EP0674583A1

EP0674583A1 - Biaxially oriented penbb film coated with antistatic coatings

Info

Publication number: EP0674583A1
Application number: EP93901464A
Authority: EP
Inventors: Cynthia Dr. Bennett; E-Won Choe; John Anthony Flint; Bodo Kuhmann
Original assignee: Hoechst AG; Hoechst Celanese Corp
Current assignee: Hoechst AG; CNA Holdings LLC
Priority date: 1992-12-09
Filing date: 1992-12-09
Publication date: 1995-10-04
Also published as: WO1994013477A1; JPH08504384A; EP0674583A4

Abstract

The invention concerns an antistatic, mono- or multilayer biaxially oriented copolyester film, wherein the copolyester is PENBB and wherein at least one surface of the film has been coated with an antistatic coating composition containing (I) a quarternary ammonium salt (QAS) and/or (II) a two component system consisting of: (a) an acrylate, styrene-derivative or acrylonitrile, and (b) an ethylenically unsaturated sulfonate salt and/or (III) an organically substituted phosphate. PENBB is a copolyester containing units of formula (1).

Description

BIAXIALLY ORIENTED PENBB FILM COATED WITH ANTISTATIC COATINGS

Background of the Invention

This invention is directed to an improved polyester film having excel- lent antistatic properties as well as improved mechanical strength and stiff¬ ness, and dimensional stability and to a method for producing such film. More specifically, the invention deals with improved biaxially oriented co¬ polyester films having improved antistatic properties coupled with altered surface properties which render the film printable or coatable with additional coatings such as photosensitive compositions, while exhibiting the improved dimensional and mechanical properties.

The growth of the packaging, reprographic, microfilm and magnetic tape markets has significantly increased the utilization of polyester film materials in these fields, particularly biaxially oriented polyethylene terepht- halate (PET). However, there are still some problems with PET films. Some of the problems encountered in these applications are caused by the limits of the PET material. Specifically, there is a need for greater stiffness (tensile modulus) and tensile strength, improved dimensional stability, UV resistance and hydrolytic stability. Another problem associated with the use of such film is the tendency of these materials to accumulate an electrostatic charge on the surface as the result of handling or processing of the film, particularly at low relative humidity. This electrostatic charge attracts not only dust and other contaminants, but additionally attracts other film. For instance, in the case of PET film supports, electrostatic charges may interfere with the colla- ting, sorting and developing of microfiche cards or transparent supports and cause these materials to stick together.

To overcome this serious problem, antistatic films have been develo¬ ped. Antistatic films are usually formed by the application of an antistatic coating onto the surface of the film. Many of these coatings have success- fully reduced the electrostatic charging properties of the film to satisfactorily low levels. However, many of these coatings can cause blocking. That is, the film coated with an antistatic layer has a coefficient of friction high enough so that one layer of the film does not slip over another or over rollers and other equipment over which the film moves during manufacture and use.

Another problem arising from the coating of an antistatic layer onto a surface of a film is the decreased clarity resulting therefrom. This property, usually termed as haze, is very important in microfilm applications. Microfilm must be readable. Light is projected through the film so that the viewer may read the information printed on the film. Poor clarity results in fuzziness and difficulty in reading because of loss of light intensity.

Yet a third problem associated with the application of an antistatic coating is its ability to remain adhered to the surface of the film, particularly where the film is later treated with printing or coating compositions.

Various antistatic coatings are disclosed in the prior art. For example, U.S. Pat. No. 4,214,035 teaches the application to PET film of an antistatic coating based on a mixture of stearamidopropyldimethyl- ?-hydroxyethylam- monium nitrate and a cross-linkable acrylic terpolymer binder, present in an approximately three to one ratio respectively. The antistatic surface of such film is not readily susceptible to the application of additional coatings, parti¬ cularly in reprographic applications.

British Pat. No. 1 ,558,064 discloses the use of certain quarternary ammonium salts as an antistatic coating for poiyolefin film such as polypropy¬ lene. These salts have the formula:

wherein A is lower alkyl, R is an aliphatic radical having 1 to 22 carbons, x and y are integers having the sum of 2 to 5, and X^" is an anion. The utiliza- tion of this material as disclosed in the patent, aside from its effectiveness as an antistatic, does not resolve the problem of the lack of adhesion of ad¬ ditional coatings over the antistatic coating.

Accordingly, it is an object of this invention to provide plastic film material having improved antistatic properties as well as good blocking properties and low haze.

Another object is to provide an antistatic coating on at least one surface of a film providing improved dimensional and mechanical stability, which coating may provide a suitable base coat or primer coat for the ap¬ plication of additional coatings.

Summary of the Invention

The present invention relates to an antistatic biaxially oriented PENBB film and the process for producing the film. More particularly, the present invention relates to an antistatic biaxially oriented PENBB film having excel- lent antistatic properties, and/or excellent adhesivity, and excellent mechani¬ cal and dimensional stability, and a process for producing the film.

The improved mechanically and dimensionally stable PENBB base film of the present invention carries an antistatic coating composition containing

I) a quarternary ammonium salt and/or II) a two-component composition consisting of a) an acrylate, styrene derivative or acrylonitril and b) an ethelenically unsaturated sulfonate salt and/or III) an organically substituted phosphate.

Similar coatings are disclosed in U.S. Patent 4,642,263 and European Applications 0 435 080 and 0 442 607. U.S. Patent No. 3,008,934 disclo¬ ses copolyesters containing as acid derived units 4,4'-bibenzoate and a host of other dicarboxylates including 2,6-naphthalic dicarboxylate. It also disclo¬ ses oriented fibers and films prepared from these copolyesters, however, biaxially oriented PENBB films are not disclosed or envisioned. In particular, those films with improved stiffness (tensile modulus) and tensile strength in both MD and TD as well as thermostability, UV stability, hydrophobicity. dimensional stability and impermeability toward gases in comparison to PET film are not disclosed in U.S. Patent No. 3,008,934.

Detailed Description of the Invention and Its preferred Embodiments The biaxially oriented copolyester film base for the purpose of this invention is made from PENBB.

PENBB as mentioned hereinbefore is a copolyester containing as acid- derived unit at least 5 mole percent of a radical of the formula:

(bibenzoate, BB")

In the case that more than 10 mole percent of terephthalic acid derived radicals are present in the copolymer, the content of bibenzoate derived units is at least 25 mole percent. Films of these copolyesters are mentioned in the unpublished German Patent Application P 4224161.8, which is incorporated herein by reference. Preferably PENBB is a copolyester wherein at least 80 mole percent of the acid derived units (NBB) consist of bibenzoate (20 to 80 mole percent, preferably 40 to 60 mole percent) and napthalate (80 to 20 mole percent, preferably 60 to 40 mole percent). The remaining 20 or less mole percent may consist of other acid derived units, which e.g. affect the melting point or the crystallization kinetics. Preferably at least 80 mole percent of the diol-derived units consist of - O(CH₂)₂-O-units. The remaining

20 or less mole percent consist of other diol-derived units, which e.g. may also affect the melting point or the crystallization kinetics. It may also be desirable to replace minor amounts of the acid- and/or diol-derived units with hydroxycarboxylic-acid-derived units, e.g. such derived from p-hydroxyben- zoic acid. In order to achieve the desired mechanical properties in the biaxial¬ ly oriented PENBB film it is recommended that the IV value (inherent viscosi¬ ty, as measured in a 1 : 1 weight-ratio mixture of pentafluorophenol and hexafluoroisopropanol at a concentration of 0.2 g/dl and a temperature of 25 ° C) of the PENBB polymer after extrusion be > 0.5 dl/g and preferably > 0.55 dl/g.

To produce the film, the polymer melt is extruded through a die onto a chill roll where it solidifies, is then biaxially oriented, heat set, optionally post treated and the wound on a roll. For a multilayer film known methods for coextrusion, in-line or off-line coating can be used. The solidified film as extruded on the chill roll should be obtained in an essentially amorphous state. To achieve this, the melt film must be pinned to the chill roll by a known method such as electrostatic pinning or vacuum, air knife or the like. The biaxial orientation of the film is achieved by stretching the film at elevated temperature in the machine (MD) and transverse direction (TD). This stretching can be either simultaneous or sequential. In the case of sequential stretching the first stretching step can be in either MD or TD, followed by stretching in the other direction. The orientation in MD can also be achieved in several steps, either one after another prior to stretching in TD, or before and after the TD stretching. Preferred temperatures for stretching lie bet¬ ween the glass transition temperature (T_g) and about 30°C above the cold crystallization temperature (T_cc) of the PENBB copolymer composition in use (both temperatures can easily be measured on amorphous films by DSC). The total stretch ratios (Λ) in MD and TD lie between 1 : 2 and 1 : 10, prefe¬ rably between 1 : 2.5 and 1 : 5. The product of the total stretch ratios should be between 1 to 30 preferably between 5 to 20. Biaxial drawing is performed such that the birefringeance is < 0.2, preferably < 0.1 to ensure adequately isotropic properties. Birefringeance as mentioned herein is the absolute value of the difference between the maximum and minimum refracti¬ ve indices in the plane of the film, as measured on common instruments such as Abbe refractometer, optical bench or compensators.

In order to optimize shrinkage properties, relaxation steps can be included in the orientation and heat setting processes. The heat setting takes place at a temperature between the cold crystal¬ lization temperature (T_cc) and the melt temperature (T_m) of the copolymer composition. In some cases a surface treatment such as corona, plasma or flame treatment should be employed before winding the film on a roll.

Prior to coating the biaxially oriented PENBB film surface with the antistatic coating composition, the film may be surface treated in a conven- tional manner by exposure to, e.g. an electric corona discharge, plasma or flame treatment. Electric corona discharge is a conventional surface treat¬ ment which is commonly performed on films to enhance their surface quali¬ ties, especially their adhesive and printing properties. Electronic corona discharge methods and apparatus are described in U.S. Patent Nos. 3,057,792 and 4,239,973. If the corona treatment followed by the coating occurs before stretch orientation, heating the film before stretch orientation will drive off the water. For biaxially oriented PENBB film, the corona treat¬ ment followed by the antistatic coating may occur during the in-line manu¬ facturing process, either before stretch orientation, or between the machine draw and transverse draw of biaxial stretch orientation, or after biaxial stretch orientation. If the corona treatment and coating steps occur after stretch orientation, it is necessary to completely dry the PENBB film before winding. If the corona treatment and coating occur before orientation, or between draw during orientation, the later orientation steps which require the film to be heated would drive off the excess water from the antistatic coa¬ ting. Preferably, for biaxially oriented FENBB film the corona treatment and subsequent antistatic coating occur between draws during the stretch orien¬ tation step.

The PENBB film is coated on the electric corona discharge treated surface preferably with an aqueous dispersion of the antistatic coating com¬ position described below. The coating composition may conveniently be applied as an aqueous dispersion or emulsion using any of the well known coating techniques. For example, the film may be coated by roller coating, spray coating, gravure coating, or slot coating. The heat applied to the film during the subsequent preheating, stretching, and heat setting stages is generally sufficient to evaporate the water and cross-link the antistatic coating, if a cross-linkable monomer comprises a portion of the antistatic coating.

The coated, biaxially oriented PENBB film may then be heat treated for a period of time necessary to crystallize the film. Crystallization imparts the improved dimensional stability and excellent tensile properties to the PENBB film. The so coated crystallized, biaxially oriented PENBB film is then wound onto a roll.

The above description deals with an aqueous antistatic coating compo¬ sition applied in an in-line (during manufacture) coating process. While this is the preferred process for the biaxially oriented PENBB film, organic solvent- based antistatic coatings as well as off-line coating (after manufacture of the film is complete) is a further aspect of the invention.

The antistatic coating can be composed of: I. a composition containing a quarternary ammonium salt (QAS), or II. a composition containing an acrylate, styrene derivative or acrylonitrile and an ethγlenically unsaturated sulfonate salt, or III. a composition containing an organically substituted phosphate.

The abovementioned coating compositions are preferably dissolved or dispersed in a liquid medium, such as water, alcohols, ethers, ketones and the like. The following data on weight ratios refer to the solids content of the solutions or dispersions only. The solids content of the solutions or dispersion depends on the film use intended and the physical parameters of the solutions/dispersions and may vary from about 1 to 99 wt.-%, preferably 5 to 70 wt.-%. Preferably, in the composition containing the QAS (I), the QAS is of the formula

wherein

R¹ is stearamido, -N ⁺ (R⁵),X^'

being C,-C₃ alkyl, with R⁶, R⁷, R⁸ being identical or

different and denoting H or C--C_B alkyl R², R³, R⁴ are identical or different and denote H, C_|-C₂₀ alkyl, or ω-hy- droxy 0,-0₄ alkyl,

X^' is an anion selected from the group consisting of halogens, sulfates, sulfonates, alkyl sulfonates, carbonates, alkyl carbonates, nitrates, phospha¬ tes, alkyl phosphates, and mixtures thereof and n is an integer ranging from 1 to 8.

Preferred QAS are those wherein R¹ is N(CH₃)₃ ⁺ or an acryiate or methacrylate radical, R² and R³ are 0,-0₄ alkyl, especially preferred -CH₃, R⁴ is -CH₃, -CH₂CH₂OH, C₁₄-C₁₈ alkyl, especially tallow, X^" is 01^', C--C₃ alkyl sulfate, especially methyl sulfate or tosylate, and n is 3. Moreover, it is preferred that the QAS is present in the composition in an amount of from about 10 to 80 wt.-% (based on the total weight of the active ingredients of the coating composition). The remainder of the active part of the composition (20 to 90 wt.-%) is a polymeric binder. It may further be desirable to include a suitable self-cross-linking moiety in an amount of up to about 10 wt.-% in the binder.

Preferably, in the composition containing the acryiate, styrene derivati¬ ve or acrylonitrile (II) these are of the formula

wherein R⁹ is -H or -CH₃ and R ⁰ is -COOR¹¹ (with R¹¹ being an alkyl group of 1 to 20 carbon atoms), phenyl or -ON. The ethylenically unsaturated sulfonate salt is preferably one according to the formula:

wherein R¹², R¹³ and R¹⁴ are -H or C C₄ alkyl,

R¹⁵ is di-C,-C₃-alkylene amine ether or thioether, p-phenylene, 0,-0₃ alkyl amido, C,-C₃-carboxy or C,-C₆ alkylene, Y is an alkali metal or -NH(R¹⁶)₂ with R¹⁶ being H or C,-C₃ alkyl and m being 0 or 1.

Specific examples of such compounds include sodium allylsulfonate, sodi¬ um methallylsulfonate, sodium crotylsulfonate, CH₃CH = CH(CH₂)₂SO₃NH₄ ,

I ³ (CH₃)₂C = CH-CH₂CH₂OCH₂CH₂SO₃K, CH₂ = CH-

H₂C= C- coo H^- S0₃Ns

CH₂CH₂SCH₂CH₂-SO₃Na, CH₂ = CH₂-CH₂CH₂-NH-CH₂CH₂-SO₃K,

CH CH₂ = CHSO₃Na, i 3 _an<j

C₂H₅- HC= 0— CONH- CH- CH- S0₃Nε

The composition contains the acryiate, styrene derivative or acryloni trile in about equal amounts based on weight as the ethylenically unsatur¬ ated sulfonate salt. The acryiate based part of the composition II contains a suitable self- cross-linking moeity in an amount of from about 1 to 10 wt.-% based on the acryiate part of the composition.

Moreover, the acryiate based part of composition II may contain up to 5 wt.-% of an ethylenic compound having a carboxy group, which com¬ pound is different from the acryiate described above. Suitable ethylenic carboxy-containing compounds are a-β-mono- or di-unsaturated carboxylic acids having 3 to 5 carbon atoms, either in the form of the free acids or their anhydrides or C,-C₃ alkyl esters. Additionally, the acrylic part of the composition II may include 0 to

29 wt.-% (based on the acryiate part of the composition) of compounds that are copolymerizable with the other components of the acrylic based part; such copolymerizable compounds may include, for example, amides of ethylenic carboxylic acids, such as acrylamide, methacrylamide, diaceto- ne acrylamide and the like; esters between an ethylenic carboxylic acid and an epoxy group-containing alcohol, such as glycidyl acryiate, glycidyl me- thacrylate and the like; hydroxyalkyl esters of ethylenic carboxylic acids, such as 2-hydroxyethyl acryiate, 2-hydroxypropyl acryiate, 2-hydroxyethyl methacrylate and the like; esters between ethylenic carboxylic acid and amino group-containing alcohol, such as dimethylaminoethyl methacrylate, diethylaminoethyl methacrylate and the like; and compounds having at least two unsaturated groups, such as divinylbenzene, diallyl phthalate, triallyl cyanurate, diethylene glycol dimethacrylate and the like.

The ethylenically unsaturated sulfonate salt part of composition II may include 0 to 70 wt.-% (based on the ethylenically unsaturated sulfona¬ te salt part of the composition) of a different compound copolymerizable with the ethylenically unsaturated sulfonate salt. Such compounds may include σJJ-mono- or diunsaturated carboxylic acids such as acrylic acid, methacrylic acid, crotonic acid, citraconic acid, itaconic acid, maleic acid, fumaric acid and the like; anhydrides of cr, ?-diunsaturated carboxylic acids, such as maleic anhydride and the like; monoalkyl esters of σ, ?-diunsatur- ated carboxylic acids, such as monobutyl maleate, monobutyl fumarate. monoethyl itaconate and the like; ammonium salts or alkali metal salts of ethylenic carboxylic acids or monoalkyl esters of σ, ?-diunsaturated carbox¬ ylic acids, such as sodium acryiate, ammonium methacrylate and the like; acrylic acid esters such as methyl acryiate, ethyl acryiate, n-butyl acryiate, isobutyl acryiate, 2-ethylhexyl acryiate, n-octyl acryiate, isononyl acryiate and the like; methacrylic acid esters such as methyl methacrylate, ethyl methacrylate, n-butyl methacrylate and the like, aromatic vinyl compounds such as styrene, σ-methylstyrene, vinyltoluene, ethylvinylbenzene and the like; vinyl cyanides such as acrγlonitrile, methacrγionitrile and the like; amides of ethylenic carboxylic acids, such as acrylamide, methacrylamide, diacetone acrylamide and the like; esters between ethylenic carboxylic acids and epoxy group-containing alcohols, such as glycidyl acryiate, glyci¬ dyl methacrylate and the like; hydroxyalkyl esters of ethylenic carboxylic acids, such as 2-hydroxyethyl acryiate, 2-hydroxypropyl acryiate, 2-hy- droxyethyl methacrylate and the like; esters between ethylenic carboxylic acids and amino group-containing alcohols, such as dimethylaminoethyl methacrylate, diethylaminoethyl methacrylate and the like; and compounds having at least two unsaturated groups, such as divinylbenzene, diallyl phthalate, triallylphthalate, diethylene glycol dimethacrγlate and the like. Preferably, the copolymerization product of the ethylenically unsa¬ turated sulfonate salt and its above-mentioned reaction partner has a mole¬ cular weight of about 3000 or more.

Preferably, in the composition containing the organically substituted phosphate (111), these phosphates are of the formula:

17

OR 0=P OM OR

wherein

R¹⁷ is C,-C,₀ alkyl R¹⁸ is C._|-C._|0 alkyl, alkali metal, ammonium, amine cation or hydrogen, and M is alkali metal, ammonium, an amine cation or hydrogen.

The organically substituted phosphates according to the above for- mula are present in the coating composition III in an amount of from about 12 to 100 %, preferably 50 to 75 % by weight based on the weight of the coating composition. The remaining portion of the composition is a suit¬ able polymeric binder.

Suitable polymeric binders which may be used include acrylic or methacrylic polymers such as polymethylmethacrylate, copolymers of me¬ thyl methacrylate with acrylates such as ethyl acryiate or butyl acryiate, and terpolymers of methyl methacrylate, ethyiacrylate and either acrylami¬ de or methacrylamide, or either N-methylolacrylamide or N-methylolmetha- crylamide. In many cases it is desirable that the polymeric binder be cross- linkable. This may be accomplished by employing up to about 10 mole-% of a "self cross-linking" functional comonomer into the binder, such as N- methylolacrylamide, or by incorporating a suitable amount of cross linking agent such as melamine formaldehyde or urea formaldehyde condensate capable of reacting with a functional group present in the polymer chain, such as amido, carboxyl, epoxy or hydroxy groups. Other suitable binders include vinyl acetate polymers such as polyvinylacetate and copolymers based on vinγlacetate, copolymers containing polymerized vinylidene chlori¬ de, i.e., copolymers of vinylidene chloride, acrylic ester and itaconic acid as disclosed in U.S. Pat. No. 2,698,240; and vinylaromatic polymers such as polystyrene, copolymers containing polymerized styrene and polyurethane resin produced from cγcloaliphatic, araliphatic, aromatic or preferably an aliphatic polyisocyanate. Examples of suitable polyfunctional isocyanates include ethylene diisocyanate, 1 ,6-hexamethylene diisocyanate, isophorone diisocyanate, cyclohexane-1 ,4-diisocyanate, 4,4'-dicyclohexylmethane diisocyanate, p-xylylene diisocyanate, 1 ,4-phenylene diisocyanate, 2,4- toluene diisocyanate, 2,6-toluene diisocyanate, 4,4'-diphenylmethane dii¬ socyanate, 2,4'-diphenylmethane diisocyanate, polymethylene polyphenyl polyisocyanates and 1 ,5-napthylene diisocyanate. 1 ,6-hexamethylene diisocyanate is particularly preferred. Mixtures of polyfunctional isocyana- tes may be used as well as polyfunctional isocyanates which have been modified by the introduction of urethane, allophanate, urea, biuret, carbo- diimide, uretonimine or isocyanurate residues.

The polymeric polyol component of the polyurethane resin may be a member of any of the chemical classes of polymeric polyols used or propo¬ sed to be used in polyurethane formulations. For example, the polymeric polyol may be a polycarbonate, polyesteramide, polyether, polythioether, polyacetal or polyolefin, but preferably a polyester.

The polyester suitably comprises a copolyester, preferably derived from one or more, preferably aromatic, polycarboxylic acids and one or more polyhydric alcohols. Suitable aromatic polycarboxylic acids for incorporation into the polyester portion of the polγurethane resin include phthaiic acid, isophthalic acid, terephthalic acid, 4,4'-bibenzoic acid and 2,6-naphthalic acid or the acid anhydrides or lower-alkyl (up to 10 carbon atoms) esters thereof. Mixtures of two or more thereof, particularly those containing a predomi- nant amount ( > 50 mole %) of terephthalic acid, isophthalic acid, 4,4'- bibenzoic acid and/or 2,6-naphthalic acid may also be employed. The aromatic dicarboxylic acid components may be present in an amount greater than 50 mole %, and preferably greater than 80 mole %, of the total acidic components of the polyester. The polyester may comprise at least one aliphatic or cycloaliphatic dicarboxylic acid, such as cyclohexane-1 ,4-dicarboxyiic acid, adipic acid, sebacic acid, trimeliitic acid and/or itaconic acid, and/or polyester-forming equivalents thereof. Adipic acid is particularly preferred. The aliphatic or cγcloaliphatic dicarboxylic acid components maγ be present in an amount of up to about 30 mole % preferablγ from 0 to 10 mole % of the total acidic components of the polγester. The polγester maγ additionallγ comprise a sulphonated polγcarbox- γlic acid, for example, the ammonium and alkali metal, particularlγ sodium, salts of 4-sulphophthalic acid, 5-sulpho-isophthalic acid and sulphoterepht- halic acid, or the acid anhγdrides or lower alkγl (up to 10 carbon atoms) esters thereof. Such acids, or derivatives, are available as alkali metal salts, particularlγ the sodium sulphonate salt, and are convenientlγ incorpo¬ rated in salt form into the polγester portion of the polγurethane resin. The sulphonic acid component is preferablγ present in a concentration of from 0 to 20 mole %, particularlγ from 1 to 10 mole %, of the total acidic com- ponents of the polγester.

Suitable polγhγdric alcohols for incorporation into the polγester in¬ clude aliphatic, cγcloaliphatic and aromatic alkγlene glγcols, such as ethγle¬ ne glγcol, 1 ,2-propγlene glγcol, neopentγl glγcol, cγclohexane-1 ,4-dimetha- nol and 1 ,3-propane diol, and particularlγ aliphatic alkγlene-oxγ-glγcols, such as diethγlene glγcol. Mixtures of two or more thereof, particularlγ those containing a predominant amount ( > 50 mole %) of ethγlene glγcol and/or diethγlene glγcol maγ also be emploγed. The polγhydric alcohol is present in a stoichiometricallγ equivalent amount of approximately 100 mole %. If desired, the polγester maγ be modified bγ the inclusion therein of one or more monohγdric alcohols, such as ethγlene glγcol monobutγl ether, benzγl alcohol and cγclohexanol.

A preferred polγester for incorporation into the polγurethane resin comprises residues of terephthalic acid, isophthalic acid, ethγlene glγcol, diethγlene glγcol and optionaliγ a sulphonated polycarboxylic acid. Adipic acid may also be included in the polyester component.

Preferably, the polymeric polyol is of low molecular weight, particu¬ larly from about 450 to 9000, and particularly from about 900 to 4500. If desired, the polγurethane resin maγ be made with one or more compounds containing a pluralitγ of isocγanate-reactive groups. A suitable additional isoγanate-reactive compound comprises an organic polyol, parti¬ cularly a short chain aliphatic polyol, preferably neopentyl glγcol. An or- ganic diamine, particularlγ an aliphatic diamine, maγ also be included either independentlγ or together with the organic polγol.

If desired, a catalγst for urethane formation, such as dibutγltin dilau- rate and/or stannous octoate maγ be used to assist formation of the polγu- rethane resin, and a non-reactive solvent maγ be added before or after for¬ mation of the medium to control viscositγ. Suitable non-reactive solvents which maγ be used include acetone, methγlethγlketone, dimethγlformami- de, ethγlene carbonate, propγlene carbonate, diglγme, N-methγlpγrrolidone, ethγl acetate, ethγiene and propγlene glγcol diacetates, alkγl ethers of ethγlene and propγlene glγcol monoacetates, toluene, xγlene and stericallγ hindered alcohols such as t-butanol and diacetone alcohol. The preferred solvents are water-miscible solvents such as N-methγlpγrrolidone, dimethγl sulphoxide and dialkγl ethers of glγcol acetates or mixtures of N-methγl- pγrroiidone and methγl ethγl ketone. Other suitable solvents include vinγl monomers which are subsequentlγ polγmerised.

The polγurethane resins are water dispersible, and a medium com¬ prising an aqueous polγurethane dispersion maγ be prepared bγ dispersing the water dispersible, polγurethane resin in an aqueous medium, preferablγ in the presence of an effective amount of a polγfunctional active hγdrogen- containing chain extender.

The resin maγ be dispersed in water using techniques well known in the art. Preferablγ, the resin is added to the water with agitation or, alter- nativelγ, water maγ be stirred into the resin.

The polγfunctional active hγdrogen-containing chain extender, if emploγed, is preferablγ water-soluable, and water itself maγ be effective.

Other suitable extenders include a polγol, an amino alcohol, ammonia, a primarγ or secondarγ aliphatic, alicγclic, aromatic, araliphatic or heterocγ- clic amine especiallγ a diamine, hγdrazine or a substituted hγdrazine.

Examples of suitable chain extenders useful herein include ethγlene diamine, diethγlene triamine, triethγlene tetramine, propγlene diamine, butγlene diamine, hexamethγlene diamine, cγclohexγlene diamine, piperazi- ne, 2-methγl piperazine, phenγlene diamine, tolγlene diamine, xγlγlene diamine, tris (2-aminoethγl) amine, 3,3'-dinitrobenzidine, 4,4'-methγlene- bis(2-chloroaniline), 3,3'-dichloro-4,4'-biphenγl diamine, 2,6'-diaminopγridi- ne, 4,4'-diaminodiphenγlmethane, menthane diamine, m-xylene diamine, isophorone diamine, and adducts of diethγlene triamine with acrγlate or its hγdrolγzed products. Also, materials such as hγdrazine, azines such as acetone azine, substituted hγdrazines such as, for example, dimethγl hγ¬ drazine, 1,6-hexamethγlene-bis-hγdrazine, carbodihγdrazine, hγdrazides of dicarboxγlic acids and sulfonic acids such as adipic acid mono- or dihγ- drazide, oxalic acid dihγdrazide, isophthalic acid dihγdrazide, tartaric acid dihγdrazide, 1 ,3-phenylene disulfonic acid dihγdrazide, ω-amino-caproic acid dihγdrazide, hγdrazides made bγ reacting lactones with hγdrazines such as -hγdroxylbutyric hγdrazide, bis-semi-carbazide and bis-hγdrazide carbonic esters of glγcols such as anγ of the glγcols mentioned above. Where the chain extender is a substance other than water, for ex- ample a diamine or hγdrazide, it maγ be added to the aqueous dispersion of the polγurethane resin or, alternatively, it may already be present in the aqueous medium when the resin is dispersed therein.

Desirably, the polγfunctional chain extender should be capable of intra-molecular cross-linking, to improve durabilitγ and resistance to sol- vents. Suitable resinous intra-molecular cross-linking agents comprise epoxγ resins, aikγd resins and/or condensation products of an amine, e.g. melamine, diazine, urea, cγclic ethγlene urea, cγclic propγlene urea, thiou¬ rea, cγciic ethγlene thiourea, alkγl melamines, arγl melamines, benzoguana- mines, guanamines, alkγl guanamines and arγl guanamines with an aldehγ- de, e.g. formaldehyde. A useful condensation product is that of melamine with formaldehyde. The condensation product may optionally be partially or totally alkoxγlated, the alkoxy group preferablγ being of low molecular weight, such as methoxγ, ethoxγ, n-butoxγ or iso-butoxγ. A hexamethox- γmethγl melamine condensate is particularlγ suitable. Another particularlγ suitable cross-linking agent is a polγaziridine.

Such polγfunctional chain extenders preferablγ exhibit at least tri functionalitγ (i.e. three functional groups) to promote inter-molecular cross- linking with the functional groups present in the polγurethane resin.

The chain extension maγ be conducted at elevated, reduced or am¬ bient temperature. Convenient temperatures are from about 5° to 95^" C or more, preferablγ from about 10" to about 45 ^*C.

The amount of chain extender emploγed should be approximatelγ equivalent to the free NCO groups in the resin, the ratio of active hγdro- gens in the chain extender to NCO groups in the resin preferablγ being in the range from 1-2 : 1. If desired, and preferablγ, the antistatic laγer maγ be cross-linked to improve its durabilitγ, hardness, cohesive strength and adhesion to the sub¬ strate, and to provide resistance to attack bγ solvents. Cross-linking maγ be promoted bγ incorporation into the antistatic composition of anγ cross- linking agent known to be effective with the binder sγstem in use. Suit- able cross-linking agents, especiallγ for polγurethanes, include the conden¬ sation product of an amine with an aldehγde. For example, melamine, diazine, urea, cγclic propγlene urea, thiourea, cγclic ethγlene thiourea, an alkγl melamine, such as butγl melamine, an arγl melamine, a guanamine, an alkγl guanamine, an arγl guanamine, a benzoguanamine, or glγcoluril, maγ be condensed with an aldehγde, such a formaldehγde. The condensation product is preferablγ aikoxγlated, e.g. ethoxγlated. A preferred cross-lin¬ king agent is a methγlated melamine-formaldehγde resin.

The amount of cross-linking agent necessary to promote the required degree of cross-linking may be readily determined by simple experimenta- tion. In general, the cross-linking agent suitable comprises up to 10% and preferably from 2 to 8%, by weight of the total components of the anti¬ static adherent composition.

Acceleration of the cross-linking maγ be effected, if desired, bγ adding a suitable catalγst to the antistatic composition. A preferred cata- Iγst for use with an amine-formaldehγde cross-linking agent comprises ammonium chloride, ammonium nitrate, phosphoric acid, citric acid, p- toluene sulphonic acid or p-dodecγlbenzenesulphonic acid. The antistatic coating compositions (I), (II) or (III) maγ be applied to one or both sides of the biaxially oriented PENBB film material at any suit¬ able stage during the manufacture, i.e., after extrusion of the sheet materi¬ al or before, during, or after biaxially orientation of the sheet. The resul- tant biaxially oriented PENBB film is found to posess markedly enhanced antistatic properties, good clarity good slip properties and maγ have good adhesive properties and durabilitγ. In addition it exhibits improved mechani¬ cal, thermal, hγdrolγtic and UV stabilitγ in comparison to similarlγ coated biaxially oriented PET film.

Claims

WHAT IS CLAIMED IS:

1. Antistatic, mono- or multilayer biaxially oriented copolyester film, wherein the copolyester is PENBB and wherein at least one surface of the film has been coated with an antistatic coating composition containing

I) a quarternarγ ammonium salt (QAS) and/or

II) a two component sγstem consisting of: a) an acrγlate, stγrene-derivative or acrγlonitrile, and b) an ethylenically unsaturated sulfonate salt and/or III) an organically substituted phosphate.

2. Antistatic biaxially oriented film according to claim 1 , wherein the antistatic coating composition contains either

I) a QAS, or II) a two component sγstem consisting of: a) an acrγlate, stγrene-derivative or acrγlonitrile, and b) an ethylenically unsaturated sulfonate salt or

III) organically substituted phosphate.

3. Antistatic biaxially oriented film according to claim 1 or 2, wherein the copolyester film is a monolayer film.

4. Antistatic biaxially oriented film according to any one or more of the preceding claims, wherein one surface of the film has been coated with the antistatic coating composition.

5. Antistatic biaxially oriented film according to any one or more of the preceding claims, wherein the QAS is of the formula

wherein

R¹ is stearamido or N⁺(R⁵)₃X^' R⁵ being C,-C₃ alkγl or with

R⁶, R⁷ and R⁸ being identical or different, denoting H or C,-C₈ alkγl R², R³ and R⁴ are identical or different and denote H, C,-C₂₀ alkγl or α/-hγdroxγ C,-C₄ alkγl

X^' is an anion selected from the group consisting of F^', CI^", Br^', sulfates, sulfonates, alkγl sulfonates, carbonates, alkγl carbonates, nitrates, phos¬ phates, alkγl phosphates and mixtures thereof and n is an integer ranging from 1 to 8.

6. Antistatic biaxially oriented film according to anγ one or more of the preceding claims, wherein the QAS is of the formula

wherein

R¹ is N(CH₃)₃ ⁺ or an acrγlate or methacrγlate radical,

R² and R³ are C¹-C₄ alkγl,

R⁴ is CH₃, CH₂CH₂OH or C,₄-C,₈-alkγl, X^' is CI^', C,-C₃ alkγl sulfate or tosγlate and n is 3.

7. Antistatic biaxially oriented film according to any one or more of the preceding claims, wherein the acryiate, styrene-derivative or acrγlonitrile are of the formula

wherein

R⁹ is H or CH₃ and R ⁰ is COOR¹¹, with R¹¹ being a C,-C₂₀ alkγl group or

R¹⁰ is phenγl or -CN.

8. Antistatic biaxially oriented film according to any one or more of the preceding claims, wherein the ethylenicallγ unsaturated sulfonate salt is one of the formula

wherein

R¹², R¹³ and R¹⁴ are H or C,-C₄ alkγl,

R¹⁵ is di-C,-C₃-alkγlene amine, di-C,-C₃-alkγlene ether, di-C,-C₃-alkγlene thioether, p-phenγlene, C,-C₃-alkγlamido, C,-C₃-carboxγ or C,-C₆-alkγlene

Y is an alkali metal or N(R¹⁶)₃ with R¹⁶ being H or C,-C₃-alkγl and m being 0 or 1.

9. Antistatic biaxiallγ oriented film according to anγ one or more of the preceding claims, wherein the organicallγ substituted phosphates are of the formula

17

OR

^•O

OR

wherein

R¹⁷ is C,-C,₀-alkγl,

R¹⁸ is C,-C,₀-alkγl, an alkali metal, ammonium, an amine cation or hγdro- gen and

M is an alkali metal, ammonium, amine cation or hγdrogen.

10. Antistatic biaxiallγ oriented film according to anγ one or more of the preceding claims, wherein the birefringeance of the film is < 0.2 and the IV-value of the PENBB is > 0.5 dl/g.

1 1. Use of a film according to claim 1 as packaging material.

12. Use of a film according to claim 1 as reprographic film.

13. Use of a film according to claim 1 as microfilm.

14. Use of a film according to claim 1 as magnetic tape substrate.