JPS6157167B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to injection molded plastic transparent products.

(Prior Art) Generally, in order to produce transparent plastic molded products such as lenses and prisms, a casting method is used in which a liquid monomer is poured into a mold to form a polymer.

According to this method, an isotropic molded product without distortion can be easily obtained. In addition, extrusion molding is used to produce transparent plastic molded products because it can produce molded products that are fairly uniform and isotropic, although not as well as cast molding.

However, with conventional injection molding, it is extremely difficult to obtain a molded product that is uniformly isotropic, and it is not used for molding products that require a high degree of uniform isotropy.

(Problems to be solved by the invention) Despite being extremely efficient as a molding method, the reason why conventional injection molding is not used to mold molded products that require a high degree of uniform isotropy. Generally speaking, in the injection molding method, the gate method is side gate method, pin gate method, direct gate method, fan gate method, or tough gate method, and the molten resin is injected into the mold at an extremely high speed. A strong shearing force acts within the resin, resulting in distortion in the molded product. Even if it appears to be a uniformly transparent molded product at first glance, if it is viewed between orthogonal polarizing plates, it is often observed that strong molecular orientation distortion occurs near the injection gate.

This molecular orientation distortion often not only causes cracks in resin molded products, but also causes molding defects such as so-called jetting, flow marks, silver streaks, weld lines, and sink marks.

Therefore, for a long time, injection molds have been devised to produce molded products with the exact shape as designed and to shorten the molding cycle. It is not enough to receive. Recently, in order to obtain molded products with fewer defects, multi-step control of injection speed, adjustment of the degree of opening of the mold, detection of injection pressure, mold clamping pressure, temperature inside the mold, etc. have been introduced from the injection molding machine side. Although progress is being made in the development of complex mechanisms such as feedback control, the current situation is that they are not satisfactory in terms of uniform isotropy of molded products.

(Means for Solving the Problems) Therefore, the present inventor previously proposed a new injection mold as Japanese Patent Application No. 127215/1984 (Patent No. 1290425), and created a uniform mold without the above-mentioned defects. It was possible to obtain an isotropic injection molded product.

In other words, the features of this mold are as follows.

The first and second gates are located between the runner and the cavity.
In the injection molding mold having a gate, the first gate constitutes a connection part between the runner and the second gate,
Its cross-sectional area is smaller than that of the runner, and the second
The gates are shaped like the shoulders of a coat hanger starting from the first gate, and are gradually expanded so that the space is flat and connected to the cavity. A constricted portion is formed perpendicular to the flow direction of the resin and in the thickness direction of the resin. When injection molded using this mold, a uniformly isotropic molded product is obtained, and the molecular orientation of the resin, which is seen in most conventional injection molded products, is
The occurrence of jetting, silver streaks, flow marks, weld lines, etc. is greatly suppressed, and the occurrence of sink marks is prevented. For example, in molded products made of transparent resins such as polycarbonate, AS resin, polystyrene, or methacrylic resin, the direction of molecular orientation due to birefringence cannot be seen even when viewed between two orthogonal polarizing plates. Therefore, the above mold can be used for injection molding of various meter covers, stereo dust covers, cover glasses for watches, etc., as well as glasses, lenses for other optical machines, prisms, etc. This is an extremely excellent mold.

However, in the case of optical lenses, etc., which require extremely high surface conditions, it is not sufficient to reduce molecular orientation distortion and the resulting molding defects.
A high degree of surface finish accuracy (low surface roughness and high surface precision) is required. As a result of intensive research into this point, the present inventor found that this can be achieved by improving the cavity portion. That is, the molded product of the present invention is obtained by super mirror polishing the inner surface of the mold shown in the above-mentioned Japanese Patent Application No. 52-127215, especially the molding cavity surface, and the surface of the molded product is Roughness is 0.2μ or less and surface accuracy is λ/ by Newton fringe test.
2 (λ = 583 mμ or λ = 546.1 mμ) or less, or an injection molded plastic transparent product with a surface precision of 30 or less fringes when observed over the entire surface to be measured, and with reduced molecular orientation distortion. . Here,
The above-mentioned surface roughness can be measured by a method similar to ^JISB0651-55 “Surface roughness measuring device (stylus type)” or ^JISB0653-57 “Surface roughness measuring device (light cutting type),” or
The values were measured according to "Newton defect" defined in DIN ^-58 4.21, and the 583 mμ is the wavelength of the D-line of a sodium lamp, and 546.1 mμ is the wavelength of the E-line of a mercury lamp.

Furthermore, the above-mentioned molded products with reduced molecular orientation strain are as follows.

In other words, methods for measuring molecular orientation strain include measuring mechanical strength, measuring by generating solvent cracks (see ASTM1693), and estimating by measuring surface hardness (for example, by measuring mechanical strength of plastics). Characteristics/Published by Nikkan Kogyo Shimbun/Written by Shozaburo Yamaguchi
(See page 80) However, the photoelastic method using a polarizing plate is used to measure molecular orientation strain.

If molecular orientation distortion exists in transparent plastic, birefringence occurs, and the greater the molecular orientation distortion, the greater the birefringence.

Therefore, a transparent plastic molded product is placed between orthogonal polarizing plates (for example, general polarizing sheet "Varilite" manufactured by Sanritsu Electric Co., Ltd.), and scattered light is applied from the opposite side to be observed. When a strain is present, a striped pattern is observed along the direction of the strain. In this case, it is easier to observe if the entire device is placed in a dark box.

In general, in injection molded products, the molecular orientation is strongest near the gate, so when observed using the method described above, even after the gate is removed from an injection molded product made by the general gate method, the molecular orientation is the strongest near the gate.
You can tell if the gate was on.

The molded product with reduced molecular orientation strain as used in the present invention refers to one in which no striped pattern occurs to the extent that the position of the gate cannot be seen even when observed by the method described above. Generally, birefringence is considered to be a sensitive indicator of molecular orientation. (e.g. LENIELSEN.MECHANICAL,
PROPERTIES OF POLYMERS.―REINHOLD
PUBLISHINC CORP N.Y1962) Now, if the refractive index in the direction parallel to the molecular chain is n‖, and the refractive index in the direction perpendicular to this is n⊥, the birefringence △n is expressed as △n=n‖−n⊥.

A molded product with reduced molecular orientation strain as used in the present invention refers to a molded product with the gate removed that exhibits a value such that △n×10 ⁴ <10 regardless of the measurement location. .

Lenses, prisms, etc. made by injection molding are △n
If ×10 ⁴ <10, it can be seen that there is no practical problem when used in optical machines or optical measuring instruments, and the molded product according to the present invention can be made with △n×10 ⁴ <10. . For conventional injection molded products, △n×10 ⁴ >
10, and in the case of strongly oriented ones, it reaches as high as Δn×10 ⁴ =100, and such molded products cannot be used for optical instruments at all.

(Example) Hereinafter, the present invention will be described based on specific examples.

First, for convenience of explanation, we will explain the mold shown in Japanese Patent Application No. 52-127215 (Patent No. 1290425).
The details are omitted.

Figure 1 is a plan view of an example of the mold;
The figure shows a sectional view taken along the line AA' in FIG. 1
The molded part is a cavity, and 2 is a runner. Molten resin normally passes from the nozzle at the tip of the injection molding machine, passes through a sprue runner, and from the runner enters the molding cavity through a gate.

The mold as described above is provided with first and second gates between the molding cavity 1 and the runner 2. 3 is its first gate, 4 is its second gate
It is a gate.

The first gate 3 constitutes a connecting part between the runner 2 and the second gate 4, and the second gate 4 is formed from the first gate 3 in a shape with a coat hanger-shaped shoulder, and is connected to the molded part cavity 1. has been done.

As can be seen from FIGS. 1 and 2, this second gate 4 has a considerably long gate land, and the gate width is wide and the thickness is thin at the part where it is connected to the molded part cavity 1. The front part following the first gate 3 forms a smooth streamlined shape like the shoulder of a coat hanger.

The three-dimensional situation of the gate section as described above will be explained in more detail using Figure 3 A, B, and C as examples.
3A is a plan view, and FIGS. 3B and 3C are elevational cross-sectional views taken along lines a-a', bb', c-c', and d-d' in FIG. 3A, As can be seen from these drawings, the first gate side is deep (thicker), and the vicinity of the cavity (drawn portion side) becomes shallower (thinner).

Further, the second gate is provided with a constricted portion 5 in the middle thereof, and a waste cavity 7 is provided at the rear of the molding portion cavity.

The other part 6 is a melt stock provided in the immediate vicinity of the first gate of the runner 2, and is a resin reservoir that is deeper than the depth of the runner.

Now, the cross section of the melted and kneaded resin running through the runner is reduced at the first gate 3, so the resin pressure is increased and shearing force is generated in the resin flow, causing the resin to be reheated and re-kneaded. will be carried out.

In the case of a normal mold, the resin from the first gate 3 to the molding cavity 1 travels straight, causing strong molecular orientation in this part, but when the second gate 4 is applied, the resin is expanded into a coat hanger shape. Because
The resin flow is smoothly expanded along the streamlines of the shoulder, spreads over the entire body, and advances toward the molding section cavity 1.

Since the gate land of this second gate 4 is quite long, the resin flow becomes a completely laminar flow by the time it reaches the entrance of the molding cavity 1, and the resin flow uniformly flows straight from the front into the molding cavity 1, forming a laminar flow. Incoming.

Therefore, since the flow enters the molding part cavity 1 in a laminar state from the beginning at the slowest speed that is uniform in each part, it enters the molding part cavity 1 while maintaining a so-called kneaded, isotropic, uniform state. The molded product molded within the cavity 1 has reduced molecular orientation strain.

Further, residual resin from the previous injection accumulates at the tip of the cylinder of the injection molding machine, that is, near the nozzle.

Normally, the temperature of the resin in this area has decreased and it is called a cold slug, but the melted and kneaded resin that comes after this resin also loses heat while running on the sprue and runner, making it fluid. Since this decreases, a more uniform and isotropic molded product can be obtained by storing this in the melt stock 6 and preventing it from entering the molding cavity.

Furthermore, after injection into the molding machine, the temperature of the resin in the melt stock 6 decreases faster than that in the cavity, so a strong contraction pressure is generated, and this pressure is applied to the first gate 2 due to the high pressure on the molding machine side.
Since it hangs on the side, it prevents the backflow of resin from inside the cavity, or in other words, prevents the occurrence of sink marks.

The sacrificial cavity 7 is a cavity for storing the resin that has passed through the gate and the inside of the molding part cavity and has been deprived of heat, so that the resin in the molding part cavity becomes more uniform and isotropic. Become.

After injection molding, the temperature of the resin inside the sacrificial cavity 7 quickly decreases, shrinkage occurs, and the shrinkage pressure becomes large.The thin part at the entrance of the sacrificial cavity solidifies and seals while the pressure remains high. We will put even more effort into preventing sink marks.

As described above, in the mold described above, the kneaded molten resin at the same temperature is filled in a laminar flow into the cavity of the molding part, so that a uniformly isotropic molded product can be obtained.

The present invention provides a molded product having a surface roughness of 0.2 μ or less and a surface accuracy of λ/2 (λ = 583 m or λ
= 546.1 mμ) or a surface precision of 30 or less fringes when observed over the entire surface to be measured. In the case of alloy steel, double vacuum melting steel is suitable as the material for the mold that can be polished to a super mirror finish to achieve this purpose. Commercially available products of this type include YAG manufactured by Hitachi Metals, Ltd.
There is MASS-11 manufactured by Daido Special Steel Co., Ltd., and vacuum melting steels such as Starback manufactured by West Germany's Atsusub Co., Ltd. and HPM-1 manufactured by Hitachi Metals Co., Ltd. are available.

Also, copper, gold, etc. are suitable as pure metals.

However, copper and gold have the disadvantage that they are easily scratched during handling of the mold.

Furthermore, as the non-metal, Pyrex glass manufactured by Corning Glass of America, Pyroceram, Neuceramics, etc. can be used depending on the case.

Among the above, alloy steels and pure metals are polished with diamond compound.

Additionally, alloy steel requires aging treatment during polishing.

Pyrex, Pyroceram, and Neuceramics are finished to a predetermined surface precision using the "sand-sliding method," which is known as a glass polishing method.

As mentioned above, the inner surface of the molding cavity was polished to a super mirror finish to a predetermined precision in Japanese Patent Application No. 52-127215 (Patent No.
1290425), and the resin was polymethyl methacrylate, so-called MMA.
By injection molding resin, polystyrene, AS resin, polycarbonate, polysulfone, polymethylbentene, etc., it is possible to obtain injection molded products with surface precision equivalent to that of the mold and with little molecular orientation distortion.

Generally, ultra-mirror polishing work after molding a resin molded product is difficult and expensive, but according to the present invention, only the mold can be polished to an ultra-mirror finish, and the surface accuracy is almost the same as that of the mold. It is possible to repeatedly obtain molded articles with

Specific examples of the molded product of the present invention will be described below.

Example 1 Figures 4 and 5 show a plan view and a cross-sectional view of a flat lens for sunglasses with a gate, and the diameter is l.
is 78 mm, and the thickness S is 2 mm.
YAG350 was used as the mold material, and 480℃ was used.
The aging process was carried out. Diamond compound is used for internal polishing of the cavity part of the mold‖
14000 to a surface precision of 10 Newton fringes can be observed, and injection molding using polymethyl methacrylate with a N200 molding machine manufactured by Japan Steel Works, Ltd. produced 28 Newton fringes. The surface accuracy that the book can be observed and △n×10 ⁴ are
A molded article with a birefringence of 2.5 or less was obtained.

Example 2 Figure 6 shows a cross-sectional view of an aspherical loupe for inspecting photographic negative film, which has an aspherical surface and a spherical back surface, and has a diameter l of 67 mm and a thickness S of 8 mm. , is a molded product with a thickness S ₁ of 2 mm at both ends. Starbuck was used as the mold material and quenched at 800°C. The inner surface of the cavity part of the mold was polished with diamond compound #14000, and the spherical part was polished to an ultra-mirror surface so that 10 Newton fringes could be observed.
When injection molding was performed using polymethyl methacrylate using a molding machine manufactured by FS150, a molded product was obtained with a surface precision in which 30 Newton fringes could be observed and a birefringence of △n×10 ⁴ of 2.5 or less.

Example 3 Figure 7 shows a slope view of an experimental prism, in which the depth _l1 is 25 mm, the height h is 3 mm, and the slope length is
It is a formed product with l ₂ of 20 mm and roof apex angle α of 60°. Copper is used as the mold material for the above molded products,
The inner surface of the cavity part of the mold was polished with diamond compound #14000 to the extent that three Newton fringes could be observed.
Polymethyl methacrylate was injection molded using a N150/75 molding machine manufactured by Sumitomo Heavy Industries, Ltd., which uses the Cycap method, and the surface accuracy was such that eight Newtonian fringes could be observed, and the compound size of △n× ¹⁰⁴ was 8 or less. A molded article with refraction was obtained.

Embodiment 4 Figures 8 and 9 show a plan view of a meter cover with a gate part and a front view of the meter cover alone, and the vertical length l ₁ is 70.0 mm and the horizontal length l ₂ is 50.0 mm. ,
The height is h17.0mm. This one is made by Japan Steel Works
This molded product was also made using a molding machine called N70B11.

HPM-1 was used as the mold material and quenched at 780℃. The inner surface of the cavity part of the mold is polished using diamond compound #8000 to achieve surface roughness.
After finishing to 0.2μ and injection molding with polymethyl methacrylate, the surface roughness was 0.12.
A molded article of μ was obtained.

Example 5 Figure 10 shows a cross-sectional view of an automobile meter cover, in which the diameter l is 110 mm, the thickness S is 1.5 mm,
It is a molded product with a radius of curvature R of 240 mm. YAG250 was used as the mold material, and aging treatment was performed at 480°C for 3 hours. The inner surface of the cavity part of the mold was polished with diamond compound #14000 to the extent that 12 Newton fringes could be observed, and then injection molded using polycarbonate using an SN350 molding machine manufactured by Shinshi Tekkosho Co., Ltd. As a result, the surface accuracy was such that 22 Newtonian fringes could be observed.
A molded article with a birefringence of n×10 ⁴ of 8.5 or less was obtained.

Example 6 Figures 11 and 12 show a plan view and a cross-sectional view of a lens for reading glasses with a gate, which is a circle with a diameter l of 78 mm and an inner and outer radius of curvature R ₁ and R ₂ of 120 mm, respectively.
It is a molded product with a length of 117.8 mm and a thickness S of 2.7 mm. YAG300 was used as the mold material for the above-mentioned molded product, and aging treatment was performed at 480°C for 4 hours. The inner surface of the cavity part of the mold was polished with diamond compound #14000, and the surface accuracy was λ/4 in the Newton fringe test. When injection molding was performed, △n×10 ⁴ was
A molded product with a birefringence of 5.7 or less and a surface accuracy of λ/2 in the Newton fringe test was obtained.

(Effects of the Invention) As understood from the description of the embodiments above, the present invention provides an injection molding die having a first gate and a second gate between a runner and a cavity. The gate constitutes a connection between the runner and the second gate, and its cross-sectional area is smaller than the cross-sectional area of the runner, and the second gate is shaped like the shoulder of a coat hanger from the first gate. Therefore, the space is gradually expanded, and the space is flat and continuous with the cavity, and a constricted part is formed in the middle thereof at right angles to the flow direction of the resin and in the thickness direction of the resin. , the molding cavity surface is molded from an injection molding die that has been polished to an ultra-mirror surface, the surface roughness is 0.2μ or less, and the surface accuracy is λ/2 in the Newton fringe test.
(λ = 583 mmμ or λ = 546.1 mmμ) or less, or for injection molded plastic transparent products with a surface precision of 30 or less fringe when observed over the entire surface to be measured, and with reduced molecular orientation strain. It has various features as described below.

That is, by making the surface precision of the injection molded product as described above, (1) transparency is improved because there is no scattered reflected light on the surface of the molded product;

(2) Uniform thickness and surface smoothness can be imparted to the coating layer of surface hardening coating in post-processing of molded products.

(3) Since there is little flow resistance of the resin within the mold, molecular orientation distortion is further reduced, resulting in a molded product with high density filling.

(4) The extremely smooth surface makes it difficult to get scratches.

(5) When the molded product is used as an optical lens such as a camera lens, telescope lens, microscope lens, television camera lens, optical measuring instrument lens, or television projector lens, the surface roughness specified in the present invention or If the surface accuracy is high, it can be used after surface hardening coating, vacuum deposition coating, or as a molded product itself.

There are other effects.

Furthermore, by reducing molecular orientation strain, (1) the physical properties of the molded product itself, such as mechanical strength, solvent crack resistance, and heat resistance, are improved;

(2) It is possible to prevent cracks from occurring during post-processing such as surface hardening coating, dyeing, and adhesion.

(3) When manufacturing optical lenses and prisms,
Since the surface precision is increased and there is no anisotropy, the accuracy of the focal length and the accuracy of the reflected image are improved, and polarization interference is reduced. .

(4) In the molded article of the present invention, the occurrence of striae, bubbles, etc. in glass can be almost completely eliminated.

(5) It has the effect of preventing molded products from deteriorating over time.

In addition to the above-mentioned effects, the molded product of the present invention also has the following effects.

(1) The molded product according to the present invention contains very little foreign matter such as what is often referred to as black dust and white dust.
Therefore, it is particularly suitable for optical lenses and prisms.

In other words, the black dust referred to here is mainly small pieces of carbonized resin, and the reason why this contamination does not occur is that by using the mold shown in the present invention, the resin flows smoothly and resin stagnation occurs. This is thought to be because the resin is difficult to carbonize. In addition, since the molded product is made of resin that is homogeneous and densely filled,
There is no generation of white dust caused by air bubbles.

(2) In molding using a normal side gate or tab gate method, the reduction in molecular orientation strain is not as low as the reduction in molecular orientation strain according to the present invention.

Therefore, even if the mold is polished with high precision, products molded using general molds such as the tab gate method or the fan gate method may have variations in wall thickness, variations in dimensional accuracy, etc. Strong orientation distortion and high precision, such as optical lenses,
Prisms etc. are difficult to draw.

However, according to the present invention, extremely high quality lenses and prisms can be obtained.

The present invention has various effects as described above, and is characterized in that the molded product can be used in a wide range of applications as described below.

(1) Optical lenses and prisms (2) Lenses, prisms, and scattering plates as electronic industry components (3) Axle meter covers and light guiding prisms (4) Nameplates for home appliances (audio, televisions, etc.)
Meter cover prism lenses (5) Meter covers and lenses for industrial electrical equipment (6) Other transparent plastic products for daily necessities

[Brief explanation of the drawing]

FIG. 1 is a plan view showing an example of a mold for molding the product of the present invention. FIG. 2 is an elevational sectional view taken along line A-A' in FIG. Figure 3 is a diagram showing the three-dimensional situation of the coat hanger type gate part of the same mold as above, where A is a plan view, B and C are lines a-a', b-b', c-c' of A,
Elevated sectional view along d-d′. 4 and 5 are a plan view and a cross-sectional view of a flat lens for sunglasses. FIG. 6 is a cross-sectional view of an aspherical loupe for inspecting photographic negative film. Figure 7 is a perspective view of the experimental prism. Figures 8 and 9 are a plan view of the meter cover with gate part and a front view of the meter cover alone. FIG. 10 is a sectional view of an automobile meter cover. 11 and 12 are a plan view and a cross-sectional view of a lens for reading glasses with a gate portion. 1...Molding section cavity, 2...Runner, 3...
...first gate, 4...second gate, 5...throttle section, 6...melt stock, 7...disposable cavity.

Claims (1)

[Claims] 1 An injection mold having a first gate and a second gate between a runner and a cavity, the mold having a first gate and a second gate.
The gate constitutes a connection between the runner and the second gate, and its cross-sectional area is smaller than the cross-sectional area of the runner,
The second gate is shaped like the shoulder of a coat hanger from the first gate, so that it gradually expands, and its space is flat and continuous with the cavity. A constriction part is formed perpendicular to the flow direction of the resin and in the thickness direction of the resin, and the molding cavity surface is ultra-mirror polished.The surface roughness is 0.2. μ or less and the surface accuracy in the Newton fringe test is λ/2 (λ = 583
An injection-molded plastic transparent product characterized by having a surface accuracy of 30 or less fringes when observed over the entire surface to be measured, and reduced molecular orientation strain.