WO1998038240A1

WO1998038240A1 - Coated plastic film for producing packaging containers

Info

Publication number: WO1998038240A1
Application number: PCT/EP1998/000977
Authority: WO
Inventors: Harald Borgholte; Jürgen Niemann; Jürgen Kaczun; Peter Eric Van Rijn
Original assignee: Ppg Industries Ohio, Inc.
Priority date: 1997-02-27
Filing date: 1998-02-20
Publication date: 1998-09-03
Also published as: DE19707786A1; AU6722798A

Abstract

The present invention relates to a plastics film for producing packaging containers, in which the film is coated with a sealable coating and with a release coat, wherein the release coat contains an acrylate copolymer which is obtainable by free-radical polymerization of: (A) a mixture comprising: (a1) at least one polysiloxane macromonomer with a number-average molecular weight of from 1000 to 40.000 and with, on average, from 0.5 to 2.5 ethylenically unsaturated double bonds per molecule; (a2) (meth)acrylic acid and/or maleic acid and/or crotonic acid; and (a3) at least one ethylenically unsaturated monomer different from (a1) and (a2); in the presence of (B) from 0.1 to 10 % by weight of at least one free-radical generator, where the amount of component (a1) is more than 0 and less than 5 % by weight, based on the total weight of the monomers used, and the formulation of the monomer mixture is preferably selected in such a way that if the monomer mixture made from (a1) to (a3) is polymerized alone the resultant polymer has a glass transition temperature of from 0 to 150 °C.

Description

COATED PLASTIC FILM FOR PRODUCING PACKAGING CONTAINERS

The present invention relates to a plastics film for producing packaging containers, an outer side of the film being coated with a seal able coating and the opposite outer side of the film being coated with an acrylate-based coating composition.

The present invention moreover relates to a process for producing packaging containers using these plastics films, to the packaging containers thus produced, and to a process for producing a multilayer coating, in which process an acryl ate-based coating composition is applied to a printing ink.

Plastics films which are intended to be used, for example, for the packaging of foods, e.g. chocolate, ice cream, nuts, potato chips and the like, are provided with adhesive coatings in order to allow an effective seal.

In addition, plastics films of the type mentioned at the outset are also applied to packaging containers made from glass and/or plastic, for example drinks bottles, in order to mark these and/or to provide them with a decorative surface. In this case too, the plastics films are provided with adhesive coatings.

The adhesive coatings in particular cases are either hot- sealable coatings, which can be sealed at elevated temperatures, or cold-sealable coatings, which are sealed at temperatures of from about 0 to 80°C.

Col d-seal able coatings and thei r properties are described, for example, in L. Pl aczek i n Coating, 18 (4) , pages 94 - 95, 1985.

Col d-seal able coatings are preferably appl ied from an aqueous phase. Pressure-sensitive adhesives, which are used in the cold-sealing process, are predominantly used in the packaging of foods, e.g. for packaging for chocolates and ice cream.

Seal able coating agents for the sealing of plastics films, such as polypropylene films, are known, for example, from US-A--

4,898.787. US-A-4,888,395 and US-A-5,070,164. The cold-sealable coatings are usually based on emulsion polymers, which have an average molecular weight of from about 20,000 to 150,000 and a glass transition temperature of from about -15°C to about +15°C. However, cold-sealable coatings have the disadvantage of poor antiblocking properties, i.e. when stored, plastics films coated with cold-sealable coatings, if stored over a prolonged period under normal storage conditions in the form of rolls, show a tendency to stick to the mutually superposed layers of film. Cold-sealable coatings therefore require the application of a protective layer on the other side of the film. The coatings used for this purpose are usually called release coats. They usually comprise polyamide resins, often in combination with cellulose nitrate and with waxes, with fatty acid amides or with silicone oils. If low-molecular- weight silicone oils or waxes are used in the release coats, however, there is the danger of migration of these constituents into the sealing layer, resulting in an undesirable reduction in seal strength.

In other areas, moreover, for example in the coating of wood, there is also the need to provide a protective layer for substrates coated with printing inks.

DE-A-4124167 has now disclosed clear coatings for the coating of automobiles, which comprise, as binders, copolyers in which from 9 to 20 % by weight of a methoxy-functional polysiloxane has been incorpor-ated by condensation. EP-A-603561 moreover discloses coating compositions which comprise, as binders, copolymers which incorporate, as coonomers, from 3 to 40 X by weight of an α,ω-hydroxy- , carboxy- and/or epoxy-functional polysiloxane. JP-A 2-163177, furthermore, discloses a coating composition based on hydroxyl -group-containing acrylate copolymers and polyisocyanates, and used in particular as a paint for buildings. The coatings here are distinguished by improved weathering resistance, achieved by incorporating from 0.5 to 15 X by weight of a polysiloxane macromonomer into the hydroxyl -group-containing acrylate copolymer as comonomer.

Finally, DE-A-19519807 discloses coating compositions, in particular for automotive repair coating, which comprise, as binders, copolymers which incorporate, as comonomer, less than 5 X by weight of a polysiloxane macromonomer.

However, the references mentioned do not describe the use of siloxane-modified acrylate copolymers in coatings for coating plastics films used for producing packaging containers, nor the use of such coatings as a protective layer over a printing ink layer. The publication Polymers Paint Colour Journal, in its April

1996 issue, pages 27 - 28, finally discloses the use of silicones in release coats. However, that article does not contain further details on the structure of the silicones used.

The object of the present invention is therefore to provide plastics films suitable for producing packaging containers and having good resistance to blocking. The plastics films should moreover fulfil the requirements which are usually placed upon plastics films used for producing packaging containers. The plastics films should therefore, for example, be sealable under the conditions usually used and have good seal strength. In addition, the coating compositions/coatings used to produce the films should allow very proble -free solvent recovery. The resultant films should moreover have very good optical properties. They should, furthermore, preferably be odor-free, in order also to be suitable for producing packaging containers for foodstuffs. Finally, the plastics films should also show no transfer of printing inks if the printed films are stored in the form of rolls.

Surprisingly, this object is achieved by means of the plastics films of the type described at the outset, wherein the coating composition applied to the side opposite to the sealable coating layer comprises, as binder, an acrylate copolymer which is obtainable by free- radical polymerization of

(A) a mixture comprising

(al) a polysiloxane macromonomer with a number-average molecular weight of from 1000 to 40,000 and with, on average, from 0.5 to 2.5 ethylenically unsaturated double bonds per molecule, or a mixture of such monomers,

(a2) acrylic acid, methacrylic acid, maleic acid, crotonic acid or a mixture of two or more of these monomers, and (a3) an ethylenically unsaturated monomer different from (al) and (a2), or a mixture of such ethylenically unsaturated monomers, in the presence of

(B) from 0.1 to 10 X by weight, based on the total amount of polymerizable monomers, of a free-radical generator or a mixture of free-radical generators, where the amount of component (al) is more than 0 and less than 5 X by weight, based on the total weight of the monomers (al) to (a3) used, and the formulation of the mixture made from (al) to (a3) is preferably selected in such a way that if the mixture made from (al) to (a3) is polymerized alone the resultant polymer has a glass transition temperature of from 0 to 150°C.

The novel plastics films may be used for producing packaging containers, in particular for foodstuffs, and are distinguished by very good resistance to blocking. The coating applied to the side opposite to the sealable coating layer moreover does not reduce the seal strength unacceptably.

The present invention therefore also provides a process for producing packaging containers using these plastics films, and the packaging containers thus produced.

Finally, coating compositions which comprise, as binders, the siloxane- odified acrylate copolymers referred to are also suitable for producing a protective layer over printing inks applied to other substrates, such as wood. The present invention therefore also provides a process for producing a multilayer coating, in which process a coating composition based on these siloxane-modified acrylate copolymers is applied to a printing ink.

The siloxane-modified acrylate copolymers used according to the invention will now be described in more detail below.

The mixture (A) used to prepare the acrylate dispersion used according to the invention comprises

(a2) acrylic acid, methacrylic acid, maleic acid, crotonic acid, or a mixture made from two or more of these monomers, and (a3) an ethylenically unsaturated monomer different from (al) and (a2), or a mixture of such ethylenically unsaturated monomers, where the amount of component (al) is more than 0 and less than 5 X by weight, based on the total weight of the monomers (al) to (a3) used, and the formulation of the mixture made from (al) to (a3) is preferably selected in such a way that if the mixture of (al) to (a3) is polymerized alone the resultant polymer has a glass transition temperature of from 0 to 150°C, preferably from 10 to 80°C.

Since the glass transition temperature of polymers prepared from ethylenically unsaturated mono-mers may be calculated from the equation

1/Tg = Σ W_n/Tg_n

Tg = glass transition temperature of the copolymer in °K W_n = proportion by weight of the nth monomer

Tg_n= glass transition temperature of the homo-polymer made from the nth monomer,

the person skilled in the art can readily select the formulation of the mixture made from components (al) to (a3) in such a way that if the mixture of (al) to (a3) is polymerized alone the resultant polymer has a glass transition temperature of from 0 to 150°C, preferably from

10 to 80°C.

Taking into account the selection criteria described above, examples of components (a3) are: acrylic or methacrylic esters, in particular aliphatic acrylates or methacrylates with up to 20 carbon atoms in the alcohol radical, e.g. methyl, ethyl, propyl , isopropyl, butyl, isobutyl, tert-butyl, n-pentyl, isopentyl, hexyl , n-octyl , 2- ethylhexyl, decyl , lauryl and stearyl acryl ates or the corresponding meth-acryl ates, preference being given to the use of methyl acrylate and methyl methacrylate, corresponding esters of other ethylenically unsaturated acids with up to 6 carbon atoms in the molecule, e.g. ethacrylic acid and crotonic acid, acrylamidomethylpropanesulfonic acid, vinyl aromatic hydrocarbons, e.g. styrene, α-alkyl -styrene and vinyltoluene, preferably styrene, amide-group-containing monomers, e.g. acryl amide, ethacryl -amide, N-methylolacryl amide and N- methylolmethacryl -amide, and nitrile-group-containing monomers, e.g. acrylonitrile and methacrylonitrile or mixtures of the monomers mentioned.

For modifying the polyacrylate resin, suitable components (al) are polysiloxane macromonomers which have a number-average molecular weight of from 1000 to 40,000, preferably from 2000 to 10,000, and have, on average, from 0.5 to 2.5, preferably from 0.5 to 2.0, ethylenically unsaturated double bonds per molecule.

The amount of the polysiloxane macromonomer(s) (al) used for modifying the polyacrylate resins is more than 0 and less than 5 X by weight, preferably from 0.5 to less than 5 X by weight and particularly preferably from 1 to 3 X by weight, based in each case on the total weight of the monomers (al) to (a3) used for preparing the polyacrylate resin.

Examples of suitable components (al) are the polysiloxane macromonomers described in DE-A-3807571 on pages 5 - 7, in DE-A-3706 095 in columns 3 - 7, in EP-B-358153 on pages 3 - 6 and in US-A- 4,754,014 in columns 5 - 9. Other acryloxysilane-containing vinyl monomers with the abovementioned molecular weights and contents of ethylenically unsaturated double bonds are moreover also suitable, for example compounds which can be prepared by reacting hydroxy-functional silanes with epichlorohydrin, and then reacting the reaction product with methacrylic acid and/or with hydroxyalkyl (meth)acrylates.

Preferred components (al) are polysiloxane macromonomers of the following formula (I):

where

R¹ is H or CH₃,

R², R³, R⁴ and R⁵ are identical or different aliphatic hydrocarbon radicals with from 1 to 8 carbon atoms, in particular methyl, or a phenyl radical, or an alkoxy radical OR', where R' is an aliphatic hydrocarbon radical with from 1 to 8 carbon atoms, m is from 8 to 80, or one or more polysiloxane macromonomers of the following formula (II)

where

R¹ i s H or CH_{3 >}

R², R³, R\ R⁵, R⁶, R⁷ and R⁸ are identical or di fferent al iphati c hydrocarbon radi cal s with from 1 to 8 carbon atoms , in particul ar a methyl radical , or a phenyl radical , m is from 8 to 80.

An example of such a polysi loxane macromonomer i s the α,ω- acryloxyorganofu ctional polydimethyl -siloxane of the formul a

H OCH3

with » 30 or 50, which is particularly preferred.

Polysiloxane macromonomers used as component (al) are also those which have been prepared by reacting from 70 to 99.999 mo of a compound (1) of the formula (1)

^■Si R^J (1)

R⁴

where R¹ is an aliphatic hydrocarbon group with from 1 to 8 carbon atoms or a phenyl radical and each of R², R³ and R⁴ is a halogen radical or alkoxy radical with from 1 to 4 carbon atoms or hydroxyl with from 30 to 0.001 o of a compound (2) of the formula (2)

HC: :C — C00(CH₂) _nSi R⁷ (2)

where R⁵ is hydrogen or a methyl radical, R⁶, R⁷ and R⁸ are each halogen, OH- or an alkoxy radical with 1 to 4 carbon atoms or an aliphatic hydrocarbon group with from 1 to 8 carbon atoms, at least one of the radicals R⁶, R⁷ or R⁸ being OH- or alkoxy, and n is an integer from 1 to 6.

Examples of suitable compounds (1) and (2) are given in WO 92/22615 on page 13, line 18 - page 15, line 9.

The reaction between the compounds (1) and (2) is brought about by the dehydrating condensation of the hydroxyl groups present in these compounds and/or of the hydroxyl groups deriving from the hydrolysis of the alkoxy groups in these compounds. Depending on the reaction conditions, the reaction includes, in addition to the dehydration reaction, a dealcoholyzating condensation. If the compounds (1) or (2) contain halogen radicals, the reaction between (1) and (2) is brought about by dehydrohalogenation.

The conditions under which the reaction between compound (1) and compound (2) is carried out are likewise described in the international patent application with the international publication number WO 92/22615 on page 15, line 23 - page 18, line 10.

Particularly preferred components (al) are polysiloxane macromonomers with from 0.5 to 1.5, on average one, methacryloyl end group and a number-average molecular weight of from 2000 to 5000.

The products obtainable commercially under the following names are moreover also suitable as component (al): polysiloxane macromonomer AK 5 and AK 30 from Toagosei Chemical Industries Co., Ltd. (represented in Germany by Marubeni), and also various products marketed by Th. Goldschmidt under the designations TEGOMER® E-Si and TEGOMER® V- Si.

Monomers used as component (a2) are acrylic acid, methacrylic acid, maleic acid, crotonic acid or a mixture of two or more of these, preference being given to acrylic and/or methacrylic acid. Acrylate copolymers whose use is preferred are obtained by using component (al) in an amount of less than 5 X by weight, preferably from 0.5 to less than 5 X by weight, particularly preferably from 1 to 3 X by weight, component (a2) in an amount of from 1 to 50 X by weight, preferably from 2 to 15 X by weight and component (a3) in an amount of from 49.5 to 98.5 X by weight, preferably from 82 to 97 X by weight, where the percentages for components (al) to (a3) are based on the total weight of components (al) to (a3).

The mixture (A) may be polymerized in bulk or in an organic solvent or a mixture made from organic solvents, in the presence of component (B). The polymerization is preferably carried out in an organic solvent or a mixture made from organic solvents, in particular in non-polar solvents with a boiling point in the range of from 60 to 100°C, preferably from 65 to 75°C, at polymerization temperatures of from 60 to 100°C, preferably from 65 to 80°C.

Examples of suitable solvents are Solvent Naphtha®, heavy benzene, various Solvesso® grades, various Shell sol® grades and Deasol®, and also higher-boiling aliphatic and cycloaliphatic hydrocarbons, e.g. various white spirits, tetralin and decalin, and also various alcohols, ethers and esters, e.g. ethanol , butyl glycol, 2- methoxypropanol , n-butanol, methoxy-butanol , n-propanol, ethyl acetate, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol diethyl ether, diethylene glycol monobutyl ether, ethyl 2-hydroxypropionate and 3-methyl -3-methoxybutanol , and also derivatives based on propylene glycol, e.g. ethyl ethoxypropionate, methoxypropyl acetate and the like.

In principle, any known free-radical generator may be used as component (B). In addition, preference is given to those free-radical generators which have a half-life time at the polymerization temperature of from 15 to 180 minutes. Examples of free-radical generators which may be used are: dialkyl peroxides, e.g. dicuyl peroxide and di-tert-butyl peroxide, peroxyesters , e.g. tert-butyl peroxybenzoate, tert-butyl peroxyoctanoate, tert-butyl peroxyacetate and tert-butyl peroxyisobutyrate, diacyl peroxides, e.g. benzoyl peroxide and acetyl peroxide, and free-radical generators based on azo compounds, e.g. 2,2- azobis(2-methylbutyronitrile). Preference is given to the use of free- radical generators based on per-compounds. Compounds particularly preferably used as component (B) are di-tert-butyl peroxide, tert-butyl perethylhexano-ate and tert-butyl peracetate.

The preparation of the acrylate copolymer may moreover take place, if desired, in the presence of from 0.5 to 1.5 X by weight, based on the total weight of the monomer mixture of (al) to (a3), of one or more chain-transfer agents. An example of a suitable compound is isooctyl thioglycolate.

To prepare the polyacrylate resin, at least 60 X by weight, preferably 100 X by weight, of the entire amount of component (al) together with some of the solvent may be placed into the reaction vessel and heated to the respective polymerization temperature. The remaining monomers are then metered in at a uniform rate at the polymerization temperature. If polysiloxane macromonomers with low reactivity (functionality < 2) are used as component (al), then likewise at least 60 X by weight, preferably 100 X by weight, of the entire amount of this polysiloxane macromonomer (al) may be placed into the reaction vessel. The polysiloxane macromonomers may, however, also be added together with the remaining monomers.

The resultant acrylate copolymers are used according to the invention as binders in coating compositions for the coating of plastics films. These coating compositions usually contain from 10 to 30 X by weight of the acrylate copolymer described above (used as solution in one or more organic solvents), based on solid resin and based on the total weight of the coating.

These coating compositions moreover usually also contain from 50 to 90 X by weight of organic solvent and from 0 to 20 X by weight, based in each case on the total weight of the coating composition, of usual auxiliaries and additives.

Examples of suitable organic solvents are the solvents listed above under the preparation of the acrylate copolymers. Examples of suitable auxiliaries and additives are flow control agents, stabilizers, thickeners, defoamers, pigments and fillers.

The coating compositions may, for example, contain insoluble, finely dispersed inorganic substances, such as talc and silica, e.g. the commercial product Syloid 63 FP from Grace.

According to the invention, these coating compositions are used in particular for the coating of plastics films. In the case of the plastics films under consideration, one outer side of the plastics film is coated with a sealable coating and the opposite outer side of the plastics film is coated with the coating described above. The coating described above and used according to the invention (release coat) here is usually applied to a printing ink layer. The coating used according to the invention (release coat) prevents mutually superposed film layers from sticking to one another during use and if the plastics films are stored for relatively long periods in the form of rolls under normal storage conditions. It also serves to prevent migration of the printing ink.

In this respect, the plastics films under consideration may either be provided with a printing ink directly at the film producer, or else (as is more common) only the application of the sealable coating takes place at the film producer, and the printing ink (and therefore also the release coat) is applied only later by the user of the plastics film. In this second case, the film producer initially provides the plastics film with a sealable coating and with an outer coating prepared from an aqueous coating composition which, like the coating described above and used according to the invention (release coat), serves to prevent adjacent film layers from sticking to one another during the storage and transport of the films on rolls. To this outer coating, the user of the film then applies firstly the printing ink and then the release coat. Wherever the coating of the plastics films with the printing ink takes place, the printed plastics films are provided, after application of the printing ink, with the coating described above and used according to the invention. In addition, unprinted plastics films are also used, in particular in the industrial sector. In this case, the plastics film is provided directly with the coating composition described above and used according to the invention, on the side opposite to the sealable coating, without prior application of the printing ink. To produce the novel plastics films, the surface of the films is generally pretreated before the sealable coating, and, if desired, the aqueous coating composition for the outer coating or the printing ink, is applied to the plastics films, in order to ensure that the coating is firmly bonded to the film. This is to avoid the coating becoming peeled off or pulled off from the film.

This, treatment is carried out by known methods, e.g. by chlorination of the plastics film,, treatment with oxidants, such as chromic acid or hot air, or by steam treatment or flame treatment. A particularly preferred pretreatment used is high-voltage corona discharge.

The plastics films are generally precoated after the pretreatment, in order to secure adhesion of the coating to the substrate film. Suitable precoating agents or primers are known from the literature and encompass, for example, alkyl titanates, and also primers based on epoxides, on melamine-formaldehyde resins and on polyethyleneimines. The latter are particularly suitable for the precoating of plastics films. These polyethyleneimines may be applied to the, if desired pretreated, plastics films either from organic or else from aqueous solution. The concentration of the polyethyleneimine in the aqueous or in the organic solution here is for example 0.5 X by weight. Suitable polyethylenei ine primers are described, for example, in DE-A- 2440112 and US-A-3,753,769. The uncoated plastics films generally have a thickness of from 0.015 to 0.060 mm. The sealable coating and, if used, the aqueous coating composition for the outer coating, and the release coat are applied to the plastics film in a usual manner, for example by gravure coating, roller coating, dipping, spraying, or with the aid of gravure or flexo printing or reverse-roll coating. The excess of coating may be removed in each case by squeegee rollers or doctors.

The sealable coatings are usually applied in an amount which, on drying, gives a smooth, uniformly distributed layer with a weight of from 0.5 to 5 g/m², preferably with a weight of from 0.6 to 1.6 g/m². The aqueous outer coatings are usually applied in an amount which, on drying, gives a smooth, uniformly distributed layer with a weight of from 0.5 to 5 g/m², preferably with a weight of from 1 to 2 g/m². The printing inks are usually applied in an amount which, after drying, gives a smooth, uniformly distributed layer with a weight of from 0.5 to 5 g/m², preferably with a weight of from 1 to 2 g/m². The coating compositions for the release coats according to the invention are usually applied in an amount which, on drying, gives a smooth, uniformly distributed layer with a weight of from 1 to 5 g/m², preferably with a weight of from 2 to 3 g/m².

The coating formed by the release coat on the plastics film, like the sealable coating layer and the outer coating layer, if present, is dried separately or together with the sealable coating layer with hot air, radiant heat or by any other usual means. The sealable coatings used for producing the plastics films are known and are described, for example, in DE-A-4341815.

Use is made, in particular, of aqueous coating compositions for sealable coats based on an acrylate dispersion. The sealable coatings are preferably sealed at a temperature of from 0 to 80°C, particularly preferably at least 30°C and very particularly preferably from 40 to 70°C.

The aqueous outer coating compositions used for coating the plastics films are likewise known and are described, for example, in DE- A-2440 112 and DE-A-4341815. The printing inks used for subsequent printing of the plastics films are likewise known.

The coating compositions described above and based on the si licone-modified acrylate copolymer may, however, also be applied over a printing ink for other applications. For example, they may also be applied over a printing ink layer which has been applied to other substrates, e.g. wood.

The invention is described in more detail below using working examples, all data on parts and percentages being by weight unless expressly otherwise stated.

1. Preparation of the acrylate copolymers 1 to 4

The amounts given in Table 1 of a mixture made from ethyl acetate and ethanol and the polysiloxane macromonomer al given in Table 1 are weighed out in a polymerization vessel made from stainless steel, with stirrer, reflux condenser, a monomer feed and an initiator feed, and heated to the temperature given in Table 1. When the reaction temperature has been reached, the feed of a mixture of the parts given in Table 1 of initiator and solvent is begun and this mixture is added dropwise to the homogeneous mixture at a constant rate within the stated time, the temperature in the reaction mixture being held constant. 15 minutes after the addition of the initiator solution has begun, a mixture of the monomers given in Table 1 is added within the stated time. After the initiator feed has ended, polymerization is continued for the time stated in each case. The mixture is then cooled and the amount of ethanol given in Table 1 is used as solvent. The resulting solution of the acrylate copolymer has the content of non-volatile fractions (1 h/130°C) and the acid number which are given in each case. Table 1: Formulation and parameters of the acrylate resins 1 to 4

Definitions for Table 1:

SV RV: amount in parts of ethyl acetate in receiver Ethanol : amount in parts of ethanol used as solvent after the continued polymerization

SV init.: amount in parts of ethyl acetate in initiator feed ABMBN: amount in parts of 2,2-azobis(2-methylbutyro-nitrile) in initiator feed

TBPEH: amount in parts of tert-butyl perethyl hexanoate in initiator feed

T react. : reaction temperature in °C Duration mon. : duration in hours of the monomer feed Duration ini . : duration in hours of the initiator feed Duration cont. polym.: duration in hours of the continued polymerization phase

MA: amount in parts (percentages, based on monomer mixture) of methyl acrylate

MMA: amount in parts (percentages, based on monomer mixture) of methyl methacrylate

MAA: amount in parts (percentages, based on monomer mixture) of methacrylic acid

IOG: amount in parts (percentages, based on monomer mixture) of isooctyl thioglycolate Siloxane: amount in parts (percentages, based on monomer mixture) of the commercially availabe polysiloxane macromonomer of the formula

with a number -average molecular weight of about 2300 and 1 double bond per molecule

SC (*) solids content in * at 60 min, 130°C Vis.: viscosity in dPa.s at 23°C of a 50 * strength solution of the acrylate copolymer in ethanol

AN: acid number in g KOH/g

2. Production of coating compositions 1 to 4 for the release coats

Coating compositions 1 to 4 for the release coats are produced from the components given in Table 2, using the acrylate copolymer solutions 1 to 4, by adjusting with ethyl acetate to a solids content of 20 *.

3. Application of coating compositions 1 to 4 and test results from the resultant coatings

A commercially available flexo-printing ink (commercial product Helioplastol HG A-2 from BASF Drucksysteme GmbH) is firstly applied with a wire-wound draw bar at a wet-film coating thickness of 6 micrometers to an oriented polypropylene 33MW647 from Mobil Plastics, Belgium which has been coated with an outer coating, and the ink is dried for 30 s at room temperature and then for 30 s at an air temperature of 60°C in a Helios laboratory heating cabinet. To the resultant printing ink layer, each of the coating compositions 1 to 4 for the release coats is applied with a wire-wound draw bar at a wet film thickness of 12 micrometers, and dried for 30 s at room temperature and then for 30 s at an air temperature of 60°C in a Helios laboratory heating cabinet.

The resistance to blocking of these coated films 1 to 4 with respect to the packaging film coated with sealable coating is determined by pressing together, for a period of 2 hours at 3.5 bar and 50°C, the film coated with the respective release coats 1 to 4 and OPP film made from oriented polypropylene 33MW647 from Mobil Plastics, Belgium, which has been coated with a sealable coating according to DE-A-4341815, Example 7.

Test strips of width 25 mm are then cut from the test surface, and resistance to blocking is then determined by peeling with the aid of an apparatus for measuring tension/elongation, the peel force being measured in g/25 mm. Table 3 gives the results of this measurement.

For all of the release coats, moreover, the effect on the sealability of the sealable coatings is studied by pressing together, for a period of 70 h at 3.5 bar and 50°C, the film coated with the respective release coats 1 to 4 and the sealable coating according to DE-A-4341815, Example 7. After this, a check is made as to whether the sealing properties of the sealable coating have changed. The results are likewise given in Table 3. The assessment "satisfactory" here means that no effect was observed. Table 3: Results of the blocking resistance test and the seal strength test

Claims

1. A plastics film for producing packaging containers, one outer side of the film being coated with a sealable coating and the opposite outer side being coated with an acryl ate-based coating composition, wherein the coating composition applied to the side opposite to the sealable coating layer comprises, as binder, an acrylate copolymer which is obtainable by free-radical polymerization of

(A) a mixture comprising

(a2) acrylic acid, methacrylic acid, maleic acid, crotonic acid or a mixture of two or more of these monomers, and

(a3) an ethylenically unsaturated monomer different from (al) and (a2), or a mixture of such ethylenically unsaturated monomers,

in the presence of

(B) from 0.1 to 10 * by weight, based on the total weight of polymerizable monomers, of a free-radical generator or a mixture of free-radical generators, where the amount of component (al) is more than 0 and less than 5 * by weight, based on the total weight of the monomers (al) to (a3) used.

2. The plastics film according to claim 1, characterized in that the formulation of the mixture made from (al) to (a3) is preferably selected in such a way that if the mixture made from (al) to (a3) is polymerized alone the resultant polymer has a glass transition temperature of from 0 to 150┬░C.

3. The plastics film according to claims 1 or 2 characterized in that it is obtainable by using component (al) in an amount of from 0.5 to less than 5 * by weight, component (a2) in an amount of from 1 to 50 * by weight and component (a3) in an amount of from 49.5 to 98.5 * by weight, where the percentages of components (al) to (a3) are based on the total weight of components (al) to (a3).

4. The plastics film according to claim 3, characterized in that it is obtainable by using component (al) in an amount of from 1 to 3 * by weight, component (a2) in an amount of from 2 to 15 * by weight and component (a3) in an amount of from 82 to 97 * by weight, where the percentages of components (al) to (a3) are based on the total weight of components (al) to (a3).

5. The plastics film according to any of claims 1 to 4 characterized in that it is obtainable by using, as component (al), one or more polysiloxane macromonomers of the following formula (I)

where

R¹ is H or CH ₃.

R², R³, R⁴ and R⁵ are identical or different aliphatic hydrocarbon radicals with from 1 to 8 carbon atoms, in particular methyl, or a phenyl radicals, or OR', where R' is an aliphatic hydrocarbon radical with from 1 to 8 carbon atoms,

m is from 8 to 80,

or one or more polysiloxane macromonomers of the following formula (ID

where

R¹ is H or CH ^╬╣ ₃>

R², R³, R⁴, R⁵, R⁶, R⁷, and R⁸ are identical or different aliphatic hydrocarbon radicals with from 1 to 8 carbon atoms, in particular methyl, or a phenyl radicals, and

m is from 8 to 80.

6. The plastics film according to any of claims 1 to 5, characterized in that it is obtainable by using, as component (al), one or more polysiloxane macromonomers of the following formula:

where m ┬½ 30 or 50.

7. The plastics film according to any of claims 1 to 6, characterized in that the sealable coating is prepared from an aqueous coating based on an acrylate dispersion.

8. The plastics film according to any of claims 1 to 7, characterized in that it has been coated with a printing ink before application of the acryl ate -based coating composition on the side opposite to the sealable coating layer.

9. A process for producing packaging containers from plastics films characterized by using the plastics film according to any of claims 1 to 8.

10. The process according to claim 9, characterized in that the sealable coatings are sealed at a temperature of from 0 to

80┬░C, preferably at least 30┬░C and particularly preferably from 40 to 70┬░C.

11. A packaging container obtainable by the process according to claims 9 or 10.

12. A process -for producing a multilayer coating on a substrate, in which a printing ink is firstly applied, and a coating composition based on an acrylate resin is applied to the printing ink, wherein the coating composition applied to the printing ink comprises as a binder, an acrylate copolymer which is obtainable by free-radical polymerization of

(A) a mixture comprising

in the presence of

13. The process according to claim 12, characterized in that the formulation of the mixture made from (al) to (a3) is preferably selected in such a way that if the mixture made from (al) to (a3) is polymerized alone the resultant polymer has a glass transition temperature of from 0 to 150┬░C.