RU2421333C1 - Method of producing moisture absorbing tape from foamed polystyrene and package made thereof (versions) - Google Patents

Abstract

FIELD: process engineering. ^ SUBSTANCE: invention relates to packages and may be used in producing moisture absorbing tape from foamed polystyrene and package made thereof. Package represents a tray extruded from foamed polystyrene sheet with bottom to accommodate products and lateral walls inclined with bottom and made flanged. Note here that said bottom is provided with recesses or holes for fluid to flow inside the bottom layers made on the tray cavity side. One-piece tray is made from foamed polystyrene sheet wherein material layers, both outside and adjoining outer surface, have closed pores while sheet material layers arranged between aforesaid layers have open pores communicated via recesses or hole with tray cavity in the zone of product laid in the tray. ^ EFFECT: product moisture absorption, simplified extrusion. ^ 3 cl, 1 dwg

Description

The invention relates to the production of packages, and in particular 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, self-service chain 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 100% of its own density. Foaming can take place during extrusion, as well as during post-formation operations, such as 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 consists of many non-communicating 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 relatively low price 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 a moisture-absorbing layer - absorbent trays, most often used for meat products, is relevant. Made entirely of polystyrene, these trays are environmentally friendly (recyclable after recycling). Their design allows you to drain juice from the product 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 held there. 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 packaging film - this is a key advantage of this type of packaging. The edges of the packaging and the packaging 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 unevenly placed 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 wet or sticky packages. The process of processing and disposal of such a tray is simplified due to the fact that all layers are made of the same 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). The blowing agent is gases (butane, isobutane, pentane, etc.), which are introduced into the cylinder of the primary extruder in a liquid state. Each extruded polystyrene foam extrusion line consists of primary and secondary extruders. 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 mandrel (cylinder 1-2 m long) and then the tape, cooled on the mandrel, enters the pulling rolls and then onto the winder. After this, the rolls with tape go through the maturation stage for several 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.

The disadvantage of this method of obtaining a tape of expanded polystyrene is that it is a known technology for the manufacture of conventional foam tape, in which most pores remain closed. Products obtained from such a tape do not have moisture-absorbing properties. To obtain packaging from IPNs with a highly absorbent layer inside, a tray is made that is considered as a basic power element. Then, a moisture-absorbing layer is formed on the working surface of the tray (the working surface is the surface on which the product is laid), which is created by laying a hydrophobic gasket, on top of which a protective layer is placed (may be made of UPU), in which holes are made for the passage of moisture (liquid) into the gasket . Despite the fact that IPN in the form of a tape has a porous structure, cooling and maturing preserves the uniformity of the structure of the tape, in which closed pores are combined with open pores. Such a tape is not hygroscopic, due to the absence of conditions for the penetration of water molecules or water droplets into internally located pores in the structure of the tape.

An example of such a package that implements the function of absorbing moisture is described in DE 29723954, B65D 81/26, 1999-12-02. This patent source describes a package that is a tray made by molding from a sheet of expanded polystyrene and includes a bottom from which flanged walls extend at a slight slope. A moisture-absorbing pad was laid on the bottom of the tray with a strike on the walls, on top of which an outer protective layer of expanded polystyrene was applied, with the edges fixed on the walls of the tray above the level of the perimeter of the strip. At the same time, holes are provided in the outer protective layer in the area of the bottom of the tray for moisture to enter the gasket. This decision was made as a prototype for the claimed device.

The disadvantage of this packaging - tray is the complexity of the design and the need to form the base tray, the protective outer layer in the form of a tray and gaskets made of a material other than foamed polystyrene, which then must be assembled and fastened with a snug fit between the layers. For single-use packaging, such a manufacturing process leads to an increase in its cost, which is unjustified in relation to packaging that belongs to the category of single-use / use.

The present invention, in terms of the method, is aimed at solving the technical problem of obtaining an IPN with a structure in which the externally located layers are made with closed pores and the internally located layer is made with open pores and is absorbent, that is, capable of absorbing moisture. The present invention in terms of the device is aimed at solving the technical problem of obtaining packaging such as a tray or substrate, with the function of absorbing moisture from the product when forming the tray from a single-layer IPN of a heterogeneous structure.

The technical result achieved in this case is to simplify the design of the package by obtaining it by one-time molding from the UPU tape having an inhomogeneous structure in thickness. In terms of the method, the technical result achieved in this case is to improve the physicochemical and operational characteristics of the IPN to enable simplification of the process of forming the package with the function of moisture absorption.

The specified technical result in terms of the method is achieved by the fact that in the method for producing a moisture-absorbing tape from foamed polystyrene, which consists in filling granules into the extrusion line of polystyrene and adding talcum powder, followed by stirring at a given temperature until a melt is formed, and then a technological additive is added to the melt in liquid form for the implementation of the foaming process, in mixing these components with the melt at a given pressure and supplying melt pressure to the line head, p and the exit from which the process of foaming polystyrene is carried out with the formation of a bubble, which is pulled onto the mandrel and sent to the pulling rolls to form a sheet web of a given width and thickness, with stirring, a hydrophobic additive is added to the melt, and when the melt leaves the extrusion line head, under normal environmental pressure, intensive cold air blowing of the outer layers of the tape to form surface layers with closed pores and maintaining open pores inside the tapes.

The specified technical result in part of the device is achieved by the fact that in the packaging for a moisture-containing food product, which is a tray made by molding from a sheet of foamed polystyrene, which includes a bottom for placing the food product, side walls that are inclined with respect to the bottom surface and made with a flange, while in the bottom from the side of the cavity of the tray, recesses or holes are made, with a depth of part of the thickness of the bottom material for draining liquid into the inner layer of the bottom, lotto made of monoblock polystyrene foam sheet in which the layers of sheet material externally located and adjacent adjacent to the outer surface are closed pores, and the layer of sheet material located between the closed pore layers is made with open, communicating pores, some of which are communicated through recesses or openings with a cavity in the tray in the area of the product in the tray.

The specified technical result in part of the device is achieved by the fact that in the substrate for a moisture-containing food product, which is a plate made by molding from a sheet of foamed polystyrene, while in the plate from the side intended to accommodate the food product, recesses or holes are made with a depth of part of the thickness of the material plates for draining liquid into the inner layer of the plate, the latter is made monoblock from a sheet of foamed polystyrene, in which layers of the sheet material are externally spaced married 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, communicating pores, some of which are communicated through recesses or openings with the cavity of the tray in the product placement area on the plate.

These features are significant and are 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.

The drawing shows a tray made of IPN with moisture-absorbing properties for products.

According to the present invention, the design of packaging for food products, especially for moisture. The invention in terms of packaging design is considered on the example of a tray, which can equally apply to packaging of a different shape, for example, in the form of a substrate or a cup-shaped shape or in the form of a different shape.

The tray is made in monoblock thermoforming in a known manner from a foam polystyrene tape and has a bottom 1, from which side walls 3 leave a slight slope through smooth arcuate transitions 2. The side walls 3 are made with flanging 4. The tray is designed for laying in and placing the food product 5, mainly moisture-containing. During storage, such a product is usually closed with a packaging film 6, which excludes or reduces the gas exchange of the product with an oxygen-containing atmosphere in order to extend the shelf life of the food product in a fresh state. Located on the bottom of the tray 1, the food product 5 releases moisture in the form of a liquid that drains to the bottom of the tray.

For the manufacture of the tray, a foam polystyrene tape was used, the feature of which is that it is a material that is uniform in thickness and area with the structure of cells or pores, which are closed in the outer layers 7 of the tape and do not communicate with the atmosphere, but in the inner layer 8 located between the outer layers 7, the cells or pores are made open, communicating with each other and with the atmosphere through open pores at the ends 9 of the tape, formed by cutting off the tray from the burr when opening the formed trays. On the bottom 1 side, in the direction of the inner layer, through the outer protective layer on the side of the tray cavity, recesses 10 or blind holes are made through which the pore cavities of the inner layer communicate with the atmosphere, and when the product is closed with a film, with the tray cavity under this film.

If it enters the bottom of the tray, liquid that has leaked or drained from a food product, for example, from chicken or from a piece of meat, flows into recesses or blind holes and penetrates into the communicating pores of the inner layer. Since a hydrophobic additive was added to the polymer during the molding of a sheet of foamed polystyrene, it is possible for water (liquid) molecules to flow into the inner layers of the tape without clinging to the roughness of the material. The addition of antistatic type in the manufacture of the tape and the molding of the product provides a reduction in roughness, ensuring a smooth surface of the tape.

Since in any porous structure obtained as a result of the natural replacement of isobutane by air (during storage of the tape for a while), locally located groups of pores are communicated with each other, as practice shows, such groups or some of them have an exit through the open end to the outside , that is, has a message with the atmosphere. This property allows the formation of a unidirectional process of slow evaporation of moisture from pores in the inner layer through the open ends of the tray. In this regard, the accumulation of liquid does not form at the bottom of the tray.

The substrate for the moisture-containing food product is a plate formed by molding a sheet of expanded polystyrene, while in the plate on the side intended to accommodate the food product, recesses or holes are made with a depth of part of the thickness of the material of the plate for draining liquid into the inner layer of the plate. The plate is made monoblock from a sheet of foamed polystyrene, in which the layers of sheet material externally located and 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 pores, communicating pores, some of which communicated through recesses or holes with the cavity of the tray in the area of product placement on the plate.

For the data of the tray and the substrate, a foam polystyrene tape is used in which the layers of the structure adjacent to the outer surface of the tape are made with closed pores, and the layer of the structure located between the outer layers is made with open interconnected pores.

The production of such a foamed tape is that along with the main polymeric material, in this case general purpose polystyrene, talc and a blowing agent are added - a gas, for example isobutane. Talc is added together with polystyrene, and gas is added somewhat later at the end of the primary extruder. Gas is introduced into polystyrene in its molten state. Bubbles of talc are a kind of conductor of gas bubbles. In this molten state, the mass passes into the secondary extruder, where it is further mixed and a certain stable state is achieved. The most important process indicators are melt pressure and temperature. Then comes the most important event - the transfer of mass into a cylindrical head and the exit of mass from the head. It is at this moment that foaming of the melt begins, as the mass leaves the head, where it was under high pressure, and is in a medium with normal pressure. In this very short period of time, the main foaming processes take place. Then the tape bubble is pulled onto the cylinder (mandrel) and moves to the pulling rolls. The frequency of their rotation and the tension force affect the characteristics of the tape. Then the tape is wound on a rewinder. This technology for the production of foamed polystyrene tape used for subsequent thermoforming of products is known and is described, for example, in RU No. 2133671, В29С 67/20, В29С 51/08, 07.27.1999.

The method of producing expanded polystyrene is carried out by mixing in the extrusion line of granular polystyrene containing talc, not more than 20 wt.% Blowing agent and not more than 1 wt.% Antistatic, foaming the mixture at a temperature above the glass transition temperature of polystyrene, followed by keeping the expanded polystyrene at room temperature however, after mixing, a partial removal of not more than 60 wt.% a blowing agent is carried out by keeping the mixture at a temperature below the glass transition temperature styrene.

The effect of talc as a nucleating additive is based on the homogeneous distribution of particles in the polymer melt and on the ability to capture gas bubbles formed at the time of foaming. Particles of talcum having a sheet-like (scaly) structure capture gas bubbles, they form aggregates of several particles in the polymer melt, inside which gas bubbles are placed. In this regard, it becomes possible to achieve a uniform distribution of gas bubbles in the polymer mass. The result is a foamed sheet with a close to uniform porous structure.

Examples of particularly suitable blowing agents are aliphatic hydrocarbons containing from 2 to 6 carbon atoms, such as propane, butane, n-pentane, isopentane, hexane, cyclohexane, etc., which can be used either as individual compounds or in mixtures, petroleum ether and halogenated derivatives of C ₁ -C ₃ aliphatic hydrocarbons, such as various chlorofluoro derivatives of methane, ethane and ethylene, such as dichloro-difluoromethane, 1,2,2-trifluoroethane, 1,1,2-trichloro ethane etc. The foaming agent is usually used in an amount of from 2 to 20, and preferably in the range of 4 to 10 by weight relative to the polymer.

Antistatic agents are those compounds that are commonly used in order to improve surface properties, finishes, free flow, and processability of styrene polymer particles. Such antistatic agents are well known and described in the technical literature, as an example, K. Johnson, Antistatic Compositions for Textiles and Plastics, Noyes Data Corporation, Park Ridge NJ, 1976 can be mentioned here. Examples of antistatic agents that can be used in the method according to the present invention are fatty acid esters, such as butyl stearate, mono-hydroxy or polyhydroxy alcohols, such as glycerol, amines, such as, for example, ethoxylated tertiary alkylamine, dialkanolamine fatty acids, amides, such as, for example, N, N- bis- (2-hydroxyethylstearamide), poly hydroxyethylene derivatives, such as, for example, polyethylene glycol hexadecyl ether, ethylene oxide / propylene oxide copolymers, aminated soaps, such as, for example, octadecylamine salt of stearic acid, amine salts of alkyl sulfates, such as, for example, octadecyl sulfate, guanidine such as, for example, octadecyl-trimethyl ammonium chloride, alkyl phosphates, such as, for example, bis-dodecyl acid phosphate, amine salts of alkylphosphinic acids, such as, for example, the octadecylphosphine salt lots with triethanolamine etc.

Antistatic agents that are preferred for use in the method according to the present invention are: an ethylene oxide / propylene oxide block; block copolymers with an ethylene oxide content in the range of 10 to 50% by weight and a molecular weight in the range of 1000 to 5000 known in the market under the trade GIENDION®, or ethoxylated tertiary alkylamine, known in the market under the trademark 1.C.1.

The amount of antistatic agent is usually not more than 1 relative to the polymer, i.e. it ranges from 0.001 to 0.5 and preferably from 0.010 to 0.1 by weight relative to the polymer.

The polymer particles can be coated with an antistatic agent by mixing methods that are well known in the literature, for example, foaming particles can be treated with an appropriate amount of antistatic agent in a rotating drum or cylinder.

Coating the particles with an antistatic agent facilitates the further sieving step, which makes it possible to obtain different fractions, each of which has a controlled particle size and is suitable for various applications.

The polymerization of styrene, preferably in an aqueous suspension, the addition of a foaming agent, preferably during polymerization, and the conversion of particles into molded products by molding inside closed molds are carried out by technical means that are widely known in the literature and are widely described, for example, in Rigid Plastic Foams by TNFezzigno Reinhold Publishing Corp. New York, USA. (1963).

Methods of extruding various foamable compositions are described in many patents, for example, in US patents N 2409910, 2525250, 2699751, 2848428, 3121911, 3770688, 3960792, 3966381, 4085073, 4146563.

A feature of the present invention is that at the moment the melt exits from the head, intensive blowing with cold air of the outer layers of the tape is carried out, thus forming surface spores with closed pores. Inside the pores can remain open.

Now about the manufacturing technology of moisture-absorbing tapes. In this case, a special hydrophobic additive is added, which allows moisture molecules to flow into the inner layers of the tape without clinging to the material of the tape. Thus, the task is to create surface layers of tape with closed pores (two layers of 5-10% thickness) and an inner layer with open pores (80-90% of thickness), the task of which is to absorb moisture.

Fatty acids make the surface of the filler hydrophobic, which, firstly, increases the compatibility of the filler with a non-polar polymer, and secondly, significantly reduces water absorption during storage of the filler. The treated filler, having, like the polymer, a hydrophobic surface, is much more easily distributed in the polymer matrix, and the final melt has a lower viscosity, which reduces the load on the equipment and prevents mechanical degradation. In addition, the absence of large pigment aggregates and low melt viscosity can improve equipment performance.

The following additives can be used in polystyrene with varying degrees of dispersion, from solutions to emulsions and various chemical nature: acrylic polymer (AP), polyvinyl acetate (PVA), superplasticizer (C-3), detergent (MS), pecked-tint washed (PTO) ), carboxymethyl cellulose (CMC), styrene butadiene latex (BDSL) at a dosage of 0.2-0.8% by weight of polystyrene.

Claims (3)

1. Packaging for a moisture-containing food product, which is a tray made by molding of a sheet of foamed polystyrene, which includes a bottom for placing the food product, side walls that are inclined with respect to the bottom surface and are made with a flange, while in the bottom with the sides of the cavity of the tray have recesses or holes with a depth of part of the thickness of the bottom material for draining liquid into the inner layer of the bottom, characterized in that the tray is made monoblock of a sheet of foamed a roll in which the layers of sheet material externally located and adjacent to the outer surface are closed pores, and the layer of sheet material located between the closed pore layers is made with open, communicating pores, some of which are communicated through recesses or openings with a cavity tray in the product placement area in the tray. 2. A substrate for a moisture-containing food product, which is a plate made by molding from a sheet of foamed polystyrene, while in the plate from the side intended to accommodate the food product, recesses or holes are made with a depth of part of the thickness of the material of the plate for draining liquid into the inner layer of the plate, characterized in that the plate is made monoblock from a sheet of foamed polystyrene, in which layers of sheet material, externally located and located adjacent to the outer surface The surfaces are made with closed pores, and the layer of sheet material located between the layers with closed pores is made with open, communicating pores, some of which are communicated through recesses or openings with the cavity of the tray in the product placement zone on the plate. 3. A method of producing a moisture-absorbing foam polystyrene tape, comprising filling granules into polystyrene into an extrusion line and adding talc, followed by stirring at a given temperature until a melt is formed, then adding a technological additive to the melt in liquid form to carry out the foaming process, mixing these components with a melt at a given pressure and supplying melt pressure to the head of the line, upon exiting from which the process of foaming polystyrene with the development of a bubble, which is pulled onto the mandrel and sent to the pulling rolls to form a sheet web of a given width and thickness, characterized in that when stirring a hydrophobic additive is added to the melt, and when the melt leaves the extrusion line head, intensive cold blowing is carried out at normal ambient pressure air the outer layers of the tape to form surface layers with closed pores and maintaining open pores inside the tapes.

Images