RU2635138C1 - Method to produce foamed polymer and line for its implementation - Google Patents

Abstract

FIELD: technological processes.

SUBSTANCE: process for production of polyethylene foam includes mixing thereof with a foaming chemical agent, extruding hot mix, forming a film and calendering thereof, cross-linking before polyethylene foaming, dicumyl peroxide is used as a cross-linking agent, azodicarbonamide is used as a foaming agent, before mixing with initial polymer the foaming and cross-linking agents are mixed with each other at a temperature below their melting point, the resulting mixture of agents is mixed with polyethylene granules in extruder with zonal temperature distribution from 105°C to 125°C, the distribution of temperatures along the zones of the extruder is carried out due to preheating of components and softening of polyethylene, the components are mixed in accordance with formula, wt %: polyethylene 84.5; cross-linking agent 0.5; foaming agent 15, the formed polyethylene matrix film of given thickness is sent for final cross-linking and subsequent foaming to the cross-linking and foaming line with preheating, cross-linking, and two zones of uniform expansion, at that, the preheating zone temperatures are 160-180°C, cross-links at 185-200°C, zones of uniform foaming at 210-230°C and 230-245°C, with the possibility for adjusting temperature in each zone, feeding the polyethylene matrix film after the extruder, moving thereof in the cross-linking and foaming line and after the line at each stage with adjustment of drawing rate; after foaming in the furnace last zone, the polyethylene foam is cooled on cooling rolls to a temperature of the cooling rolls. The foam polyethylene production line includes a mixer for components, an extruder, conveying and calendering devices, the mixer being provided with dispensers for mixing the cross-linking and foaming agents with a mixing temperature below their melting point, the extruder blending a mixture of crosslinking and foaming agents with polyethylene granules is installed after the mixing station and made by with two augers and zonal temperature distribution with three temperature zones: a charging hopper with partial softening and decomposition temperature of the components at 105°C, working area of augers with softening and melting temperature of components, distribution of components throughout the volume and mixing thereof at 105-110°C, the extruder head zone with mix viscosity decrease temperature, partial decomposition and melting of the cross-linking agent, and forming film at 125°C, after the extruder the line for cross-linking and foaming is installed and connected with the extruder outlet by the transportation and calendering device and made with four temperature zones: film preheating at 160-180°C, cross-links at 185-200°C, beginning of uniform foaming at 210-225°C, completion of foaming at 230-245°C, the cross-linking and foaming line is equipped with adjustable ventilation system, the output of the cross-linking and foaming line is equipped with film cooling rollers.

EFFECT: adjusting pore formation process, providing uniformity of pore formation, reducing pore size and dispersion of their geometric dimensions.

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Description

The invention relates to methods for producing foamed polymers that can be used as heat-insulating, sound-insulating, vibration-insulating material in construction and in the repair of residential, office, industrial premises, ventilation pipes, as well as for the manufacture of orthopedic products, elastic elements for shoes.

Known methods for producing foams, which include obtaining a mixture of molten polymer and a blowing agent under pressure, bringing the molten mixture to a temperature of at least 180 ° C, extruding the mixture into a reduced pressure region so that the mixture expands to form a foamed polymer. In addition to the main components, the mixture may contain various additives that improve the technological properties of the mixture and the operational characteristics of the final product (see RF patent No. 2484108, Extruded polymer foams containing brominated 2-oxo-1,3,2-dioxaphosphorinan compounds as flame retardants, IPC C08J 9/00, published June 10, 2013). The blowing agent includes water, carbon dioxide, or both. The main disadvantage of this method is the foaming process in the extrusion head, which does not allow you to adjust the process of pore formation, pores are formed large and with a wide spread of their sizes. The formation of large pores reduces the strength of the final product and worsens all the main indicators, such as heat, noise, vibration isolation.

A known extrusion method for producing polymer foam (RF application for invention No. 2012133296, Machinable heat-insulating polymer foam, IPC C08J 9/14, published 02/20/2014), which includes obtaining a matrix of a thermoplastic polymer at an initial softening temperature and an initial pressure of a foamable polymer composition blowing agent from water, 1,1,1,2-tetrafluoroethane and difluoromethane / 1,1-difluoromethane. The initial pressure is high enough to prevent foaming due to expansion of the blowing agent. A method for producing foam also includes cooling the foamable composition to a foaming temperature that exceeds the softening temperature if the initial temperature exceeds the foaming temperature. The method also includes extruding a foamable polymer composition through a foamable extrusion die into a pressure region below the initial one to allow expansion of the foamable composition by the blowing agent to form a polymer foam. The final product obtained by this method has an average vertical pore size in the range from 0.5 to 1.8 mm and a density in the range from 24 to 40 kg / m ³ , the reduced roughness coefficient is 3.5 mm or less. The disadvantage of the described method is the lack of crosslinking of the polymer and the use of the extrusion process for foaming, which leads to poor quality of the final product.

The closest analogue is the method of producing a product from thermoplastic, application of the Russian Federation for invention No. 2013127635, IPC В29С 44/50, published January 27, 2015, in accordance with which the method involves mixing a thermoplastic polymer with a foaming chemical agent, hot extrusion of the mixture and obtaining a sheet with a thickness of 0 5-3 mm by calendaring the extruded mixture. As a foaming chemical agent, citric acid is used. The closest analogue reflects the elements of equipment for implementing the method, which includes a mixer, an extruder, a calendaring system for moving the film and forming its parameters. The disadvantage of the described analogue is the foaming process in the extrusion head, which does not allow to control and regulate the process of pore formation, pores are formed large and with a wide spread of their sizes. In the extruder, it is only possible to set some specific temperature close to the required temperature, which is not enough to ensure good product quality. This problem is especially relevant when changing the supply lines of components or when changing the supplier of these components.

The objective of the invention is to improve the quality of the foam, its strength properties.

The technical result is the provision of regulation of the process of pore formation, ensuring uniform pore formation, reducing the size of pores and reducing the spread of their geometric dimensions.

The problem is solved and the technical result is realized in a method for producing a foam polymer, which includes mixing a thermoplastic polymer with a foaming chemical agent, hot extrusion of the mixture, forming a film and calendering to move it and form its desired thickness.

The difference of the proposed method from the prototype is the following:

- before foaming, the polymer is crosslinked;

- as a cross-linking agent take dicumyl peroxide;

- as a blowing agent take azodicarbonamide;

- before mixing with the starting polymer, foaming and crosslinking agents are thoroughly mixed with each other at a temperature below their melting point;

- the resulting mixture of agents is mixed with polymer granules in an extruder with a zonal temperature distribution from 105 ° C to 125 ° C (for polyethylene);

- the temperature distribution over the zones of the extruder is carried out from the need for pre-heating the components, softening the polymer, conducting partial crosslinking of the polymer and forming a matrix film;

- mixing is carried out in accordance with the recipe, mass. %:

Polymer 84.5 Crosslinking agent 0.5 Blowing agent fifteen

- the formed matrix film of a given thickness is sent for final crosslinking and foaming to the crosslinking and foaming line with temperature zones (for polyethylene): preheating 160-180 ° C, crosslinking 185-200 ° C, the beginning of uniform foaming 210-225 ° C, completion foaming 230-245 ° C, with the ability to control the temperature in each zone;

- the supply of the polymer matrix film after the extruder, its movement in the line itself and after the line at each stage is carried out with the ability to control the speed of drawing to form the web of the desired thickness, width and density;

- after foaming in the areas of foaming of the stitching line and foaming, the resulting foam polymer is cooled on cooling shafts to the temperature of the cooling shafts;

- after cooling, the foamed polymer film is wound on bobbins and / or cut into the size of the final product;

- trim from the edges of the matrix film and the final product is sent for processing as recyclable materials.

The problem is also solved by the construction of a foam polymer production line, including a component mixer, an extruder for forming a film from an extruded mixture, a film calendaring device for moving it and forming its parameters.

The difference between the line for the production of foam from the prototype is

- the implementation of the mixer with dispensers for mixing crosslinking and foaming agents at a temperature below their melting point;

- the extruder installed after the mixing station is twin-screw with a zonal temperature distribution from 105 ° C to 125 ° C (for polyethylene) with three temperature zones: extruder feed hopper for partial softening and melting of components with a temperature of 105 ° C, working zone screws for softening and melting the components, distributing the components throughout the volume and mixing them with a temperature of 105-110 ° C, extruder head area with a temperature of 125 ° C to reduce the viscosity of the mixture, partial decomposition and melt effects of a crosslinking agent and for film formation;

- after the extruder there is a crosslinking and foaming line connected to the extruder exit with a calendaring device made with four temperature zones (for polyethylene): preheating 160-180 ° C, crosslinking 185-200 ° C, the beginning of uniform foaming 210-225 ° C, completion of foaming 230-245 ° C, with the possibility of regulating the temperature in each zone;

- the line for stitching and foaming is equipped with a controlled ventilation system;

- the output of the stitching and foaming line is equipped with cooling rolls of the film;

- the device for calendaring the polymer film after the extruder, in the line of crosslinking and foaming and after the line of crosslinking and foaming is configured to control the speed of the film.

A known process of polymer crosslinking in order to increase its strength (www.chem21: info / info / 308651). Known crosslinking agent is dicumyl peroxide (www.chem21: info / info / 168114) and azodicarbonamide as a blowing agent (RF patent 2230078); their combined use is known with a temperature range of 190-250 ° C as a mixture of a crosslinker and a blowing agent (www.chem21: info / info / 168114); It is known to use extruders for mechanically mixing components to a homogenized state and forming films of a given width from them (promresursy.com/materialy/proizvodstvo.../exstruder-dlya-plastika.html).

However, the preliminary mixing of crosslinking and foaming agents, the mixing of components with polyethylene in an extruder with a zonal temperature distribution, and the use of extruders with a zonal temperature distribution with partial polymer crosslinking are unknown. The choice of the above temperature mode of operation of the extruder is also unknown, in which the process of chemical crosslinking of the resulting matrix web in the extruder itself partially starts, which allows to increase the strength of the web when forming its thickness on calendars. The process of zonal heating of the matrix film in the crosslinking and foaming lines according to the described temperature change algorithm is unknown; unknown designs of heating furnaces with a four-zone temperature distribution in the following sequence: first crosslinking zone 160-180 ° C, 2nd crosslinking zone 185-200 ° C, 3rd foaming zone 210-225 ° C, 4th foaming zone 230- 245 ° C and their use. Such a temperature distribution in the areas of the crosslinking and foaming line allows first complete and uniform crosslinking of the matrix polyethylene film, and then its uniform foaming, which ensures the use of these crosslinking and foaming agents with certain temperatures of their sequential decomposition at the selected type of polymer with its melting point. A high-quality crosslinking operation before foaming gives a reduction in pores and the absence of different sizes, which increases the strength of the polyethylene foam web.

High pressure polyethylene produced by KazanOrgsintez, Russia, was used as a feedstock:

- mark 15803-020 GOST 16337-77;

- mark 10803-020 GOST 16337-77.

As a blowing agent used azodicarbonamide TU 113-38-110-91-94.

Dicumyl peroxide TU 6-05-1001-75 was used as a crosslinking agent.

The method is as follows.

First, preliminary preparation of the starting components is carried out and their dosage in accordance with the recipe. Before mixing them, samples of each component are measured and placed in a moisture meter; if the humidity is not higher than required, as a rule, a tenth of a percent, then carry out the mixing operation. At higher humidity, dicumyl peroxide is explosive.

Powders of the foaming agent and the crosslinking agent after dosing are fed into the mixing tank and then to the mixing station. Thorough mixing of the agents affects the surface quality of the matrix film, the quality of the final surface of the PES, and uniform crosslinking of the web.

Next, metered granules of polyethylene and a measured mixture of agents are fed into a twin-screw extruder, where they are mixed to a homogenized state at a temperature of 105-125 ° C. Considering that the temperature of the transition of polyethylene into a viscous flowing state is 110-130 ° C, and the melting point of dicumyl peroxide is 39 ° C, but in the composite cross-linking occurs only at 150-160 ° C, three temperature zones are provided in the extruder. The first zone is the loading hopper of the extruder, in which the temperature is low and maintained at 105 ° C so that the sticking of the sharply molten polymer onto the walls does not occur. Then the whole mass is picked up by the screw, and the temperature is almost the same 105-110 ° C along the entire length of the screw - in the second zone. In the first and second zones, partial softening / melting of the granules of polyethylene and agents occurs with stirring and uniform distribution of all components in the volume of the mixture. Closer to the extruder head, the temperature is slightly increased to reduce the viscosity of the mixture and more easily push it through the gap under pressure. Without reducing the viscosity of the mixture in the third zone, when it is forced through, breaks in the formed film are possible. Thus, the third zone falls on the slit head, and it has the highest temperature at 125 ° C. In the third zone, partial decomposition and melting of the crosslinking agent and partial crosslinking of the polymer begin. For other polymers, the temperatures in the extruder zones will be different, which are selected experimentally.

Partially cross-linked polyethylene, having a stronger structure than non-cross-linked, is pressed through the head of the extruder, and a matrix is formed - a film tape of a given width. The formed matrix film is directed to the calender shafts, which are adjusted to the required thickness from 5 ± 5% to 10 ± 5% mm. The partially crosslinked matrix passed between the calender shafts is directed to the stitching and foaming line.

The stitching and foaming line is a four-zone furnace in which temperature zones are arranged in series. The first zone relates to a polymer preheating and crosslinking furnace and has a temperature range of 160 ° C to 180 ° C. At this temperature, the polyethylene matrix begins to soften and the crosslinking process of the polyethylene begins. The final crosslinking occurs at the outlet of the second zone with a temperature of 185-200 ° C in accordance with the crosslinking temperature of the resulting composite. In connection with the thorough mixing of the mixture of polyethylene with a crosslinking agent carried out at the stage of extrusion, the crosslinking of polyethylene proceeds uniformly throughout the entire volume of the matrix. Thorough mixing of the agents at the mixing station is also important for uniform crosslinking of the web. After the second heating zone, a matrix film with finally cross-linked polyethylene is fed into the foaming zone by means of rotating shafts. The foaming zone is set to a temperature range in which the used blowing agent begins to decompose with the release of gaseous decomposition products that provide active foaming - after 200 ° C. For the selected foaming agent, the temperature of the third zone - the zone of foaming start is selected 210-225 ° C, the temperature of the fourth zone - the zone of completion of foaming is 230-245 ° C. Gaseous decomposition products uniformly foam the polyethylene matrix. A foamed polyethylene film is formed. Thus, in the first two zones of the line, starting from 160 ° C, polyethylene molecules are crosslinked, and only then, when it enters the third and fourth foaming zones, where the temperature is much higher, foaming of the already crosslinked polyethylene occurs, and this is why the formation of large pores is excluded with a wide spread of their geometric dimensions. Due to the created temperature regime in the line, the pores of the polyethylene foam are small, up to 0.5 mm, equally sized.

All zones of the extruder and the lines of stitching and foaming, each time after commissioning, are adjusted to the desired temperature depending on the type of feedstock, lots of components used by different manufacturers. To do this, it is possible to adjust the temperature of all zones with the output of adjustment means to the main control panel.

A ventilation system is provided in the line for uniform distribution of air heated by gas over the entire surface, which also ensures uniform foaming of the film. Ventilation modes affect the process: correctly set ventilation modes provide airflow over the entire area, as a result, the surface is uniform, without spots and yellow stripes (foaming agent residues).

Thus, the zoning of heating allows in time to unleash the processes of crosslinking and foaming, which ensures uniform foaming. The separation of the cross-linking process into 2 stages: in the extruder and in the zones of the line, as well as the ability to select the required temperature in each zone of the line with respect to the used batches of components, allows you to completely complete the cross-linking process before foaming and get a uniform dense finely porous structure of the final product. After cooling, the final product is sent to a segment of edges and perform segments of sheets of a given size.

The method may provide for adjusting the broaching speed immediately after the slit head of the extruder, as well as the cooling shafts after the stitching and foaming line. The pulling speed determines the speed of winding the final product after it leaves the furnace; overly fast calendaring can make the canvas thinner.

After cooling the film on the calendars to ambient temperature, the crosslinked and foamed plastic film is wound on bobbins.

The improvement of all qualities of the final product occurs due to the order of operations and the zonal distribution of temperatures in the extruder and the line of crosslinking and foaming: first crosslinking and then foaming, achieved by the temperature conditions of the zonal process of obtaining the product; this eliminates the formation of large pores with a wide range of size dispersion, obtaining mesh sizes up to 0.5 mm over the entire surface. This improves the strength properties and presentation of the final product.

As shown by the test results of sheet polyethylene foam obtained by the described method and the analysis of the prototype method, the average apparent density of samples obtained in accordance with the claimed method was 33.51 kg / m ³ against the standard value of at least 33, the average elongation at break in the longitudinal direction of 134.8% at a standard value of at least 100% and for a prototype of 105%, the average breaking stress is 0.242 MPa versus a standard at least 0.2 MPa, for a prototype of 0.2 MPa, an average compression stress of 0.048 MPa at a standard value e less than 0.025 MPa, for the prototype 0.025-0.03.

By the proposed method, it is possible to obtain sheet foam from other polymers, for this it is only necessary to use other processing temperature ranges for the corresponding polymer and crosslinking and foaming agents. For example, for processing polypropylene, all temperatures need to be increased by an average of 20 ° C.

In addition, one more result is achieved - the one-stage process of obtaining a matrix film (semi-finished product); there is no need for a preliminary masterbatch (concentrate of additives), which optimizes the process, makes it more cost-effective and technologically advanced.

Claims (7)

1. A method of producing polyethylene foam, which includes mixing it with a foaming chemical agent, hot extruding the mixture, forming a film and calendering, characterized in that it is crosslinked before the foaming of polyethylene, dicumyl peroxide is taken as a crosslinking agent, azodicarbonamide is taken as a foaming agent prior to mixing with the starting polymer, the blowing and cross-linking agents are mixed with each other at a temperature below their melting point, the resulting mixture of agents is mixed granules of polyethylene in an extruder with a zonal temperature distribution from 105 ° C to 125 ° C, the temperature distribution over the zones of the extruder is carried out from the need to pre-heat the components and soften the polyethylene, partially crosslink the polyethylene and form a matrix film, mix the components in accordance with the recipe, mass . %: polyethylene 84.5; a crosslinking agent of 0.5; foaming agent 15, the formed matrix film of polyethylene of a given thickness is sent for final crosslinking and subsequent foaming to the line of crosslinking and foaming with temperature zones of preheating, crosslinking, and two zones of uniform foaming, while the temperature of the preheating zone is 160-180 ° C, crosslinking 185-200 ° C, uniform foaming zones 210-230 ° C and 230-245 ° C, with the ability to control the temperature in each zone, the supply of a matrix film of polyethylene after the extruder, its movement in line stitching and foaming and after the line at each stage is carried out with the ability to control the speed of the broach; after foaming in the last zone of the furnace, polyethylene foam is cooled on the cooling shafts to the temperature of the cooling shafts. 2. The method according to p. 1, characterized in that after cooling the foamed polyethylene film is wound on bobbins and / or cut into a size of the final product. 3. The method according to p. 1, characterized in that the trim from the edges of the matrix film and the final product is sent for processing as recyclable materials. 4. A line for producing polyethylene foam, including a component mixer, an extruder, transportation and calendaring devices, characterized in that the mixer is made with dispensers for mixing crosslinking and foaming agents with a mixing temperature below their melting point, an extruder with a mixture of crosslinking and foaming agents with polyethylene granules installed after the mixing station, made twin-screw with a zonal temperature distribution with three temperature zones: loading hopper with a temperature of partial p softening and melting components 105 ° C, the working area of the screws with a softening and melting temperature of the components, distributing the components throughout the volume and mixing them 105-110 ° C, the area of the extruder head with a temperature to reduce the viscosity of the mixture, partial decomposition and melting of the crosslinking agent and to form film 125 ° C, after the extruder a crosslinking and foaming line is installed, connected to the exit of the extruder by a transport and calendaring device, made with four temperature zones: pre-heating eva film 160-180 ° C, crosslinking 185-200 ° C, the beginning of uniform foaming 210-225 ° C, the completion of foaming 230-245 ° C, the stitching and foaming line is equipped with a controlled ventilation system, the output of the stitching and foaming line is equipped with cooling film shafts . 5. The line according to claim 4, characterized in that the extruder with a zonal temperature distribution is configured to control the temperature in each zone. 6. The line according to claim 4, characterized in that the line of crosslinking and foaming with a zonal distribution of temperatures is configured to control the temperature in each zone. 7. The line according to claim 4, characterized in that the device for transporting and calendaring the film after the extruder, in the line of crosslinking and foaming and after the line of crosslinking and foaming, is configured to control the speed of the film.