DE69516862T2 - Laser-inscribable thermoplastic resin composition - Google Patents

Description

The present invention relates to a thermoplastic resin composition having laser marking ability. More particularly, the invention relates to a thermoplastic resin composition which can form sharp marks with excellent contrast upon exposure to laser irradiation. More particularly, the invention relates to keyboards having keys with laser-marked top surfaces and methods of manufacturing such keys.

As a means of marking key surfaces, printing with an ink has been mainly used. In the case of printing on surfaces of plastic products, the surfaces must be cleaned by washing with chlorofluorocarbons to improve the adhesion of the ink thereto. It is now necessary to abolish the chlorofluorocarbon washing process to prevent the destruction of the ozonosphere or to develop a marking technology that allows permanent marking. A means of marking with laser beams that enables simple and effective printing is therefore of interest. This technology involves incorporating a light- or heat-absorbing additive into the raw materials in advance, thereby causing foaming, decomposition or carbonization under laser irradiation to induce changes in the surface of the material or fading of the pigment or dye, thereby achieving the desired marking.

Japanese Patent Publication No. 61-11771 describes a method in which a sharp mark is formed with a laser beam by introducing an amount of carbon black or graphite.

Japanese Laid-Open Patent Publication No. 1-254743 describes a method for improving the marking ability of plastics with a YAG laser, which comprises adding titanium oxide and optionally further carbon black to the plastics.

Japanese Patent Publication No. 61-41320 and Laid-Open Patent Publication No. 61-192737 describe methods for marking which utilize bleaching or decolorizing pigments, dyes, etc.

Japanese Patent Publication No. 2-47314 describes a marking method in which a volatile component or components in the resin to be marked, such as unpolymerized monomers or decomposition products, are foamed by laser irradiation to form a projection on the resin surface, thereby forming the mark.

Japanese Patent Laid-Open Publication No. 4-246456 describes that a mark with good contrast can be obtained by adding carbon black and/or graphite, which are highly heat-conductive, to the plastics.

Furthermore, Japanese Patent Laid-Open Publication No. 2-59,663 describes a method for manufacturing plastic key members using a coloring powder that reacts to thermal radiation or a dye powder that is sensitive to thermal radiation.

However, with respect to these conventional methods, the laser marking part formed by foaming has a low degree of blackness. In particular, the use of carbon black significantly increases foaming, causing a noticeable drop in the development of black color.

Colored key surfaces are very fashionable at present, and a carbon-based pigment material is often used to adjust the colors of key surfaces. Since carbon foams during laser marking, the coloring on the laser marking part tends to be dark brown, but not black, This inevitably makes the application of carbon-based pigment materials to key surfaces difficult, and it is therefore desirable to provide a fine marking with higher contrast and black coloration.

EP-A-0 190 997 describes a method for marking a macromolecular organic material containing an additive which causes decolorization by laser light (inorganic and/or organic pigment and/or polymer-soluble dye). DE-A-43 29 395 describes a material which comprises at least one thermoplastic organic polymer which contains at least one mineral black pigment and a colorant consisting of an inorganic and/or organic pigment(s) and/or a polymer-soluble dye, and which can be colored by laser light.

It is an object of the present invention to provide a keyboard with keys constructed of a thermoplastic resin composition having laser marking ability, particularly one capable of forming a sharp mark with excellent contrast, particularly with a clear development of a black color after exposure to laser irradiation, and a method of producing such keys.

According to the present invention, there is provided a keyboard having keys constructed from a thermoplastic resin composition, wherein the thermoplastic resin composition

(i) a thermoplastic resin and

(ii) a glaze having an oxide composition represented by the following formula:

R1-2O xR'2O3 · yR"O&sub2;&submin;&sub3;

includes,

where R₁₋₂O represents an oxide of a monovalent or divalent metal,

R'₂O₃ represents an oxide of a trivalent metal,

R"O₂�min;₃ stands for an oxide of a four- to six-valent metal,

x is a number in the range 0.1 to 1.2 and

y is a number in the range 1 to 12,

wherein the content of the glaze is 0.001 to 2 parts by weight per 100 parts by weight of the thermoplastic resin, the thermoplastic resin composition is markable upon exposure to laser irradiation, and the keys have laser-marked numbers or codes on their surfaces.

Examples of the thermoplastic resins used for the present invention include such resins as polyethylene, polypropylene, ABS and the like for general purposes and such engineering plastics as aromatic saturated polyesters, polycarbonates, polyamides, polyacetals and the like.

Among these, those aromatic saturated polyesters whose main acid component is derived from terephthalic acid, 2,6-naphthalenedicarboxylic acid or their ester-forming derivatives and whose main diol component is composed of at least one aliphatic diol such as ethylene glycol, trimethylene glycol, tetramethylene glycol, hexamethylene glycol, neopentyl glycol and the like are preferred. As for the polyesters, aromatic polyesters having a high crystallization rate, e.g., polybutylene terephthalate, polypropylene terephthalate, polyethylene terephthalate, polybutylene-2,6-naphthalenedicarboxylate are particularly preferred, and most preferred is polybutylene terephthalate.

Such thermoplastic aromatic polyesters may be partially substituted with a copolymerizable component. Examples of the copolymerizable components include aromatic carboxylic acids, e.g., alkyl-substituted phthalic acids such as isophthalic acid, phthalic acid, methylterephthalic acid and methylisophthalic acid, naphthalenedicarboxylic acids such as 2,6-naphthalenedicarboxylic acid, 2,7-naphthalenedicarboxylic acid and 1,5-naphthalenedicarboxylic acid, diphenyldicarboxylic acids such as 4,4'-diphenyldicarboxylic acid and 3,4'-diphenyldicarboxylic acid and diphenoxyethanedicarboxylic acid such as 4,4'-diphenoxyethanedicarboxylic acid, etc., aliphatic or alicyclic dicarboxylic acids such as succinic acid, adipic acid, sebacic acid, aze laic acid, decanedicarboxylic acid, cyclohexanedicarboxylic acid, etc., alicyclic diols such as 1,4-cyclohexanedimethanol, dihydroxybenzenes such as hydroquinone, resorcinol, etc., bisphenol such as 2,2-bis(4-hydroxyphenyl)propane, bis(4-hydroxyphenyl)sulfone, etc., aromatic diols such as ether diol obtained from bisphenols and glycols such as ethylene glycol, and hydroxycarboxylic acids such as ε-hydroxycaproic acid, hydroxybenzoic acid, ethoxyethoxybenzoic acid, etc.

The above-mentioned aromatic polyesters may be further copolymerized with not more than 1.0 mol%, preferably not more than 0.5 mol%, more preferably not more than 0.3 mol% of a polyfunctional ester-forming acid such as trimesic acid, trimellitic acid or the like or a polyfunctional ester-forming alcohol such as glycerin, trimethylolpropane, pentaerythritol, etc., as a branching component.

Preferred polycarbonate resins to be used in the present invention are those derived from dihydric phenols and having a molecular weight in the range of 10,000 to 100,000, more preferably 15,000 to 60,000, in terms of viscosity-average molecular weight. Such polycarbonate resins are usually obtained by reacting dihydric phenols with carbonate precursors according to the solution-phase or melt-phase process.

Examples of dihydric phenols include 2,2-bis(4-hydroxyphenyl)propane (bisphenol-A), 1,1-bis(4-hydroxyphenyl)ethane, 2,2-bis(4-hydroxy-3-methylphenyl)propane and bis(4-hydroxyphenyl)sulfone, etc. Among these, bis(4-hydroxyphenyl)alkanes are preferred, most preferred is bisphenol-A.

The ABS resin used for the invention is selected from known resins formed by adding acrylonitrile and butadiene in various forms to polystyrene. For example, there may be mentioned 1) a mixture of styrene-acrylonitrile copolymer resin (AS resin) with polybutadiene (BR); 2) BR grafted with styrene and acrylonitrile; 3) a molten mixture of AS resin with the aforementioned product 2); and 4) a molten mixture of a butadiene-acrylonitrile copolymer with AS resin as an example.

With respect to the thermoplastic resins to be used in the present invention, polyethylene terephthalate, butylene terephthalate, polybutylene naphthalenedicarboxylate, polycarbonate, polyamide, polyacetal, ABS, polyethylene and polypropylene are particularly preferred. These can be used either alone or as mixtures. The resin composition contains a glaze having the above-mentioned oxide composition and consists of (a) oxides of monovalent or divalent metals, (b) oxides of trivalent metals and (c) oxides of tetravalent to hexavalent metals.

Examples of the oxides of monovalent or divalent metals are K₂O, Na₂O, Li₂O, Cu₂O, CaO, MgO, CoO, PbO, ZnO, BaO, FeO, MnO, CdO, CuO, NiO and SrO.

The oxides of trivalent metals include, for example, Al₂O₃, B₂O₃, Fe₂O₃, Sb₂O₃, Cr₂O₃, Mn₂O₃ and As₂O₃.

The oxides of tetra- to hexavalent metals include, for example, SiO₂, TiO₂, SnO2, ZrO₂, CeO₂, Sb₂O₅, V₂O₅, P₂O₅, UO₃ and MoO₃.

The metal oxide glaze is used in an amount of 0.001 to 2 parts by weight per 100 parts by weight of the thermoplastic resin.

If the amount is less than 0.001 parts by weight, it is difficult to obtain a clear color development, whereas if it exceeds 10 parts by weight, a clear contrast between the unmarked surface of the molded articles and the coloring part is difficult to obtain because the homogeneous marking is impaired or damaged. Both cases are therefore undesirable.

The total content of the glaze is preferably in the range of 0.005 to 2 parts by weight, more preferably 0.01 to 2 parts by weight, per 100 parts by weight of the thermoplastic resin.

The "glaze" which does not have a fixed chemical structure, such as glass, is prepared by calcining the metal oxides (a), (b) and (c) and can be classified into various types or classes, e.g., China glaze and porcelain glaze, etc., according to the type of calcination product, feldspar glaze, lime glaze, etc., according to the starting material which is the source of the main component; or frit glaze, salt glaze, etc., according to the type of production system. It is of little significance to which of these classes the "glaze" state as recited in this invention belongs.

In the process of converting the metal oxides into the glaze state under heating, various phenomena such as dehydration, chemical reaction(s) between and among the solid phases at temperatures below the melting point or the decomposition point, decomposition of carbonates or sulfates, partial fusion of the starting materials, formation of a eutectic mixture, inter-fusion of molten salts, volatilization of a part of the starting components, etc., are involved in a complex manner.

Therefore, when such metal oxides are converted to a glaze state and vitrified, their ability to develop color can be enhanced. Furthermore, the glaze itself can promote the pyrolysis of the resin and develop colors.

The thermoplastic resin composition of the present invention may further contain a black pigment or a black dye in an amount of not more than two parts by weight per 100 parts by weight of the thermoplastic resin.

As for the black pigment or black dye, carbon-based black pigments, black metal oxides and black dyes are usually used. Of these, black metal oxides are more preferred. As for the black metal oxides, low-valence titanium oxides expressed by the formula TinO2n-1 (n = 1 to 5) are preferred. As for such low-order titanium oxides, for example, TiO, Ti₂O₃, Ti₃O₅, Ti₄O₇ and Ti₅O₉ are preferred, with TiOn (n = 1 to 1.99) being particularly preferred.

According to the present invention, other pigments and dyes may also be added, depending on the intended use of the particular composition.

With respect to such other pigments, for example, inorganic pigments, e.g. basic lead carbonate, basic lead sulfate, basic lead silicate, metal sulfide such as lithophone or zinc sulfide, and organic pigments such as azo-, azomethine-, methine-, indanthrone-, anthraquinone-, pyranthrone-, flavanthrone-, benzanthrone-, phthalocyanine-, perinone-, perylene-, dioxadine-, thioindigo-, isoindoline-, isoindolinol-, quinacridone- and quinophthalone-type pigments can be used.

Examples of organic dyes include anthraquinone disperse dyes, metal complexes of azo dyes and fluorescent dyes.

The thermoplastic resin composition of the present invention may further contain, within the range not impairing the objects of the invention, conventional additives such as a glass reinforcing agent, a granular or plate-shaped filler, a flame retardant, a release agent, a lubricant, a slip additive, a nucleating agent, a colorant, an antioxidant, a heat stabilizer, a weathering (light) stabilizer and a modifier such as an impact resistance improving agent, etc.

The thermoplastic resin composition according to the present invention can be obtained by mixing a thermoplastic resin with metal oxides in the prescribed amount by a conventional mixing method. It is preferable to disperse the components to be mixed more uniformly. Specifically, the whole or a part may be mixed simultaneously or separately in a mixing machine such as a mixer, a kneader, a Banbury mixer, a roller, an extruder, etc. to be homogenized. Further, it is also possible to obtain the composition by melt-kneading a composition which has been formed in advance by dry mixing in a heated extruder to homogenize the composition, extruding the melt into a wire shape and then cutting the product into any desired length. Melt processing of the thermoplastic resin composition of the present invention can generally be easily carried out by conventional means using conventional molding machines related to thermoplastic resins.

The present invention will now be explained with reference to the embodiments, but it should not be understood that the invention is limited by the following examples.

In the examples, marking is performed with a YAG laser (Laser Marker SL 475 E2, manufactured by NEC Corporation).

The marking is evaluated according to the degree of color difference (contrast) between a molded article surface and a marking part in which a color was developed after exposure to a laser beam and according to the foaming condition. To determine the color difference, a color analyzer TC-1800 MK-11 manufactured by Tokyo Denshoku Co., Ltd. was used and the result was expressed as a difference in brightness, ΔL*. Regarding the foaming condition, it was determined whether a uniform and fine foam was formed.

[Examples 1-10, comparison example 1-6]

A glaze (metal oxides) as identified later in an amount as specified in Table 1 was added to a thermoplastic resin, melt-kneaded together in an extruder, and pelletized. The articles injection-molded into a disk shape were marked and evaluated for the marking. In Comparative Example 1, carbon was added. In Comparative Example 2, titanium oxide was added, and in Comparative Examples 3 to 6, the thermoplastic resin alone was marked. The results are shown in Table 1 below. Table 1

The information in Table 1 refers to the following starting materials.

(a) Component

a-1) Polybutylene terephthalate (PBT) 7000 N, product of Teijin Limited.

a-2) Polyolefin HA300, product of Tonen K. K.

a-3) ABS SANTAC ST30, product of Mitsui Toatsu Chemicals, Inc.

a-4) Polycarbonate (PC) L1250, product of Teijin Chemicals, Ltd.

b) Component

b-1) Turkish Blue Glaze (main components: Fukushima Feldspar, Silica, Copper Oxide, Barium Carbonate, Asa Kaobin, Lithium Carbonate), product of Towa K. K.

b-2) Glaze

(Main components: SiO₂, Al₂O₃, B₂O₃, PbO, F) Product of Ferro Enamels (Japan) Limited

In the comparison examples:

Comparison example 1)

Carbon manufactured by Mitsubishi Kasei Corporation

Comparison example 2)

Titanium oxide manufactured by Ishihara Sangyo K. K.

In Comparative Example 3, the foaming condition was poor and the coloring parts had high brightness, and therefore the marking of the product was evaluated as "not good". In contrast, in Examples 1 to 7, both the foaming conditions and the brightness of the coloring parts were improved, and the products showed good marking.

On the other hand, in Comparative Example 2, a favorable foaming condition was achieved, but the coloring part had high brightness and a color tone different from those in the embodiments of the present invention.

In Comparative Example 1, good contrast was not obtained because the molded article surface was colored and the marked portion developed a color of high brightness.

Compared with Comparative Example 4, the foaming condition in Example 8 was improved.

Compared with Comparative Example 5, the foaming condition in Example 9 was improved.

While the product or article of Comparative Example 6 was hardly marked, that of Example 10 showed good marking, with the brightness in the coloring part being very low.

Examples 11-18

The various raw materials as shown in Table 2 were dry-blended in advance in the quantitative ratios described above, and the mixtures were each melt-kneaded in a vented twin-screw extruder having a screw diameter of 44 mm under the conditions of a cylinder temperature of 180°C to 260°C, a screw rotation speed of 160 rpm, and a conveying speed of 40 kg/h. The molten mixture was discharged as strands through the die, cooled, and cut to provide pellets for molding.

Using these pellets, key surfaces of personal computers for laser marking were formed with an injection molding machine having an injection capacity of 5 ounces under such conditions of an injection pressure of 800 kg/cm2, a cooling time of 15 seconds and a total molding cycle of 28 seconds.

The results of these experiments are shown in Table 2. Table 2

In Table 2, the information regarding codes a-1, a-3 and b-1 is the same as in Table 1. The other components T-1, T-2, T-3 and T-4 are given below:

T-1) Carbon, Ketjen Black EC 600 JD, manufactured by Lion Corporation

T-2) Titanium oxide black, M-1, manufactured by Ishihara Sangyo K. K.

T-3) a gray pigment manufactured by Dainichi Seika Kogyo K. K.

T-4) an ivory-colored pigment manufactured by Dainichi Seika Kogyo K. K.

The rating information in Table 2 has the following meanings:

: excellent property regarding the development of a black colour

X: poor property regarding the development of a black color or black color

Claims (7)

1. A keyboard with keys constructed from a thermoplastic resin composition, wherein the thermoplastic resin composition (i) a thermoplastic resin and (ii) a glaze having an oxide composition represented by the following formula: R1-2O xR'2O3 · yR"O&sub2;&submin;&sub3; wherein R₁₋₂O represents an oxide of a monovalent or divalent metal, R'₂O₃ represents an oxide of a trivalent metal, R"O₂�min;₃ stands for an oxide of a four- to six-valent metal, x is a number in the range 0.1 to 1.2 and y is a number in the range 1 to 12, and wherein the content of the glaze is 0.001 to 2 parts by weight per 100 parts by weight of the thermoplastic resin, the thermoplastic resin composition is markable after exposure to laser irradiation and the keys have laser-marked numbers or codes on their tops. 2. A method of manufacturing keys of a keyboard comprising exposing the keys made of a thermoplastic composition to laser irradiation to form sharp laser markings on the keys, wherein the thermoplastic resin composition (i) a thermoplastic resin which is at least one member selected from the group consisting of polyethylene terephthalate, polybutylene terephthalate, polybutylene naphthalenedicarboxylate, polycarbonate, polyamide, polyacetal, ABS, polyethylene and polypropylene, and (ii) a glaze having an oxide composition represented by the following formula: R1-2O xR'2O3 · yR"O&sub2;&submin;&sub3; wherein R₁₋₂O represents an oxide of a monovalent or divalent metal, R'₂O₃ represents an oxide of a trivalent metal, R"O₂�min;₃ represents an oxide of a tetra- to hexavalent metal, x is a number in the range 0.1 to 1.2 and y is a number in the range 1 to 12, wherein the content of the glaze is 0.001 to 2 parts by weight per 100 parts by weight of the thermoplastic resin and the thermoplastic resin composition is markable after exposure to laser irradiation. 3. A keyboard with keys constructed from a thermoplastic resin composition, wherein the thermoplastic resin composition (i) a thermoplastic resin which is at least one member selected from the group consisting of polyethylene terephthalate, polybutylene terephthalate, polybutylene naphthalenedicarboxylate, polycarbonate, polyamide, polyacetal, ABS, polyethylene and polypropylene, and (ii) a glaze comprising an oxide composition represented by the following formula: R1-2O xR'2O3 · yR"O&sub2;&submin;&sub3; wherein R₁₋₂O represents an oxide of a monovalent or divalent metal, R'₂O₃ represents an oxide of a trivalent metal, R"O₂�min;₃ represents an oxide of a tetra- to hexavalent metal, x is a number in the range 0.1 to 1.2 and y is a number in the range 1 to 12, wherein the oxide of a monovalent or divalent metal selected from the group consisting of K₂O, Na₂O, Li₂O, Cu₂O, CaO, MgO, CoO, PbO, ZnO, BaO, FeO, MnO, CdO, CuO, NiO and SrO, the oxide of a trivalent metal selected from the group consisting of Al₂O₃, B₂O₃, Fe₂O₃, Sb₂O₃, Cr₂O₃, Mn₂O₃ and As₂O₃, and the oxide of a four- to six-valent metal is selected from the group consisting of SiO₂, TiO₂, SnO2, ZrO₂, CeO₂, Sb₂O₃, V₂O₅, UO₃ and MoO₃, wherein the content of the glaze is 0.001 to 2 parts by weight per 100 parts by weight of the thermoplastic resin, the thermoplastic resin composition is markable after exposure to laser irradiation and the keys have laser-marked numbers or codes on their tops. 4. A method of manufacturing keys of a keyboard comprising exposing the keys made of a thermoplastic composition to laser irradiation to form sharp laser markings on the keys, wherein the thermoplastic resin composition (i) a thermoplastic resin which is at least one member selected from the group consisting of polyethylene terephtha lat, polybutylene terephthalate, polybutylene naphthalenedicarboxylate, polycarbonate, polyamide, polyacetal, ABS, polyethylene and polypropylene, and (ii) a glaze having an oxide composition represented by the following formula: R1-2O xR'2O3 · yR"O&sub2;&submin;&sub3; wherein R₁₋₂O represents an oxide of a monovalent or divalent metal, R'₂O₃ represents an oxide of a trivalent metal, R"O₂�min;₃ represents an oxide of a tetra- to hexavalent metal, x is a number in the range 0.1 to 1.2 and y is a number in the range 1 to 12, wherein the oxide of a monovalent or divalent metal selected from the group consisting of K₂O, Na₂O, Li₂O, Cu₂O, CaO, MgO, CoO, PbO, ZnO, BaO, FeO, MnO, CdO, CuO, NiO and SrO, the oxide of a trivalent metal selected from the group consisting of Al₂O₃, B₂O₃, Fe₂O₃, Sb₂O₃, Cr₂O₃, Mn₂O₃ and As₂O₃, and the oxide of a four- to six-valent metal are selected from the group consisting of SiO₂, TiO₂, SnO₂, ZrO₂, CeO₂, Sb₂O₃, V₂O₅, UO₃ and MoO₃, and wherein the content of the glaze is 0.001 to 2 parts by weight per 100 parts by weight of the thermoplastic resin and the thermoplastic resin composition is markable after exposure to laser radiation. 5. A keyboard having keys with sharp markings, wherein the keys are constructed of a thermoplastic resin composition and the sharp markings on the keys are formed by exposing the keys to laser irradiation, wherein the thermoplastic resin composition (i) a thermoplastic resin which is at least one member selected from the group consisting of polyethylene terephthalate, polybutylene terephthalate, polybutylene naphthalenedicarboxylate, polycarbonate, polyamide, polyacetal, ABS, polyethylene and polypropylene, and (ii) a glaze having an oxide composition represented by the following formula: R1-2O xR'2O3 · yR"O&sub2;&submin;&sub3; wherein R₁₋₂O represents an oxide of a monovalent or divalent metal, R'₂O₃ represents an oxide of a trivalent metal, R"O₂�min;₃ represents an oxide of a tetra- to hexavalent metal, x is a number in the range 0.1 to 1.2 and y is a number in the range 1 to 12, wherein the oxide of a monovalent or divalent metal selected from the group consisting of K₂O, Na₂O, Li₂O, Cu₂O, CaO, MgO, CoO, PbO, ZnO, BaO, FeO, MnO, CdO, CuO, NiO and SrO, the oxide of a trivalent metal selected from the group consisting of Al₂O₃, B₂O₃, Fe₂O₃, Sb₂O₃, Cr₂O₃, Mn₂O₃ and As₂O₃, and the oxide of a four- to six-valent metal are selected from the group consisting of SiO₂, TiO₂, SnO₂, ZrO₂, CeO₂, Sb₂O₃, V₂O₅, UO₃ and MoO₃, and wherein the content of the glaze is 0.005 to 2 parts by weight per 100 parts by weight of the thermoplastic resin and the thermoplastic resin composition is markable after exposure to laser radiation. 6. A method of manufacturing keys of a keyboard comprising subjecting the keys made of a thermoplastic resin composition to laser irradiation to form sharp laser markings. to form on the keys, wherein the thermoplastic resin composition (i) a thermoplastic resin and (ii) a glaze having an oxide composition represented by the following formula: R1-2O xR'2O3 · yR"O&sub2;&submin;&sub3; wherein R₁₋₂O represents an oxide of a monovalent or divalent metal, R'₂O₃ represents an oxide of a trivalent metal, R"O₂�min;₃ represents an oxide of a tetra- to hexavalent metal, x is a number in the range 0.1 to 1.2 and y is a number in the range 1 to 12, wherein the content of the glaze is 0.001 to 2 parts by weight per 100 parts by weight of the thermoplastic resin and the thermoplastic resin composition is markable after exposure to laser radiation. 7. A keyboard according to any one of claims 1, 3 and 5, wherein the thermoplastic resin composition further comprises a black pigment or a black dye in an amount of not more than 2 parts by weight per 100 parts by weight of the thermoplastic resin, the black pigment having the following formula: TinO2n-1 where n is an integer from 1 to 5.