CS251341B1 - Folyvinyl butyral film for laminated safety glass and its production method - Google Patents

Abstract

The purpose of the solution is to improve the handling stickiness and the ability to vent in polyvinyl butyral films for laminated safety glass. The improvement is achieved thanks to the characteristic surface of the film, which is given by the structure of the surface fracture with a maximum depth of surface effects of 1 to 3 μm, preferably 2 to 7 μm. The invention further relates to a method of producing this film by extrusion. The desired surface treatment of the film is achieved according to the invention by cooling the film Zlý after exiting the extrusion head /2/ in a water bath /3/ at a temperature of 20 to 50 °C and a distance from the extrusion head /2/ of 1 to 100 mm, and preferably 10 to 30 mm, while continuous water circulation is ensured at the time of the film entering the water bath /3/.

Description

The invention relates to a polyvinyl butyral film with improved handling tack and air release capability, intended for laminated safety glass, and a method of producing this film.

Polyvinylbutyral film for laminated safety glass is usually produced by extrusion on a flat head extruder. The nominal thickness of this film is 0.4 or 0.8 mm, depending on the intended application of the final product.

In the production of laminated safety glass, the foil is inserted between two glasses and the whole is first pressed at temperatures of 80 to 100 °C and pressures of 0.2 to 0.6 MPa, after which pressing is carried out in special autoclaves at temperatures of 1.0 to 160 °C and pressures of 0.6 to 1.5 MPa.

The foil is inserted between the glass panes by placing the foil on the washed glass by hand, and it is necessary for the foil to slide very well on the glass, i.e. a very low coefficient of friction between the foil and the glass is required.

Reducing the coefficient of friction between the film and the glass is achieved by modifying the polyvinyl butyral mixture by adding slip agents that migrate to the surface and the surface microfilm formed improves the sliding properties. A number of organic substances can be used as slip agents, the best of which are fatty acid amides. The disadvantage of this solution is that the migration of the slip agent to the surface can cause uneven adhesion of the film to the glass, as has been proven in numerous cases.

The surface quality of the polyvinyl butyral film, defined for example by the surface roughness K, affects, in addition to the above operation - inserting the film between the glasses - also the pre-pressing operation.

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The pre-pressing technology requires that the air trapped between the glass and the foil is removed from this space under the action of pressure. If the foil is smooth - it does not have a rough surface, the air spaces between the glass and the foil are closed during pre-pressing, which adversely affects adhesion. In such a place, tension also arises, leading over time to the formation of so-called non-adhesive spots, or blooms - defective spots, due to which the laminate must be discarded. Manufacturers try to prevent this phenomenon, for example, by patterning the surface of the foil or by providing it with longitudinal grooves on both sides, which serve to remove air during pre-pressing.

Both methods used have certain disadvantages.

The embossing of polyvinyl butyral films is a very demanding technological process, since after heating above JO °C these films sharply increase their stickiness. Embossing in terms of melt deformability requires temperatures above 100 °C. Sticking to the embossing roller can be prevented if embossing is carried out in an environment of separating liquids, for example water or various salt solutions.

A major disadvantage of embossing treatment can also be the fact that only one surface structure can be achieved, given by the structure of the embossing roller. It turns out that for foil thicknesses of 0.4 and 0.8 mm, it is necessary to have two embossing rollers, or - which is more convenient - two embossing machines.

The creation of grooves on the surface is done directly during extrusion - using grooving jaws. This is only an auxiliary treatment, which in itself is not enough to ensure the required properties of the film. Patterning is always necessary, with all the disadvantages that have been mentioned.

The disadvantages of the previously known surface treatments of polyvinyl butyral films are eliminated by the polyvinyl butyral film for laminated safety glass and the method of its production according to the invention. The essence of the invention lies in the fact that the film contains a surface fracture structure with a maximum depth of surface defects of 1 to 20 µm, preferably 2 to 7 µm. The subject of the invention is further a method of production of this film, the essence of which lies in the fact that the extruded film is

- 3,251,341 immediately after exiting the extrusion head, it is cooled in a water bath with a temperature of 20 to 50 °C and a distance from the extrusion head of 4 to 100 mm, preferably 10 to 30 mm, while continuous water circulation is ensured at the point where the film enters the water bath.

The uneven surface of the film according to the invention is created using the elastic properties of the melt. The polyvinyl butyral melt, when passing through the extrusion head, exerts a significant normal stress component in addition to the shear component. This results in an increase in the melt after exiting the extrusion head by 100 to 200 and a release of surface stress, which is transported to deformation phenomena on the surface. A so-called surface fracture occurs with a defect depth of up to 50 µm - depending on the extrusion conditions.

A very fine surface fracture structure (defects up to 10^um) causes a matte surface of the film, a coarser structure causes the film to be rough. A fine structure has a positive effect on the handling stickiness and sliding of the film on the glass, a coarser structure proves to be advantageous during the pre-pressing operation, when it enables reliable deaeration of the laminate.

The lifetime of the surface fracture structure is, however, limited in time. Tests have shown that the fine structure disappears in the free atmosphere at a distance of 100 mm from the extrusion head at an outlet speed of 0.4 ^ms1 . The coarse structure disappears later, but its lifetime is also limited. Fixation of both the coarse and fine structures is carried out by rapid cooling of the melt in a water bath under the conditions already mentioned.

The method according to the invention has a further advantage in that the deformation of the melt after exiting the extrusion head takes place over a very short path, which has a positive effect on the improvement of thickness tolerances in both the longitudinal and transverse directions. The elongation of the melt over a very short path increases the speed of orientation and thus the uniformity of its course.

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In addition to the distance of the water bath from the extrusion head and the temperature of this bath (lower values of both parameters are preferable), other parameters affect the fineness of the created structure - the temperature of the wall of the extrusion head jaws relative to the temperature of the melt and the width of the outlet slit. The higher the difference between the mentioned temperatures, the more pronounced the coarse structure of the surface fracture is.

The optimal size of the fine to coarse structure can be achieved by optimally setting all the mentioned parameters: water bath (distance, temperature), extrusion head jaws (slot width, temperature) and melt (extruded amount, temperature).

In practice, it is easiest to influence the fineness of the structure by the distance or the temperature of the water bath, while the other parameters remain at the usual level, usual in the production of polyvinyl butyralbvých films. However, it is also possible to use the values of the film surface roughness, obtained during the control measurements, to correct the production parameters so that the structure of the produced film is in accordance with the current requirements. Given that there are several ways to achieve the desired structure - several changeable parameters - it is always necessary to choose the most advantageous method, i.e. simple, economical and fast. From this point of view, the use of a computer seems advantageous.

A certain problem arising when implementing the method according to the invention was local overheating of the water at the point of entry of the melt into the bath. There was local boiling of the water and thus undulation of the surface, which led to irregular stretching and the formation of defects on the surface of the foil. This problem was solved by placing nozzles at a short distance below the surface at the point of contact of the melt with water, through which the heated water was continuously removed. An exemplary arrangement of the suction nozzles is shown in the attached drawing. Here the foil 2 exits the extrusion head 2 and enters the water bath. The suction nozzle system 4 sucks the water with the help of a pump £ ^and returns it to the lower part of the bath 6.

The following examples serve to illustrate the essence of the invention.

- 5 Example 1

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A polyvinyl butyral mixture containing 29% by weight of plasticizer was extruded at a melt temperature of 180°C into a water bath at a temperature of 20°C and a distance from the extrusion head of 25 mm. The withdrawal speed was 1.5 m/min.

The obtained polyvinyl butyral film showed the desired properties. The roughness of the film, defined by the R _g value, was 2.2 _µm . The film was milky cloudy, which indicates the presence of a fine surface fracture structure.

Example 2

In an extrusion plastometer with a flat slit with a diameter of 0.6 mm, a width of 5 mra and a length of 8 mm, a strip of polyvinyl butyral melt was extruded into a water bath. The distance of the water bath, its temperature, the outflow velocity of the melt and the temperature of the melt were gradually changed, while the effect of these changes on the surface character of the extruded strip was monitored. The results are given in the following table I.

Table I

Melt Water bath Print. tape Temperature rv print.quantity /10“* g.rain~7 temperature distance fV /mm/ appearances /degree matv/ 170 8.2 20 2 5.5 2 2 12.5 . 1 50 2 5.,5 2 2 ............12.5 ... 1 15.6 20 2 4 5.5 13.5 1 50 2 5.5 5 UJL·......... 1

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Melt Water bath Print, tape Extrusion temperature, mass temperature distance appearance /to ² g.min-7 distribution /mq/ /grade iaaty7 190 25.9 20 2 3 5.5 0 13.5 1 50 2 5 5.5 13.5 1 36.6 20 2 4 5.5 3 13.5 1 50 2 5 5.5 3 13.5 1

Note: - for lines in which no value is given, the closest value from the previous line always applies - the numerically expressed degree of matt indicates the surface: 1. glossy (visually assessed)

2. no checkmate

3. matte

4. medium matte

5. heavily matte

- 7 Example J

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A polyvinyl butyral mixture containing 26% by weight of plasticizer was extruded with a flat die at a melt temperature of 180°C into a water bath at a temperature of 10°C and a distance from the extrusion die of 100 mm.

The surface roughness of the produced polyvinyl butyral films was measured and defined by the value R of 1.7 - 1.9/um. The film was not milky cloudy, the handling stickiness of the film was high and it was assessed as non-sticking during processing.

A polyvinyl butyral mixture of the same recipe, extruded under the same conditions into a water bath at a temperature of 10°C and a distance from the extrusion head of 20 m, had a defined film roughness value Rg of 5.0 - 6.9 µm.

The film was milky cloudy with a pronounced surface fracture and non-sticky.

This procedure was verified on a number of production batches. The values obtained for operationally produced films at various distances of the water surface from the extrusion head are given in Table II.

Table II

Evaluation of the surface roughness of polyvinyl butyral films

a) Films produced by the previously used method - level distance 1 JO mm

Sample marking Surface roughness - R _Q (/um) 6.58 1.7 page 659 1.7 sh. 660 1.7 page 747 1.7 sh. 750 1.7 page 751 1.9

b) Foils produced in the described way - level distance 20 mm

Sample marking

Claims (2)

SUBJECT OF THE INVENTION A polyvinyl butyral film for laminated safety glasses having improved handling tack and deaerability in the manufacture of such glasses, characterized in that it comprises a surface fracture structure with a maximum surface defect depth of 2 to 20 U, preferably 2 to 7 µm. 2. A method according to claim 1, characterized in that the film is cooled in a water bath at a temperature immediately after leaving the extrusion head. 20 to 50 ° C and a distance from the extrusion head of 1 to 100 mra, preferably 10 to 30 mm, with continuous water circulation at the point of entry of the film into the water bath.