Method For Producing Synthetic Paper

Abstract

Synthetic paper is produced by adding a dispersion medium to a polyolefin slurry to prepare an emulsion, jetting said emulsion under an autogenous or higher pressure, and collecting and compressing the jetted fibrous paper material. The product is homogeneous and smooth and well adapted for printing and writing.

Description

The present invention relates to a method for producing synthetic paper, more particularly a special fibrous paper material containing a polyolefin.

Heretofore, various synthetic papers have been made. One is a film paper obtained by making the surface of a film microporous with capacity for absorbing ink but, at the same time, opaque by means such as pressing with an uneven surface, foaming, treating with chemicals, swelling, introducing an inorganic compound therein and extracting one component of the blend. The foregoing combination was disclosed in published German Pat. No. 1,954,477.

According to another disclosure of the prior art, paper may be obtained from staple synthetic fibers in a manner similar to making paper from pulp (British Pat. No. 1,188,322).

According to another prior art disclosure, split fiber paper is prepared using a material obtained by slitting a film into the fibrous state (French Pat. No. 1,548,246). Further, a spun bond paper may be obtained by directly collecting a melt spun fiber in a sheetlike manner [W. Hearle, Skinners Rec., 39, 647 (1965)].

According to other disclosures of the prior art, a plexifilament paper may be obtained by jetting a polymer solution directly in a filamentary state and collecting it in a sheetlike form [W. Hearle, Skinners Rec., 39, 647 (1965)], and a fibrid paper may be obtained by making a paper from fibers produced by extruding a polymer solution while shearing into a coagulating bath of said solution (U. S. Pat. No. 3,382,305).

Of these synthetic papers, the film paper, the synthetic fiber paper and the split fiber paper have shortcomings in that their thicknesses are not uniform, their surfaces are uneven and their basis weight or fiber distribution over the whole sheet are not uniform. Accordingly, because of localized differences, deviations of appearance, luster and ink absorbability are brought about. The spun bond paper and the plexifilament paper have shortcomings in that patterns due to the presence of continuous filaments appear on the surface; when said patterns are flattened, the corresponding portions of the surface are compressed in the flat state and look lustrous; these papers lack uniformity. Further, in the case of the fibrid paper, because the constituting fibrid is produced by shearing of a liquid, it is not possible to obtain sufficient molecular orientation for purposes of strength, and a paper high in tenacity cannot be obtained.

Japanese Pat. application Ser. No. 7728/1969 proposes the idea of shearing a polymer solution by means of a high speed gas stream to convert the solution into fibers, collecting the fibrious matter and using it as a filter. However, according to this method, although the resulting fiber is not branched, it is suitable when used as a filter. However, the non-branched fibers are not intertwined enough for use, and the paper product lacks uniformity.

Again, Japanese Pat. application Ser. No. 4471/1963 discloses spraying a resin emulsion to obtain a powder; however, this method does not produce a paper material having fiber intertwining properties.

An object of the present invention is to provide a synthetic paper which is free of the shortcomings of the aforementioned conventional synthetic papers and excellent in mechanical properties, intertwining characteristics, uniformity and smoothness.

Another object of the present invention is to provide a method for producing a synthetic paper which is free of surface patterns, rich in printability and excellent in luster, appearance and hand.

Other objects of the present invention will be made clear from the following description.

According to the present invention, the aforementioned objects are attained by:

1. preparing an emulsion from (A) a slurry consisting of a polyolefin and a solvent from said polyolefin, and (B) a dispersion medium having a boiling point at a pressure less than 1 atm. which is lower than the melting point (at a pressure less than 1 atm.) of said polyolefin and which is insoluble or nearly insoluble in said solvent and preferably not reactive with said solvent, wherein the volume of said dispersion medium (B) present in the emulsion is larger than the volume of the slurry (A),

2. jetting said emulsion under at least an autogenous pressure obtained by heating said emulsion from a nozzle to thereby make a fibrous paper material, and

3. collecting said fibrous paper material and compressing the same.

In the practice of the present invention, use of a slurry obtained by solution polymerizing an olefin monomer is advantageous because of the continuity of its steps; it is preferable for purposes of sheet formation in a later step that the solvent for the polyolefin in this case should have a boiling point which is lower than the melting point of said polyolefin.

In the present invention, a specified dispersion medium is added to such a slurry to prepare an emulsion. It is preferable for obtaining a paper material having good intertwining properties that the particle size of the slurry in the emulsion be about 3 - 400 microns. And by jetting such an emulsion from a nozzle at a high temperature under a high pressure, a branched paper material having good intertwining properties is obtained.

Hereinbelow, specific details of the present invention will be described.

Polyolefins as used in the practice of the present invention have a fiber-forming capacity, are obtained by polymerizing olefin monomers and may be straight chain or branched polymers.

As examples of the olefin monomers, there are included .alpha. -olefins having one - 12 carbon atoms such as, for example, ethylene, propylene, butene-1, 3-methylbutene-1, 4-methylpentane-1, hexene-1, styrene, octene-1 and decalene-1; however, said monomers are not limited thereto. It goes without saying that these olefins may be copolymerized with hitherto known copolymerizable monomers. However, in this case it is necessary that an olefin should be present in an amount of at least 50 percent by weight.

Various polymerization catalysts may be used. Generally a Ziegler-Natta type catalyst is used; however, when the monomer is ethylene, a compound having a radical, a transition metal oxide, a transition metal and a halogen compound are used as catalyst.

The Ziegler-Natta type catalysts used are generally transition metal compounds, metals of Groups 1 - IV of the Periodic Table, organometallic compounds of such metals or hydrides of such metals. However, for increasing the crystallinity of the polymer produced, an electron donor compound, a proper halide or a metal salt may be added as a third component.

The olefin may be present alone or as a mixture of at least two components. However, in the case of copolymerization of at least two components, in order that the composition of the polymer produced may be constant, the components may be equally randomly copolymerized or the monomer components may be supplied with each other and block copolymerized. Again, homopolymerization, random copolymerization or block copolymerization may be combined in one polymerization step. The polymer produced is generally crystalline and the catalyst is selected accordingly.

In the practice of the present invention, polyethylene, polypropylene or a copolymer of the two is especially preferable. Further preferable is polypropylene or a blend or graft copolymer of polypropylene and polyvinyl alcohol, polyvinyl acetate or polyacrylic acid in an amount not exceeding 30 percent of the polypropylene.

The slurry used in the practice of the present invention may be prepared by dissolving or swelling a polyolefin in a solvent. However, it is preferable from the procedural viewpoint to prepare the slurry by polymerizing an olefin monomer in a solvent which is capable of dissolving or swelling the polyolefin at a jetting temperature.

As examples, the following solvents may be used alone or in admixture:

(1) water; (2) hydrocarbons including saturated hydrocarbons having five - 11 carbon atoms such as, for example, hexene, heptane, acetone, nonane, decane, cyclohexane, methyl cyclohexane, decalin and petroleum ether; as aromatic hydrocarbons benzene, toluene, xylene and p-cymeme; as unsaturated alicyclic hydrocarbons tetralin, .alpha. -pinene and turpentine oil; (3) as halogenated hydrocarbons: aliphatic halogenated hydrocarbons such as, for example, methylene chloride, chloroform, bromoform, carbon tetrachloride, ethyl bromide, dichloroethane, ethylidene dichloride, tetrachloroethane, pentachloroethane, dichloroethane, trichloroethylene, tetrachloroethylene, isobutyl chloride and isoamyl chloride; as aromatic halogenated hydrocarbons chlorobenzene, bromobenzene and o-dichlorobenzene; (4) as monohydric alcohols aliphatic alcohols such as methanol, ethanol, isopropanol, butanol and amyl alcohol; aromatic and alicyclic alcohols such as, for example, cyclohexanol and methyl cyclohexanol; (5) as ethers aliphatic ethers such as, for example, isopropylether and butylether; aromatic and alicyclic ethers such as, for example, anisole, dioxane and furfuryl alcohol; (6) as ketones aliphatic ketones such as, for example, acetone, acetone oil and methylethyl ketone; aromatic ketones such as, for example, cyclohexanone; (7) as esters, fatty acid esters and monobasic aromatic carboxylic acid esters such as, for example, methyl acetate, ethyle acetate, propyl acetate, butyl acetate, amyl acetate, ethyl propionate, butyl propionate, isoamyl propionate, ethyl butyrate and butyl butyrate; dibasic acid and tribasic acid esters such as, for example, diethyl carbonate; hydroxy acid esters such as, for example, ethyl lactate and ethyl oxyisobutyrate; and (8) polyhidric alcohols and derivatives thereof such as, for example, .alpha. -butylene glycol.

In terms of boiling point, solvents having a boiling point from about 38.degree. C to about 192.degree. C are used in many cases. In the present invention, hexane, heptane and methylene chloride are preferably used.

In the practice of the present invention, a solvent which is capable of substantially uniformly dissolving a polyolefin at a temperature higher than the boiling point under atmospheric pressure of the solvent, under an autogenous vapor pressure or a higher pressure than that may be selected. In a step to be mentioned later, it is preferable that the boiling point of the solvent be lower than the melting point of the polyolefin.

The concentration of the polyolefin based on the solvent is preferably 5 - 70 percent by weight (although it may vary depending upon the specific gravity, it corresponds to about 38 - 100 percent by volume). For example, in case the concentration is smaller than five percent, the amount of the product is small and its production is not efficient; on the contrary, when the concentration is higher than 70 percent, due to the high viscosity the fiber is unlikely to be transformed at the time of being jetted from the nozzle. In addition, the emulsion is apt to be condensed, and this is not preferable. The condensation of the emulsion results in making the jetted fiber continuous, in which case it becomes similar to the so-called plexifilament. This is because the higher the concentration of the polyolefin based on solvent, the higher the viscosity of the polymer. The more highly viscous the polymer, the more the polymer becomes apt to condense.

An emulsion used in the practice of the present invention is obtained by adding a dispersion medium to a slurry prepared in such a manner as is mentioned above. The dispersion medium is insoluble or hardly soluble in the solvent (preferably not reacting with the solvent) and the boiling point of said medium is lower than the melting point of the polyolefin.

As examples of the dispersion medium, water and alcohols having one - 10 carbon atoms as well as mutually insoluble solvents selected from the list provided in this specification may be cited. A mixed dispersion medium may be used; especially water or a mixed liquid consisting predominantly of water is advantageous.

It is preferable to add the dispersion medium in an amount of 30 - 2,000 percent by volume to the slurry; an amount not less than 200 percent by volume is preferable.

Unless a dispersion medium in an amount of at least 100 percent by volume of the slurry is added to the slurry, a so-called continuous fiber is apt to be formed. This is because the slurry becomes a dispersion medium on the contrary or condensed. In any event this is not preferable. When expressed in terms of percentage by weight, 10 - 120 percent by weight of the slurry is preferable (in percentage by volume, the figure may vary depending upon the combination of the respective specific gravity values; however, it is about 7 - 170 percent by volume).

In case the ratio of the dispersion medium to the slurry is excessive, the jetted material assumes the form of finely divided particles and this results in the production of fibers which are very short and have poor intertwining properties when formed into paper. Moreover, the proportion of polymer in the resulting jetted material is too small and the fiber production rate is too low.

If desired, it is possible to add pigments, stabilizers, antistatic agents, binders, sizing agents or other substances to the slurry provided the added amount is in a proper proportion and does not interfere with the proper functioning of the present invention. They may be added to the liquid in advance, to the slurry, to the emulsion, or in other ways.

The emulsion is thermodynamically unstable and always shows an inclination to condense to reduce the surface free energy. Accordingly, formation of an emulsion is a competitive reaction between condensation and redivision of the dispersed phase. Accordingly, in the present invention also, it is beneficial to cover the surface of the dispersed phase with a dispersion stabilizer, for example, a surface active agent, preferably a polymer of the olefin series and a surface active agent for the emulsion to stabilize the dispersion.

As specific examples of suitable surface active agents, there are (1) anionic surface active agents, for example, carboxylic acid salts, sulfuric acid esters, sulfonic acid salts and phosphoric acid esters; (2) cationic surface active agents, for example, amine salt types and quaternary ammonium salt types: (3) anionic and cationic surface active agents, for example, amino acid salts and betaine types; and (4) non-ionic surface active agents, for example, polyethylene glycol types and polyhydric alcohol types. As percentage to be added, 0.01 - 20 percent by weight based on the slurry is preferable.

However, at high temperature, the performance of the dispersion stabilizer added to the emulsion is reduced in many cases. Accordingly, it is preferable to facilitate redivision even when the dispersed phase is condensed, and always to include a redividing operation for the dispersed phase, such as stirring. Generally, because a polymer melt has a high viscosity, being viscous, especially in case the dispersed phase is a polymer only, particles of the dispersed phase tend to condense due to contact with other particles of the dispersed phase.

In practice of the present invention, it is possible to produce a fibrous paper material by jetting the so-prepared emulsion or an emulsion while forming the same from a nozzle of a proper shape at a temperature higher than the boiling point of the solvent and preferably lower than the melting point of the polymer under an autogenous pressure or higher pressure.

If the emulsion is jetted at a temperature lower than the boiling point of the solvent, then upon being jetted from the nozzle the solvent is not gasified and is not removed from the polymer. Therefore the molecular orientation of the polymer is not fixed, but the polymer tends to be saturated. The reason why it is preferable that the jetting temperature be lower than the melting point of the polymer is the same. Namely, in the emulsion before it is caused to be jetted, the polymer is dissolved or swollen in the solvent. When it is caused to be projected through the jet nozzle, the molecules are oriented due to a shearing type action in the nozzle. However, when the emulsion is set free from the nozzle, the jetted stream expands, losing its kinetic energy and tends not to receive the shearing action. When the boiling point of the solvent and the melting point of the polymer are lower than the jetting temperature, the oriented state of the polymer received in the nozzle is fixed because the solvent is gasified upon being jetted from the nozzle. However, when the boiling point of the solvent is higher than the jetting temperature, the polymer is naturally cooled as a solution or a swollen mixture in the solvent. Because the speed of this cooling is lower than the relaxing speed of the molecular orientation, the molecular orientation naturally becomes relaxed. Even when the melting point of the polymer is lower than the jetting temperature, when the solvent is gasified at the time of jetting, the solvent is cooled to a temperature below its melting point due to the heat of evaporation; therefore, it does not matter in many cases.

Heating of the emulsion may be carried out inside a sealed container having a nozzle or spinneret (i.e., autoclave) and it is normally carried out at a temperature in the range from the dissolving temperature of the polymer in the solvent (normally above 100.degree. C) to 280.degree. C. A temperature at least 30.degree. C higher than the boiling point of the solvent is preferable.

At a temperature lower than 30.degree. C above the boiling point of the solvent, it becomes difficult to obtain a fibrous structure having a fibrillated inner structure as in the present invention. A fiber having a filled cross-section, and densely packed with polymer only, is apt to be produced.

(The dissolving temperature of the polymer may conveniently be measured as follows: 15 cc of the polymer solution containing 10 percent by weight of the polymer is prepared, which is sealed in an ampoule, heated and cooled inside an autoclave and the dissolving temperature is measured according to whether the polymer has been dissolved or not).

Jetting of the emulsion from the nozzle is carried out under an autogenous pressure brought about by heating or a higher pressure.

Because a satisfactory jetting temperature of the emulsion is obtained as above, the nozzle need not be positively heated.

In the present invention, it is not preferable to perform the emulsion jetting step by utilizing the principle of a so-called sprayer, blowing a high speed gas such as air upon an opening for flowing out the polymer emulsion and jetting the emulsion using, for example, a spray gun. At the time of jetting, even when the molecules are oriented by shearing action inside the nozzle, the jetted stream expands, losing kinetic energy and not receiving the desired shearing strength. Because the solidifying speed of the polymer is lower than the relaxing speed of the molecular orientation, naturally the molecular orientation is relaxed and the resulting material is unsatisfactorily weak.

However, these means may be used together provided conditions are controlled in a manner not to obstruct the effect of the present invention.

When a fibrous paper material is produced by the foregoing method, the shape and type of nozzle are not important because the size and length of the paper fibers produced are determined by the particle size of the dispersed phase of the emulsion. In contrast, in a method involving releasing a solution or a melted solution, since the form, size and length of the resulting fiber change according to the diameter and shape of the nozzle orifice, it is necessary to control the diameter and shape of the nozzle. As to the shape of the nozzle, the crosssection may be circular or non-circular (i.e., slit), however, a nozzle the diameter of whose inscribed circle is 0.2 - 2 mm is preferable. When the diameter is less than 0.2 mm, the nozzle tends to be prone to blockage by dust, while when the diameter is larger than 2 mm, the jetted materials tend to become intertwined with each other causing collection deviation. A ratio of length to diameter of the nozzle of 0.5 - 200 is often used; however, in the present invention there is no such limitation.

In order to produce a fibrous paper material according to the present invention, it is preferable to adjust the particle size of the emulsion to 3 - 400 microns. If the particle size is smaller than 3 microns, the jetted material is similar to powder because the particle size is too small. When the particle size is larger than 400 microns, the jetted material tends to be continuous and becomes a plexifilament.

The atmosphere into which the emulsion is jetted is not particularly critical, but conditions are preferred under which at least the solvent or the dispersion medium evaporates and solidification of the polymer can be carried out promptly. Normally, the emulsion is jetted into air at room temperature under atmospheric pressure. However, it may be jetted under a reduced pressure. If the solidification of the polymer is not carried out promptly, the orientation of the fibrous paper material jetted from the nozzle is relaxed.

Specifically, according to the present invention, when the dispersion medium and/or the solvent is gasified and at the same time the polymer is solidified because of the attendant reduction of the temperature, the polymer expands when the dispersion medium and/or the solvent is gasified, stretching the polymer which is going to be solidified, thus making a fibrous paper material in which the molecules are oriented.

The majority of the fibrous paper material so obtained consists of fibers having a size of 10 - 1,000 microns and a length of 50 - 25,000 microns, the inside of the respective fiber is a structure in which fibrils, ribbons or films whose diameter or thickness is not more than 10 microns are assembled or dispersed integrally in three dimensions, and which may be compressed to produce a flat cross-section.

If the size of the paper material of the present invention is less than 10 microns and the length of said material is less than 50 microns, this is not preferable because the tenacity of the synthetic paper produced as a result is weak. In fibrid or natural pulp, microfibrils having diameters of less than 10 microns stretch outwardly from the center and the microfibrils have a plurality of branches (diverging structures). In contrast, the paper material of the present invention has a plurality of fibrils inside; however, the number of fibrils projecting outwardly is small (converging structures). When shown schematically, a typical example of the former appears in FIG. 1 and of the latter in FIG. 2.

In the diverging structure of FIG. 1, divergent microfibrils are mutually intertwined, and the paper strength is developed accordingly. In contrast, in the converging structure of the present invention, the paper strength is developed by intertwining of the paper as a whole in a three-dimensional manner and by contact with the surfaces of the paper material. Accordingly, a length and a width greater than some dimensions of the paper material are necessary. Next, because conventional paper materials other than plexifilament have filled cross-sections, in order to increase the areas of the surfaces that come into contact with each other and develop the strength of the paper as well as obtain a paper having a smooth surface, it has been necessary to provide a thin fiber having a diameter of less than 10 microns. Because the cross-section of the paper material of the present invention consists of a bundle of fibrils, ribbons or films, the cross-section may be freely transformed by an outer force. Accordingly, a paper is produced whose surface is smooth and in which the mutually contacted surfaces are large. When shown schematically, these become FIGS. 3 and 4. FIG. 3(a) is a cross-section of conventional paper material other than a plexifilament and FIG. 3(b) shows a product obtained by pressing the same. FIG. 4(a) is a cross-section of the paper material of the present invention, and FIG. 4(b) shows a product obtained by pressing the same.

When the size of the paper material of the present invention exceeds 1,000 microns, even when the material is pressed, it cannot become completely flat and it is very difficult to produce a paper whose surface is smooth. Also, because the paper material does not tend to be soft and tends not to be freely intertwined, the paper tenacity becomes low. Again, the appearance of the paper becomes similar to that of a natural paper wherein fibers are bundled, namely, a Japanese paper. Next, it is not desired if the length of the paper materials exceeds 25,400 microns, because of behavior substantially similar to that of a continuous fiber, viz. a plexifilament. In case of length of the paper material is less than 50 microns, there is less intertwining and the paper tenacity is reduced.

In case the thickness of fibrils, ribbons or films constituting the inside of the paper material exceeds 10 microns, the surface unevenness of the resulting paper increases, the feel of the resulting paper is rough and undesirable. Again, the paper material is not desirably soft and not intertwined.

The process for producing paper material of the present invention may use a coarse screen when the material is made into paper, and as compared with fibrid and pulp, said material is superior in terms of the paper making efficiency and conservation of the screen.

As will be seen from these explanations, a three-dimensionally intertwined paper may be made from the paper material of the present invention. Accordingly, the material becomes a paper having a tenacity of at least 0.2 kg/cm.sup.2 by such means as pressing without using an adhesive. The reason why the paper material of the present invention tends to be three-dimensionally intertwined as compared with other paper materials is because the cross-section is not a filled one, because the paper material is soft and because a coarse screen such as 10 mesh may be used for making a paper; the stream of liquid and gas used in making the paper flows in a direction penetrating the screen (i.e., in the direction of the thickness of the paper).

In the practice of the present invention, it is possible to make a paper from the paper material obtained by the aforementioned method in the same manner as from pulp. However, it is also possible to blow the jetted paper material directly on a porous collecting surface such as a wire netting, collect the material and compress the same to make a synthetic paper.

A very simple method is to make a paper from fibrous sheets collected on wire transfer netting (e.g., on a conveyor belt) on a normal paper making net. However, the paper material may be jetted not only on the wire netting, but also directly on or in a fluid like water; thereafter the jetted paper material may be hit and smashed, or another component may be added and then a paper may be made therefrom. Again, the paper material may be blown on a film to make a laminated paper or collected on another flat plate. As occasion demands, a natural pulp or a synthetic fiber may be properly blended in.

The pressure for compressing the collected paper material is normally 10 g/cm.sup.2 - 100 kg/cm.sup.2 and the paper material may be heated at 50.degree. - 200.degree. C concurrently with or before this compression.

Besides, in the present invention, it is possible to carry out calender processing, heat treatment, embossing treatment, surface coating, re-compression, coloration, laminating, heat sealing and impregnation with a resin liquid.

The paper produced by using the paper material of the present invention has the following characteristics as compared with the conventional synthetic papers:

1. The surface is smooth and free from the fiber patterns as seen in a Japanese paper or a plexifilament paper.

2. The thickness is uniform.

3. The surface tenacity of the paper is high due to three-dimensional intertwining. The tear feeling when the paper is torn is like that of a fibrid paper which is less resistant and not like the tear feeling of a film, but because the fiber is thick and tenacious, the resistance at the time of tearing is large and felt discontinuously. Accordingly, when the paper is torn up a vibrating feeling is imparted to the hand and the feel is similar to that of a natural paper.

4. The fibrous paper material is lower in sieve passing property than a fibrid. Accordingly, because a more coarse screen may be used upon making a paper, efficiency is realized from the viewpoint of removing water, and the screen is free from blocking and conservation of the screen is achieved.

5. The paper may be made by a dry method, and attentive control of the fiber form is unnecessary (in case of a fibrid, the permissible range of the form is narrow).

The following examples more specifically illustrate the present invention; however, the present invention is not limited by these examples.

EXAMPLES 1 - 3

In 2,500 parts of an industrial heptane having a boiling point of 95.degree. C, 1,500 parts of propylene were polymerized using titanium trichloride and diethyl aluminum chloride as catalysts to prepare a heptane slurry of an isotactic polypropylene having a viscosity of 4.0. The percentage of this polypropylene in the slurry was 30 percent by weight.

To the so-obtained slurry, water in varied amounts as shown in Table 1 was added, further, 1 percent by weight, based on the polypropylene, of sodium dodecylbenzene sulfonate was added to prepare an emulsion.

This emulsion was heated to 160.degree. C with stirring inside a steel autoclave having an internal diameter of 18 mm and an internal depth of 100 mm (the particle size being about 5 microns). Subsequently, when a nozzle having a diameter of 0.8 mm was left open, a fibrous paper material having a diameter of about 100 microns and a length of 10,000 microns was jetted under an autogenous pressure (about 16 atmospheres).

This fibrous paper material was soft like a sponge and when it was observed under a microscope, it was found that a plurality of fine fibers having a size of about 8 microns was assembled in a reticulated state.

This fibrous paper material was collected on a 100 mesh stainless steel wire netting at a distance of 30 cm in sheet form.

Thereafter, when compressed air was blown from the back surface of the wire netting, a sheet-like paper material was peeled off from the wire netting.

This paper material was inserted between two sheets of filter paper, lightly squeezed and dried; thereafter it was pressed (40 g/cm.sup.2) by an iron at 115.degree. C for 5 minutes.

When the cross-section of a synthetic paper obtained by said ironing treatment was observed under a microscope, it was recognized that not all fine fibers were parallel to the paper surface, but some fine fibers faced in the direction of the thickness and they were intertwined three-dimensionally. The characteristics of the synthetic papers obtained were shown in Table 1. In Table 1, Comparative Examples wherein the amount of the dispersion medium was small and large were shown at the same time. ##SPC1##

The following measuring methods were used in connection with the examples:

1. 45.degree. cantilever hang length (Pierce tester method):

A 1.5 cm wide and 15 cm long test piece was made to project from a horizontal surface toward a 45.degree. inclined surface and the measured length was the length of the test piece when the free end thereof contacted said inclined surface.

2. Basis weight:

The weight and area of a test piece was measured and it was expressed as the weight per unit area so determined.

3. Apparent density:

The weight per unit volume calculated from the thickness measured by a micrometer and the area weight.

4. Tenacity and elongation:

These were measured on a 1.5 cm wide and 10 cm long text piece by using an Instron tensile tester at a tensile speed of 0.5 cm/min.

5. For of the paper material (dimension, etc.):

The test piece was enlarged by using an optical microscope or a projector and the dimension was measured.

6. Particle size of the emulsion:

Measuring the particle size at a high temperature, higher than the boiling points of the dispersion medium and the dispersed phase, under a high pressure, is difficult. Accordingly, the particle size of the emulsion in a system of the solvent, nonsolvent (and surface active agent) not added with the polymer was measured by means of an optical microscope to make it a parameter of the dispersed state.

The synthetic papers obtained in Examples 1 - 3 were white and lent themselves well to writing with a fountain pen and also with a ball point pen.

EXAMPLES 4 - 6

Example 1 was repeated except the pressure and temperature of the emulsion inside the autoclave were varied as shown in Table 2. The results appear in Table 2. ##SPC2##

The synthetic papers obtained in Examples 4 - 6 excellently accepted writing with a fountain pen and also with a ball point pen.

EXAMPLES 7 - 8

Example 1 was repeated except the particle size of the slurry in the emulsion inside the autoclave was varied as shown in Table 3. The results appear in Table 3. ##SPC3##

EXAMPLE 9

An ethylene block copolypropylene powder having a viscosity of 2.69 and a residue after extraction with boiling n-heptane of 87.3 percent, containing 9.0 percent of ethylene (melting point 165.degree. C), was prepared. This powder was added to methylene chloride (boiling point 39.8.degree. C) to prepare a slurry, which was dispersed in water to prepare an emulsion. The composition of the emulsion by volume was polymer 12/methylene chloride 88/water 200.

Besides, 1 percent, based on the weight of the polymer, of sodium dodecylbenzene sulfonate was added to the emulsion as a surface active agent. The resulting emulsion was heated to 140.degree. C inside an autoclave similar to that in Example 1, and jetted from a nozzle having a diameter of 0.8 mm (the pressure being 18 atmospheres). From the nozzle, a fibrous paper material having a diameter of about 120 microns and a length of 3,000 microns was jetted. This fibrous paper material was soft like a sponge and when observed under a microscope, it was found that a plurality of fine fibers having a thickness of about 8 microns was assembled in a reticulated state.

This jetted fibrous paper material was collected on a 60-mesh wire netting at a distance of 30 cm from the nozzle and made into a sheet. This sheet was peeled off the wire netting (by jetting compressed air from the back surface of the wire netting, the sheet could be peeled off easily), passed between a pair of chromium-plated nip rollers at room temperature to smooth the surface, and further ironed at 115.degree. C. The sheet obtained was in the form of a paper, having a basis weight of 86 g/cm.sup.2, an apparent density of 0.54 g/cc, a tenacity of 0.31 kg/cm.sup.2 and an elongation of 11 percent.

EXAMPLE 10

Polypropylene "Noblen" FB (trade name, manufactured by Mitsui Toatsu Chemical Co., Ltd., melting point 165.degree. C) was added to methylene chloride (boiling point 39.8.degree. C) to prepare a slurry, which was dispersed in water to prepare an emulsion. The composition of the emulsion by volume was polymer 12/methylene chloride 88/water 200. Besides, 1 percent, based on the weight of the polymer, of sodium dodecylbanzene sulfonate was added to the emulsion as a surface active agent. The resulting emulsion was heated to 140.degree. C inside an autoclave and jetted from a nozzle having a diameter of 0.8 mm. From the nozzle, a fibrous paper material having a diameter of 100 - 300 microns and a length of about 3 mm was jetted. This fibrous paper material was soft like a sponge and when observed under a microscope, it was found that a plurality of fine fibers having a thickness of below 8 microns was assembled in a reticulated state to form a fibrous paper material. This jetted fibrous paper material was collected on 60-mesh wire netting at a distance of about 30 cm from the nozzle and made into a sheet. By jetting compressed air from the back surface, this sheet was peeled off the wire netting and ironed at 115.degree. C. The sheet obtained was in the form of a paper, having a basis weight of 44 g/m.sup.2, an apparent density of 0.37 g/cc, a tenacity of 0.21 kg/mm.sup.2 and an elongation of 8 percent.

EXAMPLES 11 - 32

Example 1 was repeated except varying the polymer, solvent, dispersion medium and heating temperature as shown in Table 4. The results are shown in Table 4. ##SPC4##

Claims

1. A method for producing a synthetic paper from a polyolefin comprising the steps of:

1. preparing a dispersion from (A) a mixture consisting of 5-70 percent by weight of a polyolefin and a solvent for said polyolefin wherein the boiling point of said solvent is from about 30.degree. C to about 192.degree. C, and (B) in an amount of about 30 - 2,000 percent by volume based on said mixture (A), a dispersion medium having a boiling point which is below the melting point of said polyolefin, said dispersion medium being substantially insoluble in said solvent,

2. jetting said dispersion under at least an autogenous pressure obtained by heating said dispersion at a temperature in the range from at least 30.degree. C higher than the boiling point of said solvent to 280.degree. C. from a nozzle to make a paper-making fibrous material, and

2. The method according to claim 1 wherein said dispersion medium is present in an amount of about 200 - 2,000 percent by volume based on said

3. The method according to claim 1 wherein said dispersion medium is

4. The method according to claim 1 wherein the particle size of said

5. The method according to claim 1 wherein said polyolefin is selected from the group consisting of polypropylene and a polypropylene graft

6. The method according to claim 1 wherein said dispersion medium is water and said solvent for the polyolefin is a member selected from the group

7. The method according to claim 1 wherein said dispersion is heated to a temperature in a range between the dissolving temperature of said polyolefin to about 280.degree. C, and said dispersion is jetted from a

8. The method according to claim 7 wherein the jetting pressure is 5 - 70

9. A method for producing a synthetic paper from a polyolefin comprising the steps of:

1. polymerizing an olefin monomer in the presence of a solvent for the polyolefin to prepare a slurry containing 5-70 percent by weight based on said solvent of the polyolefin wherein the boiling point of said solvent is from about 30.degree. C to about 192.degree. C,

2. preparing an emulsion from said slurry and, in an amount of about 30-2,000 percent by volume based on said slurry, a dispersion medium having a boiling point lower than the melting point of said polyolefin and being substantially insoluble in said solvent,

3. heating said emulsion to a temperature from at least 30.degree. C higher than the boiling point of said solvent to 280.degree. C.,

4. jetting said emulsion under at least an autogenous pressure obtained by said heating to make a fibrous paper material, and

10. The method according to claim 9 wherein said polyolefin is a member selected from the group consisting of polyethylene, polypropylene and

11. The method according to claim 9 wherein said dispersion medium is present in an amount of about 200 - 2,000 percent by volume on said

12. The method according to claim 9 wherein said dispersing medium is used

13. The method according to claim 9 wherein the concentration of said polyolefin based on said solvent is about 5 - 70 percent by weight and the amount of said slurry is about 10 - 120 percent by weight based on said

14. The method according to claim 9 wherein said solvent is selected from

15. The method according to claim 9 wherein said dispersion medium is

16. The method according to claim 9 wherein the particle size of said

17. The method according to claim 9 wherein the jetting pressure of said

18. The method according to claim 9 wherein to said emulsion a surface active agent which coveres said slurry and stabilizes the dispersion, is added.