HK1080793A - Method for the production of low orientation thermoplastic film the film produced thus and use thereof - Google Patents

Description

Method for producing low-oriented thermoplastic films, films produced thereby and use thereof

Technical Field

The present invention relates to low oriented thermoplastic films.

Background

DE 3842796 (R * hm GmbH) describes polymethyl methacrylate (PMMA-plexiglass) films based on PMMA molding materials having a small elastomer particle size and a high elastomer content. This patent application describes a Chill-Roll process (Chill-Roll-Verfahren) in which a melt film emerging from an extrusion nozzle is taken up and cooled by a single Roll.

WO 96/30435 and EP 763560 (Mitsubishi Rayon) describe the production of PMMA films of thickness not greater than 0.3mm, based on a certain PMMA composition: impact strength modifiers based on polybutylacrylate with a certain particle diameter and PMMA matrix polymer III and (optionally) additives of melt-resistance modifiers (polymer I).

The production of the films takes place by means of a single-Roll process, the so-called Chill-Roll melt casting process (Chill-Roll-Schmelzegie β process), in which the thermoplastic melt is brought into contact with a separate metal Roll and cooled during cooling and solidification. It is emphasized that a thermoplastic melt for making a film in the desired thickness range cannot be formed between two metal rolls.

This method has significant disadvantages compared to the two-roll process, which have a decisive influence on the film quality. PMMA molding materials with improved impact resistance have a tendency to form gels, which, unlike the two-roll (smoothing) process, are not pressed under the surface of the film when formed on a separate chill roll, and therefore are present as an appearance defect. This is particularly disadvantageous in the subsequent pressing process for the manufacture of decorative films, where clearly visible defects are shown in the region of the gel body. Secondly, there is a pronounced surface haze on the surface of the film of the rear cooling roller, which is freely cooled in air, which results from the different strength of the volume shrinkage of the elastomer particles and of the PMMA matrix. This produces a pronounced "peak and valley" surface structure which scatters light, thereby causing undesirable haze effects.

DE 19544563 (R * hm GmbH) describes PMMA molding materials (not deleted) with good impact resistance for producing the films according to the invention.

DE 4018530 (R * hm GmbH) describes a process for producing solid sheets or films of less than 1mm thickness from thermoplastics having a glass transition temperature of > 50 ℃. The finishing is achieved by laying the film on a circulating belt. The resulting sheet or film has little orientation and birefringence.

EP 659829 (R * hm GmbH) describes weather-resistant films and molding materials coated therewith, which films have, in addition to a weather-resistant function, an UV-absorbing action. It consists of a PMMA hard phase and a tough phase, wherein the ultraviolet absorber is in the hard phase.

EP 391193 (Bayer AG) describes the production of optically homogeneous extruded films with a clear two-sided thickness of less than 0.6mm

1. By pressing and subsequent calendering between a painted resilient roller and a high-gloss steel roller, or

2. Forming in two extrusion steps, wherein in the first step a film with a highly smooth one side and a rough other side is produced by extrusion and subsequent calendering between a polished resilient roll and a highly smooth steel roll. In a second extrusion step, the film produced in the first step is coated with the same thermoplastic melt on the matte side and again calendered between a polished resilient roll and a highly smooth steel roll, the highly smooth side of the coated film facing the polished resilient material roll.

Method 1 has the disadvantage that large-scale production cannot be achieved, since the paint layer on the rubber roller becomes brittle quickly under the influence of high melt temperatures. To avoid the effect of high melt temperatures, the painted rubber roller can be cooled in a water bath, but the moisture causes an adverse effect on the film surface quality.

Process 2 is particularly economically disadvantageous, since the film production must be carried out in two extrusion steps. Secondly extrusion coating of the film with the melt and subsequent pressing, in particular in the thickness range required according to the invention, leads to poor surface characteristics.

EP 165075 (Exxon) describes a process for producing a two-sided glossy film composed of 10 to 85% by weight of an elastomer and 90 to 15% by weight of a polyolefin, in which an extruded film web is passed through the nip of two counter-rotating rollers at a temperature above its softening point. One of the rolls is a high gloss steel chill roll and the other roll is a roll with a high gloss rubber surface, where the film is cooled. The films thus obtained have a thickness of from 25 to 250 μm (10)^-6m) are included.

EP 294705 (R * hm GmbH) describes a process for producing a two-sided glossy film, which uses a two-sided glossy film produced beforehand and fed back in the process as a smoothing element.

EP 916474 (General Electric Company) describes a process for the production of Polycarbonate (PC) films which are coated on one side with a UV-curable coating. One side of the PC film was deformed by curling. The film has a small birefringence and a high transmittance because the refractive indices of the film and the coating are matched to each other.

EP 916475 (General Electric Company) describes the production of films consisting of thermoplastic materials with a polished surface and birefringence and having a thickness of less than 25 μm. This is achieved by a levelling machine consisting of a metal roller and a roller coated with polytetrafluoroethylene. The polytetrafluoroethylene coating is applied by a sizing process.

WO 96/40480 (Avery Derrison Corp.) describes an extrusion coating process. An optically transparent material is pressed onto an auxiliary film (12) in the nip. The composite material is then coated with a polymeric other material. The extrusion coating method together with the subsequent coloring eliminates the painting process, which is associated with solvent evaporation.

The second dyed coating can be coextruded onto the composite or can be cast from solution.

An extrusion coating process is described on page 373 of the Friedhelm Hensen (Ed.) book of "Plastics extrusion technology", FIG. 11.5, as it is described in WO 96/40480.

In DE 19813001, PMMA molding materials provided with impact resistance are processed according to DE 19544563 to form a surface-hardened, high-gloss and virtually gel-free Film which can be processed by the In-mold Film Decoration (In-Mould-Film-Decoration) method. The melt is produced by means of an extruder and fed to the calender according to the invention via a flexible lip nozzle, which is designed to produce a particularly high mold clamping force in the roller gap. The calender rolls are drum-shaped. The film is used for the surface decoration of precious thermoplastic formed pieces. Films with particularly high orientation are obtained due to the high mold closing forces in the nip.

Disclosure of Invention

The object of the invention is to develop a convenient and cost-effective extrusion method for films, by means of which thermoplastic films can be produced in the thickness range from 20 μm to 1000 μm, which have a surface structure facing the application, for example glossy, dyed, matte, uv-absorbing or light-scattering, wherein the film surfaces can have different curling deformations. The film should have a high mechanical load-bearing capacity.

This object is achieved by a method for extruding plastic through a wide-slot nozzle and for producing a thermoplastic film in the thickness range from 20 μm to 1000 μm by smoothing the melt film extruded from the wide-slot nozzle in a smoothing machine consisting of at least three or four rolls, wherein a first roll pair (1, 2) forms a smoothing nip for receiving the melt film, after which the melt film passes through a subsequent smoothing nip or a subsequent pressure nip,

it is characterized in that,

the ratio of the nozzle gap width to the film thickness is in the range from 1: 1 to 6: 1, and the quotient of the film web speed in the subsequent smoothing nip or in the subsequent pressing nip divided by the film web speed in the smoothing nip formed by the roller pair (1, 2) is in the range from 0.8 to 1.05.

The low molecular orientation of the film formed is achieved by matching the nozzle gap width, the film thickness and the quotient of the film web speed in the subsequent smoothing nip or in the subsequent pressing nip divided by the film web speed in the smoothing nip formed by the roller pair (1, 2), which accordingly contributes to an increase in the mechanical strength, in particular in the transverse direction, including the extrusion direction.

Drawings

The invention is illustrated by the following figures, but should not be limited to these embodiments.

Reference numerals:

FIG. 1: the inventive arrangement with four rollers, viewed perpendicular to the extrusion direction, is provided.

1-a second smoothing roller having an elastic surface consisting of silicon for example,

2-for example a first levelling roll with a surface consisting of polished steel,

e.g. a third leveling roll acting only as a cooling roll,

31, for example, a fourth roll with an elastic coated surface, which acts as a pressure roll,

4-a film extrusion nozzle,

a 5-fused film (for example, made of polymethyl methacrylate with improved impact toughness).

FIG. 2: the structure according to the invention for producing laminated plastics with polyethylene terephthalate film with four rollers is indicated in fig. 1.

Polyethylene terephthalate (6 ═ polyethylene terephthalate) film

Laminated plastic film (polyethylene terephthalate and, for example, polymethyl methacrylate with improved impact resistance)

FIG. 3: the invention relates to a structure with three rollers. Wherein the roller (3) and the roller (2) form a subsequent smoothing nip. The reference numerals are the same as in fig. 1.

Detailed Description

The invention relates to a method for producing films of thermoplastic material having a thickness range of 20 μm to 1000 μm, preferably 20 μm to 750 μm, particularly preferably 20 μm to 500 μm, by first extruding the plastic material through a wide-slot nozzle and then pressing the melt film emerging from the wide-slot nozzle in a finisher comprising at least three or four rolls, wherein a first roll pair (1, 2) forms a smoothing nip which receives the melt film and the melt film is guided after the smoothing nip through a subsequent smoothing nip or pressure nip, characterized in that the ratio of the nozzle slot width to the film thickness is in the range from 1: 1 to 6: 1, preferably in the range from 1: 1 to 4: 1, particularly preferably in the range from 1: 1 to 3: 1, in particular in the range from 1: 1 to 2: 1, the quotient of the film web speed in the subsequent smoothing nip or in the subsequent pressing nip divided by the film web speed in the smoothing nip formed by the roller pair (1, 2) is in the range from 0.8 to 1.05, preferably in the range from 0.85 to 1, particularly preferably in the range from 0.9 to 1.

The melt produced by means of a single-screw or twin-screw extruder (preferably a melt pump can be used to ensure a constant melt flow rate) is fed to the shaping process according to the invention via a nozzle designed for the film extrusion surface.

Preferably, melt filtration is performed between the melt pump and the extrusion nozzle. The width of the film resulting from the nozzle width may be, for example, 1500 mm. The nozzle slot opening or nozzle lip opening may be, for example, 0.6 mm. The melt temperature is selected in accordance with the usual processing temperatures of the materials used. The melt is dimensioned in a defined nip and smoothed and cooled by means of temperature-controlled rolls.

The leveler includes at least three or four rollers in total. Wherein the first two rollers form a smoothing nip for receiving a melt film from a wide slot nozzle, preferably located directly above the smoothing nip. The distance between the wide slit nozzle and the smoothing nip can typically be, for example, 2 to 20 cm.

Possible roller structure and surface conditions:

both rollers of the roller pair (1, 2) may have a steel surface.

One of the rollers of the roller pair (1, 2) may have a steel surface and the other roller may have a surface having a hardness lower than that of steel. The rollers with steel surfaces have a structured or rough steel surface or a high-gloss polished steel surface with a roughness RA of 0.002 to 0.006 or RT of 0.02 to 0.04, measured according to DIN 4768. One of the rollers preferably has a resilient, thermally stable surface, for example composed of silicone rubber or fluoro-rubber. The surface of this roller may be smooth or rough.

The roller having a surface with a hardness lower than that of steel may have a surface composed of a heat-resistant elastic material having a shore-a hardness in the range of 30 to 90.

The third roller (3) may be closely adjacent to one of the rollers of the roller pair (1, 2) so that a flat nip is formed between the two rollers through which the melt film passes under pressure.

The third roller (3) can be so far from the closest roller of the roller pair (1, 2) that no further nip is formed between them, and the third roller forms a pressing nip with a pressing roller (31) through which the melt film passes.

The ratio of the nozzle gap width to the film thickness is in a defined range in order to keep the molecular orientation of the melt film in the Machine Direction (MD) low by means of the line pressure occurring in the smoothing machine. The film thickness is in the range of 0.6 to 0.1mm, assuming a nozzle gap width of 0.6 mm. The line pressure in the smoothing nip formed in the method according to the invention is in the range from 50N/cm to 1500N/cm.

If the surface of the roll used is composed of a heat-resistant elastic material having a Shore hardness-A in the range of 30 to 90, the linear pressure is usually not higher than 300N/cm.

The nozzle gap width refers to the distance of the nozzle lip of the wide gap extrusion nozzle.

At least one further third roller (3) is connected to the first roller pair. The melt film coming out of the smoothing nip here is laid down or wound onto the roll in order to cool it and/or to shape it.

Wherein the third roller can be closer to one of the rollers (1, 2), for example to the second roller (2), so that a further smoothing nip is formed between the two rollers through which the melt film passes. The roller then applies pressure to the melt film in a manner similar to that in the first smoothing nip.

The third roll (3) may be located further from the nearest one of the pair of rolls (1, 2) so that no further nip is formed between the two rolls. In this case, the third roller forms a pressure nip with a pressure roller (31) through which the melt film passes. The pressure roller is normally undriven. It is preferably an elastic coating and serves to ensure the planar position of the film strip.

In addition to the third roll or the third and fourth roll, in some cases there may be a further roll which receives or guides the melt film or film from the third roll. Particularly in the case of a relatively thick film having a thickness in the range of 400 μm to 1000 μm, it is advantageous to use a plurality of cooling rolls in sequence.

The quotient of the speed of the film strip in the subsequent smoothing nip or in the subsequent press nip divided by the speed of the film strip in the smoothing nip formed by the roller pairs (1, 2) should be particularly small in order to avoid stretching of the melt film in the Machine Direction (MD) and the molecular orientation of the film associated therewith.

A rough roller surface is understood to mean a surface which is processed in such a way that the required period deviations from the high-gloss surface occur in the film. Such rolls are also known as embossing rolls. In the case of steel rolls, a fine rough surface may be provided, for example, by electronic engraving, laser engraving or sand blasting of the original smooth surface.

The melt temperature is selected in accordance with the usual processing temperatures for the materials used.

The following film types can be realized, for example, with the method of the invention:

a film with smooth surfaces on both sides,

a film having a smooth, rough or textured surface,

films with two rough or structured surfaces.

Generally the film may also be coextruded or laminated.

Suitable thermoplastics are:

the following materials can be considered as thermoplastic materials for the film.

Polymethyl methacrylate (PMMA), PMMA with improved impact strength (sz-PMMA), mixtures of PMMA or sz-PMMA and a fluoropolymer, for example polyvinylidene fluoride (PVDF), wherein the mixing ratio between PMMA or sz-PMMA and PVDF can be, for example, between 10: 90 and 90: 10 by weight. Fluoropolymer in the context of the present invention means a polymer which can be obtained by free-radical polymerization of an alkene-unsaturated monomer, at least one fluorine substituent being located on the double bond. Copolymers are also included herein. These copolymers may contain, in addition to one or more fluoromonomers, other monomers which can be polymerized in combination with these fluoromonomers.

Further fluorine-containing monomers include chlorotrifluoroethylene, fluorovinylsulfonic acid, hexafluoroisobutylene, hexafluoropropylene, perfluoromethylvinyl ether, tetrafluoroethylene, vinyl fluoride, and vinylidene fluoride. Of these, vinylidene fluoride is particularly preferred.

Other suitable thermoplastics are, for example, acrylonitrile-butadiene-styrene copolymers (ABS), acrylonitrile-styrene-acrylate copolymers (ASA), methyl methacrylate-Modified ABS (MABS), impact-resistant polystyrene (sz-ps), PETG (amorphous polyethylene terephthalate), Polycarbonate (PC).

Laminating the film:

in a particular embodiment, the film is produced with a polyethylene terephthalate film (e.g. Mylar)^*Film, Dupont-Teijin) or polypropylene film. A first roller consisting of a highly polished steel and a second roller with an elastic surface, for example consisting of silicone rubber, form a smoothing nip. A melt film consisting of, for example, polymethyl methacrylate, impact-modified polymethyl methacrylate or a polymethyl methacrylate/polyvinylidene fluoride mixture is extruded in the nip, wherein a 50 μm thick polyethylene terephthalate film is passed through on the side of the second roll with an elastic surface. The resulting laminated plastic may have a total thickness of, for example, 100 μm, and is passed over a third roll, adjacent to the second roll and acting as a cooling roll, where it is cooled. In this case, the third roll forms a pressure nip with a pressure roll (31), through which the cooled melt film passes.

The laminated film can then be separated again. The film thus formed had a high gloss surface on the side on which the PET or polypropylene film was placed.

The test method comprises the following steps:

the advantages of the films according to the invention can furthermore be demonstrated by the following measurements, measured in sections parallel and perpendicular to the extrusion direction.

The modulus of elasticity, the tensile strength and the elongation at break were measured according to ISO 527-3, the clamping length was 60mm and the test speed was 50 mm/min.

The pencil hardness can be determined according to ASTM D3363-92 a.

The brightness may be measured at 60 ℃ according to DIN 67530.

"haze" can be measured according to ASTM D1003. With respect to the calculation of the "surface haze", the value is obtained by subtracting the haze measured in the untreated state from the haze of the film after the silicone oil treatment on both sides.

And (3) shrinkage measurement: the "total retraction amount" was determined. For this purpose, a 100X 100mm test piece is tempered at 160 ℃ for 30 minutes.

The amount of shrinkage (thermal relaxation) is defined as the change in the dimensions of the test piece (measured at room temperature respectively), which is caused by the shrinkage of the test piece when heated to a certain temperature. It is determined as the percent retraction of the distance of the two marks on the test piece relative to the distance in the uncontracted state.

The excellent effect is as follows:

the films of the invention have a relatively small orientation of the polymer molecules, which results in advantageous mechanical properties.

The films are characterized by small shrinkage, small thickness variation and isotropic mechanical properties. The surface quality is high (fewer fish eyes/gel).

Application possibilities:

the film can have as large a selection range as possible in terms of the surface structure facing the application, for example: shiny, dyed, matte (embossed), matte (particle modified), uv absorbing, light scattering.

Films are therefore suitable for many applications and can be used, for example, in decorative films, UV-protective films, dry-paint films, scratch-resistant films for optical data carriers, and in the production of data carrier materials which are printed by means of continuous printing processes, such as gravure printing, flexographic printing, offset printing, digital printing, rotary screen printing, transfer printing; and/or by successive lamination and coating methods, such as film composite lamination, coating of thermoplastic sheets and profiles, armoring, roll coating and/or successive coating methods, such as water-repellent coating, antimicrobial coating, self-cleaning coating, anti-graffiti coating, conductive coating, optionally in combination with embossing.

Particular embodiments of the abovementioned laminated films composed of polyethylene terephthalate or polypropylene films and polymethyl methacrylate, polymethyl methacrylate with improved impact strength or polymethyl methacrylate/polyvinylidene fluoride mixtures are distinguished by high mechanical and thermal strength. The laminated films are therefore suitable for subsequent processing under high mechanical and temperature loads, as may occur, for example, in printing or coating processes. The risk of tearing and sticking to the guide roll is significantly reduced relative to prior art films.

General examples for thin film fabrication:

the production of a film from polymethyl methacrylate having improved impact toughness can be carried out, for example, in the following manner.

For example, the impact-modified polymethyl methacrylate molding materials may have the following structures. The production of such impact-resistant molding materials is known, for example, from DE 3842796C 2. It is a two-layer polymer of an inner tough layer consisting of 99% by weight of butyl acrylate and 1% by weight of allyl methacrylate and an outer hard layer consisting of 96% by weight of methyl methacrylate and 4% by weight of butyl acrylate. The impact strength modifier is extruded as a molding material in the same weight proportion as a polymethyl methacrylate matrix molding material consisting of 90% by weight of methyl methacrylate and 4% by weight of methyl acrylate to form a film.

Film extrusion equipment:

the molding material used is melted in a single-screw extruder and fed to a film nozzle, which distributes the melt over its width. The film nozzle width may be, for example, 1500 mm. The opening of the thin film nozzle opening may be, for example, 0.4 mm. The temperature of the sprayed melt was about 250 ℃. The film spray nozzles are arranged vertically above a pair of leveler rollers. One of the rollers (2) has a highly polished steel surface and the other roller has a rough surface consisting of silicone rubber. The rollers have a diameter of 400 mm. Both rolls were tempered to a temperature of 80 ℃. The film thickness was 0.15 mm. The line pressure occurring in the smoothing nip is shown in a measuring device of the extrusion setup, which is in the range of about 100N/cm. The film web is guided on the side of the steel roll with a high-gloss surface onto a third roll with a diameter of 250mm, which is spaced apart by a distance of about 300 mm. The third roll was tempered to a temperature of 60 ℃. The third roller and the fourth roller form a pressurized nip. The fourth roller has a diameter of 140 mm.

The quotient of the speed of the film web in the pressure nip divided by the speed of the film web in the smoothing nip formed by the roller pairs (1, 2) is 0.98.

The film web is then guided through a plurality of support rollers and wound onto a reel in a completely cooled state.

The resulting rough-faced film tape is of high quality in terms of mechanical properties, thickness variation, shrinkage and isotropy in the amount of gel.

Claims (12)

1. Method for producing a film of thermoplastic material having a thickness in the range from 20 μm to 1000 μm by first extruding the plastic through a wide-slot nozzle and then pressing the melt film emerging from the wide-slot nozzle in a finisher comprising at least three or four rolls, wherein a first roll pair (1, 2) forms a smoothing nip for receiving the melt film, after which the melt film is guided through a subsequent smoothing nip or a subsequent pressure nip, characterized in that the ratio of the width of the nozzle slot opening to the film thickness is in the range from 1: 1 to 6: 1 and the quotient of the film web speed in the subsequent smoothing nip or pressure nip divided by the film web speed in the smoothing nip formed by the roll pair (1, 2) is in the range from 0.8 to 1.05.

2. A method according to claim 1, characterized by: both rollers of the roller pair (1, 2) have a steel surface.

3. A method according to claim 1, characterized by: one of the rollers of the roller pair (1, 2) has a steel surface and the other roller has a surface which is less hard than steel.

4. A method according to claim 2 or 3, characterized by: the rollers with steel surfaces have a structured or matt steel surface or a highly polished steel surface with a roughness RA of 0.002 to 0.006 or RT of 0.02 to 0.04, measured according to DIN 4768.

5. A method according to claim 3, characterized by: the roller with a surface having a hardness lower than that of steel has a surface consisting of a heat-resistant, elastic material having a Shore hardness-A in the range of 30 to 90.

6. A method as claimed in one or more of claims 1 to 5, characterized in that: a third roller (3) is located in close proximity to one of the rollers of the pair (1, 2) so that a smoothing nip is formed between the two rollers through which the melt film passes under pressure.

7. A method as claimed in one or more of claims 1 to 5, characterized in that: a third roller (3) is spaced from the nearest roller of the pair of rollers (1, 2) so that no further nip is formed between the rollers, and the third roller forms a pressing nip with a pressing roller (31) through which the cooled melt film passes.

8. A method as claimed in one or more of claims 3 to 7, characterized in that: on one side of the roll, which has a surface harder than steel, a polyethylene terephthalate film or polypropylene film is introduced into the nip and, together with the extruded film material, a laminated plastic is produced.

9. A method according to claim 8, characterized by: a laminated film is produced from a polyethylene terephthalate film and polymethyl methacrylate or polymethyl methacrylate with improved impact resistance.

10. A method according to claim 8, characterized by: a laminated film was produced from a polyethylene terephthalate film and a polymethylmethacrylate/polyvinylidene fluoride mixture.

11. Film which can be produced by a process according to one or more of claims 1 to 10.

12. Use of a film according to claim 11 in a process for the manufacture of decorative films, UV-protective films, dry-paint films, scratch-resistant films for optical data carriers, and data carrier materials which are treated by means of continuous printing processes, such as gravure printing, flexography, offset printing, digital printing, roll screen printing, transfer printing, and/or by means of continuous lamination processes and coating processes, such as film composite lamination, coating of thermoplastic sheets and profiles, sheathing techniques, roll coating processes, and/or continuous coating processes, such as water-repellent coatings, antimicrobial coatings, self-cleaning coatings, write-resistant coatings, scratch-resistant coatings, conductive coatings, which can optionally be combined with embossing processes.