a thin layer, and to apply electrolytic nickel thickly thereon.

In order to increase the adhesion between the heat insulating layer and the plating layer, calcium carbonate or silicon oxide powder is mixed with the heat insulating material forming the outermost surface of the heat insulating layer, and the powder is melted by chemical corrosion to bring the surface to an appropriate level. It can be used very well if it is made to have irregularities.

The metal layer of the present invention is also coated by the thermal spraying method.
The thermal spraying method has an advantage that it can be applied to a thick wall in a single operation, and is a good method when a thick metal layer is desired. As the thermal spraying method, a gas spraying method, an arc method, a plasma method, a laser method or the like can be appropriately selected and used.

Various methods can be used to make the surface of the metal layer of the mold of the present invention grain-shaped. The etching method can be used well. The acid etching method is best used. If the outermost surface layer of the mold is a metal, it can be grained by the same method as a general mold etching method. That is, a method in which the surface of the metal layer is masked with an ultraviolet curable resin in a grain shape and then grained by acid etching can be favorably used.

An alloy of nickel and phosphorus is difficult to be etched by acid, and pure nickel is easily etched. It is preferable to appropriately use a metal layer that is easily etched and a metal layer that is not easily acid-etched. It is good practice to first form a thin nickel layer by chemical plating of a nickel alloy and then acid etch a thick metal layer formed by electroplating of pure nickel onto the grain. Further, it is possible to improve the corrosion resistance of the mold by forming a thin layer of nickel alloy on the surface of the grain-shaped metal layer by chemical plating.

When the surface of the main mold is covered with a heat insulating layer made of a heat resistant resin, and the heated resin injected into contact with the surface of the heat insulating layer, the mold surface receives the heat of the resin and rises in temperature. The lower the thermal conductivity of the heat insulating layer, the thicker the heat insulating layer, and the thinner the metal layer, the higher the mold surface temperature becomes. When there is no heat insulating layer on the mold surface of the main mold made of general metal, the mold surface temperature becomes almost the same as the main mold temperature after 0.01 seconds.
By covering the mold surface with a heat insulating layer having a thickness of 0.1 mm to 2 mm, the mold surface can be kept at the softening temperature or higher for a certain period of time.

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

FIG. 1 shows a sectional view of a synthetic resin molding die of the present invention. As shown in FIG. 1, the mold of the present invention has a heat insulating layer 2 made of a heat resistant polymer and having a thickness of 0.1 to 2 mm, which is present on the mold wall surface of the mold cavity of the main mold 1 made of metal. A thin layer 3 having a metal layer having a grain surface on its surface, the metal layer occupying more than half of the wall surface of the mold;
The thick portion 4 occupies less than half. The present invention also includes the case where the thickness B of the thin metal layer portion 3 is extremely thin, or the case where there is almost no thin metal layer portion (1-2).

Further, the effect of the present invention is great when the thick metal layer portion 4 has a shape protruding from the surface. That is, it is preferable that the metal layer thick portion 4 has many irregularities having a height F larger than the width G, and more preferably, the irregularities have a shape having a height F larger than twice the width G. This is the case of a grain shape.

The surfaces of the thin metal layer portion 3 and the thin metal layer portion 4 may be matte fine irregularities. It is preferable that one of the surface of the thin metal layer portion 3 and the surface of the thin metal layer portion 4 has a matt fine unevenness and the other has a mirror surface. A matt pattern on one side and a mirror-like surface on the other side allow good expression of the grain pattern on the surface of the molded product. The matte fine unevenness described here is much smaller than the unevenness of the grain-like unevenness of the present invention, and the ten-point average roughness (JIS B 0601) is 1/10 or less, preferably 1/20 or less. It's a small one.

FIG. 2 shows a sectional view of the grain surface of the synthetic resin molded product. As shown in FIG. 2, in the grain-shaped surface of the synthetic resin molded product 6, a surface where the area of the convex portion 7 is larger than the area of the concave portion 8 is generally used (2-1). If the area of the convex portion 9 is small and the convex portion 9 protrudes from the molded product, the surface of the molded product is easily scratched (2-2). The present invention relates to a mold for molding a synthetic resin molded product occupying most of the grain surface shown in (2-1), and a mold surface for molding the grain surface shown in (2-2) on the mold surface. Is also included locally.

FIG. 3 shows a sectional view of the grain surface of the mold.
(3-1) is a case where the grainy surface of the heat insulating layer 2 is covered with the thin metal layer 10 having a uniform thickness. That is, the difference between the thickness E of the metal layer of the convex portion and the thickness D of the metal layer of the concave portion is small and the thickness is extremely thin. In this case, there is no effect of reinforcing the convex portion on the metal layer. .

(3-2) is the case where the grain-shaped surface of the heat insulating layer 2 is covered with the thick metal layer 11 having a uniform thickness. That is, the difference between the thickness E of the metal layer of the convex portion and the thickness D of the metal layer of the concave portion is small and the thickness is large. In this case, since the metal layer is thick, Mold surface reproducibility deteriorates. Since this recess appears on the surface of the molded synthetic resin molded product, mold surface reproducibility is required,
It is necessary to improve mold surface reproducibility, and it is not preferable that the metal layer is thick.

In FIGS. 4, 5 and 6, the temperature of the main mold made of steel is 50.degree. C. and the temperature of the rubber reinforced polystyrene is 2.
The calculated value of the change in temperature distribution near the mold wall surface when injection molding is performed at 40 ° C is shown. The numerical value of each curve in the figure indicates the time (seconds) 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 (FIG. 4). When the surface of the main mold is covered with the heat insulating layer, the mold surface receives heat from the heated synthetic resin and its temperature rises. As shown in the figure, the mold surface is 0.1m
When coated with a heat insulating layer (polyimide) of m and 0.5 mm (FIGS. 5 and 6), the temperature rise of the surface of the heat insulating layer in contact with the synthetic resin increases and the temperature decreasing rate also decreases.

7, FIG. 8, FIG. 9, FIG. 10, FIG. 11 and FIG. 12 are compared with a mold in which the surface of the main mold made of steel is coated with a polyimide layer and the surface is coated with a nickel layer. When a mold coated only with a polyimide layer is used, the temperature of the main mold is set to 50 ° C., and when the temperature of the rubber-reinforced polystyrene resin is injection molded at 240 ° C. The change with time of the temperature of the resin surface (this is the temperature of the interface between the resin surface and the nickel surface or the temperature of the interface between the resin surface and the polyimide surface) after contact with the surface is shown.

FIG. 7 shows the resin surface temperature with time when the thickness of the polyimide (hereinafter referred to as PI in the figure) layer is 0.30 mm and the thickness of the nickel (hereinafter referred to as Ni in the figure) layer is 0.02 mm. Show changes. In the figure, the solid line shows the case where the polyimide layer and the nickel layer are covered, and the broken line shows the case where only the polyimide layer is covered. When only polyimide is coated, the resin surface temperature decreases with the passage of time, whereas when polyimide and nickel layers are coated, the temperature drops once and then rises again and then gradually decreases. . This is because the heat of the resin is absorbed by the nickel layer and decreases due to the large heat capacity of nickel in the surface layer. Therefore, as the thickness of the nickel layer increases,
The temperature range in which the temperature once drops increases, and the temperature in which the temperature rises again decreases.

FIG. 8 shows a case in which the thickness of the nickel layer is as thick as 0.1 mm. When the thickness of the nickel layer becomes thick, the temperature range that once drops is large and the temperature that rises again becomes low.

FIGS. 9 and 10 show the case where the thickness of the polyimide layer is 0.15 mm with the same layer structure as in FIGS. 7 and 8. Even when the thickness of the polyimide layer is 0.15 mm, the same tendency as in FIGS. 7 and 8 is observed.

11 and 12 collectively show the results of FIGS. 7 to 10. From FIG. 11 and FIG. 12, in the case of this metal mold coated with a nickel layer, when the thickness of the nickel layer becomes 0.1 mm, the surface temperature once lowered once rises again and the temperature becomes lower. It can be estimated that the surface reproducibility becomes poor. Thickness of nickel layer is 0.0
In the case of 2 mm, the resin surface temperature recovers rapidly even if it once drops, and since the temperature is high, the mold surface reproducibility during injection molding is good. From these, the thickness of the metal layer coated on the surface of the heat insulating layer is limited in order to improve the mold surface reproducibility, and in the present invention, the thickness of the thin portion of the metal layer, which particularly requires the appearance of the molded product, is reduced. And a mold for molding a molded product having a good appearance.

The change of the mold surface temperature at the time of injection molding shown in the figure can be calculated from the temperature of the synthetic resin, the main mold, the heat insulating layer, the specific heat, the thermal conductivity, the density, the latent heat of crystallization and the like. For example, AD
Using INA and ADINAT (software developed at Massachusetts Institute of Technology) and the like, it is possible to calculate by unsteady heat conduction analysis by the nonlinear finite element method, and the temperature shown in the figure is also calculated by it.

13 and 14 show the structure of polyimide that can be used for the heat insulating material of the present invention. As shown in FIG. 13, a polymer having a bent polymer chain has a large coefficient of thermal expansion,
On the other hand, as shown in FIG. 14, a polymer having a straight polymer chain has a small coefficient of thermal expansion. In the present invention, a polymer having a small coefficient of thermal expansion is preferable.

FIG. 15 shows a method of forming the metal layer of the outermost surface layer of the mold into a grain shape by the etching method. In FIG. 15, the heat-insulating layer 2 covers the wall surface of the mold forming the mold cavity of the main mold 1 made of metal (15-1). Next, the surface of the heat insulating layer 2 is coated with the metal layer 12 (15-2). Then, the surface of the metal layer 12 is coated with the photosensitive resin 13 (15-3). Then, masking of grain pattern 1
Do 4. The photosensitive resin in the portion irradiated with ultraviolet rays is cured (15-4). Next, the non-cured portion of the photosensitive resin is washed and removed to leave the grain-shaped pattern of the cured resin 15 (15-5). Next, by acid etching, the metal layer in the portion not covered with the cured resin 15 is dissolved,
A metal layer having a thin metal layer 3 having a grain surface and a thick metal layer 4 is formed to obtain a mold of the present invention (15-6).

By using the mold of the present invention, it is possible to reduce scratches on the mold surface during molding, as compared with the case of using a mold in which the outermost surface of the mold is a grain-shaped heat insulating layer. Further, the mold releasability can be improved, and further, the durability of the mold at the time of molding for a long period of time, particularly the durability of a portion having a small draft can be improved. Furthermore, the conspicuousness of the weld line of the synthetic resin molded product can be reduced, the reproducibility of the mold surface can be improved, and post-processing performed after molding can be omitted.

[0066]

EXAMPLE The following main mold, heat insulating layer and metal layer are used.

Main mold: A steel (S55C) mold for injection molding. The thermal expansion coefficient of the mold is 1.1 × 10 ^-5 /
° C. It has a mold cavity for the molded product 16 shown in FIG. The molded product has a size of 100 mm × 100 mm and a thickness of 2 mm, and has a hole 17 of 30 mm × 30 mm in the center. The gate 18 is a side gate as shown in FIG. 16, and a weld line 19 is generated in the molded product 16. The mold surface is mirror-like. Two molds are prepared.

Thermal insulation layer: After the surface of the main mold has been treated with a primer, a polyimide varnish “Trenis # 3000” (manufactured by Toray Industries, Inc.) is applied and heated at 160 ° C., and then this application and heating are repeated to obtain a predetermined amount. Thickness, and finally 290 ℃
To form a polyimide layer. The coefficient of thermal expansion of the polyimide is 3.3 × 10 ^-5 / ° C. When a metal layer is plated on the surface of the heat insulating layer, the calcium carbonate powder-containing polyimide varnish is used only on the outermost surface of the heat insulating layer.

Metal layer: The surface of the heat insulation layer containing calcium carbonate powder is etched to make it uneven, and then a nickel layer is formed by electroless plating (chemical plating) of nickel.
Further, electrolytic nickel plating is formed on the surface. The coefficient of thermal expansion of the nickel is 1.3 × 10 ^-5 / ° C.

[Embodiment] A smooth heat-insulating layer was added to the main mold.
Coated to a thickness of 3 mm and then coated with a smooth metal layer 0.06
Coat to a thickness of mm. The metal layer is etched into a skin grain shape by the process shown in FIG. Acid etching is performed to a depth of 0.05 mm to produce a skin grain-like mold of the present invention shown in (1-1) of FIG. The thin portion of the metal layer of the mold has a thickness of 0.01 mm and the thick portion has a thickness of 0.06 m.
m, and the thin portion occupies 75% of the metal layer surface.

A rubber-reinforced polystyrene resin is injection-molded by using the mold to obtain an injection-molded article having a welded line 19 with a conspicuous leather grain surface.

[Comparative Example] The mold wall surface of the main mold is made a skin grain surface by general acid etching. Rubber-reinforced polystyrene is injection-molded using the mold. The weld line 19 is highly visible in this molded product.

[0073]

EFFECTS OF THE INVENTION A molded article having a good appearance is obtained by injection molding or blow molding a synthetic resin using the heat insulating layer-coated mold of the present invention. In particular, by using the mold of the present invention, it is possible to reduce the conspicuousness of the weld line for injection-molded products such as housings for light electrical equipment and office equipment that have conventionally required a large number of weld lines and require post-processing such as painting. ,
Painting can be omitted.

[Brief description of drawings]

FIG. 1 shows a sectional view of a synthetic resin molding die of the present invention.

FIG. 2 shows a cross-sectional view of a grain surface of a synthetic resin molded product.

FIG. 3 shows a cross-sectional view of the grain surface of the mold.

FIG. 4 shows changes (calculated values) in the temperature distribution near the mold wall surface when the heated synthetic resin comes into contact with the steel main mold.

FIG. 5 shows changes in temperature distribution (calculated values) near the mold wall surface when a heated synthetic resin comes into contact with a mold in which the mold surface of a steel main mold is coated with 0.1 mm of polyimide. Show.

FIG. 6 shows changes in temperature distribution (calculated values) near the wall surface of a mold when a synthetic resin heated to contact a mold surface of a steel main mold with 0.5 mm of polyimide. Show.

FIG. 7: Synthesis when heated synthetic resin comes into contact with a mold in which the surface of a steel main mold is coated with 0.3 mm of polyimide, and the surface of which is further coated with nickel of 0.02 mm The temperature change (calculated value) of the resin surface (interface between the resin surface and the mold surface) is shown.

FIG. 8: Synthesis when heated synthetic resin comes into contact with a die in which 0.3 mm of polyimide is coated on the die surface of a steel main die and 0.1 mm of nickel is further coated on the surface. The temperature change (calculated value) of the resin surface (interface between the resin surface and the mold surface) is shown.

FIG. 9: Synthesis when heated synthetic resin comes into contact with a mold in which the surface of a steel main mold is coated with 0.15 mm of polyimide, and the surface of which is further coated with 0.02 mm of nickel The temperature change (calculated value) of the resin surface (interface between the resin surface and the mold surface) is shown.

FIG. 10: Synthesis when heated synthetic resin comes into contact with a mold in which the surface of a steel main mold is coated with 0.15 mm of polyimide and the surface of which is further coated with 0.1 mm of nickel The temperature change (calculated value) of the resin surface (interface between the resin surface and the mold surface) is shown.

FIG. 11: The surface of the main mold made of steel is coated with 0.3 mm of polyimide, and the surface is further covered with 0.0005 mm,
The temperature change (calculated value) of the surface of the synthetic resin (the interface between the resin surface and the die surface) when the heated synthetic resin comes into contact with the die coated with nickel of each thickness of 0.02 mm and 0.1 mm Show.

FIG. 12: The surface of a steel main mold is coated with 0.15 mm of polyimide, and the surface is further covered with 0.0005 mm;
The temperature change (calculated value) of the synthetic resin surface (the interface between the resin surface and the mold surface) when the heated synthetic resin comes into contact with the mold coated with nickel of 0.02 mm and 0.1 mm in thickness Show.

FIG. 13 shows a structure of a heat insulating material suitable for the heat insulating layer of the mold of the present invention.

FIG. 14 shows a structure of a heat insulating material suitable for the heat insulating layer of the mold of the present invention.

FIG. 15 shows one of the methods for producing the mold of the present invention.

FIG. 16 shows an injection molded product.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Main mold 2 Heat insulation layer 3 Metal layer thin-walled part 4 Metal layer thick-walled part 6 Synthetic resin molding 7 Convex part of wrinkled surface 8 Recessed part of wrinkled surface 9 Convex part of wrinkled surface 10 Thin metal layer 11 Thick wall Metal layer 12 Metal layer 13 Photosensitive resin 14 Mask 15 Curing resin 16 Molded product 17 Hole 18 Gate 19 Weld line

Claims (2)

[Claims] 1. A heat-resistant polymer of 0.1 to 2 mm on a mold wall surface of a mold cavity of a main mold made of metal.
There is a thick heat insulating layer, and further there is a metal layer having a grain surface on its surface, and the metal layer has a thin metal layer of a concave portion which occupies more than half of the mold wall surface and a metal portion of a convex portion which occupies less than half thereof. A synthetic resin molding die comprising a thick layer portion, and a thin metal layer portion having a thickness of 1/3 or less of a heat insulating layer thickness. 2. The mold wall of the main mold made of metal is coated with a heat insulating layer made of a heat resistant polymer, the surface of which is further coated with a metal layer, and then the outermost surface of the metal layer. A method for producing a synthetic resin molding die that makes a grainy surface by etching.