IL28173A - Injection molding process and apparatus for effecting same - Google Patents

Description

'man |Π3 TJinr —n PATENT ATTORNEYS · D'Q ID El · J 11 U OR. REINHOLD COHN | Π 3 ΊΊ1Π]"Ί "11 PR. MICHAEL COHN Γ^ ¾ ' " 3 " 3 " 0 ".l ISRAEL SHACHTER B.Sc. .Q.n 1 B 3111 ¾ N 1 U) ' PATENTS AND DESIGNS ORDINANCE SPECIFICATION Injection molding process and apparatus for effecting same I (we) CRYPLEX INDUSTRIES, INC. , a New York Corporation, U.S.A. do hereby declare the nature of this invention and in what manner the. same is to be performed, to be particularly described and ascertained in and by the following statement:- ' The present invention relates to a new molding process and apparatus for molding thermosetting materials in the manufacture of molded articles of various kinds, particularly to a process and apparatus for injection molding heat hardenable free-flowing liquid resins, and more particularly, resins of thermosetting character, such as polyester resins and epoxies .

As is well known, there are several known types of techniques for molding plastics, such as compression molding, injection molding and transfer molding.

Injection molding essentially involves heating granular plastic material in a heating cylinder to a plastic state and then forcing it under pressure by means of an injection ram or screw into cavities of a closed cold mold. Usually the amount of material delivered by the ram or screw from the heating cylinder is exactly the amount required to completely fill the cavities. The injection ram or screw forces the granular material into the heating cylinder and in so doing pushes a like amount of material in a plastic state out of the other end of the heating cylinder through the sprue and runners into the mold cavities.

With conventional equipment, the pressures required to push the molding material through the heating cylinder and into the mold varies from about 10,000 to 25,000 psi. About 25 to 7 $ of this injection pressure is transmitted into the mold, where it must be resisted by the moid clamp..

The temperature to which the material has to be heated in the cylinder depends on several factors, but usually falls between 300°F and 600°F. Ejection of the molded part from the mold is usually automatic.

The molding process or cycle is then repeated.

In the past the injection molding process has been used almost exclusively with thermoplastic materials using known injection molding techniques. However, these techniques are not suitable with thermosetting materials, which when heated to predetermined temperature, set in a relatively short time into an infusible, insoluble solid.

In compression molding the mold is opened and heated to the desired temperature, which depends primarily on the character of the molding material, and the design and dimensions of the article to be formed by molding. The necessary quantity of the molding composition is introduced into the cavity or cavities of the open mold, the hot mold parts are closed and heat and pressure is applied for a predetermined period of time to the material introduced into the mold. The action of heat and pressure is continued until the material is sufficiently cured, after which the mold is opened and the molded articles are removed. Compressive molding is relatively slow and ordinarily requires pre-polymerizing the resin composition and special handling techniques, which increase the cost of the molded articles materially. The pressures applied are from about 2,000 to 8,000psi, according to the geometry of the mold and the materials used. .

Transfer molding is generally applied to the process of' forming articles in a closed mold from a j thermosetting material and involves the use of a separate plunger and heated pot or auxiliary chamber, separate from the mold cavity. A predetermined quantity .of thermosetting material is first fed into the pot, 5 heated, and then the hot material is transferred in a plastic state under pressure from the pot through runners or channels into the closed cavity of the mold. A transfer mold is inherently complex and relatively expensive. Because of the nature of thermosetting 0 materials, it is not feasible to hold any considerable quantity of the material at a high temperature in a heating cylinder prior to molding. The material would polymerize into a solid mass. Only sufficient material for a single shot is heated at a time. !> Prior to the recent development of transfer molding, thermosetting materials were molded only by compression moldin processes. In the transfer molding process the raw material is preheated, so as to be fed into the mold in a softened, semi-plastic state under 0 pressure. Because of the properties and characteristics of the softened semi-plastic material, it is a non- Newtonian fluid. A non-Newtonian fluid is a highly viscous fluid, in which the viscous stresses are not proportional to the strain. The plastic melt does not begin to flow until after a certain stress applied to it is exceeded and hence requires a proportionately larger • ram or screw force to cause flow, than a Newtonian fluid. In the plastic melts heretofore used, the temperature of the melt increases, ordinarily its viscosity de- ■ creases, although not in a linear fashion, depending on the material being processed, since these materials are non-Newtonian fluids. Different plastic materials have different temperature viscosity curves, which are well known in the art .

In many applications low-molding pressures and low temperatures are necessary to achieve good results. Heretofore various attempts were made to provide special molding materials for use in the molding processes, which would be in a plastic state at a temperature below their minimum curing temperature.

Many applications, such as electrical and electronic components, require low molding temperature, since the heat normally used during the molding process adversely effects the electrical characteristics of the components. Also, low molding pressures do not distort delicate mold inserts oftentimes used during the potting process.

Consequently, various attempts have been made to overcome these shortcomings and encapsulate electrical or electronic components using mass production techniques with a material in its plastic state at low temperatures. polyester resins have been used to some extent in potting of electrical components, because of their good electric properties. Heretofore these materials have been limited to casting and compression molding processes, because of the difficulties in handling them with conventional injection molding techniques and equipments.. Even casting polyester resins created problems in potting or encapsulating electronic components because of shrinkage and entrapment of air bubbles, which adversely affected hermetic sealing. Epoxy materials were more commonly used in potting, since this material overcame the shrinkage problem, but the molding cycle was greater than that for polyester resins.

Molding processes and apparatus using polyester resins which are in their plastic state at a temperature below their curing temperature, have been attempted in spite of the disadvantages, but such apparatus and process was not a solution to the problems discussed above and does not provide the advantages of the apparatus and process of this invention. Transfer molding apparatus can use only relatively solid material, such as a high viscosity and non-free flowing material having the consistency of heavy putty. This high viscosity, non-Newtonian material has not been widely used in the trade because of difficulty in controlling uniform preheating of the material, which is an essential part of the transfer molding process. Thus, the advantages of using liquid thermosetting resins, such as polyesters and epoxies, were well-known, but the rapid cure, difficulties of molding, prevented its adoption for automatic operation in mass production.

Therefore, it is an object of the present invention to provide a new method and apparatus for molding materials, which are free-flowing liquid at room temperature in a quick simplified manner and which is adapted for mass production of molded articles.

It is a further object of the present invention to form articles by injection molding a Newtonian liquid polyester resin having low viscosity at room teperature, which resin is conveyed to the mold under low pressure in ,a cool liquid state and requires no pretreatment prior to use . . . t is a s ill f invention to provide a process for injection molding thermo^ setting materials and apparatus therefor, wherein a large number of articles can be simultaneously molded in a multi- cavity mold in an automatic manner with short time cycles and provide molded articles of high quality and which have a smooth surface and finish, and where removal of the molded article or articles from the cavities of the mold is done quickly, automatically and simultaneously.

Another object of the present invention is to provide an injection molding process and apparatus for a low viscosity liquid thermosetting resinous material, which does not require prepolymerizing of the material, pretreat- ment or preheating of the resinous material, or special handling techniques.

A further object of the present invention is to provide an injection molding process and apparatus therefor which is capable of plastic jacketing a delicate insert at temperatures of between about 150°F to 00°F and at pressures between 50 psi to 1500 psi rapidly, and in a short time cycle, and which hermetically seals any leads extending through the jacket.

Another object of the present invention is to provide a process and apparatus to automatically remove from a multi-cavity mold a plurality of molded pieces as a unit .

Yet another object of the. present invention is to ■provide a process and apparatus for injection molding free- flowing liquid thermosetting resins, such as polyesters, which accomplish all of the above inexpensively and yet provide fast, simple and reliable operation and finished products of high quality with good mechanical and electrical properties/ all with a minimum waste of material and allows using inexpensive molds.

Other objects and advantages of the invention will appear from the detailed description and. the drawings, wherein: Figure 1 is a front elevational view showing an injection mold in open position in accordance with the present invention) Figure 2 is a vertical sectional view taken along line 2-2 of Figure 1; Figure 2a is a fragmentary enlarged sectional view taken along line 2a-2a of Figure 2; Figure 3 is a front elevational view partly in section of different embodiment of the present- invention; Figure is a sectional elevational view of a further embodiment" of the present invention; and Figure 5 is a front elevational view, partially broken away, of the mold shown in Figure in closed position.

In injection molding a relatively large quantity, of plastic compound is heated and plasticized, and a portion is injected or shot under pressure into a closed cold mold where the material hardens . The mold is opened and the piece is removed from the mold as soon as it is rigid enough to handle and the molding process or cycle is repeated. This seemingly simple process is actually complex in practice and heretofore has not been practiced for thermosetting Newtonian liquid resins.

Since the present invention is of value for the simultaneous molding or encapsulating of a large number of j small articles, the mold shown in the drawing is con- . structed for use in molding buttons or button blanks from thermosetting polyester liquid compositions and the invention will be described in connection with the manufac- 5 ture of such articles. However, it is to be understood that this invention is not limited to those particular compositions or those particular shaped articles and may be applied to the molding of other thermosetting liquid resinous compositions and to the production . of other shaped artie le-s , including large sized items. The present process is also highly useful in molding various types of products having pressure sensitive inserts contained therein, such as encapsulation, where normally the high pressures required in conventional injection molding processes prevented such a process to be used. The high pressures involved heretofore caused the delicate inserts, such as electrical wires, semiconductors and other pressure and heat sensitive electronic and electrical components to become distorted and change the capacitive and electrical characteristics of the product. In practice the inserts are positioned in the mold cavities while the mold is open, such as by jigs or tapes. After such placement, the process is substantially the same as discussed below for button blanks.

The present invention advantageously uses liquid thermosetting resins which readily flow at room temperature and v/hich have a viscosity of about 3000 poises or under. The present invention can use liquids having the viscosity of water, and in practice liquid resins having an the viscosity of about 100 centipoises have been readily used in the apparatus and rocess of the resent invention. The viscosity of glycerin and of castor oil each at about 20°C is about 1000 centipoises . With the use of low viscosity liquid molding materials low molding pressures and low temperatures are able to be used, xvhich avoids damaging' fragile inserts and which materials set very rapidly at relatively low mold temperatures in the range of about 150°F to about 00°F. The mold temperature and molding pressure depends on the molding material used and the size of the cavity. As is known in the art, the mold is heated to a temperature sufficient to cure the molding composition in the cavity within a predetermined time. Molding pressures used range from about 50 psi to about 2000 psi. This low pressure and low temperature molding process prevents any change of electrical characteristics of a pressure or heat-sensitive insert, such as a semiconductor, wires, leads, or the like, and allows using relatively inexpensive molds.

In the present invention the free-flowing liquid thermosetting compounds, such as polyesters, are easily forced at low pressure and at a temperature lower than its minimum curing temperature into ¾ closed heated die cavity and the heated die quickly cures the liquid resinous material within a matter of seconds into the shape of the mold. The free-flowing liquid resin is able to flow com-pletely around and encapsulate any insert, so that the insert is hermetically and permanently sealed. The use of low pressure and low heat permits using relatively simple and inexpensive molds as compared to the complex, heavy and expensive transfer and injection molding techniques heretofore . used .

Referring now to Figures 1-3, a mold 9 is shown mounting plates 10a and 10b, respectively. Mounted on mold-mounting plate 10a are force retainer plates 12 mounted on opposite sides of a force block 14. Mounted to back-up or mold-mounting plate 10b is a cavity block 16. Mounted about cavity block ΐβ are cavity retainer plates l8. Advantageously the faces of the cavity block 16 or force block 14 have shallow slots (one or two mills deep) not shown, milled into them to provide venting air or other gaseous material from the cavity as the resi^fnous material enters. Force retainer plates 12 and cavity retainer plates l8 are used to back up the cavity blocks 14 and l6 against the pressures created during the injection molding process. Mounting plates 10a and 10b keep blocks 14 and 16 within retainer blocks 12 and 18, respectively, and provide a means of mounting the mold on the injection molding machine's platens, not shown.

Shown in Figure's 1-2, mold 9 is mounted in a conventional injection molding machine (not shown) for horizontal clamp so that the moving platen is vertically ori-ented and moves in a horizontal direction to close the mold and clamp it shut. If desired a vertical clamp and horizontal moving- platen may be used, as shown in Figures 4-5. Cavity block 16 has a plurality of cavities 22 in its mold face.

Injection cylinder nozzle 20 is at right angles to the direction of the clamping of mold 9 and is seated on the parting line of mold 9· As shown, the outer end of, nozzle 20 has a spherical nose surface, which mates with the sprue bushing 24, which has a recess to seat the nose surface of nozzle 20. Advantageously, cavity block 16 is heated in selected areas to a temperature sufficient to cure the composition in the cavities, which normally is between about 150°F to about 400°F. The heat is applied in any convenient manner, such as by use of a high watt density cartridge heater 26 or band type electrical heaters, which fit snugly around the portions of the cavity block 16 , which are to be heated. -Advantageously, the area surrounding sprue bushing 24 or the inlet is not directly heated and may be cooled by passage of a cooling liquid through the area of cavity block 16 adjacent sprue bushing 24, not shown.

Other methods of heating or cooling the mold may be used as is well known in the art. The temperature of the cavity block should be closely controlled to provide satisfactory results.

In carrying out the process, a relatively large quantity of a free-flowing liquid thermosetting resin, such as a polyester, having low viscosity and a suitable catalyst or hardener, are placed within a storage cylinder or container 30 , and provide a ready supply of plastic material for use in the process. The resin and the catalyst may be premixed before introduction into container 30, or added separately and then, mixed. Container 30 should be large ehough to hold a sufficient quantity of material for at least several hours of operation, preferably for a day's operation. In practice', material suffi-cient for up to two weeks' operation has been stored and used. The resin and the catalyst contained within cylinder 30 are placed at an increased pressure by any convenient method, such as by a hydraulic pressure source, pump or air pressure. The resinous composition from reservoir 30 is forced through a. line 3 to a movable shooting or injectin mechanism 36 having nozzle 20 at its end. Shooting mechanism 3 is water-cooled and water is fed into a jacket 38 via line 4θ from a source of cold or refrigerated water, not shown, which may be a large reservoir for recirculating and cooling the water, and . which may either be air cooled or cooled in any conventional manner. The water flows through line 4θ, through jacket 38 in a tortuous path and leaves jacket 38 via line 42 and is either recirculated or disposed of in some manner. The cooling water prevents any feedback' of heat from nozzle 20 , which contacts the heated cavity block ΐβ. Line 34 contains a shut-off valve 46. Shut-off valve 46, which could be automatic or time-controlled, prevents continuous shooting of the resinous material into mold 9. Shooting mechanism 36 is preferably reciprocally mounted with respect to mold 9 to prevent solidification of any resin which may dribble from or remain in nozzle 20 between injecting cycles.

As best seen in Figure 1, a thin sheet of stretchable material 50 overlies the face of force block l4. Preferably, this material is some cellulosic material, such as cellophane or silicone paper. A thin stretchable sheet of material 52 overlies the face of cavity block l6 and has a thickness of about 1 mill.

Material 52 has a greater need for stretchability and advantageously a film made of a polyvinyl alcohol, cellulose acetate, cellulose acetate butyrate, or cellulose triacetate, or other similar material. As shown, sheets 50 and 52 can be mounted for automatic feeding be'tween the faces of mold 9, such as rotatable feed rolls,. designated as 5'4 and 56 , respectively. Each time mold 9 opens, sheets 50 and 52 are advanced a. distance slightly greater than the length of the mold faces, so as to have an unused portion of film overlying the corresponding face of mold 9 for every cycle.

In operation, mold 9 is heated prior to operation and as seen in Figure 1 , is in its open position with portions of films 50 and 2 disposed between the mold faces. Shooting mechanism 36 is cooled by water circulating through jacket 38. Mold 9 is closed and clamped in its closed position, and nozzle 20 is reciprocated forward towards mold 9 and forced and held against sprue opening 24 to form a tight fit. Valve 46 is opened allowing a predetermined shot or charge of resinous composition from cylinder 30 to be fed into cavities 22 through corresponding gates βθ. Tils pressure on films 50 and , which are also heated by mold 9* causes film 52 to stretch and assume the precise shape of cavity 22 and be forced into contact with the walls of cavity block 16. After the predetermined charge of resinous composition has been injected into mold 9» which is sufficient to fill cavities 22 , valve 46 is closed cutting off the flow of resinous composition. After a predetermined period of time shooting mechanism 3β is reciprocated away from and out of contact with sprue 24 . After a further predetermined period of time the resinous composition is hard, which for buttons totals about four to eight seconds, and the moving platen or mold-mounting plate moves away from the stationary platen, thus opening mold 9 · If desired, conventional knockout pins and knockout bar systems can be arranged to remove the molded article or articles from the mold. However, the molded articles are easily removed from the cavities with the aid of film sheets 50 and 2 in the form of strips, as discussed below.

As shown in Figure 1, during the molding process sheets 50 and 52 are pressed together about the molded articles indicated at 62 and hold articles 62.

After mold 9 is opened, "these pressed together sheets containing the molded articles 62 between them are advanced out of and away from mold 9 a predetermined distance in any convenient manner, such as pressure rollers, thereby withdrawing and transporting all of the molded articles . 62 from between the mold faces and simultaneously to introduce fresh sheets of material 0 and 52 between the mold faces for the next cycle of operation. As illustratively shown, the pressed sheets 50 and 5 removably contain molded articles 62 between them and are slidably mounted over a pulley 64. After removal from mold 9, the pressed film containing molded articles 62 may be cut in strips for easy release of the molded articles 62. While one form of conveying the injection molded articles from the mold 9 is shown, other convenient apparatus may be used. With the construction shown in Figure 1, nozzle 20 and shooting mechanism 36 are moved away from the mold 9 after injection of the material to prevent solidifying of the resin material in nozzle 20 from the heat of the mold 9 and the possibility of nozzle drool interfering with the closing of the mold on such drooled material. This movement may be accomplished in any convenient manner.

If desired, shooting mechanism 36 need not be reciprocated between cycles if nozzle 20 is maintained sufficiently cool, less than 100°F, to prevent solidifica-tion of the resin which may dribble or remain in nozzle 20 between injecting cycles. This may be accomplished by refrigerating coils wrapped about nozzle 20 adjacent sprue 2 , or the use of refrigerated or cooling water passing through a jacket about nozzle 20, similar to lines 4o and 42 in jacket 33. Also, as mentioned above, sprue bushing 2 could be cooled by. a cooling liquid through the cavity block adjacent sprue bushing 24, as discussed above. Thus, as shown in Figure 2, nozzle 20 will remain fixed in this position, while mold is opened to remove the molded articles and is closed to begin the next cycle.

To avoid the difficulty inherent in injecting the material perpendicular to the dire ction of movement of the mold, the construction shown in Figure 3 may ¾e used. In Figure 3 cavity block 102 is mounted on a back- up or mold-mounting plate 108. As shown, a sprue bushin 110 passes through back-up plate 108 and mold force block Ιθβ, and communicates with the mold cavity. A nozzle 112 cooperatively mates with sprue bushing 110. Nozzle 112 has a discharge opening aligned and cooperating with the corresponding opening and passageway in sprue bushing 110. Sprue bushing 110 conducts the resinous · composition from nozzle 112 to the mold cavities either directly or through a runner system, as shown in Figure 2. Preferably, the passageway in sprue bushing 110 is tapered so that the removal of the molded product will pull the sprue out of sprue bushing 110 easily and cause the injected material to break off at or within the tip of the nozzle 112.

With the apparatus shown in Figure 3* a single ■strip of film material ll4 is disposed contiguous to the surface of mold or cavity plate 102. Strip .114 is stretchable and is preferably polyvinyl alcohol and could be equivalent to the material discussed previously with respect to sheet 52 , shown in Figure 1. If the surface of force block' 106 is coated with teflon, or has a chrome plating or coating, or is highly ' polished on the mold surface, the finished molded articles will be easil displaced from the mold surface by use of the strip 114. As shown, strip 114 can be mounted on a roll and fed through the mold at a predetermined rate in any convenient manner, such as by feed rolls, to permit a new portion of the strip 114 to be positioned between the mold plates after every cycle of operation, while simultaneously conveying the molded articles from the mold. Similarly, as discussed above, the molded articles are conveyed from between the mold faces quickly, simply and positively.

If both mold faces of the mold shown in Figures 2 or 3 are coated with teflon, or given a chrome plating, -or are highly polished, both film strips 50, or 114 , may be eliminated and the molded articles may be removed from the mold by knockout apparatus, well-known in the art or by suction apparatus, not shown.

A further embodiment is shown in Figures 4 and 5 , in which numeral 120 designates a conventional molding press having relatively movable platens 122 and 124 with mold plates 126 and 128 attached thereto, respectively. Mold plate 126 is generally flat with mold plate 128 containing a plurality of mold openings or cavities 130. As shown, a single strip of material 132 is fed through between mold plates 126 and 128 in predetermined lengths, and adjacent to plate 128 containing the mold openings or cavities I30. Strip 132 is stretchable and similar in material and feedin a aratus to sheet 2 discussed above v;ith respect to Figure 1.

The injection molding apparatus is generally designated "by numeral 13 , and is advantageously mounted on a rigid frame, not shown. Apparatus 134 includes a shooting mechanism 136 and the molding . material feeding apparatus 152.

Shooting mechanism 13β has a nozzle member 138, which is cooled by liquid flow, such as water, via inlet l40 and exit 142. The liquid is recirculated and cooled in any convenient manner. Nozzle member 138 has a nose portion 144 generally spherical, which mates with recess l 5 to insure good alignment. Nozzle member 138 is mounted for reciprocal motion in the direction shov/n.by arrow 146 by actuator 148. Actuator 148 is solenoid operated and selectably moves nose portion 144 into and out of seating contact with recess 145 by means of for-ward and rearward movement of rod 1.49.

A relatively large supply of a f ee-flowing, generally low viscosity liquid molding material 153 is stored in a supply container 154 , a portion of which is shown. Container 15 could hold- several weeks' supply of molding material in its liquid .state and could, if desired, supply several shooting mechanisms. The molding material 153 is fed to nose 144 by means of a pressure cylinder or receiver 155 containing a pressure source, which is shown as piston 1 6. Piston 156 is reciprocated by a rod 159 coupled to a source of energy, not shown, which could be a solenoid or hydraulic pressure. Piston 156 and actuator 148 are operatively interconnected so the proper sequence of action occurs once thie cycle is begun, as discussed below. Disposed in conduit 1β2 between supply container 1 4 and pressure cylinder 155 is a check valve 164 set to open at a predetermined pressure. Movement of piston 15β in a direction of arrow 158 creates a reduction of pressure in volume 157, vrhich is sufficient to open valve 164 and allow a predetermined quantity of a liquid molding material 153 to be sucked into volume 157 from container 154. Movement of piston 156 in a direction of arrow ΐβθ · increases the pressure on the liquid in decreasing volume 157, which pressure is transmitted to close valve 164, so that the molding material is forced through flexible conduit 166. Spring 165 provides a quick acting positive seal for valve 164. The pressure of the molding material 153 n conduit ΐββ opens check valve 168 by overcoming spring 169, so the liquid molding composition is emitted from the nose portion 144. When piston 1 6 completes its pressure movement, valve l68 is promptly closed by action of spring 169 and piston 1 6 is ready to begin another cycle.

Mold plates 126 and 128 are heated to a pre- determined temperature sufficient to cure the molding •composition in the cavity, which normally is between about 150°F to about 400°F, in any convenient manner, such as electric band heaters.

Operation is generally similar to that described above with respect to the other embodiments. Mold plates 128 and 126 are closed on sheet 132, such as shown in Figure 5· Piston 156 is moved in the direction 158 causing valve 168 to close and valve 164 to open. A quantity of molding material 153 s forced into volume 157 of receiver 155· Actuator 148 is actuated and forces nozzle member 138 forward toward and into contact with recess 145.

Piston 15β moves in direction l60 closing valve 164 and opening valve 168, and shoots a measured quantity of liquid molding material 153 into mold cavities 130 to fill the same. The heat of the mold and the pressure of the molding material stretches and forces'- strip 13 into intimate contact with the surface defining cavities 130. The heated mold sets the molding material quickly and piston 1 6 retracts in direction 158 and actuator 148 retracts rod 149 moving nose 1 away from recess 1^5. Platens 122 and 124 separate and sheet 132 is moved automatically a predetermined distance carrying the molded articles out of and away from the mold, so that an unused surface of film is positioned between mold plates 126 and 128. A new cycle is repeated. The molded pieces can. he removed from sheet 132 at leisure.

While sheet material 13 is shown as being used, the faces of mold plates 126 and 128 can be polished, chrome-plated or teflon-coated, as discussed above.with respect to the embodiments shown in Figures 2 and 3, and sheet 132 eliminated if desired.

Further, nozzle member- 138 can be cooled and remain in. fixed position. as shown in Figure 5* n a manner similar as discussed above with respect to nozzle 20. To reduce nozzle dribble or solidification of any composition which remains in nozzle member 138 between injecting cycles, piston 156 is moved slightly in the direction of arrow 158 after a shot is completed. This movement reduces the pressure in conduit l66 and sucks any material remaining in nose 144 into conduit l66 prior to the clos-ing of valve 168.

Using. the apparatus and process of the present invention, an entire mold plate of semiconductors were encapsulated with a liquid polyester resin in fifteen (15) seconds, which included closing the mold, injecting the plastic into the mold, hardening and opening the mold. In comparison, semiconductors are commercially encapsulated at present with epoxy resins using a transfer molding process in about three (3) minutes, or about l80 seconds. Besides the reduction in time, a factor of about 12, the present invention produces little or no waste, whereas with transfer molding process the sprue from the pot to the mold produces a large percentage of waste material adding to the cost of the molded product.

To aid a fast cycle of operations, as mold plates 126 and 128 close on sheet 132, air is withdrawn from cavities 130 via conduit l80 passing through platen l4o and communicating with the interior of the mold ca- vity. Air and other gaseous matter trapped in the closed mold and the devices, if any, to be encapsulated is forced out as the molding material is forced in via mold recess l 5. Once the cavities 130 are filled with. the molding material, the air can no longer escape. To be beneficial, the air and other gaseous matter must be withdrav/n rapidly 'to prevent entrapment of the air by the incoming plastic. Conduit l80 is coupled to a vacuum source, not shown, which is generally a pump. In conduit l8o between platen 124 and the vacuum source is a vacuum valve 182, which could be solenoid operated and operatively in-■ terconnected with actuator 148 and cylinder 155· An accumulator chamber aids quick evacuation and prevents any. flow of plastic material damaging the vacuum source, such as a pump. Valve l82 is actuated in a predetermined sequence with respect to actuator 148 and piston 156.

If inserts are to be placed in cavities 130, they may be inserted in place after a sheet of film material has been positioned over the cavity plate. The inserts, such as semiconductors, are advantageously positioned in the cavities by jigs or strips of material, carrying the inserts in predetermined position. The sheet material is softened by the heat of the mold and is easily depressed into the mold by the insert. The flow · of the molding material into the mold stretches the sheet material against the mold surface and flows easily about the insert. Additionally, as an aid in positioning the inserts into the mold, reducing the pressure in the mold, such as shov/n in Figure 4, draws the sheet material into the mold prior to the placement of the insert. Also, with liquid polyester molding material, if no sheet material is used the natural shrinkage of the material in setting aids the removal of the molded part from the mold.

With the injection molding operation taught, the overall molding cycle can be broken down into the following periods: 1. Time to close the mold and clamp; 2. Filling time or the injection stroke; 3. Hardening time or time mold remains closed with no pressure exerted on the resinous composition in the mold cavity; 4. Press opening time; . Time between cycles during which molded parts are. manually or automatically removed from the mold and new films moved into place, and insert, if These cycles are usually minimized within the limitations of the apparatus and machine.

The molding compositions employed in the present process comprise low viscosity, free-flow, liquid thermosetting resin compositions, such as polyester and epoxy resins. The polyester compositions may be of various forms, but are formed of a poly-basic acid and a poly-hydric alcohol to form a series of ester linkages, which are capable of cross-linking with a monomeric compound. These compounds are well-knox While the viscosity of the liquid resinous material as used can ary widely, the material should always be . relatively fluid and would on its own accord tend to run or flow freely at room temperature. Low viscosity liquids, less than 2000 centipoises, are readily used in the present invention.

It is apparent from the foregoing that the present invention overcomes many of the problems associated with the molding of liquid resins as heretofore used, such as prepolymerizing the resins, pre-bagging and de- . aerating the resin composition. With the present apparatus and process, the time per cycle is much faster than with the compression molding and casting methods hereto-5 fore used. The polyester resins are normally used in the present process and apparatus directly as received from the manufacturer with only a catalyst added, and if desired, coloring material, such as dyes and pigments.

The quantity of the catalyst added to the resinous com-0 position will depend upon the size of thickness of the molded article. With the present apparatus, a cycle of about one half of the time is obtained as compared with compression molding apparatus. Also, the present invention uses a simpler and less expensive mold and equipment, 5 lower pressures and temperatures than that used in transfer molding operations heretofore used in attempts to mold thermosetting plastic materials.

Of special importance in the manufacture of buttons is providing buttons with a pearly or pearlescent 0 appearance. To achieve this effect, there may be added to the resinous composition a quantity of pearl essence, such as fish scales or known artificial materials, like iridescent flakes. In flowing through the orifice of nozzle 20 or 144, the pearlescence producing material is * properly oriented to produce the maximum pearlescent effect desired, with no further action of the operator ■ required.

While the present drawing illustrates the mold for button blanks, it is understood that the present in-0 vention is not limited thereto and can be used for articles of other sha es or desi ns includin lar e sha es such as parts for .toys , . ames , jewelry, electronic and electric components and devices, and other ornamental, industrial or commercial types of items. In practice, molds having' 9o cavities have been used, with all of the molded items removed as a single unit. The conditions of molding, especially the molding temperature, pressure and time, will depend on the nature of the thermosetting composition, the type of mold insert and apparatus utilized.

Further, the conveying or transporting apparatus shovm for removing the molded articles from the mold can be used with a variety of molding operations, and is especially useful for, removing automatically a large number of molded articles.

Although particular structures and embodiments have been described by way of illustration, it should be understood that the invention should not be limited to the particular embodiments of the invention shown by way of illustration, but rather to the scope of the invention covered by the appended claims. 28173/3

Claims (9)

1. An injeotion molding apparatus for molding liquid thermosetting, resins I comprising a molding press havin relatively movable platens with a mold plate attached to each platen and an inlet recess formed by said plates, an injection nozzle, having a discharge nose, an actuator for reciprocally moving said nozzle relative to the press for selectively clamping said nozzle against said recess when the mold is closed or separating said nozzle from said recess, said nozzle being arranged, when clamped to said mold, to have its discharge nose in communication with said inlet recess, and a metering and injection device for the composition, said device comprising a cylinder having an outlet opening in communication with said nozzle and an inlet opening adapted to be placed in communication with a reservoir containing a supply of said composition, a piston reciprocally movable in said cylinder, and hydraulic power means for moving said piston in one sense o the other, said piston thereby being operable, upon movement in one sense, to draw a quantity of said composition from said reservoir into said cylinder and, upon movement in the other sense, to force said quantity of said composition out of said cylinder and into said nozzle, said chamber having a capacity in excess of the volume of said composition required to fill the total number of mold cavities provided in one of the plates and the connection between said cavities and said recess.

2. , An apparatus as claimed in Clai 1, further comprising a supply of a pliant and stretenable film and means for disposing a reach of said film within the confines f 26 - each molded article adhering thereto out of the confines of said mold while the same is Open after an injection operation, said nozzle being arranged, when in contact with said mold in the closed state thereof, to direct the flow of said compositio rom said, discharge end of said nozzle over said film.

3. An apparatus as claimed in Claim 1 or 2, wherein means are provided for, cooling said nozzle.

4. An apparatus as claimed i Claims 1, 2 or 3, wherein means are provided for heating said mold plates.

5. $. An injection molding apparatus substantially as described herein, wit reference to and as illustrated by the accompanying drawing.

6. A method of injection molding thermosetting resin compositions which are liquid at normal conditions and room temperaturet wherein a separable heated mold is used which is arranged in fixed location at a molding station and has at lease one mold cavity defined therein as well as a sprue and a parting line runner system leading from the sprue to the cavity region of the mold, wherein during each molding operation the mold is closed by means of a press and a reciprocally movable nozzle is advanced toward the molding station and clamped tightly against the mold, with the discharge end of the nozzle juxtaposed to the mold sprue, for conducting the molding composition into the mold, and wherein at the end of each molding operation after the nozzle has bee retraoted from the molding station, the mold is opened to enable the molded article or articles to be extracted therefrom; characterized in that (a) a metering and injection chamber, which is adapted to contain a quantity of the liquid molding composition somewhat in excess of that required to fill the total number of mold cavities and the runner system, is provided in the form of a cylinder with a piston reciprocally movable therein, the piston being operated in one sense to draw a metered quantity of the molding composition from a source of supply thereof into the chamber, and being operated in the opposite sense to force the metered quantity of the molding composition under lo pressure out of the chamber and to inject the composition into themold via the nozzle; (b) the mold is devoid of any reverse flow check valve structure at the entrance end of the runner system and is Continuously heated in the cavity region thereof, without interruption even during an opening of the mold between successive moldin operations, to a temperature sufficient to ensure the cure of an Injected molding composition while the same is within the mold ,(c) a thermal barrier is established during each i jection operation between the portion of the molding composition in the cavity region of the mold and the portion of the molding compositio in the nozzle to minimize the transfer of cure*-initiating heat to any portion of the composition in the nozzle (d) the piston is maintained in its last-named operated state to apply a continuous hydrostatic pressure to the molding composition in the mold while the portion of the molding composition in the heated region of the mold gels substantially completely; and - 28 - i (e) the nozzle is retracted from the mold after a time interval suf icient to permit the gelation of the molding composition in the mold hut insufficient, under the established thermal conditions,, to permit any gelation of the portion of I the molding composition inI the nozzle? (f) whereby automatic repetitive molding cycles of minimized duration can be carried out xfith maximized production rates and economies in one and the same mold without any cooling of the mold between successive cycles and without danger of shut-down necessitated by blockage of the nozzle by cured resin.

7. , The method accordin to Claim 6, wherein for the establishment of the thermal barrier the sprue region of the mold is thermally isolated from the cavity region.

8. The method according to Claim 6, wherein for the establishment of the thermal barrier the sprue region of the mold is cooled.

9. The method according to Claim 6, wherein for the establishment of the thermal barrier the nozzle i cooled. 10, The method according to any one of Claims 6 to 9 further characterized in that for the encapsulation of electrical or electronic devices o components in molded resin, which devices are placed into each cavity of the mold prior to the closing thereof, both the molding temperature and the injection pressure are adjusted so as to avoid any undue adverse effec on the electrical and mechanical properties of the encapsulated devices or components as a result of the molding operation. 28173/3 ~> - 29 - 11 p A method of injection molding thermosetting resin compositions which are liquid at normal conditions and room temperature substantially as hereinbefore described by way of example and with referenoe to the accompanying drawings· For the Applicants ARTNERS IS:CB