DE2408183A1 - SHAPE AND METHOD OF VENTILATION DURING THE WARM FORMING OF A SYNTHETIC RESIN FILM - Google Patents

Description

Patent attorneys: o / η ο λ ο ο

Dr. ing. Waiter Abitz 240818 3 Dr. Dieter F. Mori

Dr. Kans-A. Bride ", ² ° * ^pebruary

8 iiünciisn 83, Pienzenauanttr. 2a F-2449

EGG. DU PONT DE NEMORS AND COMPANY lOth and Market Streets, Wilmington, Del. I9898, V.St.A.

Form and method of venting the same during thermoforming of a synthetic resin sheet

The present invention relates to a method of draining trapped air during the thermoforming of a synthetic resin film, which is plastically flowing to a high degree is, for example a polyester film in a form. The invention also relates to a form for performing the Procedure.

US Pat. No. J> 470 281 (Knowles) relates to a method for producing a container provided with flanges using a device for producing the container which has a die with a cavity which is open at the end. A die insert is arranged at the bottom of this cavity. This die insert has an annular circumferential recess which separates a lower part from a body part of the die insert. The lower

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Part has an outside diameter that is smaller than is the outer diameter of the body part, whereby a connection between the circumferential recess and the Inside the cavity is possible. A ventilation duct is drilled through the die insert, through which the circumferential recess with a vertical ventilation channel is connected, which leads to the atmosphere through suitable lines. The ventilation channels (I3 and 14) in the Die inserts allow venting of air trapped between the cavity wall and the resin material is when the resin material takes the shape determined by the circumference of the wall surface of the cavity.

U.S. Patent 3,482,281 (Thiel) relates to an apparatus for Manufacture of thin-walled plastic objects which the pormoberflache with a number of closely spaced mutually arranged projections is provided which are solely in contact with the film and this is the general Communicate the shape of the surface of the mold from which it protrudes. The protrusions in contact with the film are numerous enough and so close together that there is a noticeable penetration of the thermoplastic material Do not allow in the gaps. This is a requirement for the thermoplastic films that are commonly used fulfilled when the distance between the projections is in a range which is approximately J5 to 15 χ greater than the film thickness is.

The present invention provides a method of venting trapped air from a mold during Thermoforming of a film for the production of a shaped article is available, which has a bottom part and has a side part or side parts, and which there-

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characterized in that a vent is provided in the mold, at least in its entrance area has a width between 25 to 75 microns.

The present invention is particularly useful for making thermoformed tablets from polyethylene terephthalate film or scroll. As a result of the extreme ductility of this polymer at the molding temperatures, it was found known mold arrangements as unsuitable for this purpose. In the manufacture of such a tablet, the Foil heated to a temperature at which it undergoes permanent deformation in order to achieve the desired shape Way to allow under pressure. The heated film is pressed under pressure into a forming cavity by the Cavity evacuated or by applying air pressure, or using an insert or punch or a Combination of cavity evacuation with one of the other methods. Regardless of the procedure used, a Device may be present to allow the escape of air between the inner surface of the cavity and the foil is enclosed so that the surface of the foil can conform to the perimeter of the shape.

Well-known shapes used in the manufacture of trays from materials previously used, for example from films made of essentially amorphous polyethylene, were used, have narrow holes generally provided at the bottom of the cavity as vents for evacuation or an escape of air to the atmosphere. However permitted the ease with which polyethylene terephthalate flows at the molding temperatures, a flow of the Material even in the smallest holes, which can be made by drilling, and which, for example, a

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150 microns in diameter, as well as in the Usually sized vent holes with a diameter from 250 to 500 microns. As a result arise very fine elongated, whisker-like projections on the tray obtained in those places where the free-flowing Polymer has been pressed or sucked into these holes.

These protrusions are unsightly and have been cut off when they are cut the same turned out to be hollow, so that they leak at the interfaces on the structure obtained result. Repeated attempts to avoid these protrusions by making even smaller holes using a laser have been found to be ineffective.

It has now unexpectedly been found that sufficient Channels for releasing or evacuating air without adverse effects can be obtained by dividing the mold in two parts or sections are produced which have a sliding fit (25 to 75 microns) therebetween with escape takes place of air via a circumferential channel, which is at the connection of the two sections. This Canal only creates a hairline-shaped elevation on the surface. There are no elongated protrusions educated.

The polymeric film can contain fillers, nucleating agents, and minor amounts of other organic polymeric modifying agents included if so desired.

The channel provided in a form according to the invention is preferably located in the circumferential area where the body part and the bottom part of the mold meet, i.e., this

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Parts can come together and are in an arcuate line or at an angle to each other Location apart by an amount of 25 to 75 microns .

The mouth of the channel is preferably in the middle of an arcuate junction or at the point of intersection an angled junction to allow air to escape from the side walls and floor to enable. The width dimension of the vent channel (25 to 75 microns.) Only needs to be on the inside surface of the mold cavity be low, which is in contact with the polymer film, as well as in a short range, for example 2.5 now, within the channel adjoining the inner surface. This critical dimensioning on the inner surface prevents the flow of the Polymer in and through the vent channel, however, allows air to escape, being the constriction only is necessary over a short area, the air can flow away more freely and the processing of the parts is simplified will.

Depending on the thermoforming process used, the air duct can be connected to a vacuum source (through other larger pipes, if desired) or it can be connected directly to the atmosphere.

To facilitate the flow of air that is otherwise locally trapped between uniform surface areas especially if the bottom of the mold is a flat surface, the surface of the mold can be sandblasted and fine grooves on the sandblasted surface.

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show which ducts to the critical de-ventilation duct form. Such grooves can be made by lightly painting over with an abrasive material, such as a ■ fine emery cloth. Light sandblasting provides a matt finish that the hides fine burrs that are created by the grooves to in the manufactured article, for example a Tray to give an acceptable appearance.

Fig. 1 shows a preferred embodiment of an invent improper shape, with parts omitted for clarity,

Fig. 2 shows a cross section of another according to the invention Form in which parts are also omitted for the sake of clarity.

The mold 10 consists essentially of two parts, namely an outer body part 11 and an inner base part These two parts are dimensioned such that the bottom part 12 slides in such a way within the body part it is added that a cavity and a vent duct of critical dimensions are formed, which, of the cavity leads away.

The body part 11 has an inner surface 1; 5, the first Has surface portions 14 and second surface portions. The bottom part 12 has an inner surface 16, the first surface portions I7 and second surface portions 18 owns.

The first surface portions 14 of the body part 11 form a body surface I9 of the cavity, which the

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Form lateral boundary surfaces of the cavity 21 and the first surface sections IJ of the bottom part form a bottom surface 20 of the cavity, which represents the bottom surface of the cavity 21.

The second surface sections 15 of the body part 11 and the second surface portions 18 of the bottom part 12 are machined in such a way that they form a sliding fit, when the bottom part 12 is assembled with respect to the body part 11 to form a mold cavity 21, however a distance remains between these parts, which a circumferential ventilation channel 22 between the cavity 21 and the outer surface 26 of the mold 10 forms.

The body part 11 and the bottom part 12 are at the meeting point of the lower peripheral edge 25 of the body surface 19 of the cavity formed at the junction of the surface 19 with the surface I5, and the upper one circumferential edge 24 of the bottom surface 20 of the cavity, which is at the junction of the surface I7 with the surface 18 is formed, arranged at a distance from one another, this meeting point being a circumferential inlet opening forms for the circumferential ventilation duct 22.

The surfaces 15 and 18 form the first channel 22.

The channel 22 is about 25 to 75 microns wide, namely Measured at least over an area of about 2.5 mm, starting from input 25. The channel 22 is at its inner end 25 in direct connection with the cavity over the entire area of the lower peripheral side Edge of the cavity, and the channel can on its outer

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End either connected to a vacuum source or to the atmosphere.

Due to the arrangement of the circumferential channel 22 in the described In this way, air present between the mold and the film is sucked against the inner surface of the mold and escapes, without pulling the film into the canal itself. The channel 22 can be expanded or with larger channels be connected to form vent channels.

Furthermore, it is not within the scope of the invention along suitable surfaces of the body part 11 and of the base part 12 to provide projections or grooves shown, which facilitate the correct arrangement of the bottom part 12 in the body part 11. In such cases, the circumferential channel 22 can be partially interrupted at the junction of these projections or grooves be.

In the case of thermoforming, the mold 10 is used in conjunction with arrangements such as a film clamping device, as at 27 in Fig. 1 for clamping a film, for example a polyethylene terephthalate film over the Mold cavity 21 is shown. Other devices, such as a heating device for the film web, the The mold and punches and a vacuum source for vacuum forming processes well known in thermoforming have become not shown in the figures for the sake of clarity

The mold 10 'shown in FIG. 2 has essentially the same parts as the mold 10 according to FIG. 1, with the proviso that the body part ^11f and the bottom part 12' are produced with a somewhat different shape.

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From Pig. 2 it can be seen that the inner surface 15 ^{1 of} the body part 11 ^f and the inner surface 16 'of the bottom part 12' are designed in such a way that, in addition to a first channel 22 ', they form a second channel 28 and a third channel 29, which communicate with the first Channel 22 'are connected. The second channel 28 and the third channel 29, in contrast to the first channel 22 ', do not have any critical width dimensions and are shown considerably larger than the first channel 22', so that the air can flow more freely through these channels and the machining of the parts 11 ' and 12 'is simplified.

The channel 29 can, if necessary, with the atmosphere or with connected to a vacuum source.

The inner surfaces Ij5 'and 16' of the body part 11 'and the Bottom part 12 'also have surface sections j50, which are in contact with one another in order to keep the parts 11 'and 12' in the correct position with respect to one another. For this suitable measures are familiar to the person skilled in the art and such an arrangement for adjusting the parts or a Sliding seat arrangement with a shape according to FIG. 1 works satisfactorily.

In some cases it has been shown to be trapped in air along surface 20 or between surface 20 and the film F drawn against this can take place. In such cases it has been shown that a light sandblasting with a subsequent arrangement of directed micro grooves on the surface 20 is a solution to the problem revealed. The grooves should be straight and preferably in a radial pattern, starting from the center of the Surface 20 to the first circumferential channel 22 to run.

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It has been found that when these grooves are made by means of an emery cloth using high Press no impressions are visible, with the exception of the sandblasted surface pattern. These grooves result an effective ventilation duct from the center of the surface 20 to the circumferential channel 22 and can thereby Eliminate air pockets even in such cases which sandblasting alone would not be enough.

In a normal vacuum forming process, a small amount of material is drawn into the channel 22, but is eliminated the critical size the problem of the occurrence of long hollow whiskers and improves the extraction of the produced Object, for example a tray, from the mold; however, in some cases it is beneficial to use air jets apply to separate the tray formed from the mold and the circumferential, hairline-shaped elevation to separate from channel 22. Release by means of air jets can be achieved when using the form according to the invention without difficulty, whereas considerable problems would arise in known forms if the articles made of materials such as polyester with a high degree of plastic flow.

In the production of a molded article using the molds of the present invention, a film F are placed laterally protruding according to FIG. 1 on the mold 10, the film as a single sheet or as continuous web can be used.

After the film has been clamped in the correct position and heated to the desired temperature, which depends on the film used and the molding process used, the

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Foil moved into cavity 21.

Bel the simplest thermoforming process, for example A simple vacuum forming, movement of the film into the mold cavity can be done by vacuum or pressure alone or a combination of vacuum and pressure takes place; this movement can be carried out by means of a punch or some other device be supported, which captures the film at the top and the film, which is in a deformable State is located in the mold cavity in such a way that the desired final shape is obtained.

The form according to the invention can be used in conjunction with known Thermoforming processes and arrangements are used in which an appropriately attached plastic film pressed or drawn into a mold, including 1) vacuum suction processes, 2) stretch molding processes, 3) two-die presses, 4) slip ring forming, 5) vacuum forming with die insert, 6) pressure forming with die insert, 7) shrinking under vacuum, 8) corrugation process, 9) pressure forming with enclosed film with contact heat and 10) pressure forming with preheating and die insert.

In the preparation of tablets, preferably made from polyethylene terephthalate, using the molds, such as 10th and 10 'and of the method according to the present invention, the film may be at temperatures between about 80 ⁰ C (178 ⁰ F) and about I50 ⁰ C (302 ⁰ F) can be thermoformed. Preferably, the polyethylene terephthalate film is preheated to a temperature between about 100 and 110 ⁰ C ^(212-0 F).

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It can be a temperature of the mold between 130 and I85 used (226 ° to 365 ⁰ P). The length of time during which the film remains in the mold depends on the polymer used and the temperature of the mold. A temperature of the mold between 150 and 155 C in conjunction with a cycle of up to 50 seconds has been found to be satisfactory. This cycle time can be reduced considerably for certain polyethylene terephthalate mixtures.

An understanding of the invention will be made through the following Example relieved.

B ice ρ i e 1

A mold for a tray with a single receiving space is used, the tray dimensions being 125 x 162.5 χ be 28 mm and the shape has steep side walls with an incline of about 3 ° to the vertical. Form corresponds to a standard type with vent holes drilled with a No. 80 drill, i.e. a size of Have microns. In this form a foil is made

amorphous polyethylene terephthalate thermoformed while the mold temperature is 110-190 ⁰ C. The tablets obtained have whiskers up to 6 ram in length. The whiskers consist of hollow tubes with closed ends, which, when broken off, form small holes in the bottom of the tray

A second shape is used for a tray with the same shape, the two-part according to the invention

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Construction is used to create a vent slot that is between 75 and about 150 microns wide lies. With the same molding conditions as in the previous case, the film is in the ventilation slot pushed in more than desired when the slot is 100 microns or more wide. This creates Problems when ejecting the tray and a weak point in the tray.

A new shape is made, with a vent between 25 and 75 microns, and that shape is complete satisfactory, i.e. the tablets made with this shape are pleasing in appearance as well as also satisfactory in their use.

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Claims (1)

F-2449 Patent claims Methods of evacuating trapped air from a mold during the manufacture of a molded article, which has a bottom part and a side part or side parts, by means of thermoforming a film, thereby characterized by having a vent in the mold is provided which has a width between 25 and 75 microns at least in its entrance area. 2. The method according to claim 1, characterized in that the vent opening from the junction between the bottom and the side wall or the side walls of the mold runs out. 5. The method according to claim 2, characterized in that substantially the inner mouth of the vent runs continuously along the circumference of said junction. 4. The method according to any one of claims 1 to j5, characterized in that that the vent opening is formed by a game between a part of the mold, which forms the bottom of the article and a separate part of the mold which is the side wall or walls of the object forms, the game being a continuous uninterrupted or partially interrupted Channel forms, which extends from a cavity formed inside the mold to the outside of the mold extends, this channel being formed between opposing walls of the two said parts. - 14 409834/0924 F-2449 5. The method according to any one of claims 1 to 4, characterized characterized in that the film is drawn into a cavity in the mold and against the cavity surface of the mold wherein the mold consists of a body part and a bottom part which is located within the body part is received and the surface portions of these two parts are spaced apart and form a channel extending from substantially the entire peripheral edge of the bottom of the cavity to Outside of the mold leads. 6. Mold for thermoforming a film by means of the process according to one of claims 1 to 5 * has many parts, which form a cavity, characterized by an outer body part with an inner surface, the sections of which form a body surface of the cavity by an inner bottom part with an inner surface, the first portions form a bottom surface of the cavity, the body surface and the bottom surface of the cavity form an inner surface of the cavity, and the body part and the bottom part at the junction of the peripheral Edge of the body surface of the cavity and the peripheral edge of the bottom surface of the cavity in the Are spaced from each other and form an entrance to a channel between them, and this entrance to the Channel at said connecting parts has a width, which is less than about 75 microns. 7. Form according to claim 6, characterized in that second portions of the inner surface of the body part and the bottom part form between them said channel and this channel in connection with the inner surface dos Cavity and with an outer surface of the form. - 15 A09834 / 0924 P-2449 8. A mold according to claim 6 or 7 »characterized in that the channel has a width between about 25 to 75 microns , namely over at least a range of 2.5 measured starting from the inner inlet thereof. 9 · Form according to any one of claims 6 to 8, characterized in that the channel communicates at its inner end in direct communication with the cavity along the overall sammten lower peripheral edge of the cavity. - 16 - A0983A / 0924