GB2233325A - Rigid printing type and a process for preparing rigid porous material - Google Patents

Abstract

A rigid printing type is made by a process comprising mixing and pulverising an easily soluble material with particulate glass having a melting point lower than that of the soluble material, a binder and a solvent which dissolves the binder but not the soluble material. The resulting powder is molded and then sintered, whereafter the soluble material is dissolved out to give multiple pores.

Description

RIGID PRINTING TYPE AND A PROCESS FOR PREPARING RIGID POROUS MATERIAL The present invention relates to a rigid printing type for a seal, a roller-type printing head, a stamp or a pen, and also relates to a process for preparing a rigid and porous material which, for example, may be used for such a rigid printing type.

Porous rubber materials have been widely used as materials for forming printing types impregnated with inks. However, rubber materials are generally too resilient, resulting in distortion or deformation of the printed letters or images, and thus they cannot be used as materials for types which are used to print precisely identical printed letters or images. For instance, rubber materials cannot be used as materials for one's registered seals. A porous metallic material has been tried as the material for a printing type, as disclosed, for example, by Japanese Patent Publication No.

30253/1987. However, such a metallic material has disadvantages that the printing face tends to be oxidized after a time and that the printed image may become dimmed or blurred by unsatisfactory transfer of the ink.

Japanese Patent Publication Nos. 131861/1985, 97164/1986 and 212257/1987 disclose oxide ceramics, nitride ceramics and carbide ceramics which may be used as materials for seals. However, these prior publications fail to disclose the use of a lower melting point glass as the starting material therefor. The ceramic materials disclosed by these prior publications have various disadvantages due to excessively high hardnesses thereof and also have the disadvantage that they are poor in ink retaining property so that they cannot be used to form printing heads which are used for multiple printing or stamping cycles.

According to one aspect of the present invention, there is provided a rigid and porous printing type made of a sintered body of glass particles and having multiple fine pores, the printing type preferably having being prepared by sintering the glass particles together with a easily soluble material which has been removed by dissolving the same by the use of a proper solvent to leave multiple fine pores. In use, the multiple fine pores can be impregnated with an ink.

It will be seen that the invention can be implemented so as to provide a rigid printing type which can be used as one's registered seal without the fear of distortion or deformation of the printed image and which has a stable printing characteristic for a long time.

According to a further aspect of the invention, provided is a process for preparing a rigid and porous material suitable, for example, for the production of a rigid printing type, comprising the steps of: kneading a mixture of (a) an easily soluble material, (b) a particulated glass having a melting point lower than that of said easily soluble material, (c) a binder and (d) a solvent which dissolves said binder but does not dissolve said easily soluble material; drying and then pulverizing said kneaded mixture to obtain a moldable powder; compression molding said moldable powder to obtain a molded body followed by optional surface treatment of the molded body; sintering said molded body at a temperature higher than the melting point of said glass but lower than the temperature at which said easily soluble material reacts with said glass; and removing said easily soluble material from said sintered body by dissolving the same by a proper solvent.

Particles of ceramic material having a melting Particles of ceramic material having a melting point higher than that of the used glass particles, such as particles of alumina, may be added to the mixture of the components (a), (b), (c) and (d) to increase the hardness of the resultant rigid and porous material.

Since a rigid printing type can be prepared as described above to have multiple continuous pores, formed by dissolution of the easily soluble material from the sintered body, an ink can be impregnated within these pores and the ink pressed out of these pores evenly to form a clear seal image when it is used, for example, as a seal head. The backside (i.e. the side opposed to the printing face) of the printing type may be attached with a sponge or like ink-absorbing strip so that the ink is continuously and spontaneously supplied from the ink-absorbing strip to the printing type by the capillary phenomenon, whereby the printing type may be used semipermanently without the need of supplemental feeding of the ink.Since the printing type is rigid because it is made of a sintered body of glass particles, it can form a precise printed image without the fear of deformation or distortion even when it is applied with a relatively high pressure. Accordingly, it can be used for an application where strict identity of the printed image is required, for example, it can be used as one's registered seal. In contrast to the conventional printing types made of metallic materials, the resulting rigid printing type may be used stably for an extremely long period without fear of oxidation of the material on the surface or in the interior thereof. Such a printing type can thus retain its favourable printing characteristics semipermanently to give a clear printed image.

The hardness of the rigid printing type may be varied within a wide range by adding particles of a ceramic material having a melting point higher than that of the used glass particles at the step of forming a slurry. The mixing ratio of the higher melting point ceramic particles in this case is less than about 10%, based on the weight of the glass particles.

The apDended drawing shows an embodiment, by way of example, of a process for preparing rigid and porous material, such as may be used as the material for a rigid printing type.

Referring to Fig. 1 showing an exemplified process for preparing a rigid and porous material according to one example of this invention, an easily soluble material 1 is mixed with a particulated glass 2 in a predetermined ratio to form a uniform mixture. The easily soluble material 1 used may be selected from various inorganic materials which do not react with the particulated glass 2 at the subsequent sintering step The easily soluble material 1 is used in the form of fine powders each having a particle size of from about 10 to about 70 microns. Various water-soluble metal salts may be used as the easily soluble material 1. In this embodiment, NaCl powders each having a particle size of less than 70 microns, a melting point of 800"C and a specific gravity of 2.16 are used.The particulated glass 2 may be selected from glass particles having various compositions, the particularly preferred being alkali glasses. The glass 2 has a melting point lower than that of the easily soluble material 1.

Glass particles, each having a particle size ranging from 1 to 80 microns, are preferred to decrease the volume shrinkage at the subsequent sintering step. For example, particles of a lower melting point glass having a melting point of 720"C and a specific gravity of 2.5 and having an average particle size of 20 microns may be preferably used.

The components 1 and 2 may be mixed in a ratio by weight of the easily soluble material (1) : the particulated glass (2) = 70 to 25 : 30 to 75.

In this embodiment, 200 parts by weight of NaCl is mixed with 300 parts of the particulated glass.

A . binder 3 may be selected from the following materials (a) High polymers which are soluble in organic solvents, such as acrylic resins, polyethylene glycol, polyvinyl chloride, polyvinyl acetate, copolymers of vinyl chloride and vinyl acetate and waxes; (b) Water-soluble high polymers, such as polyvinyl alcohol and polyvinyl pyrrolidone; and (c) Emulsions of various synthetic resins.

The binder has sufficient binding force not to cause collapsing of the preliminary compression molded body made of the mixture of the particulated glass and the easily soluble material, and has a melting point lower by about 50"C than the surface softening point of the used particulated glass.

For example, 30 parts of a polyethylene glycol having a molecular weight of from 1,500 to 20,000 is used in this embodiment. While heating the mixture at 40 to 50"C by a heater 4, a solvent 5 such as trichloroethane is added to the mixture followed by agitation to obtain a uniform admixture. Examples of the solvent used in this step include alcohols such as methanol, ethanol, propanol and butanol, ketones such as methyl ethyl ketone, cellosolves such as methyl cellosolve and butyl cellosolve, and aromatic compounds such as benzene, toluene-and xylene.

The admixture is then dried in a vacuum drier 6 until it forms a slurry which is agitated and then placed in a drier 7 maintained at 50 to 60"C so that the surfaces of the particles are attached with or covered by binder films.

It is desirous that the starting material mixture is kneaded to once form a slurry, as described above. This slurry-forming step produces a uniform rigid and porous body.

The thus obtained powder-form admixture is then pulverized in pulverizing means 8, such as an earthenware mortar, to adjust the particle size and to uniformalize the particle size. A mass of the pulverized admixture required for molding a desired printing type is weighed and subjected to an ordinary compression molding using an upper mold 9 and a lower mold 10. A mold 12, for example a phenolic resin intaglio, is placed on the pulverized admixture 11 so that the desired letter or image is formed on the top face of the compression molded body. A releasing agent may be coated over the surface of the phenolic resin intaglio 12 to facilitate easy removal of the molded body from the mold.The pressure at this compression molding step is 2 increased gradually up to about 2 to 4 tons/cm The compression molded body 13 is then sintered in an electric furnace 14 at a temperature of from about 650"C to about 770"C for about 20 to about 200 minutes. For example, the compression molded body is heated to 300"C for 20 minutes to remove the binder, and then sintered at 760 C for 20 minutes.

The sintered body is then cooled and subjected to surface treatments, such as grinding and rinsing of the surface.

The releasing agent should be removed entirely at this step, for example, by using a brush.

Letters on the surface of the thus prepared printing type may be clarified by the sand blast method or other proper method. In such a case, the phenolic resin intaglio 12 need not be used at the compression molding step.

The sintered body 13 is then placed in an ultrasonic washer 15 to be washed for 1 to 2 hours while exchanging water in the washer with fresh water to dissolve the easily soluble material 1 confined in the sintered body 13. Thus, a sintered body made of glass particles and having multiple fine pores ( = 10 to 100 microns) is prepared. Finally, the sintered body is dried in a drier 16, for example, at 1500C for 20 minutes to remove water in the fine pores. A rigid and porous body having a desired printing face and having a porosity of about 25 to 55 is thus prepared. The volume shrinkage in the practice of the process of this embodiment is less than 8%, which is optimal for the production of a printing type.

EXAMPLES: The present invention will now be described more specifically by referring to presently preferred examples thereof. In the following Examples, "parts" stands for "parts by weight" unless otherwise stated.

Example 1 Generally following to the procedure as described above, a rigid and porous body was prepared by using 100 parts of NaCl particles having an average particle size of 60 microns, 100 parts of particles of a lower melting point glass (Melting Point: 730"C) having an average particle size of 30 microns, 100 parts of particles of alumina (Melting Point: 1400 cm) having an average particle size of 60 microns, 15 parts of a higher fatty acid acting as the binder, and 200 parts of ethanol acting as the solvent. The resultant rigid and porous body had a porosity of about 35% and the volume shrinkage during the production steps was less than 5%. The thus produced printing type was very high in its hardness due to the presence of admixed alumina particles.

Example: 2 Similarly as in Example 1, a rigid and porous body was prepared by using 150 parts of CaCO3 (Melting Point: 1339"C) particles having an average particle size of 50 microns, 300 parts of particles of a lower melting point glass (Melting Point: 730"C) having an average particle size of 30 microns, 25 parts of polyethylene glycol acting as the binder, and 300 parts of trichloroethane acting as the solvent. Different from Example 1, a dilute hydrochloric acid solution was used in this Example to dissolve CaCO3 used as the easily soluble material. The thus produced rigid and porous body had a porosity of about 45% and the volume shrinkage during the production steps was less than 78. A rigid printing type could be formed by using the sintered body of this Example.

A uniform porous sintered body made of glass particles and well suited for use as a printing type can be prepared in accordance with the above examples. Particularly, since the particles of an easily soluble material, the particulated glass and the binder are pulverized by an ordinary process while using a solvent which dissolves the binder but does not dissolve the easily soluble material, followed by compression molding and sintering, formation of dense layer only on the surface of the molded body at the compression molding step can be obviated to make it possible to prepare a rigid and porous body which is significantly improved in uniformity.

Claims (19)

WHAT IS CLAIMED IS:

1. A process for preparing a rigid and porous material comprising the steps of: kneading a mixture of (a) an easily soluble material, (b) a particulated glass having a melting point lower than that of said easily soluble material, (c) a binder and (d) a solvent which dissolves said binder but does not dissolve said easily soluble material; drying and then pulverizing said kneaded mixture to obtain a moldable powder; compression molding said moldable powder to obtain a molded body; sintering said molded body at a temperature higher than the melting point of said glass but lower than the temperature at which said easily soluble material reacts with said glass; and removing said easily soluble material from said sintered body by dissolving the same by a proper solvent.

2. The process for preparing a rigid and porous material according to claim 1, wherein said easily soluble material is NaCl.

3. The process for preparing a rigid and porous material according to claim 1 or 2, wherein said easily soluble material is in the form of particles each having a particle size of from about 10 to about 70 microns.

4. The process for preparing a rigid and porous material according to claim 1, 2 or 3, wherein said particulated glass is a particulated alkali glass.

5. The process for preparing a rigid and porous material according to any one of the preceding claims, wherein said particulated glass has a particle size of from 1 to about 80 microns.

6. The process for preparing rigid and porous material according to any one of the preceding claims, wherein the mixing ratio of said easily soluble material to said particulated glass ranges between 70 to 30 and 25 to 75.

7. The process for preparing a rigid and porous material according to any one of the preceding claims, wherein said binder has a melting point which is lower by about 500C than the surface softening point of said particulated glass.

8. The process for preparing a rigid and porous material according to any one of the preceding claims, wherein said binder is used in the form of a slurry.

9. The process for preparing a rigid and porous material according to any one of the preceding claims, wherein 1 to 10 parts by weight of said binder is mixed with 100 parts by weight of said easily soluble material plus said particulated glass.

10. The process for preparing a rigid and porous material according to any one of the preceding claims, wherein compression molding is effected at a pressure of from about 2 to 4 tons/cm2.

11. The process for preparing a rigid and porous material according to any one of the preceding claims, wherein sintering is effected at a temperature of from about 6500C to about 7700C.

12. The process for preparing a rigid and porous material according to any one of the preceding claims wherein sintering is effected for a time period of from about 20 minutes to about 200 minutes.

13. The process for preparing a rigid and porous material according to any one of the preceding claims, further comprising a step of surface treatment of the sintered body subsequent to said sintering step.

14. The process for preparing a rigid and porous material according to any one of the preceding claims wherein said rigid and porous body has a porosity of from about 25% to about 55%.

15. A process for preparing a rigid and porous material substantially as hereinbefore described with reference to the accompanying drawing or with reference to Example 1 or Example 2.

16. A printing type comprising a sintered body prepared by a process according to any one of the preceding claims.

17. A rigid printing type prepared by impregnating an ink in multiple fine pores of a sintered body made of glass particles, said sintered body being prepared by any of the processes set forth in claims 1 to 16, and said fine pores having been formed by dissolving said easily soluble material from said sintered body.

18. A rigid printing type according to claim 17, wherein said easily soluble material is NaCl.

19. A rigid printing type comprising a body formed of sintered glass particles and having multiple fine pores.