Method for producing adhesive surface coatings

Details Method for producing adhesive surface coatings Method for producing adhesive surface coatings

2002-01-09

2003-04-15

Cameron, Erma (Department: 1762)

Coating processes

Direct application of electrical, magnetic, wave, or...

Polymerization of coating utilizing direct application of...

C427S512000, C427S513000, C427S517000, C427S518000, C427S519000, C427S520000, C427S535000, C427S536000, C427S538000, C427S551000, C427S553000, C427S554000, C427S556000, C427S407200, C427S409000, C427S412000, C427S412100, C427S419200

Reexamination Certificate

active

06548121

ABSTRACT:

The invention relates to a process for the production of strongly adhering coatings on inorganic or organic substrates. The invention relates also to the use of photoinitiators having at least one ethylenically unsaturated group in the production of such layers, and to the strongly adherent coatings themselves.
The adhesion of finishes, coatings or metallic layers on inorganic or organic substrates, especially on non-polar substrates such as polyethylene, polypropylene or fluorine-containing polyolefins, for example those known under the trade name Teflon®, is frequently inadequate, with the result that it is necessary to carry out additional coating steps in order to obtain satisfactory results. One possibility lies in first of all applying special priming coatings, so-called primers, and only then applying the desired coating thereto.
A further possibility comprises subjecting the substrates to be coated to plasma or corona treatment and then coating them, it being possible in addition for a procedure for grafting with, for example, acrylate monomers (J. Polym. Sci., Part A: Polym. Chem. 31, 1307-1314 (1993)) to be carried out between those two operations.
The production of low-temperature plasmas and the plasma-assisted deposition of thin organic or inorganic layers have been known for some time and are described, for example, by A. T. Bell, “Fundamentals of Plasma Chemistry” in “Technology and Application of Plasma Chemistry”, edited by J. R. Holahan and A. T. Bell, Wiley, New York (1974), and by H. Suhr, Plasma Chem. Plasma Process 3(1),1, (1983).
It is also known that, for example, plastics surfaces can be subjected to plasma treatment and as a result the subsequent finish exhibits improved adhesion to the plastics substrate. This has been described by H. J. Jacobasch et al. in Farbe+Lack 99(7), 602-607 (1993) for low-temperature plasmas under vacuum conditions, and by J. Friedrich et al. in Surf. Coat. Technol. 59, 371-6(1993) for plasmas ranging from in vacuo up to normal pressure conditions, the low-temperature plasma changing over to a corona discharge over that range.
It has now been found that coatings having especially good adhesion can be obtained with photocurable surface-coating compositions by grafting a photoinitiator having at least one ethylenically unsaturated group onto the substrate to be coated, providing the so grafted substrate with a photocurable surface-coating layer and curing that layer. The coatings obtained have a surprisingly good adhesion, the deterioration of which is insignificant even after storage or exposure to sunlight for several days.
The process is simple to carry out and allows a high throughput per unit of time, since no lengthy drying steps or slow crosslinking reactions are required. The process is especially well suited to workpieces that are composed of various plastics and/or metals or glasses and that without pretreatment would therefore exhibit different degrees of adhesion to the different components or that in the case of a conventional primer treatment exhibit different affinities for the primer.
The invention relates to a process for the production of strongly adherent coatings on an inorganic or organic substrate that comprises, in a first step
a) subjecting the inorganic or organic substrate to the action of a low-temperature plasma discharge, a corona discharge, high-energy UV radiation or electron radiation, then discontinuing the radiation or discharge; in a further step
b) under vacuum or at normal pressure, applying one or more photoinitiators containing at least one ethylenically unsaturated group to the inorganic or organic.substrate, and allowing reaction with the free-radical sites formed there; and
c1) coating the substrate so precoated with photoinitiator with a composition comprising at least one ethylenically unsaturated monomer or oligomer, and curing the coating by means of UV/VIS radiation or
c2) depositing a metal, semi-metal oxide or metal oxide from the gaseous phase, in the presence of UV light, on the substrate so precoated with photoinitiator.
Possible methods of obtaining plasmas under vacuum conditions have been described extensively in the literature. The electrical energy in such methods can be coupled in by inductive or capacitive means and may be direct current or alternating current, it being possible for the frequency of the alternating current to vary from a few kHz up into the MHz range. A power supply in the microwave range (GHz) is also possible.
The principles of plasma production and maintenance are described, for example, in the above-mentioned review articles of A. T. Bell and H. Suhr.
There may be used as primary plasma gases, for example, He, argon, xenon, N
2
, O
2
, steam or air.
The process according to the invention is not sensitive per se in respect of the coupling-in of the electrical energy.
The process can be carried out batchwise, for example in a rotating drum, or, in the case of films, fibres or woven fabrics, continuously. Such procedures are known and are described in the prior art.
The process. can also be carried out under corona discharge conditions. Corona discharges are produced under normal pressure conditions, air most commonly being used as the ionised gas. Although other gases are also possible in principle, they necessitate the use of a closed system in order to exclude atmospheric air. Another possibility comprises the use of air as the ionisation gas in corona discharges, so that an apparatus open to the outside can be used and, for example, a film can be drawn through continuously between the discharge electrodes. Such process arrangements are known and are described, for example, in J. Adhesion Sci. Technol. Vol 7, No. 10, 1105, (1993). When a corona discharge is used in an open apparatus, the procedure is preferably carried out with the exclusion of oxygen, which can be achieved by a sufficiently large flow of inert gas.
The process can also be carried out using high-energy electromagnetic radiation to treat the substrates in vacuo or with the exclusion of oxygen. A suitable high-energy electromagnetic radiation is one that is capable of generating free radicals on the surface. Examples include short-wave UV radiation and X-radiation. In that connection, mention may be made especially of electron beams, as already used for the curing of surface-coating compositions and paints and the adhesive bonding of films. It is also possible, however, to use short-wave UV radiation (especially vacuum UV radiation), such as that produced by commercially available UV lamps or by excimer lamps. Radiation having a wavelength of less than 300 nm, especially less than 260 nm, is preferred.
In addition to conventional lamps for the irradiation of large areas, it is also possible to use lasers that operate in the corresponding wavelength range for pointwise irradiation of, or for image-forming “writing” on, the surface. The use of masks or writing lasers renders possible the selective loading of only certain areas with photoinitiator, which results in different degrees of wetting and, in a subsequent coating, different degrees of adhesion.
The substrates provided with grafted-on photoinitiator can also be irradiated imagewise by irradiation through a mask, or using laser beams which are moved over the surface, with the result that there is further surface modification, but only in the irradiated areas. Using such procedures it is possible, for example, to produce patterns in which the hydrophobic/hydrophilic properties and/or metallisation vary. When the imagewise irradiation is carried out in the presence of a formulation that cures by means of radiation, it is possible to produce patterns in which the adhesion and/or tackiness and/or colour and/or other properties governed by the formulation vary.
The inorganic or organic substrate to be treated can be in any solid form. Preferably, the substrate is in the form of a powder, a fibre, a film or a three-dimensional workpiece.
Preferably, the inorganic or organic substrate is a thermoplastic, elastomeric, inherently cr

Affiliated with

Also associated with

Rating

Method for producing adhesive surface coatings does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Method for producing adhesive surface coatings, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method for producing adhesive surface coatings will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-3082374