RU2443559C1 - Method of hot forming packages, hot forming device and method of increasing package wall thickness in forming - Google Patents

Abstract

FIELD: process engineering. ^ SUBSTANCE: invention relates to production of packages. Proposed method consists in heating foamed polystyrene sheet to plastic deformation temperature and feeding it onto made die, moving said sheet toward female die and evacuating cavity between said dies. Sheet material outer layers have close pores while layer located between said layers has open intercommunicated pores. Evacuated cavity features vacuum between male die and sheet smaller than that between female die and sheet and equals the force corresponding the beginning of plastic deformation of sheet material layer between layers with close pores. Proposed method consists in heating foamed polystyrene sheet to plastic deformation temperature and feeding it onto made die, moving said sheet toward female die and evacuating cavity between said dies. Proposed device comprises appliance to implement above described method. ^ EFFECT: lower weight of thick-wall package. ^ 3 cl, 3 dwg

Description

The invention relates to the production of packages, and specifically to a method for producing a foamed polystyrene sheet, which is used to obtain packages, as well as to the design of packages obtained from such a sheet - trays, substrates, pallets and similar products by thermoforming.

With the development of fast food chains, and most importantly, chains of self-service stores, the popularity of expanded polystyrene packaging is growing. It is economical, reliable, convenient. Foamed polystyrene (EPS) is a special way foam plastic containing tiny air bubbles. There are 2 types of similar material: polystyrene (expandable polystyrene) and extruded expanded polystyrene. Extruded expanded polystyrene is made from general purpose polystyrene granules. At the stage of extrusion by special methods, foamed polystyrene tape is obtained, which is subsequently molded into certain products. It is in this way that the majority of trays and utensils are made, which can be found today in shops and fast food outlets. During extrusion, polystyrene can be foamed up to 50% of its intrinsic density. Foaming can take place during extrusion or during post-formation operations, such as blow molding or thermoforming. Successful extrusion of foamed plastic depends on the regulation of temperature and pressure inside the extruder. Thanks to the foaming process, a thick film can be made of the same amount of material as a thinner one. This fact allows for economical production. In the production of CHD, great importance is attached to the homogeneity of its cellular structure. During physical foaming without special additives, a “rough” structure foam is obtained. To form a good homogeneous cellular structure, so-called nucleation agents (or nucleators) are often added to polystyrene, which, when foaming, are foam growth centers. The more nucleusator is introduced into polystyrene, the more cells are formed, and their size will be smaller. The amount of nucleator introduced also affects the speed of the foaming process itself. One of the best inactive (passive) type nucleators is talc, the action of which is based on the formation of obstacles for the exit of the foaming gas from the polymer melt. Due to the heat-insulating properties of IPNs, two-sided heating is used during thermoforming. IPN has a structure that is a multitude of unreported cells. It is a good damping material (with sufficient thickness), a good heat insulator. Its surface is wear-resistant, which is an important factor when choosing packaging for the product.

The UPU has excellent heat-insulating properties, the dishes from the UPU for hot food products will keep them hot and not burn their hands, and the packaging for deep-frozen products will ensure their safety during transportation. Perfectly retaining moisture, UPU lets air pass in small amounts, “breathes”, which is a necessary condition for the preservation of fruits and confectionery. The ability of UPU to dampen shock and vibration effects, protecting it from deformation, makes it possible to make packaging for fragile items from it. Such packaging is quite easy to form, in addition, the IPN can be painted in any color. Packing from UPU has a low cost compared to the cost of the goods. Such packaging looks beautiful and neat, makes a good impression on the buyer.

Currently, the possibility of making packaging from expanded polystyrene with an absorbing layer - absorbent trays, most often used for meat products, is relevant. Made entirely of polystyrene, these trays are environmentally friendly (they can be recycled after disposal). Their design allows you to divert juice from the product from the surface and accumulate it in a highly absorbent layer inside the tray, away from the product. Moisture-absorbing substrates have a special multilayer structure, which allows you to absorb and retain moisture released by meat products. Through the perforated bottom surface, the liquid penetrates into the inner layer of the substrate and is retained there thanks to a special conical shape. The high moisture-absorbing properties of the inner layer make it possible to use these substrates even for products that emit large amounts of liquid. Compressed edges prevent liquid from seeping onto the film - this is a key advantage of this type of packaging. The edges of the packaging and the film remain dry and clean, which is a great advantage for both the seller and the buyer. The opaque surface of the tray hides the color of the absorbed liquid. Even if the pre-packaged meat is placed unevenly on the counter, the liquid will not leak from the sides, the film and the counter will remain clean and there will be no need to repack the wet or sticky packages. The process of recycling and disposal of such a tray is facilitated by the fact that all layers are made of one material.

Currently, the production of foamed tape consists in the fact that general-purpose polystyrene (GPPS) in granules is poured into an extrusion line. Along with it, technological additives are added: talc for the foaming process, dye for color and moisture-absorbing additive (only for the manufacture of moisture-absorbing foam tape). Foaming agents are gases (butane, isobutane, pentane, etc.), which are introduced into the cylinder of the primary extruder in a liquid state (each extrusion line consists of a primary and secondary extruder). In these extruders, gas is mixed with the molten polymer and, under high pressure, enters the head of the line, from which it emerges in the form of a bubble. It is at this moment that gas bubbles begin to grow and foam the tape. Then the tape is pulled over the mandrand (a cylinder 1-2 meters long) and then the tape, cooled on the mandrel, enters the pulling rolls and then onto the winder. After that, the rolls with the tape arrive at the maturation warehouse and are stored there for 7-10 days. During this period of time, air enters the pores of the tape and displaces gas from them. After that, the tape is fed to the molding workshop for the production of packaging of a given shape (RU No. 2089565, C08J 9/04, C08L 25/06, publ. 09/10/1997). This decision was made as a prototype for the claimed method.

By this method, it is possible to obtain tapes of foamed polystyrene, the structure of which remains porous, that is, capable of absorbing moisture.

The wall thickness of the tray simultaneously with the shape of the tray itself determines the carrying capacity of the tray, that is, the ability to bear the weight of the product without deformation of the tray itself. Therefore, trays can be produced both thin-walled (2-5 mm thick) and thick-walled (more than 6 mm thick). The release of thick-walled trays is justified by the need and demand, but at the same time, when forming thick-walled trays from a tape, the resulting product has an increased weight, which negatively affects the weight quality indicator of the product. Given that a large product contains a lot of moisture, it becomes problematic to fill all the pores with this moisture in the tray wall (pore filling is caused by the communication of pores with each other along labyrinth located channels, and with increasing wall thickness the labyrinth of pore bonds is local in nature, with which part of the pores has no communication with other pores. In this case, the filling of pores with moisture in the thick-walled tray is the same as in the thin-walled - surface).

Known from RU No. 2106958, B26F 1/24, B29C 37/00, B29C 51/00, publ. 03/20/1998, a molding method using double evacuation. This patent describes an installation for hot molding 10, which consists of two forms 9 and 11 (positions are given in the description of patent RU No. 2106958). The upper mold 9 contains a matrix with which the outer side of the product made of a foam sheet is formed, for example, the product 20. The lower mold 11 contains a punch with which the lower side of the product is molded. Cross sections of the matrix and the punch are made complementary. To form the foam sheet 16, the foam sheet is first heated in an infrared heating furnace to a certain temperature. Then, the heated portion of the foam sheet 16 is fed to the hot forming device 10, the shapes of which 9 and 10 are closed, which means that the die and punch are approaching each other to a distance of about 5 mm. The foam strip is simultaneously subjected to deep drawing on both sides with the help of a vacuum acting on both sides, which load forms 9 and 11 or the die and punch. It is envisaged that the mold for forming the outer side of the foam sheet has a matrix adjacent to the outer side, the surface of which is formed as an addition to the surface of the matrix (punch) adjacent to the inner side. The design of the device is preferably chosen such that the shapes are formed so that they can be moved to each other to a distance corresponding to the adjustable wall thickness of the product obtained by deep drawing from a foam sheet. The wall thickness of an individual product is generally from 3.0 to 6.5 mm. The molds are arranged to move to each other to a distance corresponding to the installed wall thickness of the product 20, and the wall thickness of the product 20 lies in the range from 3.5 to 6.5 mm.

This decision was taken as a prototype.

In this case, double evacuation is used for an open-porous tape, to the outer surfaces of which films with a closed-porous structure are glued (thermally).

The use of such a molding installation due to double evacuation allows you to form the necessary reliefs on the outer and inner surfaces of the product. Information indicating the expansion of the material of the tape in this patent is missing.

The technical result achieved in the present invention is to reduce the weight parameters of the thick-walled packaging obtained by single molding from the VSP from a thin-walled tape, due to the stretching of the walls of the tape during molding by double vacuum.

The specified technical result in part of the first method is achieved by the fact that in the method of forming products for packaging products, which consists in heating the sheet of expanded polystyrene to the state of the possibility of plastic deformation and feeding it into the molding unit on the punch, moving the sheet of expanded polystyrene with a punch in the direction of the matrix and creating a vacuum in the cavity between the die and the expanded polystyrene sheet and a vacuum in the cavity between the punch and the expanded polystyrene sheet to impart a matrix for the nest of the matrix, for a sheet of expanded polystyrene foam, in which layers of sheet material externally located and located adjacent to the outer surface are made with closed pores, and a layer of sheet material located between layers with closed pores is made with open, communicating with each other pores, a vacuum is formed in the cavity between the punch and the expanded polystyrene sheet after completion of the shaping process in the matrix while maintaining a vacuum in the cavity between the matrix and the expanded polystyrene sheet roll, the vacuum between the punch and the quantity of foamed polystyrene sheet is less than the vacuum in the cavity between the die and foamed polystyrene sheet and equal force on the top layer of plastic deformation of the sheet material disposed between layers of a closed cell.

The specified technical result in terms of the device is achieved by the fact that in the device for hot forming products, mainly for packaging products containing a pressure plate with elements for placing on it a heated sheet of expanded polystyrene, a matrix with slots, the shape of which repeats the external shape of the products, the mechanism for moving the pressure plate in the direction of the matrix and the system for creating a vacuum in the cavities of the nests of the matrix and on the side of the working surface of the pressure plate, the system for creating a vacuum is made with the possibility of vacuum generation from the side of the working surface of the pressure plate with a time delay after the formation of vacuum in the cavities of the nests of the matrix and the simultaneous termination of the vacuum in the cavities of the matrix and from the working surface of the pressure plate.

The specified technical result in part of the second method is achieved by the fact that in the method of increasing the wall thickness of the products for packaging products during molding, which consists in supplying the possibility of plastic deformation of the expanded polystyrene sheet to the plastic forming unit and moving this sheet with a pressure plate in the direction of the matrix, creating a vacuum in the cavity between the matrix and the sheet of expanded polystyrene to give the product the shape of the nest of the matrix and the vacuum in the cavity between the pressure plate and a sheet of expanded polystyrene after completion of the shaping process in the matrix while maintaining a vacuum in the cavity between the matrix and the sheet of expanded polystyrene, while the vacuum value between the pressure plate and the sheet of expanded polystyrene is chosen less than the vacuum in the cavity between the matrix and the sheet of expanded polystyrene and equal by force the beginning of plastic deformation of the material of this sheet.

These signs are significant and interconnected with the formation of a stable set of essential features sufficient to obtain the desired technical result.

The present invention is illustrated by specific examples of execution, which, however, are not the only possible, but clearly demonstrate the ability to achieve the desired technical result.

Figure 1 shows a device for hot molding with the introduction of a strip of IPN;

figure 2 - the formation of the surface of the tray by evacuation on one side;

figure 3 - the formation of the surface of the tray by evacuation on the other hand and the expansion in thickness.

According to the present invention, an improved technology for producing trays by thermoforming a sheet 1 of expanded polystyrene is considered. Based on such a tape, it is possible to form trays for packaging food products and substrates with a perforated single layer, which ensures the absorption of liquid by its penetration into the structure of the middle layer of the tape.

Traditionally, when forming thick-walled trays from sheet 1, the resulting product has an increased weight, which negatively affects the weight quality indicator of the product, since the wall thickness of the tray is determined by the thickness of the tape. To obtain lightweight trays with a wall thickness exceeding the thickness “a” of the sheet 1 entering the device for hot forming, it is proposed to form trays of tape, the thickness of which is significantly less than the required wall thickness of the tray.

To form a polystyrene foam sheet 1 in a hot forming apparatus, this sheet is first heated in a infrared heating furnace to a certain temperature. Then, the heated section of the sheet 1 is fed into the hot forming device (Fig. 1), the forms of which — the lower plate (punch 2) and the upper die 3 — are closed, which means that the matrix 3 and punch 2 come close to each other with a tight fit around the periphery (based on the tape or on each other upon receipt of fragments of the tape) to eliminate the loss of vacuum. Moreover, the distance between the die and the punch in the molding zone is greater than the thickness of the sheet 1 heated in the furnace.

A strip (sheet 1, a fragment of a tape) made of expanded polystyrene is subjected to deep drawing on both sides using a vacuum acting on both sides (from vacuum pumps 4), which load the die and punch. In the matrix and punch, through channels 5 are made for pumping air from the cavities formed between the tape and the molding surface of the matrix and between the tape and the molding surface of the punch.

Both the matrix and the punch are cooled by water or some other liquid, i.e. maintained at a certain temperature, which is required to ensure the curing of products molded from strip (tape). By curing the product, shape retention is ensured.

In this case, the molding process is adjusted according to the timing diagram for switching on the vacuum units for the die and punch. First, vacuumization is performed from the die side (FIG. 2) to shape the product, and then, while maintaining vacuum on the die, vacuum is performed (FIG. 3) from the punch side of the cavity (the cavity is formed by pressing the strip against the die under vacuum). At this moment, the surface of the molded tray on the side of the punch is pulled (broadened by the value of "b") and is adjacent to the surface of the punch. When pulling, the middle layer of the strip stretches with increasing porosity and width of the walls of the tray while maintaining the weight of the tray equal to the weight of the part of the tape from which this tray is molded. The tray with a wall thickness equal to "c" (c = a + b, mm) is subjected to cooling to fix the form.

A feature of this technological process is that the tape stretching process is carried out when the tape is heated, during which plastic deformation processes are possible, while the formed tape is held in the matrix sockets by the vacuum from the matrix side, when the vacuum on the punch is turned on only after completion of the molding process on the matrix, provided that between the punch and the molded tray in the matrix there is a gap equal to the broadening of the walls of the tray, and that the vacuum on the punch is less than the vacuum by matrix and is equal in strength to which plastic deformation occurs in a heated foam polystyrene tape.

Another feature of the new method is that all temperature and time regimes are maintained unchanged at which thermoforming of the material from the VSP occurs by any known method.

From this follows the possibility of formulating a new method for increasing the wall thickness of products during molding, which consists in supplying a plastic deformation of a sheet of expanded polystyrene heated to a state of possibility of plastic deformation to the molding unit and moving this sheet with a pressure plate in the direction of the matrix, creating a vacuum in the cavity between the matrix and the sheet of expanded polystyrene to give the product the shape of a matrix slot and vacuum in the cavity between the pressure plate and the expanded polystyrene sheet after completion formation process in the matrix while maintaining a vacuum in the cavity between the matrix and the expanded polystyrene sheet, while the vacuum value between the pressure plate and the expanded polystyrene sheet is less than the vacuum in the cavity between the matrix and the expanded polystyrene sheet and the force of plastic deformation starting equal material of this sheet.

Figure 1-3 schematically shows the process of expanding the thickness of the sheet 1 with a thickness of, for example, 3 mm of VSP in the installation for hot molding, which consists of two forms 2 and 3. Both forms 2 and 3 are mounted with the possibility of reciprocating movement perpendicular to the direction of transportation sheet 1. The upper form contains a matrix, described in more detail below, with which the outer side of the product made of VSP, for example, a tray, is molded. The lower mold contains, inter alia, a punch with which the lower side of the article is molded. To form sheet 1 from a VSP in a hot forming apparatus 2, the sheet is first heated in an infrared heating furnace not shown in the drawing to a certain temperature. Then, the heated portion of the sheet 1 is fed into a hot forming device, the shapes of which are closed, which means that the die and punch are approaching each other in the forming zone to a predetermined distance, for example 5-7 mm.

A strip of VSP is subjected to deep drawing on both sides with the help of a vacuum acting on both sides, with which the matrix and punch are loaded. After a certain time of evacuation and cooling in still closed forms of the thermoforming device, perforation of a smooth closed surface tray can be carried out. For this, the movable needles provided in one of the forms are extended using compressed air.

The considered principle of obtaining a broadening of the wall thickness of a tray from VSP can be applied to a VSP sheet in which the layers of sheet material externally located and located adjacent to the outer surface are made with closed pores, and the layer of sheet material located between the layers with closed pores is made with open, interconnected pores. For this type of VSP, a new method of molding products for packaging products can be formulated, which consists in heating a sheet of expanded polystyrene to the state of the possibility of plastic deformation and feeding it into the molding unit on the punch, moving the sheet of expanded polystyrene with a punch in the direction of the matrix and creating a vacuum in the cavity between the die and the expanded polystyrene sheet and the vacuum in the cavity between the punch and the expanded polystyrene sheet to give the product a shape of a die cavity. In this case, a vacuum is formed in the cavity between the punch and the expanded polystyrene sheet after the formation of the matrix is completed while maintaining a vacuum in the cavity between the matrix and the expanded polystyrene sheet, while the vacuum between the punch and the expanded polystyrene sheet is less than the vacuum in the cavity between the matrix and a sheet of expanded polystyrene and is equal in strength to the beginning of plastic deformation of the layer of material of the sheet located between the layers with closed pores.

The vacuum creation system is configured to form a vacuum from the side of the working surface of the pressure plate with a time delay after the formation of vacuum in the cavities of the nests of the matrix and at the same time terminate the vacuum in the cavities of the matrix and from the working surface of the pressure plate.

Claims (3)

1. The method of forming products for packaging products, which consists in heating the sheet of expanded polystyrene to the state of the possibility of plastic deformation and feeding it into the molding unit on the punch, moving the sheet of expanded polystyrene with a punch in the direction of the matrix and creating a vacuum in the cavity between the matrix and the sheet of expanded polystyrene and vacuum in the cavity between the punch and the sheet of expanded polystyrene to give the product the shape of a socket matrix, characterized in that for a sheet of expanded poly tyrol, in which the layers of sheet material externally located and located adjacent to the outer surface are made with closed pores, and the layer of sheet material located between the layers with closed pores is made with open, interconnected pores, in the cavity between the punch and the sheet of expanded polystyrene form a vacuum after completion of the forming process in the matrix while maintaining a vacuum in the cavity between the matrix and the sheet of expanded polystyrene, while the magnitude of the vacuum between the punch and the sheet of expanded polystyrene is less than the vacuum in the cavity between the matrix and the expanded polystyrene sheet and is equal in strength to the onset of plastic deformation of the sheet material layer located between the closed-cell layers. 2. A device for hot forming products, mainly for packaging products, containing a pressure plate with elements for placing a heated sheet of expanded polystyrene on it, a matrix with slots, the shape of which repeats the external shape of the products, the mechanism for moving the pressure plate towards the matrix, and a vacuum system in the cavities of the nests of the matrix and from the side of the working surface of the pressure plate, characterized in that the vacuum system is configured to form a vacuum from the side of the working surface and a pressure plate with a time delay after the formation of vacuum in the cavities of the nests of the matrix and the simultaneous termination of the vacuum in the cavities of the matrix and from the working surface of the pressure plate. 3. A method of increasing the wall thickness of products for packaging products during molding, which consists in supplying a plastic deformation of the expanded polystyrene sheet heated to the state of possibility of plastic deformation in the molding unit and moving this sheet with a pressure plate in the direction of the matrix, creating a vacuum in the cavity between the matrix and the foam sheet polystyrene to give the product a shape of a matrix socket and a vacuum in the cavity between the pressure plate and the expanded polystyrene sheet after completion of the shaping process in the matrix, while maintaining a vacuum in the cavity between the matrix and the expanded polystyrene sheet, the vacuum value between the pressure plate and the expanded polystyrene sheet is less than the vacuum in the cavity between the matrix and the expanded polystyrene sheet and the force of plastic deformation of this sheet .

Images