DE1965137A1 - Thermoplastic film with improved flatness and method for making the same - Google Patents

Description

KALLE AKTIENGESELLSCHAFT Our sign day sheet

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Thermoplastic film with improved flatness and method of manufacture the same

The present invention relates to a mono- or biaxially stretched, heat-set film made from orientable Thermoplastics with one versus the conventional

Films reduced flatness errors.

Stretched films made from thermoplastics, such as those made from polyolefins or polyesters, have been around for a long time known.

The stretching process gives the films certain desired properties, with particular emphasis on the improvement in tensile and elongation behavior in certain

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Directions is laid. The thermal fixation of such stretched films is also part of the state of the art. This temperature treatment leads to increased crystallinity, as a result of which the stretched films are given higher dimensional stability. Such stretched and thermoset films have, depending on the thermoplastics used, little or no shrinkage over a certain temperature range, which essentially depends on the fixing time and the temperatures chosen. Stretched and heat-set foils made of polyesters are suitable due to their strength, their large dimensional stability in a wide temperature range and their high transparency as a carrier material for magnetic tapes, drawing foils, photo films, reprographic films and in the uncoated state as a mounting foil and as a separating foil in the production of polyester casting resin " plates.

These films are made by known processes from an amorphous, non-oriented film by stretching this film at temperatures above its glass transition temperature with stretching ratios in the longitudinal and / or transverse direction of about 1: 2 to 1: H ', 5 and subsequent heat setting in Temperature range above the crystallization point and below the melting temperature produced, during

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BATH ORIGINAL

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by drawing strength, toughness and others Properties are improved, results in the heat setting through crystallization, an improvement in dimensional stability at elevated temperature.

Stretched and heat-set films of polyolefins before ä especially those made of polyethylene, preferably Kochdruckpolyäthylen, and polypropylene also have very good mechanical strength, among other desirable properties such as transparency usxt. They are therefore used, among other things, as highly stressable packaging material or as a base film for the production of composite films or coated films.

The stretching ratios for high-pressure polyethylene are usually in the range from 1 : 5 to 1: 7, with stretching temperatures of about 90 ° to 105 ° C. In the case of polypropylene, temperatures of about 150 ° C. and similar stretching ratios as in the case of polyethylene are used. The heat setting can be carried out in such a way that hot air is blown onto the stretched film in a fixing frame or is passed over heated rollers. that the dimensional stability is vua better, the higher the fixing temperature (below the melting point) and the longer the fixing time.

it is known that asymmetrically oriented films get better dimensional stability when

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the fixation takes place via two rollers, the first roller having a ^{temperature which is at least 5 °} C. higher than the second roller. The Fxxierungstemperaturen lie in polyesters in the range of 150 ° to 25O ° C, preferably at 190 ° to 220 ⁰ C, for polyolefins in the range of about 150 ° C for polypropylene. Films produced according to the known stentering or tube stretching processes have sufficient dimensional stability and high strength in the longitudinal and / or transverse direction, but flatness which is still insufficient for particularly critical applications, which is caused by different lengths in the longitudinal direction of the film between the edges of the film and the center of the film. The flatness of the known foils is usually over 1.0%. The poor flatness prevents, among other things, proper winding of the film and makes it unusable for the above-mentioned areas of application or only conditionally usable with considerable material loss.

The task was thus to produce thermoplastic tubular or flat films that had a different effect than the known films have improved flatness to create.

The film according to the invention is characterized in that it measured a flatness error of at most 0.2% transversely to the take-off direction of the film.

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The relative length difference is used as the flatness error referred to within a film web. For the measurement, a piece of foil approx. 350 m long and in the original width is placed over it two ball-bearing, lying in a horizontal plane

Rolls tensioned at 0.1 kp / mm. The longitudinal axes of the rolls are at a distance of 6 = 2 meters and are % parallel to each other. By means of a row of easily movable pins of equal length with a spacing of approx. 20 mm placed across the middle of the film web, the flat profile is reproduced through the upper ends of the pins.

In the case of a maximum deviation d of the film web from the reference plane, which can be thought through the upper roll apex, the flatness error results as a length difference Δ 6 based on the roll spacing β

Δ ί

2u -Δ-k-. 1000 or transformed to

^ o

Flatness error Ξ | - 1000 in per mille.

Another method for determining the flatness error is the visual inspection of a 10 m long film web on a flat surface, comparing it with a reference film and measuring the height of the occurring

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Bumps.

A flatness error of about 1.0% makes the film for Subsequent processing in the original width is unusable in many areas of application, but one means Flatness of - 0.2 ° / oo a substantial improvement with regard to their general operational capability.

In a preferred embodiment, the film consists of a polyester, in particular polyethylene terephthalate or a mixed or copolymer of polyethylene terephthalate with esters of the formula

^ - C - O - (CH ") _ -Q-O-

where η preferably has values between 2 and 10. Such films have been found in particular for the initially mentioned areas of application, but especially proven for use as separating films.

The polyolefin films are preferred in the packaging sector, for example for the production of heavy-duty bags

and the like. Used.

The invention also relates to a suitable method for producing the film. The method is known in

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The thermoplastic melt is pressed out of a ring or slot die, mono-axially or biaxially stretched by known measures, optionally in two stages, also with possible post-stretching, in one or both directions. The drawing temperatures and -ver- ·. ratios depend on the thermoplastic as well as on the desired further physical properties of the film. The heat setting is usually carried out in one of the known fixing frames, the film being held at the edges until the end of the fixing path in order to prevent the film from shrinking back. The fixing frames differ essentially in their length and the way in which the film web is held.

According to the invention, the heat-setting of the film is carried out in such a way that at least part of the setting time a is carried out with a steadily decreasing temperature T, which occurs through

the range i = - m * §- +1 is given and where ^T F ^b max

m has values between 0.2 and 0.6. In this equation:
Τ «= fixing temperature

T s are the temperatures during the cooling process T * T _F

f _p ^{s is the} relative temperature change during the

Cooling process; ä- ^ 1

¹ F.

^S max ^{= the} total time over which the cooling takes place
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S = the time during cooling;

sis

Max

- = the relative time changes during the

^Smax cooling; I "- 1

Max

m = range of variation of the temperature curve.

The method according to the invention, in which during part of the fixing time the specified temperature level required for fixing, ie crystallization, is uniformly reduced to 80 % _t, but at most to 40 / i of these temperatures, results in films with a flatness error of at most 0 , 2 per cent. The cooling can be carried out with a constant value for m between 0.2 and 0.6 or increasingly from 0.2 to 0.6. In a special embodiment, the process is operated in such a way that at least the last third of the fixing time is used with continuously decreasing temperatures.

The curve of the specified function is shown in the figure. The relative temperature change is on the ordinate = and the relative time change on the abscissa

S ^p

s applied.

Naturally, the equation only applies in the range 0 * | - * 1

^T F

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and is limited according to the invention to the range between 0.2 and 0.6. This area is shown hatched in the figure. Curves and 3 (according to example 3 and 2) are used as boundary lines. A temperature history curve to 5 or such according to the indicated dotted line also corresponding to the inventions \ to the invention conditions, since they are within the given with m = 0.2 and m 0.6 maximum and minimum temperature limit curves.

The process is applicable to all orientable and crystallizable polymers.

The invention is illustrated in more detail by the following examples, without being restricted thereto.

example 1

A 75 μm thick polyethylene terephthalate flat film with a width of 3 m, which was produced by extrusion and by biaxial stretching with a stretching ratio of 1: 4.5 in the longitudinal and transverse directions at a temperature of 120 ° C, was produced at a speed of 10 m / min through a fixation channel 6 m long. The fixing temperature Tp was 210 ^° C. (over the entire path length; FIG., Curve 1). The film had a density of 1.3924 g / cm3 _and a shrinkage at 150 ⁰ C and 15-

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In-minute testing time of 1.1 % or £ 1.5 in the longitudinal or transverse direction. The flatness error was great, it amounted to 0.5 per cent.

Example 2

A stretched as in Example 1 polyethylene terephthalate was fed at a rate of 10 m / min by means of a setting channel of 6 m length, at first 4 m a fixing temperature of 210 ⁰ C and had the last 1.5 m a temperature drop at its End up to 16O ° C possessed. (Figure, curve 2)

The film had the same density and dimensional stability as in Example 1. The flatness was already improved and had a value of 0.25 per cent.

Example 3

A stretched film, produced according to Example 1, was passed at a speed of 10 m / min through a fixing channel 6 m long, which had a fixing temperature of 200 ° C. for the first 3 m and its temperature for the next 1.5 m dropped to 140 ° C and up to the end of the Fixierkanals to 85 ⁰ C. The film had a density of 1.3894 g / cm ³ and a shrinkage at 150 ° C. and a test time of 15 minutes of 1.6 and 2.4 Ji in the longitudinal and transverse directions.

According to the above formula, the value 0.2 resulted for m. The film had a low flatness error of 0.15 ° / o _O.

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Al

Example 4

A stretched film, as produced in Example 1, was passed through a fixing channel at a speed of 25 m / min out of 6 m length, which had a fixing temperature of 2OO ° C for the first 3 m and its temperature in dropped to 120 ° C over the next 1.5 m and to 55 ° C at the end of the fixation channel. The film had one density and one üchrumpf as in Example 3 »but a large flatness error of 0.4 per cent.

Example 5

A stretched film, as produced in Example 1, was passed through a fixing frame 6 m in length at a speed of 10 m / min, the temperature of which over the first 4.5 m was 215 ° C. and its temperature corresponding to curve 5 in the figure sank to the last 1.5 m. The film had a density of 1.3924 g / cm · ^ and a shrinkage at 150 ° C. and a test time of 15 minutes of 1.1 and 1.5 $ in the longitudinal and transverse directions.
The film had a small flatness error of 0.15%.

Example 6

A biaxially stretched tubular film, the cut and has been laid flat, is passed through a fixing 'of 6 m in length at a speed of 10 m / min, the temperature of m on the first 4.5 150 ⁰ C was 109827/1711

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and the temperature of which fell over the last 1.5 m corresponding to m = 0.4. The film had a good flatness (0.12%), a density of 1.3760 g / cm2 and a shrinkage of 11.6 / j or Ib.5 / ° in the longitudinal and transverse directions.

Example 7

A 25 a fixation channel 6 m long. The temperature was on the first 3 m 150 ⁰ C for the next 1.5 m 110 ⁰ C and the last 1.5 m 60 ° C (m = 0.2). The film had a density of 0.910 and a shrinkage at 120 ⁰ C and 15 minutes of test time of ¹ J, 8, and 5,1,1 in the longitudinal and transverse direction. The flatness error was very small at 0.13 per cent.

Example 8

The procedure was as in Example 3 (m = 0.2), but a film made of a copolymer of polyethylene terephthalate with 5% diglycol was used. The film had a shrinkage at 135 ° C. and a test time of 15 minutes of $ 2.1 or 2.6% in the longitudinal and transverse directions. The flatness error was 0.1.6%.

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Example 9

The procedure was according to Example 7 "However, a film of a mixed polymer of polypropylene was used with 5% high density polyethylene, and stretched at 150 ⁰ C.

The film had a density of 0.911 and a shrinkage at 120 ⁰ C and 15 minutes of test time of 5.0 or, 5.3 in the longitudinal and transverse direction. The flatness error was 0.12 per cent.

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Claims (1)

Claims 1. Mono- or biaxially stretched, heat-set film made of orientable thermoplastics, characterized in that they have a measured transverse to the direction in which the film is taken off Has flatness errors of - 0.2%. 2. Foil according to claim 1, characterized in that it has a flatness error of - 0.15 per cent. 3. Foil according to one of claims 1 or 2, characterized in that that they are made of a polyester, preferably of polyethylene terephthalate or a mixed or copolymer of polyethylene terephthalate with esters of the formula - 0 - (CH _{2> n} - 0 - where η preferably has values between 2 and 10, consists. k. Film according to one of Claims 1 or 2, characterized in that it consists of a polyolefin, preferably of polyethylene or polypropylene, or of a mixed or copolymer of the polyolefins. 1098 27/1711 KALLE AKTIENGESELLSCHAFT ^1965137 Our sign day sheet K-1936 / Gbm 423 ¹ FP-Dr.Kn-df 16.12.69 5.] A method for producing a film according to one of the Claims 1 to 4 by extrusion of a melt into an amorphous, essentially non-oriented one Film, stretching at elevated temperatures and heat setting at temperatures above the stretching temperature, but below the melting point of the thermoplastic, characterized in that the heat setting the film carries out at least part of the fixing time with a steadily decreasing temperature T, which is given by the range S = - m · s - + 1 ¹ F ^b max and where m has values between 0.2 and 0.6. 6. The method according to claim 5, characterized in that the heat setting over the last third of the Fixing time carries out with steadily decreasing temperatures T in the specified range. 109827/1711 Blank page