CA2168180A1

CA2168180A1 - Thermostable polarizers

Info

Publication number: CA2168180A1
Application number: CA002168180A
Authority: CA
Inventors: Karl-Heinz Aleksander Ostoja Starzewski; Siegfried Thurm
Original assignee: Bayer AG
Current assignee: Bayer AG
Priority date: 1995-01-30
Filing date: 1996-01-26
Publication date: 1996-07-31
Also published as: KR960029090A; FI960377A0; DE19502806A1; KR100394204B1; EP0724024B1; DE59601846D1; EP0724024A1; JPH08262228A; US5705267A; CN1083987C; CN1153909A; TW282519B; FI960377A

Abstract

Thermostable, flexible polarizers having a polarizing layer of a polymer with conjugated double bondings are obtained when their surfaces are sealed by a protective layer of SiOx where x is from 1 to 2.

Description

Le A 30 925-US/ Ha/klu/S-P
2i68180 Thermostable polarizers BACKGROUND OF THE INVENTION

5 The invention relates to thermostable, flexible polarizers which contain a polarizing layer of a polymer with conjugated double bondings and with an SiOx-sealed surface. The invention furthermore relates to polarizers of this type which are additionally bonded to outer layers.

US 4,818,624 describes the stabilization of light polarizers by surface silylation 10 using an organosilane. The action is inadequate, since bleaching and colour shifts are observed after 24 hours at only from 49 to 74C (120 to 165F).

The production of l~min~tes from various substrates with adhesion interlayers isknown. US 5,049,427 describes l~min~ted polarizers which contain a polarizing core layer of a polyacetylene (PAC)-containing polymer (POLPAC) and transpa-15 rent outer layers, where the layers are bonded by means of a special polyurethane-polyurea.

Although POLPAC polarizers already have excellent properties, the stability is still inadequate under extreme conditions. After storage at 90C for 500 hours, the transmission of the polarizer for unpolarized light has changed, the change in 20 transmission ~ TUnpol being more than 5%.

Use in optical displays which are exposed to particularly high temperatures (forexample dashboards in automobiles) is only possible, however, if the decrease inthe optical properties ~ TUnpol and ~P of the polarizer under these conditions is at most 5%, where AP is the change in degree of polarization. It has been reported 25 that the optical properties of e.g. POLPAC polarizers are constant at 100C for 1,000 hours after bonding between glass plates. However, such l~min~te systems are not very suitable for the production of displays. Flexible polarizers are preferred, both with respect to the processing properties and in the context of flexible plastic displays.

SUMMARY OF THE INVENTION
The object of the invention was therefore to produce polarizers based on a polymer with conjugated double bondings in which the abovementioned problems are alleviated or avoided.
Surprisingly, it has now been found that this object can be achieved if the polarizer is sealed on its surface by an SiOx layer.
DETAILED DESCRIPTION OF. THE INVENTION
The sealing of the polarizer can be carried out by physical vapour deposition (PVD), by plasma chemical vapour deposition (plasma CVD) or by sputtering. These processes and variants thereof are known to the person skilled in the art. Preferably the process of PVD is employed.
In the case of sealing by PVD, commercial SiO is evaporated in the absence or presence of various amounts of

2 and deposited on the polarizer to be sealed. In the absence of 2 a SiO protective layer is obtained. In the presence of 2~ the oxygen content of the protective layer increases until finally, in the presence of an excess of 2~
a layer of SiO2 is deposited. SiOx having any desired values from 1 to 2 for x denotes this region. For the purposes of stabilization of the polarizer to oxygen, values of from 1.1 to 1.9, in particular from 1.4 to 1.8, are preferred.
However, values of up to x = 2 are useful for achieving mechanical properties (for example scratch resistance).

Analogously, the sealing can be achieved with the 216&180 aid of plasma CVD, in which case SiOx protective layers on the polarizer to be sealed are obtained by a chemical reaction, for example of a silane with an 2 source, such as N2O or another nitrogen oxide, and deposition.
In one variant, the protective layer can be built up successively first from relatively oxygen-depleted SiOx where x = 1.1 to 1.8 and then from relatively oxygen-rich SiOx where x = 1.4 to 2.
The SiOx protective layer preferably has a thickness of from 10 nm to 10 ~mt more preferably of from 100 nm to 1 ~m. For further stabilization, cut edges can also be sealed in the described manner.
The invention furthermore relates to a laminated flexible polarizer comprising a polarizing core layer of a polymer with conjugated double bondings and transparent, flexible outer layers applied to both sides, characterized in that the core layer sealed by means of an SiOx protective layer and the outer layers are bonded by means of a silicate layer or by means of an organic adhesive, and the polarizer laminated ln this way is flexible. The polarizer can, by means of the silicate layer, also be used for bonding to glass plates, optical lenses or prisms. If the polarizer is bonded on one side to a glass display or another glass element with the aid of a silicate layer or by means of an organic adhesive, it is sufficient to protect its free surface by means of an SiOx layer.

2~ 63~ ~

Silicate layers of this type are preferably applied to the core layer sealed by means of an SiOx protective layer and/or to the outer layers in the form of an aqueous solution.
Suitable aqueous solutions of silicates are known aqueous solutions of sodium water glass and potassium water glass.
Conventional types of water glass have, in the case of sodium water glass, solids contents of from 25 to 60% by weight and SiO2 contents of from 20 to 40% by weight; the remainder of the solids content is Na2O; and in the case of potassium water glass, they have solids contents of from 25 to 40% by weight and SiO2 contents of from 20 to 30% by weight; the remainder of the solids content is K2O. In order to obtain relatively thin silicate layers, these solutions can also be diluted with water. The SiO2 contents are preferably as high as possible, i.e. with an SiO2/Na2O weight ratio of > 3 or an SiO2/K2O weight ratio of > 2.2. Use of silicate layers renders organic adhesives, as described in large number in U. S. 5,049,427, superfluous.
The silicate layers stabilize the properties of the polarizer in addition to the SiOx layer in a layer thickness of only < 2 ~m. Preferably, from 100 mg to 2 g of water glass (solids)/m2 of surface to be bonded are required to achieve thermostable bonding of the laminate.

- 3a -Le A 30 925-US 21 681 80 In a preferred embodiment, the SiOx-sealed core layer and/or outer layer is/are subjected, before coating with the silicate solution, to treatment with a silane or with a borate. This measure improves, in particular, the bond strength.

Suitable silanes conform to the formula:

Si (Rl)n (R2)4 n in which Rl, independently of one another, are halogen or alkoxy, R2, independently of one another, are alkyl or alkenyl, and n is the number 2, 3 or 4 10 Alkyl and alkoxy radicals Rl and R2 can be substituted.

Examples of suitable silanes are tetramethoxysilane, tetraethoxysilane, methyltri-methoxysilane, dimethyldimethoxysilane, ethyltriethoxysilane, dimethyldichloro-silane, vinylmethyldichlorosilane and vinyltriethoxysilane. Silanes can also be mixed directly, for example emulsified, into the silicate solution.

15 Examples of suitable borates are boric acid and borax. Boric acid and borates can also be mixed directly into the water glass solution or dissolved therein.

The silanes and borates are applied, in particular, by dipping the SiOx-sealed core layer and/or the outer layer into a solution of the compound or, if the compound is liquid, into the pure compound and removing it again. The amount taken up is so 20 small that it cannot be reliably measured by weighing, but is usually less than 1 glm2 Outer layers have, for example, thicknesses of from 5 llm to 1 mm, preferably from 20 to 200 llm. The polarizing core layer has, for example, a thickness of from 1 to 200 llm, preferably from 5 to 50 !lm.

LeA30925-US 21 681 80 Examples of suitable outer layers are aromatic polyesters, polyacrylonitriles, poly(meth)acrylates, polysulfones, aromatic polycarbonates, cellulose acetates, cellulose acetobutyrates, polyamides, polyhydantoins, polyimides, polyamide-imides, polyparaphenylenebenzobisimidazoles and -oxazoles and polyether 5 ketones, preference being given to polyesters, poly(meth)acrylates, polycarbonates and cellulose esters. The transparency of these materials is their most important feature. They are generally employed in the form of films.

The polarizing core layer for the inventive polarizer sealed on its surfaces with SiOx7 is a polymer with conjugated double bondings. Such polymers are known.
Thus, e.g. US 3,914,017 describes the partial dehydration of polyvinyl alcohol whereby result domains of conjugated double bondings in the polymer main chain.
The thereby resulting domains of conjugated double bondings are in general rather short (average: 2-15 C=C). The dehydration can be carried out purely thermally or with acid catalysis. The polyvinyl alcohol to be dehydrated further can be grafted 15 with other vinyl monomers, e.g. with (meth)acrylates, acrylonitrile, styrene, vinyl acetate or vinyl chloride. In an analogous manner conjugated double bondings canbe formed by splitting off HCl from polyvinyl chloride or by splitting off acetic acid from polyvinyl acetate. Finally, the above mentioned PAC-containing polymer can be formed by polymerization of acetylene in a polymer other than 20 PAC being in solution. All these polymers can be employed according to the invention.

Preferably, the polarizing core layer is of a partially dehydrated polyvinyl alcohol or of PAC.

The polarizing core layer is especially preferably a polarizer made from PAC-25 containing polymer products whose matrix is a polymer containing polar groupsand which have a maximum degree of polarization P of at least 90%, preferably atleast 95%, particularly preferably at least 98%, and a maximum dichroic ratio QEof 5 or more, preferably of 10 or more, in both cases based on the region of visible light. These polarizers are employed in the form of f1lms having a 30 preferential direction produced by stretching. The degree of stretching ~ is greater than 200%, preferably at least 400%, particularly preferably from 500% to 1,000%.

Le A 30 925-US 2 1 68 1 ~ U

Especially preferred polarizing core layers consist of PAC-containing polymer products the matrix of which is a partially dehydrated polyvinyl alcohol, and the polarizing effect of which ranges from the non-visible close ultra-violett wave length area (< 450 nm) via the visible wave length area (450-700 nm) to the close infra-red area (700-850 nm). Such partially dehydrated POLPAC-polarizers can be prepared a) in that the used polyvinyl alcohol, prior to the acetylene polymerization, istempered at 150-250C until the wanted dehydration is reached which is recognized by the decoloration, thereafter acetylene is polymerized in a solution of this treated polyvinyl alcohol, a film is produced therefrom and stretched; or b) in that a POLPAC film whose matrix is polyvinyl alcohol is stretched and thereafter tempered which tempering may be carried out in the presence of air or with the exclusion of air to maintain the long-wave polarization effect.
The film may also, prior to or after the stretching, be pretreated with an acid, e.g. with HCI gas in order to accelerate the dehydration process. It is likewise possible to add to the polymer, prior to the film production, a small amount of acid, e.g. hydrochloric acid, phosphoric acid, sulphonic acid or sulphonic acid-containing substances.

The degree of polarization P for linear-polarized light and the degree of stretching are defined as follows:

transmission in the pass position minus transmission in the block position P= x 100 transmission in the pass position plus transmission in the block position E = ~

(I = length after stretching; 1o = length before stretching) LeA30925-US 21 681 ~0 The production of PAC-containing polymer products is disclosed, for example, in US 5,049,427, where acetylene is polymerized in a polymer solution in the presence of a suitable catalyst, e.g. in the presence of Ni(O)-complexes in a solution of a polymer other than PAC.

5 The polymer other than PAC is present in an amount of from 1 to 99.9% by weight, preferably from 50 to 99.9% by weight, based on the total polarizer.

Examples of suitable polymers other than PAC are polyvinyl chloride, poly-vinylbutyral, polyvinyl alcohol (PVA), partially hydrolysed polyvinyl acetate (PVAC) and other vinyl alcohol-containing (co)polymers, polyacrylonitrile, 10 acrylonitrile-containing copolymers, polyvinylpyrrolidone, methylcellulose and other cellulose derivatives, and polycarbonate. Preference is given to solutions of PVA and partially hydrolysed PVAC.

Examples of solvents for the polymers other than PAC include N-methylpyr-rolidone (NMP), dimethylformamide (DMF) and dimethyl sulphoxide (DMSO).
15 The concentration of the polymer in the solvent is from 1 to 20% by weight, preferably from 2 to 20 % by weight.

The novel laminated polarizers are distinguished by a number of outstanding properties:

1. high light transmission 20 2 high light fastness

3. thermostability of the polarizing core layer

4. excellent mechanical properties.

The novel polarizers are suitable for all areas of use in which polarization films are used, in particular in optics (for example polarizing microscopes, photography 25 and antireflection coating of sunglasses and ski goggles) and for LC-displays, for example in watches, pocket calculators, laptops, computers, projection displays,videogames, camcorders and flat-screen TV sets.

Le A 30 925-US 2 1 6 8 1 ~ O

At 80C, even unl~in~ted POLPAC films without stabilizers have good stability, the change in transmission (~T) after 500 hours at 80C in air being 2-3% and the change in degree of polarization (~P) being less than 1%.

The novel polarizer may, in addition to the conjugated double bondings, e.g. in

5 addition to the polyacetylene, contain additional, dichroic substances, for example iodine or dichroic dyes. However, polyacetylene makes up at least 50% by weight,preferably at least 80% by weight, of the total amount of dichroic substances.

Le A 30 925-US 2 1 ~ 8 ~ 80 Examples Example 1 A POLPAC film with a thickness of 11 ~m which has been stretched by 700%
had a tr~nsmi.csion T of 38.7% at 600 nm and a degree of polarization P of 99.99%. After 500 hours at 80C, the transmission had risen to 41.7% and the degree of polarization had only dropped to 99.89%.

Example 2 The same film as in Example 1 was kept at 90C, during which the transmission at 600 nm rose by 5.1% points even after 270 hours and the degree of polarization dropped by 1.84% points.

Example 3 , A sample piece of a film similar to that of Example 1, but stretched by 600% andmeasuring 60 mm x 60 mm, was attached to a rotatable substrate holder in an A 1100 vapour-deposition unit from Leybold-Heraeus, Hanau, BRD. The process chamber of the vapour-deposition unit was then closed and evacuated to approx.
10-3 Pa. 2 was then admitted to a pressure of 7 Pa, and the rotary drive of thesubstrate holder was switched on so that the latter rotated at 20 rpm. By appli-cation of a voltage of -480 V against earth to an Al plate connected as cathode, a low-pressure plasma was ignited. The samples were treated in this plasma for twominutes at a power of 5.6 watts. The voltage was then switched off, the additionof 2 was terminated, and the process chamber was evacuated to 10-4 Pa.

When this pressure had been reached, 2 was again admitted into the process chamber until a pressure Of 10-2 Pa was obtained. After this pressure had been reached, the electron-beam gun was switched on and the SiO to be evaporated (tradename Patinal, Merck, Darmstadt), which was in a water-cooled Cu crucible, was heated to approx. 1950 K within four minutes using a power of 400 W. A
movable diaphragm between the electron-beam gun and the substrate holder was subsequently removed, and the film pieces were coated at a rate of 0.5 nm/sec for Le A 30 925-US

400 seconds. The diaphragm was then replaced between the electron-beam gun and the substrate holder, the 2 addition was switched off and the coating process was terminated. After the electron-beam gun had been switched off and the evapo-ration material had been cooled, the vacuum in the process chamber was released,5 and the film coated on one side was removed, turned, and vapour deposition-coated on the uncoated side as described above.

The film coated with SiOx on both sides in a thickness of 200 nm per side was subjected, without lamination, to a 90C heat test, during which the transmission rose by only 2.1% (from 33.3% to 35.4%) in 480 hours. The degree of polarization dropped by only 0.5% (from 99.8% to 99.3%), both measured at 600 nm.

Example 4 Example 3 was repeated with a film of dehydrated and grafted polyvinyl alcohol stretched by 600 %. The polymer for this film was obtained by grafting of 15 polyvinyl alcohol with ethyl acrylate and methyl methacrylate and successive splitting off H2O with the aid of water-free hydrogen chloride. The SiO~-coatingwas 180 nm on each side. During the heat test the transmission changed by less than 2 % and the degree of polarization by less than 1 %, both measured at 600 nm.

20 Example ~

A 23 llm thick film of polyvinyl alcohol (prepared by saponification of polyvinyl acetate; degree of saponification: 99 %) was exposed to an atmosphere of HCI gasat room temperature for 5 min, thereafter stretched monoaxially to the sevenfoldlength at 200C and kept for further 15 min under stretch tension at 200C. Then25 the film was 12 ~,lm thick. Measuring with polarized light yielded a transmission of 43.9 % and a degree of polarization of 93.9 %. The film was coated with SiOx (x = 1.7) in the manner of Example 3. A repeated measuring after the heat test at 90C resulted in a change of a transmission of less than 2 % and of the degree of polarization by 0.9 %.

Le A 30 925-US
2i681~0 Ex~mple 6 A POLPAC film was treated with gaseous HCl and stretched under argon by 700 %, i.e., to the eightfold of its original length and thereafter tempered in the presence of air at 200C for 15 min. The transmission at 600 nm was 38.5 %, the degree of polarization was 99.99 %. The polarizing effect at 400 nm rose from 81 % to 96 % due to tempering. The polarizing effect at 700 nm fell only from 99.8 % to 98.1 %. After coating with SiOx and a heat test at 90C for 20 days the changes were: <2 % for the transmission and <1 % for the polarization. When the tempering was carried out under argon no polarizing change at 700 nm was 1 0 observed.

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A thermostable, flexible polarizer having a polar-izing layer of a polymer with conjugated double bondings, which has SiOx sealed surface, where x has any desired value from 1 to 2.

2. The polarizer of claim 1, wherein x has a value from 1.1 to 1.9.

3. The polarizer of claim 2, wherein x has a value from 1.4 to 1.8.

4. The polarizer of claim 1, wherein the sealing of the surface with SiOx is produced by physical vapour deposition (PVD).

5. The polarizer of claim 1, wherein the sealing of the surface with SiOx is produced by plasma chemical vapour deposition (plasma CVD).

6. The polarizer of claim 1, wherein the sealing of the surface with SiOx is produced by sputtering.

7. The polarizer of claim 1, wherein the SiOx protective layer has a thickness of from 10 nm to 10 µm.

8. The polarizer of claim 7, wherein the SiOx layer has a thickness from 100 nm to 1 µm.

9. The polarizer of claim 1, which additionally has transparent, flexible outer layers applied to both sides which are bonded to the SiOx layers with the aid of silicate or organic adhesives.

10. The polarizer of claim 9, wherein the outer layers are bonded with the aid of silicate.

11. The polarizer of claim 10, wherein the SiOx sealed polarizing layer or the outer layer or the SiOx sealed polarizing layer and the outer layers is/are subjected, before coating with the silicate solution, to treatment with a silane or with a borate.

12. The polarizer of claim 10, wherein the outer layers are bonded with a silicate solution admixed with a silane or a borate or a silane and a borate.

13. The polarizer of claim 11, wherein the layers are subjected to treatment with a silane that conforms to the formula Si(R1)n(R2)4-n in which R1, independently of one another, are halogen or alkoxy, R2, independently of one another, are alkyl or alkenyl, and n is the number 2, 3 or 4.

14. The polarizer of any one of claims 1 to 13, wherein the polymer is a polyacetylene containing polyvinyl alcohol.

15. The polarizer of any one of claims 1 to 13, wherein the polymer is a partly dehydrated polyvinyl alcohol.

16. The polarizer of claim 1, which contains additional dichroic substances.

17. The polarizer of claim 14, wherein the polymer is a polyacetylene containing polyvinyl alcohol, which polyvinyl alchohol, prior to or after the acetylene polymerization, is partially dehydrated by tempering at 150-250°C, by acid treatment, or by tempering and acid treatment.