An extrusion coatable polyester film having an aminofunctional silane primer, and extrusion coated laminates thereof.

Extrusion-coated oriented polyester film with an amino-functional silane primer and extrusion-coated laminates made therefrom

The invention relates to an oriented polyester film coated on at least one side with a water-soluble hydrolyzable amino-functional silane primer coating composition which makes the film more suitable for extrusion coating with other polymeric materials such as polyolefins.

The application is similar to another patent of the same inventor and the same applicant, entitled Polyester Film Primed With An Aminofunctional Silane, And Film Laminates Thereof, application number 240701 and filed September 6, 1988.

Oriented polyester films, especially biaxially oriented films consisting of polyethylene terephthalate (PET), have been widely used as a packaging material or base for microfilms, reprographic films, proofing films and the like. They have good optical brightness and toughness, which makes them particularly suitable for those purposes.

PET film is mainly used in laminates with other polymers and paper or aluminum foil. Often, a PET film is extruded with a polyethylene or ethylene copolymer to obtain heat sealability, adhesion to other materials such as aluminum foil, additional size (thickness), or stiffness, or to achieve properties not possible with PET alone.

Unfortunately, the surface of the PET film is not very suitable for extrusion coating with other polymers. Numerous primer coatings for the surface of a polyester film are known in the art to improve the adhesion of the film to various materials. Examples of such coatings are e.g. compositions based on vinylidene chloride polymers (U.S. Patent 2,698,240), acrylic or methacrylic disposable plastic polymers (U.S. Patent 3,819,773), and the like. Certain water-dispersible copolyesters have also been proposed for use as adhesives in laminating polyester films to each other or with polyamide films, as disclosed in U.S. Patents 3,563,942 and 3,779,993. More commonly, solution-based polyurethane adhesives or polyethyleneimine primers are used, which have solution emission and safety problems. Corona discharge treatment is also used in addition to or without priming to improve adhesion between extruded films.

It is common practice in extrusion coating for the film processor to perform corona treatment on PET film purchased from the manufacturer, prime the corona treated film, dry the primer, and extrusion coat the film with another polymer. The need for priming the film requires an additional process step, which requires expensive accessories and affects the yield. In addition, the use of solution-based primers requires additional safety and cleaning equipment and is subject to an additional tax.

For the reasons set out above, it would be advantageous for the processor to be able to obtain a pre-treated or primed film that could be directly extruded without priming or corona treatment. In order to save the same costs and problems, it would also be advantageous for the film to be directly extruded to be coated by treating or priming the film in-line during the production of the film.

In the in-line process, for safety and health reasons, it would be ideal if the primer were water-based, recyclable (i.e. does not cause extra yellowing or deterioration of physical properties when mixing primer-coated film waste with fresh polymer and re-extruding, which is necessary in the in-line process due to low conversion rate), and hard enough to allow the film to be rolled into a roll (which is necessary) clogging.

A direct extrusion-coated polyester film is disclosed in U.S. Patent 4,410,600 to PT McGrail. It shows a biaxially oriented PET film in-line coated with a crosslinked styrene / maleic anhydride copolymer. However, the coated film requires corona treatment prior to extrusion coating.

The use of silane coupling agents to improve the bonding properties of polyethylene and polyester films is also known. For example, polyester films and polyethylene films primed with either vinyltrimethoxysilane or chloropropyltrimethoxysilane have been successfully laminated using a hot melt adhesive such as ethylene / vinyl acetate terpolymer or elastomeric polyester, as described in E. Plueddemann, Agonding, Agonding, Bonding Through, Bonding York, 1985. In addition, the use of N-2-aminoethyl-3-aminopropyltrimethoxysilane (sold under the tradename Z-6020, manufactured by Dow Chemical) as a primer to improve the adhesion of an ionomer resin (ethylene / methacrylic acid copolymer salt) to glass and polycarbonate films is disclosed in U.S. Patent 4,663,228. Silanes of the same type, such as N-3-aminopropyltrialkoxysilanes, are known to improve adhesion between polyurethane films and glass substrates, as disclosed in EP-A-171,917.

None of these prior art inventions address the problems associated with direct extrusion coating of films, in particular the coating of polyester with polyethylene, ethylene copolymers and ionomers or other polymeric films, without additional primers or additional corona treatment.

Accordingly, the present invention relates to an oriented polyester film which can be extrusion coated directly with other polymers without the need for additional primers or additional corona treatment.

The present invention also relates to a primed polyester film in which the primed film waste can be recycled without further yellowing or deterioration of the properties of the re-extruded product.

Most prior art primers use volatile solvents, requiring equipment for handling solvents, equipment for protecting workers, and equipment for disposing of waste solution .

It is therefore an object of the invention to provide a water-based primer which can be used in most existing systems without the need for expensive accessories.

These and other objects of the invention can be achieved by using an oriented polyester film having a primed composition on at least one side and a second polymer layer attached to the primed surface, which film is characterized by what is set forth in the characterizing part of claim 1.

The useful amino-functional silanes used in the invention can be represented in their non-hydrolyzed form by the general formula:

(R ^ IR ^ SilR³) where R¹ is a functional group containing at least one primary amino group, R² is a hydrolyzable group, for example a lower alkoxy group, an acetoxy group or a halide, and R³ is a non-reactive non-hydrolysable group, for example a lower alkyl or phenyl group; and (a) is 1 or greater; (b) is 1 or greater; (c) is 0 or greater; and a + b + c = 4.

In general, the amino-functional silane is hydrolyzed in water and applied to one or more surfaces of the oriented polyester film by any conventional method, such as spray coating or roll coating. After the silane primer coating has dried, the primed polyester film receives a direct extrusion coating of one or more polymers. The extrusion coating can be performed by any conventional method. The primer coating helps the polyester film to bond to the extrudate, forming a laminate.

In its broadest sense, the present invention relates to an oriented polyester film having an effective amount of a primer to improve the adhesion of the film to a direct extrusion coating with one or more polymers, wherein the primer in non-hydrolyzed form is represented by the general formula:

(R¹) aSi (R²) b (R³) _c where R¹ is a functional group containing at least one primary amino group, R² is a hydrolyzable group and R³is a non-reactive non-hydrolyzed group; and (a) is 1 or greater; (b) is 1 or greater; (c) is 0 or greater; and a + b + c = 4.

In its broadest sense, the present invention is also represented by a laminate having an oriented polyester film, a primer, and one or more directly crosslinked polymers; wherein the primer in non-hydrolyzed form is represented by the general formula:

(R¹) aSi (R²) b (R³) _c where R¹ is a functional group containing at least one primary amino group, R² is a hydrolyzable group and R³ is a non-reactive non-hydrolyzed group; and (a) is 1 or greater; (b) is 1 or greater; (c) is 0 or greater; and a + b + c = 4.

Silanes are water-soluble or water-dispersible after hydrolysis, with amino-functional silanes being particularly water-soluble. The inventor of the present invention has found that aminosilanes provide good adhesion between the extrusion-coated polymer and the polyester film without additional priming or corona treatment. Aminosilane-primed polyester film waste can be recycled.

Amino-functional silanes useful in the purposes of the invention in their non-hydrolyzed form are represented by the general formula:

(R)_aSi (R²) b (R³) c where R¹ is a functional group containing at least one primary amino group, R² is a hydrolyzable group which is a lower alkoxy group of 1 to 8 carbon atoms, an acetoxy group or a halide, and R³ is a non-reactive non-hydrolyzable group which is a lower alkyl group or a phenyl group of 1 to 8 carbon atoms; and (a) is 1 or greater; (b) is 1 or greater; (c) is 0 or greater; and a + b + c = 4. Examples of aminosilanes of the formula are N-2-aminoethyl-3aminopropyltrimethoxysilane, N-3-aminopropyltrimethoxysilane, 4-aminobutyltriethoxysilane, 4-aminobutyldimethylmethoxysilane and p-aminophenyltrimethoxysilane. The preferred silane is N-2-aminoethyl-3-aminopropyltrimethoxysilane of the formula:

B₂N (CH₂) ₂NH (CH₂) ₃Si (OCH₃) ₃

The hydrolyzed aminosilane is applied to the film as an aqueous solution at any suitable stage during the preparation of the film, i.e. before or during the stretching step, or it can also be applied to the finished film. The resulting primed polyester film has been found to adhere to extrusion-coated polymer films.

The primer composition is prepared by mixing the aminosilane with water at concentrations of about 0.2 to 6 weight percent. A weak acid, such as acetic acid, may optionally be added to facilitate hydrolysis. At least one of the hydrolyzable groups in the silane is hydrolyzed to the silanol group (SiOH). The hydrolysis product of aminosilane is thought to have a partially hydrolyzed cyclic structure in which the amino groups probably form ionic bonds with the silicone portion of the molecule. The term 'hydrolyzed' as used herein may also refer to such partially hydrolyzed structures.

A preferred oriented polyester film for the purposes of this invention is polyethylene terephthalate, although the invention is equally applicable to crystalline polyester based films prepared by polycondensation of glycol, e.g. ethylene glycol or butanediol or mixtures thereof with terephthalic acid or terephthalic acid with diphenic acid or sebacic acid or their polyester-forming equivalents, the polyesters being prepared by methods well known in the art. The film can be prepared by methods also well known in the art using well known equipment.

For example, the polyester is melted and extruded as an amorphous film onto a polished rotary casting drum, whereby the polymer forms a casting film. The film is then stretched in one direction, either in the extrusion direction (longitudinally) or perpendicular to the extrusion direction (transverse) in the case of a unidirectionally oriented film, and in two directions in the case of a biaxially oriented film, i.e., the film is stretched in both longitudinal and transverse directions. The first stretch, which improves the strength and toughness of the film, can be 3 to 5 times.

The hydrolyzed aminosilane primer in the form of an aqueous solution according to the invention can be applied by inline coating in one or more steps during film preparation, namely: in the pre-drawing step at a point between the casting of the amorphous film and the first stretch, as disclosed in GB Patent 1,411,564; in the intermediate drawing step after unidirectional stretching but before biaxial stretching is disclosed, for example, in U.S. Patent 4,214,035; or in the post-drawing phase after biaxial stretching but before film wrapping. Normally, the heat introduced into the film during the stretching step or final finishing steps is sufficient to evaporate water and other volatiles and to dry the primer, but a separate drying step is required if the coating is applied after those heating steps.

In a preferred embodiment, the primer is applied after the film has been stretched in one direction, but before the film has been stretched in the orthogonal direction. In another preferred embodiment, the polyester film is first stretched longitudinally prior to coating. In this preferred embodiment, after longitudinal stretching, the film is coated in any manner well known in the art. For example, coating 99131 can be enhanced by roll coating, spray coating, slit coating, or dip coating. In a preferred embodiment, the polyester film is coated using a groove roll coating. The unidirectionally stretched film can also be subjected to corona treatment in corona treatment equipment prior to coating, as is known in the art. The corona treatment reduces the hydrophobic nature of the polyester film surface, which makes it easier for the water-based pad to wet the surface and thus improves the adhesion of the primer to the surface.

The aminosilane of the invention is applied to the film as an aqueous solution having a concentration of about 0.2 to 6% by weight of hydrolyzed aminosilane. A weak acid, for example acetic acid, phosphoric acid or the like, is then added in an amount of about 0.2% by weight to facilitate hydrolysis. The preferred concentration of aminosilane is 0.25 to 2.5% by weight. The preferred concentration is such that the weight of the final dry primer is about 0.49x10 '.⁶kg / m² (Ο, ΙΟχΙΟ '⁶ lbs per square foot). The weight of the coating can be considerably higher if the coating takes place as an off-line coating (i.e. applied to the finished film in a separate coating step), whereby the dry coating weight is 4.9x10 '⁶ kg / m² (LOxlO '⁶lbs / ft²) or higher gives good results.

The coating of the invention may be applied to one or both sides of the film or may be applied to one side of the film and a different coating such as an acrylic or methacrylic disposable plastic coating may be applied to the opposite side as disclosed in U.S. Patent 4,214,035. The coating can also be applied to a different primer to which it adheres and which is already on the surface of the film, such as an acrylic disposable plastic coating as disclosed in U.S. Patent 3,819,773.

The coating composition may also contain other ingredients to the extent that such ingredients do not reduce the adhesion promoting effect of the hydrolyzed aminosilane. These may include small amounts of colloidal silicon, dyes, pH adjusters, wetting agents, and the like. The primer is used as a continuous coating on the surface of the film, the term also being meant to include coatings in which the primer may consist of many islands or discrete areas.

The waste film generated during production, which is coated with the primers according to the invention, can be ground and mixed with fresh polyester and re-pressed into an oriented film. The film thus obtained, which contains significant amounts of recycled primer waste, deteriorates very little despite the coating impurities, and the color formation is also low. The primed film of the invention thus provides a commercial advantage to film manufacturers over many other primed films, for example films primed with vinylidene chloride-containing polymers, as disclosed in U.S. Patents 2,627,088 and 2,698,240, which when recycled tend to degrade and stain the product as described above.

Laminates can be made by well-known extrusion coating methods in which a molten polymer film is deposited on the surface of a continuously moving primed web or film. Polyester laminates with polyethylene, ethylene / vinyl acetate copolymers, vinyl alcohol, polyvinyl acetate and other polymers are easy to make by the extrusion coating process.

Polyethylene-coated PET film has particularly useful properties, such as good sealability and adhesion to other materials such as aluminum foil. Although the inventor is not sure, it is believed that the amino group of the primer reacts with the heated, oxidized polyethylene when it is extruded onto the PET film, thus firmly binding the primer to the polyethylene.

The thickness of the polyester film suitable for use in the invention generally ranges from 0.006 to 0.254 mm (0.25 to 10 mils) or more.

The following examples illustrate the invention.

Well Production

N-2-aminoethyl-3-aminopropyltrimethoxysilane (AE-APTMS) (sold by Dow Corning under the trade name Z-6020 and Union Carbide under the trade name A-1120) or N-3-aminopropyltrimethoxysilane (APTMS) was dispersed in ordinary tap water to form a concentrated water25. - 1.5% by weight of AE-APTMS (or other aminosilane, if indicated). Acetic acid was added at a concentration of 0.2% by weight to facilitate hydrolysis.

The polyethylene terephthalate polymer was melted and extruded through a slit nozzle onto a casting drum maintained at about 20 ° C. The melt became solid and a cast film formed. The cast film was stretched longitudinally at a draw ratio of about 3.5: 1, maintaining the temperature at about 80 ° C.

The longitudinally drawn film was corona treated in a corona discharge apparatus and then coated with a raster roll with the hydrolyzed aminosilane solution prepared above.

The corona-treated, longitudinally drawn, coated film was dried at about 100 ° C. The film was then stretched in the transverse direction at a draw ratio of 3.9: 1 to obtain a bi-directionally drawn film. The thickness of the drawn film was about 0.0127 to 0.0762 mm (0.5 to 3 mils). The bidirectionally drawn film was then heat set at a maximum temperature of 230 ° C.

The dry weight of the coating was (0.50x10 '⁶ lbs / ft²) .

about 2.5x10 ⁶ kg / m²

Examples 1-8

A polyethylene terephthalate film was prepared and coated as described in FILM PREPARATION and the film thickness was 0.0127 mm (0.5 mils). The film was coated with aqueous aminosilane according to Table 1. For each coating composition, a roll of 30 m (100 ft) long laminating film was prepared and passed through an extrusion coater and coated with about 0.0254 mm (1 mil) thick low density polyethylene (LDPE) (USI resin having a melt index of 14). The melt temperature was 327 ° C (620 ° F) and the nozzle distance from the film was about 20 cm (8 inches). No additional corona treatment or priming was used.

TABLE 1

<td>Film</td><td>primer composition</td><td>Primer pa</td>

<td></td><td>(weight-%)</td><td>(Kg / mm²)</td>

<td>Example 1</td><td>Unprimed vert.</td><td> -</td>

<td>Example 2</td><td>0.25% AE-APTMS *</td><td>1,32x10 ''</td>

<td>Example 3</td><td>0.5% AE-APTMS *</td><td>2,68x10 ''</td>

<td>Example 4</td><td>1.0% AE-APTMS *</td><td>5,37x10 ''</td>

<td>Example 5</td><td>1.5% AE-APTMS *</td><td>8,00x10 ''</td>

<td>Example 6</td><td>0.5% APTMS **</td><td>2,00x10 «</td>

<td>Example 7</td><td>1.0% APTMS **</td><td>4,00x10 ''</td>

<td>Example 8</td><td>1.5% APTMS **</td><td>6, 00x10 '«</td>

* AE-APTMS is N-2-aminoethyl-3-aminopropyltrimethoxysilane ** APTMS is N-3-aminopropyltrimethoxysilane

The adhesion of the polyethylene to the un primed control film of Example 1 was 1.6x10³ kg / m (0.09 lbs / inch) using ASTM tests D882 and E4. The adhesion of the polyethylene to the films of Examples 2-8 was so good that the Kah99131 layers were not separated from each other to allow the peel test to be performed. Separation at the PET / LDPE interface could not be achieved with hot water, toluene or tetrahydrofuran. Adhesion was excellent with both APTMS (N-3-aminopropyltrimethoxysilane) and AE-APTMS (N-2-aminoethyl-3-aminopropyltrimethoxysilane).

Examples 1-28

A polyethylene terephthalate film was prepared and coated as described in FILM PREPARATION and the film was 0.0127 mm (0.5 mils) thick. The film was coated with aqueous aminosilane according to Table 2. For each coating composition, a roll of 30 m (100 ft) long laminating film was prepared and passed through an extrusion coater and coated with approximately 0.0191 mm (0.75 mil) of SURLYN^R 1652 with ionomer resin. The melting point was 307 ° C (585 ° F). Half of each sample was corona treated with 2.5 kVA before extrusion coating and the other half was not corona treated. Another roll of the same laminating film was coated with 0.0191 mm (0.75 mil) Norchem 1014 LD polyethylene, which was extruded at 625 ° C. Like SURLYN^RWhen age was used, half of each sample was corona treated and the other half was not. Peel strength was measured using an Instron tester and ASTM tests D882 and E-4. During the extrusion coating step, strips of untreated polyester were placed between the ends of the layers for a non-stick area from which the layers could be separated for the peel test.)

TABLE 2

Membrane Base composition

Corona Adhesion (% by weight) (kg / mm)

SURLYN^R LDPE

<td>E.g</td><td> 9</td><td> 0,25%</td><td>AE-APTMS</td><td>Yes</td><td> 0,047</td><td> 0,022</td>

<td>E.g</td><td> 10</td><td> 0,25%</td><td>AE-APTMS</td><td>No</td><td> 0,051</td><td> 0,022</td>

<td>E.g</td><td> 11</td><td> 0,50%</td><td>AE-APTMS</td><td>Yes</td><td> 0,039</td><td> 0,026</td>

<td>E.g</td><td> 12</td><td> 0,50%</td><td>AE-APTMS</td><td>No</td><td> 0,076</td><td> 0,024</td>

<td>E.g</td><td> 13</td><td> 1,00%</td><td>AE-APTMS</td><td>Yes</td><td> 0,043</td><td> 0,022</td>

<td>E.g</td><td> 14</td><td> 1,00%</td><td>AE-APTMS</td><td>No</td><td> 0,043</td><td> 0,023</td>

<td>E.g</td><td> 15</td><td> 1,50%</td><td>AE-APTMS</td><td>Yes</td><td> 0,045</td><td> 0,025</td>

<td>E.g</td><td> 16</td><td> 1,50%</td><td>AE-APTMS</td><td>No</td><td> 0,045</td><td> 0,025</td>

<td>E.g</td><td> 17</td><td> 0,25%</td><td>APTMS</td><td>Yes</td><td> 0,057</td><td> 0,023</td>

<td>E.g</td><td> 18</td><td> 0,25%</td><td>APTMS</td><td>No</td><td> 0,052</td><td> 0,026</td>

<td>E.g</td><td> 19</td><td> 0,50%</td><td>APTMS</td><td>Yes</td><td> 0,040</td><td> 0,022</td>

<td>E.g</td><td> 20</td><td> 0,50%</td><td>APTMS</td><td>No</td><td> 0,056</td><td> 0,021</td>

<td>E.g</td><td> 21</td><td> 1,00%</td><td>APTMS</td><td>Yes</td><td> 0,028</td><td> 0,022</td>

<td>E.g</td><td> 22</td><td> 1,00%</td><td>APTMS</td><td>No</td><td> 0,032</td><td> 0,023</td>

<td>E.g</td><td> 23</td><td> 1,50%</td><td>APTMS</td><td>Yes</td><td> 0,035</td><td> 0,030</td>

<td>E.g</td><td> 24</td><td> 1,50%</td><td>APTMS</td><td>No</td><td> 0,039</td><td> 0,023</td>

<td>E.g</td><td> 25</td><td colspan="2">copolyester *</td><td>Yes</td><td> 0,018</td><td> 0, 008</td>

<td>E.g</td><td> 26</td><td colspan="2">copolyester *</td><td>No</td><td> 0,004</td><td> 0,001</td>

<td>E.g</td><td> 27</td><td colspan="2">unprimed</td><td>Yes</td><td> 0,019</td><td> 0,018</td>

<td>E.g</td><td> 28</td><td colspan="2">unprimed</td><td>No</td><td> 0,002</td><td> 0,002</td>

* A film primed with a water-dispersible copolyester according to U.S. Patent 4,493,872.

When PET is unprimed or copolyester-primed, corona treatment prior to coating is necessary to obtain the slightest adhesion between the polyester film and SURLYN.^r 1652 or Norchem^R Between the 1014 film. Even when corona-treated, the adhesion of the unprimed and copolyester-primed PET film was not as good as that of the aminosilane-primed film. Corona treatment of the aminosilane-based film was also not necessary and was indifferent to adhesion. Adhesion was good with both AE-APTMS and APTMS at concentrations as low as 0.25% by weight.

Thus, it is apparent that the primed film of the invention can be extruded and that the extruded laminate fulfills the object, purposes and advantages previously set forth for the invention. Although the invention has been described in connection with specific embodiments thereof, it will be apparent that many alternatives, modifications, and variations will be apparent to those skilled in the art in light of the foregoing description. Therefore, all such alternatives, modifications, and modifications that are within the spirit and scope of the invention are intended to be included.