Method of making self-adhesive tapes.

The invention relates to difficult-to-print adhesive tapes made from olefin polymers or copolymers and polyesters and to those made from polyvinyl chloride, which can be present both as foils, composite foils and in the form of fabric-laminated supports, where the foil material can be mono- or biaxially stretched, and has a process for the production of printable self-adhesive tapes and printable and printed self-adhesive tapes obtainable by this process.

In order to obtain sufficient anchoring and adhesion of paints, primer layers, release lacquers and similar spreads on such films, it is customary to treat the surface of such films in a known manner by means of electrical charges (corona treatment), by flame treatment, by treatment with chemical agents or to activate using other suitable methods. These pretreatment methods change the surface of the film by increasing the surface tension to such an extent that the physical-chemical conditions for receiving, adhering and fixing printing inks and spreads on such film surfaces are created. For the production of self-adhesive tapes from the carrier materials mentioned, Depending on the type and properties of the selected self-adhesive, the latter are often pretreated on one or both sides using one of the methods described and then - if necessary using additional special primer and anchoring layers (primer) - coated on one side with the self-adhesive and on the opposite side free of adhesive If necessary, provide the side with an adhesive-repellent coating (release lacquer). Primer or anchoring layers usually consist of an elastomer and / or plastic solution or dispersion and in many cases each contain a component of the two layers to be connected.

Plastic-repellent coatings or release coatings, which are applied in the form of thin spreads on the adhesive-free back, in particular of self-adhesive tapes that have a smooth film as a carrier, have the task, after winding up such an adhesive tape into a roll, the a) transition of the self-adhesive layer from to prevent the front of the carrier from sticking to the adhesive-free back (rewinding) b) To prevent splicing of stretched PP films and also to enable the adhesive tape to roll off the roll easily, for example in unrolling devices and automatic machines, even if the pressure-sensitive adhesive tape wound into rolls has been stored under unfavorable temperature conditions for a long time. Because, as is known, a back cover only has sufficient separating properties with respect to the self-adhesive layer if it has less adhesion to the adhesive than to the carrier itself, to which it has to adhere so firmly that a transition to the adhesive layer of the next winding occurs when rolled up Security is prevented.

If such adhesive tapes are to be subsequently printed on the back, the release lacquer or the adhesive-repellent coating normally prevents sufficient anchoring of the print or the color, so that when a printed self-adhesive tape is unwound into a roll, there is a tendency for the printing ink to separate from the adhesive layer is carried away and thus passes from the printed back to the adhesive layer. Even the selection of a release varnish suitable for the back coating of self-adhesive tapes based on foils presents a particular problem, especially since the known adhesive-repellent coating compositions and release varnishes that can be used for this purpose are generally not universally usable, but can only be used in conjunction with very specific carrier materials and adhesive compositions , the difficulties with the selection become even greater, if such back covers are also to be printed with conventional printing inks.

The problem to be solved here is to find and develop a composition which can be used as a coating for the back of self-adhesive tapes and which, when an adhesive tape is unwound into a roll, not only prevents the adhesive from moving from the next winding, but also prevents the transfer of printing inks and prevents printing marks from the back of the backing onto the adhesive layer.

Backside coatings are known which have a certain limited release effect compared to the self-adhesive on the opposite side of the film carrier and can also be printed. Self-adhesive tapes produced in this way can be wound up into a roll without special cover foils or intermediate layers, without a transition of the pressure from the back of the carrier to the adhesive layer taking place when rolling (CA-PS 772 120, DE-OS 2 018 929). Such separating coatings (separating layers) are, however, limited in their applicability to very specific films, in particular those made of polyvinyl chloride, and also require adhesives which have only a low to moderate adhesive strength.

If such backside coatings are used in conjunction with different types of film carriers and more adhesive self-adhesive compositions, it is essential to provide the print with an additional release coating after printing on the adhesive tape and before winding it up to a roll, which then has to be dried again. Machines and devices have been developed which, in conjunction with a printing press, first apply a primer to the back of the adhesive tape provided with the release varnish, the drying ink after drying and another layer of release varnish after drying again.

Only by overpainting or overprinting the printing ink after drying with a release varnish - preferably in the form of a solution of the varnish in a suitable volatile organic solvent - in this case can it be ensured that the desired low rolling force of the self-adhesive tape wound up on the roll is achieved and at Unrolling does not result in a transition from parts of the separating layer or the printing ink to the adhesive layer.

Especially in the case of thin biaxially stretched polypropylene films, which can be quite elastic, or strongly longitudinally stretched PP films, which easily splice, a low rolling force is required before printing in order to process the material.

The object of the above invention is to develop a release lacquer for the back coating of self-adhesive tapes, which, in addition to having good adhesive strength on the carrier film, has both good adhesion-preventing properties compared to adhesives of different compositions and also an excellent absorption capacity for conventional printing inks and the desired low rolling force is achieved either by overpainting with a release coating in the same operation or by mixing the printing ink with a release agent, without the need for an additional application of a special primer.

The invention thus relates to a process for the production of self-adhesive tapes which can be printed with conventional printing inks, in which a carrier film made from an olefin polymer or copolymer, in particular polypropylene, from polyvinyl chloride or a polyester, which - if necessary after previous surface treatment and / or use of additional special primer and anchoring spreads (primer) - is provided on one side with a self-adhesive layer and on the opposite side with an adhesive-repellent back coating, which is characterized in that in order to achieve the desired printability at the same time good adhesive-repellent effect on the back of the carrier film, preferably after conventional surface treatment by means of electrical charges (corona treatment), by flame pretreatment or by treatment with chemical agents, coated with a thin coat of the solution of a lacquer in a volatile organic solvent and then dried, which consists of a mixture of a) chlorinated polyolefins with a chlorine content of 30 to 45% or polyvinylidene chloride or a vinylidene chloride copolymer and b) a release agent.

The process according to the invention has the advantage over the known processes that - without additional anchoring primers of primer and release agent, printing ink and release agent can be applied separately but in one operation or as a mixture - a very easily unrollable adhesive tape can be produced which the achievable low rolling force values ​​do not differ, or only insignificantly, from those of the corresponding unprinted adhesive tape.

For printable release lacquers of such easy rollability (0.7 to 0.9 N / cm at a roll speed of 30 m / min and 1.0 to 2.5 N / cm at a roll speed of 0.3 m / min) and higher In order to achieve adhesive strength both on the substrate and in relation to the printing ink, the basic chemical and physical properties of lacquer and coloring materials must be coordinated so that they achieve the desired effects optimally.

The release agent in the coating compositions according to the invention should preferably consist of a polyvinyl carbamate, in particular of polyvinyl stearyl carbamate. The polyvinyl carbamates which can be used as release agents and which advantageously contain at least 14 carbon atoms to about 30 carbon atoms in the alkyl side chain are known compounds which are prepared by reacting polyvinyl alcohol with a suitable long-chain isocyanate (DE-PS 955 983). In addition, other compounds are also suitable for the purpose according to the invention which contain on the one hand one or more long-chain alkyl radicals with 12 to 20 carbon atoms (in particular stearyl or stearyl groups) in the molecule and, on the other hand, polar groups, such as those already used to achieve water- or adhesive-repellent effects with different technical products have been proposed.

According to one embodiment of the invention, the release lacquer consists of a mixture of a) 70 to 95% by weight of chlorinated polyolefins (chlorinated polyethylene or polypropylene or corresponding chlorinated copolymers) with a chlorine content of 30 to 45% and b) 5 to 30% by weight. -% of a polyvinyl carbamate. In addition to 75 to 85% by weight of chlorinated polyolefins, it preferably contains 15 to 25% by weight of the polyvinyl carbamate, in particular approximately 20% by weight.

According to a further embodiment, the release lacquer used in the process according to the invention consists of a mixture of a) 30 to 80% by weight of polyvinylidene chloride or a vinylidene copolymer and b) 20 to 70% by weight of a polyvinyl carbamate, preferably 35 to 45% by weight. -% polyvinylidene chloride or a vinylidene chloride copolymer and correspondingly 55 to 65% by weight of polyvinyl carbamate, in particular approximately 60% by weight.

Suitable vinylidene chloride copolymers are those which are prepared by copolymerizing vinylidene chloride with up to 30% by weight of one or more ethylenically unsaturated monomers, such as in particular acrylonitrile and / or vinyl chloride, in particular copolymers of 70 to 95% by weight. Vinylidene chloride with 5 to 30 wt .-% acrylonitrile and / or vinyl chloride.

In the event that another of the above-mentioned release agents is to be used instead of polyvinyl carbamate in the separating varnishes listed above, the weight ratio of the two varnish components must be varied accordingly, which can be accomplished without difficulty by the person skilled in the art by simply trying out his knowledge.

The release lacquers are expediently applied in the form of a solution of the selected lacquer in a volatile organic solvent or solvent mixture in such an amount to the preferably pretreated rear surface of the carrier film that, after drying in a conventional drying device, an application amount of 0.3 to 2.0 g / m², preferably from 0.5 to 1.0 g / m², is obtained. Suitable solvents are trichloroethane, lower alcohols, ketones, such as acetone, methyl ethyl ketone (butanone) and cyclohexanone, and aromatic hydrocarbons, such as toluene or mixtures thereof. Solvent systems which lead to homogeneous polymer mixtures are preferably used.

The usual printing ink compositions can be used as solvent-based printing inks, the specific composition of which depends on the printing process, the printing base and the fastness properties and which, in addition to dyes, binders, such as polyvinyl acetate, chlorinated polyolefins, nitrocellulose, thickeners, drying agents and optionally fillers. Printing inks based on polyvinyl acetate, as are used for PVC adhesive tapes, are particularly preferred. According to the invention, these anchor particularly well, whereby different types of supports (PP, PVC, polyester) can be printed with the same equipment using the same printing ink, to products that are easy to unroll and with advantages in warehousing.

According to a preferred embodiment of the method according to the invention, the printing ink may also have a release agent, in particular a polyvinyl carbamate_- in an amount of up to 30% by weight, the same or a chemically similar release agent being expediently chosen as in the lacquer used to achieve the printability of the film surface. When this measure is carried out, the affinity for the printing ink is present twice, namely once between the chlorinated polyolefins of the paint and the binder (polyvinyl acetate) of the paint, on the other hand, and on the other hand through the fusion of the release agent contained in both the paint and the printing ink by means of the heat brought in by drying (eg IR drying).

However, UV printing inks can also be used according to the invention, and these can be processed in book or flexographic printing, depending on the consistency. All that is required is the appropriate UV equipment on the printing press.

In the process according to the invention, the customary self-adhesive compositions of the rubber / resin type can be used as self-adhesive compositions, natural rubber, synthetic rubber, rubber-like block copolymers as well as polyisobutylene and the usual adhesive resins being used as the resin component. In addition, strongly adhesive compositions based on acrylic acid ester polymers and copolymers can also be used as self-adhesive compositions. In the latter case - as in special cases depending on the selected carrier material - it has proven to be useful to apply an additional thin coat of the release varnish to the printed release layer in order to achieve the desired ease of unwinding of the adhesive tape wound into a roll in these special cases as well , and to block the high affinity between acrylate self-adhesive compositions and polyvinyl acetate of the printing ink.

The invention also relates to self-adhesive tapes produced by the process and printable using customary printing processes, with a backing film made of an olefin polymer or copolymer, in particular polypropylene, made of polyvinyl chloride or a polyester, which, after cutting the adhesive tape wound into rolls, are initially stored and closed in the desired widths can be printed later, as well as the self-adhesive tapes printed in this way.

The invention is illustrated by the following examples:

example 1

A biaxially stretched polypropylene film with a thickness of 30 μ, which had previously been pretreated on both sides by corona or flame pretreatment, was coated on one side with a release coating solution of the following composition using a conventional applicator:<tables id="tabl0001" num="0001"><img file="EP0178552A2_D0001.tif" /></tables>coated in such an amount that an application amount of 0.8 g / m was obtained after drying. Subsequently, in the same operation, a conventional self-adhesive layer was applied to the uncoated opposite side of the carrier film with the interposition of a thin primer or anchoring layer consisting of an elastomer / plastic dispersion, which consisted of a mixture of natural rubber and polyisobutylene and polyterpene resin. The material thus produced is easy to unroll. It was cut into single rolls. These rolls were then printed with an ink of the following composition and dried as required:<tables id="tabl0002" num="0002"><img file="EP0178552A2_D0002.tif" /></tables><tables id="tabl0003" num="0003"><img file="EP0178552A2_D0003.tif" /></tables>

A self-adhesive tape produced in this way could, after being wound up into a roll, also be pulled off the roll easily with little unrolling force, without parts of the release lacquer or the pressure on the adhesive layer being transferred.

Example 2

A monoaxially stretched polypropylene film with a thickness of 90 μ, which had previously been pretreated on one side by corona treatment, was coated on the pretreated side using a conventional applicator with a release lacquer solution of the following composition:<tables id="tabl0004" num="0004"><img file="EP0178552A2_D0004.tif" /></tables>coated in such an amount that after drying an application rate of 0.7 g / m² was obtained. The procedure was then as in Example 1.

A self-adhesive tape with the advantageous properties described in Example 1 was obtained.

Example 3

Finishing of the carrier film analogous to example 1 or 2.

The rolls of adhesive tape thus produced were then printed with commercially available printing inks, for example based on polyvinyl acetate, and overcoated in the same operation.

Example 4

Finishing of the carrier film again as in Example 1 or 2

These tapes are printed with UV printing inks and overcoated in the same step after the UV treatment.

Since there are no color solvents such as ketones, esters, toluene etc. in this process on the printing presses, and only ethyl alcohol and low-boiling paraffins are used for overcoating, this production is very environmentally friendly without special precautions.