GB2029266A

GB2029266A - Thermal recording elements

Info

Publication number: GB2029266A
Application number: GB7922224A
Authority: GB
Original assignee: Fuji Photo Film Co Ltd
Current assignee: Fujifilm Holdings Corp
Priority date: 1978-06-26
Filing date: 1979-06-26
Publication date: 1980-03-19
Also published as: DE2925766A1; GB2029266B

Abstract

A thermal recording element has on a support a conventional recording layer (preferably of a metal such as Sn, Bi or In) and, to give protection with minimum loss of sensitivity, a protective layer of an organic high molecular weight material (such as a chlorinated polyethylene), a fatty acid having more than 10 carbon atoms or an amide thereof being present in or on the protective layer, preferably in an amount of 0.1 to 20 wt% when used in the layer.

Description

SPECIFICATION Thermal recording elements The invention relates to a thermal recording element for recording information by thermally deforming the recording layer using high intensity radiation and, more particularly it relates to a high density thermal recording element having a novel protective layer.

Various recording elements, such as silver halide light-sensitive materials, have been used for recording using high intensity radiation (such as a laser), such as a recording element wherein the recording layer has a high optical density, which, when heated locally in the irradiated portions by high intensity irradiation, undergoes physical deformation such as fusion, evaporation or aggregation, whereby information is recorded by the difference in optical density between the irradiated and nonirradiated portions. Such a thermal recording element has the advantage that processings such as development and fixing are unnecessary to form the recorded image, a dark room is unnecessary for recording since the recording layer is not sensitive to ordinary room light, high contrast images are obtained, and also additional (add-on) recording of information is possible.

Recording using such a thermal recording element is generally performed by converting the information to be recording into an electric time-succession signal and scanning the recording element by a laser beam, the intensity of which is modulated according to the electric signal. The advantage of this recording method is that the recorded image is obtained in real time.

Recording elements such as mentioned above are described in, for example, M. L. Levene et al, Electron, Ion andLaserBeam Technology (the records of the 1 itch Symposium held in 1 969), Electronics, 18th March, 1968, page 50; D. Maydan, The Bell System Technicaljournat Vol. 50, page 1761 (1971); and C. O. Carlson, Science, Viol.154, page 1550(1960). Metals, dyes and plastics are used as the recording layers for the thermal recording elements. In the thermal recording elements using metals as the recording layers, there are elements constructed of a thin layer of a metal such as bismuth, tin or indium, on a support which is able to record images with high resolving power and high contrast.However, such recording element having thin-metal layers generally reflects more than 50% of laser light used for recording, making it impossible to utilise the energy of the laser light effectively and hence has such a disadvantage that the power of the laser light used for recording must be higher, which means the laser source must have a high output for recording at high scanning speed, and thus the recording apparatus used becomes larger and expensive.

Various recording elements having high recording sensitivity have been studied and as an example, a recording element comprising a thin layer of selenium and bismuth and a thin layer of germanium formed thereon for reducing the light reflectance is disclosed in Japanese Patent Publication No.40,479/71. However, the use of these elements is undesirable since#there is a possibility of toxicity problems and the recorded images are unsatisfactory.

As another example of a recording element having a reflection-preventing layer, the formation of a reflection preventing layer absorbing the light in the wave length region of the laser on a metal recording layer is disclosed in Japanese Patent Applications (OPI) Nos. 151,151/75 and 74,632/76.

However, even if a reflection-preventing layer is used, it is very difficult to completely eliminate light reflection and even if light reflection could be completely eliminated, a laser light source of high power would be required to produce thermal deformation and hence a recording element having higher sensitivity is needed.

Since the recording layer, in particular a metal layer, of the above-mentioned thermal recording element is liable to scratches, a protective layer is sometimes formed on the recording layer to prevent or reduce scratchin#g. The protective layer must transmit the light beam of high energy and density used for recording, possess high mechanical strength, be reluctant to react with a recording layer, exhibit good coating property and be easily formed. As materials used for protective layers, there are inorganic materials such anal203, Six2, SiO, MgO, ZnO, MgF2 of Cut2, and the organic materials disclosed in Japanese Patent Applications (OPI) Nos. 96,716/74, 59,626/76,75,523/76, 88,024/76 and 134,633/76.However, in recording elements having protective layers possessing effective strength as described in the above specifications, the recording sensitivity is greatly reduced in comparison to recording elements having no protective layer. For example, when an effective polymer is used for the protective layer, the thickness of the protective layer must be at least 3 y #m in order to function adequately and in this case, the recording energy required for recording on the recording element is two to three times the amount of energy required without the protective layer.On the other hand, when the thickness of the protective layer is less than 1 Cl m, the reduction in recording sensitivity as described above may be avoided but the mechanical strength of the recording element is reduced greatly and, in fact, the recording element is not practical.

When an organic high molecular weight material or a polymer is used on the protective layer, it is necessary to prevent the reduction in recording sensitvity as much as possible and at the same time maintain the strength of the protective layer for practical use. However, when a polymer layer having good adhesivity to the recording layer, good film-forming property and high softening point is used, the reduction in sensitivity is great. It has been difficult to resolve these conflicting requirements.

This invention is directed to overcoming the problems surrounding the use of conventional thermal recording elements as mentioned above.

The invention provides a thermal recording element having on a support, in turn, (a) a thermal recording layer, and (b) a protective layer comprising mainly a polymer, and a higher fatty acid having 10 or more carbon atoms or an amide thereof is present in or on the protective layer.

The support used in this invention can be any support generally used in a thin type of recording element, for example, it may be a plastics material such as polyethylene terephthalate or a poycarbonate, or sheet of glass, paper or metal or a metal foil, and in particular, polyethylene terephthalate is particularly preferred since it is light in weight and is tough, does not stretch much, can form a very thin film and is transparent.

The recording layer is primarily responsible for the change in the optical transmission or light reflectance as the result of thermal deformation, such as fusion, evaporation or aggregation in the portions irradiated by laser beam.

It is preferred that the recording layer used in this invention is a layer having high optical density and is formed of a material having high covering power in a thin layer, preferably a metal. Also, the recording layer can be not only a layer of a single material having a high covering power (e.g. a metal layer), but also a laminate of a metal laye#r and a layer of another material used for increasing recording sensitivity, and a layer composed of a mixture of a metal and another material for increasing recording sensitivity. Various layer structures and materials may be selected.

Suitable metals for the recording layer are Mg, So, Y, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Mn, Re, Fe, Co, Nii Ru, Rh, Pd, Ir, Pt, Cu, Ag, Au, Zn, Cd, A!, Ga, In, Si, Ge, Te, Pb, Po, Sn, As, Sb, Bi, Se and Te and they may be used alone or in combinations of two or more. The particularly preferred properties of a metal used as the recording layer are that its toxicity is low, the energy required for fusing or evaporating the metal layer is low, and the film or layer of the metal can be easily formed. The most preferred metals are Sn, Bi and In.The thin layer of the metal can be formed on a support or a subbing layer or other layer on the support in a single or double layers by various methods (such as vacuum deposition, sputtering, ion plating, electroplating or electrolessplating) as a single metal or in combination or alloy or two or more such metals.

The thickness of the metal layer should be capable of providing the necessary optical density for images and, for example, is generally 300 to 1,500 A depending on the kind of metal used. Also, in the case of forming the metal layer on a support by vacuum deposition, sputtering or ion plating, the layer structure of the metal differs with the kind of the support, the temperature, the degree of vacuum and the speed of vacuum deposition, and hence the thickness of the metal layer necessary for obtaining a desired optical density depends on a combination of factors.

It is preferred that the metal is used together with a material which increases the recording sensitvity of the material in the form of a co-deposited mixture or a laminate with the metal(s). The material may increase the recording sensitivity by preventing reflection or other means, and examples of such materials are metal oxides, such as PbO, W03,Ti03, SiO, SiO2 or Zero2, chalcogen compounds such as Ge, In, Sn, Cu, Ag, Fe, Bi, Al, Si, Zn or V; metal halides such as PbX2, AgX, SnX2, SbX5or SbX3 where X is fluorine, chlorine, bromine or iodine; and an element of group IVB, VB orViB selected from P, As, Sb, Ge, Si and Te.It is preferred that these materials have low toxicity, have low hygroscopicity or deliquescence, or low deterioration with the passage of time by the dark reaction with the metal recording layer and they can easily form a layer or film thereof. The use of GeS, SnS or Pbl2 is particularly preferred. The thickness of a sensitvity-increasing layer depends upon the nature and thickness of the metal layer but is usually 50 to 1,000 A.

The recording layer may be formed directly on a support or on a subbing layer provided on a support to improve the adhesivity of the recording layer.

Suitable materials for the layer include chlorinated polyethylene and chlorinated polypropylene.

As the higher fatty acid having 10 or more carbon atoms or the amides thereof used in this invention, there are, for example, lauric acid, myristic acid, palmitic acid, stearic acid, behenic acid, oleic acid, linolic acid, linolenic acid, arachidonic acid and the amides of these acids. Of these, the higher fatty acids having 14 to 21 carbon atoms and the amides thereof are preferred. The carbon atom number used herein is the total number of carbon atoms including the carboxy group in the high fatty acid.

These fatty acids or the amides may be used alone or as a combination of two or more acids or amides.

Also, these components may be incorporated in the protective layer of a polymer described later or they may be provided (as a separate layer) on the protective layer. When the fatty acid or amide is in the protective layer, it is preferred that the amount of the higher fatty acid or amide be 0.1 to 20% by weight based on the weight of the protective layer. When used as a separate top layer, it is preferred that the thickness of the protective layer be 0.01 to 1 Mm, preferably 0.03 to 0.2 ym.

As the polymer used for the protective layer in this invention, there may be used gelatin, gelatin derivatives, cellulose derivatives, dextrane, latex-like vinyl compounds for improving the dimensional stability of photographic materials, or a synthetic polymer as described in U.S. Patent No. 3,142,586, 3,193,386, 3,062,674, 3,220,844,3,287,289 or 3,411,911.Examples of suitable classes of polymers are the water-insoluble polymers of an alkyl acrylate, alkyl methacrylate, acrylic acid, sulfoalkyl acrylate or sulfoalkyl methacrylate and the polymers having cyclic sulfobetaine units as described in Canadian Patent No. 774,054. Examples of actual suitable polymers are cellulose acetate, cellulose propionate, cellulose nitrate, butyl cellulose, benzyl cellulose, carboxymethyl cellulose, hydroxethyl cellulose, nitrocellulose, cellulose acetate butyrate, cellulose acetate phthalate, cellulose acetate propionate, polymethyl methacrylate, polyvinyl pyrrolidone, polyethylene, polyethylene glycol, polyethylene oxides, polystyrene, polyisobutylene, polyvinyl alcohol, polyvinyl acetate, polyvinyl formal, polyvinyl acrylamide, polyvinyl butyral, polyvinyl pyridine, polyvinylidene chloride, a copolymer of methyvinylether and maleic acid anhydride, a butadiene-styrene copolymer, a vinyl chloride-vinyl acetate copolymer, a vinyl chloride-vinyl acetate-maleic acid terpolymer, a polyacrylate, a polyacrylamide, a polysulfoalkyl acrylate, a polysulfoalkyl methacrylate, a polyamide, chlorinated rubber, terpene resin, alginic acid or the derivatives thereof, an onium salt halide series conductive polymer, and a phenol resin. These polymers may be used alone or as a mixture thereof. Also, the above-mentioned higher aliphatic acid or the higher aliphatic acid amide may be added to the polymer. In any cases, a protective layer of the polymer may be formed by dissolving the material in a known solvent and coating the solution.

The thermal recording element of this invention has the merit that the protection of the recording layer is improved without reducing the recording sensitivity and has the effect that the preservative property is improved and the formation of scratches during handling is greatly reduced.

Then, the invention will further be explained by the following examples. Unless otherwise indicated all parts, percentages and ratio are by weight.

EXAMPLE 1 A recording layer having a two-layer structure was formed by forming on a polyethylene terephthalate film of 100 cm thickness first a metalylayeroftin of thickness 350 A and then a layer of a sensitivity-increasing compund shown in Table 1, each under a vacuum of 5 x 10-5 torr. The transmission optical density of each sample thus prepared was in the range of 1-2. The samples at this stage are referred to as samples Ar to A8.

Then, a toluene solution of chlorinated polyethylene ("LTA-905", chlorine content of 65~69% by weight, viscosity in a 20 wt.% solution at 250C of 4-7 c.p.s., made by Sanyo Kokusaku Pulp Co., Ltd.) was coated on one surface of each of the samples at a dry thickness of 3 yim. The samples at this stage are referred to as samples B1-B8.

To prepare further samples, the layer of the chlorinated polyethylene as described above was coated on one surface of each of samples A1-A8 at a dry thickness of 0.6 ssm. The samples at this stage are referred to samples C1-C8. Furthermore, a solution of 1 g of stearic acid and 0.3 g of behenic acid (organic fatty acids) in 2 liters of hexane was coated on the surface of each of samples C,~C8 at a dry thickness of 0.05 ym. The samples in this state are referred to as samples D1~D8 Each of these samples was recorded by scanning the recording layer side thereof with an argon ion laser beam (wavelength 5145 A) focused at a beam diameter of 25 microns by a tens at a scanning speed of 1 9 meters/sec., and the minimum laser output intensity forming a record of 10 ssm diameter on each sample was determined. The surface strength of each recording element sample was measured by means of a Heidon-18 surface strength tester, made by Shin Tokyo Kagaku K.K. using an R ball stylus (R = 0.4 mm) and the minimum load forming a scratch on the surface when a load was applied thereon was employed as the indicator for the surface strength.

The results are shown in Table 1.

TABLE 1

Sensitivity-increasing Minimum Output Surface Strength layer Required (mW) (9) Thickness Sample Compound (A) No. An 8 n Cn Dn A# Bn Cn - D Pal2 200 1 100 275 125 125 5 70 50 1500 Cul 300 2 100 275 125 125 5 70 50 1500 Agl 350 3 100 275 125 125 5 70 50 1500 Snl, 200 4 100 275 125 125 5 70 50 / 1500 AgO 300 5 100 275 125 125 5 70 50 1500 Sncl 400 6 100 275 125 125 5 70 50 1500 GeS 200 7 175 275 225 225 5 70 50 1500 SnS 150 8 200 275 250 250 5 ' 70 50 ; 1500 As is shown in Table 1 , in samples B1-B8 each having a chlorinated polyethylene layer 3 am thick on the recording layer, the surface strength was passably high as compared with samples A1-A8 but the minimum laser output required was high, i.e., the recording sensitivity was very poor. In samples C1-C8 each having the polyethylene layer 0.6 #m thick the recording sensitivity was almost the same as that of samples A1-A8 respectively but the surface strength was inferior to samples B1-B8.

However, in samples D1-D2 of this invention, the recording sensivity was the same as that of each the C samples and also the surface strength was very high.

EXAMPLE 2 The same procedure as in Example 1 was followed using bismuth in place of tin as the metal layer, and almost the same results as in Example 1 were obtained.

EXAMPLE 3 A recording layer was formed on a polyethylene terephthalate film of 100 #m thickness by vacuum depositing thereon (a) tin at a thickness of 350 A as a metal layer and (b) germanium sulphide GeS at a thickness of 200 A to form two layers under a vacuum of 5 x 10-5 Torr. The sample in this stage is referred to as sample A.

Then, on each of two A samples was coated the foliowing solution (1) of the polymer shown below or solution (2) of the polymer shown below as a protective layer at a thickness of 3 ssm and 0.6 #u respectively.

Solution (1): 10% toluene solution of polystyrene.

Solution (2): 10% methyl ethyl ketone solution of polyurethane ("Estan 571 5", made by Goodrich Co.).

These samples thus formed are shown in Table 2.

TABLE 2 Solution Coated Thickness of Protective layer Solution (1) Solution (2) 3 ym Sample B, Sample B2 0.6 #m Sample C1 Sample C2 On each of samples C1 and C2 was further coated a solution of 1 g of stearic acid and 0.3 g of behenic acid in 2 litres of hexane at a dry thickness of 0.05 ym. The sample at this stage is referred to as sample D1 and sample D2.

The minimum output of laser required for laser recording and the surface strength were measured for these samples and the results are shown in Table 3.

TABLE 3 Laser output Surface strength (m. watt) (g) Sample A B C D A B C D 1 175 450 225 225 70 15 1500 2 450 225 225 500 100 1500 EXAMPLE 4 On sample C2 in Example 3 was coated stearic acid amide dissolved in turpentine oil at a dry thickness of 0.05 ym. When the same test as in Example 1 was applied to the sample, the minimum output of laser required for laser recording was 225 m.watt and the surface strength of 1.5 kg. That is, as is clear by the comparison with the case of sample D2 in Example 3, when the higher fatty acid amide was used in place of the stearic acids the same results as in the case of using the higher fatty acid were obtained.

EXAMPLE 5 Recording elements were prepared in the same manner as in the case of preparing samples C1-C7 in Example 1, but using the coating composition having the following formula in place of the chlorinated polyethylene layer as the protective layer.

Chlorinated polyethylene (same as in Example 1) 4 9 Methyl ethyl ketone 50 g 2-methoxy ethanol acetate 50 g Stearic acid 30 g The same tests as in Example 1 were carried out on these samples and the same results as in Example 1 were obtained. That is, in the sample of this invention corresponding to sample C1, the recording laser output was 125 m. watt and the surface strength was 1.5 kg and in the sample of this invention corresponding to sample C7, the recording laser output was 225 m. watt and the surface strength was 1.5 kg. Thus, it was confirmed that when the higher fatty acid amide was used in place of the higher fatty acid as well as when the higher fatty acid or higher fatty acid amide was contained in the protective layer in place of coating on the recording layer, the same results as above were obtained.

EXAMPLE 6 When stearic acid amide was used in place of stearic acid in Example 5, the same results as in Example 5 were obtained.

Claims

1. A thermal recording element having formed on a support a recording layer and a protective layer comprising an organic high molecular weight material formed thereon, wherein a higher fatty acid having more than 10 carbon atoms or the higher fatty acid amide thereof is present on or in the protective layer.

2. A recording element as claimed in Claim 1, wherein said support is polyethylene terephthalate.

3. A recording element as claimed in Claim 2, wherein said recording layer is a metal layer.

4. A recording element as claimed in Claim 3, wherein the metal layer has a thickness of 300 to 1,500 Angstroms.

5. A recording element as claimed in Claim 3 or 4, wherein said recording layer comprises a layer of tin, bismuth or indium.

6. A recording element as claimed in Claim 3. 4 or 5, wherein said recording layer includes a layer of germanium sulphide, tin sulphide or lead iodide.

7. A recording element as claimed in any preceding claim, wherein said higher fatty acid is lauric acid, myristic acid, palmitic acid, stearic acid, behenic acid, oleic acid, linolic acid or arachidonic acid.

8. A recording element as claimed in any preceding claim, wherein 0.1 to 20% by weight of said higher fatty acid or amide is present in the protective layer.

9. A recording element as claimed in any preceding claim, wherein the thickness of the protective layer is 0.01 to 1 millimicrons.

10. A thermal recording element as claimed in Claim 1, substantially as hereinbefore described with reference to any of the Examples.