WO1997032718A1

WO1997032718A1 - Polymeric substrates having scratch- and wear-resistant coating

Info

Publication number: WO1997032718A1
Application number: PCT/IL1997/000067
Authority: WO
Inventors: Menashe Barkai
Original assignee: Coatec Ltd.
Priority date: 1996-03-07
Filing date: 1997-02-20
Publication date: 1997-09-12
Also published as: AU1809197A

Abstract

A composite (10) having a surface of scratch resistance greater than that of commercial window glass comprises an organic polymeric planar-configured substrate (12), such as polycarbonate, coated on at least one side with a thin film of material selected from refractory inorganic oxides comprising a mixture of Al2O3 and SiO2 (14), which film is bound to the substrate by means of an inorganic binder (16), the coating also being resistant to peeling or disintegration when the composite is subjected to environmental, mechanical or thermal stresses.

Description

POLYMERIC SUBSTRATES HAVING SCRATCH-ANDWEAR-RESISTANT

COATING

FIELD OF THE INVENTION The present invention relates to transparent composites characterized by scratch and wear resistance.

BACKGROUND OF THE INVENTION In recent years, various attempts have been made to find polymer-based substitutes for glass. This is due to the fact that, while glass - particularly clear glass used for covering light transmitting openings - has generally good optical qualities, it is brittle and heavy. Accordingly, the use of polymer-based materials - which are relatively flexible and lightweight - in place of glass, would be advantageous. One type of polymeric material that has seen use in recent years as a replacement for glass in automobiles, as well as in the building industry, is polycarbonate. Polycarbonate is particularly useful for vehicle applications due its light weight and high impact resistance

A disadvantage of polycarbonate and of other polymeric materials, however, is that they scratch very easily, and thus they are considered inferior to glass, particularly in environments requiring good optical transmission qualities. In an attempt to provide the considerably more flexible, lightweight polymeric materials with required scratch resistance, it is known to "plate" a polymeric panel with a hard polymeric film. This is done by dipping or spraying a polymeric substrate such as polycarbonate, using e.g. a siiicone-based polymer solution such as is marketed by Tokoyama, Japan, and which is subsequently cured The resulting product, while representing some improvement on previously available polymer-based products, was unsuitable for use in place of glass, however. This was due to cracking of the hard polymeric film when bent, and a tendency to discolor and generally deteriorate during prolonged exposure to UV radiation. Moreover, such a product is far from achieving the scratch resistance of glass.

It is also known to impart scratch- and wear-resistance to the surfaces of polymeric substrates, including polycarbonates, by coating with a refractory material, notably silica. Examples of this approach are described below.

In JP05342672-A, a recording element, such as a photomagnetic disk, said to have improved wear-resistance, is prepared by coating e.g. a polycarbonate substrate with Siθ₂ (e.g. at 100 nm thickness) by conventional RF sputtering.

In JP02145390-A, it is claimed that the base of a heat-transfer recording medium comprising a plastic film (e.g. of polycarbonate), when coated with spherical silica powder, optionally silicone-coated, is thereby made abrasion-resistant.

US 4842941 describes the preparation of a polycarbonate article, said to be highly abrasion-resistant, by coating first with an adherent resin composition (e.g. acrylic, and/or "organosilicons") and then, by means of plasma-enhanced chemical vapor deposition, with an abrasion-resistant top layer, which in Examples is silica. Other possible top layer ingredients mentioned are silicon carbide, silicon nitride, silicon oxynitride, silicon carbonitride, boron oxide, boron nitride, aluminum oxide, aluminum nitride, tantalum oxide, iron oxide, germanium oxide, germanium carbide and titanium dioxide. This patent does not suggest the use of any mixtures as the abrasion- resistant top layer. US 4190681 describes a polycarbonate article, said to be inter alia abrasion- and scratch-resistant, which has been primed with acrylic resin and coated with a thin layer containing silica (described as a glass), applied under vacuum by means of radio frequency induction heating. No reason is given in this patent, as to why other mentioned top layer ingredients, or their mixtures with silica, might be preferable, compared to the use of silica only.

In JP 53057848-A, an optical part (e.g. of polycarbonate) at 60- 100°C is coated with SiO and Si0₂ by vacuum evaporation, in order to impart inter alia improved scratch-resistance and anti-reflective properties.

JP 53037045-A claims that a heterogeneous SiOx (x=1-2) deposited on a plastic lens as substrate, e.g. by vacuum evaporation or sputtering, prevents reflection and exhibits high adhesion and resistance to scratches and abrasion.

JP 55052001 -A asserts that inter-alia scratch resistance on an optical part (e.g. of methacrylate or polycarbonate) is achieved by coating with an antireflection film comprising Siθ₂ and alternately layers 0f Zr0₂ and Si0₂. US 3991234 describes coating an ophthalmic quality lens comprising diallyl glycol carbonate polymer or an aromatic polycarbonate, with SiO or SiO/Siθ₂ mixture by vacuum evaporation of SiO in an oxygen atmosphere, followed by applying under vacuum an evaporable glass coating which may be e.g. Si0₂ or a borosilicate glass; the coating is said to possess improved adhesion.

The entire contents of the above-mentioned US Patents and Japanese Patent Publications are deemed incorporated by reference herein.

Persons in the art will appreciate that merely stating that the surface of an article of manufacture is "abrasion-resistant" does not convey, in a scientific manner, neither the degree of abrasion resistance of that surface, nor whether the surface is likely to withstand the stress of abrasion over a prolonged period of time. Both the Taber Abrasion Test and the Gardner Hazemeter Test, which are used in coordination (since the abraded surfaces are subjected to the Haze Test) are referred to in the above-cited US 4842941 and US 4190681. The rigor of the Taber Test depends on the total weights applied, and the number of cycles used in the test. US 4842941 utilizes 1000 g total weights and 300 or 1000 cycles It is believed, however, that in order to predict the likely practical utility of abrasion-resistant surfaced articles, with a greater degree of certainty, in withstanding the stresses of prolonged abrasion, by use of the described tests, would require these surfaces to pass a Taber Test including a much greater number of cycles than has been evidenced in the closest prior art.

It has surprisingly been found that in accordance with the present invention, it is possible to achieve a Δ% Haze result of below 1.5, and even zero, or little more than zero, after both 1000 and 5000 cycles in the Taber Abraser using 1000 g total weights.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a novel, scratch resistant composite, particularly for use in glazing applications as a substitute for glass. It is a further object of the invention to provide such a composite which possesses abrasion-resistance superior to the nearest prior art products, as evidenced by the results of scientific tests which are recognized in the art Other objects of the invention will appear from the description herein.

The present invention thus provides in one aspect, a composite which comprises an organic polymeric planar-configured substrate coated on at least one side with a thin film of material selected from refractory inorganic oxides comprising a mixture of AI₂O3 and Si0₂, such that the thus-coated surface has a scratch resistance greater than that of commercial window glass, said thin film of coating material being bound to said substrate by means of a thin film of inorganic binder, such that the coating is resistant to peeling or disintegration when the composite is subjected to environmental, mechanical or thermal stresses.

The present invention also provides in another aspect, a composite which comprises an organic polymeric planar-configured substrate coated on at least one side with a thin film of material selected from refractory inorganic oxides comprising a mixture of AI₂O₃ and Si0₂, such that the thus-coated surface has a scratch resistance greater than that of commercial window glass, said thin film of coating material being bound to said substrate by means of a thin film of inorganic binder, and also being bound to a superimposed hydrophobic layer by means of a thin film of adhesive, such that the coating is resistant to peeling or disintegration when the composite is subjected to environmental, mechanical or thermal stresses.The inventor has surprisingly found notwithstanding the fact that in this aspect of the invention, the thin refractory oxide film is masked by adhesive and hydrophobic layers, the composite having a smoother surface is nevertheless resistant to disintegration when it is subjected to environmental, mechanical or thermal stresses, and the thus-treated surface of the composite still has a scratch resistance greater than that of commercial window glass.

In another aspect, the invention provides as a new composition of matter, a composite which comprises an organic polymeric planar- configured substrate coated on at least one side with a thin film of material selected from refractory inorganic oxides, such that the thus- coated surface has a Δ% Haze value in the range of 0-1.5, after subjecting to both 1000 and 5000 cycles in a Taber Abraser at 1000 g total weights.

To the best of the inventor's knowledge, the composites of the present invention have scratch-resistant and durable qualities superior to any comparable available products. BRIEF DESCRIPTION OF THE DRAWINGS The present invention will be more fully appreciated and understood from the following detailed description, taken in conjunction with the drawings, in which: Fig. 1 is a schematic cross-sectional view of a particular embodiment of a composite in accordance with the present invention;

Fig. 2 is a schematic representation of apparatus suitable for preparing the composite of a particular embodiment of the invention; and Fig. 3 is a schematic cross-sectional view of a further particular embodiment of a composite in accordance with the present invention.

DETAILED DESCRIPTION OF THE INVENTION The substrate used in the composite of the invention may be constructed from any suitable organic polymeric material known for the manufacture of sheet-like products. The substrate is preferably but need not be transparent, and may be but need not be rigid. Suitable substrate materials are, for example, polycarbonate, acrylic resin, e.g. polymethylmethacrylate (PMMA), and polyvinyl chloride. Suitable substrates also include polymers which have been precoated e.g. with silicones, such as silicone-precoated polycarbonate. The composites of the invention may take the form of rigid transparent articles, but are not restricted thereto. Such articles may be, but are not limited to, glazing panels such as windows for houses or automobiles. The term "planar- configured", as a description of the substrate, is intended to convey only that the substrate is sheet-like, insofar as the thickness will be very small compared with length and breadth. However, the substrate may be e.g. a film, foil or panel; and it may be straight or curved, or shaped in any manner useful in commerce. The substrate may be coated in accordance with the invention or either one side or on both sides. It will be appreciated that where necessary one side of the substrate may be protected by a temporary removable coating, where in a process for preparing the composite, the desired composite product of the invention is to be coated on one side only. Coating of a substrate may be achieved by coating first one side and then the other, on by coating both sides simultaneously. Such simultaneous coating is achievable especially by applying sputtering or CVD deposition techniques. The presently preferred inorganic binder to be applied to polycarbonate directly, is silicon mono-oxide SiO, but any other binding substances which will achieve good adhesion between the particular substrate and the coating material and therefore make the metal oxide coating resistant to peeling and disintegration under the conditions to which it will be subject in practice, may be employed. A person of the art will appreciate that selection of the binder will depend on the nature of the substrate, as well as the nature of the coating material Other possible binding materials may be selected from elemental metals, or e.g., from Ai₂θ₃(see e.g. Example 1 , below), HfO₂, SiO₂, Snθ₂, TiO₂ and ZrO₂. Preliminary experiments indicate that Ti0₂ and ZrO₂ may be suitable binders for PMMA. The refractory inorganic oxide coating material comprises AI₂θ3, and Si0₂, and optionally in addition, at least one member selected from the group consisting of Al₂0₃, HfO₂, SiO₂, Sn0₂, Ti0₂ and ZrO₂.

It is thus within the contemplation of the present invention, according to a particular embodiment thereof, that both the binder and the oxide coating may be selected from the same group of oxides mentioned in the preceding paragraph. It has been found that use as the coating material of a mixture of Al₂0₃ and SiO₂ e.g. of about 10 to about 40% Al₂0₃ and about 90 to about 60% SiO₂, by volume, achieves a stress-free film having excellent scratch resistance, but of course the invention is not limited to such a mixture. In a preferred embodiment of the invention, such a mixture of alumina and silica is codeposited by thin film deposition technology, which is essentially known per se. The metal oxide scratch-resistant film wilt preferably have a thickness in the range 10Onm to 6μm, whereas the binder layer may have an exemplary thickness .in the range 5 to 40nm

As indicated above, composites according to the invention may be prepared by applying successive binding and scratch-resistant layers to the substrate by any suitable method known to practitioners of thin film deposition technology, e.g. by applying a technique selected from sputtering, thermal evaporation (E-gun or thermal source), cathodic arc discharge, and even chemical vapor deposition (CVD). Deposition may be carried out with plasma assistance, i.e. by bombarding the substrate with energized ions during the deposition process, in order to achieve layers having higher densities and potentially greater scratch resistance. Moreover, it is preferable, in accordance with a particular embodiment, to submit the substrate surface to glow discharge, e.g. for 30-300 seconds, prior to deposition of binder. Different coating materials may be deposited simultaneously or consecutively.

In the aspect of the invention in which a hydrophobic layer is superimposed on the thin film of refractory oxide coating layer, the hydrophobic layer being adhered to the oxide coating layer by a thin adhesive film, the latter, e.g. SiO_2l is applied to the oxide coating layer by methods known per se in thin film deposition technology. The hydrophobic layer may comprise, e.g., silicone polymers, and may be applied to the thin adhesive film either by thin film technology, for example in the same apparatus use for depositing the oxide coating layer, or by an external step such as spraying, carried out outside such apparatus.

Referring now to Fig. 1, which is not drawn to scale, this shows in cross-section a composite 10 of an embodiment of the invention, provided with scratch-resistant surfaces on both sides (although the invention includes equally a composite provided with a scratch-resistant surface on one side only). Composite 10 is formed from a polymeric substrate 12, a protective (scratch-resistant) oxide layer 14 thereon, and a binder layer 16, for binding protective layer 14 to substrate 12, which may be of any preferred thickness, and may be selected to have a particular transparency or opacity, as desired. The protective layer 14 and binder layer 16 are deposited e.g. by the methods mentioned and exemplified elsewhere herein. Such methods are known and do not form per se part of the invention. Protective layer 14 is preferably a codeposited mixture of amorphous AI₂O₃ and Si0₂ , and preferably also has a thickness in the range 100nm to 6μm. Binder layer 16 may be for example SiO and may have an exemplary thickness .in the range 5 to 40nm.

The invention will be illustrated by the following non-limiting Examples.

EXAMPLE 1 Figure 2 is a schematic representation of an exemplary apparatus, shown generally by reference numeral 20. Substrate holder 22 is rotated about vertical axis 24 in a horizontal plane. The substrate 26 (for example polycarbonate sheet ("LEXAN"®), or polycarbonate precoated with a silicone based polymer ("MARGARD"®), both of GE Plastics, Holland) is attached to the underside of holder 24 by means not shown. In a first stage of production, substrate 26 is subjected to a glow discharge from source 28, whereby substrate 26 is bombarded, e.g. for 100 seconds, with low energy atoms and ions (not shown). In a second stage, SiO as the thin film binder layer in the case of "LEXAN", or AI₂O₃ as such binder layer in the case of "MARGARD", is applied from thermal source 30, to a thickness of 20 nm. In a third stage, AI₂O3 and Si0₂. in a 20:80 volume ratio are applied from E-gun thermal sources 32 and 34, respectively, to a total thickness of 3μm. During operation, the apparatus is subjected to vacuum applied in the direction of the arrows via outlet 36 by pump means (not shown). The product, which had a visual transparency substantially unchanged from the untreated polycarbonate sheet, was removed from the apparatus, and has the configuration described with reference to Figure 1, above, except that the substrate has been treated on one side only, if desired, the substrate can be reversed on the substrate holder and the process repeated, in order to similarly treat the second side of the substrate. It is contemplated that by using plasma assist technology at each stage of deposition in this example, a product having layers of relatively higher density and potentially higher scratch resistance could be obtained.

EXAMPLE 2 The starting material for this Example was the product of

Example 1 , which was further treated while still in the same apparatus. The product is shown generally at 11 in Figure 3, where reference numerals which are the same as in Figure 1 have the same meaning as in that Figure. With reference to Figures 2 and 3, after applying the thin film of codeposited AI₂O3 and SiO₂, SiO 2 alone was applied from E-gun thermal source 34, in order to form an external adhesion layer 40, of 100 nm thickness. The product was at this stage removed from the apparatus, sprayed with a silicone solution ("Separator Spray" by Molykote) followed by curing of the thus-applied hydrophobic layer 42 at 60°C for about 30 minutes. Excess silicone was removed by washing with detergent, and the product was then washed with water and dried in air at ambient temperature. The residual adhered hydrophobic layer was substantially a monolayer, of estimated thickness about 0.3-1 nm. The product had a smoother surface than the product of Example 1 , but similar stress- and scratch-resistance and transparency properties.

PROPERTIES OF THE COMPOSITE PRODUCTS OF THE INVENTION The following tests utilized samples prepared from 100 x 100 x 3 mm polycarbonate squares. Stress Tests. It was found that a 1-5 μm film of SiO ₂ on a polycarbonate substrate, without an intermediate binder, developed high compressive stresses and partially peeled off in the Scotch tap test (US Military Standard C 48497A, ASTM D-3359). By comparison, the products of Examples 1 and 2 did not exhibit peeling under similar conditions, and did not disintegrate even when subjected to numerous successive alternate immersions in boiling and freezing water. Scratch Tests. The Teledyne Taber Abraser model 5150 was employed to test the products of Examples 1 and 2, with 2 x 500 g loads, for 1000 or 5000 cycles. The results are as follows:

Run no. Cycles Weight (g) Silicone- Hydrophobic Δ% Haze precoated coating

1 1000 1000 yes yes 0

2 1000 1000 yes no 0.13

3 1000 1000 no yes 0.78

4 1000 1000 no no 1.01

5 5000 1000 yes yes 0

6 5000 1000 yes no 0.22

7 5000 1000 no yes 1.10

8 5000 1000 no no 1.35

0 These results show that the products of the invention can achieve a Δ% Haze result of < 1.5, and even zero, or slightly above zero, after both 1000 and 5000 cycles in the Taber Abraser using 1000 g total weights.

5 ADVANTAGES OF THE INVENTION

The composites of the invention have the potential advantages of plastic materials of high impact strength and lightness of volume, yet the scratch resistance of the surface is similar to that of glass. Moreover, it is within the scope of the invention to incorporate in the composites light or heat filters or reflecting layers, or layers having other desired optical properties.

It will be appreciated by persons skilled in the art that the scope of the present invention is not limited to what has been shown and described hereinabove merely by way of example. Rather, the scope of the present invention may be inferred from the claims, which follow.

Claims

1. A composite which comprises an organic polymeric planar- configured substrate coated on at least one side with a thin film of material selected from refractory inorganic oxides comprising a mixture of AI₂O3 and Si0₂, such that the thus-coated surface has substantially a scratch resistance greater than that of commercial window glass, said thin film of coating material being bound to said substrate by means of a thin film of inorganic binder, such that the coating is resistant to peeling or disintegration when the composite is subjected to environmental, mechanical or thermal stresses.

2. A composite according to claim 1 , which is further characterized by at least one of the following features: (a) said substrate is selected from polycarbonate, acrylic resin and polyvinyl chloride; (b) said coating material comprises additionally at least one member selected from the group consisting of Hf0₂, SnO_2l TiO₂ and ZrO₂; (c) said thin film of in¬ organic binder has a thickness within the range 5 to 40 nm; (d) said thin film of coating material has a thickness within the range 100 nm to 6 μm

3. A composite according to claim 2, wherein said coating material consists of a mixture of AI₂O3 and Siθ_2.

4. A composite according to claim 3, wherein said coating material is a mixture of, by volume, about 10 to about 40% AI₂O₃ and about 90 to about 60% SiO_2.

5. A composite according to claim 4, wherein said substrate is a polycarbonate substrate.

6. A composite according to claim 5, wherein said substrate is a polycarbonate substrate which has been precoated with a silicone- based polymer.

7. A composite which comprises an organic polymeric planar- configured substrate coated on at least one side with a thin film of material selected from refractory inorganic oxides comprising a mixture of Al₂0₃ and Si0₂₎ such that the thus-coated surface has substantially a scratch resistance greater than that of commercial window glass, said thin film of coating material being bound to said substrate by means of a thin film of inorganic binder, and also being bound to a superimposed hydrophobic layer by means of a thin film of adhesive, such that the coating is resistant to peeling or disintegration when the composite is subjected to environmental, mechanical or thermal stresses.

8. A composite according to claim 7, which is further characterized by at least one of the following features: (a) said substrate is selected from polycarbonate, acrylic resin and polyvinyl chloride; (b) said coating material comprises additionally at least one member selected from the group consisting of Hf0₂, Sn0₂, TiO₂ and ZrO₂; (c) said thin film of in¬ organic binder has a thickness within the range 5 to 40 nm; (d) said thin film of coating material has a thickness within the range 100 nm to 6 μm

9. A composite according to claim 8, wherein said coating material consists of a mixture of AI2O3 and Si0₂.

10. A composite according to claim 9, wherein said coating material is a mixture of, by volume, about 10 to about 40% AI2O3 and about 90 to about 60% SiO₂.

11. A composite according to claim 10, wherein said substrate is a polycarbonate substrate.

12. A composite according to claim 11 , wherein said substrate is a polycarbonate substrate which has been precoated with a silicone- based polymer.

13. A composite which comprises an organic polymeric planar- configured substrate coated on at least one side with a thin film of material selected from refractory inorganic oxides, such that the thus- coated surface has a Δ% Haze value in the range of 0-1.5, after subjecting to both 1000 and 5000 cycles in a Taber Abraser at 1000 g total weights.

14. A composite according to claim 13, which is further characterized by at least one of the following features: (a) said substrate is selected from polycarbonate, acrylic resin and polyvinyl chloride; (b) said coating material comprises a mixture of AI₂O₃ and SiO₂ and optionally at least one member selected from the group consisting of HfO₂, SnO₂, TiO₂ and ZrO₂; (c) said thin film of coating material is bound to said substrate by means of a thin film of inorganic binder, which preferably has a thickness within the range 5 to 40 nm; (d) said thin film of coating material has a thickness within the range 100 nm to 6 μm; (e) said thin film of coating material is bound to a superimposed hydrophobic layer by means of a thin film of adhesive.

15. A composite according to claim 14, wherein said coating material consists of a mixture of AI₂O₃ and SiO₂.

16. A composite according to claim 15, wherein said coating material is a mixture of, by volume, about 10 to about 40% AI₂O₃ and about 90 to about 60% SiO₂.

17. A composite according to claim 16, wherein said substrate is a polycarbonate substrate. 16 18. A composite according to claim 17, wherein said substrate is a polycarbonate substrate which has been precoated with a silicone- based polymer.