JPH0866927A - Matte synthetic resin injection-molded article and manufacture thereof - Google Patents

Abstract

PURPOSE: To obtain an injection-molded article, which has a uniform matte surface and an inconspicuous weldline or the like by a method wherein molding is performed with a main mold wherein the molding wall surface on the surface of a molded article side for constituting the cavity is covered with a heat insulating layer, which is made of heat resistant polymer having a specified value of thermal conductivity and has fine rough surface, in a thickness of a specified value. CONSTITUTION: The synthetic resin injection-molded article is one having a weldline. Its molding wall surface on the front surface of the molded article constituting the cavity of a main mold made of metal is covered with a heat insulating layer having a fine rough surface, by which synthetic resin injection- molded article having a uniform matte surface is produced. The heat insulating layer is produced by applying heat resistant polymer, in which 5-50wt.% of fine particle is mixed and the thermal conductivity of which is 0.00005-0.002cal/ cm.sec. deg.C, in the thickness of 0.05-0.5mm.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a synthetic resin injection-molded article having a matte surface and a method for producing the same.

[0002]

2. Description of the Related Art A synthetic resin injection-molded article having a matte surface is generally injection-molded by using a metal mold having a fine uneven surface. However, the injection-molded product obtained by this method is generally pointed out to have a defect that the fine uneven surface of the mold is not sufficiently reproduced, or unsightly marks such as weld lines and flow marks are conspicuous. It has been demanded.

It has been attempted to improve these appearance defects under molding conditions. The mold temperature has the greatest influence among various molding conditions, and the higher the mold temperature is, the more preferable. However, if the mold temperature is increased, the cooling time required for the cooling and solidification of the plasticized resin becomes longer, and the molding efficiency is lowered.

Therefore, there is a demand for a method of improving the reproducibility of the mold surface without increasing the mold temperature, and not increasing the required cooling time even if the mold temperature is increased. 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 method of improving mold surface reproducibility by coating a mold wall forming a mold cavity with a substance having a low thermal conductivity is disclosed in US Pat. No. 3,544,518 for injection molding.

[0006]

SUMMARY OF THE INVENTION It is an object of the present invention to provide an injection-molded article which has a uniform matte surface, has less conspicuous weld lines and the like, and is molded with high productivity, and a method for producing the same. Is.

As a method for matting the surface of the mold, a sandblast method has been generally used. In the heat-insulating layer-covering mold, the sandblasting method is first considered to make the surface of the mold matt. We performed sandblasting on the surface of the heat-insulating layer-coated mold to make it matte, and then injection molded synthetic resin.The injection-molded product had a uniform matte surface, even though the surface of the mold was evenly matte. I found that it does not erase. That is, the unsightly weld line dent that appears when molding with a matte surface mold of a general metal mold is eliminated, but the defective phenomenon that the weld part and the general part of the injection molded product become a non-uniform matt surface It turned out that it appears remarkably.

The present invention provides an injection-molded article with improved appearance defects.

[0009]

That is, according to the present invention, the surface wall of the mold on the surface of the molded product constituting the mold cavity of the main mold made of metal has a thermal conductivity of 0.00005 to.
Matte shape characterized by being molded using a mold coated with a heat insulating layer of a fine uneven surface made of a heat-resistant polymer of 0.002 cal / cm · sec · ° C to a thickness of 0.05 to 0.5 mm Of the synthetic resin injection molded article.

In the above invention, a heat insulating layer-covering mold in which a fine uneven surface is formed by applying a heat insulating material comprising a heat resistant polymer containing 5 to 50% by weight of fine powder to the outermost surface of the heat insulating layer,
Alternatively, a mold is preferably used in which the surface of the heat-insulating layer made of a heat-resistant polymer is sandblasted to make it uneven, and then the heat-resistant polymer is poured into the recesses of the uneven surface to adjust the degree of unevenness.

Further, according to the present invention, in an injection-molded product of synthetic resin, (1) the surface wall of the molded product constituting the mold cavity of the main mold made of metal has a thermal conductivity of 0.0000.
0.05 to 0.5 m in the heat insulation layer of the fine uneven surface made of a heat resistant polymer of 5 to 0.002 cal / cm · sec · ° C.
(2) The injection molded product has a weld portion, and the recess of the weld line of the weld portion is 2 μm or less,
(3) The surface of the injection-molded product is a matte surface having a glossiness of 30% or less, and a matte synthetic resin injection-molded product in which the general part and the weld part of the molded product have a uniform matte surface. Is.

The present invention will be described in detail below.

The synthetic resin usable in the present invention is a thermoplastic resin usable in general injection molding. For example, generally used for injection molding of styrene polymer, ABS resin or its copolymer, olefin polymer such as polyethylene and polypropylene, modified polyphenylene ether resin, vinyl chloride polymer or its copolymer, polycarbonate, polyamide, polyester, etc. It is a thermoplastic resin.

When these resins are mixed with various reinforcing materials or various fillers, or when they are polymer alloys, a great effect is obtained. For example, one or more kinds of rubber, glass fiber, asbestos, calcium carbonate, talc, calcium sulfate, wood powder and the like can be blended with the above resin.

In particular, rubber-reinforced polystyrene and ABS resin can be most preferably used in the present invention.

The injection-molded article of the present invention is a molded article having a weld line, and may be a one-point gate molded article or a multi-point gate molded article. The molded product of the present invention is typically a molded product such as a housing for light electric appliances and electronic devices. From this viewpoint, a molded product having a multi-point gate is particularly preferable. The multi-point gate described here refers to a mold having two or more gates in one mold cavity, preferably 2 to 10
It has gates. Even a single-point gate is a good target of the present invention when the molded product has many holes and a large number of weld lines are formed in the molded product.

The metal of the main mold material described in the present invention generally means iron or various steel materials containing iron as a main component, aluminum or alloys containing aluminum as a main component, zinc alloys such as ZAS, and beryllium-copper alloys. It includes metal molds used for molding synthetic resins. Particularly, steel materials can be used favorably.

The heat-resistant polymer used in the heat insulating layer in the present invention has a glass transition temperature of 100 ° C. or higher, preferably 150.
℃ or higher, and / or melting point is 230 ℃ or higher, preferably 2
A heat resistant polymer having a temperature of 50 ° C. or higher can be favorably used. The heat conductivity of the heat resistant polymer is generally 0.00005 to 0.002.
cal / cm · sec · ° C. Further, the heat-resistant polymer is preferably a tough polymer having a breaking elongation of 5% or more,
More preferably, it is 10% or more. The breaking elongation is measured according to ASTM D638, and the tensile speed at the time of measurement is 5 mm / min.

Polymers that 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 various amorphous heat resistant polymers soluble in organic solvents, various polyimides and modified epoxy resins. Etc. can be used satisfactorily.

Examples of the non-crystalline heat resistant polymer include polysulfone, polyether sulfone, polyallyl sulfone, polyarylate and polyphenylene ether.

Although there are various kinds of polyimide, linear high molecular weight polyimide and partially crosslinked polyimide can be preferably used. In addition, thermoplastic polyimide, polyetherimide,
A polyimide or the like which forms an imide ring by heating after coating can be favorably used. Generally, a straight chain type high molecular weight polyimide has a large breaking elongation and excellent durability, and can be favorably used.

Injection molding has an economic value in that a molded product having a complicated shape can be obtained by a single molding. To coat the surface of this complicated mold with a heat-resistant polymer and firmly adhere it, apply a heat-resistant polymer solution, a heat-resistant polymer precursor solution, a monomer or semi-cured product of the heat-resistant polymer, etc. Most preferably, it is then heated to form a heat resistant polymer. Therefore, it is preferable that the heat-resistant polymer or the heat-resistant polymer precursor of the present invention can be dissolved in a solvent to form a low-viscosity fluid.

Epoxy resins, silicone-based resins, melamine-based resins and the like having flexibility are similarly favorably used. Particularly, the modified epoxy resin having flexibility is preferably used. For example, a polyamide-modified epoxy resin, a polymer alloy made of a mixture of epoxy resin and polyetherimide, a polymer alloy made of a mixture of epoxy resin and polyethersulfone, and the like can be used favorably.

The thickness of the heat insulating layer is 0.05 mm to 0.5 m
It is appropriately selected within a very narrow range of m. It is preferably 0.1 mm to 0.3 mm, and particularly preferably,
It is from 0.1 mm to less than 0.25 mm. The temperature of the main mold is 80 ° C. or lower, preferably 65 ° C. or lower, and it is preferable to cool to room temperature or higher for molding.

In injection molding, the mold temperature and the molding cycle time are closely related. That is, in injection molding, the relationship between the mold temperature (Td) and the required cooling time (θ) in the mold is theoretically 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: Cylinder temperature (° C) Tx: Softening temperature of molded product (° C) ) Α: Thermal diffusivity of resin Td: Mold temperature (° C)

The cooling time (θ) is 2 times the wall thickness (D) of the molded product.
It is proportional to the power and is a function of the (Tx-Td) value. That is, it is a function of the value obtained by subtracting the mold temperature from the softening temperature of the synthetic resin. When this value is small, the variation of this value gives a large variation to the cooling time, but when this value is large, the variation given to the cooling time becomes small.

Covering the main mold with a heat-insulating layer functions in the same way as increasing the thickness of the molded product and lengthening the cooling time, while decreasing the mold temperature shortens the cooling time. Work towards. From the standpoint of molding cycle time, it is preferable that the heat insulating layer has a thin thickness and can improve the appearance. In the present invention, an extremely narrow range of the heat insulating layer thickness of 0.05 to 0.5 mm is good in terms of balance between appearance improvement and molding cycle time.

When the surface of the main mold is covered with a heat insulating layer, and the heated resin injected into contact with the surface of the mold, the mold surface receives the heat of the resin and rises in temperature. The lower the thermal conductivity of the heat insulating layer and the thicker the heat insulating layer, the higher the mold surface temperature.

In the present invention, the injected synthetic resin has a temperature of 80.degree.
It is preferable to perform injection molding in a state where the mold surface temperature is equal to or higher than the softening temperature for at least 0.1 seconds after coming into contact with the cooled mold surface. If there is no heat insulating layer on the mold surface, the mold surface temperature will be almost the same as the main mold temperature after 0.1 seconds, but the mold surface will be covered with a heat insulating layer to bring it to a temperature above the softening temperature. Possible, and preferably 0.2
The mold surface temperature is at or above the softening temperature for at least seconds, more preferably at least 0.3 seconds.

The change in mold surface temperature during injection molding can be calculated from the temperature of the synthetic resin, the main mold, the heat insulating layer, specific heat, thermal conductivity, density, latent heat of crystallization and the like. For example, ADINA and A
It can be calculated by unsteady heat conduction analysis by the nonlinear finite element method using DINAT (software developed at Massachusetts Institute of Technology) or the like.

The softening temperature of the resin described here is the temperature at which the synthetic resin can be easily deformed. For the amorphous resin, the Vicat softening temperature (ASTM D1525), and for the hard crystalline resin, the heat deformation temperature (ASTM D648 load 18). .6
kg / cm ² ), heat distortion temperature (AS
TM D648 load 4.6 kg / cm ² ). The hard crystalline resin is polyoxymethylene, nylon 6, nylon 66, etc., and the soft crystalline resin is various polyethylene, polypropylene, etc.

The fine uneven surface of the heat insulation layer described in the present invention is a part of selected uneven surfaces among the so-called matte surfaces, and the uniform matte surface of the present invention is synthesized. It is the surface that provides the resin injection molded product. The surface roughness is 0.1 to 10 μm in center line average roughness (Ra) measured in JIS B 0601, 1 to 100 μm in maximum height (Rmax), and 1 to 100 μ in ten-point average roughness (Rz).
The surface selected from m. More preferably, R
It is a fine surface unevenness selected from 0.5 to 5 μm for a, 5 to 50 μm for Rmax, and 5 to 50 μm for Rz.

The injection-molded product of the present invention has a matte surface with a glossiness of the injection-molded product of 30% or less, preferably 20% or less, and the general part and the weld part of the molded product have a uniform matte surface. The depression of the weld line is 2 μm or less, preferably 1.5 μm or less, more preferably 1 μm or less.
Gloss is measured according to JIS K7105, reflection angle 60 °
Done in. The fact that the matte surface has a uniform matte surface means that the matte surface is uniform with the naked eye, and generally, the difference in shade of the matte surface is 0.5% or less in terms of glossiness, More preferably, it is 0.3% or less. The depression of the weld line can be measured by observing the cross section of the weld portion with a microscope.
That is, a photograph of a cross section near the weld line is taken, a tangent line is drawn on the surface of the molded product of the cross section photograph, the distance between the tangent line and the bottom of the dent of the weld line is measured, and this is used as the dent of the weld line.

When injection molding is generally carried out using a mold having a heat insulating layer having a fine uneven surface, the gloss of the welded part of the injection-molded product is different from that of the general part, and it is difficult to form a uniform matte surface. The present invention is a molded product in which this point is improved, a uniform matte surface is provided, and the weld dent is reduced to substantially eliminate the conspicuous weld line. In the present invention, by eliminating the conspicuousness of the uniform matte surface and the weld line, it is possible to use the housings of various light electric devices and electronic devices which have been used by coating after molding until now without coating. Next, the present invention will be described in more detail.

When the heat-plasticized synthetic resin is injected into a cooling metal mold which is generally used for injection molding, the synthetic resin starts cooling from the contact surface immediately after contacting the wall surface of the mold. Then, a solidified layer of the synthetic resin is immediately formed on the mold wall surface, and the thickness of the solidified layer increases with the passage of time. The rate of increase in the thickness of the solidified layer depends on the temperature of the synthetic resin, the softening temperature of the synthetic resin, the thermal conductivity of the synthetic resin,
The latent heat of crystallization of the synthetic resin, the temperature of the mold, the thermal conductivity of the mold, etc., but generally, the solidified layer is formed after a few microseconds to tens of microseconds of the synthetic resin contacting the mold, It is considered that the solidified layer becomes thicker with the passage of time. In such general injection molding, it is considered that a thin solidified layer has already been formed on the surface layer of the synthetic resin that contacts the mold wall surface when the injection pressure required to reproduce the mold surface is applied to the synthetic resin. In order to improve the mold surface reproducibility of the synthetic resin in such a state, it is necessary to press the resin surface of the thin solidified layer against the mold wall surface to reproduce the mold surface, and it is necessary to apply a considerably high pressure. Therefore, in general injection molding, the mold surface reproducibility near the gate where the injection pressure is high is good, and the mold surface reproducibility at the resin flow end where the injection pressure is low is poor.

On the other hand, when injection molding is performed using a mold in which the surface of the metal mold is covered with a heat insulating layer, the heat insulating layer is heated by the injected synthetic resin to raise the temperature, and then cooling is started. The synthetic resin that is in contact with the mold wall covered with a heat insulating layer of appropriate thickness is kept above the softening temperature of the synthetic resin for several hundred microseconds after the contact, and no solidified layer is formed during that time. , Then a solidified layer begins to form.
Therefore, when the heat-insulating layer-coated mold is used, it becomes possible to apply a pressure necessary for reproducing the mold surface to the synthetic resin on the mold wall surface in a state where the solidified layer is not yet formed on the mold surface. It is the next time that such a state can be achieved. That is, the synthetic resin temperature is high, the softening temperature of the synthetic resin is low,
The mold temperature is high, the heat insulating layer has a certain thickness above a certain level, and the synthetic resin is under a certain pressure as soon as possible after the synthetic resin comes into contact with the mold. Of these, the former three items cannot be freely selected from the required performance, productivity, cost, etc. of the molded product, and the latter two items must be selected. If the pressure applied to the mold wall is applied to the resin with the solidified layer not yet formed on the mold surface, the mold surface reproducibility will be extremely good, and even if the resin pressure pressed to the mold wall is slightly low, good mold The surface reproducibility is extremely improved.

In the injection-molded article having the weld line of the present invention, pressure is applied to the synthetic resin in the vicinity of the weld line (hereinafter abbreviated as "weld portion") for a very short time after the synthetic resin comes into contact with the mold. As a result, the reproducibility of the mold surface in the welded part becomes extremely good, and the appearances of the general part and the welded part become non-uniform. This phenomenon is a peculiar phenomenon that appears prominently when a heat insulating layer-coated mold is used, and this phenomenon is a phenomenon that we have discovered, and it is required to make it uniform. The present invention provides a molded article with improved appearance nonuniformity.

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

1, 2 and 3 show the main mold temperature of 50.
Shown are the calculated values of the change in temperature distribution near the wall surface of the mold when the rubber-reinforced polystyrene was injection molded at 240 ° C. 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, and the mold surface receives heat from the heated synthetic resin and rises in temperature. As shown in the figure, when the mold surface is covered with a heat insulating layer (polyimide) (FIGS. 2 and 3), the temperature of the surface of the heat insulating layer in contact with the synthetic resin increases, and the temperature decreasing rate also decreases.

When the synthetic resin is coated with the heat insulating layer, the mold surface temperature becomes higher as the time after the synthetic resin comes into contact with the mold wall becomes shorter, and the mold temperature is greatly increased by the heat insulating layer coating. The same effect can be obtained, and the increase of the molding cycle tom is small.

This will be described in more detail with reference to the injection-molded article shown in FIGS. In FIG. 4, the synthetic resin injected from the gate 1 flows around the hole 2 and merges at the weld to form the weld line 3. In FIG. 5, when injection molding is performed with a die coated with a heat insulating layer having a fine uneven surface, the fine uneven surface of the heat insulating layer is transferred to the surface of the molded product. However, in general, when injection molding is performed with a heat-insulating layer-coated mold that is finely rugged by sandblasting, the degree of fine ruggedness of the welded portion 5 of the molded product 4 increases, and when molded with a black colored resin, the welded portion 5 becomes dark, It was discovered that part 6 became whitish and did not result in a molded article of uniform gloss as described in this invention. The cause of this is not clear, but it is estimated as follows. The cause will be described with reference to FIGS. 6 and 7.

In the injection molding of the molded product shown in FIG. 5, the pressure applied to the mold wall surfaces of the weld portion 5 and the general portion 6 is modeled in FIG.
Shown in In FIG. 6, the pressure applied to the general part 6 of the molded product is the curve 7, and the pressure applied to the weld part 5 is the curve 8. Curve 9 is the pressure on the gate. That is, the pressure applied to the general portion 6 gradually rises as the injection time elapses, whereas the pressure applied to the weld portion 5 becomes high at the same time when the synthetic resin comes into contact with the mold wall surface.

As shown in FIG. 2, the heated synthetic resin comes into contact with the mold wall surface of the heat insulating layer to heat the surface of the heat insulating layer, and the cooling immediately starts. In Figure 2, the mold surface is 1 after 0.52 seconds.
The temperature is below 00 ° C, and the synthetic resin in contact with the mold surface is also decreased. In order to reproduce the mold surface better, the heated synthetic resin comes into contact with the mold wall surface and high pressure is applied to the resin at the same time, that is, high pressure is applied to the resin while the mold wall surface and the surface layer of the synthetic resin are at high temperature. This is necessary. As shown in FIG. 6, in the weld portion, the synthetic resin comes into contact with the mold wall surface, and at the same time, a high pressure is applied to the resin, so that fine irregularities on the mold wall surface are more accurately reproduced.

FIG. 7 illustrates this process as a model. The mold wall surface is composed of the heat insulating layer 10 having a fine uneven shape shown in 7-1. When injection molding is performed with this mold, the resin pressure gradually increases after the synthetic resin 11 comes into contact with the mold wall surface in the general part of the molded product, so the mold wall surface and the surface layer of the resin cool during the pressure increase, Can not penetrate deeply into the fine irregularities on the mold wall (7-
2). On the other hand, in the weld portion of the molded product, the synthetic resin 11 comes into contact with the mold wall surface and at the same time the resin pressure rises, so that the synthetic resin can penetrate deep into the fine irregularities of the mold (7-
3). As a result, in the welded portion 5, the surface irregularities of the molded product are larger than in the general portion 6, and in the black colored synthetic resin, the welded portion becomes blackish and a uniform matte state is not obtained.

Such a phenomenon is a problem peculiar to the injection molding of the heat-insulating layer-coated mold, and the present invention provides a molded product in which this defective phenomenon is improved. The present invention is a molded product in which the matte surface of the welded part and the general part has a uniform glossiness. In order to make the surface unevenness of the welded part and the general part of the molded product uniform, it is necessary to select an appropriate degree of unevenness for the fine unevenness of the surface of the heat insulating layer. The heat-insulating layer-coated mold for molding the molded product of the present invention can be produced by various methods. However, carefully selected sand blasting and subsequent processing, or application of finely powdered insulation coatings to the insulation layer is best used in the present invention.

Generally, in order to form a matte surface, the fine uneven surface of the heat insulating layer can be formed by a sandblast method or the like. The size of the formed irregularities is adjusted by the size of the sand particles to be sprayed, the material of the sand particles, the spraying air pressure (spraying speed), and the spraying time. However, it is difficult to form a uniform matte surface in the weld portion and the general portion, which is the object of the present invention, simply by making the fine irregularities by the ordinary sandblasting method. The molded article of the present invention can be obtained by using a mold surface having an appropriately selected uneven shape. For example, as shown in FIG. 7-4, by injecting a solution of the heat insulating material into the bottom of the concave and convex portions formed by sandblasting and heating the heat insulating material 12 to the bottom of the concave portion, the depth of the concave portion can be reduced. It is possible to form a uniform matte surface in the general portion and the welded portion by molding using a heat-insulating layer-covered mold in which the temperature is adjusted. In addition, an uneven heat-insulating layer-coated mold suitable for the present invention is obtained by a method of sandblasting using a ceramic or the like having a very limited grain size or a grain shape, or a method of combining this with another type of sandblasting. You can also

However, the heat-insulating layer having a fine uneven surface which can be best used in the present invention is obtained by applying a heat-insulating material composed of a heat-resistant polymer containing 5 to 50% by weight of fine powder to the outermost surface of the heat-insulating layer. It is formed. As fine powder, particle size is 0.001
~ 300 μm of silicon oxide, calcium carbonate, clay,
Inorganic fine powder such as kaolin can be used. Silicon oxide fine powder having an extremely small particle size of 0.001 to 0.1 μm (fine powder marketed under the trade name of “Aerosil” or the like), or silicon oxide fine particles having an average particle size of about 0.1 to 50 μm ("Tospearl" made by Toshiba Silicon Co., Ltd., Toray Co., Ltd.
"Trefill" etc.) can be used particularly well. A good coating can be obtained by blending these fine powders with a heat insulating coating, for example, a coating such as a polyimide precursor solution, preferably in an amount of 5 to 50% by weight, more preferably 10 to 40% by weight. By applying this to the surface of the heat insulating layer, a favorable fine uneven surface heat insulating layer-covering mold that can be used in the present invention can be obtained.

"Aerosil" (manufactured by Nippon Aerosil Co., Ltd.), which can be best used as an inorganic fine powder, is made of high-purity silicon oxide (SiO ₂ ) and has a specific surface area of 50 to 50.
Fine particles of about 400 m ² / g are produced. Each particle has a spherical shape, and silanol groups are present on its surface. This silanol group interacts with silanol groups of other particles by hydrogen bonding to form a three-dimensional network structure. When agitated or vibrated, this network structure is decomposed and the viscosity is reduced. In the static state, the network structure of particles is regenerated and the viscosity increases. When 5 to 50% by weight of "Aerosil" is blended with a heat-insulating material coating such as a polyimide precursor solution and spray-coated on the surface of the main mold or the heat-insulating layer, the blended coating has a low viscosity during spray coating and can be coated. When it adheres to the mold surface, it becomes highly viscous and forms an appropriate fine uneven surface. Although the Aerosil-blended heat insulating layer may form the entire heat-insulating layer, it only needs to be present on the outermost surface of the heat-insulating layer, and generally the outermost surface of the heat-insulating layer has a thickness of about 5 to 30 μm as this Aerosil-blended heat insulating layer. . It was found that this fine uneven surface is extremely preferable as a fine uneven surface heat insulating layer mold for molding the molded article of the present invention.

There are various types of fine particles of silicon oxide commercially available under the trade names of "Tospearl", "Trefil", etc., which have a uniform particle size and a wide particle size distribution. By blending, various heat insulating layers having surface irregularities can be obtained.

When the heat insulating material containing fine particles or fine powder of silicon oxide or the like forms the outermost surface of the heat insulating layer, the effect of making the heat insulating layer less likely to be damaged becomes remarkable.

In the present invention, the injection-molded article of the present invention having a uniform matte surface and no visible weld lines is obtained by molding using the heat-insulating layer-coated mold thus produced.

Although the present invention has been described with reference to the simple shaped molded product shown in FIGS. 4 and 5, the housing of the light electric device has a complicated shape molded by a multi-point gate, and such a complicated product is used. In the case of shaped articles, in addition to the difference in matteness between the general part and the welded part, there is often a difference in matteness between the left and right across the weld line. The difference between the left and right sides across the weld line occurs when there is a difference in the flow velocity of the left and right resins. The resin on the side with a high flow velocity is applied with the resin pressure quickly after it contacts the mold wall surface, and the resin on the slow side is applied with the resin pressure slowly after contacting the mold wall surface, which tends to cause a difference in the mold surface reproducibility between left and right. . The present invention is also effective in such a case.

[0054]

[Example] The following molds and materials are used.

Main mold: made of steel (S55C) and has a mold cavity for the molded product shown in FIG. The molded product has a size of 100 mm × 100 mm and a thickness of 2 mm, and has a 30 mm × 30 mm hole in the center. The gate is a side gate as shown in FIG. The mold surface is mirror-like. Three main dies are prepared, two of which are chrome plated.

Surface fine irregularity main mold: The main mold surface not plated with chromium is made into a matte surface by sandblasting. The matte surface is NO. NH1008 (blast air pressure 3.7kg /
cm ² ) is used.

Polyimide precursor and polyimide after curing: Linear high molecular weight polyimide precursor solution "Treney # 3000" (manufactured by Toray Industries, Inc.). After curing, the polyimide has Tg of 300 ° C. and thermal conductivity of 0.0005 ca.
l / cm · sec · ° C, breaking elongation 60%.

Polyimide-coated mold: A polyimide precursor solution was applied to a chrome-plated main mold, heated to 160 ° C. to partially imidize, and then the coating and heating at 160 ° C. were repeated 8 times, and finally 290. Heat to ℃ 100
% Imidized to cover the mold surface with polyimide, and the surface is mirror-polished to form a polyimide-coated mold having a thickness of 150 μm.

Surface finely roughened polyimide-coated mold (A), (B), (C), (D): (A): The surface of the polyimide-coated mold is sandblasted to give a matte surface. Matting is NO. NH1008 (Spraying air pressure 1.8
kg / cm ² ).

(B): Polyimide solution is applied to the surface of the mold (A) having a finely-roughened surface, and a polyimide solution is applied (thickness of 5 μm as polyimide solid content) on the surface of the polyimide to adjust the depth of the recesses on the surface of the polyimide.

(C): "Aerosil # 200" (manufactured by Nippon Aerosil Co., Ltd.) was added to a polyimide precursor solution in an amount of 30% by weight based on the solid content and placed in a tumbler. , And then thoroughly mixed, and then spray-apply the Aerosil-blended polyimide precursor solution to the polyimide-coated mold surface and heat it to form an Aerosil-blended polyimide layer having an average thickness of 15 μm on the outermost surface to form a fine uneven surface. To do.

(D): Stirring with a tumbler was performed without glass beads, and the mixture was filtered through a # 200 stainless steel mesh to prepare a polyimide precursor solution containing Aerosil.
Other than that is performed like (C), and it is set as a fine uneven surface.

Injection-molded synthetic resin: Asahi Kasei Polystyrene 492 (manufactured by Asahi Kasei Kogyo Co., Ltd.) black colored product. Vicat softening temperature is 105 ° C.

Injection molding conditions: synthetic resin temperature 230 ° C., main mold temperature 50 ° C. injection molding

Measurement of surface irregularity pattern: Measured with a surface roughness profile measuring instrument "Surfcom 570A" manufactured by Tokyo Seimitsu Co., Ltd.

[Example 1] Injection molding is carried out using a mold (B) having a surface finely textured polyimide coating. The matteness of the general part and the welded part of the molded product is uniform, the glossiness is 5%, and the dent of the weld line is 1 μm or less, and a good uniform matte injection molded product is obtained. FIG. 8 shows a surface uneven pattern. The surface uneven pattern of the mold is shown in 8-1, the surface uneven pattern of the general part of the molded product is shown in 8-2, and the surface uneven pattern of the weld part of the molded product is shown in 8-3. Both have almost the same degree of surface irregularity.

[Comparative Example 1] Injection molding is carried out using a main mold having a finely textured surface. If you use this mold that is not covered with a heat insulating layer, unsightly weld lines will occur in the molded product,
The recess of the weld line is 5 μm.

[Comparative Example 2] Injection molding is carried out using a mold (A) coated with a finely textured polyimide coating die (A). The dent of the weld line of the molded product is 1 μm or less, but there is a difference in the matting degree between the general part and the welded part, and a uniform matt shaped product cannot be obtained. That is, the weld part is dark and the general part is whitish. FIG. 9 shows the surface uneven pattern. 9-1 shows the surface unevenness pattern of the polyimide-coated mold, 9-2 shows the surface unevenness pattern of the general part of the molded product, and 9-3 shows the surface unevenness pattern of the weld part of the molded product. The surface unevenness pattern is obviously different between the general part and the weld part of the molded product.

[Embodiment 2] Injection molding is carried out using molds (C) and (D) coated with finely textured polyimide. The matteness of the general part and the welded part of the molded product is uniform, and the glossiness is 2% for both the general part and the welded part of (C), and 11% for both the general part and the welded part of (D). The dents in the weld line are both less than 1 μm and hardly noticeable, and a good uniform matte injection molded product is obtained. FIGS. 10 and 11 show the surface unevenness pattern of the molded product molded in (C) and (D).

[0070]

EFFECTS OF THE INVENTION According to the present invention, good matte injection molding with less conspicuous weld lines can be obtained. Until now, such molded products have been produced by matting the molded product. However, in recent years, environmental damage due to evaporation of the paint solvent has become a major social problem, and reduction of production cost is required. With this molded product, a molded product that can be used practically without coating after molding is obtained, and its economic effect is enormous.

[Brief description of drawings]

FIG. 1 is a graph showing calculated values of changes in temperature distribution near a wall surface of a mold when injection molding is performed.

FIG. 2 is a graph showing a calculated value of a temporal change in temperature distribution near a mold wall surface covered with 0.1 mm of polyimide when injection-molded.

FIG. 3 is a graph showing a calculated value of a time change of a temperature distribution near a mold wall surface covered with 0.1 mm of polyimide when injection-molded.

FIG. 4 is a perspective view showing an example of an injection molded product.

5 is an explanatory view of the injection-molded product shown in FIG.

FIG. 6 is a graph showing changes over time in resin pressure applied to a mold wall surface during injection molding.

FIG. 7 is an explanatory diagram showing, as a model, how the injection-molded synthetic resin fills the fine irregularities on the mold surface.

FIG. 8 is a graph showing surface irregularity patterns of a mold and a molded product in Example 1.

FIG. 9 is a graph showing a surface unevenness pattern of a mold and a molded product in Comparative Example 2.

10 is a graph showing a surface unevenness pattern of a molded product in Example 2. FIG.

FIG. 11 is a graph showing a surface unevenness pattern of a molded product in Example 2.

[Explanation of symbols]

 1 gate 2 hole part 3 weld line 4 molded product 5 weld part 6 general part 7 resin pressure curve applied to general part 8 resin pressure curve applied to weld part 9 resin pressure curve applied to gate part 10 heat insulating layer 11 synthetic resin 12 heat insulating material

Claims (4)

[Claims] 1. The thermal conductivity of the surface wall of the mold on the surface of the molded product constituting the mold cavity of the main mold made of metal is 0.000.
0.05 to 0.5 for the heat insulating layer on the surface of fine irregularities made of a heat-resistant polymer of 05 to 0.002 cal / cm · sec · ° C.
A method for producing a matte synthetic resin injection-molded article, which comprises molding using a die coated to a thickness of mm. 2. A heat-insulating layer-coated mold having a fine uneven surface formed by applying a heat-insulating material made of a heat-resistant polymer containing 5 to 50% by weight of fine powder to the outermost surface of the heat-insulating layer. The method for producing a matte synthetic resin injection-molded article according to claim 1. 3. A heat-insulating layer made of a heat-resistant polymer is sandblasted to make it uneven, and then the heat-resistant polymer is poured into the recesses of the uneven surface, and the mold is formed using a mold having a controlled degree of unevenness. The synthetic resin injection-molded article according to claim 1. 4. A synthetic resin injection-molded article comprising: (1)
The heat conductivity of the molded product surface side mold wall surface that constitutes the mold cavity of the main mold made of metal is 0.00005 to 0.00
An injection-molded article molded using a mold coated with a heat-insulating layer having a fine concavo-convex surface made of a heat-resistant polymer of 2 cal / cm · sec · ° C to a thickness of 0.05 to 0.5 mm, (2)
The injection-molded product has a welded part, the recess of the weld line in the welded part is 2 μm or less, and (3) the surface of the injection-molded product is a matte surface having a gloss of 30% or less, and A matte synthetic resin injection molded product with a uniform matte surface in the general and weld parts.