JPH1016001A - Forming of synthetic resin molding with wall of ununiform thickness and mold used for this forming - Google Patents

Abstract

PROBLEM TO BE SOLVED: To efficiently injection-mold a synthetic resin molding with a wall of uniform thickness consisting of a thick wall part and a thin wall part. SOLUTION: In a method for forming a molding with a wall of ununiform thickness using a mold with a cavity consisting of a thin wall part and a thick wall part, the difference between the maximum thickness a1 of the thick wall part of a mold cavity and the minimum thickness a2 of the thin wall part is given as A, and the difference between (the thickness a1 of the mold cavity + the thickness b1 of a heat insulating layer) at the maximum thick wall part of the mold cavity and (the thickness a2 of the mold cavity + the thickness b2 of the heat insulating layer) at the minimum thin wall part of the mold cavity is given as B. Then the injection molding is performed using the mold coated with the heat insulating layer which has a relationship of A>=0.5mm, A>=B. Thus it is possible to set the temperature of the mold at a low level and thereby shorten the cooling time of the mold.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an injection molding method for various synthetic resin molded articles having uneven thickness portions, and a heat insulating layer coated mold used for the method.

[0002]

2. Description of the Related Art In injection molding of a synthetic resin molded product, a molten resin is injected and filled into a mold cavity, and pressure is applied to the cavity through the molten resin of a spool until the gate portion is cooled and solidified, and the pressure is maintained. It is common practice to obtain a molded article in a mold after the gate has solidified. In general, in such filling and pressure-holding steps in injection molding, pressure distribution occurs in the cavity due to flow resistance and cooling of the molten resin,
Non-uniform cooling is apt to occur, and is particularly noticeable in an ultra-thin molded product having a thin portion having a thickness of 1 mm or less, particularly when the thickness of the thin-walled molded product is 1 mm or less.

[0003] With respect to the method of injection molding an ultra-thin uneven thickness molded article having a thin portion of a thickness of 1 mm or less, use of a flowable resin, high-speed injection molding, a method of increasing a mold temperature, a high injection pressure or Injection molding is performed using conditions such as employing high pressure-holding conditions, but this is not sufficient.

[0004] The use of a high-flowable resin tends to improve the filling property of a thin-walled molded product, but there is a problem in that the molecular weight of the synthetic resin is reduced, the mechanical strength of the resin is reduced, and its use is restricted. When a high injection pressure or a high holding pressure is adopted, the sink in the thick portion is reduced, but the residual stress in the thin portion having a high cooling rate is increased, and the molded product is likely to be deformed or warped. There is a problem that the above disadvantage occurs. Among these factors, the mold temperature has the greatest effect on the effect, and increasing the mold temperature is very effective. However, when the mold temperature is increased, the cooling time required for cooling and solidifying the plasticized resin increases, and the molding efficiency decreases. For this reason, there is a demand for a method of improving the resin fluidity in the mold without increasing the mold temperature and a method of preventing the required cooling time from being prolonged even if the mold temperature is increased.
There is also a method in which holes for heating and cooling are attached to the mold, and heating and cooling of the mold are repeated by alternately flowing a heat medium and a coolant.However, this method uses a large amount of heat and cools The time gets longer.

A method of improving the mold surface reproducibility by coating the mold wall surface forming the mold cavity with a substance having low thermal conductivity is disclosed in US Pat. No. 3,544,518 regarding injection molding. .

Japanese Patent Application Laid-Open No. 53-86754 discloses a mold in which a heat insulating layer is coated on a mold wall surface, and a thin metal layer is coated on a cross-sectional surface of the mold.

Further, the present applicant has proposed a method of forming an ultra-thin molded article in a favorable manner. The mold cavity thickness is extremely thin, 1 mm or less, and the thickness of the mold wall surface is made of a heat-resistant polymer. Using a mold covered with a heat insulating layer having a thickness of 0.01 mm to 1 mm, the main mold is heated to a predetermined temperature (softening temperature of thermoplastic resin −
A molding method for injection molding in a state of cooling to 20 ° C. or lower has been proposed (Japanese Patent Application Laid-Open No. 7-178753).

[0008]

The conventional molding method in which the mold wall surface of the mold is covered with a heat insulating layer is effective for molding a thin molded article having a uniform thickness or a small change in thickness. However, when a molded article having a relatively large thickness change, for example, a molded article having a thick part and a thin part is formed, the cooling required for cooling and solidifying the resin filled in each part even if it is covered with a heat insulating layer. There is a difference in time. Therefore, if the mold is released in accordance with the cooling and solidification time of the resin in the thin portion, sinks may occur in the thick portion, and if the mold is released in accordance with the cooling and solidification time of the resin in the thick portion, the mold wall surface may be reduced. However, there is a problem that the time required for cooling and solidifying is longer than when the heat-insulating layer is not covered, and the molding efficiency is reduced.

The present invention solves the above-mentioned problems, and provides a synthetic resin uneven thickness molded product having a thick portion and a thin portion in an economical and efficient molding cycle without increasing the temperature of the entire mold. The purpose is to mold. It is a further object of the present invention to improve the transferability of the mold surface and to mold a synthetic resin uneven thickness molded product having excellent surface properties in an economical and efficient molding cycle.

[0010]

Means for Solving the Problems The present inventor has made it more efficient to produce a synthetic resin uneven thickness molded product having a thick portion and a thin portion, particularly a synthetic resin uneven thickness molded product having a minimum thickness of 1 mm or less. As a result of intensive studies on a method of forming well, it has been found that the above object can be achieved by controlling the coating thickness of the heat insulating layer depending on the thickness of each part of the molded product, and the present invention has been completed.

That is, a first aspect of the present invention is a method of molding a synthetic resin uneven thickness molded product using a mold having a mold cavity having a thick portion and a thin portion, wherein a maximum thickness of the thick portion of the mold cavity is obtained. The difference between the thickness of the mold and the minimum thickness of the thin portion is A, (the thickness of the mold cavity + thickness of the heat insulating layer) at the thickest portion of the mold cavity and (the thickness of the mold cavity + thickness of the heat insulating layer) at the thinnest portion of the mold cavity. Is B, A ≧ 0.
A method for molding a synthetic resin uneven thickness molded article characterized by injection molding using a heat-insulating layer-coated mold having a relationship of 5 mm and A ≧ B (particularly preferably A> B).

The first molding method of the present invention further has the following features: "A = 0.5 to 10 mm, 0.7A ≧ B"; and "the minimum thickness of the mold cavity of the thin portion is: 0.1 to 1 mm "and" the heat-insulating-layer-coated mold has a metal layer in close contact with the heat-insulating layer ".

A second aspect of the present invention is a mold used for injection molding of a synthetic resin uneven thickness molded article, which has a mold cavity having a thick portion and a thin portion, and has the largest thickness of the mold cavity. The difference between the thickness and the minimum thickness of the thin portion is A, and the (mold cavity thickness + insulation layer thickness) at the maximum thickness portion of the mold cavity and the (mold cavity thickness + insulation layer thickness) at the minimum thickness portion of the mold cavity. When the difference is B, A ≧ 0.
A mold having a relationship of 5 mm and A ≧ B.

The second mold of the present invention further has a feature that “A = 0.5 to 10 mm, 0.7A ≧ B”.
That the minimum thickness of the mold cavity of the thin part is
0.1 to 1 mm "and" having a metal layer in close contact with the heat insulating layer ".

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail.

The synthetic resin usable in the molding method of the present invention is a thermoplastic resin usable in general injection molding. For example, styrene polymers, ABS resins or copolymers thereof, olefin polymers such as polyethylene and polypropylene, modified polyphenylene ether resins, polyacetal resins, vinyl chloride polymers or copolymers thereof, polycarbonate, polyamide, polyester, methacrylic resin And so on. In particular, polyacetal resin, polypropylene, polycarbonate, and the like used for parts of various electronic devices can be favorably used.

Particularly great effects are obtained when various reinforcing materials and various fillers are blended with these resins, or when a polymer alloy or the like is used. For example, one or more of rubber, glass fiber, calcium carbonate, talc, calcium sulfate, wood flour and the like can be mixed with the above resin.

The molded article molded by the molding method of the present invention is a synthetic resin uneven thickness molded article generally used for housings of light electric equipment, electronic equipment, office equipment, various automobile parts, various daily necessities, various industrial parts, etc. It is. The molding method of the present invention is extremely effective for molding a synthetic resin uneven thickness molded product having a mold cavity thickness of the thinnest thin portion of 0.1 to 1 mm. An example of such an uneven thickness molded product is a hinge portion. And a wedge-shaped thin light guide plate for a backlight of a liquid crystal display.

The material of the mold according to the present invention is a metal used for a general mold. For example, iron or a steel material containing iron as a main component, aluminum or an alloy containing aluminum as a main component, a zinc alloy, a beryllium-copper alloy, or the like can be used. In particular, a mold made of a steel material can be used favorably. It is preferable that the mold wall surface constituting the mold cavity of the mold made of these metals is plated with chrome or nickel. Chromium plating or nickel plating has excellent adhesion to the heat insulating layer and also has excellent corrosion resistance. In injection molding, since heating and cooling are repeatedly applied to the mold, it is very important that the adhesion is stable and large, and in order to withstand tens of thousands of moldings, the above plating effect is large and preferable. is there.

The heat insulating material used in the heat insulating layer according to the present invention preferably has a thermal conductivity of 1/10 or less of the thermal conductivity of the metal forming the mold, particularly preferably 1/2.
It has a thermal conductivity of 0 or less. Specific examples include various heat-resistant resin polymers, various ceramics, and the like, and the most preferably used is a heat-resistant polymer. The heat-resistant polymer has a glass transition temperature of 150 ° C. or higher, preferably 200 ° C.
It is a heat-resistant polymer having a melting point of 200 ° C or higher, more preferably 230 ° C or higher, and / or a melting point of 200 ° C or higher, preferably 250 ° C or higher, more preferably 280 ° C or higher. The heat conductivity of the heat-resistant polymer is preferably as small as possible.
cal / (cm · sec · ° C.) or less, and a general polymer has this thermal conductivity or less. The toughness of the heat-resistant polymer is preferably 10% or more. The elongation at break is performed according to ASTM-D638, and the tensile speed at the time of measurement is 5 mm / min.

The polymer which can be suitably used as the heat-insulating layer according to the present invention is a heat-resistant polymer having an aromatic ring in the main chain, and various amorphous heat-resistant polymers, various polyimides and epoxy resins dissolved in an organic solvent. It is a resin or the like. Examples of the non-crystalline heat-resistant polymer include polysulfone, polyether sulfone, polyallylsulfone, polyarylate, polyphenylene ether, polybenzimidazole and the like. There are various kinds of polyimides, and they are classified into a linear type and a thermosetting type, and various types are known as respective polyimide precursors. Regarding the heat insulating layer used in the present invention, that the thermal conductivity is low, that the heat resistance is excellent, that the tensile strength, the elongation is large and that it is strong in the cooling and heating cycle, that the application to the mold body is good, that the mold and Is preferred because of its good adhesion. For example, trade names are Kapton (Toray), Novax (Mitsubishi Chemical), Upilex S or Upilex R (Ube Industries), Larc
TPI (manufactured by Mitsui Toatsu Chemicals) and the like are preferred. In order to firmly adhere the polyimide layer to the mold, it is most preferable to apply a precursor solution of linear high molecular weight polyimide to the mold and then heat to form the polyimide. The precursor of the linear high molecular weight polyimide is synthesized by, for example, subjecting an aromatic diamine and an aromatic tetracarboxylic dianhydride to a ring-opening polyaddition reaction. These polyimide precursors are heated to cause a dehydration cyclization reaction to form a polyimide. The polyimide precursor polymer is
Good adhesion to the mold due to polar groups such as carboxyl groups. The above polyimide precursor polymer is dissolved in a solvent such as N-methylpyrrolidone and applied to the mold wall. To the polyimide precursor solution, to adjust the viscosity at the time of coating, to adjust the surface tension of the solution, to add an additive to adjust the thixotropic property, and / or to increase the adhesion with the mold Minor additives can be added. Among these polyimides, pyromellitic dianhydride-based polyimide is most preferable because of its excellent heat resistance and mechanical properties. Particularly, a varnish modified for coating can be used favorably.

As the epoxy resin, an epoxy resin cured product combined with a curing agent or an epoxy resin mixed with various fillers in an appropriate amount can be used (hereinafter, the epoxy resin cured product is referred to as an epoxy resin). Epoxy resins generally have a large coefficient of thermal expansion and a large difference in the coefficient of thermal expansion from a metal mold.
However, glass, silica, clay,
Powder of talc, calcium carbonate, alumina, mica, etc.
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 thermal expansion coefficient from a metal mold can be used favorably as the heat insulating layer of the present invention.

Also, a compounded epoxy resin having a toughness by adding a tough thermoplastic resin such as nylon and various compounds which provide a toughness such as rubber to an epoxy resin or a compounded epoxy resin with a filler is preferably used. it can. In particular, a polymer alloy cured by blending polyethersulfone or polyetherimide with an epoxy resin has excellent toughness and can be used favorably.

The mold cavity generally has a complicated shape. It is extremely difficult to form a heat insulating layer by applying a coating to the surface of the mold cavity and the mold wall of a complicated shape in a mirror-like manner. Therefore, the applied coating layer is polished later, Is preferably polished by a numerically controlled machine tool such as a numerically controlled milling machine and then polished to a mirror finish.

In the present invention, by providing a thicker heat insulating layer as the thickness of the mold cavity decreases over both the thick wall and the thin wall of the mold cavity, the resin in the thick wall becomes unnecessary. The cooling time of the whole molded article can be shortened without delaying the cooling and solidification of the molded article.

In the mold cavity according to the present invention, the difference A between the maximum thickness of the thick portion and the minimum thickness of the thin portion is 0.5 mm.
That is all. When A is less than 0.5 mm, the merit of controlling the thickness of the heat insulating layer in each part is small. Also, depending on the shape and size of the molded product, A is 1
It is preferably 0 mm or less.

Also, in the present invention, (the thickness of the mold cavity + the thickness of the heat insulating layer) at the thickest portion of the mold cavity
The difference B between (the thickness of the mold cavity and the thickness of the heat insulating layer) in the minimum thin portion of the mold cavity satisfies the relationship of A ≧ B, and preferably 0.7A ≧ B. A <
In the case of B, although it depends on the viscosity of the molten resin and the shape and size of the molded product, the effect of the present invention is generally small.

The sum of the thickness of the mold cavity and the thickness of the heat insulating layer is preferably such that the maximum value is within three times the minimum value, and if it exceeds three times, the cooling efficiency of the mold is liable to decrease. The effect of the invention is small.

The thickness of each part of the heat insulating layer is usually up to 5 mm.
It is preferably set to the following, more preferably 0.01
mm to 3 mm, particularly preferably 0.1 mm
２2 mm. If the thickness of the heat insulating layer exceeds 5 mm, the cooling effect of the mold decreases, and the molding efficiency tends to decrease.
In general, it is preferable that the higher the mold temperature, the thinner the heat insulating layer made of the heat-resistant polymer is coated, and the lower the mold temperature, the thicker the heat insulating layer. When the upper and lower mold walls forming the mold cavity are covered with a heat insulating layer, the sum of the thicknesses of the upper and lower heat insulating layers is the thickness of the heat insulating layer.

In the present invention, as the mold covered with the heat insulating layer, a mold coated with a heat insulating layer coated on the mold wall surface constituting the mold cavity and / or the mold wall surface constituting the core mold can be used. . A mold in which a heat insulating layer is coated on both the mold wall surface and the core mold wall surface that constitute the mold cavity,
The injected synthetic resin has a large flow assisting effect, which is preferable.

In order to further improve the smoothness of the surface of the heat insulating layer of polyimide or the like, to further improve the scratch resistance of the surface, to improve the releasability, or to transfer the finely processed surface favorably. Alternatively, a metal layer can be provided in close contact with the heat insulating layer. When the surface of the mold is covered with a heat insulating layer and the injected synthetic resin comes into contact with the surface, the surface of the mold is heated by the heat of the synthetic resin. The lower the thermal conductivity of the heat insulating layer and the thicker the heat insulating layer, the higher the mold surface temperature. Therefore, it is preferable that the thickness of the metal layer adhered on the heat insulating layer is smaller. The thickness of such a metal layer is 0.001 mm
範 囲 1 mm.

The thickness of the metal layer is preferably uniform. If the thickness variation of the metal layer is large, the mold surface reproducibility of the thick portion of the metal layer is deteriorated, and the fluidity of the synthetic resin material changes.

The metal layer can be coated in various ways, but is well coated by plating. The plating described here is chemical plating (electroless plating) and electrolytic plating. Generally, plating is performed through some of the following steps. That is,
Pretreatment (chemical plating is performed in contact with the heat insulation layer) → Chemical corrosion (chemical etching with acid or alkali: making the surface moderately uneven) → Neutralization → Sensitivity treatment (metal that has a reducing power on the synthetic resin surface) Activation is achieved by adsorbing salt → activation treatment (noble metal such as palladium having a catalytic action is applied to the heat insulating layer resin surface) → chemical plating (chemical nickel plating, chemical copper plating, etc.) → electrolytic plating ( Electrolytic nickel plating, electrolytic copper plating, electrolytic chrome plating, etc.).

Also, a thin metal plate as a metal layer can be attached to the surface of the heat insulating layer. The thin metal plate is, for example, SUS304H, a copper plate, or the like. The SUS304H tension annealing material is preferably used because it hardly warps.

In the present invention, when a metal layer is provided in close contact with the heat insulating layer, the adhesive layer can be regarded as a heat insulating layer.

Next, the operation of the present invention will be described.

In general, the pressure loss of a fluid flowing between parallel plates is expressed by the following equation. ΔP = β × LηQ / H ² ΔP: pressure loss H: distance between parallel plates (mold cavity thickness) η: viscosity β: constant Q: flow rate L: flow distance

That is, the pressure loss is proportional to the viscosity and the flow distance, and is proportional to the square of the distance between the parallel plates. In the injection molding, as is clear from the above equation, the pressure loss increases as the distance from the gate increases, and the resin pressure pressing the mold surface decreases.

In addition, the viscosity η in the above formula is such that the injected synthetic resin is cooled at a portion in contact with the mold surface and rises with time, so that the force pressed against the mold surface over time,
And the fluidity in the flowing direction decreases.

Therefore, the transferability of the mold surface tends to be reduced at the flow end. In particular, when L and η in the above formula are large and H is small, that is, when a large thin molded product is injection-molded with a high-viscosity synthetic resin, problems arise in fluidity and mold surface transferability. .

According to the present invention, by molding the thin portion of the mold cavity with a heat insulating layer thicker than the thick portion, the molding speed can be reduced without delaying the cooling rate particularly at the thin portion, thereby reducing the fluidity of the synthetic resin. Things.

In synthetic resin injection molding, mold temperature and molding cycle time are closely related. Generally, the relationship between the mold temperature (Td) during molding and the required cooling time in the mold (θ) is expressed by the following equation. θ = − (D ² / 2πα) · ln [(π / 4) ｛(Tx−
Td) / (Tc−Td)｝] θ: Cooling time (sec) D: Maximum thickness of molded product (cm) Tc: Heated resin temperature during molding (° C) Tx: Softening temperature of synthetic resin (° C) α : Thermal diffusivity of synthetic resin Td: Mold temperature (° C)

That is, the cooling time (θ) is proportional to the square of the maximum thickness (D) of the molded product, and is expressed by (Tx−Td) / (Tc−T).
d) is a function.

Coating the mold with the heat insulating layer has the same function as increasing the thickness of the molded product and extending the cooling time. For this reason, the thickness of the heat insulating layer covering each part of the mold cavity is almost the same over the entire area of the mold cavity so that the cooling time of the entire molded product is minimized, that is, the cooling time of the thick part is not unnecessarily long. It is preferable to set the cooling time to about the same. This makes it possible to improve the flowability of thin parts and improve the transferability of the mold surface without lowering the molding efficiency of the entire molded product, thereby achieving an economical molding cycle (minimizing the cooling time of the entire molded product). Can be realized.

Next, a specific example of the present invention will be described with reference to the drawings.

FIGS. 1 to 5 are sectional views showing the vicinity of the mold cavity of the mold coated with a heat insulating layer according to the present invention. In these figures, 1 is a fixed mold, 2 is a movable mold, 3 is a core mold, 4 is a heat insulating layer, 5 is a mold cavity, and 6 is a metal layer. A1 is the thickness of the thickest part of the mold cavity 5,
a2 is the thickness of the minimum thin portion of the mold cavity 5, b1 is the thickness of the heat insulating layer 4 at the thickest portion of the mold cavity 5, b2
Indicates the thickness of the heat insulating layer 4 at the minimum thin portion of the mold cavity 5, and A and B described above are respectively A = a1−
a2, B = (a1 + b1)-(a2 + b2).

FIGS. 1 and 2 show examples of the configuration of a mold used for molding a wedge-shaped thin-walled molded product, where A>B> 0. The core mold 3 is housed in the movable mold 2, and the core mold 3 has a heat insulating layer 4
Is provided. FIG. 2 shows a case where a metal layer 6 adhered to the heat insulating layer 4 is provided on the upper surface of the core mold 3 of FIG.
The surface shape of the metal layer 6 is not limited to a mirror surface, but may be
An uneven pattern, a prism shape, or the like can also be used.

FIGS. 3 and 4 show the case where B = 0. FIG. 3 shows a configuration example of a mold used for molding an uneven thickness molded product having a hinge portion, and a heat insulating layer 4 is provided on both the fixed mold 1 and the movable mold 2 that constitute the mold cavity 5. FIG. 4 shows an example of a mold configuration used for molding a molded product having a tapered inclined surface on the left and right sides and an extremely thin portion in the center. As in FIGS. The core mold 3 is housed in the movable mold 2, and a heat insulating layer 4 is provided in a portion constituting the mold cavity 5.

FIG. 5 shows the case where B <0, and the rate of increase in the thickness of the heat insulating layer 4 can be made larger than that in the example of FIG. That is, the thickness of the heat insulating layer 4 at the end of the thin portion can be increased, and even when the length of the molded product is particularly long, or when the distance from the gate position (not shown) to the thin portion is long, the thin portion can be increased. , And the transferability of the mold surface can be improved.

[0050]

EXAMPLE In this example, a mold as shown in FIG.
= 2.5 mm, thickness w2 of the minimum thin part a2 = 0.8 mm, and a wedge-shaped (tapered) uneven thickness molded article was injection molded.

The material of the mold is steel (S55C), the surface of the mold is mirror-finished, and the surface is hard chrome plated. The thermal conductivity of the steel material is about 0.2 cal / cm · sec · ° C. The gate position is the side gate of the thick part (b), and the size of the gate is 20 mm in width and 2 mm in height.

The core mold 3 was covered with a heat insulating layer 4 made of a polyimide resin as follows. First, the surface of the core mold 3 is subjected to a primer treatment, and a polyimide varnish (trade name: Treeneth # 3000: manufactured by Toray Industries, Inc.), which is a straight-chain polyimide precursor, is applied thereon and heated at 160 ° C. After partial imidization, the coating and heating at 160 ° C. were repeated to form a heat insulating layer having a predetermined thickness. The thickness b1 of the heat insulation layer at the thickest part of the mold cavity is set to 0.2 mm, the thickness b2 of the heat insulation layer at the thinnest part is 0.7 mm, and then 2
The polyimide layer was formed by heating to 90 ° C. The polyimide layer has a softening temperature of 300 ° C. and a thermal conductivity of 0.0005 c.
al / cm · sec · ° C., elongation at break was 60%.

Next, a metal layer 6 was formed on the heat insulating layer 4. More specifically, a curable epoxy resin is applied to the outermost surface of the heat insulating layer 4 made of the polyimide layer, and 0.0
A 5 mm metal plate (SUS304H) was placed, heated at 80 ° C., and bonded.

The mold coated with a heat insulating layer produced by the above method was used as a dynamometer injection molding machine (M-150, manufactured by Meiki Co., Ltd.).
AII), molding temperature: 235 ° C, mold temperature set value: 70 ° C, molding cycle: 45 seconds, injection speed: 50
Injection molding was performed using methacrylic resin (trade name: Delpet 80NH, manufactured by Asahi Kasei Kogyo Co., Ltd.) under molding conditions of mm / sec and holding pressure: 60 kgf / cm ² . As a result, an uneven-thickness molded plate having no defect in the thin portion, no sink in the thick portion, and excellent surface properties was obtained.

As a comparative example, the shape of the mold cavity 5 was exactly the same as that of the present embodiment, but injection molding was performed under the same molding conditions using a comparative mold having no heat insulating layer 4. As a result, the molded product was not filled at the end of the thin portion, and a good molded product was not obtained. This molded product was 15% unfilled as compared to completely filled.

Using the mold of the present example and the comparative mold described above, the same uneven thickness molded article was injection molded by changing the holding pressure. FIG. 6 shows the result of comparing the mold filling property of each molded article with the weight of the molded article. As can be seen from FIG. 6, according to the present invention, the filling property of the resin is increased, and the thin portion can be favorably formed without increasing the holding pressure. Similarly, the temperature of the entire mold can be set low, and the cooling time required for cooling and solidifying can be reduced.

[0057]

As described above, according to the present invention,
A synthetic resin uneven thickness molded product having a thick portion and a thin portion can be molded in an economical and efficient molding cycle without increasing the temperature of the entire mold. Further, when a metal layer is provided on the heat insulating layer, a synthetic resin uneven thickness molded article having excellent surface properties in addition to the above effects can be formed.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating an example of a heat-insulating-layer-coated mold according to the present invention.

FIG. 2 is a cross-sectional view illustrating an example of a heat-insulating-layer-coated mold according to the present invention.

FIG. 3 is a cross-sectional view illustrating an example of a heat-insulating-layer-coated mold according to the present invention.

FIG. 4 is a cross-sectional view illustrating an example of a heat-insulating-layer-coated mold according to the present invention.

FIG. 5 is a cross-sectional view illustrating an example of a heat-insulating-layer-coated mold according to the present invention.

FIG. 6 is a diagram showing a relationship between holding pressure and resin filling properties in Examples and Comparative Examples.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Fixed type 2 Moving type 3 Core mold 4 Heat insulation layer 5 Mold cavity 6 Metal layer

Claims (8)

[Claims] 1. A method of molding a synthetic resin uneven thickness molded product using a mold having a mold cavity having a thick portion and a thin portion, wherein the maximum thickness of the thick portion of the mold cavity and the thickness of the thin portion are reduced. The difference between the minimum thickness is A, and the difference between (mold cavity thickness + insulation layer thickness) at the maximum thickness portion of the mold cavity and (mold cavity thickness + insulation layer thickness) at the minimum thickness portion of the mold cavity is B. A molding method of a synthetic resin uneven thickness molded product, wherein injection molding is performed using a heat-insulating layer-coated mold having a relationship of A ≧ 0.5 mm and A ≧ B. 2. The method according to claim 1, wherein A = 0.5 to 10 mm and 0.7A ≧ B. 3. The method for molding a molded article with uneven thickness of a synthetic resin according to claim 1, wherein the minimum thickness of the mold cavity of the thin portion is 0.1 to 1 mm. 4. The heat-insulating-layer-coated mold has a metal layer adhered on the heat-insulating layer.
3. The method for molding a molded article of uneven thickness of a synthetic resin according to any one of 3. 5. A mold used for injection molding of a synthetic resin uneven thickness molded article, comprising a mold cavity having a thick portion and a thin portion, wherein the maximum thickness of the mold cavity and the minimum thickness of the thin portion are provided. Is the difference between the thickness of the mold cavity and the thickness of the mold cavity at the thickest part (mold cavity thickness + insulation layer thickness) and the smallest part of the mold cavity (mold cavity thickness + insulation layer thickness).
A mold having a relationship of A ≧ 0.5 mm and A ≧ B, where B is a difference from the mold. 6. The mold according to claim 5, wherein A = 0.5 to 10 mm and 0.7A ≧ B. 7. The mold according to claim 5, wherein a minimum thickness of the mold cavity of the thin portion is 0.1 to 1 mm. 8. The mold according to claim 5, further comprising a metal layer adhered on said heat insulating layer.