JP3363500B2 - Mold and injection molding method using the same - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a mold for molding a thermoplastic synthetic resin, and an injection molding method using the same.

[0002]

2. Description of the Related Art US Pat. No. 3,544,518 discloses a method of improving mold surface reproducibility by coating a mold wall surface for molding a mold cavid with a substance having a small thermal conductivity. Further, Japanese Patent Application Laid-Open No. 62-37107 describes a method in which a breathable heat insulating layer is provided on the mold surface to prevent the occurrence of silver streaks.

These mold surface heat insulating layer coatings are carried out for the purpose of improving the surface of the molded product, and thus the heat insulating layer has been provided on the mold wall surface on the surface side of the molded product. A hard thermoplastic synthetic resin having a small elongation at break, such as methacrylic resin (hereinafter PMMA
A residual stress is likely to remain in the molded product during injection molding, and cracks easily occur when the injection molded product comes into contact with a solvent or the like during coating or assembly. This occurs particularly often in brittle synthetic resins having a small elongation at break and is generally called stress crack, and the resistance to this is called stress crack resistance (hereinafter abbreviated as SCR), and improvement is required. There is.

As a conventional method for improving SCR, a molded product is annealed after molding to reduce residual stress, or a mold temperature is increased to obtain a molded product with less residual stress. The method etc. are performed. However, the annealing method increases the cost due to the addition of post-processing, and increasing the mold temperature prolongs the molding cycle time and lowers the productivity.

Polyphenylene ether (hereinafter abbreviated as PPE) is widely blended with polystyrene, rubber-reinforced polystyrene and the like and widely used as a modified PPE. In the modified PPE, benzene rings and the like in the polymer are likely to associate with each other, and thus cracks are likely to occur at the ends of the injection molded product. There is a demand for an economical molding method that reduces the occurrence of cracks.

[0006]

DISCLOSURE OF THE INVENTION The present invention is a mold for improving stress cracks and the like of these molded products, and an injection molding method using the same. That is, it is a more economical solution to what has been solved by the conventional annealing method or by raising the mold temperature.

The present invention is directed to a molded article back having ribs and / or bosses on the mold wall forming a mold cavity made of metal.
Face wall only, or ribs and / or
Corresponds to the edge and / or corner of the back surface of the molded product
The thermal conductivity is 0.002cal / cm only on the mold wall.
The mold is covered with a heat insulating layer made of a synthetic resin of sec. Further, it is a mold in which a heat insulating layer is coated on the corners of the mold wall surface. Furthermore, the present invention is an injection molding method in which a synthetic resin is injected into the mold. There are ribs, bosses, etc. on the back surface of the injection-molded product, the shape is complicated, and the residual stress of the injection-molded product is more likely to remain. Further, when the molded product is assembled and put into practical use, the back surface of the molded product having ribs and / or bosses often comes into contact with oil and solvent of internal mechanical parts, and further,
Transparent molded products are also painted on the back side to give a deeper appearance. According to the present invention, it is possible to reduce the residual stress of a molded product, which is a problem on the rear surface or the end surface of the molded product having such ribs and / or bosses, and improve the SCR. In particular, the residual stress of the molded product is the largest at the end and the corner of the molded product, and when contacting with the solvent, cracks are intensively generated at the end and the corner of the molded product. The present invention aims to improve the SCR by covering the end surface portion and the corner portion of the mold wall surface with a heat insulating layer to reduce the residual stress at the end portion and the corner portion of the molded product.

PMMA or polystyrene is hard,
It features injection molded products with excellent transparency and gloss. Therefore, the injection molding method for reducing gloss is not a preferable method. By covering the mold surface with a heat insulating layer,
Although a method for improving the gloss of a molded product has been widely proposed,
The resin used here is a resin that does not originally have a good appearance, such as a rubber-reinforced resin or a glass fiber-containing resin. Therefore, the heat insulation coating on the surface of the mold has hitherto been performed on the mold wall surface on the surface side of the molded product. PMMA, polystyrene and the like can be obtained with a usual mirror-like chrome-plated mold to obtain a molded product having sufficiently excellent gloss. Therefore, in terms of appearance, it is not necessary to cover the mold surface with a heat insulating layer with PMMA or the like. In particular, when the thickness of the heat insulating layer becomes thicker, the elasticity of the heat insulating layer cannot be ignored, and PM
With a resin such as MA, it becomes difficult to obtain a molded product having a mirror-like luster like a conventional chrome-plated mold.

A mold covered with a heat insulating layer is 1) applicable to a mold having a mold cavity of complicated shape 2) a small increase in cooling time is required 3) it is required to withstand repeated molding of tens of thousands of times Therefore, it has been found that for this purpose, the heat insulating layer is required to have the following. Being a thin layer on the outermost surface of the mold, and having a low thermal conductivity and excellent heat resistance with respect to the heat insulating material, having a large tensile strength and elongation and being resistant to cold and heat cycles, surface hardness Is large, has excellent abrasion resistance, can be applied to the mold body well, and has excellent corrosion resistance when the heat insulating layer is formed or when the synthetic resin is molded using the mold.

We have conducted a deeper study on this, and even if the surface of the main mold is coated with a thin synthetic resin, if a heat insulating layer made of a synthetic resin satisfying certain conditions is used, injection can be performed tens of thousands of times. The present invention was discovered by discovering that it withstands molding. That is, in injection molding, the heat-plasticized resin injected into the mold comes into contact with the cooled mold wall surface to immediately form a solidified layer on the contact surface, and the subsequently injected resin has a solidified layer and a solidified layer. When it reaches the flow front, it moves toward the mold wall surface and comes into contact with the mold wall surface to form a solidified layer. That is, the injected resin flows so as to press the mold wall surface from above, and does not flow so as to drag the mold wall surface.

Therefore, if the surface of the mold is covered with a thin heat insulating layer made of a selected synthetic resin, the heat insulating layer will not be directly worn by the injected resin and can withstand tens of thousands of injection moldings. I found it. The main mold material used in the present invention is
Iron or steel containing 50% by weight or more of iron, aluminum or an alloy containing 50% by weight or more of aluminum, zinc alloy, copper alloy, for example, beryllium copper alloy, etc. To do. In particular, steel materials can be used most preferably.

In the present invention, it is preferable that the mold wall forming the mold cavity of the main mold is coated with chromium plating and / or nickel plating. Various heat-resistant resins can be used as the heat insulating material that can be favorably used in the present invention. Linear high molecular weight polyimides can be successfully used in the present invention.
The heat insulating material will be described using polyimide as an example.

Generally, polyimide is classified into linear type and thermosetting type, and there are various types of polyimide precursors thereof.
It is classified in Table 1 below.

[0014]

[Table 1]

In injection molding, a heated and plasticized synthetic resin is injected into a cooled mold and then cooled and molded in the mold, so that the mold surface is 100 after each molding.
The heating and cooling up to ℃ are repeated. Polyimide and iron and other metals have different coefficients of thermal expansion by an order of magnitude, and each time heating and cooling up to 100 ° C is repeated,
Severe stress is generated at the interface between the metal and the polyimide. As a polyimide capable of withstanding this stress for tens of thousands of times, it is necessary that both the breaking strength and the breaking elongation are large, and the adhesive force with the mold is also large, and a tough linear polymer polyimide is most preferable.

Table 2 shows examples of linear type high molecular weight polyimides which can be favorably used in the present invention. In addition, Tg represents a glass transition temperature, and n represents the number of repeating units.

[0017]

[Table 2]

The Tg of the linear polyimide varies depending on the constituents, and examples are shown in Tables 3 and 4. According to the findings of the present inventors, a higher Tg is preferable, and it is 200 ° C. or higher, more preferably 230 ° C. or higher.

[0019]

[Table 3]

[0020]

[Table 4]

Injection molding has an economic value in that a molded product having a complicated shape can be obtained by molding once. In order to coat this complicated metal surface with polyimide and firmly adhere it, it is preferable to apply a polyimide precursor solution and then heat to form the polyimide. The linear high molecular weight polyimide is formed by applying the precursor solution to the wall surface of the mold and then heating. Further, the polyimide has a Tg of 20.
It is a high heat resistant resin of 0 ° C or higher, excellent in strength and elongation,
The elongation at break is preferably 10% or more. The adhesion to the mold wall surface is preferably 500 g / mm width or more.

The linear polyimide precursor is synthesized, for example, by subjecting an aromatic diamine and an aromatic tetracarboxylic dianhydride to a ring-opening polyaddition reaction.

[0023]

[Chemical 1]

[0024] These polyimide precursors are heated to cause a dehydration cyclization reaction to form a polyimide. The most preferred linear polyimide precursor for the present invention is polyamic acid, and the repeating unit of a typical example thereof and the repeating unit of a polyimide obtained by imidizing the same are shown below.

[0025]

[Chemical 2]

[0026]

[Chemical 3]

[0027]

[Chemical 4]

[0028]

[Chemical 5]

The above-mentioned polyimide precursor polymer has good adhesion to the mold because it is a polar group such as a carboxyl group.
By reacting and forming a polyimide on the mold surface, a thin polyimide layer adhered to the mold surface can be obtained. The above polyimide precursor polymer is dissolved in a solvent such as N-methylpyrrolidone and applied on the wall surface of the mold. The adhesion between the polyimide and the main mold is preferably 500 g / 10 mm or more at room temperature, more preferably 1 kg / 10 mm width or more. This is the peeling force when the adhered polyimide was cut into a width of 10 mm and pulled at a speed of 20 mm / min in the direction perpendicular to the adhesive surface. Although this varies considerably depending on the measurement location and the number of times of measurement, it is important that the minimum value is large, and a stable and large peeling force is preferable. The adhesion force described here is the minimum value of the adhesion force of the main part of the mold. When the main metal is chrome-plated or nickel-plated, a stable peeling force is brought about, which is particularly preferable in the present invention. The smaller the thermal conductivity of the heat insulating layer is, the more preferable, but the thermal conductivity is 0.
Those of 002 cal / cm · sec · ° C or less can be used.

The linear high-molecular-weight polyimide used in the present invention preferably has a high strength and elongation, and particularly, a high elongation at break is preferable for a heat and cold resistance cycle, and the elongation at break is 10% or more. Preferably, more preferably 20
% Or more. The method for measuring the elongation at break is ASTM D638
Carry out according to. Although polyimide has been described as the heat insulating material that can be used in the present invention, a heat-resistant resin having properties similar to those of polyimide can be basically used, and the invention is not limited to polyimide. Various aromatic heat-resistant resins, thermosetting resins, etc. can be used if properly selected.

The thickness of the heat insulating layer is preferably in the range of 0.01 mm to 2 mm. Preferably from 0.05 mm to 0.5
mm, and more preferably 0.07 mm to 0.3 m
m. If it is less than 0.01 mm, the effect is low, and if it exceeds 2 mm, the molding cycle time becomes long. It corresponds to the back side of the molded product having the ribs and / or bosses described in the present invention .
The mold wall surface is a mold wall surface that molds the back side of the molded product that is not visible from the front during use. In the injection mold, the moving side mold generally forms the back side of the molded product.

In the present invention, only the mold wall surface corresponding to the mold wall surface on the rear surface side of the molded product having the ribs and / or bosses is coated with the heat insulating layer, and the mold wall surface on the front surface of the molded product is formed by the conventional mirror surface chrome plating. And the like, an excellent appearance can be maintained and the SCR can be improved. The end surface portion of the mold wall surface of the present invention is generally a wall surface in the thickness direction. If the thickness of the molded product is too thin, it will be difficult for the resin to flow, and if it is too thick, the molding cycle time will be long, which is not preferred, and generally 1 mm to 5 m.
It is m thick. The wall surface in the thickness direction of the mold cavity is the wall surface in the thickness direction of the molded product, and the rib portion is the wall surface in the thickness direction of the rib at the tip of the rib.

The corner portion of the mold wall surface of the present invention is a corner portion where the mold cavity is bent at an angle of 30 degrees or more, preferably 45 degrees or more, more preferably 60 to 90 degrees. It is a department. Some of the corners are rounded. In order to improve the resin flow in the mold cavity or to maintain the strength of the molded product, the corners of the mold cavity are often rounded. In the present invention, since the residual stress is more likely to remain as the radius of curvature is smaller, the effect of the present invention is great at such an acute angle portion, and when the radius of curvature is preferably 5 mm or less, more preferably 2 mm or less. The effect of the present invention is great.

The temperature of the main mold is cooled to 70 ° C. or lower, preferably 60 ° C. or lower and the molding chamber temperature or higher. Generally, the mold temperature is 70 ° C or less and injection molding is performed.
When the temperature is higher than 0 ° C, the molding cycle time becomes long and the molding efficiency is lowered. Further, if the temperature is lower than the molding chamber temperature, dew condensation is likely to occur on the mold surface. The mold of the present invention is generally applicable to injection-molded synthetic resins, but the resins that can be particularly preferably used are hard thermoplastic synthetic resins and polyphenylene ether (PPE) resins. The hard thermoplastic synthetic resin described here is a brittle resin having a breaking elongation of 10% or less measured by ASTM D638, and PMMA
Is the most representative resin. The PMMA described here is a polymer containing methyl methacrylate as a main component. For example, methyl methacrylate obtained by copolymerizing 15% by weight or less of an alkyl acrylate such as a methyl methacrylate polymer, ethyl acrylate, butyl acrylate, or 2-ethylhexyl acrylate. And a heat-resistant PMMA obtained by copolymerizing methyl methacrylate with maleic anhydride and styrene. Styrene resins such as polystyrene, styrene-acrylonitrile copolymer, styrene-methylmethacrylate copolymer, styrene-α-methylstyrene copolymer and the like can be used as well.

PMMA and styrene resins have a large surface hardness, excellent transparency, and a molded product having a good appearance can be obtained.
Various molded products are made for that purpose. The surface of the die is sufficiently polished, and then hard chrome plating is performed on the die surface, and PMMA or the like is injected into the die having a mirror-like surface to obtain a mirror-like injection molded product. PP which can be favorably used in the present invention
As the E-based resin, those widely used as modified PPE, which are generally blended with polystyrene, rubber-reinforced polystyrene, etc., or the PPE polymer itself is reacted with carboxylic acid anhydride, styrene monomer, etc. Is a chemically modified PPE or the like. The structural formula of a PPE polymer is shown by the following general formula.

[0036]

[Chemical 6]

(Wherein Ar represents a divalent aromatic residue, and n represents an integer of 5 or more), and polyphenylene ethers having at least one end with an --OH group. is there. Specific examples thereof include poly (2,6-dimethylphenylene-
1,4-ether), poly (2-methyl-6-ethylphenylene-1,4-ether), poly (2,6-diethylphenylene-1,4-ether), poly (2,6-dichlorophenylene) Ether), poly (2-chloro-6-
Methylphenylene-1,4-ether), poly (2,6-)
Phenylphenylene-1,4-ether), poly (2-
Methyl-6-n-propylphenylene-1,4-ether), poly (phenylene-1,3-ether) and the like. Poly (2,6-dimethylphenylene-1,4-
Ether) is the most widely used and is most preferred.

The present invention will be described with reference to the drawings. 1 and 2
Shows only the part according to the present invention in the cross section of the mold of the present invention. FIG. 3 shows an injection molded product. FIG. 4 shows a situation in which the synthetic resin flows through the mold cavity. FIG. 5 shows the orientation distribution of the cross section of the molded product at different injection speeds. FIG. 6 shows the relationship between the temperature of the injected synthetic resin, the mold temperature, the injection speed, the injection time and the thickness of the solidified layer. FIG. 7 shows a temperature distribution change at the time of injection molding near the surface of a general mold wall. FIG. 8 shows a temperature distribution change near the surface of the mold wall in which the surface of the mold wall is covered with a heat insulating layer.
FIG. 9 shows an apparatus of the cantilever method for measuring the SCR of a molded product. FIG. 10 shows a state where cracks are generated when the injection molded product is dipped in a solvent.

In FIG. 1, fixed side mold 2 and moving side mold 2
It is molded by injecting a synthetic resin into the mold cavity 3 formed from. The mold wall surface 4 formed by the stationary mold 1 forms the surface side of the molded product, and the mold wall surface 5 formed by the moving mold 2 is
The back side of the molded product having ribs and / or bosses is formed. Generally, ribs 6 that reinforce the molded product are provided on the back side of the molded product.
There are also bosses for assembling molded products, and they have a complicated shape. In the present invention, the heat insulating layer 7 is coated only on the mold wall surface corresponding to the mold wall surface on the rear surface side of the molded product having the ribs and / or bosses . The heat insulating layer 7 can cover the entire mold wall surface on the back surface side of the molded product having ribs and / or bosses , but the heat insulating layer only on a part of a complicated shape such as ribs or bosses. The present invention also includes the case where the entire back surface is not covered, such as the case where the back surface is coated or the heat insulating layer is non-uniform. Up to now, it has been common sense to coat the mold wall on the surface side of the molded product when the mold wall is coated with a heat insulating layer. However, as shown in FIG. 1, the present invention provides a back surface having ribs and / or bosses. It is characterized in that only the mold wall surface corresponding to the surface side is covered.

FIG. 2 shows an end face portion 8 of a mold wall forming a mold cavity 3 composed of a stationary mold 1 and a moving mold 2 and / or
Or the corners 9, the thermal conductivity of 0.002cal / cm ·
1 shows a mold of the present invention coated with a heat insulating layer of sec · ° C. or less. In FIG. 3, the present invention relates to the end surface 13 of the molded product 10 and
And / or the end face 12 of the molded product, if it has a hole 11.
The heat insulating layer is coated on the mold wall surface corresponding to.

In FIG. 4, the surface of the synthetic resin injected into the cooled mold 14 in contact with the wall surface of the mold is immediately cooled to form a solidified layer 15 which cannot flow. Then, the subsequently injected resin flows inside the solidified layer 15 and has a higher flow velocity toward the center of the mold cavity, and the flow front 16
It reaches (flow front) and goes toward the mold wall surface,
A so-called fountain flow is performed. Flow velocity 17, flow velocity distribution 18, and shear velocity distribution 19 are shown in the figure. The shear rate is greatest at the boundary between the flowing resin and the solidified layer, and heat generation by this shear and cooling by heat transfer to the mold occur at the same time. The higher the injection speed, the greater the shear heat generation,
In the region where the shear heat generation and the heat transfer cooling are balanced, the flow in the mold progresses well. Also, the higher the speed of injection, the thinner the solidified layer.

FIG. 5 shows the relationship between the compounding degree and the injection speed in the cross-sectional view of the injection-molded product. The higher the speed of injection, the less the overall orientation. The shaded area in the figure corresponds to the solidified layer during molding, and the higher the speed of injection, the less the overall orientation. The shaded area in the figure corresponds to the solidified layer during molding, and the higher the speed of injection, the thinner the solidified layer. FIG. 6 is a diagram showing changes in the thickness of the solidified layer during molding, in terms of resin temperature, mold temperature, and injection speed. As shown in FIG. 6, the thickness of the solidified layer is greatly affected by the mold temperature. Increasing the mold temperature is the most effective for thinning the solidified layer. However, increasing the mold temperature prolongs the molding cycle time and lowers the molding efficiency. In the present invention, as a means for minimizing the increase in molding cycle time and increasing the mold surface temperature, coating the mold surface with a heat insulating layer is used.

FIGS. 7 and 8 show calculated values of changes in the temperature distribution near the mold wall surface when injection molding was performed at a main mold temperature of 50 ° C. and a resin (polystyrene) temperature of 240 ° C. The numerical value of each curve in the figure shows the time (seconds) after the heated resin comes into contact with the cooled mold wall. The heating resin comes into contact with the mold wall surface and is rapidly cooled, and the surface of the mold receives heat from the heating resin and rises in temperature. As shown in FIG.
When the surface of the mold is covered with a heat insulating layer (polyimide), the temperature of the surface of the heat insulating layer that comes into contact with the resin increases, and the rate of temperature decrease also decreases. When the resin is in contact with the mold wall when it is covered with a heat-insulating layer, the smaller the time is, the mold surface temperature becomes significantly higher, which is equivalent to a large increase in the mold temperature due to the heat-insulating layer coating. And the increase in molding cycle time is small. The fact that the time after the resin comes into contact with the mold wall is small corresponds to high injection speed and high-speed injection, and the number of seconds in the figure is the time from when the resin contacts the mold surface until high injection pressure is applied. Equivalent to. The values in FIGS. 7 and 8 are not calculated for the shear heat generation of the synthetic resin during injection molding. The effect of high-speed injection molding is considered to be even greater. The mold surface temperature change can be calculated from the temperatures of the synthetic resin, the main metal, and the heat insulating layer, specific heat, thermal conductivity, density, latent heat of crystallization, and the like. The values shown in the figure are values calculated by unsteady heat conduction analysis by a nonlinear finite element method using ADINA and ADINAT (software developed at the Massachusetts Institute of Technology).

As shown in FIGS. 4 to 6, the higher the mold temperature is,
Also, the faster the injection speed, the thinner the solidified layer. Further, as shown in FIG. 8, when the mold surface is covered with a heat insulating layer, the mold surface temperature rapidly increases as the injection speed increases, and as a result, the solidified layer becomes extremely thin. The injected resin is brought into contact with a cooled mold to be rapidly cooled, and a solidified layer is immediately formed. The inner core layer sandwiched between the solidified layers is filled and then gradually cooled. Therefore, a cooled solidified layer is formed on the surface layer of the molded product, and the inner core has a large shrinkage ratio, so that the molded product retains compressive force in the surface layer and tensile force in the inner core. The thinner the solidified surface layer, the stronger the compression force of the surface layer, and the stronger the impact resistance and SCR of the molded product. This is similar to tempered glass formation (tempering).

The glass can be tempered either thermally or chemically. Thermal tempering can be accomplished by blowing cold air onto warm glass. This causes the surface of the glass to quickly solidify. And, when the inside of the glass also cools and contracts, a compressive force is applied to the surface of the glass, and fine flaws never spread, and the flaws do not cause breakage of the glass. On the other hand, tensile stress corresponding to this pressure occurs inside the glass. The tempering described above significantly increases the resistance of the glass to bending and impact. Similar to glass, synthetic resin has a higher compressive strength than tensile strength, so molded products with compressive force applied to the surface layer have impact resistance and SCR.
And a good molded product can be obtained by the present invention.

When the inner core cross section in which the tensile force acts is larger than the surface layer cross section in which the compressive force acts, the compressive force in the surface layer becomes stronger and the SCR also becomes stronger. In the present invention, by covering the mold wall surface with a heat insulating layer, the solidified layer at the time of molding is thinned, thereby increasing the compressive force of the surface layer generated in the molded product, and remarkably improving the SCR which is a drawback of hard synthetic resin etc. It is possible to provide the molded product.

[0047]

EXAMPLES Experiments were conducted using the following materials and methods. (1) Injection-molded synthetic resin PMMA: "Delpet 80N" manufactured by Asahi Kasei Kogyo Co., Ltd. Modified PPE: "Zylon 300H" manufactured by Asahi Kasei Kogyo Co., Ltd. (2) Main mold material 1) Steel material: S55C, thermal conductivity Is 0.12 cal / cm
-Sec- ° C (3) Type surface coating material 1) Chrome plating: hard chrome plating, 0.02 mm thickness 2) Polyimide Polyimide (A): Linear polyimide precursor, polyimide varnish "Trenice # 3000" (Toray Industries, Inc. ), Product name).

The Tg of the polyimide after curing is 300 ° C. thermal conductivity 0.0005 cal / cm · sec · ° C. 60% elongation at break Polyimide (B): linear polyimide precursor, polyimide varnish “Larc-TPI” (Mitsui Toatsu Co., Ltd., trade name ".

The polyimide after curing has a Tg of 256 ° C., a thermal conductivity of 0.0005 cal / cm · sec · ° C., and an elongation at break of 25% Polyimide (C): a straight-chain polyimide precursor, polyamide-imide “A1-10” ( Amoco Japan Ltd. product) solution.

The Tg of the cured polyimide is 230 ° C. thermal conductivity 0.0005 cal / cm · sec · ° C. Breaking elongation 40% (4) Main mold surface polyimide coating method Hard polyimide plating using a polyimide precursor solution. A polyimide coating layer was formed on the surface of the main mold by the following method. The surface of the mold is thoroughly degreased, then polyimide (A) is applied, heated to 160 ° C., this application and heating are repeated to thicken, and finally heated to 290 ° C. to form a polyimide layer. Next, a diamond paste is applied to the buff and polished to form a mirror-like linear polyimide coating layer having a predetermined thickness. Cut the coating layer to a width of 10 mm, and
The adhesion is measured by pulling at a speed of mm / min in the direction perpendicular to the coated surface. The adhesion is 2.0 to 2.2 kg / 10 mm width. Other polyimides were also formed in the same manner.

[0051]

[Example] PMMA was injection-molded under the following mold conditions. The SCR of the injection-molded product was measured by the cantilever method using the device shown in FIG. Mold: 380mm × 70mm × 30mm
The entire wall surface of the mold of the main mold made of steel having the mold cavity was plated with chrome, and the side wall surface of the mold was coated with polyimide (A) to a thickness of 0.11 mm. Molding conditions: Injection cylinder temperature 260 ° C Mold temperature 60 ° C Injection time 4 seconds Pressure holding time 10 seconds Cantilever method: In FIG. 9, one end of the molded product 21 is fixed to the support base 20, and the other end is loaded. 22 is added, and the solvent 23 impregnated in the paper is made to act on the center of the molded product 21. The surface stress of the molded product can be changed by changing the load. By changing the surface stress and the solvent, the time at which the molded product breaks is measured.

SCRs were measured on the front surface side of the molded product (the outermost surface of the mold is plated with chrome) and the rear surface side of the molded product (the outermost surface of the mold is covered with polyimide). The results are shown in Table 5.

[0053]

[Table 5]

As shown in Table 5, on the back surface side of the molded article on which the breaking layer was coated on the mold, the breaking time increased with either ethanol or xylene, and the SCR was greatly improved.

[0055]

[Practice side 2] Using polyimide (B) or polyimide (C), an experiment was conducted in the same manner as in implementation side 1, and similar results were obtained.

[0056]

Example 3 A mold of a steel material mold having a flat mold cavity of 38 mm × 70 mm × 3 mm, the mold cavity wall of which is entirely chrome-plated, and the entire surface of which is chrome-plated. PMMA was injection-molded under the same conditions as in Example 1 by using a metal mold having a thickness of 0.1 mm. The obtained molded product was added to a solvent having the following composition at 250 ° C.
FIG. 10 shows the state of the cracks generated by soaking for 5 seconds in air, followed by air-drying. Solvent: Origin thinner # 210 (Origin Electric Co., Ltd.)
Made) (10-1) of FIG. 10 is a molded product formed by a mold in which the entire wall surface of the mold is plated with chrome, and a large number of cracks 25 are generated on the end face 24 of the molded product. (10-2) is (10-
It is a molded product obtained by coating the end face of the mold with polyimide of 0.1 mm thickness in 1) and molding, and cracks 25 on the end face 24 of the molded product.
Is much less.

[0057]

Example 4 Using the mold shown in Example 3, modified PPE was injected into the mold at 60 ° C. and injection-molded. The molding conditions were an injection cylinder temperature of 260 ° C., an injection time of 5 seconds, and a pressure holding time of 10 seconds. The obtained molded product was immersed in n-hexane at 25 ° C. for 1 minute, air-dried, and cracks were observed. . The molded product formed by using the mold whose end face was coated with polyimide had obviously few cracks on the end face of the molded product.

[0058]

According to the present invention, the residual stress of the injection molded product is reduced and the SCR at the time of coating can be improved.

[Brief description of drawings]

FIG. 1 is a sectional view of a mold of the present invention.

FIG. 2 is a sectional view of a mold of the present invention.

FIG. 3 is a diagram of a molded product obtained by the present invention.

FIG. 4 is a diagram showing a situation in which synthetic resin flows in a mold cavity.

[Figure 5] Orientation distribution chart of the cross section of the molded product with different injection speeds

FIG. 6 is a diagram showing the relationship between the temperature of the synthetic resin to be injected, the mold temperature, the injection speed, the injection time and the thickness of the solidified layer.

FIG. 7 is a diagram showing a temperature distribution change at the time of injection molding in the vicinity of a general mold wall surface.

FIG. 8 is a diagram showing a temperature distribution change at the time of injection molding in the vicinity of the mold wall surface in which the mold wall surface is covered with a heat insulating layer.

FIG. 9 is a diagram of a device of a cantilever method for measuring SCR of a molded product.

FIG. 10 is a state diagram of cracks generated when an injection molded product is immersed in a solvent.

[Explanation of symbols]

1 Fixed mold 2 Moving mold 3 type cavity Type 4 wall 5 type wall 6 ribs 7 heat insulation layer 8 end face 9 corners 10 molded products 11 holes 12 end faces 13 End face 14 mold 15 Solidified layer 16 Flow tip 17 Flow rate 18 Flow velocity distribution 19 Shear rate distribution

─────────────────────────────────────────────────── --- Continuation of the front page (56) Reference JP-A-55-55839 (JP, A) JP-A-54-142266 (JP, A) JP-A-62-37107 (JP, A) JP-A-62- 208919 (JP, A) JP 61-222708 (JP, A) JP 5-131456 (JP, A) JP 2-235714 (JP, A) JP 61-79611 (JP, A) (58) Fields surveyed (Int.Cl. ⁷ , DB name) B29C 33/38 B29C 45/37

Claims (4)

(57) [Claims] 1. A back surface of a molded product having ribs and / or bosses on a mold wall surface forming a mold cavity made of metal.
The thermal conductivity is 0.002cal only on the mold wall corresponding to
A mold covered with a heat insulating layer made of synthetic resin having a temperature of not more than / cm · sec · ° C. 2. The thermal conductivity is 0.002 cal only in a mold wall surface forming a mold cavity made of a metal, only a mold wall surface corresponding to an end surface and / or a corner of a back surface of a molded product having ribs and / or bosses. A mold covered with a heat insulating layer made of synthetic resin having a temperature of not more than / cm · sec · ° C. 3. An injection molding method for injecting a synthetic resin into a mold according to claim 1 or 2. 4. The injection molding method according to claim 3, wherein the synthetic resin is a hard thermoplastic synthetic resin.