Provided is a composition useful for obtaining a high gloss coating, for example, a high gloss paint. The composition includes an isocyanate which is at least partially masked by one or more masking agent, and having a degree of liberation with respect to the masking agent at 120 xc2x0 C. of 5 % or less. A polyol has a glass transition temperature of about 40xc2x0 C. or more, a hydroxyl number of about 20 mg KOH/g or more and an average molecular weight Mn of about 500 g/mol or more. Also provided is a process for preparing the composition, wherein the isocyanate, the polyol and any other components are preblended in a blender. The polyol and other meltable components of the blend are melted, homogenized and dispersed in an extruder having one or more screws. Further provided are paint compositions, wherein the paint is a high gloss paint. The compositions are environmentally friendly and result in high gloss coatings having beneficial mechanical properties.

1. Field of the Invention
The present invention relates to a novel family of compositions containing masked isocyanates and polyols. The invention relates more particularly to powders, including mixtures of powders, and to their use as powders in coatings such as paints, particularly to high gloss coatings and paints.
2. Description of the Related Art
For reasons associated with protection of the environment and safety at work, it is increasingly sought to eliminate the use of solvents in coating techniques and particularly in paints. More particularly, reducing VOCs (Volatile Organic Compounds) is an increasingly current preoccupation in the paint and varnish industry. With this aim, the development of products with higher solids content makes it possible to decrease the amounts of solvents required to achieve the application viscosity, and thus to reduce the solvents evaporated during drying of paint film.
Another alternative is to use products in aqueous phase in which the water has replaced the organic solvents as the agent carrying the organic binder. However, a small amount of organic solvent is required to use and form the film of paint. Furthermore, they give rise to water-soluble residues which may be tricky and expensive to process.
In this context, coating techniques using powders are increasingly being developed. A few details of this technique should be given herein in order to gain a better understanding of the present invention. The technique uses a very finely powdered material for which air acts as a vector.
In general, an electrostatic charge of several kilovolts applied between a gun and the article to be painted allows the coating precursor powder, which is to be sprayed by the applicator gun, to be attracted and retained.
Firing of the article between 150 and 200xc2x0 C. allows melting, spreading and then crosslinking of the paint powder (paint being considered the ultimate example for coatings) in order to obtain a uniform and homogeneous layer of the coating.
This technique is non-polluting and has an application yield of close to 100% by virtue of the possibility of recycling the unused powder.
Among the families of products which may be used in this field, mention should be made of the following. The majority of the market is occupied by so-called xe2x80x9cepoxy-polyester hybridxe2x80x9d powder paints, followed by polyesters and polyurethanes, and then so called xe2x80x9cepoxyxe2x80x9d powders.
In order to obtain good quality strength on exteriors (in particular with respect to UV radiation and moisture), it is essential to use coatings based on TGIC (triglycidyl isocyanurate)- polyester or polyurethane which, alone, makes it possible to achieve the required levels of performance.
The coating powders may be in several finishes (surface, aspect, color, sheen, etc.). For example, copending application Ser. No. 09/240,598, filed Feb. 1, 1999, now U.S. Pat. No. 6,291,624, the entire contents of which are herein incorporated by reference, describes compositions for obtaining matt or satin coatings. Such coatings are defined therein as having a coefficient of reflection which is at most equal to about 50% at a 60xc2x0 angle of incidence.
The compositions of interest in the present case can advantageously provide high gloss coatings. As used herein, a high gloss coating is one which, when applied to a metal support and after crosslinkling, has a coefficient of reflection which is greater than 80%, preferably greater than 85%, more preferably greater than 90% and most preferably greater than 95%, for a 60xc2x0 angle of incidence.
For further details regarding the techniques of powder painting, reference may be made to the following books: P. Grandou and P. Pastour, Peintures et Vernis [Paints and Varnishes], I les constituents, II techniques et industries [techniques and industries]; pub. Hermann; R. Lambourne, Paints and Surface Coatings, theory and practice, pub. Halsted Press; Powder Coating, The Complete Finisher Hand Book, the Powder Coating Institute; and Myers and Long, Treatise on Coatings, 5 volumes, pub. Marcel Dekker.
U.S. Patent No. 3,991,034, to Takeo et al, discloses a polyester resin composition suitable for preparing a powder paint, which comprises a polyester and a polyisocyanate blocked with an alkyl p-hydroxybenzoate. The composition is characterized as being a thermosetting polyester resin composition. The alcohol functionality and the extent of crosslinking of the disclosed compositions are relatively low. The mechanical properties of the coatings formed are therefore lacking.
To overcome or conspicuously ameliorate the problems associated with the related art, it is an object of the invention is to provide compositions which make it possible to obtain high gloss coatings with superior mechanical properties. The compositions are easy to use, and the coatings which can be obtained therefrom advantageously have a high gloss finish and good weather resistance.
It is a further object of the invention to provide a process for preparing the compositions.
It is a further object of the invention to provide paint compositions wherein the paint is a high gloss paint. The paint compositions can be prepared by the so-called powder technique using the inventive compositions.
Other objects and aspects of the present invention will become apparent to one of ordinary skill in the art on a review of the specification and claims appended hereto.
These aims and others which will appear hereinbelow are achieved by provision of a composition useful for obtaining a high gloss coating. The composition features an isocyanate which is at least partially masked by one or more masking agent, and having a degree of liberation with respect to the masking agent at 120xc2x0 C. of 5% or less. A polyol has a glass transition temperature of about 40xc2x0 C. or more, a hydroxyl number of about 10 mg/g or more and an average molecular mass Mn of about 500 g/mol or more.
In accordance with a further aspect of the invention, a composition useful for obtaining a high gloss coating is provided. The composition features an isocyanate which is at least partially masked by one or more masking agent, having a glass transition temperature of about 20xc2x0 C. or more. A polyol has a glass transition temperature of about 40xc2x0 C. or more, a hydroxyl number of about 10 mg/g or more and an average molecular mass Mn of about 500 g/mol or more. At least one of the following conditions apply:
the composition further comprises a carboxylic function, with the proviso that, when the carboxylic acid function which is free or in the form of a salt, is greater than 30 mg KOH/g, the amine content is lower than 0.6% (equivalent) of the isocyanate (masked and free);
the composition is essentially free of an esterification, catalyst, especially a carbamatation catalyst, which is solid and/or non-liposoluble;
the composition is essentially free of a matt-effect wax; and
the composition further comprises a liposoluble catalyst.
According to a further aspect of the invention, a process for preparing the compositions is provided. The process involves the steps of preblending the isocyanate, the polyol and any other components in a blender, and melting, homogenizing and dispersing the polyol and other meltable components of the blend in an extruder having one or more screws.
In accordance with a further aspect of the invention, high gloss paint compositions comprising the composition are provided.
As used herein, the term xe2x80x9caboutxe2x80x9d is used to emphasize the fact that the value is rounded up and that, when the figure(s) furthest to the right of a number are zeros, these zeros are positional zeros and not significant figures unless, of course, otherwise stated.
Also as used herein, the term xe2x80x9cessentially freexe2x80x9d means that the component in question is absent from the composition, or is present in such an insignificant amount that a high gloss coating can be obtained from the composition.
A carboxylic function is advantageously in intimate mixture with the a isocyanate component of the composition. It is even desirable for a carboxylic function to be grafted onto the isocyanate system via an agent bearing both a reactive function (i.e., having a so-called labile hydrogen) with the isocyanate function and a carboxylic function (COOH in salt form or, advantageously, in free form). It is highly desirable for this agent bearing a carboxylic function to be a masking agent.
It is preferable for the masking group to bear the labile hydrogen which reacts with the isocyanate function via an oxygen in order to give the sequence xe2x80x94NHxe2x80x94COxe2x80x94Oxe2x80x94(i.e., Rxe2x80x94NCO+HOxe2x80x94 greater than Rxe2x80x94NHxe2x80x94COxe2x80x94Oxe2x80x94).
According to the present invention, a composition useful for obtaining a high gloss coating includes an isocyanate and a polyol. The isocyanate is advantageously masked with at least one masking group bearing at least one ester function derived from acid functions and especially acid and ester functions. The masking may be mixed and may involve several masking groups.
The masked isocyanate has a xe2x80x9cliberationxe2x80x9d or xe2x80x9cdeblockingxe2x80x9d temperature, typically quantified by the octanol test (described below), which is the lowest temperature at which the masking agent of the masked isocyanate is {fraction (9/10)} (mathematically rounded-up) displaced by a primary monoalcohol (generally octanol).
In order to ensure a good shelf life, it is preferable to choose masked isocyanate functions whose octanol test shows a xe2x80x9cliberationxe2x80x9d at 80xc2x0 C., advantageously at 90xc2x0 C., which is at most equal to 90%.
In the structure of the isocyanate(s), it is desirable for the part of the skeleton connecting two isocyanate functions to contain at least one polymethylene chain (CH2) xcfx80, where xcfx80 represents an integer from 2 to 10, advantageously from 4 to 8. This preference results in improved mechanical performance levels. When there are several chains, they may be similar or different. In addition, it is desirable for at least one and preferably all of these chains to be free to rotate and thus be exocyclic.
According to the present invention, the masked isocyanate, pure or as a mixture, is derived from a polyisocyanate; that is to say a compound having at least two isocyanate functions, advantageously more than two. Fractional values are possible since a mixture of more or less condensed oligomers is generally present. This polyisocyanate itself is usually derived from a precondensation or a prepolymerization of unitary diisocyanate (occasionally referred to in the present description as xe2x80x9cmonomerxe2x80x9d).
In general, the average molecular mass of these prepolymers or precondensates is 2000 or less (one significant figure), more commonly 1000 or less (one significant figure, preferably two).
Thus, among the polyisocyanates used for the invention, mention may be made of those of the biuret type and those whose di- or trimerization reaction has led to four-, five- or six-membered rings. Among the six-membered rings, mention may be made of the isocyanuric rings obtained from a homo- or a hetero-trimerization of various diisocyanates alone, with other isocyanate(s) (mono-, di-or polyisocyanate(s)) or with carbon dioxide, in which case a nitrogen of the isocyanuric ring is replaced by an oxygen. Oligomers containing isocyanuric rings are preferred.
The preferred polyisocyanates are those which have at least one aliphatic isocyanate function. In other words, at least one isocyanate function masked according to the invention is connected to the skeleton via an sp3-type carbon advantageously bearing a hydrogen atom, preferably two. It is desirable for the sp3-type carbon itself to be borne by an sp3-type carbon and advantageously carry dio one, preferably two, hydrogen atoms, in order to prevent the isocyanate function from being in a neopentyl position. In other words, it is recommended to choose as the monomer (which, in general, bear two isocyanate functions) at least one compound which bears at least one aliphatic function which is neither secondary nor tertiary nor neopentyl.
In the case of a mixture obtained from several (generally two) types of monomers, it is preferable that the monomers satisfy the above conditions and/or (advantageously xe2x80x9candxe2x80x9d) a condition regarding the presence of a polymethylene chain (CH2) xcfx80, to represent at least ⅓, advantageously xc2xd, preferably ⅔ of the masked isocyanate functions. Excellent results can be obtained with mixtures containing two-thirds HMDT (hexamethylene diisocyanate trimer) with IPDI (isophorone diisocyanate) or IPDT (isophorone diisocyanate trimer), the two being masked according to the invention. nBDI (norbornane diisocyanate) and its trimer are similar to the IPDI and IPDT.
The case in which all of the isocyanates are aliphatic and satisfy the above criterion is preferred.
The agents leading to the masking groups characteristic of the invention are advantageously selected from those which are obtained from the condensation of an aromatic derivative hydroxylated on the ring and bearing a function chosen from nitrile and, preferably, carbonyl functions with an isocyanate. The condensation takes place on the phenol function.
Among the members of the family of masked isocyanates, it is convenient to choose those for which an apparent melting point may be determined, this measurement being carried out at room temperature (20xc2x0 C.). This melting point should be 30xc2x0 C. or more (one significant figure), advantageously 50xc2x0 C. or more
It is preferable to choose an agent from among those of formula (I):
Ar(R)n(Yxe2x80x94Z)m(OH)pxe2x80x83xe2x80x83(I)
where Ar is an aromatic residue on which are grafted n substituents R, m polar functions Z selected from nitriles and carbonyl groups, and p hydroxyl functions.
Values of n, m and p are such that the sum n+m+p is at most equal to the number of substitutable chain members; p is advantageously at most equal to two and is preferably equal to one.
Advantageously, m is at most equal to two and is preferably equal to one.
Advantageously, n is at most equal to three, preferably chosen from zero, one and two, and is more preferably equal to zero.
R represents substituents that are inert towards the masking reaction and, in general, corresponds to hydrocarbon chains, usually alkyl chains in the etymological sense of the term, namely an alcohol whose hydroxyl function has been removed.
Two vicinal substituents R may be connected together to form a ring which may, for example, be aromatic.
Z is advantageously selected from groups having a carbonyl function. Among these functions, mention should be made of alkoxycarbonyl functions (ester functions), amide functions, ketone functions, with the preferred condition that there be acidic hydrogens [that is, the function advantageously does not bear hydrogen or, if it does, the corresponding pKa is at least equal to about 20 (one significant figure, preferably two), and more preferably at least equal to about 25] xcex1 to the carbonyl function (ester, ketone or amide). Thus, the preferred amides (including lactam or even urea) are advantageously substituted, preferably, sufficiently for there to be no hydrogens on the nitrogen of the amide function or such that there be no reactive hydrogens.
Y is chosen from divalent groups, advantageously xe2x80x94Oxe2x80x94, xe2x80x94Sxe2x80x94, xe2x80x94NRxe2x80x94 and xe2x80x94CRxe2x80x2Rxe2x80x3xe2x80x94 with Rxe2x80x2 and Rxe2x80x3 selected from hydrocarbon radicals, advantageously alkyls, of 1 to 6 carbon atoms, advantageously of 1 to 4 carbon atoms, preferably methyl, more preferably hydrogen; and preferably Y represents a single bond.
It is preferable for the polar function(s) Z (generally chosen from the nitrile function and/or the carbonyl functions) not to be vicinal to the group Z as, for example, in salicylic acid.
The aromatic residue Ar comprises one or more hetero- or homocyclic, advantageously fused rings. It is preferable for Ar not to contain more than two rings and preferably not more than one ring.
The aromatic residue Ar may consist of one or more heterocyclic or homocyclic rings, usually homocyclic on account of their ease of access. The value of six-membered heterocycles, which have a liberation temperature very much lower than that of the corresponding homocycles, should, however, be pointed out.
It is desirable for the total number of carbons in the aromatic derivative hydroxylated on the ring to be at most equal to 20, preferably equal to 10 (one significant figure).
This ring is advantageously six-membered, the ring units consisting of carbon or nitrogen with the number of substituents required for the valency of these atoms.
Among the acids and derivatives, especially esters, which give the most satisfactory results, mention should be made of acids grafted onto a benzene ring. Thus, meta-hydroxybenzoic acid and, especially, para-hydroxybenzoic acid, and their derivatives, give good results.
As has been mentioned above, it is possible to provide several groups (preferably two for economic reasons) masking the isocyanate functions. This diversity may be achieved by mixing various masked (in general with only one masking group) compounds or preferably by coreaction. These masking groups may all be as defined above or only some of them may correspond to this definition. In the latter case, it is preferable for those (that is to say the sum of those) which bear a carbonyl (ester or acid) function advantageously to correspond to the above formula (I) and to correspond to at least about 10% (expressed as blocked isocyanate function), advantageously to about 20%, preferably to one third.
The presence of a carboxylic acid function (xe2x80x94COOH) and in particular of a carboxylic acid function grafted directly onto an aromatic ring, preferably a benzene ring, makes it possible to increase the melting point of the blocked isocyanate. However, it is preferable, in order to retain the excellent mechanical properties of the system according to the present invention, for the amount of acid function present (in terms of equivalents) to be at most equal to about {fraction (9/10)}, advantageously to about ⅘, preferably to ⅔, more preferably one third of the isocyanate functions. When the carboxylic functions are borne by agents which are not released under the baking conditions, in order to preserve the crosslinking power, it is desirable for the amount of acid borne by the agents which is not released to be not more than xc2xd, advantageously ⅓, of the total amount of isocyanate functions (free, masked, associated with an unreleasable masking agent (e.g., aminocaproic acid).
The beneficial effects of the acid functions on the glass transition temperature (Tg) can be obtained from 5% (equivalent) of the isocyanate functions present, preferably from about 10% (equivalent) of the isocyanate functions present, and most preferably from at least 20% (equivalent) of the isocyanate functions present, to obtain an effect which is close to the inflection point of the curve. The melting point and the glass transition temperature (Tg) continually overlap with the acid content up to 100% (equivalent) of the isocyanate functions present.
In the case involving an ester/acid couple, and in particular in the case involving an alkyl hydroxybenzoate/hydroxybenzoic acid couple, beneficial properties can be obtained in the region of a {fraction (90/10)} molar ratio; i.e., about {fraction (9/10)} of ester and about {fraction (1/10)} of acid. The presence of the acid functions to a level of about {fraction (1/10)}, in particular carboxylic, allows good catalysis of the crosslinking.
The effects outlined above for the isocyanate compounds masked with two or more masking agents can be obtained either with a mixture of two or more to isocyanates masked with a single masking agent or with isocyanates masked simultaneously or successively with two or more masking agents. The latter case gives better results correlated to the existence of so-called mixed molecules, i.e., molecules for which at least one of the isocyanate functions is masked with a group bearing an acid function and in which at least one of the other isocyanate functions is masked with a group not bearing an acid function. The positive effects of the presence of these so-called mixed molecules are experienced once they correspond to (i.e., once they bear) about 5% of the isocyanate functions, advantageously 10%.
Thus, one of the most advantageous uses of the present invention comprises using isocyanates which are at least partially masked by a compound bearing an acid function, advantageously by a compound of formula I where Z is an acid function. It is recommended that the isocyanate then be masked by a group other than that bearing the acid function, and that the acid function of the masking system be between 90 and 10% (expressed as blocked isocyanate function), the other masking agent or agents may be either masking agents which are known per se (which satisfy the liberation temperature and the unmasking constraints specified in the present description), or an ester corresponding to formula I. The latter alternative form is preferred. For the synthesis of these compounds, reference may be made to the general procedures of patent application No. EP 0 680 984 A, the entire contents of which are incorporated herein by reference, which gives good results for the operation of (optionally partial) masking by a compound of formula I.
The masking agents most commonly used are those mentioned in M. Wicks, xe2x80x9cBlocked Isocyanates,xe2x80x9d Process in Organic Coatings, Vol. 3 (1975), p. 731. Their deblocking temperature is advantageously greater than 90xc2x0 C.
The masking agents can be divided into three groups:
those in which the labile hydrogen is borne by a chalcogen;
those in which the labile hydrogen is borne by nitrogen; and
those in which the labile hydrogen is borne by carbon.
Among those in which the labile hydrogen is borne by a chalcogen, preferably a light chalcogen (i.e., sulphur and oxygen), typically oxygen is used. Among the latter, mention may be made in particular of:
products containing an  greater than Nxe2x80x94OH sequence, such as, for example, oximes (=Nxe2x80x94OH) or hydroxyimides ([xe2x80x94COxe2x80x94]2Nxe2x80x94OH);
phenols (in the strict sense), especially those in which the aromatic ring is electron-poor, such as the hydroxybenzoates described by the present invention; and
mention may also be made of the compounds described in application EP-A-661,278.
Among those in which the labile hydrogen is borne by a nitrogen, mention may be made in particular of:
monosubstituted amides, and in particular lactams, typically caprolactam; imides ([xe2x80x94COxe2x80x94]2Nxe2x80x94H), especially cyclic imides such as succinimide;
unsaturated nitrogenous heterocycles which are, in particular, 5-membered (advantageously diunsaturated), preferably containing at least two hetero atoms (preferably nitrogen); among the latter, mention may be made of diazoles (such as glyoxalines and pyrazoles), triazoles or even tetrazoles; and
mention may also be made of the compounds described in application EP-A-661,278.
The masking agents in which the labile hydrogen is borne by carbon are essentially compounds of malonic nature, i.e., a radical RCH less than  bearing two electron-withdrawing groups (such as carbonyl, nitrile, Rf. i.e., perfluoroalkyl).
The above masking agents (alone or as a mixture) can be used to carry out the present invention provided that the following two conditions are satisfied:
they are combined with an agent (advantageously a masking agent) bearing carboxylic functions) and a reactive function (which can advantageously be released on baking) with the isocyanate functions (with the preferences indicated in the present description);
the compounds obtained from the reaction between the isocyanate, on the one hand, and the masking agent and the agent bearing carboxylic functions), on the other hand, has the required glass transition temperature (Tg) and melting point.
One of the advantages of using carboxylic groups according to the present invention lies in the fact that it allows masking groups to be used which, in the absence of carboxylic group, would not have a sufficient melting point or glass transition temperature (Tg) for use in powder application. This is the case in particular for triazoles, which, when they are unsubstitulted (each of the isomers alone or as a mixture in any proportion of the isomers), are particularly cost-effective.
When only one masking agent is used, it is desirable for this to be a compound according to formula I where Z is ester, with the preferences indicated in patent application No. EP 0 680 984 A, page 2, lines 41 to 50.
As has already been mentioned according to the present invention, it is preferable for the melting point of the compound or of the mixture of compounds obtained to have an apparent melting point which is at least equal to about 30xc2x0 C., preferably 50xc2x0 C.
It is also preferable for the glass transition temperature to be 10xc2x0 C. or, more preferably 20xc2x0 C. or more, and more preferably 25xc2x0 C. or more.
It is preferable to choose the compounds according to the present invention such that they react completely with a primary alcohol at 250xc2x0 C. in less than half an hour.
For purposes herein, the reaction is considered to be complete if it proceeds to 90% or more.
As has been mentioned above, the isocyanates for which the invention is most advantageous are those whose nitrogen atom is linked to a carbon of Sp3 hybridization, and more particularly aliphatic isocyanates, and especially polymethylene diisocyanates (for example TMDI [tetramethylene diisocyanate] and HMDI [hexamethylene diisocyanate=OCNxe2x80x94(CH2)6xe2x80x94NCO]) and their various condensation derivatives (biuret and the like) and di- and trimerization derivatives (in the field under consideration the term triner refers to mixtures derived from the formation of isocyanuric rings from three isocyanate functions; in fact, along with the actual trimer, there are heavier products derived from the trimerization).
According to the present invention, it is desirable for the percentage of residual free isocyanate function to be 5% (equivalent) or less, advantageously 3% (equivalent) or less, preferably 1% (equivalent) or less. As used herein, the term xe2x80x9ccompletely blockedxe2x80x9d means that the residual free isocyanate function is about 5% (equivalent) or less.
The highest melting points or glass transition temperatures are obtained with a percentage of residual free isocyanate function not exceeding 0.5%. The contents of aromatic derivative hydroxylated on the ring are also advantageously low, that is to say 5% or less, advantageously 3% or less, preferably 1% or less.
On the other hand, the presence in the isocyanate of unmasked trimers of cycloaliphatic monomers such as IPDT or nBDT up to a content of ⅓ by weight have a favorable effect on the glass transition temperature (Tg) and do not in any way hinder the production of a high-quality coating. Such compositions can readily be obtained by mixing the unmasked trimer in the molten masked compound.
The compositions in accordance with the invention further include a polyol compound (also referred to herein as xe2x80x9cresinxe2x80x9d, xe2x80x9cpolymerxe2x80x9d and xe2x80x9chydroxylated polymerxe2x80x9d). Polyol compounds which may be used are those which can provide powder paints or powder varnishes having a high gloss, such as hydroxylated acrylic resins and/or linear or branched, hydroxylated, saturated or unsaturated polyesters having an appropriate molecular weight and capable of being crosslinked by a reaction with the isocyanate prepolymer which is at least partially masked.
As described above, the isocyanate prepolymer is provided with masked (or blocked) active functions and it is activated thermally by liberation of the blocking agent, by exchanging the isocyanate groups which react with the hydroxyl groups of the binder, in the presence or absence of catalysts.
This system makes it possible to obtain powder paints having a suitable viscosity on melting and a glass transition temperature of about 40xc2x0 C. or more, thereby allowing for chemical and physical stability during storage.
The possible functionality of the carboxyl function, which defines the molecular weight of the polymer, thus allows a double-crosslinking with aromatic or aliphatic epoxy resins and/or hydroxyalkylamides.
The content of acidic groups is determined by the acid number of the material, expressed in milligrams of potassium hydroxide required to neutralize the free acidity of one gram of polyol.
The acid number of the polyol is typically about 20 mg KOH/g or less, advantageously 15 mg KOH/g or less. It is also advantageously 2 mg KOH/g or more, preferably 4 mg KOH/g or more. Hydroxylated polymers whose acid number is between 3 and 15 mg KOH/g can advantageously be used.
The hydroxyl number corresponds to the milligrams of potassium hydroxide required per gram of resin in order to neutralize the excess acetic acid liberated during acetylation (with acetic anhydride) of the hydroxylated polymer. For further details, reference may be made to standard ASTM-E222.
The hydroxyl number of the hydroxylated polymer is typically about 20 mg KOH/g or more, preferably about 30 mg KOH/g or more, and more preferably about 40 mg KOH/g or more. The upper limit is typically 400 mg KOH/g or less.
The glass transition temperature of the polyol is typically 40xc2x0 C. or more, preferably 40xc2x0 C. to 100xc2x0 C.
The number-average molecular weight Mn of the polyol is typically about 500 g/mol or more, preferably from about 1000 to 6000 g/mol. The molecular weight is determined by gel permeation chromatography (GPC). The technique uses, as gels, two polystyrene gels (Ultrastyragel(copyright) at 104 and 500 {dot over (A)}), THF as the solvent and sulphur as the standard.
When the composition in accordance with the invention is used as a coating composition, for example, as a paint composition, the isocyanate and the polyol are components of a binder. The glass transition temperature of the binder is typically from 20xc2x0 C. to 100xc2x0 C., preferably from 40xc2x0 C. to 100xc2x0 C.
The number-average molecular weight Mn of the binder is advantageously from 500 to 15,000 g/mol.
Its degree of branching, i.e., the average number of free OH functions per molecule of the hydroxylated polymer is between 2 and 4. It is desirable for the degree of branching to be between 2 and 4, advantageously between 2.5 and 3.5.
Branching may be obtained using polyols having a functionality of more than two (in general triols) or polyacids (often used in the form of anhydride in order to reduce the amount of water released during the reaction) having a functionality of more than two. In particular, trimellitic acid, especially in the form of anhydride is very favorable.
In the case of hydroxylated polyesters, the product of the esterification of one or more aliphatic, aromatic or cycloaliphatic di- or polycarboxylic acids or anhydrides or their methyl esters, which contain 2 to 36 carbon atoms, is used. For example, mention may be made of adipic acid, succinic acid, sebacic acid, suberic acid, azelaic acid, decanedicarboxylic acid, glutaric acid, terephthalic acid, isophthalic acid, phthalic acid or anhydride, naphthalenedicarboxylic acid, hexahydrophthalic acid or anhydride, 1,4-cyclohexanedicarboxylic acid, dimerized fatty acids and trimellitic anhydride.
The molecular weight of the polymer may be adjusted by adding aliphatic or aromatic monocarboxylic acids, or their methyl esters, having 2 to 18 carbon atoms.
The percentage of the acid(s) or anhydride(s) described above within the polymer mixture is from 20 to 70%, preferably from 30 to 60%, taken individually or mixed.
If the polymer of the present invention is unsaturated, di- or polycarboxylic acids or anhydrides unsaturated as olefins, such as maleic acid or anhydride, tetrahydrophthalic acid or anhydride, fumaric acid, hexachloroendomethylenetetrahydrophthalic acid or anhydride, methylmaleic acid, itaconic acid or derivatives of dicyclopentadiene, or of methylmaleic, itaconic, maleic or fumaric acid may be used.
Among the polyhydroxylated alcohols which are useful for synthesizing the polyester are: ethylene glycol, 1,2- or 1,3-propylene glycol, 2-methylpropanediol, diethylene glycol, dipropylene glycol, 1,4-butanediol, 2,3-butylene glycol, 1,6hexanediol, 1,5-pentanediol, neopentyl glycol, cyclohexanedimethanol, triethylene glycol, neopentyl glycol hydroxypivalate, tetraethylene glycol, polyethylene glycol, polypropylene glycol, dibutylene glycol or polyethylene glycols, trimethylpentanediol, butylethylpropanediol, glycerol, trimethylolpropane, hexanetriol, pentaerythritol, sorbitol, trimethylolethane and tris(2-hydroxyethyl) isocyanurate. The percentage of these may range between 10 and 60% by weight based on the composition, preferably between 10 and 50% by weight.
For the preparation of the polyesters, and in particular during creation or conversion of the ester bond, it is indicated to use catalysts which are known xe2x80x9cper sexe2x80x9d for the esterification; these catalysts, which may be found in the final composition if not filtered, may be used alone or as a mixture. The composition is preferably essentially free of catalysts which would adversely affect the desired sheen (i.e., high gloss) of coatings formed from the composition. Such catalysts which are to be avoided include, for example, those of low liposolubility and solid form. The low liposoluble catalysts are only sparingly soluble or are insoluble in the media (e.g., chlorobenzene+octanol) of the octanol test (see below). Thus, the esterification catalyst is preferably liposoluble and non-solid. An exemplary such catalyst is dialkylcarboxyloxyltin (e.g., DBTL).
Among the catalysts which may be used in the context of the present invention, mention should be made more particularly of those based on Lewis acids, which are advantageously organic. Among the Lewis acids, mention should be made of those based on titanium, such as titanium tetrachloride, tetra-n-butyl titanate, isopropyl titanate, tetrakis(2-ethylhexyl) titanate, titanium acetylacetonate, stearyl titanate, nonyl titanate or cetyl titanate, those based on vanadium such as isopropyl vanadate or n-butyl vanadate, those based on zirconium such as zirconium tetrachloride, n-propyl zirconate or n-butyl zirconate, those based on tin such as anhydrous or hydrated tin chlorides, dibutyltin oxide, tin octanoate, butyltin hexanoate, tin oxalate, monobutyltin oxide, monobutylchlorotin dihydroxide, dibutyltin dilaurate, dibutyltin diacetate and monobutyltin tris(2-ethylhexanoate).
In the event an insoluble catalyst is used, it is desirable to eliminate or reduce its presence in the final composition, for example, by filtration.
Addition of the compounds of the above types makes it possible in particular to reduce the manufacturing time and the emission of volatile compounds, and allows optimization of the final color of these polyols which is particularly suitable for the present invention.
In the case where a methyl ester (of di- or polycarboxylic acids) is used at the start, it is very desirable to use those of the above catalysts which are known for giving satisfactory catalysis of the transesterification, or to introduce other catalysts which are known to do this, for example zinc carboxylates, antimony trioxide or any other catalyst known to those skilled in the art in the technical field of condensation. The amounts to be used are advantageously between xc2xd and 1%. by weight of the initial charge.
Besides working in an inert atmosphere, in order to improve the polymer or to protect it from coloration during the esterification process, it is preferable to add antioxidant additives such as triphenyl phosphate, tris(nonylphenyl) phosphate, stearylpentaerythritol diphosphite or equivalents thereof. These compounds are preferably used in an amount at least equal to 5 per thousand and at most equal to 15 per thousand.
In order to obtain the polyester mentioned above, techniques which are known per se are used. Typical reaction conditions include, for example, a final temperature of between about 200xc2x0 C. and 260xc2x0 C., and an absolute pressure between 5 hectopascals and 800 kilopascals.
The acid number and the hydroxyl number should be controlled. The alkalinity is adjusted to the point at which it is possible to obtain the best properties of covering of the polyurethane. Thus, before unloading, in principle in a refrigerated chamber, catalysts, antioxidants and any additive required for the final application should be incorporated.
The polyesters used for the present invention have a glass transition temperature (Tg) of between 40 and 80xc2x0 C., preferably between 50 and 70xc2x0 C., in order to give the system the stability required during storage. It is possible to use mixtures of amorphous and crystalline polyesters, the appropriate proportions of which should allow both good chemical and physical stability. The Tg of the polymer is determined by calorimetry by differential analysis (DSC).
In the case in which hydroxylated acrylic polymers are used, only one binder is typically used, the Tg being between 40 and 100xc2x0 C. Alternatively, mixtures comprising from 0 to 30% by weight of an acrylic polymer, with a Tg of from xe2x88x9220 to 50xc2x0 C., or from 70 to 100% by weight of a hydroxylated acrylic polymer, with a Tg of from 40 to 100xc2x0 C., can be employed. With the mixture, the system may be treated easily and have good stability during storage, as well as good chemical and mechanical properties.
The hydroxylated acrylic polymers may be obtained by reacting alpha,beta-unsaturated ethylene monomers, in particular vinylaromatic monomers and esters of alpha,beta-unsaturated ethylenecarboxylic acids. Mention may be made, for example, of styrene and its derivatives, such as methylstyrene or chlorostyrene. In the case of products for exteriors, they can be present in amounts of from 5 to 54% by weight, preferably from 10 to 25% by weight of the monomers as a whole. Amounts less than 5% by weight may adversely affect the corrosion resistance.
Among the alpha,beta-unsaturated ethylene acid esters, mention may be made of acrylic and methacrylic acid esters such as methyl acrylate, ethyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, dodecyl acrylate, methyl methacrylate, ethyl methacrylate, butyl methacrylate, 2-ethylhexyl methacrylate and lauryl methacrylate. Preferably, the unsaturated esters are present in an amount of from 5 to 8% by weight, and correspond to a mixture of esters of alkyl having from 1 to 3 carbon atoms and from 4 to 20 carbon atoms, for example a mixture of methyl methacrylate and butyl acrylate.
The hydroxyl functionality of the acrylic polymer is imparted by the copolymerization of monomers having hydroxyl groups, such as hydroxyethyl methacrylate and acrylate, and hydroxypropyl acrylate and methacrylate, in amounts of from 5 to 80% by weight. This percentage, which relates to the monomers as a whole, being necessary in order to obtain the hydroxyl number indicated.
The acrylic polymer may have a certain acid number, normally less than 15, derived from the addition of acrylic acid, methacrylic acid, itaconic acid or fumaric acid and/or of maleic acid or anhydride.
To prepare the acrylic polymers, the various monomers are mixed together and are reacted by free-radical polymerization. Among the initiators which may be used, mention may be made in particular of benzoyl peroxide, tert-butyl hydroperoxide, di-tert-butyl peroxide and azobisisobutyronitrile. Chain-transfer agents such as mercaptopropionic acid, dodecyl and lauryl mercaptan may be used to adjust the molecular weight.
The polymerization is carried out in solution, using a solvent in which the monomers are soluble, such as toluene, xylene, butyl acetate, propylene glycol methyl ether acetate, etc. Once the polymerization is complete, the reaction mixture is evaporated, under vacuum, in order to remove the organic solvent and to recover the solid polymer. The residual content of solvents or volatile compounds should be less than 0.5% by weight.
When the hydroxylated acrylic polymers are used in accordance with the conditions described above, satisfactory crosslinking with a prepolymer containing isocyanate functions masked according to the present invention is indeed obtained. The mechanical properties, however, remain insufficient for uses in which they are subject to bad weather. Thus, it is preferred to use polyisocyanate and saturated polyester systems.
The acid number of the polymer makes possible reaction of the carboxyl groups with aliphatic, aromatic and/or betahydroxyalkylamide polyepoxides. Double-crosslinking is thus obtained.
The catalyst content in the binder is typically at least equal to 0.5% by weight, advantageously at least equal to 1% by weight and preferably at least equal to 2% by weight. It is preferable for the content not to exceed 5% by weight, advantageously 3% by weight, preferably 2% by weight. As most catalysts are based on elements of metallic nature, it may be more practical to express this characteristic in terms of atomic equivalents. In this case, it is expressed that a content at least equal to 0.003 equivalent per kg mass (of binder), advantageously 0.005, preferably 0.01 equivalent, should be achieved, and it is preferable for the content not to exceed, on a mass basis, 0.3 equivalent, advantageously 0.2 equivalent, preferably 0.1 equivalent per kg mass (of binder).
It is desirable to avoid or at least minimize the amount of certain catalysts in the compositions, as they are deleterious to the sheen of coatings formed therefrom. Such catalysts are known to enhance a matt finish. Particularly when there are free carboxylic acid functions present in the masking agent, it is desirable to keep the content of such matt-enhancing catalysts to less than 0.6% by weight, preferably less than 0.4% by weight, more preferably less than 0.2% by weight of the composition, and most preferably absent from the composition. Such a catalyst content is particularly desirable when the carboxylic acid functions (free or in the form of a salt, especially when the carboxylic acid functions are borne by an aromatic nucleus) content of the composition is greater than that corresponding to 40 mg KOH/g, even greater than 20 mg KOH/g or 30 mg KOH/g.
Catalysts which should be avoided include, for example, inorganic salts [having a catalytic activity] and/or organic salts (including salts derived from hydrocarbons, such as, for example, those corresponding to the xe2x80x9canionxe2x80x9d CH3CH2xe2x80x94), such as sulphonate, carboxylate, acetylacetonate, phosphate, phosphonate or phosphinate, which have few or no methylene or methyl units.
Additionally, mention may be made of those which are reputed to catalyze allophanation reactions, tin II salts, such as pyruvate, oxalate, halide and in particular chloride, organic bases in which the basic function is borne by a nitrogen or phosphorus atom, such as phosphines and amines.
The catalysts may be introduced at various steps in the preparation of the powder paint, in particular during the blending before the final extrusion or during the preceding operations, in particular in the polyols after the condensation.
The binder of the present invention makes it possible to obtain high gloss coatings using additives, fillers, pigments and manufacturing processes known to those familiar with the manufacture of powder coatings. The presence of (matt-effect) waxes in the coating composition, however, should be avoided to ensure the formation of high gloss coatings. The fillers and pigment together may reach ⅔ of the mass of the binder.
In the formulation of paints, the appropriate pigments which make it possible to obtain the desired color should be present, it being possible for these pigments to range between 1 and about 50% by weight of the total of the powder paint. Typical pigments include, for example, titanium dioxide and titanium dioxides treated with zirconium oxide. Fillers may thus be used in the formulation in amounts of between 5 and 40% by weight.
Paints or varnishes which can be prepared according to the present invention may also contain the various types of additives, which are known per se, such as degassing agents, levelling agents, antioxidants and UV absorbers (anti-LTV agents or anti-UV agents).
Thus, as recommended degassing agents, mention may be made of benzoin, present in particular in an amount of from 0.5 to 3% by weight, which makes it possible to release the volatile compounds from the film during hardening and to prevent defects such as the formation of craters or pits.
The spreading additives recommended are acrylic polymers, fluoro polymers or polymeric siloxanes, in amounts of from 0.5 to 5% by weight added directly as a xe2x80x9cmaster batchxe2x80x9d into suitable polymers or absorbed onto silica.
In order to improve the exterior strength and the resistance to over-firing or to hardening in ovens with direct gas injection, it is recommended to add to the formulations UV-absorbing compositions and/or antioxidants of the primary and/or secondary type, of the phenolic type or alkyfaryl phosphates. Such additives may be present in the formulation in an amount of from 0.5 to 2% by weight of the paint as a whole.
In order to reduce the hardening (crosslinking) temperature, catalysts for formation of urethane, such as DBTDL (dibutyltin dilaurate) may be added to the formulation, directly into the premix or as a master batch.
The powder paints which form the subject of the present invention may advantageously be manufactured by melt-blending the compounds of the formulation. Firstly, they are preblended in a blender and are then melted, homogenized and dispersed in an extruder which has one or more screws.
It is desirable for the mixing, blending and extrusion temperature to be at most equal to about 130xc2x0 C. or less, advantageously about 110xc2x0 C. or less, preferably 100xc2x0 C. or less (3 significant figures). It is desirable for the extrusion temperature to be about 60xc2x0 C. or more, advantageously to about 70xc2x0 C. or more, preferably from about 80 to 90xc2x0 C. The extruded material obtained is left to cool and is passed through a mill until a paint composition having the desired particle size is obtained. In general d90 is about 200 micrometers or less, advantageously 100 micrometers or less (two significant figures), and d10 is about 20 micrometers or more, advantageously about 50 micrometers) or more. Such a composition can be applied, for example, to metal supports such as steel, aluminum or other alloys, glass, plastic or wood.
The ratio between the polyol(s) and the isocyanate(s) is defined by the deblocking stoichiometry. The amount of isocyanate stoichiometrically required to react with all of the free hydroxyl is generally chosen, with a tolerance of 20%, advantageously of 10%, preferably of 5%. As it is preferable to have an excess of isocyanate, slightly offset ranges are preferred. In other words, the amount of isocyanate to be added is advantageously at least equal to about 90% and at most equal to about 120% of the stoichiometric amount; preferably, it is at least equal to 95% and at most equal to about 110% of the stoichiometric amount; the most common and thus the most desirable range is at least equal to 100% (three significant figures) and at most equal to 105% of the stoichiometric amount. When systems having a high proportion of free acid (for example at least ⅔ of the masked isocyanate functions, see above) are used, it may be envisaged to increase the ratio between isocyanate and hydroxyl function from 10 to 30 points (%) approximately relative to the above values.
The powder obtained may be applied with an electrostatic gun or by a fluid bed. The preferred application of the present invention is that carried out with the Corona-discharge and Corona-effect electrostatic gun or by friction (triboelectric).
The substrate onto which the paint is applied, typically steel or aluminum, may or may not be preheated before the application. Once applied, the powder is melted and hardened in an oven for 10 minutes to two hours at a temperature of from 140 to 220xc2x0 C., depending on whether or not the system is catalyzed, generally for 10 to 30 minutes at a temperature of from 180xc2x0 to 220xc2x0 C.
Bearing in mind the preceding text, a person skilled in the art will adapt the firing by recalling that increasing the firing temperature makes it possible to decrease the firing time, and vice versa.
The present invention will be better understood with the aid of the illustrative examples which follow, in which various paint compositions are compared.

Compositions useful for obtaining high gloss coatings, methods of using such compositions and coatings thus obtained


A method of establishing a reference in an optical touch input system and a corresponding display panel, includes emitting light by emitters located at respective first, second, and third corners of the display panel, and receiving direct light by a detector located at a fourth corner of the display panel, the detector at the fourth corner detecting respective first, second, and third impulse signals generated by the direct light of the emitters located at the respective first, second, and third corners, the respective first, second, and third impulse signals corresponding to pixel positions of the detectors located at the fourth corner and correlating the respective pixel positions of the respective first, second, and third impulse signals with respective predetermined first, second, and third reference angles of the display panel.

1. Field of the Invention
This disclosure relates to a method of sensing touch, and more particularly, to an optical touch input system configured to detect correct touch without reference to errors caused by positional variation and misalignment of optical sensor modules located in at least three corners of a display panel. Retro-reflectors are configured to retro-reflect light emitted by the optical sensor modules.
2. Discussion of the Related Art
In general, a touch input system is one of the components that interface between telecommunication devices having a variety of display types. A user may touch a screen of the touch input system by using a pen or finger.
The touch input system is an input device used by a wide variety of people because of its convenience and ease of use. As a result, the touch input systems are used in many applications, for example, certificate-issuing devices used in banks or public offices, various medical apparatus, guide devices used in sightseeing, guide devices for traffic systems, and the like.
The touch input system may be categorized into a resistive type touch input system, a micro capacitive touch glass, an ultrasonic wave glass, and an infrared type touch input system, based on a touch recognition type.
The resistive type touch input system is made of two transparent conductive layers. A bottom layer is formed of glass having a conductive material coated thereon, and a top layer is formed of film having conductive material coated thereon. The two layers are spaced apart by a predetermined distance by a micro-printed spacers, which electrically insulate the two layers. A predetermined voltage is applied to the two layers, respectively. When a finger, touch pen, or other object touches the top layer, a resistance of the top layer (X axis) or the bottom layer (Y axis) changes according to the location of the touch. Predetermined X and Y locations corresponding to the changed resistive values are computed by a controller, and the controller displays coordinates on a monitor or data is inputted and used as coordinate data.
The micro capacitive touch glass is made of a transparent glass sensor having a thin conductor coated thereon. An electrode pattern is precisely printed along an edge of a conductor layer, and a transparent glass protection coating layer is in close contact with the conductor layer to protect and cover the sensor. A voltage is applied to a screen, and the electrode pattern forms a low voltage field on a touch sensor conductive surface. When an object or finger touches the screen, minute currents are generated at touch points. The distance of the current flow from each corner is proportional to the distance from the corner to the object, such as the human finger. Accordingly, the touch screen controller computes the ratio of the current flow to detect the touch point coordinates.
The ultrasonic wave touch glass is made of 100% glass, and is not affected by surface damage or abrasion, compared with the other types of screen surfaces, where damage or abrasion would reduce the usage life of such a touch screen. A touch screen controller transmits an electric signal of 5 MHz to a transmitting converter configured to generate ultrasonic waves. The reflected waves pass over the panel surface. When a user pushes the touch screen surface, part of the ultrasonic waves passing the touch point is absorbed by the user. A received signal and a lost or reduced signal in a digital map may be identified by a controller, and a coordinate value of the point corresponding to the current change of the signal may be calculated accordingly. This process may be independently implemented with respect to the X and Y axes.
The infrared type touch input system uses an inherent property of an infrared ray in that a line-of-sight path is required. The infrared ray is blocked when it encounters an obstacle. A portion of the touch input system having pressure applied thereto by an object blocks the infrared rays emitted along horizontal and vertical directions. The X and Y coordinates of the blocked points are sensed. The infrared type touch input system identifies the touch point from the blockage of infrared scanning beams. To form a invisible infrared matrix, an infrared ray beam is emitted from a predetermined surface of each of X and Y axis, and the emitted infrared ray is received by the sensors on opposite sides of the touch input system.
Each touch input system has different advantages, and the infrared type touch input system has been receiving attention because of its convenience of installation and because it requires a very small pressure for activation and sensing.
An infrared type touch input system of related art will be described in reference to FIG. 1 as follows.
FIG. 1 is a plan view illustrating an infrared type touch input system of the related art.
As shown in FIG. 1, the infrared type touch input system includes a panel 10, infrared sensors 5 (and emitters) provided at two adjacent corners of the panel 10, and a reflector 7 provided in each of three sides of the panel 10.
In the related art panel, light emitted from the infrared sensors 5 (emitters) located in both opposite ends of the panel 10 is reflected, and the emitted light is blocked by the touch of the object, such as a finger. An angle formed by the light received may be computed to determine the location of the touch.
When the infrared type panel of the related art uses only two cameras, touch resolution is low in an upper area because a dead zone is generated, as shown in FIG. 1. Each point shown in FIG. 1 is the lowest resolution measurable by using triangulation.
Such a dead zone is generated in a predetermined area in which an angle formed by the infrared sensors 5 is greater than predetermined value, and touch detection cannot be implemented in the dead zone. Thus, touch sensing accuracy may deteriorate in this predetermined area, and thus it is necessary to compensate for the reduced accuracy. To compensate, the infrared sensors are positioned on the far outer corners of the touch panel so as to position the dead zone outside the viewing perimeter of the liquid crystal panel. Therefore, the touch input system is required to have a size greater than the size of the liquid crystal panel. As a result, a non-effective area exists and the touch input system must be larger than is otherwise required.
Typically, the touch input system and the liquid crystal panel are separate components. In manufacturing, complex methods are required to combine elements of each panel with each other and to couple the touch input system to a liquid crystal module.
Furthermore, it is difficult to select accurate coordinates in such a touch input system of the related art, and there is a disadvantage that only one touch point at one time can be recognized. In other words, when two points are simultaneously touched on the touch input system, the touch input system fails to recognize the touch or it recognizes only the first of the two touches, which may cause an error.
Two infrared sensors and reflectors may be used to determine touch coordinates by using triangulation. Typically, two light sources and sensors are located in an upper area of the touch input system, and the reflectors are located in three surfaces to retro-reflect the light emitted from the light sources. The light is blocked when the panel is touched with an object, which is sensed by a controller, and a corresponding angle of the received light is computed to recognize the touch. Tolerance or variation in the physical orientation of the infrared sensors (misalignment) may occur during manufacture and assembly of the infrared type touch input system of the related art, and such misalignment may cause touch errors.

Optical touch input system and method of establishing reference in the same


A method for operating a cellular mobile radio network includes the step of allocating authorizations to selected mobile stations for a radio operation in particular in zones where radio interference is hazardous or radio traffic is undesired. The authorizations are stored in a local access authority register. Base stations, which are associated with cells that contain zones which are to be kept free of radio traffic, verify the presence of an authorization for each registering mobile station, and allow or prevent operation of the mobile station depending on the verification result. A control configuration for operating a cellular mobile radio network is also provided.

Field of the Invention
The invention relates to a special method for operating a cellular mobile radio network in order to ensure the safety of zones where radio interference is hazardous. The invention also relates to a correspondingly configured cellular mobile radio network. The invention further relates to a method of setting up xe2x80x9czones free of mobile radio operationxe2x80x9d for other reasons, for example in theaters, at the opera and in restaurants.
The continuing explosive development of mobile radio technology has led to hundreds of millions of mobile telephones being produced and sold, and being in daily use, in developed industrial countries. In these countries, there is virtually no place left in which there is no mobile radio traffic. The mobile radio traffic is, of course, particularly busy at traffic nodes and other focal points of daily life. Some of these zones are highly susceptible to dangers from radio interference due to the company-internal or operation-internal wireless information traffic taking place there, that is to say external radio traffic can lead to serious interference with the internal information processes there.
The danger to airborne traffic and, especially, to airport operation from mobile radio traffic is known in this context. In the past, aircraft accidents have already occurred which were virtually undoubtedly caused by interference from mobile telephones used in an aircraft. Thus, for some time, airline passengers have normally been requested to switch off their mobile telephones before entering an aircraft. However, due to carelessness or when an urgent call is expected, some airline passengers ignore this request, so that it is impossible to reliably ensure the safety of air traffic against interference from mobile radios by making such requests to airline passengers.
Risks similar to those in air traffic exist in clinics, particularly in intensive care zones, in which a large number of wireless information links, particularly between implanted medical-electronic equipment and external programming devices, or emergency paging systems for doctors, are operated. Here also, people having mobile telephones are occasionally requested to switch off their mobile telephones in certain zones. However, such requests cannot be reliably effective in this situation either.
In addition, it has already been tried to use technical devices, in particular jamming transmitters installed in relatively small zones, in order to make it impossible to make mobile telephone calls in safety-relevant zones. However, this has in fact resulted in a disadvantageous effect since mobile telephones react to such jamming by maximizing the transmitted power to search for the network, and thus increase the effect of the interference originating from them, unless the person having the mobile telephone actually switches it off.
It is accordingly an object of the invention to provide a method for operation a cellular mobile radio network and a control configuration for a cellular mobile radio network which overcome the above-mentioned disadvantages of the heretofore-known methods and devices of this general type and which reliably prevent interference caused by a mobile radio operation, irrespective of the subjective behavior or actions of network subscribers, in zones where radio interference is hazardous or a radio operation is undesired.
With the foregoing and other objects in view there is provided, in accordance with the invention, a method for operating a cellular mobile radio network, which includes the steps of:
allocating, to selected mobile stations, specific authorizations for a radio operation in zones to be kept substantially free of mobile radio traffic;
storing the specific authorizations in a local access authority register or database of a mobile radio network;
verifying a presence of one of the specific authorizations for a mobile station registering with a base station assigned to one of the zones to be kept substantially free of mobile radio traffic; and
selectively allowing and blocking an operation of the mobile station registering with the base station, depending on a result of the verifying step.
The invention includes the fundamental idea of forcibly preventing, from the network end, the operation of mobile telephones in zones where radio interference is hazardous or a radio operation is undesired, for example in aircraft and in areas of hospitals. The invention is also based on the realization that there should be specific approved exceptions to this forcible prevention of mobile radio traffic in the corresponding zones, in order to preclude undesirable disadvantageous effects. Such disadvantageous effects could occur if mobile radio traffic, which is desirable or even necessary for the work being carried out in the zones where radio interference is hazardous or a radio operation is undesired, were also to be prevented indiscriminately.
The invention thus provides for the network operator to allocate a specific authorization for mobile radio traffic in radio cells which have zones where radio interference is hazardous or a radio operation is undesired, and for a check for the presence of the appropriate authorization to be carried out for each mobile station registering there, before the mobile station is allowed to carry out mobile radio operations. If there is no specific authorization, specific technical processesxe2x80x94graduated in accordance with preferred embodiments of the inventionxe2x80x94are initiated which on the one hand reliably prevent mobile radio traffic from the unauthorized mobile station, and on the other hand are used to limit as far as possible the disadvantages for the user of such a mobile station.
A preferred embodiment of the method according to the invention includes the transmission of the call number of a mobile telephone registering in a zone where radio interference is hazardous or radio traffic is undesired, by the corresponding mobile station to the operation and maintenance center or OMC, which has a special associated local access authority register. The data stored there are used to carry out an immediate check as to whether the mobile station is or is not authorized to carry out mobile radio traffic in this zone, and the registration process is carried out if the result is positive while, if the result is negative, the corresponding call number is inhibited in a limited area and/or for a limited time. This is done via the responsible mobile switching center or MSC.
In accordance with another mode of the invention, the mobile switching center activates an information storage device, such as a mail box, or an information diversion device, such as a call diversion device, if no match is found in the authorization check.
Another preferred embodiment of the method according to the invention provides that, in the latter casexe2x80x94that is to say when there is no relevant access authorizationxe2x80x94the mailbox of the mobile station attempting to register is at the same time activated automatically via the mobile switching center. This prevents important messages from being entirely lost for the time when this mobile station is prevented from actively making mobile radio calls.
A further preferred embodiment in this case also provides for a xe2x80x9csyntheticxe2x80x9d call or service message (SMS) to be delivered to the registering mobile station, in order to inform the user about the existence of the inhibition or blocking, via the mobile switching station. In this case, depending on the specific system architecture, it is either possible to produce a text message on the display or to produce voice information which is output via the earpiece. In principle, of course, the relevant user can also be informed by an actual call from the operation and maintenance center; however, due to the complexity and required expense, this should be regarded as a transitional solution in order to increase user acceptance during introduction of the proposed method.
In accordance with yet another mode of the invention, if no match is found in the comparing step, an initial, time-limited registration for the mobile station is carried out for registering with the base station, and information is generated for notifying, via the mobile switching center, the mobile station of a limited blocking.
In accordance with a further mode of the invention, information is transmitted to the mobile station via the operation and maintenance center or via a memory/output control unit associated with the mobile switching center.
With the objects of the invention in view there is also provided, in a cellular mobile radio network including mobile stations, base stations with respectively assigned radio cells, and a mobile switching center connected to the base stations, a control configuration, including:
a local access authority register for storing specific authorizations relating to an operation of the mobile stations in selected ones of the radio cells, the selected ones of the radio cells containing zones to be kept substantially free of mobile radio traffic;
verification devices provided at given ones of the base stations associated with the selected ones of the radio cells for providing a verification of an authorization of the mobile stations registering with the given ones of the base stations, by interaction with the local access authority register; and
a blocking device associated with the mobile switching center for selectively inhibiting a given one of the mobile stations for at least one of a limited time and a limited area.
The partly functional description of features of the invention makes it clear that the device features of the proposed system largely correspond to the method features, especially since the essential features for implementation are databases and access and transmission protocols, which should be regarded both as method elements and apparatus elements.
In a preferred embodiment of the network architecture, the local access authority register mentioned above is in the form of an intelligent network (IN) which, in particular, is associated with the operation and maintenance center of the mobile radio network, where it can expediently be accessed via a special server. The inquiry and answer control, originating from the base station responsible for the relevant radio cell and ending with the mobile switching center which implements any inhibition or blocking, includes provisions which essentially correspond to the provisions used or method steps implemented for equipment authentication by access to the equipment identity register EIR. These include provisions or processes with which a mobile telephone which has been lost is inhibitedxe2x80x94with the difference that, for the proposed solution, the inhibition is not fundamentally unlimited throughout the network, but is implemented such that it is limited to the corresponding radio cell where radio interference is hazardous or radio traffic is undesired, or is limited to a predetermined time period.
At present, it is considered that limiting the area covered by the inhibition is particularly worthwhile for the purposes of the proposed solution but, in principle, at least a combination with a time limit is also feasible in order, for example, to allow the inhibition to be maintained for the time period of a flight without incurring considerable data transmission and processing effort in the network just to maintain the inhibition for the mobile station, which is moving quickly while in flight.
The proposed solution can be implemented in an advantageous manner particularly in conjunction with a detailed and exact planning of the radio field, wherein picocells and very small cells are being established. Specifically, the more precisely it is possible to define a zone where radio interference is hazardous or radio traffic is undesired, this zone also being referred to as a xe2x80x9cservice free zonexe2x80x9d, the less significant are the limitations necessarily associated with the proposed action, and the higher the level of user acceptance will be. In this context, a differentiated definition of different safety levels is also possible for zones which are to varying degrees prone to experience radio interference or which are endangered by the consequences of mobile radio traffic to different extents. Differentiation is also possible in terms of the authorization profiles of the end users; for example it would be feasible to allocate local authorizations to the ground personnel at airports and to allocate global authorizations to flying personnel, or else to selected employees of the legal authorities or the like. Such details can be controlled on a specialist basis in the course of system planning.
In accordance with another feature of the invention, an information storage device, such as a mail box, is assigned to a mobile station. An activation device for activating an information storage in the information storage device depending on an authorization verification is provided.
In accordance with yet another feature of the invention, an information diversion device, such as a call diversion device, associated with the mobile switching center is provided. An activation device activates the information diversion device depending on an authorization verification.
In accordance with a further feature of the invention, a dispatch device transmits, via the mobile switching center, a call, a service message or any other information suited for notifying a mobile station about a limited blocking.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a cellular mobile radio network and a method for operating such a network, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.

Cellular mobile radio network and method for operating such a network