RECORDING LIQUID AND RECORDING METHOD BY USE THEREOF

Abstract: A recording liquid is provided which comprises a dye as a component for forming an image and a liquid medium for dissolving or dispersing said dye, the liquid containing a compound having a three-dimensional molecular structure with an empty space therein, and having a molecular weight of 400 or more and a solubility of 3% or more in water. The com­ pound may be a cyclic compound having a plural number of pyranose rings. A recording method employing the above-­ mentioned recording liquid is also provided.

Description: This invention relates to a water-based recording liquid which enables images to be recorded at high speed with rapid fixing and excellent water resistance of the fixed image. It enables high quality images to be produced not only on paper specifically designed for ink jet recording but also on other kinds of paper for business and domestic use e.g. copying paper, writing paper, bond paper, continuous business form paper, etc., as well as on various cloths. The liquid exhibits excellent storage stability. The invention also relates to a recording method in which recording is performed by attaching onto a recording medium droplets of the recording liquid. Ink jet recording systems record images by forming ink droplets using various ink ejection systems and attaching a part or the whole of the ink droplets onto a recording medium such as paper, converted paper, plastics film, fabric, etc. Various dyes or pigments dissolved or dispersed in a liquid medium comprising water or water and a water-soluble organic solvent have been known and used as inks for ink jet recording. Such inks are generally required to have the performance characteristics mentioned below: (1) formation of a recorded image of high quality without feathering; (2) rapid fixing of the ink; (3) avoidance of clogging of the nozzles of the printer, even where printing is interrupted for a period of time; (4) good frequency response characteristics so that the ink can be ejected in conformity with the printer's speed of printing; (5) high storage stability; (6) high safety; (7) good durability of the printed image, for example in respect of resistance to water and light. In order to satisfy some or all of the above requirements, considerable research has been carried out both on the ink and on the printer, and considerable improvements have been made in some of the above characteristics. However, in spite of the extensive research which has been carried out up to now, there is still room for improvement of the characteristics of the ink with respect to: (1) avoidance of feathering on a recording medium having exposed fibers, and improvement in the fixing characteristics of the ink; (2) improvement of the frequency response characteristics to enable high speed recording to be carried out; (3) improvement of water-resistance of the recorded image even where the dye used is water-soluble; (4) improvement in storage stability while still satisfying the requirements (1) - (3). Firstly, referring to the feathering or fixing characteristics on a recording medium in which the fibres are exposed, particularly when printing on ordinary general purpose paper such as copying paper, writing paper, bond paper or continuous business form paper as the recording medium, feathering of the ink occurs along the fibers of the paper and the fixing characteristics are inadequate because of the influence of the sizing agent present in ordinary paper. In order to give resistance to feathering and improved fixing characteristics, it has already been proposed to carry out the recording using an ink having a strongly alkaline pH (Japanese Laid-Open Patent Publication No. 57862/1981), a method in which recording is carried out with the use of an ink containing a large amount of a surfactant (Japanese Laid-Open Patent Publication No. 29546/1980), a method in which recording is carried out using an ink which is solid at normal temperatures and is liquidified by heating (Japanese Laid-Open Patent Publication No. 108271/1983). However, a strongly alkaline ink is dangerous when in contact with the skin, and there is the further disadvantage that with some papers containing particular kinds of sizing agents both the feathering and fixing characteristics are not satisfactory. Where a large amount of surfactant is added, feathering is commonplace depending upon the quality of the paper, and there may be the further problem that ejection of the ink is interrupted either by retraction of the ink from the orifice surface or wetting the whole surface of the orifice with ink, depending upon the conditions of the printer head. Where recording is carried out with an ink which is solid at ambient temperatures and is liquidified by heating, there is some improvement both with respect to feathering and fixing of the printed image. In this method a feeding device comprising an ink dissolving or heating device is required to be present within the printer head, there is the disadvantage that the printer will inevitably be increased in size and cost. Most investigations concerning improvement in frequency response to permit high speed recording have been concerned with mechanical details such as the head construction, and little investigation has been carried out on the ink with respect to improvement of the ejection response frequency. Generally speaking, the frequency response characteristics are improved with decrease in viscosity of the ink, but there is a corresponding reduction in stability of ejection. It is therefore difficult to develop an ink which both has improved frequency response characteristics and maintains ejection stability. Particularly in the on-demand type ink jet system there are problems of poor frequency response characteristics at a driving frequency of 1 KHz or above, and this tendency becomes more marked when the driving frequency is raised to as high as 2 KHz or 4 KHz. This is a particularly serious problem in thermal or piezoelectric ink ejection systems. Many possible solutions have been put forward to deal with the problem of water resistance, for example using an ink containing an oil dye or pigment, and the use of a special paper treated with an agent which imparts water resistance. However, these methods give rise to the fresh problems of storage stability and increased cost of the recording paper. The problem of storage stability is substantially solved for aqueous inks which comprise a conventional water-soluble dye and water-soluble liquid medium, but at present there has been proposed no ink which satisfies all of the above-mentioned requirements (1) to (3) simultaneously. The problem with which the present invention is concerned is to provide a recording liquid which exhibits rapid fixing both on paper specially intended for ink jet recording and also on ordinary general purpose paper having fibers exposed at its surface and which may have been subjected to sizing, for example copying paper, writing paper, bond paper and which gives a printed image with little feathering. A further problem with which the invention is concerned is improvement of the frequency response characteristics obtained using the ink even at high driving frequencies so that images can be printed at high speed. A yet further problem with which the invention is concerned is the production of an ink which gives water-resistant images despite using a water-soluble dye. In one aspect the invention provides a water-based recording liquid, comprising a water-soluble dye as a component for forming an image and a liquid medium for dissolving or dispersing said dye, said liquid comprising water and a compound having (a) a three-dimensional molecular structure with an empty space therein; (b) a molecular weight of 400 or more; and (c) a solubility of 3% or more in water. In another aspect the invention provides a recording method in which the recording is carried out by attaching onto a recording medium droplets of the aforesaid recording liquid. According to a still further aspect of the present invention, there is provided an ink jet recording method which performs recording by ejecting droplets of a recording liquid of the invention at a driving frequency of 1 kHz or higher. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention is based on a discovery obtained as the result of intensive study about a liquid medium composition with good water resistance, fixing characteristic and printing quality of ink in a recording medium as having fibers exposed on the recording surface. The compound having a three-dimensional molecular structure (three-dimensional structure formed by bonding of atoms or molecules) having an empty space therein which characterizes the present invention is a compound having inclusion ability to incorporate another substance in its empty space, more particularly a compound called a host molecules having an empty space for including other substances. The present invention is characterized by containing a host molecule having inclusion ability, and a guest molecule is a whole dye molecule or a part thereof in the ink constituting components. The reason why water resistance, fixing characteristic, and printing quality are excellent in recording medium by use of the ink containing a compound in a three-dimensional molecular structure having internal empty space has not been clarified yet. It is presumed that an inclusion compound is formed by incorporating a dye molecule or a part thereof into the internal space to increase affinity for recording medium, particularly ordinary paper having been subjected to sizing as compared with the dye alone, whereby fixing characteristic and water resistance is improved. Further, it is considered that formation of an inclusion compound improves wettability toward the head constituting members, thereby improving frequency response characteristic. Also, since containment of these compounds is not accompanied with considerable lowering in surface tension of ink, no adverse effect is observed on ejection stability. Further, it may be estimated that the dye molecule becomes apparently larger by formation of an inclusion compound to lower its flowability, whereby recording of excellent print quality without feathering can be obtained. According to the investigations by the present inventors, for obtaining good printing quality without feathering, the size of the host compound contained is important in view of the flowability of the inclusion compound containing the dye, and more specifically, the molecular weight of the host compound shall be 400 or higher, more preferably 800 or higher. Therefore, with an ink containing a host compound such as urea, thiourea, deoxycholic acid and 18-crown-6 which has been said to have inclusion ability as described in Japanese Patent Publication No. 43843/1978, its feathering prevention effect is insufficient to make it difficult to obtain a record with high print quality. Further, according to the investigations by the present inventors, in view of long-term storage stability of ink, the solubility of the host molecule in water shall be not less than 3 %, and more preferably not less than 5 %. For example, as described in Japanese Laid-open Patent Publication No. 14569/1981, an ink containing β-cyclodextrin which has a solubility of less than 3 % in water (solubility: 1.58 %) has the drawback that it is liable to form a precipitate during storage for a long term. Examples of the compound having a molecular weight of 400 or more in a three-dimensional structure having internal space formed by bonding of atoms and molecules, and having a water solubility of 3 % or more, namely the host compound, to be used in the present invention may include valinomycin type natural antibiotics, various polyether compounds, nigericin type natural antibiotics, or cyclic compounds having a plural pyranose rings, for example, those having formed cyclic compounds through 1,4 and 1,6 bonding of monosaccharides such as glucose, fructose, galactose, etc., and disaccharides such as saccharose, maltose, lactose, etc., but the present invention is not limited to these substances. Among them, a particularly preferable substance is cyclodextrin comprising six or more α-D-glucopyranose groups bonded through α-1,4 bonding to form a cyclic compound, and these compounds exhibit marked effect. Among cyclodextrins, α-cyclodextrin formed by cyclization of bonding of six glucose molecules, and γ-cyclodextrin formed by bonding of eight glucose molecules, and further derivatives of the above cyclodextrin, for example, maltosylcyclodextrin having maltose bonded for the purpose of improving solubility, etc. are satisfactory. The content of the above compound may be in the range of from 0.1 to 20 % by weight, preferably from 0.2 to 15 % by weight, more preferably from 0.5 to 10 % by weight, based on the total weight of ink. If the content of the above compound is less than 0.1 % by weight, no marked effect can be obtained on improvement of fixing characteristic, printing quality and ejection stability, while if it exceeds 20 % by weight, the ink is not suitable for ink jet recording in such points as increased viscosity of ink or clogging of ink, in nozzles. As other components constituting the ink of the present invention, first as a water-soluble dye, there may be included direct dyes, acidic dyes, basic dyes, food dyes, reactive dyes, vat dyes, soluble vat dyes, etc. The criteria for "water-solubility" for the ink of the present invention is water-solubility of 1 % or higher at 20 °C, which solubility will not cause any problem in performance of ink. The content of these dyes may be determined depending on the kind of the liquid medium component, the characteristics required for the ink, etc., but generally within the range of from 0.2 to 20% by weight, preferably from 0.5 to 10% by weight, more preferably from 1 to 5% by weight. As the aqueous liquid medium for dissolving the dye as mentioned above in the present invention, any media used for ink for ink jet recording in general may be available. For example, water optionally with an organic solvent mentioned below may be preferably used. Examples of the organic solvent may include alkyl alcohols having 1 to 5 carbon atoms such as methyl alcohol, ethyl alcohol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, sec-butyl alcohol, tert-buytl alcohol, isobutyl alcohol, n-pentyl alcohol, etc.; amides such as dimethylformamide, dimethylacetamide, etc.; ketones or ketoalcohols such as acetone, diacetone alcohol, etc.; ethers such as tetrahydrofuran, dioxane, etc.; polyalkylene glycols such as polyethylene glycol, polypropylene glycol, etc.; alkylene glycols with alkylene group containing 2 to 6 carbon atoms such as ethylene glycol, propylene glycol, butylene glycol, triethyleneglycol, 1,2,6-hexane triol, thiodiglycol, hexylene glycol, diethylene glycol, etc.; glycerine; lower monoalkyl ethers of polyhydric alcohols such as ethylene glycol monomethyl (or ethyl) ether, diethylene glycol monomethyl (or ethyl) ether, triethylene glycol monomethyl (or ethyl) ether, etc.; lower dialkyl ethers of polyhydric alcohols such as triethylene glycol dimethyl (or ethyl) ether, tetraethylene glycol dimethyl (or ethyl) ether, etc.; sulforane, N-methyl-2-pyrrolidone, 1,3-dimethyl-2-imidazolidinone; and so on. The essential components of the ink of the present invention are as described above, and other known various additives such as a dispersing agent, a surfactant, a viscosity contoller, a surface tension controller, or an optical brightener may be added as desired. For example, there may be employed a viscosity controller such as polyvinyl alcohol, celluloses, water-soluble resins, etc.; a surfactant such as cationic, anionic or nonionic surfactants; a surface tension controller such as diethanolamine, triethanolamines, etc.; a pH controller based on a buffer solution; an antifungal agent, etc. Also for making up an ink to be used for the ink jet recording with electrically charged ink, a specific resistance controller containing an inorganic salt such as lithium chloride, ammonium chloride, sodium chloride, etc. may be added. In the case of applying for the ink jet recording method employing ink ejected by action of heat energy, the thermal property (e.g. specific heat, coefficient of thermal expansion, thermal conductivity, etc.) may be sometimes controlled. The ink of the present invention as described above is frequently demanded to have the performance for stable ejection from a printer head, particularly the performance for stable ejection at a driving frequency of 1 KHz or higher. Therefore it is desired to be controlled in the properties to be of the low viscosity type, having preferably a viscosity at 25°C of 5 cp or less, a surface tension of 35 to 65 dyne/cm, more preferably a viscosity of 3 cp or less. If the viscosity of the ink exceeds 5 cp, even the ink containing the host compound having the inclusion ability according to the present invention may be sometimes insufficient in printing quality, fixing characteristic and frequency response characteristic on ordinary paper. The ink to be used in the present invention obtained as described above, is above all excellent in water resistance, fixing characteristic and printing quality on ordinary paper generally employed in business and domestic uses and having fibers exposed on the recording surface, and further subjected to sizing, such as copying paper, writing paper, bond paper, continuous business form paper, etc., and effectively used as the ink for ink jet recording of various systems, and can perform excellent recording. The ink of the present invention is capable of responding precisely to driving frequency for high speed recording for which increasingly higher response ability is required from 1 Khz, to 2 Khz, and 4 Khz, and so on. The ink enables excellent recording for long term, generally with an on-demand type ink jet system, especially the one employing piezoelement or thermal energy. The present invention is described in more detail by referring to the following Examples, Comparative examples. In the sentences, all parts and % are by weight. Example 1 C.I. Food Black 2 3 parts Glycerine 12 parts Ethylene glycol 8 parts Etylene glycol monophenyl ether 2 parts Water 80 parts α-Cyclodextrin 5 parts Of the above components, α-cyclodextrin was firstly dissolved in water, then the dye C.I. Food Black 2 was added and the mixture was stirred for one hour, and further glycerine, ethylene glycol, and ethylene glycol monophenyl ether were added, followed by stirring at 40°C for 3 hours. Then, after adjustment of the pH of the mixture to 7.5 with 0.1% aqueous solution of sodium hydroxide, the mixture was pressure filtered through Fluoropore Filter (trade name, produced by Sumitomo Denko K.K.) with a pore size of 1µ to obtain an ink (A) of the present invention. Next, by use of this ink, printing was performed on a commercially available copying paper, bond paper, by means of an ink jet printer utilizing a heat-generating element as the ejection energy source for the ink (orifice size 40 x 50 µm, heater size 30 x 150 µm, nozzle number 24, driving voltage 24.5 V, frequency 2 KHz) as the ink jet recording device, and the printed products obtained were evaluated for fixing characteristic, printing quality, storability, and water resistance. Ink properties and evaluation results are shown in Talbe 1. Example 2 C.I. Acid Red 35 1.5 parts Glycerine 9 parts 1,3-dimethyl-2-imidazolidinone 10 parts Water 81 parts α-Cyclodextrin 1 part Of the above components, α-cyclodextrin was firstly dissolved in water, then the dye C.I. Acid Red 35 was added and the mixture was stirred, and further glycerine, 1,3-dimethyl-2-imidazolidinone were added, followed by stirring at 40°C for 3 hours. Then, after adjustment of the pH of the mixture to 7.5 with 0.1% aqueous solution of sodium hydroxide, the mixture was pressure filtered through Fluoropore Filter (trade name, produced by Sumitomo Denko K.K.) with a pore size of 1µ to obtain an ink (B) of the present invention Example 3 (Preparation of ink (C)) C.I. Direct Blue 86 3 parts Diethylene glycol 15 parts Ethylene glycol 5 parts Diethylene glycol monophenyl ether 0.7 parts Water 80 parts γ-cyclodextrin 1 part Of the above components, γ-cyclodextrin was firstly dissolved in water, then the dye C.I. Direct Blue 86 was added and the mixture was stirred, and further diethylene glycol, ethylene glycol, and ethylene glycol monophenyl ether were added, followed by stirring to 40°C for 3 hours. Then, after adjustment of the pH of the mixture to 7.5 with 0.1% aqueous solution of sodium hydroxide, the mixture was pressure filtered through Fluoropore Filter (trade name, produced by Sumitomo Denko K.K.) with a pore size of 1µ to obtain an ink (C) of the present invention. Example 4 C.I. Direct Black 154 3 parts Diethylene glycol 12 parts N-methyl-2-pyrrolidone 8 parts Nonionic surfactant (Nissan-nonion P223 (trade name), produced by Nippon Yushi K.K.) 0.1 part Water 80 parts Maltosylcyclodextrin (Isoelite P(trade name), produced by Nikken Kagaku K.K.) 2 parts Of the above components, maltosylcyclodextrin was firstly dissolved in water, then the dye C.I. Direct Black 154 was added and the mixture was stirred, and further diethylene glycol, N-methyl-2-pyrrolidone, and the nonionic surfactant were added, followed by stirring at 40°C for 3 hours. Then, after adjustment of the pH of the mixture to 7.5 with 0.1% aqueous solution of sodium hydroxide, the mixture was pressure filtered through Fluoropore Filter (trade name produced by Sumitomo Denko K.K.) with a pore size of 1µ to obtain an ink (D) of the present invention. Example 5 (preparation of ink E) C.I. Direct Yellow 86 2 parts Triethylene glycol 8 parts Ethylene glycol 6 parts 1,3-dimethyl-2-imidazolidinone 6 parts Water 80 parts α-Cyclodextrin 1 part γ-cyclodextrin 0.7 parts Of the above components, α- and γ-cyclodextrin were dissolved first in water, and then the dye C.I. Direct Yellow 86 was added and the mixture was stirred, and further triethylene glycol, ethylene glycol, and 1,3-dimethyl-2-imidazolidinone were added, followed by stirring at 40°C for 3 hours. Then, after adjustment of pH to 7.5 with 0.1% aqueous solution of sodium hydroxide, the mixture was pressure filtered through Fluoropore Filter (trade name, produced by Sumitomo Denko K.K.) with a pore size of 1 µ to obtain an ink (E) of the present invention. Example 6 C.I. Food Black 2 2 parts Glycerine 12 parts Ethylene glycol 8 parts Ethylene glycol monophenylether 2 parts Water 80 parts Monensin (nigericin type natural antibiotic) 4 parts Of the above components, monensin was dissolved first in water, then the dye C.I. Food Black 2 was added thereto and the mixture was stirred, and further glycerine, ethylene glycol, and ethylene glycol monophenyl ether were added thereto, followed by stirring at 40°C for 3 hours. Then, after adjustment of pH of the mixture to 7.5 with 0.1% aqueous solution of sodium hydroxide, the mixture was pressure filtered through Fluoropore Filter (trade name, produced by Sumitomo Denko K.K.) with a pore size of 1µ to obtain an ink (F) of the present invention. Comparative example 1 Of the components in Example 1, the components excluding α-cyclodextrin were mixed by stirring for 3 hours, and then after adjustment of the pH of the mixture to 7.5 with 0.1 % aqueous solution of sodium hydroxide, the mixture was pressure filtered through Fluoropore Filter (trade name, produced by Sumitomo Denko K.K.) with a pore size of 1µ to obtain an ink (G) for comparative purpose. Comparative example 2 Of the components in Example 2, the components excluding α-cyclodextrin were treated in the same manner as in Comparative example 1 to obtain an ink (H) for comparative purpose. Comparative example 3 Of the components in Example 3, the components excluding γ-cyclodextrin were treated in the same manner as in Comparative Example 1 to obtain an ink (I) for comparative purpose. Comparative example 4 Except for using saccharose in place of α-cyclodextrin in Example 1, the treatment was conducted in entirely the same manner as in Example 1 to obtain an ink (J) for comparative purpose. Comparative example 5 In Example 4, maltosylcyclodextrin was excluded and 0.5 parts of a nonionic surfactant (Nissan-nonion P223 (trade name), produced by Nippon Yushi K.K.) were added and the treatment was conducted in the same manner as in Comparative example 1 to obtain an ink (K) for comparative purpose. Comparative example 6 Of the components in Example 1,β-cyclodextrin was used in place of α-cyclodextrin, following otherwise the same procedure as in Example 1, to obtain an ink (L) for comparative purpose. Comparative example 7 Of the components in Example 1, 18-crown-6 was used in place of α-cyclodextrin, following otherwise the same procedure as in Example 1, to obtain an ink (M) for comparative purpose. Comparative example 8 Of the components in Example 6, urea was used in place of monensin, following otherwise the same procedure as in Example 6, to obtain an ink (N) for comparative purpose. The same recording as in Example 1 was also practiced for the inks (B - N) in Examples 2 - 6 and Comparative examples 1 - 8. Ink properties and evaluation results are shown in Table 1. Examples 7 - 21 and Comparative examples 9 - 23 By use of the inks A - E, G - K obtained in Examples 1 - 5 and Comparative examples 1 - 5, solid printing with an area of 15 x 4 cm² and character printing of 130 alphabet letters were effected on a commercially available copying paper by use of the printers A and B shown below by setting the frequency within the range of 1 to 6 KHz, and followability of ink and shot accuracy were examined for evaluation of frequency response of ink. The evaluation results are shown in Table 2. Here, the followability of ink means the property of ink fed into a nozzle smoothly following ejection of an ink droplet from the nozzle, and the shot accuracy means the accuracy of the points shot by ink droplets on a recording medium. (Printer A) An ink jet printer utilizing a heat-generating element as the ejection energy source (heater size 30 x 150 µm² and having 24 nozzles with an orifice size of 40 x 50 µm²) (driving voltage 24.5V). (Printer B) Utilizing a piezoelectric element as the means for applying pressure on ink ink, ink is ejected by mechanical displacement given to the piezoelectric element with electrical signals. An ink jet printer having 8 nozzles with orifice diameter of 50 µm and passage length of 40 mm (driving voltage: 60V). As described above, according to the present invention, ink jet recording is rendered possible, which can give printing with good water resistance to paper specially prepared for ink jet recording but also to plain papers in general with fibers exposed on the recording surface, and further subjected to sizing, for example, copying paper, writing paper, bond paper, continuous business form paper, with rapid fixing speed and yet with little feathering. Further since the ink of the present invention is excellent in storing stability, it has become possible to perform ink jet recording which is safe and excellent in ejection stability and operability of ink over a long term. Further since frequency response of ink is good, high speed and stable recording with high driving frequency is rendered possible.

Claims: A water-based recording liquid, comprising a water-soluble dye as a component for forming an image and a liquid medium for dissolving or dispersing said dye, said liquid comprising water and a compound having (a) a three-dimensional molecular structure with an empty space therein; (b) a molecular weight of 400 or more;and (c) a solubility of 3% or more in water. A recording liquid according to Claim 1, wherein said compound has a molecular weight of 800 or more. A recording liquid according to claim 1, wherein the compound having the three-dimensional molecular structure is a cyclic compound having a plurality of pyranose rings and having a solubility of 3% or more in water. A recording liquid according to Claim 3, wherein said cyclic compound is a cyclodextrin other than β-cyclodextrin or is a derivative of a cyclodextrin. A recording liquid according to any preceding claim, wherein said compound has a solubility of 5% or more in water. A recording liquid according to any preceding claim, wherein the content of said compound is within the range of 0.1 to 20% by weight of the total weight of the recording liquid. A recording liquid according to any preceding claim, having a viscosity at 25 °C of 5 cp or less. A recording liquid according to Claim 7, having a viscosity of 25 °C of 3 cp or less. A recording liquid according to any preceding claim, having a surface tension at 25°C of 35 to 65 dyne/cm. A recording method which performs recording by attaching onto a recording medium, droplets of a recording liquid according to any preceding claim. A recording method according to Claim 10, wherein said recording medium is sized paper. An ink jet recording method which performs recording by ejecting at a driving frequency of 1 kHz or higher droplets of a recording liquid according to any of claims 1 to 9. An ink jet recording method according to Claim 12, wherein the ejection system of the recording liquid is of an on-demand type. An ink jet recording method according to Claim 12, wherein the ejection system utilizes a piezoelectric element. An ink jet recording method according to Claim 12, wherein the ejection system utilizes heat energy.

Inventors: KOIKE, SHOJI, TOMIDA, YASUKO
Applicants: CANON KABUSHIKI KAISHA
Application year: 1988
Main classification: C09D11
IPC codes: C09D11