NL8304098A - METHOD FOR FORMING FIXED IMAGES - Google Patents

Description

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Oeé-Nederland B.V., in Venlo

Method for forming fixed images

The invention relates to a method for forming fixed images on image receiving material, in which an image is applied to a medium using thermoplastic resin-containing toner powder, the surface of which consists of material which has a less affinity for the softened toner powder than the image receiving material, and the pressurized toner powder is transferred to the image receiving material, the toner powder being soaked by heating before and / or while passing through the printing zone.

Such a method is described, inter alia, in British Patent Specification 1,245,426 and US Pat. Nos. 3,554,836 and 3,893,761. In these methods, a powder image formed, for example, on a photoconductive or magnetizable image recording material is transferred by pressure application to a medium 15 the surface of which consists of a material that has a low affinity for the softened powder, for example silicone rubber.

Subsequently, the powder image, again by pressure application, is transferred to image receiving material, the powder being softened by heating before and / or during the passage of the pressure zone, so that it acquires such viscous properties that, as a result of the pressure applied to it, , forms a cohesive layer which preferably at least partially penetrates the image receiving material. After cooling, the image is permanently bonded to the image receiving material. The heating of the powder is effected by heating the media on which the powder image is located before the transfer to the image receiving material, and optionally the image receiving material itself. The temperature is controlled in such a way that the powder softens sufficiently that it can be deformed and pressed into the image-receiving material at a relatively low pressure, but also does not soften so strongly that the cohesion in the powder becomes so low that when separation of the medium 8304098 *% -2- and the image-receiving material powder cleavage occurs and part of the powder image remains on the medium.

Toner powders containing as epoxy resin or polystyrene as thermoplastic resin have hitherto been proposed for use in the method according to the preamble. Operating systems can be realized by using such toner powders, but it has been found that these systems have shortcomings.

In a system in which only the medium is heated to soften the toner powder, a high medium temperature of at least 130 ° C is necessary to heat the toner powder in a relatively short time at a temperature within its operating range. The working area is the temperature range within which the temperature of the toner powder must be within for this powder to transfer completely and well adhering from the medium to the image receiving material. At the bottom 15, this working area is limited by the temperature at which just complete transfer and good adhesion of the powder melt is obtained, and at the top it is limited by the temperature at which just no splitting of the powder melt occurs.

The required high medium temperature has the drawback that the image recording material (for example the photoconductive element), with which the warm medium is repeatedly contacted, is subjected to a high thermal load, which is disadvantageous for the life of the image recording material.

Another drawback of this system is that the working area, probably as a result of thermal degradation of the medium, is constantly getting smaller and after a few tens of thousands of loads of the medium a situation is already reached where a practical working area no longer exists.

Reduction of the medium temperature to 100 è. 105 ° C is possible if the image receiving material is also heated to about 80 ° C before it is contacted with the medium. However, this system has the disadvantage of a considerably higher energy consumption and it imposes limitations on the choice of the image receiving material.

35 Image receiving material containing thermoplastic substance, such as, for example, glued paper and ink preprinted paper containing thermoplastic resin, cannot be processed in this system, 8304098 because the resin in the paper is softened and the softened resin is partially transferred to the image recording material through the medium, making it unsuitable for further use. Also in this system the working area gradually decreases, although the speed at which this occurs is slower than in the system, in which only the medium is heated to soften the powder image.

The invention provides a method as described in the preamble, characterized in that the image is applied with the aid of toner powder, which contains crystalline polyester 10 with a melting point between 50 and 100 ° C as thermoplastic resin.

The process according to the invention achieves a sufficiently wide operating range, which is located at considerably lower temperatures than has hitherto been established in such processes using the previously proposed toner powders. This achieves a significantly lower energy consumption and a longer life of the medium. When the method according to the invention is used in an electrophotographic copying process, it is furthermore achieved that the load of the photoconductive image recording material is reduced, which improves the service life of this material.

In an attractive embodiment of the method according to the invention, in order to soften the toner powder, only the medium to which the toner powder is applied image-wise is heated. The working range is then in most cases 20 ° C to 30 ° C, while its lower limit is usually at a medium temperature which is slightly higher than the melting point of the crystalline polyester contained in the toner powder.

However, the method according to the invention can also be carried out by supplying the heat, which is necessary for the softening of the toner powder, exclusively or mainly to the image receiving material. Also in this embodiment there is a wide working range of usually at least 20 ° C.

The correct location and size of the working area, in addition to the properties of the toner powder itself, are also determined by the geometry of the device in which the method according to the invention is carried out, the speed with which the device operates, the composition and the hardness from the medium to which the toner powder is applied image-wise, the manner in which the powder image is softened and the pressure with which the softened toner powder is transferred to the image-receiving material is 8304098-4%. In particular, the contact time between the medium carrying the powder image and the image receiving material is a strongly determining factor for the working area.

For a specific arrangement, the operating range can be easily determined by measuring the temperature range within which complete transfer and good adhesion of the powder image to the image receiving material are obtained. A reasonable indication of the location and size of the working area of a particular toner powder can be obtained by measuring the viscosity properties of the toner powder. In general, the working range of the toner powder corresponds to the temperature range within which the loss compliance (J ") of the toner powder, measured at a frequency which is 0.5 x the reciprocal of the contact time in the device used for carrying out the method according to the invention, is between 10 "1 * and 15 10" ° m / N. The viscosity properties of the toner powder are measured in a rheometer, where moduli G "and G" are determined as a function of frequency at a number of different temperatures. The curves found are then reduced to one temperature, the reference temperature.

20 The loss compliance (Jn) is calculated as a function of the frequency from this reduced curve. From the loss compliance frequency curve, the shift factors of the lower and upper limit temperature (J "= 10" 6, respectively 10- ^ m2 / N) of the working area can be read. The lower and upper limit temperature of the working area can then be are calculated using the WLF equation, which is drawn from the shift factors found in the measurements at different temperatures.

The toner powder used in the method according to the invention contains crystalline polyester with a melting point between 50 and 100 ° C and preferably between 60 and 85 ° C. The melting point of the crystalline polyester is determined by melting the polyester, then cooling the melt at a cooling rate of 10 ° C / minute to 20 ° C and then immediately reheating the solid mass at a heating rate of 10 ° C / min. minute. During the second heating step, the melting point 35 is recorded as being the temperature at which the maximum endothermic heat effect is observed. The number average molecular weight of the crystalline polyester is preferably at least 5000 and 8304038 I-5- most preferably between 8000 and 45000.

When the method according to the invention is carried out in a device in which a relatively short contact time for the transfer of the powder image from the medium to the image-receiving material, the powder image is preferably formed with toner powder which is crystalline polyester with a number average molecular weight between 8000 and 25000. contains. In such a device, the medium consists, for example, of a roller with a diameter of 20 to 40 mm, which roller is provided with a several tenths of a millimeter thick coating of silicone rubber and the transfer of the powder image from the medium to the image receiving material is carried out in the pinch this roller with a similar roller, which presses against the medium with a force of about 80-100 N / cm.

The number average molecular weight of the crystalline polyester is determined by GPC measurement with a low angular laser-light scattering detector.

Examples of suitable crystalline polyesters are: polycaprolacetone (Tm + 60 ° C), polyhexamethylene bacate (Tm + 65 ° C), polyhexamethylene adipate (Tm + 55 ° C), polyhexamethylene oxalate (Tm + 65 ° C), 20 polyethylene adipate (Tm + 60 ° C), polydecamethylene azelate (Tm + 70 ° C), polydecamethylene bacate (Tm + 76 ° C), polytetramethylene suberate (Tm + 56 ° C), polyethylene (methyl) terephthalate (Tm + 70 ° C), polytetramethylene bacate (Tm + 61 ° C), Polyethylene Suberate (Tm + 65 ° C), Polyethylene Bacate (Tm + 76 ° C), Polydecamethylene Oxalate (Tm + 80 ° C), Polyde-Camethylene Adipate (Tm + 78 ° C), Polydecamethylene Decanedioate (Tm + 82 ° C), polydecamethylene octadecane dioate (Tm + 93 ° C), polyhexamethylene dodecanedioate (Tm + 76 ° C), polyhexamethylene decamethylene bacate (Tm + 64 ° C), polydecamethylene sebacate terephthalate (Tm + 71 ° C ), and polydecamethylene-2-methyl-1,3-propanediol dodecanedioate (Tm + 72 ° C).

In addition to crystalline polyester, the toner powder used in the method according to the invention also contains a coloring material, which may consist of carbon black or inorganic or organic pigment or dye. Furthermore, the toner powder may contain other additives, the nature of which depends on the manner in which the image is applied with the aid of the toner powder.

For example, toner powder for the development of latent magnetic 8 7 f ». A A 0 q

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-6- images, or toner powder, which is supplied with magnetic transport means to an electrostatic image to be developed, must still contain magnetically attractable material, usually in an amount between MO and 70% by weight. Also, toner powders serving for the development of electrostatic images can be made electrically conductive in a manner known per se, by finely distributing electrically conductive material in the powder particles or depositing them on the surface of the powder particles. If, for the development of electrostatic images, one uses the toner powder in a so-called two-component developer, the powder particles can still contain a charge control agent, which ensures that the powder particles, upon the triboelectric charge, take on a charge whose polarity is opposite to that of the polarity. of the electrostatic image to be developed. The known materials can be used as magnetically attractive material, electrically conductive material or charge control agent.

Incorporation into the toner resin of fillers, such as magnetically attractable pigment or carbon black, results in the loss compliance of the toner powder being reduced compared to that of corresponding toner resin, which does not contain fillers. In particular, when the toner powder for use in the method of the invention contains crystalline polyester with relatively low number average molecular weight of, for example, 5000-15000, it may be necessary to include fillers in the toner powder in order to achieve the loss compliance of the toner powder at the desired level to bring. If the toner powder does not also have to be magnetically attractable and / or electrically conductive, instead of magnetically attractable and / or electrically conductive fillers, inert fillers such as talc, silica, clay, titanium dioxide and zinc oxide can also be included in the toner powder. An electrically conductive filler, which already has a clear influence on the loss compliance and the electric conductivity of the toner powder when using relatively small amounts of 5 to 15% by weight, is carbon black with a specific surface area of at least 750 m / g and an oil absorption between 250 and 400 ml / 100 g.

8304098 I * '- ί -7-

The toner powder can be prepared in a known manner by melting the crystalline polyester, finely distributing the coloring material and any other additives in the melt, cooling the melt to a solid mass and the solid mass to 5 particles of the desired particle size, which is usually 8-30 microns.

In the preferred embodiment of the method according to the invention, in which the toner powder is softened by heating only the medium, the toner powder is applied to this medium 10 by pressure transfer from a photoconductive or magnetic image recording material, it is possible that the upper limit of the working area is not limited by the temperature at which splitting of the powder ravages occurs, but by the temperature at which the toner powder is already softened from the image recording material to the medium during the pressure transfer and partly adheres to the image recording material. It has been found that in this case the upper limit of the working range can often be increased by storing the toner powder for some time, for example 2-7 days, at an elevated temperature, but below the softening temperature of the toner powder, for example at approximately 50 ° C. . During storage at elevated temperature, the percentage of crystalline polyester resin in the toner powder increases, but it is not clear whether the increase in the crystallinity percentage is responsible for the increase in the upper limit of the working range.

The process according to the invention can be carried out in the previously known devices such as, for example, described in British patent specification 1 245 426, US patents 3 554 836, 3 893 761 and 4 068 937 and European patent application 0045102.

Preferably, only the medium on which the powder image is formed before transfer to the image receiving material is heated.

The working area, as mentioned before, is wide and is at a considerably lower level than the working area of the known toner powders based on polystyrene or epoxy resins.

The invention is further illustrated by the following examples.

8304098

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Example 1 2500 g of polycaprolactone with a number average molecular weight of about 21,000 were melted and 2500 g of magnetically attractable pigment (Bayferrox 318M from Bayer A.G., W-Germany) were finely divided in the melt. The melt was then cooled to room temperature and the solid mass ground to particles having a particle size between 10 and 30 microns.

The toner powder thus obtained was used in an electrophotographic copying machine as described in European patent application No. 0 045 102. The medium on which the powder image formed on the photoconductive image recording material was applied by pressure transfer consisted of a metal roller with a diameter of 25 mm, which roller was provided with a first, approximately 500 micrometer thick coating of pigmented, RTV silicone rubber (RTV 200/201 from the 15 company Possehl, W. Germany) and a second, approximately 70 μm thick coating over it of a non-pigmented RTV silicone rubber obtained by cross-linking an α-ω-hydroxy-polymethylsiloxane with a tetraethylsilicate under the influence of dibutyltin dilaurate.

For the softening of the powder image, only the medium was heated. 20 Océ plain paper was used as image reception material. The working area was at a medium temperature of 65-85 ° C. If the toner powder, prior to use, was stored at 50 ° C for 5 days, the operating range was 70-100 ° C.

After 80,000 copies were made, the working area 25 had hardly narrowed.

Using the toner powder just described, the method of the invention was also performed by realizing the softening of the powder image by heating both the medium and the image receiving material. The working area was now at a medium temperature between 40 and 45 ° C and an image receiving material temperature between 70 and 100 ° C.

Example 2

In the method described in Example 1, toner powder was prepared having the composition: 50 wt% polycaprolactone with a number average molecular weight of about 15,000 50 wt% magnetically attractable pigment (Bayferrox 318M).

8304098 ...... ........ 'mfr -9- 1500 g of this toner powder was dispersed in a dispersion containing: 24 g of carbon with a particle size between 10 and 250 nanometers 12 g of hydrophobic silica 5 10 g polyvinyl alcohol 3000 ml ethanol 7000 ml water. ,

The dispersion was heated to + 65 ° C with continuous stirring and kept at this temperature for about 10 minutes. It was then cooled to room temperature and the now carbon-coated toner particles were separated from the liquid. The toner powder obtained had a specific resistance of 7.10 ^ Ohm.m.

The toner powder was used in the electrophotographic copier mentioned in Example 1. The operating range was at a medium temperature of + 7Q-125 ° C.

Example 3

Toner powder was prepared in the manner described in Example 1 comprising: 50 wt% polycaprolactone having a number average molecular weight of about 43000.

50% by weight of magnetically attractable pigment (Bayferrox 318M).

The toner powder was used for the magnetic brush development of electrostatic images, which were formed on a photoconductive image recording material, of which the photoconductive layers were composed, as described in example 5 of the Dutch patent application no. 7808418 and the carrier consisted of a plastic film covered with a layer of aluminum that had been screened as described in European patent application no. 0037193. The electrostatic images were formed by electrostatically charging the image recording material, projecting the image of an original onto the photosensitive side of the material and also the material via its carrier to illuminate. The powder images formed on the image recording material were transferred to unheated Océ plain paper in a transfer fixing device, such as used in an Océ 1900 copier.

The working area was at a medium temperature of 70-95 ° C.

Example 4

The procedure of Example 1, wherein only the medium was heated to soften the powder, was repeated using a toner powder of the following composition: 42.5 wt% polycaprolactone having a number average molecular weight of about 9200 50% by weight magnetically attractable pigment (Bayferrox 318M) 7.5% by weight carbon black with an average particle size of about 30 nanometers, a specific surface area of about 1000 m2 / g and an oil absorption of about 340 ml / 100g.

The working area was now at a medium temperature of 75 to 95 ° C.

Substantially the same result as described above was obtained when using a toner powder of the composition just described, which, however, contained polycaprolactone having a number average molecular weight of 5200 as a thermoplastic resin.

Example 5 In the manner described in Example 1, the following toner powders A to F were prepared with the following composition: A. 42.5 wt.% Polyhexamethylene bacate having a number average molecular weight of about 18,000.

50 parts by weight magnetically attractable pigment (Bayferrox 318M) 20 7.5 parts by weight carbon black with the specifications given in example 4.

B. 42.5 weight percent polyhexamethylene adipate with a number average molecular weight of about 17,000.

50 parts by weight of magnetically attractable pigment (Bayferrox 318M). 7.5 parts by weight of carbon black with the specifications given in Example 4.

C. 50 weight percent polyhexamethylene dodecanedioate with a number average molecular weight of about 18,000.

50% by weight of magnetically attractable pigment (Bayferrox 318M).

30 D. 43 wt. (Polyhexamethylene decamethylene sebacate with a number average molecular weight of about 22,250.

50 parts by weight magnetically attractable pigment (Bayferrox 318M) 7 parts by weight carbon black with the specifications given in example 4.

35 E. 50 weight parts polydecamethylene dodecanedioate with a number average molecular weight of about 22,000 50 weight parts magnetically attractable pigment (Bayferrox 318M).

8304098 -11-

50% by weight of polyethylene suberate having a number average molecular weight of about 22,000 50% by weight of magnetically attractable pigment (Bayferrox 318M).

The powder images formed with these toner powders on a photoconductive image recording material were transferred to unheated Océ plain paper in a transfer fixing device, such as used in an Océ 1900 copier. The working range for the different toner powders was determined at the medium temperature below:

10 Powder A: + 85 - + 110 ° C Powder D: + 75 - + 100 ° C

Powder B: + 65 - + 85 ° C Powder Ei + 90 - + 115 ° C

Powder C: + 85 - + 115 ° C Powder F: + 85 - + 105 ° C

8304098

Claims (5)

A method of forming fixed images on image receiving material, wherein an image is applied to a medium using thermoplastic resin-containing toner powder, the surface of which consists of material which has a less affinity for the softened toner powder 5 than the image receiving material, and the pressurized toner powder is transferred to the image receiving material, the toner powder being soaked by heating before and / or during the passage of the printing zone, characterized in that the image is applied using toner powder which as crystalline polyester thermoplastic resin with contains a melting point between 50 and 100 ° C. 2. A method according to claim 1, characterized in that the image is formed with toner powder containing crystalline polyester with a melting point between 60 and 85 ° C. Method according to claim 1, characterized in that the image is applied with toner powder containing crystalline polyester with a number average molecular weight of at least 5000. Method according to claim 2, characterized in that the image 20 is applied with toner powder containing crystalline polyester with a number average molecular weight between 8000 and 45000. Method according to one or more of the preceding claims, characterized in that the powder image is softened by heating only the medium on which the image is applied. 8304 0 9 8