FR2572813A1 - PROCESS FOR PREPARING POLYMERIC LIQUID COATINGS HAVING MULTIPLE OPTICAL ANSWERS AND COATINGS THUS OBTAINED - Google Patents

Abstract

THE PRESENT INVENTION CONCERNS LIQUID POLYMERIC CRYSTALLINE COATINGS WHICH PRESENT MULTIPLE OPTICAL RESPONSES, THESE COATINGS BEING OBTAINED WITHOUT VARIING THE TEMPERATURE DURING THE PHOTOPOLYMERIZATION OPERATION. BY PHOTOPOLYMERIZING CERTAIN COATING REGIONS SELECTIVELY AT DIFFERENT SPEEDS FROM OTHER COATING REGIONS, COATINGS CAN BE OBTAINED WHICH SHOW DIFFERENTIAL FIXED OPTICAL RESPONSES. APPLICATION ESPECIALLY IN THE FIELD OF ADVERTISING.

Description

PROCESS FOR PREPARING LIQUID COATINGS

  POLYMERS HAVING MULTIPLE OPTICAL RESPONSES

AND COATINGS SO OBTAINED

  The present invention relates to a method for preparing liquid crystalline liquid coatings, and more particularly to liquid crystalline liquid coatings which exhibit different optical reactions in various

areas of the coating.

  Studies on liquid crystals have been reported in increasing numbers in the literature in recent years. Many uses have been found for these

  materials, in particular as optical displays.

  Recently, articles have appeared in the scientific literature relating to cholesteric liquid crystals that include polymerizable portions. A number of articles have appeared in Russian literature describing solution polymerized cholesterol derivatives having liquid crystal properties. However, a particular interest has been brought to the recent discovery that cholesteric liquid crystalline materials having defined optical properties could have these properties substantially fixed by a photopolymerization process for

  give coatings whose optical responses are practically

  insensitive to temperature.

  U.S. Patent Application No. 450 088, filed December 1982, and related patent applications disclose certain cholesterol derivatives which have acrylate moieties in the side chain at position 3.

  compositions comprising these materials have been shown to be

  optical properties varying from infrared to ultraviolet portions of the spectrum, the optical properties being fixed by photopolymerization. In addition, coatings comprising more than one optical response have been described in U.S. Patent Application Nos. 660,038 and 660,278, filed October 12, 1984. In one embodiment,

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  these patent applications describe a method in which the temperature is adjusted so that a desirable optical response is obtained, and the coating is then selectively masked so that various regions of the coating are protected from first exposure to light-emitting radiation. The first stage of photopolymerization substantially fixes the optical responses in the regions receiving the radiation, but leaves the masked regions uncured, so that by adjusting the temperature, the regions

  unpolymerized have a different optical response.

  By a new irradiation of the structure, we realize a

  coating in which a multiple optical response is obtained

  naked in various areas of the coating. The term "optical response" and the related terms used in the

  this description shall have the meanings indicated in

aforementioned patent applications.

  Although these coatings have original properties

  it is not always desirable to

  multiple optical displays by temperature adjustment.

  Accordingly, it is an object of the present invention to provide a photopolymerized liquid crystal coating in which multiple optical responses are obtained without

have to adjust the temperature.

  Another object of the present invention is to realize

  be a coating that gives multiple optical responses

  the coating also having a triple optical response

  dimensional. These objects of the present invention, as well as others,

  will be clear from the following detailed description

  preferred embodiments.

  The present invention relates to crystal coatings

  cholesteric liquids which exhibit multiple optical responses, these coatings being obtained without

  vary the temperature during the photopolymer operation

  authorization. By selectively allowing certain areas of the coating to photopolymerize at different speeds relative to other regions of the coating, it is possible to obtain

  coatings with different optical responses

  -competitive. The present invention relates to a process for preparing a polymeric coating having a fixed optical response, which

  process comprising the steps of providing a coating

  element comprising a photopolymerizable cholesteric liquid crystalline monomeric material; selectively aligning at least a portion of said coating such that said aligned portion has an optical response; and successively exposing said coating to light-curing radiation under conditions such that selected regions of said coating are polymerized at different speeds relative to other regions of said coating, such that the

  hardened coating has different optical responses

  -competitive. The present invention also relates to a photopolymerized cholesteric liquid crystalline coating having a differential fixed optical response, which coating is obtained by sequentially exposing the coating to a photopolymerizing radiation under conditions such that selected regions of that coating are polymerized at different rates by compared to other regions of this

coating.

  Monomers that can be used to achieve

  the present invention are the cholesteric liquid crystals

  which have a photopolymerizable side chain and have a desired optical response in the visible spectrum. The preferred monomers are those described in the above-mentioned US Patent Application No. 450 088.

  it must be taken into account that these materials may be used

  in the form of single monomers, mixtures of monomers or mixtures comprising monomers and other

  non-mesogenic polymerizable or non-polymerizable.

  To practice the present invention, a composition comprising a photopolymerizable cholesteric liquid crystalline monomer and a photoinitiator and, if desired, other mesogenic or non-mesogenic monomeric materials and / or non-polymerizable diluents is prepared. , non-mesogenic. The material is then prepared as a coating or film and subjected to a temperature such that the coating or film has the desired optical response. The material will then be photopolymerized so that selected regions of the film cure at different speeds compared to other regions of the film.

  film. This can be accomplished in a variety of ways.

  For example, the polymerization of the surface can be carried out in the presence of oxygen, which, as is well known

  in the art, will tend to inhibit the photopoly reaction.

  merization. If a negative is placed which selectively hides the coating of the polymerizing radiation on the coating or film, no hardening will occur in the masked region, but it will occur in regions where the mask does not protect the coating from radiation . However, in the exposed regions, the surface will be incompletely hardened due to inhibition by oxygen, while the internal regions of the exposed region will be fully cured. If the mask is then removed and the surface scanned thoroughly with nitrogen or other inert gas, a difference in optical response will be noted on the surface of the coating. Previously masked regions will have an optical response, while unmasked regions and

  Inhibited by oxygen will tend to have a different color.

annuity.

  The surface can also be partially masked and then subjected to photopolymerizing radiation in an inert atmosphere, resulting in complete hardening of the unmasked regions. If the mask is then removed and if one sweeps with a mixture of nitrogen and oxygen the surface which remains

  hardened, the exposure of this surface to photo-

  polymerisation will lead to a different cure rate

  annuity. After final curing in an inert atmosphere, a noticeable color difference will be observed between the cured regions initially and subsequently. Tri-dimensional effects can also be created using two different masks in combination with the above procedures. For example, a first mask can be placed on a film which is then irradiated in the air. The mask is then removed, and the entire surface of the film is irradiated in the air. A second mask is placed on the film and irradiated in an inert atmosphere, and this mask is then removed, and the entire film is irradiated

  in an inert atmosphere. The result is a film that pre-

  feels three-dimensional images.

  Different cure rates can also be achieved by using a totally inert atmosphere, but by subjecting part of the surface to high intensity radiant energy, and other regions of the surface to radiant energy of lower intensity. As a different photopolymerization speed is achieved in

  these various regions, the product obtained will have answers

its different optics.

  The present invention will be more clearly understood with reference to the following examples which are given as

  illustration and not limitation.

  In the following examples, compounds corresponding to the acrylate derivatives Va and Ve as described in United States Patent Application No. 450 088, were used to prepare monomeric films. These compounds have the structure

HO 0

IIl He i

CH2-C-C-O-A-C-OH

  YH y where A = R2 = (CH2) n. For compounds Va, n = 10 and for compounds Ve, n = 3. For both compounds, y = O.

Example 1

  A composition comprising 47% by weight of each of compounds Va and Ve, 3% by weight of pentaerythritol triacrylate as crosslinking diluent, 2% by weight of benzophenone as photoinitiator and 1% by weight of Irgacide is prepared.

  651 as a photoinitiator. Irgacure 651 is a 2,2-

  dimethoxy-2-phenyl-acetophenone.

  The composition was melted completely at 93 ° C (200 ° F), allowed to cool to room temperature, and run.

  an application of 0.051 mm (0.002 inch) at room temperature

  biante on a Mylar movie. Uncured material appears

  blue-green at a 90 (specular) angle of view.

  The applied film is placed in a chamber; it is coated with a negative that selectively hides parts of the surface, and the chamber is partially scanned with

  nitrogen, leaving some residual oxygen. The coating

  masked is then subjected to a UV energy of 150 joules

  (ie 5 watts / cm2 for 30 seconds), for

  create an image which, in the exposed regions, is green

  yellow under a specular view. The chamber is then opened, the mask is removed, and the chamber is closed and swept completely with nitrogen to remove all oxycin. The entire film is then exposed to an energy of 300 eyes (ie, 5 watts / cm for 60 seconds) to completely polymerize the film. The polymerized film contains a yellow / green image with a green-blue background when examined at a specular angle. EXAMPLE 2 A composition comprising 48.25% by weight of each of compounds Va and Ve, 3% by weight of pentaerythritol triacrylate as crosslinking diluent and 0.5% by weight of Irgacure 651 is prepared and a film is prepared as he was

  described in Example 1, which also gives a green appearance.

  bluish. The film is covered with a negative that protects

  selectively certain regions of the film and the film

  The masked cell is then exposed to a radiant energy of 150 joules (i.e., 5 watts / cm 2 for 30 seconds) to produce a partially cured film which has a

  yellowish-green appearance in exposed areas.

  The negative is removed from the film, and the entire film is exposed to air at a radiant energy of 50 joules (5 watts / cm 2 for 10 seconds). After the second exposure,

  the film is provided with a second negative to mask selectively

  the film is placed in a nitrogen chamber which is then completely flushed with nitrogen. The film is exposed to a 150 joules radiant energy (i.e., 5 watts / cm 2 for 30 seconds) to produce an image which, in the most recently exposed regions, is bluish-green at an angle of

specular view.

  The second negative is removed, and the entire film

  is exposed to a radiant energy of 300 joules (that is,

  that is, 5 watts / cm for 60 seconds) in a completely swept nitrogen chamber to completely polymerize the film. The film obtained contains two images. From a 90th angle of view, the first image seems to be above

  the second image; that is, it has a triad effect

  dimensional. From an angle of view of 45 °, the second image appears to be above the first image. In either case, the first image appears light green-yellow, the

  second image appears bluish-green, and the background appears green

dark yellow.

  The invention is not limited to the descriptions and illus-

  above, but covers all changes

  referred to by the claims below.

Claims (8)

  A process for preparing a polymeric coating having a fixed optical response, characterized in that it comprises the following steps: - a coating comprising a photopolymerizable cholesteric liquid crystalline monomeric material,   - selectively aligning at least part of this   such an aligned portion has an optical response, and this coating is successively exposed to a photopolymerizing radiation under conditions such that selected regions of said coating are polymerized at different speeds from other regions of said coating; coating   cured, thus presenting different optical responses -competitive.   2. Method according to claim 1, characterized by   he understands the steps of exposing   this coating to a light-curing radiation while selectively masking portions thereof of said radiation, said exposures being made at substantially constant temperature, while selectively varying the oxygen content of the atmosphere adjacent to the surface; of this coating.   3. Method according to claim 2, characterized in that it comprises the following steps: (a) provide this coating with a first mask and irradiate the masked coating in an atmosphere that comprises oxygen, (b) remove this first mask and irradiate this coating in an atmosphere that comprises oxygen, (c) provide this coating with a second mask and irradiate this masked coating in an inert atmosphere, and (d) remove the second mask and irradiate this coating in an inert atmosphere.   4. Method according to claim 1, characterized by the   This coating is selectively exposed to radiation   photopolymerization of varying intensity.   5. Cholesteric liquid crystalline film photopolymer   merited having a differential fixed optical response,   characterized in that it is obtained by sequentially exposing said coating to photopolymerizing radiation under conditions such that selected regions of said coating are polymerized at different speeds from other regions of this coating.   6. The coating according to claim 5, characterized by   the fact that it is successively exposed to a photo-   polymerizing while selectively -masking portions of this film to this radiation, these exposures being   made at a substantially constant temperature while   selectively vary the oxygen content of the atmosphere   adjacent to the surface of this material.   7. The coating of claim 6, characterized by   the fact that it includes a three-dimensional image.   8. Coating according to claim 5, characterized in that it is obtained by selectively exposing this   photopolymerizing radiation of varying intensity.