PL143304B1 - Method of eliminating viscoelastic melt surface unstablity causing surface roughness while extrusion moulding ethylene polymers - Google Patents

Description

The present invention relates to a method of eliminating the surface fracture of an alloy causing surface roughness during the extrusion of ethylene polymers. In particular, the invention relates to a method for eliminating surface melt fracture during the extrusion of a molten linear ethylene copolymer with a narrow molecular weight distribution under such conditions of flow rate and melt temperature as would otherwise give rise to this viscoelastic industrial grades of the alloy. low density is produced in thick-walled autoclaves or tubular reactors at pressures up to about 345 MPa and at temperatures up to 300 ° C. The molecular structure of this high pressure low density polyethylene is highly complex. The number of permutations in the ordering of the blocks that make up a polymorph is almost infinite. High-pressure resins are characterized by a complex molecular architecture of a branched long chain. The long-branched long chains have a great influence on the rheology of the resin feet. High pressure polyethylene resins also show short-chain branching in the spectrum, typically 1 to 6 atoms in length, controlling the crystallinity of the resin. The frequency distribution of such branches in the form of short chains is such that, on average, most chains contain the same average number of branches. The distribution of branches in the form of short chains characterizing high pressure low density polyethylene can be regarded as narrow. Low density polyethylene can exhibit various properties. It is flexible and exhibits a good combination of tensile strength, impact strength, burst strength and tear strength. In addition, it retains its strength down to relatively low temperatures. Some resins show no kru-2 143 304 volatile even at temperatures as low as -70 ° C. Low density polyethylene has good chemical resistance and is relatively insensitive to acids, bases and inorganic solutions. However, it is sensitive to the action of hydrocarbons, halogenated hydrocarbons, oils and greases. Low density polyethylene has excellent dielectric strength. More than 50% of all production of low density polyethylene is converted into films. This film is mainly used for packaging, e.g. for packing meat, frozen food, ice cream, products intended for reheating in bags, textiles and paper products, products for self-service sale, for industrial flooring, for transport bags and for shrink films for transport to pallets. Large amounts of wide and thick film are used by construction and agriculture. Most low density polyethylene film is made by extrusion blow molding sleeve. The foils produced in this way vary in size from pipes with a diameter of 5 cm and less, which are used for sowing as sleeves or bags, to huge sleeves, which when laid flat have a width of about 6 m, which, after cutting along one edge and opening, measures up to 12 m Polyethylene can also be produced under low to moderate pressures, by homopolymerization of ethylene or by copolymerization of ethylene with various alpha olefins, using contact catalysts based on transition metal compounds of variable value. These resins have little or no they branch as long chains and the branching occurs only in the form of short chains. The length of the chain is regulated by the type of comonomer. The branch frequency is regulated by the concentration of the comonomer (s) used in the copolymerization process. The frequency distribution of the branches depends on the type of transition metal catalyst used in the copolymerization. The branch distribution in the form of short chains characterizing low density polyethylene produced with transition metals catalysts can be very broad. Linear low density polyethylene can also be produced by high-pressure methods known in the art. US No. 4,302,566, devoted to the preparation of ethylene copolymers in a fluidized bed reactor, discloses that ethylene copolymers having a density of 0.91 to 0.96, a melt index greater than or equal to 22 to about 32, and a relatively low residual catalyst content, can be produced by relatively high yields when the monomer (s) are copolymerized in the gas phase using a complex, high-activity, Mg-Ti-containing catalyst mixed with an inert carrier. US No. 4,302,565, devoted to polymerization catalysts, their preparation method and their use in ethylene copolymerization, discloses that ethylene copolymers with a density of 0.91 to 0.96, a flow rate index greater than or equal to 22 to about 32, and a relatively low residual catalyst content. can be prepared in the form of pellets with relatively high yields if the monomer (s) is copolymerized in the gas phase with a complex, highly active, Mg-tactalizer which has been impregnated onto a porous, packable carrier. According to the above-mentioned patents, with the use of a Mg-Ti-containing complex catalyst, they have a narrow molecular weight distribution Mw / Mn, ranging from about 2.7 to about 4.1. The geology of the polymers largely depends on the molecular weight and the distribution of molecular weight. Two aspects of rheological properties are important when extrusion of foil; cutting and elongation. In the foil extruder and the extruder die, the polymer melt is subjected to a strong deformation with the occurrence of shear. When the extruder screw pumps the melt into and through the foil extrusion die, the alloy is subjected to a high shear rate. Most of the foil extrusion processes seem to be sheared the alloy at speeds in the range of 100 - 5000 s | 1. It is known that polymer alloys exhibit a viscosity-reducing effect under the action of shear force, i.e. the properties of non-Newtonian liquids. W143 304 3 measures of shear rate increase the viscosity / the ratio of shear stress r to shear rate A / decreases. The degree of viscosity decrease depends on the molecular weight, its distribution and the particle configuration, e.g. the presence of long chain branches in the polymer. Short-chain branches show little effect on the effective viscosity. In general, it can be stated that high-pressure low-density polyethylenes have a wide molecular weight distribution and show a marked decrease in viscosity under the shear force involved in the extrusion rate. On the other hand, the resins with a narrow molecular weight distribution used in the process of the invention show a slight reduced viscosity at the shear rates of the extrusion currents involved. As a result of these differences, the narrow molecular weight resins used in the process of the invention require higher strength and higher extrusion pressures than low density high pressure polyethylenes with a wide molecular weight distribution and equivalent to the average molecular weight of the polymers of the polymers. when cutting. With a straight cut, the rate gradient of the deformed resin is perpendicular to the flow direction. Testing for deformation is experimentally convenient, but does not provide information relevant to understanding the reaction of the material in the film-making processes. While the effective viscosity can be defined in terms of shear stress and shear rate, that is: J7shear = 712 / A where: 17 shear = effective viscosity / puz /; 7 * 12 = shear stress / pumpkins / cm2 /; A = shear rate / s | V, then the tensile viscosity can be defined in terms of normal stress and strain rate, that is: jjext = ir / t where rj ext = tensile viscosity / poise / ir = normal stress / dyny / cm2 /, e. = Strain rate / s " (1) During the extrusion of an ethylene polymer with a high molecular weight, in particular polymers having a narrow molecular weight distribution through the mouthpieces, as is the case with other such polymers, "viscoelastic melt instability" occurs when the extrusion rate exceeds a certain critical value. "Viscoelastic melt fracture" is a general term used in the polymer processing industry to describe the various surface irregularities of extruded articles during the extruding of graded polymers through the die. The occurrence of viscoelastic melt fracture severely limits the speed at which an industrial first system can produce quality products. Nason conducted a tactical study of this phenomenon in 1945, and since then a number of researchers have worked to understand the mechanisms behind its occurrence. A critical review of the literature on viscoelastic fracture of the alloy was presented by C.J. S. Petrie and M.M. Denn / American Institiute of Chemical Engineers Journal, vol. 22, pp. 209 - 236, 1976), who found that the current understanding of the mechanisms leading to the occurrence of viscoelastic instability in melt polymers is far from complete. The characteristics of the viscoelastic instability of the melt polymer are usually determined by using a conventional capillary rheometer, such as may be obtained from Instron Corporation, Canton, Mass. The experiment consists in loading a solid polymer into the cylinder, melting the polymer in the cylinder by applying heat, forcing the molten polymer at a certain temperature through a capillary mouthpiece of known dimensions, determining the relationship between the flow rate and the pressure drop when passing through the capillary die, and examining the characteristics of the extrusion surfaces at a given surface. Two solutions can be used to send the molten polymer through the capillary die: adjusting the pressure in the cylinder or by applying a weight (a type of a foot gauge gauge) or by creating a gas pressure (which requires measuring the flow rate), or by regulating volumetric displacement using a piston in this cylinder / which requires the measurement of the pressure in the cylinder / .4 143 304 From the knowledge of the required pressure in the cylinder / P / for a given flow rate / Q /, the apparent shear stress and the apparent shear rate will be calculated at a given temperature for a given polymer, using the following expressions: apparent shear stress = 4L apparent shear rate = _— ttD3 where: AP is the pressure drop at the mouthpiece, Q is the volumetric flow rate through the mouthpiece, D is the diameter of the capillary, and L is capillary length. These apparent values are usually represented in log co-ordinates along with the observed surface characteristics of the extrudate product. In the above calculations, there are a number of implicit assumptions, namely: The flow in the capillary is steady, laminar, and fully developed; There is no friction loss in the cylinder; Plyniecie plinu is Newtonian; Fluid flow is independent of time; Viscosity is independent of pressure; Isothermal flow; There is no slip on the walls of the capillary. So to get the real values, make corrections for the calculated values of the shear stress and the shear rate. The procedures for making these corrections are extensively described in standard monographs on the subject (see, for example, van Wazer, J.R. and others "Viscosity and Flow Measurement", Intersicience, 1966 /. However, most reports on the viscosity characteristics of molten polymers only make corrections for variations from fully developed flow and Newtonian flow. Other assumptions were either neglected or considered negligible in the technical calculations. From the German patent description No. 821 551, internally polished tubular nozzles made of steel or non-ferrous alloys are known. From the German patent description No. 2 434 367 the extruder nozzle / containing Metal insert. However, these devices do not provide the proper extrusion characteristics in terms of surface roughness. The surface characteristics of the extruded product generally show that at low shear stress the resulting extrudate is smooth and shiny. At a critical stress value, the extruded product shows a loss of surface gloss. The loss of gloss is due to the fine roughness of the surface of the extruded product, which is visible under the microscope at small enlargements (20 - 40x). This state is represented by an "attack" of surface irregularities, and most researchers believe that this occurs at a crystal velocity of a linear flow through the mouthpiece. At extrusion speeds above the critical one, two main types of irregularities in the extruded articles can be identified for most polymer alloys: surface irregularities and general irregularities. The surface irregularities (hereinafter referred to as surface melt fracture) occur under apparently steady flow conditions over the entire range of flow rates dependent on the molecular characteristics of the polymer. They are characterized by micro-inequalities placed tightly next to each other on the circumference of the extruded product. In its more advanced form, this resembles a defect generally known as "shark skin". Surface viscoelastic fracture, as the name implies, is limited to the surface of the extrudate product only, and the core appears to exhibit no irregularities. 143 3 * 4 5 Surface melt fracture to a greater or lesser extent is shown by most low-pressure thermoplastics, only with high pressure density / HP - LDPE / and polyvinyl chloride / PVC /. The surface melt fracture found little reflection in the literature compared to the more noticeable general irregularities that occur at high extrusion rates. The available literature on the melt surface fracture provides the following information. (a) The occurrence of the melt surface fracture does not depend on the dimensions of the die (diameter, L / D ratio and taper angle at the entrance) and the materials used in the construction of the die. / b / The occurrence of the viscoelastic fracture of the alloy is significantly delayed when the melt temperature is increased. (c) Linear structured polymers (for example high density polyethylene) have shown an increased tendency to surface melt fracture compared to polymers with branched structures. / d / Polymers with a narrow molecular weight distribution show a greater degree of surface melt fracture than polymers with a broad distribution. There is a general agreement in the views of various researchers that the surface viscous fracture results from the effects of the melt melt at the output. it is subjected to high local stresses as it separates from the mouthpiece, which causes a cyclical increase and decrease of forces stretching the surfaces. As a result, there is differential elastic relaxation between the surface layer and the core of the extrudate product. As the extrusion rate is further increased, the exiting extrudate exhibits general irregularities (hereinafter referred to as general melt fracture) which are no longer confined to the extrusion surfaces. products. This is a catastrophic failure of the extruded products and, therefore, much attention has been paid to it in the literature. Tordella's term "viscoelasticity of the alloy ** was initially intended to describe the general irregularities occurring at high extrusion rates. In contrast to the surface instability of the alloy, general viscoelasticity. Viscoelastic fracture occurs under transient conditions, with spiral flow disturbance at the mouthpiece entrance and the presence of pressure and flow rate fluctuations. Generalized flow fracture occurs at approximately constant stress / 105 m2 / shear stress / 105. Since the molecular characteristics of the polymer, the extruded products show a variety of distortions, ranging from those exhibiting a certain periodicity (alternating smooth and rough, wavy, bamboo-like, screw threads, etc.), up to random distortion, not showing any regularity. The extensive literature on the general viscoelastic fracture of the alloy shows the following: (a) The occurrence of the general viscoelastic fracture occurs at a critical shear stress and is relatively independent of die length, die diameter and temperature. / b / The critical stress for the overall viscoelastic fracture does not depend on the molecular weight distribution, while the critical shear rate increases with the width of the distribution. / c / Mouthpiece entry has a major impact on the critical shear rate for the overall viscoelastic fracture to occur. / d / The critical shear rate increases as the L / D ratio of the die increases and the melt temperature increases. A number of mechanisms have been proposed to explain the general viscoelastic instability of the alloy and the discrepancy in either the mechanism or the place of initiation of this defect. It has been proposed to recognize that the overall melt fracture is due either to the entry effects or to the working surface of the die. The proposed mechanisms include: rupture of the melt in the mouthpiece entrance area due to exceeding the strength of the alloy and propagation of the resulting spiral instability from the entrance into the mouthpiece mouth; inertial phenomena of the Reynolds turbulence type; a "slip-stick" phenomenon in the working area of the mouthpiece; and theological phenomena such as pressure-induced crystallization and particle orientation at the entrance. The effect of capillary-die construction materials on the critical stress for overall melt viscoelastic instability with respect to low-density polyethylene resins, studied by Tordella / Journal of Applied Polymer Science, vol. 7 pp. 215 - 229, 1963 / and Metzger and Hamilton / Society ofPlastics Engineers Transactions, vol. 4, pp. 107-112, 1964). They found that the critical stress for the overall viscoelastic instability of the alloy did not depend on the materials of construction of the die, which included: stainless steel (polished and very rough); glass; graphite; brown; sintered bronze; In conclusion, it can be concluded that the available literature indicates that the surface melt fracture mechanism is completely different from the general melt fracture mechanism and that they are initiated in different areas of the die. It is believed that the surface fracture of the alloy is related to the phenomenon related to the general viscoelastic fracture. exiting the mouthpiece, while the overall melt fracture is a phenomenon related either to the working area of the mouthpiece or to the entrance to the mouthpiece. It is generally accepted that the surface melt fracture is due to the high local stress at the mouthpiece exit, but there is no consensus on the mechanism of the overall melt viscoelastic instability. Linear low density polyethylenes (LLDPE) have a substantially linear molecular structure with a very narrow molecular weight distribution / MWD /, in contrast to conventional, high-pressure low density polyethylenes / HP - LDPE /, which have long chain branches and a much wider distribution of molecular masses / MWD /. In foil applications, products made of LLDPE resins significantly exceed those of HP - LDPE resins due to differences in molecular structure. However, the extrusion of LLDPE resins using conventional HP-LDPE-optimized film die cutters is limited by the severe viscoelastic instability of the alloy at the extrusion rates currently used in the industry. LLDPE resins flow qualitatively in many ways. linear polymers with a narrow molecular weight distribution (see Fig. 5). Fig. 5 shows typical data obtained with a conventional capillary rheometer for LLDPE resin for film production, in combination with the observed surface characteristics of the extruded articles. The resins were extruded at a temperature of 220 ° C through a capillary die made of carbon steel with a hole diameter of about 1 mm and a length of 20.3 mm (L / D = 20). A capillary rheometer was used using an adjustable volumetric displacement. Figure 5 shows the relationship, apparent shear stress, apparent shear rate, or flow curve, calculated in accordance with the methods adopted. The graph in Figure 5 illustrates the key characteristics of LLDPE resins. Below the shear stress of approximately 124.2 - 138 kPa (assumed fire values, unless otherwise stated), the flow curve has a constant slope of 0.66 and the exiting extruded articles are smooth and shiny. At a shear stress of approximately 138 kPa / a shear rate of approximately 70 s ~ V, the extruded product exhibits a loss of surface gloss which exhibits a micro-rough surface under the microscope. This represents the occurrence of the surface viscoelastic fracture of the alloy. However, it should be noted that in the vicinity of the condition for the occurrence of the surface viscoelastic instability of the alloy, the flow curve shows a discontinuity in the form of a change in slope. In the range of stresses of approximately 138-448 kPa, the flow curve has a slope of approximately 0.46 and the extruded articles exhibit an increasingly severe surface melt fracture which eventually takes the form of a "shark skin" type surface. In this range, the flow is steady, with no visible fluctuations in the measured pressure or flow rate. At a shear stress of approximately 414 - 448 kPa, the flow becomes undetermined, with both pressure and flow rates varying between two low and extreme values. the extrusion extruded articles suitably show relatively smooth and rough surfaces. This represents the general viscoelastic instability of the alloy for this resin. It is necessary to conclude that the constant shear stress of approximately 448 kPa, given in Fig. 5, is based on the mean value for the fluctuating pressure at a given piston speed given for illustration only and should not be interpret it as a measured constant value. Due to the unstable flow through the capillary, the entire determination of the flow curve is not warranted. However, the data presented in Fig. 5 indicate that the flow curve shows a second discontinuity at the time of the overall melt fracture. With a further increase in shear stress, the extruded articles become completely deformed and do not show any regularity. It was found that the above observations are also generally valid for other LLDPE resins. In particular, it turned out that the occurrence of surface melt fracture occurs at a relatively constant value of the shear stress, rather than at a constant linear velocity through the die, as reported in the literature. The actual value of the critical stress may, however, vary slightly, depending on the molecular weight distribution / MWD / and the comonomers / u / used. Moreover, the first discontinuity of the flow curve is reproducible and has proved to reasonably represent the conditions of surface fracture of the alloy. For a given resin, the critical stress appears to be relatively independent of: (a) the melt temperature; / b / mouthpiece opening diameter / c / mouthpiece size ratio L / F; and / d / convergence angle of the input. The superficial viscoelastic fracture of the alloy occurs over a wide range of LLDPE shear stresses. Under the industrial filmmaking conditions of conventional die-cuts, surface melt fracture mainly occurs in LLDPE resins. Any mechanism of surface melt fracture in LLDPE resins must satisfactorily explain the occurrence of this first discontinuity. The mechanism proposed in the literature, based on the phenomena of the exit from the mouthpiece, intended to explain the occurrence of surface melt fracture, does not satisfactorily explain the first discontinuity of the flow curve for linear polymers with narrow particle mass distribution, such as LLDPE resins. To justify the existence of a first discontinuity in the flow curve and possibly an alternative mechanism for the occurrence of surface melt fracture, it is necessary to review the base on which the flow curve is normally determined. One of the key assumptions inherent in the analysis of capillary measurements is the condition of no slip on the mouthpiece wall. To date, researchers working with high viscosity linear polymers with a narrow molecular weight distribution have not considered the importance of this assumption, especially in the presence of surface melt fracture under apparently steady flow conditions. Measurements can be made on a capillary rheometer. There are known methods for determining the validity of this assumption / see e.g. F.N. Cogswell, "PolymerMelt Rheology- A Guide to Industrial Practice", Halstead Press, 1981, p. 136 /. This includes standard measurements at a given temperature using a series of capillary mouthpieces with a constant L / D but different capillary diameters and plotting the apparent shear rate as a function of the reciprocal of the capillary radius (l / R) with the apparent shear stress as parameters. In the absence of skidding on the wall, the apparent shear rate will be independent of the capillary radius. However, in the presence of skidding, the apparent shear rate at a given shear stress will be a linear function I / R with a slope equal to four times the sliding speed. Figure 6 shows the data obtained for the LLDPE resin for film production at a temperature of 220 ° C using a series of capillary mouthpieces / diameters in the range 0.5 - 2.06 mm / with a constant value L / D / 20 /. It can be seen from this graph that below the shear stress of 138 kPa, the measured value of the apparent shear rate does not depend on the capillary radius, which indicates no slip. On the other hand, at a shear stress of 138 kPa, which is close to the critical stress, for the occurrence of surface melt fracture, the apparent shear rate measured is a linear l / R function, with a sliding speed of 1.27 cm / s. At higher stresses, the sliding speed increases and the extruded products show increasing surface roughness. Thus, these measurements clearly show that the initiation of the slip at this critical stress is primarily responsible for the first discontinuity in the flow curve. Increased sliding speed reduces the pressure required at higher flow rates and hence the measured flow curve shows a greater shear drop above the critical stress. Viscoelastic fracture of the alloy occurs simultaneously, with the same critical shear stress. This is not a simple coincidence, it is suggested by the mechanism of surface melt fracture, which satisfactorily explains the occurrence of the first flow curve discontinuity. initiation of a slip on the working area of the mouthpiece. The slip of the flowing polymer results from the interruption of adhesion at the interface of the phases under flowing conditions and occurs at a critical stress. Adhesion is a surface phenomenon and strongly depends on the type of surface and the direct contact of the cooperating surfaces. Poor adhesion with conventional construction materials used on the working surfaces of the mouthpieces is primarily responsible for the initiation of slip and the surface fracture of the alloy caused by the surface. The surface fracture of the melt viscoelastic can be eliminated under industrial manufacturing conditions by the appropriate choice of materials for the working surfaces of the mouthpieces that show improved adhesion to the flowing polymer. It has been found that standard tests with capillary rheometer do not provide the conditions for determining the suitability of the material for the working areas of the mouthpieces. industrial machinery. The occurrence of surface fracture of the polymer in a given metal capillary die can be completely different from that in, for example, a film blown extrusion die with working surfaces of the same metal. Under the conditions of foil production, the surfaces of some metals used for the working area of the mouthpiece show a certain transitional state, with a so-called "induction" period, during which direct contact is created between the flowing polymer and the metal surface, which promotes adhesion at the interface of the phases, with almost complete elimination surface fracture of the alloy. Meanwhile, capillary mouthpieces made of the same metals show no or only little effect of construction materials on the occurrence of surface melt fracture. Thus, the importance of capillary measurements, particularly with regard to determining the effect of construction materials on the surface melt fracture of polymer melt under industrial production conditions, is questionable. Earlier researchers who reported that materials were not affected by surface melt instability of linear polymers such as high-density polyethylene resins did not take this aspect into account. The suitability of a given metal surface for the working area of the die must therefore be determined under real industrial production conditions, not by using a capillary rheometer. There are a number of ways to overcome surface melt fracture under industrial manufacturing conditions. They aim to reduce the shear stresses present in the die and include: increasing the melt temperature; modifying the geometry of the mouthpiece; and the use of a lubricant to reduce the friction of the resin against the walls. Increasing the melt temperature is unfavorable in production as it slows down the rate of film formation due to instability of the sleeve and reduced heat build-up. Another method for eliminating the surface defect of a shark skin type is disclosed in US Patent No. US No. 3,929,782. In this method, the melt surface fracture experienced in extrusion of the polymer is adjusted or eliminated by cooling the outer material layer so that it exits the die at a reduced temperature while the melt mass remains at an optimal temperature. However, this method is difficult to implement and control. The method disclosed in US Patent No. US No. 3,920,782 is clearly based on the inventor's conclusion that the occurrence of surface viscoelastic instability of an alloy under its operating conditions with resins is essentially taking the function of exceeding the critical linear velocity of its resin flow through its mouthpieces at its operating temperatures. On the other hand, in the method according to the invention, the surface occurrence of the viscoelastic strength of the alloy in the resins processed under the applicant's operating conditions is primarily the function of exceeding the critical shear stress. US No. 3,382S3S discloses methods of designing mouthpieces for coating wires and cables by high-speed extrusion of plastics such as polypropylene, high and low density polyethylene, and copolymers thereof, which are sensitive or sensitive to the taper angle of extruder mouthpieces. The mouthpieces of this patent are designed to prevent the general melt fracture when extrusion of plastic coatings into wires, which occurs at much higher shear stresses than those encountered with surface melt fracture during film production. US No. 33,825 discloses a method of designing a mouthpiece taper angle such that a curvilinear configuration of the mouthpiece is produced / Fig. 6 and 7 of this patent /, which converges in the direction of the resin flow. Caused as a result. This reduces the overall distortion as a function of solely the angle of entry into and / or the angle of convergence of the mouthpiece. Meanwhile, the surface viscoelastic fracture of the alloy is not sensitive to taper angles at the mouthpiece entrance and the method according to the invention is related to the reduction of the surface viscoelastic fracture of the polymer as a function of the structural materials used for the working area of the mouthpiece, including the exit from it, as a result of which a much faster result can be achieved. shearing without occurrence of surface melt fracture during film production. US No. 3,879,507 discloses methods of reducing melt viscoelastic fracture during the extrusion of a foamed composition in the production of films or sheets. This method consists in increasing the working length of the mouthpiece and / or slightly increasing the convergence of the mouthpiece gap, while maintaining the same or reducing the mouthpiece gap, which is clearly relatively narrow compared to the prior art (see column 4, lines 2 - 6) and has a width of 0.64 mm (see column 5, line 10). The tent of viscoelastic melt fracture is caused by the premature formation of bubbles on the surface. However, this type of viscoelastic melt fracture is completely different from the instability that occurs during LLDPE resin processing during film production. In other words, such instability is not a result of the rheological properties discussed above. Modifications are made to reduce shear stress in the working area of the mouthpiece below the critical stress level (approximately 138 kPa) or by enlarging the mouthpiece gap / US Patents US Nos. 4,243,619 and 4,282,177 / or by heating the lips of the mouthpiece to temperatures well above the melt temperature. Increasing the gap of the mouthpiece results in thick extruded articles that have yet to be pulled and cooled during the production of the film by extrusion blow molding. Although LLDPE polyethylenes exhibit excellent tensile characteristics, thick extruded elements lead to an increased molecular orientation towards the machine, resulting in directional imbalance and deterioration of critical film properties such as tear strength. In addition, thick extruded elements reduce the effectiveness of conventional cooling. which for stable operation requires a reduction in operating speeds. Technology based on the use of a wide gap also has other disadvantages. The desired gap 10 143 304 is a function of the extrusion rate, the melt number of the resin and the melt temperature. The wide gap configuration is not suitable for processing conventional grades of low density high pressure polyethylene (HP - LDPE). Thus, changes in the width of the mouthpiece gap are required to provide the expected by the manufacturer the operational flexibility of a given production line. The concept of a heated lip tends to reduce stress at the mouthpiece exit and entails extensive modifications, requiring the effective isolation of the hot lips from the rest of the mouthpiece and from the air ring. U.S. Patent US No. 3,125,547 discloses polyolefin compositions containing the addition of a fluorocarbon polymer to improve extrusion characteristics and produce extruded articles without the effects of viscoelastic melt fracture, at high extrusion rates. It is based on the inventor's conclusion that the "slip-stick" phenomena occurring at high extrusion speeds and the arrow structure of the surface of the extruded product caused thereby are due to poor lubrication in the mouthpiece opening. The use of fluorocarbon polymer is to improve lubrication and reduce stress in order to obtain extruded products free from the effects of viscoelastic melt instability, while the method of the invention is based on the opposite reasoning, namely that it is precisely the lack of adhesion and not the lack of lubrication. at the interface of the polymer / metal phases in the working area of the mouthpiece, it is the cause of both surface and general viscoelastic instability in the case of LLDPE resins. The present invention therefore aims to improve adhesion at the interface by properly selecting the material of construction for the working area of the mouthpiece, including the exit from the mouthpiece, to obtain extruded articles without the drawbacks of viscoelastic melt fracture. US No. 3,125,547 drastically reduces the stress on mouthpieces made of conventional materials, which clearly suggests modification of the rheological properties of the polyolefin resin due to the presence of the fluorocarbon polymer. Meanwhile, the method according to the invention, which provides a different material of construction for the working area of the mouthpiece, produces extruded products without defects caused by viscoelastic melt instability, without significantly affecting the stresses or the rheological properties of the resin. US No. 4,342,848 discloses the use of polyvinyloloctadecyl ether as a processing modifier to obtain a smoother surface of extruded articles and to improve film properties of high density polyethylene resins. However, this additive has been found not to be suitable for reducing viscoelastic melt instability in LLDPE resins. Additives intended to be used as processing aids to reduce the effects of viscoelastic melt instability in extruded articles are expensive and increase the cost of any concentration needed and may be unacceptable for resins such as LLDPE resin granules intended for household products. Such additives affect the rheological properties of the basal resin, and excessive amounts can adversely affect the critical properties of the film such as gloss, transparency, sticking of the sheets and weldability of the product. In the method of the invention, it is possible to eliminate the surface viscoelastic instability by the changes introduced in the mouthpiece. that is, by employing the working surface of the mouthpiece made of a material which provides increased adhesion between the working surface of the mouthpiece and the polymer. The usefulness of the method according to the invention stems from the discovery that the primary mechanism responsible for the occurrence of surface melt fracture in LLDPE resins is the initiation of the sliding of the polymer melt on the mouthpiece wall. Slip is caused by the loss of adhesion on the surface of the polymer / metal interface under flow conditions and occurs at a critical shear stress. Adhesion is a surface phenomenon, strongly dependent on the type of surface and the tightness of surface contact. Thus, techniques to ensure good adhesion at the interface, the flowable polymer / wall of the mouthpiece will eliminate the viscoelastic fractures of LLDPE resins. Improvement in adhesion can be achieved by the correct choice of mouthpiece construction materials for a given resin. In the event that only one surface of the mouthpiece's opposing working surfaces is made of a material that provides improved adhesion, then the viscoelastic melt instability is reduced or eliminated on the surface of the polymer adjacent to the resin. surface showing improved adhesion. If, on the other hand, the two surfaces of the opposing working surfaces of the mouthpiece are made of a material exhibiting improved adhesion, then both surfaces of the polymer will exhibit reduced melt viscoelastic instability. Films intended for packaging use must have a specific combination of key properties, providing a wide range of applications and different applications. general industry acceptance. These properties include the optical quality of the film, eg haze, gloss and transparency. Mechanical properties such as puncture resistance, tensile strength, impact resistance, stiffness and tear strength are also important. In the case of packing perishable goods, vapor permeability and gas permeability are important. The efficiency and correct operation of the film processing equipment and its use for packaging depend on such properties of the film as friction coefficient, sheet sticking, film sealing and bending strength. Low-density polyethylene has a wide range of applications such as food and non-food packaging. Commonly made low-density polyethylene bags include bulk items, textile packaging bags, dry cleaning bags and garbage bags. made of low-density polyethylene, it can be used as the lining of drums for the transport of many solid and liquid chemicals, as well as a cover to protect the contents of wooden crates. Low density polyethylene film can also be used in a variety of agricultural and horticultural applications, such as plant and feed protection, melting, and fruit and vegetable storage. In addition, low-density polyethylene films can be used for building purposes as damp and vapor barrier. Finally, low density polyethylene films can be coated and printed on them for magazines, books, etc. Having a unique combination of the above-mentioned properties, low density high pressure polyethylene is the most important thermoplastic material for packaging films. About 50% of the total amount of such films for packaging is made of it. The films made from the polymers of the invention, preferably ethylene copolymers, offer an improved combination of final properties and are particularly suited to many applications where high pressure low density polyethylene is currently used. Improvement of any of the film properties such as elimination or reduction of surface area Melt fracture or the improvement of the resin extrusion characteristics or the improvement of the film extrusion process itself is of paramount importance for the acceptance of this film as a substitute for high pressure low density polyethylene in many end-use applications. The attached figures show the equipment and test results discussed in this description. Fig. 1 shows a cross-sectional view of a ring-shaped extruder mouthpiece with a ring-star lead. Fig. 2 shows an enlarged section of the mouthpiece part with the inlet spiral. Fig. 3 shows the configurations of the working area of the mouthpiece with surfaces in the form of inserts that are facing each other to increase adhesion. Fig. 4 shows the configurations of the working area of the mouthpiece, in which the facing surfaces that provide increased adhesion are made in the form of a solid structure of the mouthpiece collar and spike. In Fig. 5, a flow chart of the LLDPE resin for film production is given. Finally, Fig. 6 is a graph showing the slip characteristics of the LLDPE resin for the production of films. The invention relates to a method of eliminating the surface fracture of the melt causing surface roughness during the extrusion of ethylene polymers under the conditions of adhesion between the material forming the conventional working surface. the die forming the head and a polymer that would otherwise cause a highly viscoelastic melt instability, characterized in that the polymer extends through a die having a working surface made of a material different from that of the working surface of a conventional mouthpiece, which material increases the adhesion between the working surfaces. the die with a polymer sufficient to eliminate the surface fracture of the alloy. Preferably, both facing surfaces contain a material that increases adhesion to the adjacent polymer. As used herein, the term "conventional material or mouthpiece surface" means the mouthpiece or mouthpiece surface made of nickel-plated or chrome-plated steel. The material that increases the adhesion compared to conventional materials is an alloy containing from 5 to 95% by weight of zinc and from 95 to 5% by weight of copper, thereby eliminating the surface fracture of the alloy causing the roughness of the polymer surface, adjacent to that of an alloy containing zinc and copper. Preferably, a melted ethylene polymer can be extruding through a mouthpiece of the type such as a spiral ring mouthpiece, slotted mouthpiece, etc., typically a ring mouthpiece having a narrow mouthpiece slit, with a width greater than 0.13 mm, preferably 0.13-1 mm. In the case of processing LLDPE resins, it is no longer necessary to extrude the molten ethylene polymer through a die having a gap width greater than 1.27 to about 3 mm as suggested in US Pat. US No. 4,243,619. Conventionally, the design of the mouthpiece working area has been based on the use of a nickel-plated or chrome-plated steel surface. Figure 1 is a cross-sectional view of a spiral-star feed ring-shaped die 10 through which a molten thermoplastic ethylene polymer is extruded to produce a single-layer thick-walled film. or thin-walled / The mouthpiece block 12 includes channels 14 for directing the polymer to the mouthpiece exit. During the extrusion of the molten thermoplastic ethyl polymer, it spreads into the mouthpiece channels 14. Fig. 2, in turn, shows the cross-section of the mouthpiece with a spiral lead-in, the spiral sections J, the entry sections to the working surface H and the working surfaces of the mouthpiece G. Fig. 1 and Fig. 2, the mouthpiece outlet port is shown at the exit of the mouthpiece, generally identified by reference numeral 16. The exit opening forms an exit in the form of a mouthpiece slot 18, which forms the opposing surfaces of the lips of the mouthpiece 20 and 20, extending the opposing faces of the mouthpiece. working surfaces of the mouthpiece 22 and 22. As shown in Figs. 3 and 4, the working area of the mouthpiece has a configuration in which the facing surfaces are made of a material with enhanced adhesion, such as metal or a metal alloy with improved adhesion characteristics. unlike conventional nickel or chrome steel. These surfaces may be formed by brass inserts 24 which are attached in a suitable manner, for example attached detachably to the spike and collar of the mouthpiece. The inserts may be detachably attached to the modified pin and flange using any suitable device, such as threaded elements housed inside the inserts, which, however, are screwed into mating threaded elements in the appropriate surface of the flange or collar. The length of the inserts, measured in the flow direction of the extrudate product, should preferably correspond to the length of the working area of the mouthpiece, although shorter lengths may also be used. Other techniques may also be used to create the desired mouthpiece working surface with improved adhesion, such as coating the working surface of the mouthpiece area with a suitable material or alternatively by fabricating either a section of the mouthpiece working area or even the entire bar and flange of a suitable material, as shown in Fig. 4. The viscoelastic melt fracture is reduced at the surface of the polymer adjacent to the surface of the material having improved adhesion. As a result, this method can be used in connection with the invention disclosed in U.S. Patent No. 143,304. No. 4,348,349. Advantageously, therefore, it is possible to reduce the viscoelastic melt fracture on both sides of the film by directing the molten polymer through the working area of the mouthpiece in which only the surface of the film in which the viscoelastic fracture effect is to be reduced is adjacent to the surface having improved adhesion while where on the second surface, the viscoelastic melt fracture would also be eliminated, as disclosed in this specification. The method of the invention also allows the processing of multilayer films where one layer is made of LLDPE resin and the other layer is made of a resin which under the operating conditions does not it is subject to the phenomenon of viscoelastic melt fracture. Thus, in the method of the invention, the LLDPE resins can be passed through the die in contact with the surface with improved adhesion, while the resins that are not subject to the phenomena of viscoelastic melt fracture are extruded upon contact with the second working surface of the die, resulting in a multilayer film, both of which are surfaces that are susceptible to viscoelastic melt fractures causing surface roughness. As mentioned earlier, the working area of the mouthpiece adjacent to the polymer melt is made of a material exhibiting improved adhesion. So, for example, in the case of brass surfaces in the working area of the mouthpiece, the surface viscosity of the alloy in the working area of the mouthpiece is initially during start-up, which is believed to be due to the presence of an absorbed oxide layer, after a short induction period, which depends on the extrusion rate, the extruded product becomes free of surface viscoelastic fractures j alloy and will remain so for a period depending on the extrusion rate. After this period, the surface viscoelastic fracture of the alloy reappears. This is believed to be due to the degradation of the brass surface as a result of the brass dezincification at the temperatures used to process the LLDPE resins, which affects the adhesion characteristics at the polymer / brass interface. It has been found that the addition of a suitable stabilizer to the resin eliminates these dependencies. ¬ durability of brass surfaces. Thus, for long term operation it is advantageous to use a suitable stabilizing agent which can be incorporated into the masterbatch to be added to the copolymer. A suitable stabilizing agent for use with brass is a ethoxylated fatty tertiary amine, commercially available named Kemamine AS 990 from Witco Chemical Corporation, Memphis, Tennessee. Other conventional stabilizers may also be used. The addition of 50-1500 ppm, preferably an addition of 300-800 ppm, of the tertiary amine is effective in eliminating the recurrence of the viscoelastic fracture of the melt upon contact with brass. This stabilizer may be included in masterbatches conventionally used to provide the desired anti-stick and anti-skid characteristics. The films of the invention may be blow molded. In this process, a polymer with a narrow molecular weight distribution is pressed out of the melt by an extruder. The extruder may have a screw having a length to diameter ratio from 15: 1 to 21: 1 as disclosed in US Patent No. US No. 4,343,755, relating to a method of extruding ethylene polymers. The described extruder screw has a feeding, transition and measuring section. Optionally, the extruder screw may also include a mixing section, such as that described in US Pat. US Nos. 3,486,192, 3,730,492, and 3,756,574, which are provided herein for information. Preferably, the mixing section is at the end of the screw. An extruder which can be used may have a length to internal diameter ratio of the cylinder from 18: 1 to 32: 1. The extruder screw used in the method according to the invention may have a length to diameter ratio of 15: 1 to 32: 1. For example, when an extruder screw with a length to diameter ratio of 18: 1 is used in the 24: 1 extruder, the remaining space in the extruder barrel can be partially filled with various types of plugs, torpedoes or static mixers to reduce the residence time of the polymer melt. The extruder screw can also be used for of the type disclosed in US Pat. US U.S. Patent No. 4,329,313. The molten polymer is then extruded through the die as will be described below. 14,143,304 The polymer is extruded at a temperature from about 163 ° C to about 260 ° C. The polymer is extruded vertically upwards in the form of a tube, although it can also be extruded downwards or to the side. After the molten polymer is extruded through the ring-shaped die, the foil tube is blown to the desired size, cooled or allowed to cool and flattened. The foil tube is flattened by passing the foil through a crushing device and a set of squeezing rollers. The squeezing wheels are driven, thus making it possible to stretch the foil tube away from the annular mouthpiece. Overpressure gas, for example air or nitrogen, is maintained inside the tube sleeve. As with conventional film making processes, gas pressure is regulated to achieve the desired degree of expansion of the film tube. The degree of expansion as measured by the ratio of the circumference of the fully blown tube to the circumference of the mouthpiece ring is in the range 1: 1 to 6: 1, preferably in the range 1: 1 to 4: 1. The tubular extrudate is cooled by known techniques such as air cooling, water quenching, or mandrel cooling. The tensile characteristics of the polymers disclosed herein are excellent. The stretching, defined as the ratio of the width of the mouthpiece gap to the product of the film thickness and the blown ratio, is below about 250. Very thin films can be produced using high stretch of these polymers, even if they are heavily contaminated with foreign particles and / or gel. Thin films with a thickness of about 0.013 to 0.076 mm can be produced such that the maximum MD elongation is from about 400% to about 700% and the TD is from about 500% to about 700%. Moreover, these films are not seen as "splitting". "Splitting" is a qualitative term that describes the tear responses to blot the film at high formation speeds. "Cleavage" reflects the speed at which cracks propagate. This is a utility characteristic of certain film protrusions and is not understood theoretically. As the polymer moves away from the ring-shaped die, the extrudate cools below its melting point and solidifies. As crystallization takes place, the optical properties of the extrudate change and a matte line is formed. The position of this matte line above the annular mouthpiece is a measure of the cooling rate of the foil. The cooling rate has a very pronounced effect on the optical properties of the film produced. Ethylene polymer can also be extruded in the shape of a rod or other solid cross-section, using the same mouthpiece geometry only for the outer surface. Furthermore, the ethylene polymer may be extruded into the tube through a ring-shaped die. The films formed according to the invention may be extruded through the foil forming slot. This method of making a film is well known in the art and involves extruding a sheet of molten polymer through a slit and then cooling the extrudate with, for example, a chilled roller or a water bath. The mouthpiece used will be described below. In the chilled roll method, the films can be extruded horizontally and placed on top of the chilled roll, or can be extruded down and pulled under the chilled roll. The cooling rates of the extrudate product in the fracture process are very high. Cooling with a chilled roller or a water bath is so fast that while the extruded film cools below its melting point, crystallite nucleation takes place very rapidly, there is little time for supermolecular structures to grow and spherulites are limited to a very small size. extruded from a slotted mouthpiece are significantly superior to those of films produced using slower cooling rates in the extrusion of blown sleeve film. The temperatures of the blend in the slit extrusion process are typically much higher than those of the sleeve extrusion process. The mechanical strength of the alloy is not a process limitation in this film extrusion method. Both the effective viscosity and the tensile viscosity are lowered. Films can generally be extruded at higher throughputs than those used and made by sleeve blown extrusion. Higher temperatures lower the shear stresses in the mouthpiece and raise the exit threshold for the appearance of surface melt viscosity. 143 304 15 The film produced by the method of the invention has a thickness of about 0.0024 mm to about 0.500 mm, preferably from about 0.0025 mm to about 0.250 mm, most preferably from about 0.0025 mm to about 0.100 mm. A film with a thickness in the range of 0.0025 to 0.100 mm has the following properties: a puncture resistance greater than about 0.32 kg cm / m; elongation at break over 400%, tensile strength from about 4.22 to about 16.86 kgm / cm3 and tensile strength from about 13.795 MPa to about 48.28 MPa. The composition of the film according to the practice adopted in the technique incorporate various conventional additives such as anti-sticking agents, lubricants and antioxidants. The polymers that may be used in the process of the invention are ethylene homopolymers or copolymers containing 80 or more mole percent ethylene and up to 20 mole percent of one or more of an alpha olefin containing 3 to 8 carbon atoms. The listed 3 to 8 carbon alpha olefins should not contain any branches on any of their carbon atoms which are closer than the fourth carbon atom. Preferred 3 to 8 carbon alpha olefins are propylene, butene -1, pentene -1, hexene -1, methylpentene -1, and octene -1. The ethyl tepolymers have a flow rate index of from about 18 to about 50, preferably from about 22 to about 30. The homopolymers have a density of about 0.958 to about 0.972, preferably from about 0.961 to about 0.968. The copolymers have a density of from about 0.89 to about 0.96, preferably from about 0.917 to about 0.955, and most preferably from about 0.917 to about 0.935. The density of the copolymer at a given level of the copolymer flow rate in the first row depends on the amount of comonomer containing 3 to 8 carbon atoms, co-polymerized with ethylene. 0.96. Thus, the introduction of gradually increasing amounts of comonomers into the copolymers causes the copolymer to gradually decrease in density. The amount of each of the various comonomers containing from 3 to 8 carbon atoms needed to achieve the same result will vary from monomer to monomer under the same reaction conditions. In the case of a fluidized bed process, the polymers of the invention are granular materials, which have a tapped density of about 240 to about 520 kg / cm3 and an average grain size of about 0.13 to about 1.5 mm. For the purposes of producing the film according to the invention, the preferred polymers are copolymers, in particular copolymers having density from about 0.917 to about 0.924 and a standardized rate of flow velocity from about 0.1 to about 5.0. The films produced according to the invention have a thickness of about 2.5 µm to about 250 µm, preferably from about 2.5 µm to about 125 µm. Having set out the general spirit of the invention, some specific embodiments of the method of the invention are illustrated in the following examples. It should be understood, however, that the invention is not limited to these examples as it may be carried out with various modifications. EXAMPLE I. This example illustrates a conventional method of extruding ethylene polymers into pipes. Ethylene-butylene copolymer was prepared by the method disclosed in US Patent No. US No. 4,302,566; It is available from Union Carbide Corporation under the trade name Bakelite GRSN 7047. This copolymer was dry blended with 4% conventional masterbatch containing conventional anti-sticking agent, lubricant, antioxidants and 320 ppm by weight of Kemamine AS 990. had a nominal density of 0.918 g / cm3, a nominal flow rate of 1.0 dag / min and a nominal flow rate of 26. The copolymer was formed into the shape of a tube by passing the resin through a conventional screw extruder with a diameter of 63.5 mm, equipped with a polyethylene screw as described in the description U.S. Patent US No. 4,329,313 with a Maddock type mixing section followed by a conventional chrome 16 143 304 mouthpiece having a 12.7 mm working area, 76.2 mm diameter mouthpiece flange and 74.168 mm diameter mouthpiece pickup, resulting in a gap width of approximately 1 mm. The sides of the working area of the mouthpiece were parallel to the flow axis of the polymer melt. The resins were pressed through the die at a rate of 29.94 kg / hr at 221 ° C. Serious viscoelastic instability of the alloy was observed on both surfaces of the pipe, leading to roughness of the surface of the extruded product. Example 2 This example demonstrates the improved results compared to Example 1, obtained by using a free-cutting brass flange and collar, containing 35% zinc, 61.5% copper, 3% lead and 0.5% iron. The tap surface has improved adhesion compared to the conventional chrome steel surface of Example I. The ethylene-butylene polymer was identical to that of Example I and contained a masterbatch. The polymer was formed into a tube by passing the resin through a conventional 63.5 mm diameter screw extruder and sections mixing of Example 1, with the difference that there was a brass working area of the mouthpiece. The resins were pressed through the die at a rate of 29.94 kg / hr at 220 ° C. After the initial start-up / induction period /, there was no surface melt fracture at any of the tube surfaces. Example III. This example shows a conventional process to extrude another type of ethylene polymer in the production of pipes. Ethylene-butylene copolymer was prepared by the method disclosed in US Pat. US No. 4,302,566; it is available from Union Carbide Corporation under the trade name Bakelite. The copolymer also contained 4% masterbatch as in Example I. This copolymer had a density of 0.918 g / cm3, a nominal flow rate and a nominal flow rate. The copolymer was formed into a tube by passing the resins through a conventional 63.5 mm diameter screw extruder and mixing section of Example 1 and through the die of Example 1. Resins were extruded through a die at a rate of 30.84 kg / h at 229 ° C. Serious melt fracture was observed on both surfaces of the tube, leading to rough extruded product surfaces. Example IV This example illustrates the conventional process of extrusion of yet another ethyl polymer during the production of the tubes. Terpolymerethylene with butylene and hexylene was prepared as described in US Pat. US No. 4,320,566; It is available from Union Carbide Corporation under the trade name DEX - 7652. The copolymer also contained 4% masterbatch as in Example I. This copolymer had a density of 0.918 g / cm3, a nominal flow rate of 1.0 g / min nominal flow rate coefficient flows cia. The terpolymer was formed into a tube by passing the resins through a conventional 63.5 mm diameter screw extruder and the mixing section of Example 1 and through the die of Example 1. The resins were extruded through the die at a rate of 30.84 kg / hr at 220 ° C. A severe melt fracture was observed on both surfaces of the tube, leading to a rough surface of the extrudate. Example 5 This example shows a conventional method of extrusion of another ethylene polymer in the production of the tubes. An ethylene butylene hexylene terpolymer was prepared according to the method described in US Pat. US No. 4,302,566; It is manufactured by the company Union Carbide Corporation under the trade name DEX - 7653. The copolymer also contained a premix of 4%, as in Example I. This copolymer had a nominal density of 0.918 g / cm3, a nominal flow rate of 0.5 g / min and nominal flow rate 26. The copolymer was formed into a tube by passing the resins through a conventional screw extruder 63.5 mm in diameter and the mixing section of Example 1 and through the mouthpiece of Example I. Resins pressed through the die at a rate of 30.84 kg / h at 229 ° C. C. Severe melt fracture was observed on both surfaces of the tube, leading to roughness of the extrudate surface. Example VI. This example demonstrates improved results compared to Example III, obtained by using a free-cutting brass flange and collar with a nominal zinc content of 35%, 61 , 5% copper, 3% lead, and 0.5% iron. 143 304 17 The ethylene-bottle copolymer was identical to Example III and contained a masterbatch. The polymer was formed into a tube by passing the resin through a conventional screw extruder 63.5 mm in diameter and the mixing section of Example I and the mouthpiece of Example I, with the difference that there was a brass working area of the mouthpiece. The resins were pressed through the die at a rate of 30.84 kg / h and a temperature of 229 ° C. After the initial start-up (induction period), no surface melt fracture occurred on any of the pipe surfaces. Example VII.This example demonstrates the improved results over Example IV obtained by using an automatic brass flange and collar with a nominal zinc content of 35% , 61.5% copper, 3% lead and 0.5% iron. Terpolymerethylene with butylene and hexylene was identical to Example IV and contained a premix. The terpolymer was formed into a tube by passing the resins through a conventional 63.5 mm diameter screw extruder and the mixing section of Example 1 and the mouthpiece of Example 1, with the difference that there was a brass working area of the mouthpiece. The resins were extruded through the mouthpiece at speed. 30.84 kg / h at 220 ° C. After the initial start-up (induction period), there was no surface melt fracture at any of the tube surfaces. Example VIII. This example demonstrates improved performance compared to Example V by using a machined brass die flange and pin with a nominal content of 35% zinc, 61.5% copper, 3% lead and 0.5% iron. The terpolymerethylene with butylene and hexylene was identical to Example V and contained a premix. The terpolymer was formed into a tube by passing the resins through a conventional extruder 63.5 mm in diameter and the mixing section of Example I and the mouthpiece of Example I, with the difference that there was a brass working surface of the mouthpiece. The resins were pressed through the die at a rate of 30.84 kg / h at 229 ° C. After the initial start-up / induction period /, no surface alloy instability was present on any of the pipe surfaces. Example IX. This example demonstrated improved results compared to Example I, obtained by using a free-cutting brass flange and collar with a nominal 35% zinc content, 61, 5% copper, 3% lead and 0.5% iron with the gap width reduced to about 0.5 mm. The ethylene-butylene polymer was identical to Example 1 and contained a masterbatch. The polymer was formed into a tube by passing the resins through a conventional screw extruder with a diameter of 63.5 mm and a mixing section from Example 1 and through a mouthpiece having a slot width of 0.5 mm. Other features of the mouthpiece are the same as in Example I. The sides of the mouthpiece working area were parallel to the flow axis of the polymer melt. The resins were extruded at a rate of 29.94 kg / h at a temperature of 220 ° C. After the initial start-up (induction period), no surface melt fracture occurred on any of the tube surfaces. Example X This example demonstrated improved performance over Example III, obtained by using a free-cutting brass flange and collar with a nominal 35% zinc content, 61 , 5% copper, 3% lead, and 0.5% iron, with the gap width reduced to about 0.5 mm. The ethylene copolymer was identical to Example III and contained a resilience. The copolymer was formed into a tube by passing the resins through a conventional 63.5 mm diameter extruder and the mixing section of Example 1, and through a die having a 0.5 mm gap. Other features of the mouthpiece are the same as in Example I. The sides of the mouthpiece working area were parallel to the flow axis of the polymer melt. The resins were extruded at a rate of 30.84 kg / h at a temperature of 229 ° C. After the initial (induction period), no surface melt fracture occurred on any of the tube surfaces. Example 11 This example demonstrated improved results compared to Example IV by the use of a machined brass flange and collar with a nominal 35% zinc content, 61, 5% copper, 3% lead and 0.5% iron, with the gap width reduced to about 0.5 mm. The polymerethylene with butylene and hexylene was identical to Example IV and contained a premix. The terpolymer was formed into a tube by passing the resins through a conventional 63.5 mm diameter metering extruder and a mixing section of Example 1, and through a die having a 0.5 mm wide aperture. Other features of the mouthpiece are the same as in Example I. The sides of the working area of the mouthpiece were parallel to the flow axis of the polymer melt. The resins were extruded at a rate of 30.84 kg / hour at a temperature of 220 ° C. After the initial start-up (induction period), there was no surface melt fracture at any of the tube surfaces. Example XII. This example demonstrates improved performance over Example V by using the flange and pin of a machined brass die with a nominal 35% zinc, 61.5% copper, 3% lead and 0.5% iron. Terpolymerethylene with butylene and hexylene was identical to Example V and contained a masterbatch. The terpolymer was formed into a tube by passing the resins through a conventional extruder 63.5 mm in diameter and the mixing section of Example 1 and through a die having a gap of 0.5 mm in width. The resins were pressed through the die at a rate of 30.84 kg / h and a temperature of 229 ° C. After the induction period, no surface melt fracture was present on either surface of the tube. Example XIII. This example demonstrated improved results compared to Example I, obtained by using a machined brass die flange and pin with a nominal zinc content of 35%. 61.5% copper, 3% lead, and 0.5% iron, with the gap width reduced to about 0.25 mm. The ethylene butylated polymer was identical to Example I and contained a master batch. The polymer was formed into a tube by passing the resin through a conventional an extruder with a diameter of 63.5 mm and a mixing section from Example 1 and through a mouthpiece having a slit 0.25 mm wide and a working area 3.2 mm long. The sides of the working area of the mouthpiece were parallel to the flow axis of the polymer melt. The resins were extruded at a rate of 29.94 kg / h at a temperature of 221 ° C. After the induction period, no surface melt fracture occurred on either surface of the tube. Example 14 This example demonstrated improved results compared to Example I, obtained by using a machined brass die flange and spike with a nominal zinc content of 35%, 61 , 5% copper, 3% lead and 0.5% iron, with the gap width reduced to about 0.25 mm. The ethylene-butylene copolymer was identical to the Example and contained no premix or stabilizer (Kemamine AS 990). The copolymer was formed into a tube by passing the resins through a conventional 63.5 mm diameter extruder and the mixing section of Example 1 and through a mouthpiece having a 0.25 mm wide slit and a 3.2 mm operating area. The sides of the working area of the mouthpiece were parallel to the flow axis of the polymer melt. The resins were extruded at a rate of 29.94 kg / h at a temperature of 222 ° C. There was no induction period, and no surface melt fracture was observed on either side of the tube. Example 15 This example demonstrates improved performance with respect to another ethylene-butylene copolymer by using a machined brass die flange and pin with a nominal 35% zinc, 61.5% copper, 3% lead and 0.5% iron. The ethylene-butylene polymer was made by the method disclosed in US Pat. No. 4,302,566; it is manufactured by the company Union Corporation under the trade name Bakelite GRSN-7081. Conventional antiblocking agent, lubricant, antioxidants and 320ppm Kemamine AS 990 stabilizer were incorporated into the copolymer. No additional masterbatch was used. The copolymer had a nominal density of 0.918 g / cm3, a nominal flow rate of 1.0 dag / min and a nominal flow rate of 26. The copolymer was formed into a tube by passing the resin through a conventional extruder 63.5 mm in diameter and the mixing section of Example I and through a mouthpiece having a slot width of 0.5 mm as in Example IX. The resins were extruded at a rate of 41.3 kg / h and a temperature of 222 ° C. After a short period of induction, no surface melt fracture was observed on any of the pipe surfaces. 143 304 19 Example XVI. This example shows the results for a different ethylene copolymer obtained by using a machined brass die flange and pin with a nominal content of 35 % zinc, 61.5% copper, 3% lead and 0.5% iron. When extruded through the conventional mouthpiece of Example 1, this resin exhibits a severe rough surface roughness of the shark skin type caused by the surface melt viscoelastic fracture. The ethylene butylene copolymer was prepared as disclosed in US Pat. No. 4,302,566; it is manufactured by Union Carbide Corporation under the trade name Bakelite GRSN-7071. This copolymer further contained 5% white concentrate in the form of a masterbatch with the symbol MB-1900, which is South West Plastics Company. In addition, 800 ppm by weight of the stabilizer Kemamine AS 990 was dry mixed with the copolymer. The copolymer had a nominal density of 0.922, a nominal flow rate of 0.7 dag / - min, and a nominal flow rate factor26. and by a mouthpiece having a slit 0.25 mm wide and a working area 3.2 mm long as in Example XIII. The resins were extruded at a rate of 31.75 kg / h and a temperature of 222 ° C. As before, no surface melt fracture was observed on either side of the pipe. Example XVII. This example shows the results for another ethylene copolymer by using an automatic brass mouthpiece collar and spike with a nominal zinc content of 35%, 61 , 5% copper, 3% lead and 0.5% iron. Upon being drawn through the conventional mouthpiece of Example 1, this resin exhibited a severe rough surface roughness of a shark skin type caused by surface melt fracture. Ethylene hexylene copolymer was prepared as disclosed in US Pat. US No. 4,302,566, it is manufactured by Union Carbide Corporation under the trade name Bakelite DEX-8218. This copolymer further contained 5% white concentrate in the form of a masterbatch MB-1900 by South West Plastcs Company. Additionally, 800 ppm by weight of Kemamine AS 990 stabilizer was dry blended with the copolymer. The copolymer had a nominal density of 0.928 g / cm3, a nominal flow rate of 0.7 g / min and a nominal flow rate of 26. The resins were formed into a tube shape by passing it through a conventional tube. an extruder having a diameter of 63.5 mm and a mixing section of Example I, and through a mouthpiece having a slit 0.25 mm wide and a working area 3.2 mm long as in Example XIII. The resins were extruded at a rate of 31.75 kg / h and a temperature of 222 ° C. As previously, no melt fracture was observed on either side of the tube. Example 18 This example shows the results obtained with the shifted configuration of the chrome mouthpiece shown in US Pat. US No. 4,348,349, where there is a reduction in surface fracture of the alloy on the tube side in contact with the positive-offset mouthpiece. The ethylene-butylene polymer was identical to Example 1 and did not contain a masterbatch. Instead, the stabilizer copolymer was dry-mixed with 800 ppm by weight dry mixed Kema¬ mine AS 990. The copolymer was formed into a tube by passing the resins through a conventional 63.5 mm diameter extruder and mixing section of Example 1 and a conventional 76.2 mm diameter mouthpiece having a gap of approximately 1 mm and a working area of approximately 35 mm. . The sides of the mouthpiece working area were parallel to the flow axis of the polymer melt, except that the top surface of the mouthpiece ring protrudes approximately 3mm beyond the collar. The resins were pressed through the die at a rate of 29.94 kg / hr at 221 ° C. As disclosed in U.S. Patent No. No. 4,348,349, a severe surface roughness was observed on the outside of the tube with only little or no markings inside the tube.Example XIX In this example, it has been shown that results similar to the offset configuration of the mouthpiece can also be obtained without moving the mouthpiece lip, while using 20 143 364 the mouthpiece collet made of automatic brass, with a nominal content of 35% zinc, 61.5% copper, 3% lead and 0.5% iron, and a conventional chrome mouthpiece flange The ethylene-butylene polymer was identical to Example I and did not contain a masterbatch. with the copolymer, 800 ppm by weight of Kemamine AS 990 stabilizer was dry blended. The copolymer was formed into a tube by passing the resins through a conventional extruder 63.5 mm in diameter through the mixing section of Example 1 and through a conventional die having a gap width of about 1 m. mm, formed by a conventional 76.2 mm diameter mouthpiece collar and a brass mouthpiece collar a with a diameter of 74.2 mm. The collet and collar had frontal surfaces lying in one plane and showed no displacement like in Example XVII. Other features of the mouthpiece were as in Example XVII. The sides of the mouthpiece working area would be parallel to the flow axis of the polymer melt. The resin was pressed through the mouthpiece at a rate of 29.94 kg / h at 221 ° C. For a short period of induction, the surface co-elastic fracture of the alloy was observed on the outside of the tube where the alloy touched the chrome flange of the mouthpiece, but no viscoelastic friction was observed inside the tube where the alloy was in contact with the brass surface. Compared to Example XVIII, obtained by using an automatic brass mouthpiece with a nominal content of 35% zinc, 61.5% copper, 3% lead and 0.5% iron, and a conventional mouthpiece flange with a positive chrome offset The ethylene-butylene copolymer was identical to Example 1 and contained no premix. Instead, 800 ppm by weight of a stabilizer (kemamine AS 990) was dry blended with the copolymer. The copolymer was formed into a tube by passing the resins through the conventional extruder of 63.5 mm in diameter and the mixing section of Example 1 and through the mouthpiece of Example 18, with the difference that there was a positive shift of about 3 mm in the collar. Other features of the die were such that as in Example XVII. The sides of the working area of the mouthpiece were parallel to the flow axis of the polymer melt. The resins were pressed through the die at a rate of 30.4 kg / h and a temperature of 221 ° C. After a short period of induction on both surfaces of the tube, only slight signs of viscoelastic melt fracture were observed. flow velocities and melt temperatures that would otherwise cause a highly viscoelastic melt instability, characterized in that the polymer is extruded through a die having an opposing working area, at least one of these surfaces being made of an alloy containing about 5 - 95% by weight of zinc and about 95 - 5% by weight of copper, while the ethylene copolymer contains a stabilizing agent, as a result of which the viscoelastic instability of the alloy on the surface of the polymer in the vicinity of this surface is eliminated made of an alloy containing zinc and copper. 2. Method according to claim The method of claim 1, wherein the alloy surfaces in the working area of the mouthpiece are inserts fixed to the collar and collar of the mouthpiece. 3. The method according to claim The method of claim 2, wherein the inserts extend over the entire length of the working area. 4. The method according to claim The method of claim 2, characterized in that the inserts extend over a portion of the length of the working area. 5. The method according to claim The method of claim 1, wherein the mouthpiece collet and the mouthpiece collar are made of this alloy. A method according to claim A process as claimed in claim 1 wherein the stabilizing agent is a dioxetylated fatty tertiary amine. 7. The method according to claim The method of claim 6, wherein the fatty tertiary amine is added to the ethyl copolymer in an amount from about 50 to about 1500 ppm. 143 304 21 8. A method according to claim 6. A process as claimed in claim 1, characterized in that the alloy also contains tin or aluminum, or lead or mixtures thereof. 9. The method according to claim The process of claim 1, wherein the alloy is about 30 to 40% by weight zinc and about 70 to 60% by weight copper. 10. A method according to claim The method of claim 9, wherein the mouthpiece collet and the mouthpiece collar are made of this alloy. 11. The method according to claim 11 The mouthpiece of claim 1, wherein the distance between the lips of the mouthpiece is from about 0.13 to about 1 mm. 12. The method according to claim B. A method according to claim 1, characterized in that the extruded polymer is a copolymer containing 80 or more mole% ethylene and up to 20 mole% of at least one alpha olefin with 3 to 8 carbon atoms. The process of claim 12, wherein the copolymer has a melt index of about 0.1-5.0 FIG. I + - £ FIG. 2143 304 fi / 8 FIG. 3 FIG. 4143 304 1—1 1 MM! TTT Q r D 1 1 1 l MIII o / '1 1 1 IJJJ1 ^ 7 i i i i im. 040 0 X. 600 L 220 * C. —U ^ 1 1 1 II 1 iJo1102o5 & b4 FIG. 5143304 600h 400h 200K FIG. 6 Printing House of the Polish People's Republic. Mintage 100 copies Price PLN 220 PL

Claims (1)

1. Claims 1. Method of eliminating the surface fracture of the alloy causing surface roughness during the extrusion of a molten linear ethylene copolymer with a narrow molecular weight distribution under such conditions of flow velocity and melt temperature that would otherwise result in a highly viscoelastic occurrence ¬ of pure melt instability, characterized in that the polymer is extruded through a die having a working area forming adjacent surfaces, at least one of these surfaces being made of an alloy containing about 5 - 95% by weight zinc and about 95 - 5% by weight copper. and the ethylene copolymer contains a stabilizing agent, thereby eliminating the viscoelastic melt instability on the polymer surface adjacent to that surface of an alloy containing zinc and copper. 2. Method according to claim The method of claim 1, wherein the alloy surfaces in the working area of the mouthpiece are inserts fixed to the collar and collar of the mouthpiece. 3. The method according to claim The method of claim 2, wherein the inserts extend over the entire length of the working area. 4. The method according to claim The method of claim 2, characterized in that the inserts extend over a portion of the length of the working area. 5. The method according to claim The method of claim 1, wherein the mouthpiece collet and the mouthpiece collar are made of this alloy. A method according to claim A process as claimed in claim 1 wherein the stabilizing agent is a dioxetylated fatty tertiary amine. 7. The method according to claim The method of claim 6, wherein the fatty tertiary amine is added to the ethyl copolymer in an amount from about 50 to about 1500 ppm. 143 304 21 8. A method according to claim 6. A process as claimed in claim 1, characterized in that the alloy also contains tin or aluminum, or lead or mixtures thereof. 9. The method according to claim The process of claim 1, wherein the alloy is about 30 to 40% by weight zinc and about 70 to 60% by weight copper. 10. A method according to claim The method of claim 9, wherein the mouthpiece collet and the mouthpiece collar are made of this alloy. 11. The method according to claim 11 The mouthpiece of claim 1, wherein the distance between the lips of the mouthpiece is from about 0.13 to about 1 mm. 12. The method according to claim The process of claim 1, wherein the extruded polymer is a copolymer containing 80 or more mole% ethylene and up to 20 mole% of at least one of the alpha olefins with 3 to 8 carbon atoms. B. The method according to claim The process of claim 12, wherein the copolymer has a melt index from 0.1 to 5.0. FIG. I + - £ FIG. 2143 304 fi / 8 FIG. 3 FIG. 4143 304 1—1 1 MM! TTT Q r D 1 1 1 l MIII o / '1 1 1 IJJJ1 ^ 7 i i i i im. 040 0 X. 600 L 220 * C. —U ^ 1 1 1 II 1 iJo1102o5 & b4 FIG. 5143304 600h 400h 200K FIG. 6 Printing House of the Polish People's Republic. Mintage 100 copies Price PLN 220 PL