JPH09239796A - Production of plastic molded product - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a highly accurate molded product by using a crystalline resin. SOLUTION: A crystalline thermoplastic resin (polypropylene in a drawing) is molded into an almost final shape at load bending temp. (H.D.T) of 60 deg.C on a basis of a wt. determined so that the resin pressure in a mold cavity becomes atmospheric pressure. This molding matrix is inserted into the mold cavity having a transfer surface and heated to temp. of 160 deg.C (B-point) equal to or higher than thermal deformation temp. (A-point) but equal to or lower than melt temp. Tm(o) to be thermally expanded. The transfer surface is transferred to the resin in the mold cavity by the resin inner pressure caused by this thermal expansion. Thereafter, the molded matrix is gradually cooled to temp. equal to or lower than H.D.T (60 deg.C) through a route of (B→C) and taken out as a molded product in a state near to almost atmospheric pressure.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a plastic molded article, and more particularly to a method for producing a highly accurate molded article without a sink mark by using a crystalline thermoplastic resin. Office machines such as machines, facsimiles, laser printers, precision equipment such as cameras, video cameras, video projectors, compact discs and CDs
-It is preferably applied to information equipment such as ROM.

[0002]

2. Description of the Related Art Molded articles using a crystalline thermoplastic resin (hereinafter referred to as a crystalline resin) such as polyethylene, polypropylene, nylon, polybutylene terephthalate are mainly formed by injection molding. However, molded products using these crystalline resins have sink marks, and the molded crystalline resins undergo dimensional change due to crystallization immediately after molding, and moreover, the dimensional changes are remarkable, making them highly accurate parts. Is currently not used.

In order to solve this, it has been attempted to use a composite material in which a crystalline resin is filled with an inorganic filler or a reinforcing material to reduce the shrinkage rate and the deformation amount. However, molded articles using these composite materials cannot be made to have a high degree of precision without sink marks, and at present, such problems have not been solved.

On the other hand, an amorphous thermoplastic resin such as polymethylmethacrylate, polystyrene, polycarbonate, acrylonitrile-styrene (hereinafter referred to as an amorphous resin) does not crystallize, or even if it crystallizes, it is very difficult. Since it is very small, the dimensional stability of the molded product is good and it is widely used for high precision parts. This amorphous resin is characterized in that the glass transition temperature of the amorphous resin is higher than the deflection temperature under load. Taking advantage of this characteristic, the amorphous resin is softened at a temperature higher than the glass transition temperature. A high-precision molding method for cooling is known.
-19327, Japanese Examined Patent Publication 3-33494, Japanese Examined Fair 5-
No. 73570.

The injection compression molding method described in Japanese Patent Laid-Open No. 61-19327 discloses a high precision molding product such as an optical lens which is injection-compression molded using an amorphous resin such as polymethylmethacrylate, polystyrene or polycarbonate resin. This is a molding method in which the resin in the mold cavity that is heated to the resin melting temperature and injected is made to have a uniform temperature distribution in the softening temperature range, and then the deflection temperature under load to remove the resin from the softening temperature range. It is a method of cooling the resin while minimizing the occurrence of temperature nonuniformity of the resin due to cooling by gradually cooling the resin.

The thick resin molding method disclosed in Japanese Examined Patent Publication No. 3-33494 relates to a method for molding a super thick molded product such as a penta prism with high accuracy using an amorphous resin such as polymethylmethacrylate. In this method, the resin filled in the mold cavity is heated to near the melting temperature to remove the internal strain, rapidly cooled to the glass transition temperature, and gradually cooled while heating from the glass transition temperature.

The injection molding method described in JP-B-5-73570 relates to a method for molding an optical product such as a lens by using an amorphous resin such as polymethylmethacrylate. The glass of the amorphous resin is used. After injecting and filling the resin into a mold cavity that has been preheated to a temperature not lower than the transition temperature, the mold temperature is gradually lowered to a temperature not higher than the glass transition temperature of the resin and lowered to cure the molding material in the cavity. It is a molding method.

Amorphous resins have little or no crystallization even if they occur, and have a lower deflection temperature under load than the glass transition temperature. By cooling from the above softened state, a high precision molded product can be obtained. On the other hand, a crystalline resin has a large dimensional change due to crystallization, and a highly accurate molded product cannot be obtained even as a composite material filled with an inorganic filler or a reinforcing material. In order to obtain a highly accurate molded product using a crystalline resin, a molding method that does not pass through a temperature at which a specific volume change due to crystallization occurs is applied. As this method, Japanese Patent Laid-Open No. There is a publication of 163119.

The method for producing a plastic molded article described in Japanese Patent Laid-Open No. 4-163119 discloses a method in which a resin heated to a flow temperature is injected and filled into a mold at a temperature not higher than a heat deformation temperature.
This is a method in which the mold temperature is heated so that the resin temperature becomes equal to or higher than the glass transition temperature, the temperature is maintained for a predetermined time, and the temperature is gradually cooled to the heat deformation temperature or lower.

[0010]

However, when resin molding is performed using a crystalline resin having a large shrinkage rate due to crystallization by the injection molding method, a high precision molded product cannot be obtained at present. An amorphous resin that does not crystallize enables highly accurate molding of a molded product. The reason for this is, of course, when injection molding is performed using a crystalline resin, a remarkable decrease in specific volume due to crystallization of the resin hinders high precision. Therefore, if a molding method that does not go through the process of significantly reducing the specific volume is found, it is possible to improve the accuracy of the molded product made of this crystalline resin.

For this purpose, rather than high-pressure filling of the molten resin from the high temperature side, the specific volume of the resin from the low temperature side is changed from the low temperature side as in the method for producing a plastic molded article described in JP-A-4-163119. It may be heated to a temperature at which the change abruptly occurs or less and at which the shape can be easily deformed. This method is described in the above-mentioned JP-A-4-163.
Although the amorphous resin has already been known from Japanese Patent No. 119, the crystalline resin is not specifically described.

It is an object of the present invention to obtain a highly accurate molded product using a crystalline resin by eliminating the step of passing a temperature which causes a change in specific volume due to crystallization in the injection molding process.

[0013]

According to a first aspect of the present invention, a crystallized molded base material having a substantially final shape is molded from a crystalline thermoplastic resin with a constant weight, and the molded base material is at least one. After inserting into a mold cavity having a transfer surface, the mold is clamped, and the thermoplastic resin constituting the molding base material is heated to a temperature not lower than a deflection temperature under load and lower than a melting temperature, and the mold cavity volume is constant. , The temperature below the deflection temperature under load of the thermoplastic resin by using the internal pressure of the resin generated in the normal direction of the transfer surface due to the thermal expansion of the thermoplastic resin and the expansion due to the decrease in the crystallinity to bring it into close contact with the transfer surface, followed by cooling. The molded base material is taken out from the mold cavity at the temperature of 1 to obtain a molded product having the transfer surface.

According to a second aspect of the present invention, in the method for producing a high-precision molded article according to the first aspect, after heating the molding base material to a temperature not lower than the deflection temperature under load of the molding base resin and lower than the melting temperature, The mold cavity volume is reduced, the mold cavity is compressed and deformed, and a constant resin internal pressure is generated, and then the mold cavity volume is made constant.

According to a third aspect of the present invention, in the method for producing a high precision molded product according to the first aspect, the heating temperature of the molding base material is such that the rate of decrease in crystallinity of the molding base material is 50%.
The temperature range is as follows.

According to a fourth aspect of the present invention, in the method for producing a high precision molded product according to the first aspect, the weight of the molding base material is
The molding base material is cooled and adjusted so that the resin internal pressure when passing through the deflection temperature under load falls within the pressure range of atmospheric pressure to 10 MPa.

According to a fifth aspect of the present invention, in the method for producing a high precision molded product according to the first aspect, the molding base material is annealed in advance to increase the crystallinity of the molding base material. Is.

According to a sixth aspect of the present invention, in the method for producing a high precision molded article according to the first aspect, as the crystalline thermoplastic resin, an inorganic filler, a reinforcing material or the like is added to the crystalline thermoplastic resin. It uses a filled composite material.

According to a seventh aspect of the present invention, in the method for producing a high precision molded product according to the first aspect, the transfer surface of the mold cavity is used as a mirror surface and is applied to an optical component such as a lens, a mirror or a prism. is there.

The invention of claim 8 is the method of manufacturing a high precision molded product according to claim 1, which is applied to a microfabricated component such as a Fresnel lens, a disk, a diffraction grating, etc. as a transfer surface of the mold cavity. Is.

According to a ninth aspect of the present invention, in the method for producing a high precision molded article according to the first aspect, the crystalline thermoplastic resin is mixed with a crystal nucleating agent for promoting crystallization. .

[0022]

BEST MODE FOR CARRYING OUT THE INVENTION The method for producing a high-precision molded product of a crystalline resin according to the present invention was found by the present applicant in the process of earnestly researching a high-precision forming method for an amorphous resin. The molding method will be described and the case of molding an amorphous resin and a crystalline resin will be described. FIG. 1 is a diagram for explaining an example of a conventional high-precision molding method using a p-v-T diagram of an amorphous resin polycarbonate, where the pressure p is (MP
a), the specific volume v is (cm ³ / g), the temperature T is (° C.), Tgo is the glass transition temperature under atmospheric pressure (148 ° C.),
HDT is the deflection temperature under load (° C). In the pvt diagram of the amorphous resin polycarbonate shown in FIG.
The amorphous resin molding process to obtain highly accurate molded products is
Follow the path ABCD shown in FIG. A high temperature molten amorphous resin heated to 280 ° C. was filled with a resin internal pressure of 130 MPa (path A-B), and the temperature was the same as that of the mold cavity kept at a glass transition temperature of 148 ° C. or higher at 170 ° C. Until it becomes uniform temperature (B-C route),
The molded product is taken out at 130 ° C., which is lower than the deflection temperature under load (HDT: 135 ° C.) of the resin by cooling in a state where the temperature is made uniform (C-D route). A filling pressure is required so that the internal pressure of the resin becomes almost zero at the temperature below the deflection temperature under load of the resin. The filling pressure is 100 to 160 MPa, and the capacity of a normal injection molding machine is sufficient.

FIG. 2 shows p- of crystalline resin polypropylene.
It is a figure for demonstrating the example of the conventional shaping | molding method using a v-T diagram, and p, v, and T are using the same unit as the case of FIG. P- of the crystalline resin polypropylene shown in FIG.
In the v-T diagram, the melting temperature of polypropylene resin is 2
At 30 ° C., the resin internal pressure is 160 MPa, and when a filling pressure equal to or higher than the resin internal pressure shown in FIG. 1 is generated, the path of ABCD is traced as in the case of FIG. However, the temperature at point D, which intersects with the line where the resin pressure is zero, is approximately 140 ° C., which is higher than the deflection temperature of the resin under load (HDT: 66 ° C.).
The fact that the resin internal pressure becomes zero at this temperature means that atmospheric pressure or less, that is, negative pressure is generated in the cavity at this temperature or less, and sinking occurs because the resin can be deformed. . Therefore, even if an injection molding method called a high-precision molding method for an amorphous resin is applied to a crystalline resin, a high-precision molding cannot be obtained. That is, the reason why the dimensional accuracy of the crystalline resin is poor is that in the conventional injection molding method, the dimensional change is caused by the shrinkage caused by cooling and crystallization immediately after injection filling, and the progress of crystallization after molding. is there. Therefore, it suffices to solve both the above-mentioned shrinkage and dimensional change. For the latter dimensional change, it is sufficient to raise the mold temperature to complete crystallization in the mold, but the former shrinkage However, the conventional injection molding method cannot basically solve the problem. In other words, crystalline resin undergoes crystallization that causes a rapid change in specific volume below the melting temperature, so the internal pressure of the resin in the mold cavity is below atmospheric pressure, which is called negative pressure, and the resin is not exposed to the outside of the mold. The air flows into the interior, causing sink marks. Thus, the change in specific volume due to the crystallization hinders the accuracy of the crystalline resin from being increased. Therefore, if a molding method that does not pass the state change temperature that causes a change in the specific volume is found, it is possible to improve the accuracy of the crystalline resin. That is, instead of high-pressure filling of the crystalline resin melted from the high temperature side, the molding base material molded into a substantially final shape is inserted into the mold cavity and clamped, and the temperature at which the specific volume change suddenly changes from the low temperature side. It suffices to heat to the temperature below which the shape can be easily changed.

However, it is not always necessary to heat the molding base material having a substantially final shape under a constant cavity volume. For example,
For the crystallization obtained by rapid solidification that has not progressed, crystallization once progressed with heating, the volume of itself decreased, and sufficient pressure could not be generated on the transfer surface, resulting in negative pressure at the time of removal. A sink mark occurs. If the shape is taken into consideration, the base material becomes too large to enter the mold cavity. Therefore, the base material must have a crystallinity of a certain level or higher, preferably the highest crystallinity of the resin material, so as to minimize the change in specific volume due to crystallization due to heating. For this reason, the forming base material may have a certain weight so that the internal pressure of the mold cavity becomes approximately atmospheric pressure at the deflection temperature under load (HDT).

That is, as a method for producing a high-precision molded product of a crystalline resin according to the present invention, at least one transfer surface is formed by crystallizing a molded base material of crystalline thermoplastic resin having a substantially constant shape with a constant weight. After inserting into a mold cavity with a mold, the mold is clamped, heated above its deflection temperature under load and below its melting temperature, and is generated perpendicularly to the transfer surface due to thermal expansion of the resin and expansion due to a decrease in crystallinity under a fixed cavity volume. After the transfer surface is transferred using the internal pressure of the resin, the product is cooled and the molded product is taken out at a temperature below the deflection temperature under load.

That is, when the crystalline resin is heated to a temperature above the deflection temperature under load, the elastic modulus of the crystalline resin is lowered and the crystalline resin is easily deformed, and the crystallinity is lowered more than the monotonous thermal expansion of the resin. After the resin is brought into close contact with the transfer surface due to the generation of the internal pressure of the resin due to the rapid expansion, the temperature is kept uniform and cooled, and the internal pressure of the resin becomes the atmospheric pressure or less at the load deflection temperature or less. Is a method for obtaining a high-precision molded product having a highly accurate transfer surface without sink marks. It is necessary to make the temperature uniform and cool in order to minimize the unevenness of the pressure distribution. The temperature variation is 10 ° C or less, preferably 5 ° C or less, and the cooling rate is 15 ° C / min or less, preferably It should be 8 ° C / min or less. The deflection temperature under load (HDT) here is ASTM: D648 in consideration of the deformation when the molded product is taken out.
It is a value at a load of 1.84 MPa defined in (corresponding to claim 1).

Further, the volume of the cavity when heating the molded base material in the final shape is preferably as constant as possible. If the cavity volume fluctuates significantly, not only the resin internal pressure varies, but also the pressure distribution in the cavity becomes non-uniform, and sink marks and deformation due to release of residual pressure occur, making it impossible to obtain a highly accurate molded product. However, since the material forming the mold also expands and contracts due to heat, the volume change cannot be made zero. For this reason, it is preferable to minimize cavity volume variations.

FIG. 3 is a view for explaining a mold structure for explaining a second embodiment of the molding method according to the present invention. In the figure, 1 and 2 are molds, 3 is a compression piece (mirror surface). (Piece) 4 is a cavity, 5 and 6 are mirror surfaces, 7 and 8 are heating / cooling plates, and 9 is a heating / cooling pipe. The mold structure shown in FIG.
The moving side compression piece 3 attached to the heating / cooling plate 7 on the movable platen (not shown) side and the heating / cooling plate 8 on the fixed platen (not shown) side of the injection molding machine (not shown), respectively. And a mold 2 having a mirror surface 6 on the fixed side, and a heating / cooling plate 7, 8
Maintain the temperature of the molds 1 and 2 at a predetermined temperature by hot water or cold water flowing through the heating / cooling pipe 9.

In the mold structure shown in FIG. 3, a molding base material (a base material molded into a substantially final shape with a weight such that the internal pressure of the resin becomes atmospheric pressure at the deflection temperature under load) is inserted into the cavity 4. When tightened and heated to a temperature not lower than the heat distortion temperature and not higher than the melting temperature, if a pressure fluctuation occurs due to the thermal expansion of the mold material and the expansion difference of the molding base material, the compression piece 3
Drive to minimize pressure fluctuations and prevent sink marks. Also, the cavity volume may be kept constant and heated and cooled, but as a mold structure with improved insertability of the molding base material, the molding base material is heated to a temperature above its deflection temperature under load and below its melting temperature. Therefore, after the cavity volume is reduced and the cavity is compressed and deformed, the cavity volume may be made constant (corresponding to claim 2).

In the above-described embodiment of the present invention, the molding base material is heated to utilize the thermal expansion and the expansion that reduces the crystallinity. However, if the crystallinity is too low, the resin internal pressure increases. Pass. In order to withstand the pressure, the mold must be made large, and burrs are generated, which is not preferable. For this reason, as a measure of the reduction rate of crystallinity, 5
It is preferably 0% or less, more preferably 30% or less (claim 3
Corresponding to).

Since the molding method of the present invention utilizes the resin internal pressure, basically, when the resin internal pressure is equal to or higher than the deflection temperature under load and equal to or lower than atmospheric pressure, that is, negative pressure, sink marks are liable to occur. On the contrary, if a pressure (10 MPa) above a certain level, which is lower than the deflection temperature under load, remains, the pressure is released when the mold is opened, and the deformation occurs. Therefore, the resin internal pressure around the deflection temperature under load is very important. Therefore, the weight of the molding base material is adjusted such that the internal pressure of the resin when the molding base material is cooled and the deflection temperature under load passes is within the pressure range of atmospheric pressure to 10 MPa (corresponding to claim 4).

The crystallized molding base material having a substantially final shape can be obtained by injection molding, press molding, compression molding, vacuum molding or the like, but the crystallinity changes depending on the molding method and molding conditions at that time. Since this molding method utilizes the decrease in the crystallinity of the crystallized base material, the following problems occur if this crystallization is insufficient. Once the crystallization progresses during heating (particularly when the heating rate is slow), the crystallization lowers, and the quality of the molded product is not stable. The decrease in the crystallinity of the forming base material also means that the crystallinity varies. Again, the quality of the molded product is not stable. A decrease in crystallinity means a decrease in density. Therefore, when the molding base material having a constant weight and insufficient crystallization is inserted into the cavity having a constant volume, the volume of the molding base material becomes large. Therefore, when an attempt is made to insert a molding base material having such a weight that the resin internal pressure becomes close to the atmospheric pressure at the deflection temperature under load, the size of the molding base material becomes larger than that of the cavity, and it may not be possible to insert. Therefore,
It is preferable to anneal a molded base material of a substantially final shape made of a crystalline resin to increase the crystallinity in advance (corresponding to claim 5).

As described above, the crystalline material may be used alone, but in many cases, it is spherical (calcium carbonate, magnesium hydroxide), plate-shaped (talc, mica) for increasing, modifying, and strengthening. ), And a fibrous (glass fiber, carbon fiber) inorganic substance is filled. In fact, the crystalline resin itself has a large temperature difference between the deflection temperature under load and the melting point of the resin. For example, in the case of polypropylene, the deflection temperature under load is 60 ° C., and the melting point is 176 ° C., while the deflection temperature under load is considerably low. Therefore, heating temperature 165 ℃
In such a case, the temperature difference between the heating temperature and the deflection temperature under load becomes 100 ° C. or more, and it takes time to heat and cool, and depending on the shape, it must be cooled to 50 ° C. and taken out. Further, even when the load is 0.45 MPa, that is, even when the shape is such that no deformation occurs during mold opening and removal, the load deflection temperature is 102 ° C., and the temperature difference between the heating temperature and the load deflection temperature is large. However, when a composite material containing a filler is used, the deflection temperature under load can be significantly improved. For example, when 20% glass short fibers are filled, the deflection temperature under load is 110 ° C., and when 20% glass long fibers are provided, the deflection temperature under load is 140 ° C. Differences from the heating temperature are 55 ° C. and 25 ° C., respectively (corresponding to claim 6).

In the above-described method for molding a crystalline resin, if at least a part of the cavity has a mirror surface, the transfer surface will also have a mirror surface. Further, if cooling is performed at a speed at which crystallization can be completed, there is no change over time, and therefore it can be used for optical parts such as lenses, mirrors, prisms, etc. Further, if at least a part of the cavity is a microfabricated surface, the transfer surface is also a microfabricated surface. Therefore, it can be used for microfabricated components such as Fresnel lenses, disks, and diffraction gratings (corresponding to claim 8).

Further, the difference between the heating temperature and the molded product take-out temperature determines the molding cycle. However, if the cooling rate is too fast, the temperature distribution and the pressure distribution are generated and the accuracy is lowered, but in the uniform thickness shape, this effect is small. However, if the cooling rate is high, sufficient crystallization cannot be achieved. In order to solve this, a crystal nucleating agent for promoting crystallization may be added to the resin. As a crystal nucleus material, NaHP
Phosphorus compounds such as O ₄ , Pb ₃ (PO ₄ ) ₂ and Na ₇ P ₅ O ₁₆ ,
Fine powders of ore such as ribden, rutile, kaolin and asbestos, inorganic compounds such as graphite, molybdenum disulfide, silica and talc, and organic powders such as polyethylene terephthalate are included (corresponding to claim 9).

[Examples] Examples and comparative examples for obtaining a convex lens-shaped molded product of a crystalline resin will be described below.
FIG. 4 is a diagram for explaining a shape of a molded product and a mold structure according to an example of a molding method according to the present invention and a comparative example of a conventional molding method, and FIG. 4A shows a cross-sectional shape of the molded product. FIG. 4 (B) is a cross-sectional view of the mold structure.
0 is a molded product, and the part that has the same function as in FIG.
The same reference numerals as in FIG. 3 are attached. The molded product shown in FIG. 4 is a convex lens having an outer diameter D = 50 mm, a radius of curvature R = 50 mm, a central portion thickness tmax = 15 mm, and an end portion thickness te≈4 mm. The mold shown in FIG. The mirror surface 5 and the mirror surface 6 form a mold cavity 4 having a constant volume. The surface accuracy of the mirror surfaces 5 and 6 corresponding to both spherical surfaces of the convex lens is 0.2 μm over the entire surface. In Comparative Example 1 shown below, the molds 2 and 3 are provided with gate portions (not shown) through which molten resin flows.

COMPARATIVE EXAMPLE 1 Crystalline polypropylene was used as the molding resin, and the molding was carried out by the conventional molding method. FIG. 5 shows the temperature and pressure in the mold cavity in the molding of Comparative Example 1 over time. The figure shows the time (mi
n), and the vertical axis shows pressure (MPa) and temperature (° C). First, a crystalline polypropylene is heated to 230 ° C. to obtain a molten resin, and the molten resin is heated to a temperature of 1 or lower than the melting temperature.
After filling the mold cavity 4 kept at 70 ° C with a resin pressure of 160 MPa and sealing the gate, the resin temperature is cooled to a temperature equal to the mold temperature to a uniform temperature, and while maintaining a uniform temperature, 4 After gradually cooling at a cooling rate of ° C / min, the molded product was taken out at 50 ° C, which is a deflection temperature under load of 60 ° C or less.
The molded product thus obtained had sink marks, was inferior in surface accuracy, and could not be precisely measured.

[Example 1] This is an example of the case where crystalline polypropylene was used as the molding resin and was molded by the molding method according to the present invention. Fig. 6 is a p-v- line of the crystalline resin polypropylene to which Example 1 is applied. FIG. 7 is a diagram showing the temperature and pressure in the mold cavity over time in the molding of Example 1 shown in FIG. 6, where the horizontal axis represents time (min) and the vertical axis represents pressure (MPa). ) And temperature (° C). At a load deflection temperature of polypropylene of 60 ° C., a molding base material having a substantially final shape having a weight such that the resin internal pressure becomes atmospheric pressure in the mold cavity 4 is molded by injection molding, and 1
It was annealed at a temperature of 00 ° C. for 24 hours for sufficient crystallization. This is inserted into a mold cavity 4 having at least one transfer surface, in this case, the transfer surfaces 5 and 6 shown in FIG. 4, and then the mold is clamped, which is 160 ° C. which is a temperature above the deflection temperature under load and below the melting temperature. Up to the transfer surfaces 5 and 6 by using the internal pressure of the resin generated perpendicularly to the transfer surfaces 5 and 6 due to the thermal expansion of the resin and the expansion due to the decrease in the crystallinity (AB in FIG. 6). Path), so that pressure deviation due to temperature distribution during cooling does not occur, the material is slowly cooled at a temperature gradient of -4 ° C / min and taken out at a temperature of 55 ° C below the deflection temperature under load (B- in Fig. 6). A molded product having a highly accurate transfer surface was obtained. The surface accuracy of the obtained molded product is 0.9.
It was as precise as μm.

Example 2 In Example 2, short glass fiber 2 was used.
A molding example of a polyacetal resin containing 5% is shown. First,
A molding base material of a substantially final shape having a temperature of 163 ° C. in the cavity shown in FIG. 4 and having a resin internal pressure of atmospheric pressure is injection-molded and annealed at a temperature of 130 ° C. for 24 hours. To fully crystallize. After inserting this into a mold cavity 4 having at least one transfer surface, the mold is clamped, and heated to a temperature of 175 ° C., which is a temperature above the deflection temperature under load and below the melting temperature, to determine the thermal expansion and crystallinity of the resin. Using the resin internal pressure generated at right angles to the transfer surface due to the expansion due to the drop, it is brought into close contact with the transfer surface, and then slowly cooled so that the pressure distribution due to the temperature distribution during cooling does not occur.
The product was taken out at a temperature of 155 ° C., which was lower than the deflection temperature under load, to obtain a molded product having a highly accurate transfer surface. The surface accuracy of the obtained molded product was as high as 1.5 μm.

[Example 3] Example 3 shows another example of the present molding method when a crystalline resin polypropylene containing 30% by weight of talc is used as a crystal nucleus material. First, at a deflection temperature under load of 110 ° C., a molding base material having a substantially final shape and having a weight such that the resin internal pressure becomes atmospheric pressure in a mold cavity has at least one transfer surface as shown in FIG. It is inserted into the cavity 4 and heated to a temperature of 165 ° C., which is a temperature above the deflection temperature under load and below the melting temperature, to cause thermal expansion of the resin due to temperature rise and expansion due to decrease in crystallinity. After moving and compressing it to make close contact with the transfer surface, cool it slowly and take it out at 105 ° C below the deflection temperature under load so that the pressure distribution due to the temperature distribution during cooling does not occur. A molded product having The surface accuracy of the obtained molded product was as high as 1.3 μm.

[0041]

【The invention's effect】

Effect corresponding to claim 1: A crystallized molding base material of substantially final shape is molded with a constant weight made of a crystalline thermoplastic resin, and the molding base material is formed into a mold cavity having at least one transfer surface. After insertion, the mold is clamped and heated to a temperature above the deflection temperature under load of the thermoplastic resin that constitutes the molding base material and below the melting temperature, and the thermal expansion of the thermoplastic resin under conditions where the mold cavity volume is constant. And, by making use of the internal resin pressure generated in the normal direction of the transfer surface due to the expansion due to the decrease in crystallinity, it is brought into close contact with the transfer surface, then cooled and the molded base material is cooled at a temperature not higher than the deflection temperature under load of the thermoplastic resin. Since it was taken out from the mold cavity to obtain a molded product having the transfer surface, the temperature falls after passing through the temperature region where the crystalline resin is crystallized and the specific volume changes, and the deflection temperature under load is reached. , Resin specific volume Resin pressure due to increased increases, the molded article is in close contact with the transfer surface of the mold cavity, since retrieved by heat deflection temperature below without shrinkage occurs in the crystalline resin, it is possible to obtain a high-precision molded products.

Effect corresponding to claim 2: In the method for producing a plastic molded product according to claim 1, after heating the molding base material to a temperature above the deflection temperature under load of the molding base resin and below the melting temperature. Since the mold cavity volume is reduced to cause compressive deformation, and a constant resin internal pressure is generated, the mold cavity volume is made constant,
When the mold is clamped, the mirror surface piece can be prevented from being deformed by receiving a local pressure, the life of the mold can be extended, and the reliability can be improved.

Effect corresponding to claim 3: In the method for producing a plastic molded article according to claim 1, the heating temperature of the molding base material is set so that the rate of decrease in crystallinity of the molding base material is 50%. In the temperature range below, the decrease rate of the crystallinity is low, so that the resin internal pressure generated in the mold cavity can be small. Therefore, a strong mold is not required, deformation of the mold can be prevented, and the life of the mold can be extended. Further, it becomes easy to take a large number of pieces, and the productivity can be improved.

Effect corresponding to claim 4: In the method for producing a plastic molded article according to claim 1, the weight of the molding base material is set so that the internal pressure of the resin is large when the molding base material is cooled and the deflection temperature under load is passed. Since the pressure is adjusted so as to fall within the range of atmospheric pressure to 10 MPa, it is possible to obtain a highly accurate molded product without sink marks or deformation.

Effect corresponding to claim 5: In the method for producing a plastic molded product according to claim 1, since the molding base material is annealed in advance to increase the crystallinity of the molding base material, Insertion into the cavity can be improved by stabilizing the quality and increasing the density of the base material.

Effect corresponding to claim 6: In the method for producing a plastic molded article according to claim 1, as the crystalline thermoplastic resin, an inorganic filler, a reinforcing material or the like is added to the crystalline thermoplastic resin. Since the filled composite material is used, not only the physical properties of the resin composition such as strength, heat resistance and dimensional accuracy are improved, but also the deflection temperature under load can be increased, making it easier to take out at high temperatures and shortening the molding cycle. can do.

Effect corresponding to claim 7: In the method for manufacturing a plastic molded product according to claim 1, by applying the transfer surface of the mold cavity as a mirror surface to an optical component such as a lens, a mirror or a prism. Since an inexpensive general-purpose material can be used as the molding resin, a low-cost optical component can be obtained.

Effect corresponding to claim 8: In the method of manufacturing a plastic molded product according to claim 1, as a transfer surface of the mold cavity, it is applied to a finely processed component such as a Fresnel lens, a disk, a diffraction grating. Due to
Since inexpensive general-purpose materials can be used for molding resin, low-cost microfabricated parts can be produced.

Effect corresponding to claim 9: In the method for producing a plastic molded article according to claim 1, by adding a crystal nucleating agent for promoting crystallization to the crystalline thermoplastic resin, Since the crystallization can be promoted, the cooling rate can be increased and the molding cycle can be shortened.

[Brief description of drawings]

FIG. 1 is a diagram for explaining an example of a conventional high-precision molding method using a pvT diagram of an amorphous resin polycarbonate.

FIG. 2 is a diagram for explaining an example of a conventional molding method using a pvt diagram of a crystalline resin polypropylene.

FIG. 3 is a view for explaining a mold structure for explaining a second embodiment of the molding method according to the present invention.

FIG. 4 is a diagram for explaining a shape of a molded product and a mold structure according to an example of a molding method according to the present invention and a comparative example of a conventional molding method.

FIG. 5 is a diagram showing a time-dependent temperature / pressure overpass in a mold cavity in Comparative Example 1;

6 is a pvT diagram of the crystalline resin polypropylene to which Example 1 is applied. FIG.

FIG. 7 is a diagram showing a time course of temperature and pressure in a mold cavity in the molding of Example 1 shown in FIG.

[Explanation of symbols]

1, 2 ... Mold, 3 ... Compression piece (mirror surface piece), 4 ... Cavity, 5, 6 ... Mirror surface, 7, 8 ... Heating / cooling plate, 9 ...
Heating / cooling pipe.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Jun Watanabe 1-3-6 Nakamagome, Ota-ku, Tokyo Inside Ricoh Company (72) Inventor Kiyotaka Sawada 1-3-6 Nakamagome, Ota-ku, Tokyo Share Inside Ricoh Company (72) Inventor Hidenobu Kishi 1-3-6 Nakamagome, Ota-ku, Tokyo Inside Ricoh Company

Claims (9)

[Claims] 1. A mold after molding a crystallized molding base material having a substantially final shape with a constant weight made of a crystalline thermoplastic resin, and inserting the molding base material into a mold cavity having at least one transfer surface. Tighten and heat to a temperature above the deflection temperature under load of the thermoplastic resin constituting the molding base material and below the melting temperature, and under the condition that the mold cavity volume is constant, the thermal expansion and crystallization of the thermoplastic resin. Of the molding base material at a temperature equal to or lower than the deflection temperature under load of the thermoplastic resin by using the internal pressure of the resin generated in the normal direction of the transfer surface due to the expansion due to the decrease in temperature A method for producing a plastic molded article, characterized in that the molded article having the transfer surface is obtained. 2. The molding base material is heated to a temperature above the deflection temperature under load of the molding base material resin and below the melting temperature, and then the mold cavity volume is reduced to cause compression deformation and a constant resin internal pressure. 2. The method for producing a plastic molded article according to claim 1, wherein the mold cavity volume is made constant after the occurrence of the above. 3. The plastic molded article according to claim 1, wherein the heating temperature of the molding base material is set to a temperature range in which the reduction rate of the crystallinity of the molding base material due to heating is 50% or less. Manufacturing method. 4. The weight of the forming base material is set such that the internal pressure of the resin when the forming base material is cooled and the deflection temperature under load passes through is from atmospheric pressure to 10 MPa.
The method for producing a plastic molded article according to claim 1, wherein the pressure is adjusted so that the pressure range is a. 5. The method for producing a plastic molded article according to claim 1, wherein the molded base material is annealed in advance to increase the crystallinity of the molded base material. 6. The plastic molded article according to claim 1, wherein the crystalline thermoplastic resin is a composite material in which the crystalline thermoplastic resin is filled with an inorganic filler, a reinforcing material, or the like. Manufacturing method. 7. The method for producing a plastic molded product according to claim 1, wherein the transfer surface of the mold cavity is used as a mirror surface and is applied to an optical component such as a lens, a mirror or a prism. 8. The method for producing a plastic molded product according to claim 1, wherein the transfer surface of the mold cavity is applied to a microfabricated component such as a Fresnel lens, a disc, a diffraction grating or the like. 9. The method for producing a plastic molded article according to claim 1, wherein the crystalline thermoplastic resin is blended with a crystal nucleating agent for promoting crystallization.