JPH03505185A - Plastic molding method and its mold - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention] name of invention Plastic molding method and its mold Technical field The present invention relates to an improved method of molding plastics and a mold for the method. present invention is for molding plastic optical molded products such as optical discs and lenses. injection molding of plastics or plastics for producing e.g. honograph records. Particularly suitable for compression molding of sticks.

Background technology Almost all molding operations involve applying pressure and heat to deform the plastic. into the desired shape. The shape is then fixed by cooling. thermoplastic material mold It must be cooled below its melting point or glass transition temperature before being removed from the container. heating , deformation under pressure and cooling under pressure are required in this order.

For example, injection molding is used to produce molded articles from amorphous or crystalline thermoplastics. It is known to use the shape method. In this method, thermoplastic melting Molding in which the body passes through a small opening called a gate to define the shape of the finished molded product pushed out into space. The mold is much cooler than the plastic melt.

When the plastic melt first contacts the mold surface, thin counterfeits are attracted by the sticky stick. Regardless of the molecular orientation of the solidifying melt that is aroused, the outer solidified region The relatively stress-free intermediate layer allows molecules in the melt to contact the outer solidified region and Formed during solidification. Large flow shear stresses orient these molecules in the flow direction let This intermediate layer is highly oriented and subjected to large shear stresses .

The outer and middle layers together form a region called the skin. I like this The insulating region thermally insulates the central core of the flowing plastic melt. core stays hotter than the skin for a longer time, giving the molecules in the core region time to reorient. available. As a result, the core region has less flow-induced orientation and less shear stress. The only possible orientations and layers can be seen in FIGS. 1-3. In Figure 1, A rectangular molding space 1 is filled with molten plastic 2 through a gate 3.

The hydrodynamic skin-core structure within the molding space 1 during filling is shown in FIG. Skip the plastic melt on the top and bottom surfaces of the molding space. The tube 4 thermally cools the central core 5 of the flowing plastic melt during mold filling. Insulate. As shown in Figure 3, the skin has an outer layer identified as zone I and a highly oriented and highly shear-enabled, formed by an intermediate layer identified as a zone ■ be done. The core band is identified as band ■ in FIG. Figures 1.2 and 3 beams, R, Schmidt, RkD, G, E, 5chenectady, New York. “The Interrelationship of Flows, Structurers, and Anonymous” This is a drawing from de Blovaties in injection molding. .

Crystalline polymers also exhibit flow-induced orientation effects. Plastic cold mold table In contact with the surface, the thin oriented layer solidifies to form small crystalline regions of do. The crystals thus formed act as nucleators, and they Since it is oriented, the crystals grown from it are also oriented. middle and center The amorphous area develops in much the same way as described for amorphous plastics.

Under typical injection molding conditions, the flow rate varies significantly in the molding space, so the skin thickness This results in fluctuations. The mechanical and physical properties of the molded part are depending on the thickness distribution and the degree of orientation and crystallinity at various positions of the molded part. change.

During flow, applying high pressure to the core region pushes out the core material, causing shear in the intermediate layer. Shear forces become high and molecular orientation occurs.

When the molding space is completely filled, the pressure increases rapidly. The molded product may continue to cool down. As the thickness of the solidified layer increases, the high pressure is maintained. The volume of the molded product is determined by the volume of the molded product. It decreases as the pressure increases, and depending on the injection pressure, the gate closes or the pressure is removed. Fill with more plastic until the After closing the gate, the solidified layer becomes thicker. The molded part continues to cool until it is hard enough to remove the molded part. molding As the item cools, the pressure decreases and the specific volume decreases. The outer coagulation layer is This known method maintains the dimensions of the molded part while the core area continues to cool and shrink. Additional residual stresses are generated in the injection molding process.

Several other problems are also inherent in this known injection molding process. molding At various locations on the article there will be parts with varying wall thicknesses. excessive Filling occurs in areas of the part that are filled too early and before other spaces. Occurs within the molding space of a filled family mold or multi-space mold. overfilling is also a game where hot plastic is forced together with relatively cool plastic. Occurs in the area near the root. Overfilled regions are highly stressed and have low strength This causes distortion, distortion, and the molded product gets caught in the mold. To reduce these problems, Common methods include changing the part thickness, repositioning the gate, and changing the injection pressure distribution. This includes measuring and reducing pressure during filling.

Density differences, molecular orientation, thermal gradients, and crystallinity of plastic molded products cause distortions. . Furthermore, a weld line is formed at the location where the two melt paths meet. Before the converging melt If there is a large enough temperature difference at the ends, a weak weld line will result. minimize this problem The conventional method for including. It is also possible to redesign the molded part to reposition the weld line.

Birefringence refers to the property of having two different refractive indices, which makes it possible to divide light rays passing through a material into two. Separates into two diverging beams. The orientation of molecules and residual stress within the plastic Causes birefringence in stick molded products. Orientation stress is plotted with respect to birefringence. , a linear relationship was found. The greater the degree of orientation, the greater the birefringence. . with flow-induced orientational stresses and large temperature gradients as in known injection molding processes. Both the stress caused by cooling through the glass transition temperature, which is Ru. Birefringence affects plastic optical moldings such as lenses and optical discs. This is a big problem.

Osawa George, Tsuge Morio, Takatsu Akimitsu, Okuneshi Toyoji, Ta Junji Nariki and Shinichi Mikami discuss their literature “Computer Optical Memo "Thermosetting resin base material for Lee disc", November 15, 1986, Applied Optics (A In Volume 25, No. 22 of ppliedOptics, he states: When an optical disc base material is used as one unit of computer memory, refraction is is one of the most important properties of This property is due to the carrier-to-noise ratio ( This is because it is directly related to CNR) and bit error ratio. In particular, as a signal Magneto-optical disks using delicate Kerr rotation angles are smaller than 5 nm. A small (double bath) birefringence is required, and a near zero birefringence is targeted. Ru.

The birefringence index is calculated using the following formula [Brewster formula] Ru: In the above formula, (δγ)/2π = birefringence (single pass) (nm); δ = deceleration degree; λ = wavelength of light (nm); C = photoelastic modulus (cm”/dym); t = base material (thickness nm); and (σ, −σ,) = principal stress difference (dyn/cm”) Ru.

The principal stress difference defined here is (1) uneven residual molding pressure and (2) molding shrinkage. caused by non-uniformity of Generally, the higher the molding pressure, and The greater the molding shrinkage, the more uneven the residual stress becomes. This means that the principal stress The result is a large difference. Therefore, to minimize the birefringence, the residual stress must be minimized. It is necessary to ” Achieving precise tolerances on crystalline plastic molded parts formed by known injection molding methods. It is difficult to achieve this. This is because crystallization causes additional shrinkage and typically This is because mold-specific molding conditions cause large variations in crystallinity throughout the molded product. Conclusion Crystal growth allows molecular segments to come close and line up with each other. , requiring time and large molecular mobility. The slower the cooling, especially the polymer The slower the cooling from the melting point to the glass transition temperature, the greater the degree of crystallization. It becomes. Crystallization also occurs more easily under low pressure. This is because molecular mobility increases Because it does. As previously discussed, in known injection molding processes, the skin area and the core region, which cool at very different rates as they pass from the melting point to the glass transition temperature. This causes variations in crystallization.

In the literature (e.g. “Plastic Object Handbook” 2nd edition, p. 34) See Nis, Nis, Preset Lens Co., Cincinnati, Ohio. ), all molded obtik moldings minimize molding irregularities. It is generally accepted that cooling must occur at the same rate during the cooling cycle. recognized. To this end, the text generally states that in order to control the cooling rate, It states that the mold is made with heating and cooling conduits. With such complexity Localized cooling and heating can be expensive, operator dependent, and not always effective. It can't be.

Thick-walled molded parts cannot produce pores under typical molding conditions using known injection molding methods. It is very difficult to mold without any lull. For example, Amoco Chemical's To About rlon [poly(amide-imide)] Bulletin TAT- 35 generally has a molded part thickness range of 0.03 to 0.5 inches, with a thickness of 0.62 5 inches is possible with special resin grades, and provides design guidance. Ru. Walls and gates should be made of plastic, as thick-walled moldings solidify very quickly. The metal cannot enter the molding space sufficiently to compensate for shrinkage. for this problem One known solution is to slowly introduce the polymer into the hot mold until enough Preventing the plastic from solidifying until the tick is injected to compensate for the shrinkage It is. However, such solutions require additional operations before starting molding and This is disadvantageous as it adds cost and reduces the efficiency of the molding operation.

Disclosure of invention The object of the present invention is to avoid the above-mentioned problems of known plastic molding methods. An improved method for forming molded products by molding plastic materials and a mold for the same are proposed. It is to provide. More specifically, an object of the present invention is to solve the above-mentioned skin layer formation. minimize, eliminate, or suppress and while the part solidifies in the mold. Improved injection molding process and injection method that reduces temperature gradients across the molded part The purpose is to provide molding molds.

Another object of the present invention is to minimize flow-induced molecular orientation and low injection pressure, single mold, family mold and Formation of higher quality and more accurate parts from molds and multi-cavity molds, better control of crystallization , minimal birefringence, strong weld lines, more uniform plastic moldings, plastic moldings Improved injection molding resulting in smaller part deviations and thicker molded parts without pores. An object of the present invention is to provide an injection molding method and an injection mold for the same.

These and other purposes are used to mold plastic materials to form molded articles. , is achieved by the following method of the invention.

That is, Prepare a mold having at least one molding space of the shape of the molded product to be molded, and Introducing molten plastic into the molding space and reducing the amount of molten plastic in the molding space. The molded product is cooled until it partially solidifies, and the molded product is removed from the molding space. , in the molding process of plastics to form molded articles: a substantial part of the nucleic acid shaped space surface. during the molding of the molded article to a temperature equal to or higher than the solidification temperature of the molten plastic. According to the present invention, the molding method further comprises a step of the temperature of at least a substantial portion of the molten plastic for a significant period of time during molding. during which, in the case of injection molding, the molding space is maintained near or above the solidification temperature of Fill the molten plastic and fill the center of the molten plastic in the molding space. Cooling from a temperature above the solidification temperature to the solidification temperature, thereby causing the solidification plastic of the molded article to of the forming space surface to reduce orientational stresses induced by flow and temperature gradients in the stick. The plastic is removed after a substantial portion reaches a temperature above the solidification temperature of the molten plastic. As the outer surface of the stick begins to solidify, it will touch the outer surface of the plastic in the body molding space. The temperature difference with the center does not exceed 0.5°F per 0.001 inch of molded part thickness. (62.5°F for molded 8 0.125 inch thick) .

A distinctive feature of the invention is that at least a substantial portion of the molding space surface is melted during molding. Heat is introduced into the molding space to raise the temperature above the solidification temperature of the plastic. This is obtained from the heat of the melted plastic. This is the molding space or its Achieved by insulating the molding space by providing a layer of material with low thermal diffusivity nearby. In one form of the invention, the insulation layer is in contact with the molten plastic during molding. It is located beneath another layer of material that forms the contacting mold space surface. Another form of the invention , the layer of insulating material is itself a component that comes into contact with the molten plastic during molding. forming at least a substantial portion of the shape space surface. The molding space can be covered or covered as necessary. plated to prevent welding or other interaction between the molten plastic and the insulation. May be prevented. Preferably, the molding space that comes into contact with the molten plastic during molding All surfaces are insulated to ensure temperatures above the solidification temperature of molten plastic during plastic molding. The temperature of the entire surface is increased.

In the process of injection molding a plastic material according to the present invention, the plastic material When the plastic first contacts the mold surface, the surface temperature of the molding space increases as the molten plastic solidifies. The layer of plastic in contact with the molding space surface is much lower than the curing temperature. solidify. The solidified layer is such that at least a substantial portion of the mold surface is coated according to the invention. The point in the molding process at which the temperature is above the solidification temperature of the molten plastic Then, remelt it.

The injection mold of the present invention according to the disclosed embodiment includes a pair of half molds, each half having a formed of a metal insert such that the metal insert acts as a heat sink. and means for cooling the insert. A layer of insulation is applied to each half adjacent to the molding space. Applied throughout the metal insert. The layer of insulation itself is made of melted plastic during molding. or a layer of insulating material under the metal insert. the insert can be located in the shape of the other material layer forming the molding space surface. You can take it.

The thermal diffusivity and temperature resistance of the intermediate material in the mold between the metal insert and the molding space are The temperature of the surface of the molding space is controlled from the molten plastic injected into the molding space during the molding process. Storing enough heat to raise the temperature above the solidification temperature of the plastic to be tried. Select so that you can. This intermediate layer can be used as a heat insulating layer alone or in combination with a heat insulating layer. It can be formed in combination with an insert forming a surface. The insulation layer is formed by the mold groove. In the disclosed embodiment of the present invention, metal inserts and The outside perimeter of the heatsink and heatsink should also be insulated to control heat flow from the molding space and plastic material that securely molds the molding space surface adjacent to the outer edge of the molding space. Raise the temperature to above the solidification temperature of the material. Injection molds also have multiple molding spaces. and each molding space is insulated for molding according to the injection molding method of the present invention. You can also.

The injection molding method of the present invention forms optical molded articles such as optical discs or lenses. It is particularly applicable to molding plastic materials for always have high quality optical components can be manufactured.

The method and mold of the present invention can also be applied to compression molding methods for producing molded products from plastics. Applicable. In this method, the molding material is heated and placed between two mold halves. It will be done. The mold halves are then pressed together to cause the material to flow into the desired shape. Book According to the invention, heat from the material being molded increases the temperature of the split mold surface over a long period of time. Raise the temperature above the stick solidification temperature. This is different from the conventional compression molding method. Eliminates the need to first heat and then cool the sea urchin mold. Such compression molding method is Producing high-quality phonograph records from thermoplastics such as polyvinyl chloride It is useful for

Other objects, features and advantages of the invention set forth three embodiments of the invention by way of illustration. It will become clearer from the following description in conjunction with the accompanying drawings.

Brief description of the drawing Figure 1 shows the injection of molten plastic into a rectangular molding space by a known injection molding method. Fig. 2 is a schematic diagram of filling dynamics for flow; FIG. 3 is a cross-sectional view of the compact, illustrating the hydrodynamic skin-core structure; FIG. is a cross-sectional view of a compact similar to illustrating morphological bands and band formation; FIG. 4 shows an injection mold according to the first aspect of the invention for manufacturing an optical disc. is a cross-sectional view of; FIG. 5 is a cross-sectional view of an injection mold according to a second aspect of the invention; FIG. 6 is a cross-sectional view of an injection mold according to a third embodiment for manufacturing a double-convex lens; Figure 7 shows a sample of crystalline polyethylene plastic injection molded in a conventional metal mold. Illustrating the results of computer thermal analysis of temperature, the temperature distribution is shown on the outer surface of the plastic. The point at which the plastic melt is introduced into the molding space is defined as 0 toward its center line. ゜0 seconds, then 0.05 seconds, 2.32 seconds, 8.82 seconds and 12.82 seconds FIG. 8 is a similar view to FIG. 7, and shows the injection mold of the present invention. Thermal analysis when the molding space surface was raised above the assimilation temperature of polyethylene using indicates; Figure 9 shows the center and surface of polyethylene when using the mold of the present invention, and shows the temperature change on the mold surface as a function of time; FIG. 10 shows the mold cavity of the mold of the present invention when the outer surface of the plastic is beginning to solidify. The outer surface of the plastic and the inner Shows the temperature difference between the core; FIG. 11 shows the two types of molding space lining and insulation material in the mold according to the invention. The mold surface temperature for different combinations is determined by introducing molten plastic into the molding space. It is shown as a function of time since; Figure 12 shows an optical fiber formed by molding polycarbonate plastic according to a known method. When forming a disc, the temperature of the plastic in the molding space of a conventional metal mold is Figure 13 shows the center and surface of the polycarbonate of Figure 12 and the gold Illustrating the temperature change as a function of time on the surface of a metal mold; FIG. 14 is the same as FIG. 13 when an optical disc is injection molded according to the present invention. The following graph is shown below.

FIG. 15 again shows the mold shown in FIG. 16, but in accordance with the present invention. This shows the dimensions of the mold components for manufacturing heavy convex lenses; Figures 16A and 16B show that the double convex lens is in an all-metal mold (Figure 16A) and The constant temperature line (equal crosstalk) when solidification begins in the mold according to the present invention (Figure 16B) and Figures 17A and 17B show that the lens is almost completely solidified in these figures. Similar to FIGS. 16A and 16B except for the point in time.

BEST MODE FOR CARRYING OUT THE INVENTION Referring to the drawings, an injection mold 6 according to a first aspect of the invention is shown in FIG. There is. Mold 6 includes a pair of mold halves 7 and 8, each mold half having a metal insert 9 and 10 configurations of mold heat sinks, the inserts 9 and 10 each having cooling grooves 11 and 10. and 12 are provided. When molten plastic is injected into a mold, heat is released from the mold. A cooling liquid is flowed through grooves 11 and 12 to remove the . Shown in Figure 4 When the mold halves 7 and 8 are placed adjacent to each other as shown in FIG. A molding space 13 for the plastic is defined. Thermal insulation layer or insert 1 according to the invention 4 and 15 are located on the respective surfaces of metal inserts 9 and 10. melted plastic Metals and glass that give plastics the desired hardness, abrasion resistance, chemical resistance and heat resistance. Surface inserts or layers 16 and 17 of glass or other material respectively provide thermal insulation. placed facing the sexual inserts 14 and 15 and inside them as shown in FIG. The side surfaces define the surface of the molding space. These surface layers also protect against excess heat. from the plastic to reduce the total cooling time. The present invention shown in FIG. In mold 18, inserts 16 and 17 are not used and insulation insert 1 4 and 15 define the surface of the molding space. Molding cavities in each of molds 6 and 18 The outer ends between the It is insulated with insulation. The center gate 21 is inserted into the molten plastic under pressure during injection molding. In order to introduce the metal insert 10, the insulation insert 15, and the mold of FIG. The molds 18 in FIGS. 6 and 5 extend through the surface layer 17. Tightening plate 22, "A" plate 23, "B" plate 24 and support plate 25 are typical of standard mold bases. It is. Number 4 is the sprue bush.

In the mold 6 of FIG. 4, the surface layers 16 and 17 and the insulation inserts 14 and 15 are , the molten plastic injected into the molding space 13 by the center gate 21, and Mold heat dissipation consisting of metal inserts 9 and 10 with cooling grooves 11 and 12 It constitutes an intermediate medium between the container and the container. In the mold 18 of FIG. and the mold radiator is formed only by insulation inserts 14 and 15. There is. If necessary, apply a thin coating or plating to the surface of the molding space consisting of the insulation insert. to give the plastic melt the desired hardness, abrasion resistance, chemical resistance, heat resistance and Welding resistance may also be provided.

Mold 28 in FIG. 6 has two other molds, 26 and 27 have insulation inserts 14 and 15, which acts as a radiator to reduce the cooling rate in the thick parts of the plastic molded product. temperature to further equalize the temperature throughout the molded part and remove excess heat during cooling. The difference is that nickel metal is added to reduce the gap. vinegar In all molds, the intermediate medium was selected according to the invention to have a low thermal diffusivity. Therefore, when molten plastic is injected into the molding space 13, the surface of the molding space is covered with molten plastic. The temperature rises rapidly to above the solidification temperature of the plastic. The heat resistance of the intermediate medium is , sufficient to cause controlled release of heat from the molten plastic in the molding space to the mold radiator. high temperature, so that the cooling of the melt is delayed and the temperature gradient inside the melt is minimized. Select sea urchin. In this way, the intermediate medium according to the invention is combined with the plastic melt. Acting as a barrier between the mold radiator and the mold, it ensures uniform melt cooling and homogeneous Guide to the molded product.

The heat capacity of an intermediate medium is a measure of its heat storage capacity, and is shown in equation (1) below. is equal to the product of density, specific heat and volume so that

C=(ρ) (Cp) (V), (1) In the above formula, C=heat capacity (BTV/'　F), ρ = density (bond/cubic inch), ■=Volume (cubic inch) Cp=specific heat The heat resistance of the intermediate medium is related to its heat insulation property, and as expressed by the following formula (2), is equal to the thickness divided by the thermal conductivity multiplied by the heat transfer cross section.

R=L (43200)/kA, (2) in the above formula, R = heat resistance (seconds/”F/BTU).

L=inch thick) k = thermal conductivity (BTU/hour/ft/F) A = cross-sectional area (square inch) Thermal diffusivity is a property that determines the rate at which a material responds to changes in temperature. It's heat transfer It is the value obtained by dividing the conductivity by the product of density and specific heat.

a = τ Tange 1,000 inches/second (3) Thermal diffusivity is the square of the thickness, heat resistance and heat capacity It is also equal to the value divided by the product of the quantity.

α=→ inch/second (4) The values of heat capacity and heat resistance depend on the thermal properties and the material of the intermediate medium, i.e. the insulation layer or insertion. objects 14 and 15, and insulating members 19 and 20, and if used, the front Due to the geometry of the surface inserts or layers 16 and 17, and the geometry design of such materials , especially the thickness.

The effect produced by the molds 6.18 and 28 of the invention is that at least the actual molding space is During molding, the temperature of the surface of the qualitative part, e.g. most of the surface and preferably the entire surface, Molten plastic injected into the molding space by the temperature of the molten plastic itself It is to raise the temperature to the solidification temperature or higher. Fills the molding space very quickly Otherwise, the skin on the injected plastic will be minimal or non-existent during polymer flow. strong orientation and high shear stress will not occur. plastic molded sky During the initial period of contact with the surface, a very thin layer of plastic can solidify and - The surface temperature of the perfect model is rising. However, the mold and method of the present invention This thin solidified skin remelts when the mold surface temperature rises above the solidification temperature. It remains there for a sufficient period of time to melt and cause the molecules to become non-oriented.

The mold of the present invention has the advantageous thermal insulation effect that the skin provides to the core in conventional injection molds. Apply the fruit to the entire molded part. According to the method of the present invention using the mold of the present invention, the molding space The plastic melt on the surface of The melt region is held near and above the solidification temperature of the plastic for a period of time, while The temperature in the core of the plastic melt continues to fall towards the solidification temperature. Therefore, According to the present invention, compared to molding using conventional molds, the plastic material is removed during solidification of the melt. The temperature gradient in the melt is greatly reduced. The plastic melt undergoes molecular reorientation. stays hot long enough for this to occur, and this causes a thin skin to form and This occurs even when remelting. In the present invention, this occurs for the entire thickness of the molded article. , since there is not only a central core, it takes longer to cool the molded part than when using traditional methods. It takes.

In the mold 6 of FIG. 4, the metal inserts 9 and 10 are made of copper or stainless steel. cooling grooves 11 and 12 are formed therein. Cooling grooves are necessary Used only when

By way of example, the insulation layers or inserts 14 and 15 and the insulation members 19 and 20 are Xydar manufactured by Dart Industries It can be formed from a liquid crystal polymer such as (trade name) SRT-300. insulation insert The thickness of 14 and 15 is, for example, 0.062 inch thick, and the crystalline plus For example, 60% crystalline polyethylene plastic with a density of 0.953 (Dow Chemical EP245), at a molding space height or thickness of 0°125 inches. When molding plastic by introducing it into a 70°F mold at 440°F, surface layer 1 6 and 17 can be 0.062 inch thick aluminum. This program The solidification temperature of the plastic is 255-260°F.

The molten crystalline polyethylene plastic passes through the center gate 21 and enters the molding space 13. When the polyethylene is injected, the mold surface temperature rises to above the solidification temperature of polyethylene within a fraction of a second. and remains at or near the solidification temperature for about 30 seconds, while forming space 13 The temperature of the melt in the center of the mold cools towards the solidification temperature, which causes A temperature gradient occurs, but this gradient occurs when the surface of the molding space is above the solidification temperature of the plastic. less than 63”F (0.5°F x 125 mil) during solidification after rising stomach.

Another insulating material that can be used to form the insulation layer or inserts 14 and 15 is A polyimide resin such as Vespel (trade name) manufactured by U Chemical. table Surface inserts or layers 16 and 17 may also be formed of glass instead of metal, or as desired. Some of them impart hardness, heat capacity and resistance to wear, chemicals, heat and welding. can be formed from other materials.

Surface layers 16 and 17 in mold 6 are also omitted as shown in mold 18 in FIG. can. The space 13 in the molds 6 and 18 in FIGS. 4 and 5 is, for example, an amorphous mold. It is effective in forming optical elements such as optical discs from plastic. The result is a thin, flat, annular space. Of course, the space is a lens like the one shown in Figure 6. Other shapes can be used, such as convex bodies to form holes. 16-layer surface layer A heat insulating material that can be used without using 17 is, for example, quartz glass. present invention The method is applicable to plastics other than the previously described crystalline polyethylene plastic materials. It is also useful for molding. Other types of materials like amorphous plastics and Other thermoplastic materials can be molded by the mold and method of the invention. The mold can also be used for compression molding, which does not require heating the mold.

Thermal analysis of molds of the present invention and conventional metal molds common to conventional practices can be Computers and commercially available finite element analysis software, especially the NISA program. program, a finite element for personal computers with heat transfer modules. For both crystalline and amorphous plastics using a child product, Don't follow me. The computer model is a two-dimensional model with radius-specific thickness variations. (quasi-3D) for all simulation experiments except for the convex lens which is (quasi-3D). Ta.

For crystalline plastic, 60 with a density of 0.943 with a total wall thickness of 0.125 inches. % crystalline polyethylene plastic (Dow Chemical EP245) as a model . The plastic was introduced into the 97° surface of a 70" mold at 440 degrees F. The temperature fluctuation thermal conductivity and specific heat values found in were used for analysis. crystalline plastic The solidification temperature of the metal mold is 255 to 260"F. The analysis results of the metal mold are shown in Figure 7. where the solidified skin thickness is 0.0025 inches in 0.05 seconds, 2.32 0°014 inches in seconds, 0.031 inches in 8.82 seconds (based on molded product thickness), and so on. It can be seen that the total thickness of the molded article is reached in 12.82 seconds. 300°F during solidification There is a temperature gradient. These results are based on the “injection molding process” by Ervin Rubin. This agrees well with the time of 13.9 seconds for complete solidification published in ``Theory and Practice''. Ru. Rubin's time is injected into a 70° mold and solidifies at 266°F. For polyethylene with a density of 0.945 at 45°F.

Xydar 5RT-300 as a heat insulating (low thermal diffusivity) material and O on the mold surface. The results of thermal analysis of the mold of the present invention using aluminum of 0.125 inch to 0.125 inch are as follows. It is shown in Figure 8. The experiment was conducted using 0.062 inch (7) SRT-300 Te, aluminum surface. Thickness is 0.0.032.0゜062.0.070.0.078, o, 1oos Call o.

0125 inches. As can be seen from Figure 8, in all cases, gold The mold surface temperature rises above the solidification temperature of polyethylene, and remains near the solidification temperature for a long time. or kept above the solidification temperature. The polymer does not form a coagulated skin during flow. It can be injected at low pressure and speed. During this period, the center of the molded product will change as shown in Figure 9. Continue to cool the sea urchin. This means that the part passes through the solidification temperature at a rate that promotes crystallization. During heating, a desired temperature gradient is created throughout the molded article. From Figures 8 and 9 As can be seen, the temperature gradient is The surface solidifies after the adjacent outer surface of the plastic is raised to a temperature above the solidification temperature of the plastic. It is less than 50@F when it starts. Aluminum value of zero melts polyethylene Xydar is placed on the surface of the body (this means that the surface of the molding space is coated or plated) Otherwise the melt may be welded with Xydar. shown only to determine the degree of anger for the thickness. However, Xydar The surface of the molding space can be coated or plated as necessary to prevent welding. can. Electroless nickel plating is an example of a suitable protective coating. plastic melting Other insulating materials, such as melt-resistant fused silica, may also form the mold cavity surfaces. Can be used for insulation inserts.

FIG. 10 shows various thicknesses of alumina as surface layers 16 and 17 in the mold 6 of FIG. Curve of temperature difference between the outer surface and center of a plastic molded part for aluminum , which was derived from the thermal analysis described above. As can be seen from Figure 10, Between the plastic and 0.062 inch Xydar 5RT-300 insulation material Minimum temperature gradients are obtained when using approximately 0.085 inch thick aluminum. It will be done. The core of polyethylene is 260 in 43.82 seconds for aluminum O ” F solidification temperature and as a surface layer on the insulation insert 0.125 in. If there is aluminum, it will reach 260″F in 38.32 seconds. As time increases, time decreases.

0.062 inch aluminum as surface layer 16 and 17 on molding space surface , the temperature in the center of the plastic drops by more than 150'F, while the surface From 55°, it becomes 270”% above the solidification temperature and returns to 255°.Similarly, 0° For aluminum that is 125 inches thick, the temperature at the center of the plastic is 10 o°, while the surface changes from 255° to 260° and returns to 255°. child The behavior is due to the thermal gradient within the plastic as it cools below its solidification temperature. Set to a desirable small value. These temperature gradients are 0.5°FX molded product thickness (mil) smaller. When using 0.125 inch aluminum, the first 0°1 second The 0,002 inch solidified surface skin that forms will remelt after 3.3 seconds. , 0.062 inch thick aluminum with little flow-inducing orientation remaining In the surface layer, it takes only 1.3 seconds for the mold surface to exceed the solidification temperature of the plastic. No. An aluminum layer is placed between the Xydar insulation layer or insert and the plastic melt. If no mold is present, the surface of the insulation insert forming the molding space will be It solidifies within the temperature range and rises above the warm temperature.

The above thermal analysis used Xydar insulation material as insulation inserts 14 and 15. It was made by Xydar insulation material if other insulation materials are used The thickness of the new material required to achieve the same temperature and time as shown in the simulation below It can be estimated from the finite construction (5) of the set.

Delta time = L squared / twice the thermal diffusivity (5) where L is the thickness of the insulation material be.

The relationship for Vespel insulation material versus Xydar thickness is Lv squared/thermal expansion. 2 times the diffusivity" L x squared / 2 times the thermal diffusivity, and: L, = 0.062 inch, and when Lv=0.098 inch, it is expressed by the following formula.

Using aluminum as a surface layer between the plastic and the insulation material in the molding space The same heat storage is achieved under the following conditions: AXLllxwa xCa + AXLx XWX XCX=AxL,,xWa xCa +AxLv XwV xCv where L = thickness, W = density, A2 area, C=specific heat.

If L, = 0.085 inches, , = 0.060 inches, the above formula becomes the below formula. shown.

Lam = [(LX XWx xCx - Lv XWv xCv) 7w, X C&　　　+L.

Thus, for example, the overall Thermal conductivity can be calculated. For example, using a 0°060 inch aluminum surface layer The heat flow through the 0.098 inch thick Vespel insulation material is 0.062 inch thick Xyda with 0.085 inch thick aluminum faster than the flow of heat through the intermediate medium with r. Results of thermal analysis of the above materials is shown in FIG. As shown in Figure 11, 0.098 inch thick Vespel /0,060 inch thick aluminum surface layer cools the mold surface faster. The calculation result that . is confirmed by the thermal analysis result. The mold surface temperature is xy It reaches 270”F for the dar type and 267°4°F for the Vespel type. reach Both temperatures are higher than the solidification temperature.

Amorphous to form an optical disc with a thickness of 0.04 inches, which is typical of optical discs. This book describes the molding of optical discs using polycarbonate as a plastic. Other thermal analyzes of the mold according to the invention were compared with values for conventional metal molds. The polycarbonate Bonate has a solidification temperature of about 305°F. The molding space surface is 250°F and Polycarbonate injected at 660°F into a metal mold with a mold temperature of 200°F. Figure 12 shows the results of a computer simulation regarding the , in the same figure, as soon as the molten plastic is introduced into the molding space, the solidified skin begins to form. At 0.2 seconds after introduction, the thickness of the skin is about 0,000 inches. Ru. Typical filling time into the molding space for optical discs passes through a thick solidified layer 0.2-0.4 seconds to minimize orientation and stress due to flow. Then , close the gate and print the part or reduce overfill stress. Change the injection stress. The outer edges and central gate portion of the molding These parts are required for optical discs and are highly stressed by continuous cooling. low birefringence, which limits the area of the disk used for data storage . According to this simulation, the center of the molded product becomes solid, or It takes 4.6 seconds to cool down to the glass transition temperature. This conventional injection mold According to the molding method, the plastic material is introduced into the mold and then the plastic material is Until the center of the molded product cools below the solidification temperature, a very large temperature is generated in the molded product. It is also clear from FIGS. 12-13 that there is a degree gradient.

In contrast, according to the present invention, a 0.012-inch nickel molding cavity in an injection mold The intersurface layer is lined with a 0.050 inch thick Vespel insulation layer. There is. The behavior of the amorphous polycarbonate plastic and the temperature of the mold surface were determined in the first Shown in Figure 4.

Similar mold surface temperature and plastic behavior diagrams are found in polyester, which is a crystalline plastic. Obtained for ethylene. When introducing molten plastic into the molding space, As clearly shown in Figure 14, the temperature gradient decreased significantly and the mold surface temperature also increased. The temperature rises above the solidification temperature of the plastic. Therefore, compared to traditional injection molding, The above-mentioned advantages of the present invention can be obtained by substantially reducing the birefringence in the optical disk. can be reduced or eliminated. Two made of polycarbonate plastic Concerning the molding of heavy convex lenses, 1. Another thermal analysis of the mold according to the present invention was conducted for conventional metal molds. The results were compared with the analytical values. The lens has a spherical surface radius of 25 mm on both sides. It was the diameter. The thickness at the ends was 1.3 mm, and the thickness at the center was 8 mm.

Regarding optical quality Lexan OQ 1010-111 manufactured by GE, the analysis Thermal conductivity and temperature variable specific heat were adopted. Solidification (glass transition) temperature of this material was approximately 305°F. The mold 28 in FIG. 17 and nickel-based heat sinks 26 and 27, the stain of the present invention We conducted a simulation. The insulation layer and ends 14 and 15 are Xydar 5RT −300, and metal inserts 9 and 10 were made of beryllium copper alloy. . Other important dimensions are shown in FIG.

Injected at 600°F into a 200°F all-metal mold with a surface temperature of 240°F. polycarbonate, and a 180”F composition with a surface temperature of 240°F. Regarding the polycarbonate injected at 575''F into the mold (Fig. 6, 28) Therefore, from the efficiency of zero analysis performed by computer simulation, the symmetry Considering that the thickness of the pie-cut section is one quarter of the cross-sectional area and 0.008 radian. This model is based on the following.

The results of the analysis are shown in Figures 16A, 16B, 17A and 17B, which figures are , constant temperature of the plastic lens at a specific time after injection of the plastic (isothermal) line is shown. Figure 16A shows the difference between plastic and all-metal alloys (conventional method). Indicates the The result of using the method and mold according to the invention is that a portion of the lens is solid. The time at which it begins to change is shown in FIG. 16B. The plasti in the conventional method The maximum temperature difference during the test is about 295°F, with lines in close proximity as much as 37.8°F apart. As shown in Figure 2, there is a very sharp temperature gradient at the surface. Improvement method of the present invention The maximum temperature difference in the plastic at is only 165°F and 18.6 The temperature gradient is far Loose.

Figures 17A and 17B show that the plastic lens is completely solidified for each mold. Indicates approximate time. Maximum temperature difference in lens in all-metal mold is 110° It is F. For the mold according to the invention, the maximum temperature difference in the lens is 63°F. . 13°F apart for all-metal molds and 7.8°F for molds according to the invention. As can be seen from the degree of proximity of distant equimixers, the temperature in the improved method of the present invention The slope is less severe.

From the above description of the invention, it can be seen that by the method of the invention using the injection mold of the invention, It is recognized that the molded article can be injection molded so that it has a homogeneous structure. Furthermore, growth for a considerable period of time while the form space is filled and the center of the part is cooled. If the polymer is near or above its solidification temperature, i.e. melting or glass transition temperature, Temperature maintained to minimize flow and temperature gradient induced orientation and stress becomes. When the entire part of the molded product and the entire molding space of the multi-space mold are filled, Since the polymer is in a molten state, the filling is very even throughout the part. Ru. Also, since the convergence front of the melt is easily maintained at around the same temperature, the present invention A strong fusion surface is formed. Even in the case of thick-walled molded products, voids can occur for the same reason. It can be molded without any problems. First a solidified skin of minimum thickness is formed and then the skin is remelted. By melting and relaxing the molecules, molecular orientation is minimized. Injection of the present invention The mold controls the temperature gradient and cooling rate during molding, allowing the polymer to The crystallization is high and uniform, thus resulting in high quality moldings and close tolerances. Control is greatly improved. This is achieved without the need to install heating means in the mold. be done. Since birefringence is linearly related to molecular orientation, injection molding according to the method of the present invention Injection molded into a net shape with excellent optical, physical and mechanical properties in the mold Optical molded products, such as lenses and optical discs, must have minimal or no orientation. is possible.

Although specific examples of three embodiments have been shown according to the present invention, the present invention is not limited to these. However, many variations and modifications are possible as will be apparent to those skilled in the art. The method of the invention can also be applied to injection molding of plastics other than those specifically described. It is applicable, and the injection mold of the present invention has a shape other than that shown in the drawings. You can also do it. In particular, the plastic material is placed between the mold halves and compression molded. In this way, the present invention can be used for compression molding of plastics that does not require a gate in the mold. Can be used with molds and molds. The invention is therefore limited to the details disclosed. including all variations and modifications that fall within the scope of the claims. It is.

Engraving (no changes to the content) FIG.6 FIG. 7 Hey ra milk le FIG. 15

Claims (31)

[Claims] 1. preparing a mold having at least one molding space of the shape of the molded product to be molded; Introducing molten plastic into the molding space and reducing the amount of molten plastic in the molding space. The process of cooling the molded product until at least a portion of it solidifies, and then removing the molded product from the molding space. In a plastic molding method for forming a molded article, including: the substance of the surface of the molding space The target area is heated to a temperature higher than the solidification temperature of the molten plastic while molding the molded product. A molding method characterized by improvements including a step of 2. The temperature of at least a substantial portion of the molding space surface is maintained at a temperature of at least a substantial portion of the molding space surface for a significant period of time during molding. The molding space is maintained near or above the solidification temperature of the molten plastic. is filled with molten plastic and the center of the molten plastic in the molding space is Cooling from a temperature equal to or higher than the solidification temperature to the solidification temperature, thereby causing the solidification process of the molded article. Further steps to reduce orientational stresses induced by flow and temperature gradients in the plastic The molding method according to claim 1. 3. At least a substantial portion of the surface of the molding space has a temperature above the solidification temperature of the molten plastic. When the outer surface of the plastic begins to solidify after reaching the temperature, the plastic in the molding space The temperature difference between the outer surface and center of the plastic is the thickness of the molded product expressed in mils x 0.5 3. The method of claim 2, wherein the temperature does not exceed .degree. 4. solidifying the molten plastic during molding of at least a substantial portion of the surface of the molding space; molten plastic into which heat is introduced into the molding space to bring the temperature above the temperature Claim 1 further comprising means for insulating said molding space so as to obtain heat from said molding space. Forming method in Section 1. 5. The means for insulating the molding space has low thermal diffusivity at or near the surface of the molding space. 5. The method of claim 4, comprising applying a layer of material having the following properties. 6. Cuts on or near all surfaces of the molding space that come into contact with molten plastic during molding. 6. The method of claim 5, comprising applying a layer of thermal material. 7. Claim wherein the layer of insulating material forms at least a substantial portion of the molding space surface. Forming method in Section 5. 8. forming the molding space surface and also acting as a radiator to remove excess heat and cooling. of other materials that reduce the cooling time and so even out the temperature throughout the molded part during molding. - A method according to claim 5, in which a layer of the insulating material is located below the above-mentioned layers. 9. During molding, molten plastic is injected into the molding space. The molding method according to claim 1, wherein the mold contains. 10. The entire surface of the molding space is at the solidification temperature of the molten plastic while molding the molded product. The molding method according to claim 1, wherein the molding method is performed at a temperature of at least 50°C. 11. When molten plastic first comes into contact with the mold surface during molding, the molding space The temperature of the surface is lower than the solidification temperature of the molten plastic, and the surface is brought into contact with the surface of the molding space. solidify the contacting plastic layer and at least a substantial portion of the molding space surface. During molding, the layer solidifies when the temperature reaches the solidification temperature of the molten plastic. The method of claim 1, wherein the molding method is remelted. 12. The molded article has little flow-induced molecular orientation, residual stress, and birefringence. Optical molded articles such as lenses or optical discs with Forming method in item 1 of the requested scope. 13. The mold has a plurality of molding spaces, and all molding spaces of the mold are melted during molding. The molding method according to claim 1, wherein the molding method is filled with melted plastic. 14. Claims in which the molten plastic is compression molded in a mold to form a molded article. Molding method in item 1. 15. Plastic molding for forming a molded article, characterized in that it includes the following means: Injection mold for: A hand that defines at least one molding space of the shape of the molded product to be molded. step, a step in the mold that allows molten plastic to flow into the molding space. a gate, and a substantial portion of the molding space surface is injected into the mold during molding. Means for raising the temperature above the solidification temperature of molten plastic. 16. At least a substantial portion of the surface of the molding space is heated below the solidification temperature of the molten plastic. The means for bringing the temperature above to the temperature of at least a substantial portion of the molding space during molding. maintain the temperature near or above the solidification temperature of the molten plastic for a period of time; During this time, the molding space is filled with molten plastic, and during that time the molding space is filled with molten plastic. Cooling the center of the molten plastic from a temperature equal to or higher than the solidification temperature to the solidification temperature; This reduces the flow and temperature gradient induced reactions in the solidified plastic of the molded part. 16. The injection mold of claim 15, which reduces or eliminates forces. 17. A means for raising the temperature to a temperature higher than the solidification temperature is provided above the molding space. 16. The injection mold of claim 15, comprising means. 18. The heat insulating means has a low thermal diffusivity disposed at or near the surface of the molding space. 18. The mold of claim 17, wherein the material layer has the shape of: 19. Claim 18, wherein said layer forms at least a substantial portion of the molding space surface. How to form a term. 20. The molding space forms a surface and provides a heat sink to remove excess heat and reduce the cooling time. one or more other materials that reduce the 19. The injection mold of claim 18, wherein the thermal insulation layer is located below the upper layer. 21. The injection molding according to claim 20, wherein the material layer forming the surface of the molding space is metal. Extrusion mold. 22. A layer of insulating material is placed between the metal insert of the mold and the molding space, and Injection mold according to claim 18, provided with means for cooling the metal insert. . 23. 19. The injection mold of claim 18, wherein the layer of insulating material is a liquid crystal polymer. . 24. The insulation layer stores sufficient heat from the molten plastic injected into the molding space. Then, the temperature of the surface of the molding space is raised above the solidification temperature of the plastic to be molded. 19. The injection molding mold according to claim 18, wherein the thickness of the heat insulating layer is selected such that the thickness of the heat insulating layer is increased. 25. Claim 17, wherein the insulation means is also provided with respect to the gate of the mold. Section injection mold. 26. The means for heating the entire surface of the molding space to a temperature equal to or higher than the solidification temperature is used to heat the entire surface of the molding space to the melt during molding. Injection molding according to claim 15, which is performed at a temperature equal to or higher than the solidification temperature of the molten plastic. Type. 27. For forming optical molded products such as lenses or optical discs into molded products. 16. The injection mold according to claim 15, wherein the molding space is configured as a sea urchin. 28. the means for defining at least one molding space defines a plurality of molding spaces; An injection mold according to claim 15. 29. The following mold is used to define at least one molding space of the shape of the molded product to be molded. Plastic injection molding method for forming molded products, characterized by the use of: The mold includes a radiator means spaced apart from the molding space and a heat sink means spaced apart from the molding space. an intermediate medium disposed between the radiator means and the molten plastic in the molding space; the intermediate medium includes means for injecting molten plastic into the molding space; After the molten plastic is released, the temperature of the surface of the molding space quickly rises to a temperature higher than the solidification temperature of the molten plastic. It has low thermal diffusivity and moderate thickness so that it rises quickly, and The intermediate medium retards the cooling of the melt and reduces the internal temperature gradient of the melt. controlling heat from the molten plastic in the molding space to the radiator means to It has high enough thermal resistance to release. 30. means for defining at least one molding space in the shape of a molded article to be molded; spaced from the molding space to remove heat from the molten plastic introduced into the space. radiator means disposed at a distance from the radiator, and the molding space disposed between the radiator means and the radiator means; containing an intermediate medium that has been The intermediate medium absorbs the surface of the molding space when the molten plastic is introduced into the molding space. Low heat so that the temperature rises quickly to above the solidification temperature of the molten plastic has diffusivity and moderate thickness, and The intermediate medium retards the cooling of the melt and reduces the internal temperature gradient of the melt. controlling heat from the molten plastic in the molding space to the radiator means to Characterized by having a high enough thermal resistance to release; A mold for plastic molding. 31. At least one material is placed between the molding space and the intermediate medium to form the molding space. forming a surface between the plastic and at least one of the materials, excluding excess heat. to have the required shape and heat capacity to make the temperature more uniform throughout the rack. 31. The mold of claim 30, comprising: