NL9400315A - Multi-layered, self-adhesive, surface protective film based on polyolefin. - Google Patents

Description

Multi-layered, self-adhesive, surface-protective film based on oolvalene.

The invention relates to a multi-layer, self-adhesive polyolefin surface protection film for the protection of the surfaces of plastic sheets during storage and transport, for further processing and for shaping by thermoforming the sheets.

It is known from DE-C-2.718-510 to provide the surfaces of thermoplastic plastic sheets of polymethyl methacrylate (PMMA) after manufacture with a protective film, which is prepared from low-density polyethylene with a melt index between 1 and 4 g / 10 min and the tack side has been pretreated by Corona discharge to improve the adhesion of the film to the plastic sheet. At a surface temperature of 60-100 ° C, the adhesion of this protective film strength is fluctuating, so that it can come loose in the area of the edge or on the entire surface, or, in the other extreme case, tear the film may come when it is removed from the plates or molded parts. The strong spreading width of the adhesion depends on the surface temperature of the plate during film application and, moreover, on the surface condition of the film, e.g. the micro roughness of a blown film, as well as fluctuations in the pretreatment intensity and tolerances resulting from the production in the polyethylene granulate,

European patent 357 * 487 describes a thermal conversion method for PMMA plates with a reduced viscosity of at least 1.5. At least one surface is protected with a polyethylene film pretreated by Corona discharge. The polyethylene has a density <0.935 and a melt index lower than 1.0g / 10 min. The protective film must have a satisfactory adhesion (eg 0.6 N / cm) to the PMMA plates and must always be can be removed without surface residues.

In addition, it is known to manufacture self-adhesive, surface protective films of polyethylene, where one surface of the film is provided with a Corona pretreatment between 40 and 44 mN / m and subsequently coated with a glue based on polyacrylic acid esters or based on natural rubber. see international patent application 9Ο-Ο6Ο.99Ο / Ο9). The self-adhesive, surface-protective films, however, are distinguished by an even and more reproducible adhesion to plastic plates, by the thermal load during storage or by thermal forming, but when the protective film on the tear edges is removed with a jerk, it is easy to create small adhesive residues. that are visible on transparent molded parts such as skylights.

In practice, it has been found that coextrusion, two or more layers of polyethylene protective films with an adhesive layer of an ethylene-vinyl acetate copolymer with a vinyl acetate content of about 18% by weight at a temperature drop during storage and during transport and in particular during thermal forming, react with a strong increase in adhesion to the plastic sheets.

At a low vinyl acetate content of the adhesive layer of about 9% by weight, the adhesion at room temperature for machining the plates by cutting, milling or drilling is too low, so that the film peels off in the edge region of the machining edges.

An increase in the bonding value can be achieved by the known measure of a Corona pretreatment, but here again the marked increase in the bonding values with increasing temperature is disadvantageous. Particularly in thermoforming, the increase in adhesion due to a reduction in film thickness in deep drawn regions of the molded articles is so negative that the protective film tears easily upon removal by the final consumer.

The prior art problem solutions were only partially satisfactory. Therefore, the aim was to provide improved surface protective films, avoiding, if possible, without reducing the residual profile of requirements, the disadvantages described, and which after the thermal load, in particular during the thermoforming, with substantially the same or preferably a significantly lower peeling resistance as for the load room temperature of the plastic plates can be removed.

The object is accomplished by the multilayer surface-protecting film of the present invention.

Thus, the present invention relates to a multi-layered, self-adhesive, surface protective film SF based on a polyolefin, which is composed of a carrier layer T, consisting of one or more layers which are composed of polyolefin with a layer thickness in the range of 20-150 µm, and an adhesive layer HS with a layer thickness in the range of 5 µm, preferably 5-20 µm, consisting of 99.5-80% by weight of an ethylene-vinyl ester copolymer, preferably with a vinyl ester content of 2 to 20 wt.%, Preferably 17 to 10 wt.%, And / or polyethylene or mixtures thereof and 0.5-20 wt.%, Preferably 2-20 wt.%, Adhesion promoting resins TF. The multilayer surface-protecting films SF are preferably co-extruded through a flat or round die (see Becker-Braun, Kunststoff-Hand-buch, New Edition, Vol. 1, pp. 443-61, C Hanser, 1990? HF Mark etal., Encyclopedia of Polymer Science & Engineering, 2nd edition, volume 6, pp. 608-631, J. Wiley, 1986, Ullmann's Encyclopedia of industrial Chemistry, volume 5, volume A 11 , p. 89 (90, VCH, 1988).

It is of great practical importance that the surface protective film SF after laminating on plastic plates KF at room temperature and with a greater residual heat after the production of the plates according to the extrusion process, shows a sufficient adhesion for the practical application and that this adhesion (measured as shell value in cN / cm) after a thermal load due to storage or transport conditions, only slightly increases, respectively. drops to low shell values after thermal forming. The protective film can therefore easily be removed from the plates or molded parts without residues.

The polyolefins serving as foil base are homo- or copolymers of C2-C8 olefins. In a special embodiment, polyethylene is used, for example that with an MFI (according to ASTM D 1238) of 0.1-8 g / 600 s and a density of 0.91-0.9 ^ kg / m3 (according to ASTM DI505) (see Ullmann's Encyclopedia of Industrial Chemistry, 5th Edition, Vol. A 21, pp. 89-516, VCH, 1992).

The preparation of the ethylene-vinyl ester copolymers of the adhesive layer HS is also known (see Houben-Weyl, 4th edition, Vol. E 20, 7OO-7IO, 1120, 1126, G. Thieme-Verlag, 1987, HF Mark et al., Encyclopedia of Polymer Science and Engineering, Vol. 17, 425-445, J. Wiley, 1989)

Vinyl ester comonomers in particular include vinyl acetate, vinyl propionate, vinyl butyrate, as well as the esters of branched aliphatic acids, such as pivalic acid, 2-ethylhexyl acid and the R Versaticacids. If the adhesive layer contains HS polyethylene, it is preferably polyethylene with a density of 0.91-0.9 ^ kg / m3. 10 to 60% by weight is mentioned as a hold for the polyethylene content of the adhesive layer HS.

The adhesion-promoting resins TF are already used in the art as a so-called "tackifier" (= additives for elastomers) in the field of glue preparation, in particular adhesives containing solvents or hot-melt adhesives or coating adhesives for self-adhesive tape. A permanent increase in the adhesive strength is achieved by adding the tackifier. The tackifiers generally have a relatively low molar mass, usually in the range of 200-2000 g / mol, with a wide distribution of the molar mass and a glass transition temperature Tg above that of the elastomers, as well as sufficient compatibility with the elastomers; in practice, the softening points thereof are in the range of 50-150 ° C. (see HF Mark etal., Encyclopedia of Polymer Science Engineering, vol. 1, pp. 509-510; vol. 13. pp. 347 ~ 348, J. Wiley; Salas, Handbook of Pressure SensitiveAdhesion Technology, 2nd edition, pp. 38- 60, Van Nostrand Reinhold, 1989).

Tackifiers of the type described chemically belong to the group of the resins, the terpene oligomers, the coumarone-indene resins, the dealiphatic, petrochemical resins and the modified phenolic resins. Deterpene tackifiers are, as is known, prepared by polymerization, in particular cationic polymerization, from naturally occurring terpenes such as the pines, lemons, and others.

The aliphatic, petrochemical resins are generally obtained by oligoraerization of the C5 and C9 petroleum fractions; in particular, hydrogenated fractions are also mentioned. For example, hydrogenated hydrocarbon resins based on C9 fractions such as copolymer with indene, α-methylstyrene and vinyl toluene are mentioned. Also of particular interest is a hydrogenated hydrocarbon resin based on polymerized cyclopentadiene which is subsequently hydrogenated.

For the preparation of the surface protective films, the co-extrusion of the polyolefin-carrier layer T and of the adhesive materials HS forming the adhesive layer HS is offered in particular according to a method known per se (see Kunststofftechnik, coextrudierte Folien undPlatten, VDI- Verlag, 1990).

The following Table A gives an overview of prepared film types SF and comparative film types according to the prior art (percentages in% by weight, see examples; film types 1-4 are known in the art).

Table A

Mace type: Composition:

1 Corona pretreatment LDPE

2 Adhesive film 9% vinyl acetate 3 Adhesive film 9% vinyl acetate + Corona pre-treatment 4 Adhesive film 1B% vinyl acetate 5 Adhesive film A) B% vinyl acetate + 2% kw resin 6 Adhesive film A) B% vinyl acetate + 6% kw resin B) 9 Adhesive film % vinyl acetate + 3% kw resin 8 Bonding film B) 9% vinyl acetate + 10% kw resin 9 Bonding film B) 9% vinyl acetate + 20% kw resin

The SF surface protection films of the invention particularly serve for the protection of acrylic glass sheets and polycarbonate sheets, especially with regard to their thermal transformation, whereby the SF surface protection films can remain on the plastic sheets. The acrylic glass plates generally consist of commercially available PMMA or known copolymer of methyl methacrylate, known per se, preferably with a reduced viscosity of at least 1.5. which may be efficiently modified, e.g. with stabilizers known per se or also other additives, e.g. can be made fireproof or anti-static. The acrylic glass windows may, as is commonly customary in practice, be colored in a manner known per se (see Ullmann's Encyclopedia of Industrial Chemistry, 5th Edition, Vol. A20, 459-507. VCH, 1992). For example, acrylic glass plates come with so-called cast material, belt material or also extruded material are eligible (see H.F. Mark et al., Encyclopedia of Polymer Science & Engineering, 2nd edition, Vol. 1, 276-278, J. Wiley, 1985).

The polycarbonate sheets are commercially available resp. correspond to the prior art (see Kirk-Othmer, 3rd Edition, Vol. 18,480-494, J. Wiley, 1982). Generally, the thickness of the plate is in the range of 0.5 to 12 mm.

The adhesion sought for the practical application of the protective film on plastic sheets, measured as peel resistance strips with a width of 50 mm under a pull-off angle of 180 ° and a pull-off speed of 100 mm / min, must be at 50-180 cN / cm to loosen in the area of the edge or after machining of the sheets provided with protective film by cutting, milling or drilling in the area of the edge of the machining edges, only for the protection during transport are adhesive values between 10 and 100 cN / cm, however, the adhesion should not increase further after hot storage or after shaping by thermal transformation, but should preferably decrease.

Typical laboratory conditions after application of the protective films to polymethyl methacrylate sheets under the same pressure for strips of 50 mm width under a draw-off angle of 180 ° and a pull-off speed of 100 mm / min for the peel resistance of different protective foils according to the prior art described (type 1-4) and according to the characteristic type (5-9) of the protective film according to the invention, the following table B shows:

Table B

Advantageous effects

The use of the resins TF in combination with copolymers which can be extruded, preferably with ethylene-vinyl ester copolymers, for co-extruded surface protective films is new and has led to the development goal that the adhesion value of the surface-protecting films prepared therefrom is true. is also markedly increased, but that after a temperature increase of the plates provided with protective films, depending on the choice of adhesion-promoting resins, the adhesion increases only slightly or even decreases considerably. This effect, which is caused by migration from the surface of the adhesive layer into the underlying layers of the adhesive layer or carrier layer, is of particular significance for the further processing of the plastic sheets provided with a protective film by thermoforming.

Examples

I. Preparation of the surface protective film SF

The carrier layer T forms an LD polyethylene film with the following data:

Data: MFI = 2.0 g / 600 s, thickness: 38 µm density: 0.923 g / cm3

On this foil base, a 12 µm thick adhesive layer is co-extruded through a flat nozzle, consisting of: A) 94-98% ethylene-vinyl acetate copolymer with 7-10% vinyl acetate with an addition of 2 -6 # hydrogenated hydrocarbon resin, based on the C9 fraction, copolymer with indene, α-methylstyrene and vinyltoluene.

B) 80-95 # ethylene-vinyl acetate copolymer with 7-10 # vinyl acetate and adding 5-20 # hydrogenated hydrocarbon resin based on cyclopentadiene which has been polymerized and hydrogenated.

I-B Preparation of the SF surface protection film by co-extrusion II Coating the plastic sheets

The surface protective films obtained according to the invention are laminated to the plastic plates at a pressure of 1 bar to k bar over the entire surface, without air inclusions, at temperatures (roller / semi-finished product) from 20 ° C to 80 ° C with a laminating roller. .

III Thermal transformation of the coated plastic sheets

The plastic sheets, in particular PMMA sheets, obtained as described above can be thermally transformed in a manner known per se. Heating takes place in a circulation oven or by IR radiation.

Result: '

The protective films according to A) excel in that by adding 2-6% adhesion promoting resin, preferably by adding 6% ARKON F-125, the adhesion to plastic plates is clearly increased, but after a temperature increase only a little increases and reaches a level where the film can be easily removed without residue.

In the protective film B), the adhesion of the protective film to plastic sheets by addition of 5-20% adhesion promoting resin, preferably 20% ESCOREZ 5320, is also markedly increased.

Due to the effect of the temperature, for example in thermoforming, there is even a drastic reduction of the adhesion, so that the protective film after deformation can easily become even with extreme molded parts, such as sanitary objects, despite a strong reduction in film thickness. deleted.

Claims (10)

Multi-layer, self-adhesive, surface-protecting film based on a polyolefin, characterized in that the surface-protective film SF is composed of a carrier layer T, consisting of one or more layers composed of polyolefins with a layer thickness in the range 20-150 µm and an adhesive layer HS with a layer thickness in the range 5 "40 µm, consisting of 99.5-80 wt.% of a polymer selected from the group consisting of ethylene-vinyl ester copolymers, polyethylene or mixtures thereof and 0.5-20 wt% of one or more adhesion promoting resins (tackifier) TF. 2. Multilayer, self-adhesive, surface-protecting film according to claim 1, characterized in that. that the carrier layer consists of polyethylene. Multilayer, self-adhesive, surface-protecting film according to claims 1 and 2, characterized in that the ethylene-vinyl ester copolymer has a vinyl ester content of 2-20% by weight. Multilayer, self-adhesive, surface-protecting film according to claim 3, characterized in that the ethylene-vinyl ester is ethylene-vinyl acetate. Multi-layered, self-adhesive, surface-protecting film according to claims 1 to 4, characterized in that the adhesive layer contains HS polyethylene. Multi-layered, self-adhesive, surface-protecting film according to claim 5, characterized in that the polyethylene content is 10% by weight to 60% by weight. Multilayer, self-adhesive, surface-protecting film according to claims 1 to 6, characterized in that it was prepared by co-extrusion through a flat or round nozzle. 8. Use of the surface protective film according to claims 1 to 7 for coating plastic surfaces. The use of the surface protective film according to claim 8 for laminating polyacrylate plastic sheets. 10. Use of the surface protective film according to claim 9 for laminating polycarbonate plastic sheets. 10. Molded article, consisting wholly or in part of a plastic sheet using a protective film according to any one of claims 1 to 7.