SK71794A3 - Method of production of polyvinylalcohol follies and device for its realization - Google Patents

Abstract

The polyvinylalcohol foils being able of a biological decomposition are produced of the polyvinylalcohol granulate, while its modification is provided and after that, the subsequent extrusion is applied. The modification process is divided into two individual devices, as well as the softening reactor (1) and the cooling device (2). A product containing water in 0,8 up to 3,0 weight percent is gained, when the above mentioned procedure is applied. The extruder (4) is equipped with special worm and its compression rate is 1:1,5 up to 2,5. The polymer melt is blown at the pressure of 15,0 up to 30,0 MPa with the use of low pressure blowing head (5). After having cooled, this foil is guided to humidifying chamber (7), through the pinch rolls (12), and this chamber consists of the fixed and moving rolls, and after having loaded them based on the standard procedure with the use of the rolling device (8) the conditioning procedure is provided in the conditioning chamber (9).

Description

Title of the Invention: A process for the production of polyvinyl alcohol films and an apparatus for making the same

Technical field

The invention relates to the field of processing of polymers, in particular to a process for the production of polyvinyl alcohol films, which are biodegradable and to apparatus for carrying out the process by blow molding.

BACKGROUND OF THE INVENTION

In recent years, foils that are biodegradable and hence polyvinyl alcohol-based films have become increasingly important in packaging.

At present, two different processes for the production of these films are known, the so-called wet and dry processes.

Wet process, pouring from an aqueous solution of polyvinyl alcohol, respectively. from a solution containing also a plasticizer and optionally other ingredients followed by film drying, used in Japan and America, energy / dissolution of PVA1 at 95 ° C, solution fitment, drying (and technologically) requires special machinery that is different from that used in thermoplastics processing / very demanding, which is reflected in the price of foil *

The dry process, by extrusion from a thermoplastic granulate prepared by modification of PVA1, is more advanced and allows the use of similar devices as in the production of thermoplastic film. Since PVA1 decomposes below the melting point and is unprocessable without further treatment, its melting point is lowered by the addition of plasticizers1 such as e.g. polyhydric alcohols having a boiling point above 250 ° C (DE 2 812 684, OE 2 841 238), which are added in the form of aqueous solutions. Additional additives, antioxidants, anti-blocking agents, lubricants and the like are added to achieve certain film properties.

Softening is generally carried out in duplicator reactors under vigorous stirring at atmospheric pressure by heating the reaction mixture to 100 to 150 ° C and cooling it after softening is complete. A disadvantage of the process is the increased water content of the product above 5% by weight, which causes bubbles to holes during further blow molding. Half-feeding the screw during extrusion for water vapor removal only partially solves this problem *

Also known is a softening process * in which an optimal modification of PVA1 and a low water content below 1% by weight * is achieved by varying the pressure and temperature during softening (PV 700-92). · Proceay softening * drying and cooling are carried out in a single reactor cooling the reactor. The disadvantage of this process is both the time required for the entire modification process and the problems of further processing into films. Almost completely removal of unbound water causes thermal decomposition of the material during extrusion due to the absence of a stabilizing effect of the water against the thermal load. It manifests this by coloring the film in yellow to brown and by negatively changing the rheological properties of the polymer melt.

SUMMARY OF THE INVENTION

SUMMARY OF THE INVENTION The present invention relates to a process for the production of polyvinyl alcohol films by modifying polyvinyl alcohol granules in the presence of a plasticizer and optionally other auxiliaries and subsequent extrusion which is carried out in such a way that the modification is two-stage. with a water content of 0 * 8 to 3 * 0% by weight, melts at a compression ratio of 1: 1.5 to 2.5, the melt is filtered after filtration at a pressure of ΙξΟ up to 30.0 MPa, the film is moistened at relative humidity after cooling 50 to 100%, winds in a conventional manner and condition.

Apparatus for the production of polyvinyl alcohol films according to the present invention comprising a plasticizer * extruder, an air conditioning column consisting of a softening reactor * to which a cooling apparatus is connected, a special screw helicopter with a low compression ratio * resulting in a low-pressure blowing head * 3 movable and movable cylinders, located between exhaust and retractor and from the air conditioning chamber ·

Advantages of the process according to the invention include a substantial reduction of the polyvinyl alcohol modification reaction time * which is achieved by dividing the softening and cooling process into two separate apparatuses. Another advantage is that modified polyvinyl alcohol having a water content of 0.8 to 3% by weight is obtained. which, on the one hand, ensures the stabilizing effect of the water against the thermal load during extrusion * tJ *, no bubbles are formed and, on the other hand, the water does not release and does not cause film blowing problems.

The equilibrium between air humidity and film is quickly achieved by passing the blown film through the humidifying chamber * to facilitate winding of the softened film · The humidifying chamber allows the length of the film path * to be varied continuously relative humidity and film temperature. There is a partial recovery of water * which evaporates during processing.

The use of a screw extruder with a low compression ratio eliminates the shear load. * No homogenization zone is required.

The advantage of the low pressure blow head is that it reduces the residence time of the melt in the head and thus prevents the degradation of PVA1.

The process of the present invention achieves an increase in production capacity of at least 70% at a minimum investment cost.

Clarification of the attached picture

Shown is a diagram of a polyvinyl alcohol film production line. To the softening reactor 1; The reaction mixture is cooled in a separate cooling apparatus 2 * at which it is advantageous to place the modified polyvinyl alcohol container 3. The modified polyvinyl alcohol is fed into an extruder 4 with a special screw equipped with a melt filter and a melt. is blown out through the low-pressure blow head Between the draw-off rollers 12 e the winding device J3 A humidification chamber 7 consisting of a set of fixed and movable cylinders is placed, the desired climatic conditions being preferably achieved by a separate air-conditioning device.

DETAILED DESCRIPTION OF THE INVENTION

In a 90 L stainless steel duplicator reactor equipped with a special horizontal axis stirrer, a thermometer and a pressure gauge, 30 kg of polyvinyl alcohol having a saponification value of 140 mg KOH / g and a viscosity of 4% aqueous solution at 20 ° C of 8 mPas are added. at 1S0 rpm a plasticizer mixture consisting of 3.4 kg of glycerin and 1.1 kg of water is added over 10 min. · The reactor is hermetically sealed, the speed is reduced to 80 rpm and the batch temperature is raised to 50 rpm over 50 min. 115 ° C by heating steam at 0.4 MPa through the reactor jacket. The pressure in the reactor rises to 180 kPa. Upon reaching these parameters, the vent valve is opened, the heating is stopped, and the water vapor from the reactor is extracted by means of a vacuum pump at 15 kPa. After 10 minutes of drying, the water content of the batch drops to 1.2% by weight and the batch temperature drops to 102 ° C. After the vacuum has been removed, the reactor contents are discharged into a cooling apparatus consisting of an 80 L stainless steel duplicator equipped with a vertically mounted stirrer, thermometer and vent hole covered with fabric. The modified polyvinyl alcohol is cooled through the jacket of the cooling apparatus with cooling water at 23 ° C at a stirrer speed of 70 rpm. After the temperature has been reduced to 45 ° C, the modified polyvinyl alcohol is discharged into a container from which it is fed into a special screw extruder / compression ratio of 1: 1.8, without mixing zone / at a temperature regime of 20, 210, 205, 200, 190, 180 ° C, After passing the melt of the polyvinyl alcohol through the filter, it is extruded through a low-pressure blow head (head temperature 175 ° C) at a pressure of 180 MPa.

At the same time, the melt cools slowly, through the take-off rollers, it is subsequently fed into a humidification chamber in which the temperature is 20 ° C and the relative humidity is 75%. After passing through the humidifying chamber for 2 min, the film is wound in a conventional manner on a winding machine. · After winding, the film is placed in the air-conditioning chamber for 24 h under the following conditions: temperature 20 ° C, relative humidity 65% water.

Example 2

The procedure is as in Example 1 except that polyvinyl alcohol with a saponification number of 140 mg KOH / gas with a viscosity of 4% aqueous solution of 18 mPas is used. After drying under reduced pressure of 15 kPa and cooling in a cooling apparatus, a thermoplastic granulate is obtained. polyvinyl alcohol with a water content of 1.5% by weight, which is fed into an extruder with five heating zones, equipped with a special screw / compression ratio 1: 2, without mixing and compression zone / at a temperature regime of 20, 215, 210, 205, 200 and 190 ° C. After filtering the melt, it is extruded through a low-pressure blow head / head temperature of 180 ° C / at a pressure of 20p MPa · After blowing the balloon to the desired size, the melt is slowly cooled by means of a conventional cooling ring. placed in-line where the temperature is 25 ° C and the relative humidity is 85%. After passing through the humidification chamber during

The film is wound in the usual way for 2.5 minutes. · After the film is wound, the film is placed in the air conditioning chamber for 30 hours at a temperature of 23 ° C and a relative humidity of 60%.

Made foil Is slowly soluble in cold water ·

Example 3

The procedure is as in Example 1 except that polyvinyl alcohol with a saponification number of 28 mg KOH / g and a viscosity of a 4% aqueous solution of 20 mPas is used. The plasticizer mixture consists of 4.5 kg of glycerin and 1.5 kg of water. The batch temperature is raised to 120 ° C, at which pressure in the reactor rises to 200 kPa. After drying at a pressure of 15 kPa and cooling to 45 ° C, a free-flowing polyvinyl alcohol granulate with a water content of 2.2% by weight is obtained, which is discharged into a storage tank · From the storage tank it is fed into an extruder with five heating zones. : 2.5, without mixing and special compression zone / at temperature mode 20, 230, 225, 220, 210 and 200 ° C. After filtering, the melt is extruded through the low pressure blow head / head temperature 190 ° C / at 23p MPa · After blowing the balloon to the desired shape, the melt is slowly cooled at the same time · The foil passes through the draw rollers and in which the temperature is 30 ° C and the relative humidity is 95% · After passing through the humidification chamber within 3 min, the film is wound in a conventional manner. After winding, it is placed in a climate chamber for 20 h at 25 ° C and 65% relative humidity.

Made film is not soluble in cold water *

Industrial applicability of the invention

The polyvinyl alcohol films produced according to the present invention are suitable for subsequent finalization on sacks, bags and the like, or for direct use in packaging machines. They can be used in food, healthcare and other areas than special packaging material.

Claims (6)

PATENT CLAIMS Process for the production of polyvinyl alcohol films by modifying polyvinyl alcohol granules in the presence of a plasticizer and optionally other excipients and subsequent extrusion, characterized in that the modification is two-stage, wherein in the first pressure stage the softening is carried out and 0.8 to 3.0% by weight, melts at a compression ratio of 1: 1.5 to 2.5, the melt is blown at 15 to 30 MPa after filtration, the film is moistened at 50 to 100% relative humidity after cooling, winds in the normal way and condition, Method according to Claim 1, characterized in that a product having a water content of 1.1 to 1.5% by weight is prepared by modification. Method according to Claim 1, characterized in that the modified polyvinyl alcohol is melted at a compression ratio of 1: 2. Production method according to claim 1, characterized in that the melt is blown at a pressure of 18 to 22 MPa. Apparatus for carrying out the production method according to claim 1, comprising a plasticizer, an extruder, an air conditioning chamber, characterized in that it consists of a softening reactor (1) to which a cooling apparatus (2), an extruder (4) with a special screw is connected and a low compression ratio resulting in a low pressure blow head (5), a humidification chamber (7), consisting of a set of fixed and movable cylinders situated between the take-off rolls (12) and a winding device (8) and an air conditioning chamber (9). Apparatus according to claim 5, characterized in that a modified polyvinyl alcohol container (3) is located downstream of the cooling apparatus (2).