DE10150898A1 - Heat sealing compound for aluminum foils against polypropylene and polystyrene - Google Patents

Abstract

The invention relates to a hot sealing system comprised of an olefin polymer or of an olefin polymer A, of a methacrylate polymer B, of a graft polymer A-X consisting of the above-mentioned constituents and of a solvent or solvent mixture. The hot sealing system is characterized by having a high thermal stability and short sealing times.

Description

Field of the Invention

In the field of packaging of food and tablets have Polystyrene (PS) and polyvinyl chloride (PVC) for some time now also polypropylene (PP) and polyethylene terephthalate (PET). not pretreated Polypropylene is a very critical plastic for the paint sector, as it is very common Adhesion problems occur. This problem is with heat sealing stored slightly differently against polypropylene (PP is not coated here, but "glued"), but also present. So you can at Polystyrene or PVC sealing proven polymethacrylate resins such. B. Do not use PLEXIGUM P 24 or PLEXIGUM N 80 because they are sealed is not reachable with them.

PLEXIGUM P24 is a copolymer of methyl methacrylate and butyl methacrylate and is marketed by Röhm GmbH & Co. KG.

PLEXIGUM N80 is and is a methyl acrylate-ethyl methacrylate copolymer also brought to the market by Röhm GmbH & Co. KG.

With PLEXISOL PM 555 (manufacturer: Röhm GmbH & Co. KG), a special solvent - based binder system based on polyolefin / polymethacrylate in Butyl acetate / methyl ethyl ketone, has succeeded in developing a binder that excellent for sealing aluminum foil against polypropylene suitable is. In addition, with PLEXISOL PM 555 it is also possible to perform equally good sealing against polystyrene and PVC.  

PLEXISOL PM 555 must be used to achieve aluminum adhesion with PVC Copolymers such as B. ®VINYLITE VMCH primed, but can also in appropriate combination can be used as a single-layer system.

Vinylite VMCH is an acidic PVC polymer (distribution: Union Carbide).

State of the art

Instead of vessels and containers made of wood or inorganic Materials such as metal, glass, ceramics are common in the present Kicked plastic products. The requirements are particularly high in everyone Trap if the vessels or containers for receiving or preserving Serve food.

A key aspect of food preservation, be it through Dehydration, freezing or sterilizing is the total prevention microbial growth. This often results in the constraint, the containers sealed gas-tight. In addition, the plastic containers mechanical stability, control of water content, as well as the influence of Atmosphere and light. (See Ullmann's Encyclopedia of Industrial Chemistry 25th Ed. Vol. A11, 523-560; 583-618 VCH 1988; there the applicable standards were also discussed).

To close plastic containers in food technology, especially with dairy products such as yoghurt cups, widely with a Sealing wax coated aluminum lid used.  

Such aluminum covers often represent a three-layer laminate, its outer layer often made of (biaxially oriented) polyethylene terephthalate (O-PET), biaxially oriented polypropylene (OPP) or polyamide (O-PA) or made of Cellulose consists. In contrast, the heat-sealable inner layer usually exists made of polyethylene, ethylene copolymers or polypropylene (US Pat. No. 4,753,708; G. Stehle, Neue Verpackung 9/91, pp. 94-101). Against the use of Aluminum z. B. for packaging food are becoming more and more Economic and ecological reasons brought up for discussion, in particular the high energy consumption in the manufacture of aluminum.

Plastic foils are therefore used instead of aluminum, which are provided with a sealable lacquer. The sealing wax is the adapted plastic used. As a relatively inexpensive material for sealable films with good mechanical strength and good Hard PVC plays a very important role in barrier properties, whereby as Sealing varnish layer usually serves an acrylic resin whose adhesive strength and Melting point can be modified appropriately by additives.

DE-A 35 31 036 describes plastic films which can be produced by coextrusion described, which consist of a sealable layer of impact-resistant polystyrene, a block copolymer and a lubricant.  

In EP-A 0 406 681, however, the problem with the use of heat-sealable plastic foils instead of aluminum foil. As a rule, the much narrower is noticeable Working time. Mostly there is a very narrow processing area of 10-20 ° C, which must be kept fairly constant in order to trouble-free production and proper use of the sealed Guarantee pack. For filling systems with several cavities for simultaneous filling of cups this requirement is not always fulfilled. EP-A 0 406 681 had set itself the task after the Coextrusion process according to DE-A 35 31 036 producible films Polystyrene base u. a. to improve so that the processing range and the Processing security can be increased.

Furthermore, flawless production should also be possible on filling systems with several Filling cavities are ensured. In practice, this depends on the application higher sealing temperatures with corresponding quality requirements the plastic films.

According to EP-A 0 406 681, these requirements were met by a the coextrusion process or sealable produced by lamination Plastic film consisting of two layers A and C and optionally a layer B. and, if appropriate, in each case one layer of an adhesion promoter D for connecting in each case two of the layers A, optionally B and C, consisting of 1 to 50% a layer of a heat-sealable, impact-resistant polystyrene A, up to 95% a carrier layer B and 1 to 99% of a high melting point Plastic layer C, the sum of the strengths or the weight of A and optionally B and C is 100 each.  

task

The task was to achieve high adhesive strength at a relatively high level To reach temperatures (high heat resistance) because of such short Cycle times for coating the film and for the food packer reached become.

There was also the task of the well-known heat sealant for aluminum and To improve plastic films so that instead of the usual solvent-based binder system made from butyl acetate and methyl ethyl ketone a solvent system that can be used in the HAPS list is listed. It should also be striven for that with the usual cycle times, which at heat sealing of aluminum or plastic films are used, sufficiently high strength of the closure can be achieved.

Furthermore, there was the task of developing a heat sealant that the subsequent to the application of the heat sealant printing process, stable remains. Binders of the prior art can after short printing times Lead deposits on the transport rollers of the printing press, so that a secure transport of the film to be printed is no longer possible. The Printing press must be stopped, partially disassembled, and cleaned. Some of the setup and cleaning times required for this are not available Relationship to machine runtime. With the binder according to the invention is a easy printing over a long period of time possible.  

solution

The object is achieved by a film-forming dispersion of at least two different types of polymers A and B, with type A being a Is an olefin copolymer or an olefin polymer.

The olefin polymers and copolymers to be used according to the invention, corresponding to A, are known per se. It is primarily about Ethylene, propylene, butylene or / and other α-olefins with 5-20 C atoms built-up polymers, as already recommended as heat-sealable compositions have been. The molecular weight is generally from 10,000 to 300,000, preferably between 50,000 and 150,000. Olefin copolymers of Types are to be used, for example, in the German published documents DE-OS 16 44 941, DE-OS 17 69 834, DE-OS 19 39 037, DE-OS 19 63 039 and DE-OS 20 59 981 described.

Buna 6170 (manufacturer: Bayer AG), for example, can be used as the olefin polymer. be used.

Ethylene-propylene copolymers are particularly useful; are also Terpolymers with the addition of the known ter components, such as ethylidene Norbornen (see Macromolecular Reviews, Vol. 10 1975) is possible, but it is to take into account their tendency to network in the aging process. The Distribution can be largely statistical, but it can also be advantageous Sequence polymers with ethylene blocks can be applied. The ratio of Monomeric ethylene-propylene is variable within certain limits set at about 95% for ethylene and about 95% for propylene as the upper limit can be.  

By definition, polymer type B consists of polyacrylate and / or polymethacrylate sequences. These are taken on their own, e.g. B. in the form of a corresponding homo- or copolymer, soluble in the solvent system L. The polymer B or segment X is generally composed of more than 50% by weight, preferably 80 to 100% by weight (for example if based on segment X) from monomers of the formula I.

wherein R _{1 is} hydrogen or methyl and R _{2 is} an alkyl radical, an araliphatic or aromatic radical having 1 to 30 carbon atoms, preferably 1 to 20 carbon atoms.

Polymer B may also contain:
Monomers of the formula II

wherein R ' _{1 represents} hydrogen or methyl and / or polymerizable acid anhydrides and / or monomers of the formula III

wherein R " _{1 is} hydrogen or methyl and Z is an optionally alkyl-substituted phenyl radical, a -COR ₃ radical, a

represents an -OR ₄ radical or a chlorine atom and in which R ₃ and R _{4 represent} an optionally branched alkyl radical having 1 to 20 carbon atoms or a phenyl radical and n represents 0 or 1, and / or monomers of the formula IV

wherein R ₅ and R _{6 are} hydrogen or a radical -COOR ' ₇ , R ₆ , hydrogen or a radical -CH ₂ COOR " ₇ with the proviso that the compound of formula IV must contain two carboxyl-containing groups and wherein R ₇ , R ' ₇ and R " _{7 represent} hydrogen or an optionally branched alkyl radical having 1 to 20 carbon atoms or phenyl. The polymer B may optionally also contain proportions of the monomers of the formula V.

wherein R ''' _{1 has} the meaning of R ₁ and Bs for a nitrogen-containing functional radical such as a -CN group, a group -CONR ₉ R ₁₀ , wherein R ₉ and R ₁₀ independently of one another are hydrogen or an alkyl radical having 1 to 20 Carbon atoms, or in which R ₉ and R ₁₀ , including nitrogen, form a heterocyclic 5- or 6-ring or in which Bs represents an (inert) heterocyclic radical, in particular a pyridine, pyrolidine, imidazole, carbazole, lactam, Residue or alkylated derivatives thereof is or Bs is -CH ₂ OH, or wherein Bs is

-COO-QR ₁₁

possesses wherein Q ₉ R _'10 wherein R' represents an optionally alkyl-substituted alkylene radical having 2 to 8 carbon atoms and R ₁₁ is -OH, -OR ''_'7 or a radical -NR''' _7, R ' ₉ and R' _{10 have} the same meanings as R ₇ , R ₈ and R ₉ , e.g. B. together with the nitrogen atom, optionally including a further heteroatom, form a five- to six-membered heterocyclic ring.

Examples of the monomers of the formula I are methyl methacrylate, Ethyl methacrylate, propyl methacrylate, butyl methacrylate and isobutyl methacrylate called. The monomers of formula I are also called standard methacrylates designated.

Examples of the monomers of the formula II are acrylic acid or Called methacrylic acid.

Particular examples of monomers of the formulas III and IV may be mentioned Styrene, α-methylstyrene, vinyl chloride, vinyl acetate, vinyl stearate, vinyl methyl ketone, Vinyl isobutyl ether, allyl acetate, allyl chloride, allyl isobutyl ether, allyl methyl ketone, Dibutyl maleate, dilauryl maleate, dibutyl itaconate. The proportion of the monomers of the Formula II-V at segment X 'is generally between 0 and 50% by weight, preferably at 0 to 20 wt .-%, (based on the monomers of the segment X '). The proportion of the monomers of the formulas II and / or V in the segment X 'is in generally do not exceed 20% by weight, as a rule it is from 0 to 10% by weight, preferably 0 to 5% by weight.

Specifically, segment X is based on proportion and composition expediently chosen with a view to the desired technical function become. The proportion of polar monomers of the formulas II and V is in generally not exceed 20 wt .-%, preferably it is 0 to 10 wt .-% (based on the monomers of the segment X '), particularly preferably at 0 to 5% by weight. C- and N-vinylpyridine and Vinyl pyrrolidine, vinyl pyrrolidone, vinyl carbazole, vinyl imidazole and their Alkyl derivatives, especially the N-vinyl compounds, as well as the  Hydroxy- and dialkylaminoalkyl esters of acrylic or methacrylic acid, especially Dimethylaminoethyl (meth) acrylate, dimethylaminopropyl (meth) acrylate, hydroxy ethyl (meth) acrylate. The segments B and X are generally in Weight ratio 1:20 to 20: 1, preferably 1: 4 to 1: 1.

In addition, there is a polymer AX in the heat seal system, which is a polyolefin grafted by B.

In general:
The graft polymer AX is generally prepared by preparing a dispersion from component A with the aid of a suitable emulsifier and grafting component X onto this under the appropriate reaction conditions. The emulsifier can have a structure similar to the AX system. The processes for producing suitable emulsifiers of the AX type are known per se. So z. B. be carried out according to the method of transmission grafting.

Production of the graft polymers AX

In general:
The graft polymer AX is generally prepared by preparing a dispersion from component A with the aid of a suitable emulsifier and grafting component X onto this under the appropriate reaction conditions. The emulsifier can have a structure similar to the AX system. The processes for producing suitable emulsifiers of the AX type are known per se. So z. B. The method of transfer grafting can be used: (See also Houben-Weyl, Methods of Org. Chemistry, Vol. 1411, p. 114, HAJ Battaerd, GW Tregear, Polymer Reviews, Vol. 16, Interscience (1967)) ,

A 10-50%, preferably 20-30% solution of an OCP in a suitable solvent which is inert under polymerization conditions, which normally has a boiling point above the process temperature. As solvents such. B. butyl acetate, aliphatic cycloaliphatic and aromatic hydrocarbons in question. These are added to these OCP solutions Monomers of the formula I or possibly the other monomers II-III in the specified ratios and polymerized with the addition of one or more, preferably peroxidic radical initiators at 50 temperatures of 60-150 ° C. usually within 4-8 hours. One should strive for one if possible complete sales. Peresters such as tert-butyl peroctoate are preferred Use. The initiator concentration depends on the number of the desired Graft sites and the desired molecular weight of the segment X. Im generally the initiator concentration is between 0.2 and 3% by weight, based on on the polymer.

If necessary, to adjust the desired molecular weight Segments X and controllers can also be used. As a controller are z. B. Sulfur regulators, especially regulators containing mercapto groups, e.g. B. Dodecyimercaptan. The concentrations of regulators are generally 0.1 up to 1.0% by weight, based on the total polymer. Another method of Production of the graft polymers A-X represents the hydroperoxidation of an OCP first step. The chain-like formed in this way Hydroperoxide groups can undergo graft polymerization in a subsequent step initiate the vinyl monomers. (See H.A. J. Battaerd, G.W. Tregear, Polymer Reviews loc. cit.).

A process for the production of suitable block polymers consists, for. B. in anionic polymerization. You can, for example, proceed in such a way that isoprene or butadiene with a suitable anionic initiator (e.g. organometallic compound) polymerized and the "living" anionic Chain ends with z. B. alkyl methacrylate or styrene. The so produced Polymers are then hydrogenated under conditions under which the  existing functional groups are not attacked. In terms of Details of the manufacture can be found in the relevant literature, e.g. B. Houben-Weyl, Methods of Org. Chemistry, 14/1, S. flOff .; Block Copolymers, 5 D.C. Allport, W.H. Janes, Appl. Sci. Publishers Ltd., London, 1973; graft Copolymers, H.A. J. Battaerd, G.W. Tregear, Polymer Reviews Vol. 16 (1967); Block and Graft Polymers. W. J. Burlant, A. S. Hoffmann, Reinhold Publishers Corp., New York, 1960.

In addition to the polymer types A and B and the graft polymer AX there is also a solvent system in the heat seal system according to the invention.

The solvents to be used for the solvent system L are so select that they meet the requirements of coating technology for Plastics and metals correspond. The - if necessary in a mixture - solvents to be used should be inert and generally harmless, the boiling point does not exceed 105 ° C at 760 Torr.

A mixture of esters of aliphatic carboxylic acids is used as the solvent aliphatic alcohols and aliphatic hydrocarbons in question.

Acetic acid, propynic acid or butyric acid come as the aliphatic carboxylic acid in question.

Aliphatic alcohols are ethanol, propanol, isopropanol, n-butanol, 2- Butanol, 2-methyl-1-propanol or 2-methyl-2-propanol in question.

The aliphatic hydrocarbons are pentane, hexane, heptane, octane, Nonane, decane, undecane or dodecane in question.

The aliphatic hydrocarbons can also be in the form of their Mixtures of isomers and in mixtures with one another. It can too Cycloalkanes and substituted cycloalkanes are used.  

When choosing L is also on the compatibility between the Polymer components A and X. In case of incompatibility between A and X can represent L an equally good solvent for both components, the dispersion then forms due to the incompatibility.

In the case of compatibility between A and X, L must be chosen so that it at a given temperature, a better solvent system for X than for A represents, the dispersion then forms due to the different Solution quality. According to the invention, L is preferably a solvent chosen such that the olefin copolymers in the temperature range between 40 and swell 150 ° C to 5 to 300 wt .-% ("degree of swelling").

The degree of swelling is defined as follows: an OCP film 1 mm thick, 2 cm Length, 0.5 cm width with known weight is given at a defined Temperature - in the example shown at 90 ° C - in the solvent immersed and stored isothermally for 24 hours with the solution tweezers removed, freed of adhering swelling agent by means of a filter paper and weighed immediately afterwards. As a measure of the swelling, the Weight gain defined as a percentage of the initial weight. The Swelling measurement should be carried out at the temperature at which the concentrated OCP Dispersion is to be produced. According to the invention this temperature the swelling is 5 to 300 wt .-%. requirement for the applicability of the criterion is that among those given above Conditions the maximum swelling of the OCP is reached.

Mixtures of the solvents described above also come for the carrier system in question. The proportion of the solvent system L in the Polymer dispersions concentrated according to the invention can, for. B. 80 in particularly favorable case down to 20 wt .-%, preferably below 70, practically mostly 55 to 40 wt .-%.  

Manufacture of the heat seal system

With the aid of a suitable emulsifier, as explained above, a Dispersion or a suitable adjustment of the polymer compatibility homogeneous solution of component A in the solvent system L and component X is then grafted on under suitable reaction conditions. In general, the proportions of A and X are in weight ratios of 1 5 to 5 to 1. The content of the total polymer based on the total Dispersion is at least 10% by weight, in practice 40 to 80% by weight are aimed for, normally 45 to 60 wt .-%.

According to the method according to the invention, heat-sealable ones are used Obtain coating compositions in dispersion that have sufficient stability for possess the processing process. The stability of the dispersions is at least several days, normally several weeks to months.

The heat seal systems according to the invention are characterized by medium Adhesive strength and a high thermal stability.

Examples Foil material used

Soft aluminum foil 40 µm
Polypropylene film, extruded from granules JE 6100 (Shell) 0.2 mm

Recipe for the heat seal solution

Before processing, PLEXISOL PM 555 must be stirred well, as with prolonged storage there is the possibility of phase separation.

PLEXISOL PM 555 has one in delivery form (manufacturer: Röhm GmbH & Co. KG) Solids content of approx. 45% and is further processed with MEK to 30%  diluted. PVC has been used to promote adhesion on the aluminum foil. Copolymers proven. They are either applied as a primer or used in combination with PLEXISOL PM 555. At our Both options were examined. It was both with Vinylite VMCH primed as well as in a ratio of 99/1 to 90/10 or 85/15 VMCH combined.

Application of the heat seal solution in the laboratory

The primer was applied as a 10% solution of Vinylite VMCH in ethyl acetate the K-Handcoater No. 2 on the aluminum foil (10 × 20 cm). This corresponds to a dry layer of 0.5-1.5 µm.

The PLEXISOL PM 555 heat seal solution was created with the K-Handcoater No. 4 reared. Dry layer thicknesses of 7-9 µm were obtained.

Drying of the coated foils in the laboratory

The primed film became 1 minute after a short flash-off time (10-20 minutes) Dried 180 ° C in a forced air oven.

The films coated with heat-sealing lacquer were applied at different for 1 minute Temperatures (160 ° C, 200 ° C) dried, but also 5 seconds at 205 ° C, like common in practice.

Heat sealing and determination of the seal seam strength according to different demand

The seals were made with the heat sealer (HSG / ET) from Brugger carried out.

sealing conditions

Temperature: 180 ° C, 200 ° C, 220 ° C
Pressure: 6 bar
Time: 1 sec.
Sealing area: 10 × 10 mm

To determine the seal seam strength, samples were cut into 15 mm wide strips cut and with the tensile testing machine from Instron, model no. 1195 or Zwick, model No. 1454 at a speed of 100 mm / min. drawn. It care was taken to ensure that during the withdrawal attempt the parts of the film separated from one another with the remainder unused Form an angle of 90 ° C.

As a rule, the tests were carried out without prior stress on the sealed samples, but were also stored after 28 days in Tap water at 23 ° C and water storage at + 80 ° C for 1 hour.

The determination of the burst pressure resistance of the mass according to the invention Sealed films were based on the information sheet for testing Packaging no. 41, published as a technical-scientific supplement "Verpackungs-Rundschau", 32 (1981), No. 8, p. 58.

The PP cups were sealed with a laboratory Beaker sealing device VL-1600.

Heat sealing and determination of the burst pressure resistance according to different demand

The seals were made using the VL-1600 laboratory cup sealer BHS carried out. For this, cups from Knauer were labeled Uniplast E 30 and an outer diameter of 7.5 cm.

seal condition

Temperature: 180 ° C, 200 ° C, 220 ° C
Pressure: 0.75 bar (corresponds to 1400 N total pressure of the sealing plant)
Time: 0.65 sec.

Lid samples with a diameter of 7.5 cm were punched out of the film (self-made punching device) and placed on the cup filled with water at approx. The burst pressure resistance was determined after 4 different loads:

• a) immediately after sealing,
• b) after 30 min. Cooling at room temperature,
• c) after 28 days of storage of the lying with the sealing surface down cup,
• d) after one hour of water storage at 80 ° C and 30 min. Cooling at Room temperature.

The burst pressure resistance measurement immediately after sealing is a measure of that Heat resistance. The measurement after cooling serves to determine the Basic strength in the state of use or initial value for the Resistance measurements.

Results of the experiments

See table  

Claims (11)

1. Heat-sealable coating system suitable for sealing various types of substrates, consisting of a film-forming dispersion of at least two different polymer types A and B and an organic solvent system L, characterized in that
polymer type A is an olefin polymer or an olefin copolymer,
the polymer type B is a (meth) acrylate copolymer containing standard methacrylates and in total up to 15% methacrylic acid and / or acrylic acid and / or another polymerizable acid,
and the two types of polymer are present in the A: B weight ratio of 0.4 to 2, in addition there is a polymer in the dispersion which contains components which correspond to the two types of polymer A and B. 2. Heat seal system according to claim 1, characterized in that the solvent system is a solvent mixture of the components
L1.) Esters of aliphatic carboxylic acids with aliphatic alcohols and
L2.) Is aliphatic hydrocarbons,
where the weight ratio L1.): L2.) is between 1 and 200 and the boiling point of the solvent system is a maximum of 105 degrees Celsius under normal conditions. 3. solvent system according to claim 1, characterized in that it from a mixture of aliphatic hydrocarbons with 5-12 There are carbon atoms in the chain, the chain also being branched can. 4. solvent system according to claim 1, characterized in that it from a mixture of esters of aliphatic carboxylic acids with 2-4 Carbon atoms in the chain with aliphatic alcohols with 2-4 Carbon atoms in the chain. 5. solvent system according to claim 1, characterized in that it from a mixture of aliphatic hydrocarbons with 5-12 There are carbon atoms in the chain, the chain also being branched can and from a mixture of esters of aliphatic carboxylic acids with 2-4 Carbon atoms in the chain with aliphatic alcohols with 2-4 Carbon atoms in the chain.   6. solvent system according to claim 4, characterized in that the volume ratio between esters and aliphatic Hydrocarbons is between 1 and 200. 7. solvent system according to claim 4, characterized in that the boiling point of the solvent system between 70 degrees Celsius and 105 degrees Celsius. 8. solvent system according to claim 4, characterized in that the boiling temperature of the solvent system between 85 degrees Celsius and 100 degrees Celsius. 9. Process for sealing heat-sealable substrates, characterized in that uses a coating system according to any one of the preceding claims becomes.   10. The method according to claim 8, characterized in that one coated an aluminum foil with the coating system and against a plastic selected from the group of plastics polypropylene, Polyethylene, polystyrene, polyester or polyvinyl chloride seals. 11. Solvent system according to claim 6, characterized in that it from a mixture of propyl acetate (40 to 70 vol .-%), ethyl acetate (24 to 45 vol .-%) and iso-octane (5 to 15 vol .-%) is composed.