DE2415659C3 - Antistatic coating of polyester films - Google Patents

Description

From US-PS 29 52 356 a method for antistatic treatment of polyester films is through Applying a copolymer, which can also contain acrylic or methacrylic units, and subsequent treatment with an antistatic saline solution is known. In the second process step, the antistatic material slowly diffuses in the coating layer. However, this means that the antistatic salt cannot penetrate deeply and firmly into the coating mass be stored, so that the antistatic film does not have a good abrasion resistance. Furthermore, the known method is very complex and expensive.

The object of the invention is. accordingly a simple and economical method of antistatic Finishing of polyester films so that the excellent antistatic properties achieved here the fol'en remain intact even with stronger, mechanical stress.

This object is achieved according to the invention by the method specified in claim 1 or by the Antistatic coated film according to claim 2 dissolved.

In one embodiment of the invention, the method consists in making a linear polyester film extruded from the melt, quenched to an amorphous state and thereafter stretched in mutually perpendicular directions biaxially oriented, with the antistatic composition before termination of the Stretching process is applied to the film surface. In another embodiment, the antistatic mass applied to the film after the stretching process is complete. The invention also relates to antistatic foils produced by the process described here.

Polyester films can be made from any thermoplastic film-forming polyesters, formed by condensation of a dicarboxylic acid or its lower alkyl ester with a glycol can be. These polyesters can be obtained by condensation of one or more dicarboxylic acids or their lower alkyl esters, e.g. B.

Terephthalic acid, isophthalic acid,

Phthalic acid,

2,5-, 2, ö- or 2,7-naphthalenedicarboxylic acid,

Succinic acid, sebacic acid, adipic acid,

Azelaic acid, dibenzoic acid and

Hexahydroterephthalic acid or

Di-p-carboxyphenoxyethane

with one or more glycols, e.g. B.

Ethylene glycol, 1,3-propanediol,

1,4-butanediol, neopentyl glycol and

1 ^ -Cyclohexanedimethanol

getting produced. Of course, the polyester film consist of a mixed polyester of any of the foregoing materials. The preferred one Polyester film is a polyethylene terephthalate film.

The lithium nitrate of the antistatic mass is used to create the desired antistatic properties. Surprisingly, it was found that when applying lithium nitrate alone to a linear Polyester film before or during stretching for the purpose of orientation in the film, the antistatic properties the stretched film very weak b -:> d and the Coating is cloudy. However, if the lithium nitrate is applied in a mass that has a special Contains a binder that anchors the lithium nitrate to the surface of the film and makes the coating resistant to abrasion good antistatic properties can be developed and the coating is clear.

The coating can be applied to one side or to both sides of the film.

It has been found that a coating weight of about 100 or more than 100 μg / dm ^{2 of} the lithium nitrate component gives satisfactory antistatic properties on one or on each side of the finished film. The actual proportion of lithium nitrate in a practical coating composition, which is necessary to achieve at least this coating weight of lithium nitrate, depends on the type of coating technique used and the coating point in the film production process, ie on whether the film is stretched after coating or not.

The lithium nitrate is applied from an aqueous medium in which the acrylic or methacrylic polymer or copolymer is dispersed by the emulsifier.

Crosslinkable acrylic polymers or copolymers are suitable as polymeric binders. the Crosslinkable acrylic or methacrylic polymers or copolymers can be prepared from acrylic or methacrylic acid or containing their functional groups, such as hydroxyl, carboxyl, amide and oxirane groups Esters are formed. A nonionic emulsifier such as nonylphenol condensed with ethylene oxide is suitable in connection with such binders.

Preferably the crosslinkable acrylic or methacrylic binder also comprises a condensation product of one Amines, e.g. B. melamine, urea and diazines or their derivatives, with formaldehyde, which can be alkylated. A a suitable binder is that based on ethyl acrylate / methyl methacrylate / acrylamide - Mixed polymer and an ethylamine / formaldehyde condensate. If desired, a crosslinking catalyst,? .. B. Ammonium chloride, intended to crosslink the acrylic or methacrylic binder. These binders will be particularly preferred, since the coated films are used in film production together with fresh polymer can be returned without the

overall properties of the resulting film suffer.

The coating compound applied to the film can also contain antioxidants, dyes, pigments, lubricants, anti-stick agents and / or glidants, ie comminuted solids that are insoluble in the coating, such as, for. B. starch, talc, zinc oxide, calcium carbonate, silica, titanium dioxide, Fe ₃ O ₄ , silicates, aluminates, aluminosilicates and individual particles of polymeric materials such as polyvinyl chloride or ι ο Polymethylmetlu.crylat

The antistatic properties, which are shown in a specific surface resistance of less than about 10 ¹² Ω / unit area at a relative humidity of about 50%, ensure the prevention ι? tion of the deposition of atmospheric! Dust on the film surface. In order to achieve this level of surface resistance, a coating weight or a surface ^{concentration of at least 100 μg / dm 2} lithium nitrate is required on one or on each side of the finished film. In general, an actual surface concentration of about 100 ^ g / dm ^{2 is} used because, despite a further reduction in the surface resistance with a higher surface concentration of lithium nitrate, no noticeable improvement in the prevention of dust accumulation on the film surface is achieved and the clarity of the FoIi; becomes less. The values given here for the surface concentration of the lithium nitrate are determined by aqueous extraction of the coating and brass of the amount of lithium in the extraction solution

The coating weight or surface concentration of the binder is preferably about 1.7 times the surface concentration of lithium nitrate, but can deviate from this value, although in the case of significantly higher or lower coating weights there is a lack of the coating become visible.

The preferred polyester is polyethylene terephthalate. Films from it are subjected to alignment in a known manner by being subjected to a Temperature from 78 to 125 ° C extends.

Various known types of apparatus designed to stretch continuous lengths of film in the machine and transverse directions are useful in the stretching processes of this invention. The film can be stretched in any order, ie the stretching can first take place in the longitudinal or transverse direction and then in the other direction, or it can be stretched in both directions at the same time. For example, the film is expediently stretched in the machine direction by running it between or around two slow rollers heated to the desired temperature and then between or around two or more high-speed rollers a small length of film is fed between the fast and slow rollers. The film can be stretched in the transverse direction in a stretching apparatus. Oven heating is preferred when stretching in a stretching apparatus. Preferably, the longitudinal stretching is carried out at a temperature of 78 to 1OfJ ⁰ C and the transverse stretching at a temperature ⁽ⁱ i> 80 to 125 ° C, preferably at 100 to 125 ° C. The film may be of any commonly used in the manufacture of polyester films applied The draw ratio is generally up to about 4.5 times in each direction, and useful draw ratios are about 3.5 times in each direction.

The biaxially oriented film may zweckmä3igerweise at a temperature of 150 to 24O ⁰ C, preferably at 195 to 215 ° C, heat set.

According to the invention, the antistatic mass can be applied to the film before the stretching process is finished, for example on the amorphous film, d. H. before starting any stretching. So can the coating compound onto the amorphous film after extrusion and quenching and before the first stretching process be applied. Alternatively, the antistatic mass can be applied to the film after this was stretched in one direction and before stretching in the second direction. As most of the commercial Biaxially stretched polyester films are produced by a process in which they are first stretched in the longitudinal direction and then stretched in the transverse direction and then heat-set, the Antistatic mass applied to the film surface in such a process after it has already been in Has not yet been stretched in the longitudinal direction but in the transverse direction. Some biaxially oriented films are only used in Transverse direction stretched; the coating process according to the invention is then used to coat these films before the start of stretching or after Transverse stretching.

Alternatively, the antistatic composition can be applied to the film surface after the Stretching and heat fixing are finished.

The antistatic properties of many common antistatic agents are inactivated when the agents stretching and heat setting, which are used in the manufacture of polyester films Find. Surprisingly, the antistatic properties that can be achieved according to the invention are below Such conditions are not destroyed, but optimized at heat setting temperatures below 220 ° C.

After applying the antistatic mass to the film surface, the medium from which the Application done, usually removed by drying. This is expediently done in an air oven at a temperature of about 80 to 125 ° C or by radiant heat. When the slide is in is stretched transversely in a stretching machine, the heating and stretching generally take place in one Hot air oven so that drying can take place during transverse stretching.

The coating can be carried out in a known manner, for. B. by roller coating, slot coating or knife coating.

The coated films obtained according to the invention have excellent antistatic properties. They also have excellent clarity and good sliding properties.

The antistatic films of the present invention are particularly for use in printing processes inclusive Suitable for picture montage techniques where it is important to prevent the accumulation of dust particles on the Avoid foil surface. The antistatic films also show good adhesion to the Image assemblies used common adhesives .., printing inks, light-sensitive diazo materials and matt sheets. Assembly adhesives can be made using chlorinated hydrocarbons, e.g. B. Carbon tetrachloride

or 1,1,1-trichloroethane, removed from the surface without a noticeable loss of the antistatic effect

The invention is illustrated in more detail by the following examples.

example 1

A polyethylene terephthalate film was made from the Taste extruded and quickly into an amorphous one Quenched state on a cooled rotating casting roll. The cast film was in the extrusion direction stretched at about 85 ° C to about 3.5 times its original dimension and then through Roller coating coated on both sides with an aqueous dispersion of the following composition, in which the specified parts relate to weight:

Crosslinkable acrylic binder with 4.5 parts

87 wt .-% copolymer of ethyl acrylate, methyl methacrylate and

Methacrylamide

(45% by weight, 50% by weight and 5% by weight)

and 13% by weight ethylated melamine

Formaldehyde resin

Lithium nitrate 3.0 parts

Nonylphenol, with an average of 8 moles 0.15 parts

Ethylene oxide condenses as an emulsifier

Distilled water 92.0 parts

be truded, which contained about 10 wt .-% of recycled coated film, without - apart of a weak yellow color - the film properties have been significantly impaired.

Example 2

A conventional, biaxially oriented and heat-cured film made of polyethylene terephthalate was coated on both sides with an aqueous antistatic dispersion of the composition given in Example 1 to a final coating weight of 110 μg / dm ^{2 of} lithium nitrate on each side. The finished film had a surface resistance of about 10 ¹⁰ n / unit area at a relative humidity of 50%. It was resistant to the accumulation of dust particles on its surface. The static coefficient of friction of the coated film was about 0.7. The film showed good adhesion to top coatings such as e.g. B. printing inks and diazotype materials, and film waste could be used again as in Example 1 without the overall properties of the resulting film - apart from a slight visible yellow coloration - were significantly impaired.

Example 3

Example 1 was with an aqueous dispersion of a coating material according to the following composition repeated, the specified parts refer to the weight:

30th

The coated film was restored to about 3.5 times its original size in the transverse direction at about 110 ° C Dimension stretched and then fixed with heat at 200 ° C.

The finished film had a total dry ^{coating weight of 250 μg / dm 2} (ie lithium nitrate and binder) on each side and a surface resistance of about 3 × 10 Ω / unit area at a relative humidity of about 50%. The static coefficient of friction of the coated film was about 0.7 The film was resistant to dust accumulation on its surface and exhibited good adhesion to other coatings such as printing inks and diazo materials.

The antistatic coated film could reex-

Crosslinkable acrylic binder made from 5.4 parts

87% by weight of a copolymer of ethyl acrylate. Methyl methacrylate and Methacrylamide

(45% by weight, 50% by weight and 5% by weight) and 13% by weight of ethylated melamine-formaldehyde resin

Lithium nitrate 3.2 parts

Nonylphenol, which has an average of 8 moles 0.15 parts

Ethylene oxide was condensed as an emulsifier

Distilled water 91.0 parts

The film obtained had a total dry coating weight on each side of 250 μg / dm ² (lithium nitrate + binder) and showed essentially the same properties as the film described in Example 1.

Claims (2)

Patent claims: 1. A process for the antistatic treatment of polyester films by applying a salt-containing polymer coating, characterized in that the films are odc with an aqueous dispersion of an acrylic or methacrylic polymer containing lithium nitrate. -copolymer and optionally an amine-formaldehyde polycondensate, and optionally a crosslinking catalyst as a binder and a nonionic emulsifier coated on one or both sides in such a way that the surface concentration of LiNO _{3 is} at least 100> g / dm ² , and then dries, with the film can be stretched before or after coating. 2. Antistatic polyester film, characterized in that it is coated on one or both sides with an antistatic layer of at least 100 μg / dm ² lithium nitrate and an acrylic or methacrylic polymer or copolymer as a binder.