CA1057911A - Transparent paper - Google Patents
Transparent paperInfo
- Publication number
- CA1057911A CA1057911A CA234,678A CA234678A CA1057911A CA 1057911 A CA1057911 A CA 1057911A CA 234678 A CA234678 A CA 234678A CA 1057911 A CA1057911 A CA 1057911A
- Authority
- CA
- Canada
- Prior art keywords
- weight
- pulp
- transparent paper
- pva
- paper
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
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Classifications
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- D—TEXTILES; PAPER
- D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
- D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
- D21H5/00—Special paper or cardboard not otherwise provided for
- D21H5/12—Special paper or cardboard not otherwise provided for characterised by the use of special fibrous materials
- D21H5/20—Special paper or cardboard not otherwise provided for characterised by the use of special fibrous materials of organic non-cellulosic fibres too short for spinning, with or without cellulose fibres
- D21H5/205—Special paper or cardboard not otherwise provided for characterised by the use of special fibrous materials of organic non-cellulosic fibres too short for spinning, with or without cellulose fibres acrylic fibres
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- D—TEXTILES; PAPER
- D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
- D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
- D21H13/00—Pulp or paper, comprising synthetic cellulose or non-cellulose fibres or web-forming material
- D21H13/10—Organic non-cellulose fibres
- D21H13/12—Organic non-cellulose fibres from macromolecular compounds obtained by reactions only involving carbon-to-carbon unsaturated bonds
- D21H13/18—Polymers of unsaturated acids or derivatives thereof, e.g. polyacrylonitriles
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- D—TEXTILES; PAPER
- D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
- D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
- D21H21/00—Non-fibrous material added to the pulp, characterised by its function, form or properties; Paper-impregnating or coating material, characterised by its function, form or properties
- D21H21/14—Non-fibrous material added to the pulp, characterised by its function, form or properties; Paper-impregnating or coating material, characterised by its function, form or properties characterised by function or properties in or on the paper
- D21H21/26—Agents rendering paper transparent or translucent
Abstract
Abstract of the Disclosure The transparent paper obtained by subjecting to a transparentizing treatment with moisture, heat and pressure a fibrous matrix sheet of a mixture of natural pulp with synthetic pulp formed of a blended polymer system consisting essentially of polyvinyl alcohol-acrylonitrile copolymer and a acrylonitrile-styrene copolymer.
Description
Background of the Invention This invention relates to transparent paper, particularly to improved transparent paper formed of a mixture of synthetic pulp and natural pulp.
Heretofore, transparent papers composed of natural pulp such as glassine papers have been practically used.
However, those transparent papers have various disadvantages in practical use owing to the use of heavlly beaten natural pulp.
One of the greatest disadvantages is that the conventional transparent papers ar e very sensitive to moisture or water and tend to cause stretching, curl and corrugation. The conventional transparent papers are not therefore suitable for offset printing in which damping water is used and for the secondary processing with an aqueous coating composition. The conventional transparent papers further have such a disadvantage that the blister phenomenon occurs when heated because they have a relatively high equilibrium moisture and a high bulk density owing to a high hydration of pulp.
In addi~ion, in the preparation of such ~ conventional transparent papers, it is necessary to use pulp which can be beaten easily and some special beating conditions are required in connection with the structure of a beating device in order to accelerate hydration of pulp as highly as possible. Furthermore, the heavy beating results in a decrease in freeness of pulp which in turn _2- ~
restricts the paper making speed.
Recently, Japanese Laid-Open Patent Publication No.
35, 608 of 1974 disclosed an improved method for making transparent paper in which polyethylene fibers or polypropylene fibers are mixed with wood pulp to form paper and then a heat at a temperature above the melting point of the resins which constitute the above fibers andapressure are applied to the resultant paper. However, such poly a!-olefin fibers have a poor dispersibility in water, and accordingly it is difficult to obtain a uniform texture of paper.
In addition, since the action is carried out by heating under pressure the paper at a temperature above the melting point of the resins which constitute the fibers, the transparency of the poly c~olefin fiber part is too high compared with that of natural pulp part and consequently it is extremely difficult to obtain a sheet having a uniform transparency. The transparent paper including poly d-olefin fibers has poor affinity to water, therefore, it can hardly be used for offset prLing and secondary processing with an aqueous coating composition, though it has an improved dimensional stability. Further, upon the transparentizing treatment with heat and pressure, it tends to adhere to a heating roll to form a piling of poly ~-olefin fibers thereon.
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10579~1 An object of the invention is to provide a novel transparent paper which at least partly mitigates the above disadvantages of the conventional transparent paper and pro-vides various new advantages which have heretofore never been obtained with conventional transparent papers.
Another object of the invention is to provide an improved transparent paper which is formed of a mixture of synthetic pulp of a polyvinyl alcohol-acrylonitrile copolymer and an acrylonitrilestyrene copolymer with natural pulp.
The invention will become apparent from the following detailed description.
The present invention provides transparent paper obtained by moistening a fibrous matrix in the form of a sheet material so as to have a moisture content within the range -of 5 to 40% and then pressing the thus moistened sheet material with press means having a press surface temperature of 130C
to 250C, said fibrous matrix consisting essentially of:
a) 6 to 60 parts by weight on dry basis of synthetic pulp formed from stable fibres having a length of 1.0 to 25 mm and having a self-bondable microfibril structure of pulp fibres having a diameter of 0.01 to 5 microns at their minimum dimensions and a length at least five times their average diameter, the synthetic pulp having a f~eeness of 50 to 600 cc CSF and being of a blended polymer system which ~ .
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consists essentially of 5 to 40% by weight of polyvinyl alcohol- ~
acrylonitrile copolymer comprising a poly- ;
vinyl alcohol component which has an average degree of polymerization of 500 to 3400 and is chemically bonded to an acrylonitrile component, the polyvinyl alcohol component content being 20 to 80% by weight, and the polyvinyl alcohol-acrylonitrile copolymer being dispersed in 60 to 95~ by weight of acrylonitrilestyrene copolymer in which the acrylonitrile component content is 5 to 45% by weight; and b) 94 to 40 parts by weight on dry basis of natural pulp .
The polyvinyl alcohol-acrylonitrile copolymer is hereinafter referred to as "PVA-AN copolymer" and the acrylonitrile-styrene copolymer is hereinafter referred to as "AN-S copolymer".
In the PVA-AN copolymer,-polyvinyl alcohol is hereinafter referred to as "PVA" which is the hydrophilic component and acrylonitrile is hereinafter referred to as "AN" which is a hydrophobic component are chemically bonded to each other, for example, either in the form of a graft copolymer or in the form of a block copolymer. Preferably, the PVA-AN copolymer is a graft copolymer.
If desired, the blended polymer system may further include unreacted PVA in an amount of 23% or less by weight and/or an acrylonitrile polymer in an amount of 35~ or less by weight each with respect to the total amount of the blended polymer system.
The PVA-AN graft copolymer can be obtained by aqueous heterogeneous polymerization or solution homogeneous polymerization. The average degree of polymerization of PVA iS preferably within the range of 600 to 1800. The degree of saponification of PVA is preferably 60~ or more. The polymerization of PVA with AN to form a graft copolymer may be carried out by dissolving PVA in a solvent for poly-merization, for example, dimethyl sulfoxide;
mixing and dissolving 25 to 500% by weight (based on the amount of PVA) of AN in the resultant PVA solution; and polymerizing them with use of a catalyst for polymerization, for example, persulfate at a room temperature or at a relatively low temperature such as 70~C
or below. The final product after this^polymerization, may include a PVA-AN graft copolymer, unreacted PVA and polyacrylonitrile.
In the reaction for obtaining the PVA-AN copolymer, a small amount of an AN polymer which is not bonded to the hydrophilic component and an unreacted hydrophilic component which is not bonded to AN may be produced as by-products.
However the existence of those by-products in the blended polymer system would be harmless so far as the system includes the PVA~AN
copolymer and the AN-S copolymer in the before mentioned amounts, respectively. Accordingly it is unnecessary to remove those by-products from the final product of polymerization for obtaining the PVA-AN graft copolymer . What is important is that the AN component and PVA component are chemically - bonded to each other and the copolymer has the before mentioned PVA content, whereby it becomes possible to impart an excellent hydrophilic property, an excellent dispersibility in water and an excellent self-adhesive property to the resultant synthetic pulp.
When the AN component and the PVA component are simply blended and exist in the system, it is impossible to impart such P~ - 7 -1057gll ', characteristics to the resultant synthetic pulp.
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There may be an alternative polymerization method in which AN is added to an aqueous solution of PVA and then polymerization is c`arried out. The PVA-AN graft copolymer which is produced by this method can be isolated by reprecipitation and then filtration.
The PVA content in the graft copolymer should be within the range of 20 to 80% by weight, preferably within the range of 35 to 65% by weight. In case the PVA content is less than 20% by weight, the molecular weight of the grafted polyacrylonitrile component would become too large, impairing the processability and impeding the development of the hydrophilic property of the res~ltant synthetic pulp. On the other hand, if the PVA content exceeds 80% by weight, when the resultant fiber or pulp is made into an aqueous slurry, PVA would flow out into water and the slurry would cause foams which become obstacles to beating and paper making.
The use of PVA having an average degree of polymerization of less than 500 will result in decrleasing the water resistance of the paper. On the other hand, if the average degree of polymerization of PVA used exceeds 3400, the hydrophilic property of the resultant fiber will be degraded and fibrillation will not be carried out smoothly, and accordingly the synthetic pulp having desired properties would 105791~
never been obtained.
In preparing the PVA-AN copolymer, in addition to AN, less than 40 mol% of a vinyl monomer other than AN, but which is copolymerizable with AN, for example, vinyl acetate, methyl acrylate, styrene and vinyl chloride, may also be copolymerized.
The AN content in the AN-S copolymer used in the invention should be within the range of 5 to 45% by weight, preferably, within the range of 15 to 40% by weight. When this AN content exceeds 45% by weight, the compatibility of the AN-S copolymer with the PVA-AN copolymer would be too high, impairing the forms or characteristics of the resultant fibrils, On the other hand, whenthe AN content is less than 5% by weight, the solubility of the AN-S copolymer in a solvent (dimethyl sulfoxide) is reduced, and accordingly a spinnable concentrated solution of the blended copolymers cannot be formed. Therefore, the uniform synthetic pulp cannot be obtained.
The AN-S copolymer whi~h is used in the invention can be prepared through the utilization of any of conventional techniques of random copolymerization such as an aqueous heterogeneous polymerization and a mass polymerization.
_ g _ ~057~11 The blended polymer system for the synthetic pulp according to the invention comprises 5 to 40% by weight of a PVA-AN
copolymer and 60 to 95% by weight of such an AN-S copolymer.
If the amount of the PVA-AN copolymer is less than 5% by weight, it is difficult to fibrillate the fibers by beating, and the fibers will have only low hydrophilic property. When such synthetic pulp is mixed with wood pulp to make a paper, the paper having excellent physical properties could not be obtained.
On the o ther hand, if the amount of the PVA-AN copolymer exceeds 40% by weight, both the water resistance and the dimensional stability to moisture of the resultant paper would be decreased.
It is not desirable that the amount of AN-S copolymer is less than 60% by weight because the coagulation ability of the fibers in a coagulation bath is reduced, The blended polymer system for the synthetic pulp is never limited to those consisting of said two copolymers only.
The system may contain unreacted PVA and an AN polymer produced as by-products in the process of the graft copolymerization and may further contain another acrylonitrile polymer.
A greater part of unreacted PVA are removed in the state of an aqueous slurry in the process of making fibers and pulp.
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,, _ 1~)5~911 However, the amount of PVA in the blended polymer system initially prepared should not exceed 23% by weight. If the amount o:E unreactéd PVA exceeds 23% by weight, it will cause to produce foams in the aqueous slurry.
The amount of the AN polymer in the b lended system prepared should not exceed 35% by weight. If the AN polymer amount exceeds 35% by weight, the excessive fibrillation would be caused.
i As to the addition of an AN polymer to the blended polymer system, a separately prepared linear polymer may be used.
One having a molecular weight of about 20, 000 to 100, 000 is preferable, It may contain the aforementioned vinyl monomers which can be used in the gr~ copolymerization as a copolymerizable component in such an amount within the range not exceeding 40 mol %.
Among the methods for preparing synthetic pulp from the above mentioned blended composition, there are included a method of beating fibers produced from the above system and a method for preparing pulp materials directly from the blended polymer composition .
As methods for producing fibers, there may be included a flush spinning method and an emulsion flush spinning method ~ .
lV5791~
in addition to the conventional spinning methods such as a wet spinning method, a dry wet spinning method and a phase separation spinning method. Among them the wet spinning method is most preferable. A further explanation of the wet spinning method will be given below.
The composition including the PVA-AN copolymer and the AN-S copolymer is dissolved in a solvent such as dimethyl sulfoxide.
This solution is then wet spun by a conventional method into an aqueous spinning bath, for example, an aqueous solution of dimethyl sulfoxide containing up to the maxirnum of 80 % by weight of dimethyl sulfoxide to produce an undrawn water-containing gel filament. Such undrawn filament may be drawn in a hot water j ~ath or in an atmosphere of steam. Further, the drawn filament may be subjected to a heat treatment for fixing its length or relaxing in a ho.t water bath or in an atmosphere of steam.
A draw ratio is preferably more than -3.0,but this is not intended to limit the scope of the present invention. The use of the undrawn filament is not harmful to achieve the objects of the, invention. However, in the case of using the undrawn filament, it is necessary to pay close attention to handle it because the undrawn filament has a low strength.
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Referring to the heat treatment for relaxation, a , relaxation ratio is preferably more than 45%, but this is not intended to limit the scope of the invention. By such procedures, a fine pulp having a good dispersibility is easily obt~ined. - When the draw ratio is not more than 3. O, the filament which is subjected to such heat treatment is rather cut than fibrillated in the process of beating. However, when the beating is carried out without subjecting the filament to the hest treatment, the objects of t~ invention can be achieved with the draw ratio being not more than 3. O.
What is important is that the above fibrious material consists of a hydrophilic component (PVA-AN graft copolymer) and a hydrophobic component (AN-S copolymer) and that the hydrophilic component is dispersed in the hydrophobic component and exists in the form of being arranged as an independent phase in the direction of the fiber axis.
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Such fibrous material is easily fibrillated by beating, and accordmgly a pulp or pulp like material having an excellent hydrophilic property, a dispersibility in water~ and a self-adhesive property can be obtained.
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The obtained filaments are then be cut into staple fibers having a length of 1. 0 to 25 mm.
Instead of the aforementioned heat treatment prior to the process of cutting, fibers may be subjected to a heat treatment in a hot water or in an atomosphere of steam. In such a case, it is desirable that the temperature for the treatment is within the range of 90 to 120C and treatment time is within the range between 30 seconds and 8 minutes, however, those are not intended to limit the scope of the invention .
The fibers which are obtained according to th- above method can easily be fibrillated by means of beating which is usually applied to wood pulp, and may be made into pulp having an excellent dispersibility in water.
The above staple fibers are made into an aqueous dispersion having a concentration of 1 to 20% by weight and subjected to a beating treatment by use of the conventional beating devices such as beaters, refiners, PFI mills and ball mills.
The synthetic fiber prepared according to the invention has a self-bondable microfibril structure. The pulp part icles are entangled each other by the microfibrils. Each of tke fibers may have a diam'eter of 0. 01 to 5 microns, preferably 0. 05 to 3. 0 microns, at its minimum dimension portion. The length of each of t-he fibers may be more than five times, preferably twenty times, the average diameter.
The synthetic pulp may be solely or partly of a latent microfibril structure. The term "latent microfibril structure"
refers to fibrous material itself obtained according to the invention, or to the fibrous material a part of which is crushed in the process of beating andis ;present in the form of microfibrils. Namely, the latent microfibril structure is a precursor which can be entirely converted to the microfibrils with sufficient beating.
When the beating with use of ~he conventional beating devices is carried out to such an extent that the beaten fibrous materials become suitable for forming a paper like sheet, a greater part of the pulp material is occupied by the microfibril structure. In the process of beating, powder like minute particles which are smaller in size than the above microfibrils may be produced as by-products, but those are not essential to the invention.
When the minimum di~nension of the above microfibril structure does not meet such requirements that t~he diameter is at least O. 01 microns and the length is more than five timesthe average diameter.
the entanglement of the pulp particles is degraded, and accordingly , .
lV5791~
the strength and texture of the resultant paper are impaired.
Since the pulp material of the invention contains the microfibril structures and the latent microfibril structure~, the freeness of the pulp can be controlled at wlll by varying the beating conditions. In addition, a paper having an excellent wet strength is obtained without any additives such as binder since the microfibrils have the self-adhesive property.
The structure of the synthetic pulp prepared according to the invention may be defined by a freeness which is determined according to Japanese Industrial Standard JIS P-8182 with use of Canadian Standard Freeness testing machine. The freeness of the pulp material of the invention should be within the range of 50 to 600 cc, preferably within the range of 100 to 400cc.
When the freeness is less than 50cc, the tear strength of the resultant paper is lowered and the paper making speed is lowered to such an extent that the paper making is substantially impossible.
On the other hand, the freeness exceeds 600cc, the pulp loses the paper making ability, and a paper having a good texture, a good surface uniformity and good physical pPoperties is not obta ined .
The tranSparent paper according to the invention ~OS79~1 -is obtained by subjecting a sheet comprising 6 to 60 parts by weight on dry basis of the above synthetic pulp and 94 to 40 parts by weight on dry basis of natural pulp to a transparentizing treatment with moisture, heat and pressure.
f As the natural pulp, wood pulp is most preferably used, but other natural pulp such as one which is prepared from bast fibers or animal fibers may also be used.
If the amount of the synthetic pulp is less than 6 parts by weight, the resultant base sheet is not sufficient for Fractical use in the respects to its transparency, wet-strength, tensil strength, folding strength, and dimensional stability, though these properties of the base sheet are improyed when compared with a transparent base sheet consisting of the conventional natural pulp only. On the other hand the amount of the synthetic pulp exceeds 60 parts by weight, the mechanical strength becomes uneven, especially the tear strength and the folding strength are reduced. Preferably, the sheet is formed of 10 to 50 parts by weight of synthetic pulp and 90 to 50 parts by weight of natural pulp.
The synthetic pulp and the natural pulp mixed in the above proportions are made into a sheet with use of a conventional wet system paper making machine. In the process of the paper f ' lOS7~11 making, the conventional additives such as sizing agents, fixing agents, releasing agents, antistatic agents, fillers and dyestuffs may be added to the system.
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Application in the paper making process of starch, polyvinyl alcohol, carboxymethyl cellulose, sodium alginat~, solutions or emulsions of synthetic resins or conventional transparentizing agents may also be carried out by size-pressing, impregnation or coating.
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The weight of the resultant sheet material may be controlled within the range 25 to 200 g/m, but this is not intended to limit the scope of the invention.
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According to the invention it is possible to obtain a high transparency without using a heavily beaten pulp which is used to make a conve~ntional transparent paper Heretofore, it has been necessary to use a heavily beaten pulp having a CSF
(Canadian Standard Freeness) of 50 to 150 cc to make conventional transparent paper. However, according to the invention, an excellent transparency can be o'otained with use of usually or slightly beaten pulp. Therefore, the disadvantages inherent with use of the heavily beaten natural pulp, such as a decrease in the rate of paper making, a decrease in physical properties such as dimensional stability, tear strength and folding strength ~OS7~11 and the generation of blister phenomenon can be avoided a cc ord ing to the invention .
The thus obtained sheet materi~l is then transparentized by moistening the sheet to a moisture content within the range of 5 to 40%, and then passing it through a pressure equipment having a surface temperature of above 130C to impart heat and pressure. The moisture content is given by the following formula Weight of water contained in the sheet Moi~ture content = X100 Weight of the sheet containing water If the moisture content is less than 5%, a uniform transparency of the sheet is not obtained. While, when the moisture content exceeds 401O, the physical strength of the sheet is reduced, causing adhesion to the roll of the pressure equipment and making troubles such as a break. Among the typical moistening methods, there may be included a method of coating water by coater, a method of spraying water and a so-called electrostatic moistening method. In the moistening process, various additives such as sizing agents, releasing agents, antistatic agents;
dystuffs and transparentizing agents may be added to water.
~057911 - -For the pressing treatment any conventional means such as a super calender and a machine calender, an eguipment having two rolls which form a nip, and a hot press type eq-llipment may be utilized.
In the process of transparentizing treatment with use of those equipments the sheet material is pressed at least one time by a pressure equipment having a surface temperature of 130C or above, whereby a desired transparency of the sheet is obtained However, in view of 'the fact that the synthetic polymers which constitute the synthetic pulp are decomposed at about 250C, it is necessary to be careful so as not to raise the temperature of the sheet to above 250C. The pressure which is applied to the sheet material.- is controlled at will depending on the thickness of the sheet, the mixing ratio of pulps and the condition of moistening.
But it may be usually within the range of about 100 to 500 kg/cm, preferably about 120 to 400 kg/cm.
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The transparent paper according to the invention has such various advantages as described below, as compared with conventional transparent paper such as glassine paper or transparent paper formed of poly ~t olefin fibers and wood pulp.
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The synthetic pulp described can be uniformly dispersed in the sheet in the form of microfibrils having numerous micro voids and has hydrophilic moieties in itself. Therefore, the water contained in the sheet functions as a plasticizer not only for natural pulp but also for synthetic pulp. In addition, when the sheet is subjected to the treatment with heat and pressure, the water contained in the sheet is removed accompanying air which is filled in the micro voids, whereby an inherent clarity of the polymers which constitute the synthetic pulp are developed effectively, and accordingly an excellent transparency is obta ined .
The equilibrium moisture (at 20C, 60% RH) of the untreated sheet material of the invention varies with the mixing ratio of synthetic pulp, for example, it is about 6 % when the sheet consists of 10 parts by weight of synthetic pulp and 90 parts by weight of natural pulp, and it is about 4 % when the sheet consists of 60 % by weight of synthetic pulp and 40% by weight of natural pulp.
When it is intended to obtain a desired transparency, it is found that there is such a relation between the mixin-g -ratio of synthetic pulp and the moisture content that an increase in the amount of synthetic pulp saves the moisture content. Therefore, when the mixing ratio of synthetic pulp is 60 %, it is sufficient for achieving . .
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the effect that the moisture content is at least 5 %. When the mixing ratio of synthetic pulp is 10 %, the moisture content is preferably more than 20 %.
As is understood from the abovê descriptions, the transparent paper according to the invention has following advantages:
(a) It has a uniform and high transparency.
(b) It has excellent physical properties such as a tensile strength and a folding strength.
(c) It has an excellent stability to moisture or water, whereby the disadvantages such as curl, stretching and corrugation can be avoided.
(d) The blister phenomenon which occurs when it is heated can be avoided.
(e) It is suitable for various uses such as offset printing use and secondary processing use.
(f) It offers various advantages in preparation such as an - increase of ,the rate of paper making, a reduction of beating treatment and a simplified transparentizing treatment .
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This invention includes not only a sheet which is wholly transparentized but also a sheet which is partly transparentized .
The transparency of the resultant paper may be controlled at will according to its use. For example, it is generally controlled at more than 50 % u~hem the paper is used for a master for duplication. For a tracing paper or a paper for plotter, it is controlled at more than 60 %. And it is controlled at more than 80 % when the paper is used for a glassine paper.
The transparency is given by the following formula:
Transparency = 100 - (value of opacity) wherein the value of opacity is measured by Hunter reflectometer according to JIS P-8138.
The invention will be further illustrated by reference to the following examples, however, the invention is not limited to those examples but includes wide variations.
Unless otherwise indicated, parts and % signify parts by weight and % by weight, respectively.
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Exa mple A PVA-AN graft copolymer in which the ratio of PVA to AN i6 50/50 was obtained by grafting AN to PVA having a degree of polymerization of 1400 according to a~n ordinary radical polymerization method with use of persulfate salt as a catalyst.
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An AN-S copolymer in which the ratio of AN to styrene is 24/76, having an intrinsic viscosity of 0. 54 (determined in MEK
at 30C ) was obtained according tOa conventional suspension polyme r ization .
One part by weight of the above PVA-AN graft copolymer and 4 parts by ~veight of the above AN-S copolymer were diss`olved in 15 parts by weight of dimethyl sulfoxide (hereinafter referred to as "DMSO") to obtain a 25% spinning solution.
A wet spinning with that solution was carried out in a water/
DMSO (45/55) bath from a spinning nozzle having a diameter of 0. 08mm to obtain a continuous filament having a denier of 7 and a PVA
content of 10% . The draw ratio was 2 times. Thus obtained filament was cut into staple fibers having a length of about 10mm and the fibers were then beaten with use of a single discrefiner under the conditions of a pulp concentration of 3 % and the clearance of 50 mic:rons to obtain a synthetic pulp (A) whose CSF was 200cc. The a verage diameter of the fibrils was 8 microns, the minimum diameter in a fibril was 0. 5 microns and the ratio of the length by the average diameter was about 50.
Separately, bleached broad-leaved wood kraft pulp (L) having a CSF of 480cc, bleached needle-leaved wood pulp (N) having a CSF of 350cc, heavily beaten bleached needle-leaved wood kraft pulp (N') having a CSF of lOOcc and heavily beaten bleached broad-leaved wood kraft pulp (L') having a CSF of 120cc were prepared. The above synthetic pulp (A) and the natural pulp (L) (N) (L') (N') were formed intoa sheet witha manual paper-making sheet machine (with 80 mesh metal screen) manufactured by Toyo Seiki Co., Ltd. according to the formulations shown in the following Table 1.
As a control, a bleached needle-leaved wood kraft pulp (N') having a CSF of lOOcc and a bleached broad-leaved wood kraft pulp (L') having a CSF of 120cc were mixed with the above synthetic pulp (A) to form a sheet under the condition shown in Table 1 in the same manner as in th~ above.
The moisture contents of the thus obtained dry sheets were controlled as shown in Table 1 by applying water to the sheets with a wire wound coating rod. Then, the sheets were subjected , lOS'7911 to a transparentizing treatment in which the sheets were made to pass through a nip of a two stack pressure equipment provided with an elastic roll and a hard chrome plated metal roll (surface temperature at 150C) under the linear pressure of 135 kg/cm for four times in all, reversing the sheet upside-down. Various characteristics of the obtained transparent papers are shown in Table 1.
The transparent papers obtained according to the invention were superior in the paper making ability, the transparency, the physical properties and the secondary processability, compared with that of Control. The transparent paper according to the invention had a good balance of quality.
Example 2 Two kinds of filam~ts having PVA contents of 30% and 10%
respec~ively, were made by a conventional spinning method similarto that described in Example 1 froma 25% solution in DMSO of a mixture of one part by weight of a PVA-AN copolymer obtained by grafting AN to PVA having a degree of polymerization of 1800 according to an ordinary radical polymerization method with uæe of persulfate salt as a catalyst in which the ratio of PVA/AN
is 80/20, with 1. 67 and 7 parts respectively by weight of an AN-S copolymer having an intrinsic viscosity of 0. 65 determined 105~91~L
in MEK at 30C which is obtained by a conventional suspension polymerization method, in which the ratio of AN/styrene is 30/70. The draw ratio was 3. 5 times and each of the obtained two kinds of filaments had a denier of 5. The filamen~s were cut into staple fibers having a length of about 3 mm and the staple fibers were then beaten in the same manner as in Example 1, respectively, to obtain two kinds of synthetic pulp. One was a synthetic pulp (B) whose PVA content was 30% and having a CSF of 195 cc, and the other was a synthetic pulp (C) whose PV~ content was 10%
and having a CSF of 240 cc.
The average diameter of the fibrils having a PVA content of 30% was 2 microns, the minimum diameter in the fibril was 0. 2 microns and the ratio of the length by the average .
diameter was about 90, and the average diameter of the fibrils having a PVA content of 10 % was 4 microns, the minimum diame~er in the fibril was 0. 3 microns and the ratio of the length by the average diameter was about 70.
Separately, a bleached needle-leaved wood kraft pulp (N"~ having a CSF of 280cc and a bleached broad-leaved wood kraft pulp ~L") having a CSF of 450cc were prepared.
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A sheet was formed with use of the above synthetic pulps (B) and (C) and natural pulps (N' ')and (L' ' ) in the same manner as in Example 1 under the condition as shown in Table 2.
The moisture content of the resultant sheet was adjusted at the value shown in Table 2 in the same manner as in Example 1.
Then, the sheet was made to pass through the two stack calender which was used in Example 1 under the conditions of the surface temperature of the roll at 140C and t~e linear pressure at 220kg/cm for four times in all, reversing the sheet upside-down, to obtain a transparent paper. The properties of the resultant transparent papers are shown in Table 2.
Example 3 Two kinds of filaments having PVA contents of 7 % and 20% respective;Ly, were made by a wet spinning method similar to that disclosed in Example 1 from a 25% solution in DMSO of a mixture of one part of a PVA-AN graft copolymer obtained by grafting AN to PVA having a degree of polymerization of 1100 according to an ordinary radical polymerization method with use of persulfate salt as a catalyst in which the ratio of PVA/AN was 60/40, with 7. 57 and 2 parts, respectively, of an AN-S copolymer having an intrinsic vi scos ity ()f 0. ~5 determined in MEK at 30C which was obtained by a conventional mass polymerization method, in which the ratio ofAN/styrene was 20/80.
The obtained tWG kinds of filaments had the same denier of 10. Those filaments were cut into staple fibers having a length of about 5 mm and the staple fibers are then beaten in the same manner as in Example 1 to obtain two kinds of synthetic pulp.
One was a synthetic pulp (D) whose PVA content was 7% having a CSF of 230cc, and the other was a synthetic pulp (E) whose PVA content was 20% having a CSF of 200cc. The average diameter of the fibrils having a PVA content of 7 % was 13 microns, the minimum diameter in the fibril was 0. 8 microns and the ratio of the length by the average diameter was about 45, and the average diameter of the fibrils having a PVA content of 20 %
was 8 microns, the minimum diameter in the fibril was 0. 5 microns and the ratio of the length by the average diameter was about 55.
Separately, the same bleached needle-leaved wood kraft pulp (N) -and bleached broad-leaved wood kraft pulp (L) as in E~ample 1 were prepared. The above synthetic pulps (~) and (E) and natural pu1ps (N) and (L) were mixed in such proportions as shown in Table 3 to form a dry sheet with a Fourdrinier test machine manufactured by Mitsubishi Kakoki Co., Ltd. at the lOS7911 paper making rate of 20m/min.
The moisture content of the resultant sheets were adjusted at the value shown in Table 3 by water coating with use of a pilot coater. Then, the sheets were made to pass through 4 nips of a super calender which was provided with alternatively arranged chilled rolls having a highest surface temperature of 160C and cotton rolls under the linear pressure at 220kg/cm to obtain transparent papers. The properties of the resultant transparent papers are shown in Table 3.
Control 3 A transparent paper was obtained in the same manner as in Example 1-4 except that a commercially available pulp prepared from poly 0(-olefin fiber was used instead of the synthetic pulp (A) which was used in Example 1-4, and that the adjustment of moisture content was not carried out. The transparency of the resultant transparent paper was only 60 %. Besides, a macroscoplc unevenness of transparency was remarkably appreciated. The offset printabilities of the above transparent paper and that of the transparent paper obtained in Example 1-4 were examined, respectively. The transparent paper of Example 1-4 showed a good ink acceptability and gave a good result in printing. On the contrary, the transparent paper obtained in this control showed a poor ink acceptability due to its poor water absorbability, and microscopic white-spots were remarkably appreciated .
Example 4 A continuous filament having a denier of 7 and having a PVA
content of 7 % was prepared by a conventional spinning method similar to that in EKample 1 from a 25% solution in DMSO of a mixture of one part of a PVA-AN graft copolymer obtained by grafting AN
to PVA having a degree of polymerization of 2600 according to an ordinary radical polymerlzation method with use of persulfate salt as a catalyst, in which the ratio of PVA/AN was 30/70, with 3. 29 parts of an AN-S copolymer having an intrinsic viscosity of 0. 54 determined in ME K at 30C which was obtained by a usual suspension polymerization method, in which the ratio of AN/styrene was 24,/76.
The obtained filament was cut into staple fibers having a length of about 10 mm and then the staple fibers Iwere beaten in the same manner as in Example 1 to obtain a synthetic pulp (F) having a CSF of 280cc. The average diameter of the fibrils was 13 microns, the minimum diameter in the fibril was 0. 8 microns and the ratio of the length by the average diameter was about 45.
105791~
The bleached needle-leaved wood kraft pulp tN) and the bleached broad-leaved wood kraft pulp (L) which were used in Example 1 were mixedw~hthe above synthetic pulp (F) in such propl3rtions as shown in Table 4. The resultant mixed pulp was made into two sheets with a Fourdrinier test machine manufactured by Mitsubishi Kakoki Co., Ltd. at a rate of 20 m/min. The moisture contents of the resultant dry sheets were controlled at the value shown in Table 4 by-spraying 3 % aqueous solution of glycerin as a plasticizer with use of a spray-type damping equipment attached to a pilot coater.
Then, the sheets were made to pass through 4 nips of a super calender provided with alternatively arranged chilled rolls having a highest surface temperature of 150C and cotton rolls under the linear pressure of at most 200kg/cm to obtain a transparentized papers, The properties of the obtained transparent papers are shown in Table 4. The transparent papers obtained in Example 4 showed excelIent properties having a good balance of quality. To the contrary, the transparent paper obtained in Control 4 had an undesirable texture due to its poor dehydration property, and showed a poor ' t workability in super calendering due to its poor tear strength and folding strength and showed a bad ink acceptability in offset printing, Furthermore, the corrugation~ of the resultant transparent A
1~)5793LiL
paper were appreciated.
:E~ample 5 A continuous filament having a PVA content of 28 % was made by-a wet spinning method similar to that described in Example 1 from a 25% solution in DMSO of a mixture of one part of a reaction product obtained by grafting AN to PVA having a degree of polymerization of 1800 according to an ordinary radical polymerization method with use of persulfate salt as a catalyst, which consisted of 74 % by weight of PVA-AN copolymer (75/25), (20% by weight of unreacted PVA and 6 % by weight of a homogenous acrylonitrile polymer, with 1. 7 parts of an AN-S copolymer (havingan intrinsic visoosity of 0.71 determined in MEKat 30C) which was obtal~ned by a conventional suspension polymerization method, in which the ratio of AN/styrene . was 15/85. The obtained filament having a denier of 7 was cut into staple fibers having a length of about 5mm and the staple fibers were then beaten in the same manner as in Example 1 to obtain a synthetic pulp (G) having a CSF of 240cc. The average diameter of the fibrils was 4 microns, the minimum diameter in a fibril was 0 3 microns and the ratio of the length by the average diameter was about 70.
10~7911 Separately, a bleached needle-leaved wood kraft pulp (N"') having a CSF of 550cc a bleached broad-leaved wood pulp (L"') having a CSF of 620cc were prepared, The above synthetic pulp (G) and the natural pulps (N"') and (L"') were mixed and made into two sheets under the conditions shown in Table 5. As a Control, a sheet composed of the above natural pulps (N"') and (L"') only was prepared under the condition shown in Table 5.
The moisture contents of the resultant sheets were adjusted at the values shown in Table 5 by coating a 0. 3 % aqueous solution containing sodium chloride as an antistatic agent on one side surface of the sheet with use of a wire wound coating rod.
Then the sheets were made to pass through a two stack type calender provided with an elastic roll and a hard chrome plated metal roll (surface temperature at 150C) four times under linear pressure of 210kg/cm, reversing both sides of sheets, to obtain transparentized papers. The properties of the resultant papers are shown in Table 5.
The transparent papers obtained in this Example were superior to that obtained in Control in the respects of the transparency, the physical properties and the secondary processability. The properties of the transparent papers !
1~57911 according to the invention transcended those which the glassine paper should possess.
Example 6.
A continuous filament having a PVA content of 10%
was made by a wet spinning method similar to that disclosed in E xample 1 from 25% solution in DMSO of a mixture of one part of a PVA-AN graft copolymer obtained by grafting AN to PVA
having a degree of polymerization of 800 according to a conventional radical polymerization with use of persulfate salt as catalyst, in which the ratio of PVA/AN was 40/60, with 3 parts of AN-S
copolymer havingan intrinsic viscosity of 0.75 determined n MEK at 30C and having a ratio of AN/styrene at 20¦80, which was obtained by a common suspension polymeri zation method.
The draw ratio was 2. 0 times.
The resultant filament having a denier of 10 was cut into staple fibers having a length of about 5 mm, and the staple fibers were then beaten in th e same manner aæ in Example 1 to obtain a synthetic pulp (H) having a CSF of 260 cc. The average diameter of the fibrils was 7 microns, the minimum ,1 ~
10579~1 diamer in the fibril was 0. 5 microns and the ratio of the length by the average diameter was about 50.
The same bleached needle-leaved wood kraft pulp (N"') and bleached broad-leaved wood kraft pulp (L"') as those which used in Example 5 were prepar ed.
The above synthetic pulp and natural pulps (N"') and (L"') were mixed at the mixing ratio shown in Table 1) and then made into three sheets with use of a commercially available Fourdrinier paper machine provided with a wire cloth having a width of 1975mm, at a paper-making rate of 50 m/min.
As a control, a sheet composed of the above natural pulps (N"') and (L"') only was prepared in the same manner as the above.
The moisture contents o~ each sheet thus prepared was adjusted at the value shown in Table 6 by coating a 0. 2 %
aqueous solution containing a commercially available wax emulsion as a releasing agent with a commercially available bar coater.
Then, each sheet was made to pass 16 nips of a super calender provided with alternatively arranged chilled rolls having a highest -~6 1~)579~
surface temperature of 160C and cotton rolls under the linear pressure of at most 400 kg/cm to o'btain a transparentized paper, The properties of the resultant transparent papers are shown in Table 6.
It was clearly appreciated that the transparent papers obtained in this :Example showed an excellent transparency and excellent properties having a good balance of q uality with increasing the mixing ratio of synthetic pulp even when the moisture content was relatively low. On the contrary, the sheet composed of natural pulp only which was obtained in Control had an insufficient transparency though, it was treated at high moisture content .
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1057S~
Note:
1) Talc filler (~): The amount of ash in a dry p~per determined according to Japanese . Industrial Standard JIS P-8128
Heretofore, transparent papers composed of natural pulp such as glassine papers have been practically used.
However, those transparent papers have various disadvantages in practical use owing to the use of heavlly beaten natural pulp.
One of the greatest disadvantages is that the conventional transparent papers ar e very sensitive to moisture or water and tend to cause stretching, curl and corrugation. The conventional transparent papers are not therefore suitable for offset printing in which damping water is used and for the secondary processing with an aqueous coating composition. The conventional transparent papers further have such a disadvantage that the blister phenomenon occurs when heated because they have a relatively high equilibrium moisture and a high bulk density owing to a high hydration of pulp.
In addi~ion, in the preparation of such ~ conventional transparent papers, it is necessary to use pulp which can be beaten easily and some special beating conditions are required in connection with the structure of a beating device in order to accelerate hydration of pulp as highly as possible. Furthermore, the heavy beating results in a decrease in freeness of pulp which in turn _2- ~
restricts the paper making speed.
Recently, Japanese Laid-Open Patent Publication No.
35, 608 of 1974 disclosed an improved method for making transparent paper in which polyethylene fibers or polypropylene fibers are mixed with wood pulp to form paper and then a heat at a temperature above the melting point of the resins which constitute the above fibers andapressure are applied to the resultant paper. However, such poly a!-olefin fibers have a poor dispersibility in water, and accordingly it is difficult to obtain a uniform texture of paper.
In addition, since the action is carried out by heating under pressure the paper at a temperature above the melting point of the resins which constitute the fibers, the transparency of the poly c~olefin fiber part is too high compared with that of natural pulp part and consequently it is extremely difficult to obtain a sheet having a uniform transparency. The transparent paper including poly d-olefin fibers has poor affinity to water, therefore, it can hardly be used for offset prLing and secondary processing with an aqueous coating composition, though it has an improved dimensional stability. Further, upon the transparentizing treatment with heat and pressure, it tends to adhere to a heating roll to form a piling of poly ~-olefin fibers thereon.
:
10579~1 An object of the invention is to provide a novel transparent paper which at least partly mitigates the above disadvantages of the conventional transparent paper and pro-vides various new advantages which have heretofore never been obtained with conventional transparent papers.
Another object of the invention is to provide an improved transparent paper which is formed of a mixture of synthetic pulp of a polyvinyl alcohol-acrylonitrile copolymer and an acrylonitrilestyrene copolymer with natural pulp.
The invention will become apparent from the following detailed description.
The present invention provides transparent paper obtained by moistening a fibrous matrix in the form of a sheet material so as to have a moisture content within the range -of 5 to 40% and then pressing the thus moistened sheet material with press means having a press surface temperature of 130C
to 250C, said fibrous matrix consisting essentially of:
a) 6 to 60 parts by weight on dry basis of synthetic pulp formed from stable fibres having a length of 1.0 to 25 mm and having a self-bondable microfibril structure of pulp fibres having a diameter of 0.01 to 5 microns at their minimum dimensions and a length at least five times their average diameter, the synthetic pulp having a f~eeness of 50 to 600 cc CSF and being of a blended polymer system which ~ .
' :
10579~
consists essentially of 5 to 40% by weight of polyvinyl alcohol- ~
acrylonitrile copolymer comprising a poly- ;
vinyl alcohol component which has an average degree of polymerization of 500 to 3400 and is chemically bonded to an acrylonitrile component, the polyvinyl alcohol component content being 20 to 80% by weight, and the polyvinyl alcohol-acrylonitrile copolymer being dispersed in 60 to 95~ by weight of acrylonitrilestyrene copolymer in which the acrylonitrile component content is 5 to 45% by weight; and b) 94 to 40 parts by weight on dry basis of natural pulp .
The polyvinyl alcohol-acrylonitrile copolymer is hereinafter referred to as "PVA-AN copolymer" and the acrylonitrile-styrene copolymer is hereinafter referred to as "AN-S copolymer".
In the PVA-AN copolymer,-polyvinyl alcohol is hereinafter referred to as "PVA" which is the hydrophilic component and acrylonitrile is hereinafter referred to as "AN" which is a hydrophobic component are chemically bonded to each other, for example, either in the form of a graft copolymer or in the form of a block copolymer. Preferably, the PVA-AN copolymer is a graft copolymer.
If desired, the blended polymer system may further include unreacted PVA in an amount of 23% or less by weight and/or an acrylonitrile polymer in an amount of 35~ or less by weight each with respect to the total amount of the blended polymer system.
The PVA-AN graft copolymer can be obtained by aqueous heterogeneous polymerization or solution homogeneous polymerization. The average degree of polymerization of PVA iS preferably within the range of 600 to 1800. The degree of saponification of PVA is preferably 60~ or more. The polymerization of PVA with AN to form a graft copolymer may be carried out by dissolving PVA in a solvent for poly-merization, for example, dimethyl sulfoxide;
mixing and dissolving 25 to 500% by weight (based on the amount of PVA) of AN in the resultant PVA solution; and polymerizing them with use of a catalyst for polymerization, for example, persulfate at a room temperature or at a relatively low temperature such as 70~C
or below. The final product after this^polymerization, may include a PVA-AN graft copolymer, unreacted PVA and polyacrylonitrile.
In the reaction for obtaining the PVA-AN copolymer, a small amount of an AN polymer which is not bonded to the hydrophilic component and an unreacted hydrophilic component which is not bonded to AN may be produced as by-products.
However the existence of those by-products in the blended polymer system would be harmless so far as the system includes the PVA~AN
copolymer and the AN-S copolymer in the before mentioned amounts, respectively. Accordingly it is unnecessary to remove those by-products from the final product of polymerization for obtaining the PVA-AN graft copolymer . What is important is that the AN component and PVA component are chemically - bonded to each other and the copolymer has the before mentioned PVA content, whereby it becomes possible to impart an excellent hydrophilic property, an excellent dispersibility in water and an excellent self-adhesive property to the resultant synthetic pulp.
When the AN component and the PVA component are simply blended and exist in the system, it is impossible to impart such P~ - 7 -1057gll ', characteristics to the resultant synthetic pulp.
.
There may be an alternative polymerization method in which AN is added to an aqueous solution of PVA and then polymerization is c`arried out. The PVA-AN graft copolymer which is produced by this method can be isolated by reprecipitation and then filtration.
The PVA content in the graft copolymer should be within the range of 20 to 80% by weight, preferably within the range of 35 to 65% by weight. In case the PVA content is less than 20% by weight, the molecular weight of the grafted polyacrylonitrile component would become too large, impairing the processability and impeding the development of the hydrophilic property of the res~ltant synthetic pulp. On the other hand, if the PVA content exceeds 80% by weight, when the resultant fiber or pulp is made into an aqueous slurry, PVA would flow out into water and the slurry would cause foams which become obstacles to beating and paper making.
The use of PVA having an average degree of polymerization of less than 500 will result in decrleasing the water resistance of the paper. On the other hand, if the average degree of polymerization of PVA used exceeds 3400, the hydrophilic property of the resultant fiber will be degraded and fibrillation will not be carried out smoothly, and accordingly the synthetic pulp having desired properties would 105791~
never been obtained.
In preparing the PVA-AN copolymer, in addition to AN, less than 40 mol% of a vinyl monomer other than AN, but which is copolymerizable with AN, for example, vinyl acetate, methyl acrylate, styrene and vinyl chloride, may also be copolymerized.
The AN content in the AN-S copolymer used in the invention should be within the range of 5 to 45% by weight, preferably, within the range of 15 to 40% by weight. When this AN content exceeds 45% by weight, the compatibility of the AN-S copolymer with the PVA-AN copolymer would be too high, impairing the forms or characteristics of the resultant fibrils, On the other hand, whenthe AN content is less than 5% by weight, the solubility of the AN-S copolymer in a solvent (dimethyl sulfoxide) is reduced, and accordingly a spinnable concentrated solution of the blended copolymers cannot be formed. Therefore, the uniform synthetic pulp cannot be obtained.
The AN-S copolymer whi~h is used in the invention can be prepared through the utilization of any of conventional techniques of random copolymerization such as an aqueous heterogeneous polymerization and a mass polymerization.
_ g _ ~057~11 The blended polymer system for the synthetic pulp according to the invention comprises 5 to 40% by weight of a PVA-AN
copolymer and 60 to 95% by weight of such an AN-S copolymer.
If the amount of the PVA-AN copolymer is less than 5% by weight, it is difficult to fibrillate the fibers by beating, and the fibers will have only low hydrophilic property. When such synthetic pulp is mixed with wood pulp to make a paper, the paper having excellent physical properties could not be obtained.
On the o ther hand, if the amount of the PVA-AN copolymer exceeds 40% by weight, both the water resistance and the dimensional stability to moisture of the resultant paper would be decreased.
It is not desirable that the amount of AN-S copolymer is less than 60% by weight because the coagulation ability of the fibers in a coagulation bath is reduced, The blended polymer system for the synthetic pulp is never limited to those consisting of said two copolymers only.
The system may contain unreacted PVA and an AN polymer produced as by-products in the process of the graft copolymerization and may further contain another acrylonitrile polymer.
A greater part of unreacted PVA are removed in the state of an aqueous slurry in the process of making fibers and pulp.
, ~
,, _ 1~)5~911 However, the amount of PVA in the blended polymer system initially prepared should not exceed 23% by weight. If the amount o:E unreactéd PVA exceeds 23% by weight, it will cause to produce foams in the aqueous slurry.
The amount of the AN polymer in the b lended system prepared should not exceed 35% by weight. If the AN polymer amount exceeds 35% by weight, the excessive fibrillation would be caused.
i As to the addition of an AN polymer to the blended polymer system, a separately prepared linear polymer may be used.
One having a molecular weight of about 20, 000 to 100, 000 is preferable, It may contain the aforementioned vinyl monomers which can be used in the gr~ copolymerization as a copolymerizable component in such an amount within the range not exceeding 40 mol %.
Among the methods for preparing synthetic pulp from the above mentioned blended composition, there are included a method of beating fibers produced from the above system and a method for preparing pulp materials directly from the blended polymer composition .
As methods for producing fibers, there may be included a flush spinning method and an emulsion flush spinning method ~ .
lV5791~
in addition to the conventional spinning methods such as a wet spinning method, a dry wet spinning method and a phase separation spinning method. Among them the wet spinning method is most preferable. A further explanation of the wet spinning method will be given below.
The composition including the PVA-AN copolymer and the AN-S copolymer is dissolved in a solvent such as dimethyl sulfoxide.
This solution is then wet spun by a conventional method into an aqueous spinning bath, for example, an aqueous solution of dimethyl sulfoxide containing up to the maxirnum of 80 % by weight of dimethyl sulfoxide to produce an undrawn water-containing gel filament. Such undrawn filament may be drawn in a hot water j ~ath or in an atmosphere of steam. Further, the drawn filament may be subjected to a heat treatment for fixing its length or relaxing in a ho.t water bath or in an atmosphere of steam.
A draw ratio is preferably more than -3.0,but this is not intended to limit the scope of the present invention. The use of the undrawn filament is not harmful to achieve the objects of the, invention. However, in the case of using the undrawn filament, it is necessary to pay close attention to handle it because the undrawn filament has a low strength.
1~57911 .
Referring to the heat treatment for relaxation, a , relaxation ratio is preferably more than 45%, but this is not intended to limit the scope of the invention. By such procedures, a fine pulp having a good dispersibility is easily obt~ined. - When the draw ratio is not more than 3. O, the filament which is subjected to such heat treatment is rather cut than fibrillated in the process of beating. However, when the beating is carried out without subjecting the filament to the hest treatment, the objects of t~ invention can be achieved with the draw ratio being not more than 3. O.
What is important is that the above fibrious material consists of a hydrophilic component (PVA-AN graft copolymer) and a hydrophobic component (AN-S copolymer) and that the hydrophilic component is dispersed in the hydrophobic component and exists in the form of being arranged as an independent phase in the direction of the fiber axis.
1, .
Such fibrous material is easily fibrillated by beating, and accordmgly a pulp or pulp like material having an excellent hydrophilic property, a dispersibility in water~ and a self-adhesive property can be obtained.
!
The obtained filaments are then be cut into staple fibers having a length of 1. 0 to 25 mm.
Instead of the aforementioned heat treatment prior to the process of cutting, fibers may be subjected to a heat treatment in a hot water or in an atomosphere of steam. In such a case, it is desirable that the temperature for the treatment is within the range of 90 to 120C and treatment time is within the range between 30 seconds and 8 minutes, however, those are not intended to limit the scope of the invention .
The fibers which are obtained according to th- above method can easily be fibrillated by means of beating which is usually applied to wood pulp, and may be made into pulp having an excellent dispersibility in water.
The above staple fibers are made into an aqueous dispersion having a concentration of 1 to 20% by weight and subjected to a beating treatment by use of the conventional beating devices such as beaters, refiners, PFI mills and ball mills.
The synthetic fiber prepared according to the invention has a self-bondable microfibril structure. The pulp part icles are entangled each other by the microfibrils. Each of tke fibers may have a diam'eter of 0. 01 to 5 microns, preferably 0. 05 to 3. 0 microns, at its minimum dimension portion. The length of each of t-he fibers may be more than five times, preferably twenty times, the average diameter.
The synthetic pulp may be solely or partly of a latent microfibril structure. The term "latent microfibril structure"
refers to fibrous material itself obtained according to the invention, or to the fibrous material a part of which is crushed in the process of beating andis ;present in the form of microfibrils. Namely, the latent microfibril structure is a precursor which can be entirely converted to the microfibrils with sufficient beating.
When the beating with use of ~he conventional beating devices is carried out to such an extent that the beaten fibrous materials become suitable for forming a paper like sheet, a greater part of the pulp material is occupied by the microfibril structure. In the process of beating, powder like minute particles which are smaller in size than the above microfibrils may be produced as by-products, but those are not essential to the invention.
When the minimum di~nension of the above microfibril structure does not meet such requirements that t~he diameter is at least O. 01 microns and the length is more than five timesthe average diameter.
the entanglement of the pulp particles is degraded, and accordingly , .
lV5791~
the strength and texture of the resultant paper are impaired.
Since the pulp material of the invention contains the microfibril structures and the latent microfibril structure~, the freeness of the pulp can be controlled at wlll by varying the beating conditions. In addition, a paper having an excellent wet strength is obtained without any additives such as binder since the microfibrils have the self-adhesive property.
The structure of the synthetic pulp prepared according to the invention may be defined by a freeness which is determined according to Japanese Industrial Standard JIS P-8182 with use of Canadian Standard Freeness testing machine. The freeness of the pulp material of the invention should be within the range of 50 to 600 cc, preferably within the range of 100 to 400cc.
When the freeness is less than 50cc, the tear strength of the resultant paper is lowered and the paper making speed is lowered to such an extent that the paper making is substantially impossible.
On the other hand, the freeness exceeds 600cc, the pulp loses the paper making ability, and a paper having a good texture, a good surface uniformity and good physical pPoperties is not obta ined .
The tranSparent paper according to the invention ~OS79~1 -is obtained by subjecting a sheet comprising 6 to 60 parts by weight on dry basis of the above synthetic pulp and 94 to 40 parts by weight on dry basis of natural pulp to a transparentizing treatment with moisture, heat and pressure.
f As the natural pulp, wood pulp is most preferably used, but other natural pulp such as one which is prepared from bast fibers or animal fibers may also be used.
If the amount of the synthetic pulp is less than 6 parts by weight, the resultant base sheet is not sufficient for Fractical use in the respects to its transparency, wet-strength, tensil strength, folding strength, and dimensional stability, though these properties of the base sheet are improyed when compared with a transparent base sheet consisting of the conventional natural pulp only. On the other hand the amount of the synthetic pulp exceeds 60 parts by weight, the mechanical strength becomes uneven, especially the tear strength and the folding strength are reduced. Preferably, the sheet is formed of 10 to 50 parts by weight of synthetic pulp and 90 to 50 parts by weight of natural pulp.
The synthetic pulp and the natural pulp mixed in the above proportions are made into a sheet with use of a conventional wet system paper making machine. In the process of the paper f ' lOS7~11 making, the conventional additives such as sizing agents, fixing agents, releasing agents, antistatic agents, fillers and dyestuffs may be added to the system.
.
Application in the paper making process of starch, polyvinyl alcohol, carboxymethyl cellulose, sodium alginat~, solutions or emulsions of synthetic resins or conventional transparentizing agents may also be carried out by size-pressing, impregnation or coating.
.
The weight of the resultant sheet material may be controlled within the range 25 to 200 g/m, but this is not intended to limit the scope of the invention.
.
According to the invention it is possible to obtain a high transparency without using a heavily beaten pulp which is used to make a conve~ntional transparent paper Heretofore, it has been necessary to use a heavily beaten pulp having a CSF
(Canadian Standard Freeness) of 50 to 150 cc to make conventional transparent paper. However, according to the invention, an excellent transparency can be o'otained with use of usually or slightly beaten pulp. Therefore, the disadvantages inherent with use of the heavily beaten natural pulp, such as a decrease in the rate of paper making, a decrease in physical properties such as dimensional stability, tear strength and folding strength ~OS7~11 and the generation of blister phenomenon can be avoided a cc ord ing to the invention .
The thus obtained sheet materi~l is then transparentized by moistening the sheet to a moisture content within the range of 5 to 40%, and then passing it through a pressure equipment having a surface temperature of above 130C to impart heat and pressure. The moisture content is given by the following formula Weight of water contained in the sheet Moi~ture content = X100 Weight of the sheet containing water If the moisture content is less than 5%, a uniform transparency of the sheet is not obtained. While, when the moisture content exceeds 401O, the physical strength of the sheet is reduced, causing adhesion to the roll of the pressure equipment and making troubles such as a break. Among the typical moistening methods, there may be included a method of coating water by coater, a method of spraying water and a so-called electrostatic moistening method. In the moistening process, various additives such as sizing agents, releasing agents, antistatic agents;
dystuffs and transparentizing agents may be added to water.
~057911 - -For the pressing treatment any conventional means such as a super calender and a machine calender, an eguipment having two rolls which form a nip, and a hot press type eq-llipment may be utilized.
In the process of transparentizing treatment with use of those equipments the sheet material is pressed at least one time by a pressure equipment having a surface temperature of 130C or above, whereby a desired transparency of the sheet is obtained However, in view of 'the fact that the synthetic polymers which constitute the synthetic pulp are decomposed at about 250C, it is necessary to be careful so as not to raise the temperature of the sheet to above 250C. The pressure which is applied to the sheet material.- is controlled at will depending on the thickness of the sheet, the mixing ratio of pulps and the condition of moistening.
But it may be usually within the range of about 100 to 500 kg/cm, preferably about 120 to 400 kg/cm.
!
The transparent paper according to the invention has such various advantages as described below, as compared with conventional transparent paper such as glassine paper or transparent paper formed of poly ~t olefin fibers and wood pulp.
t , .
'' ' ~ ' ', - 105791~
The synthetic pulp described can be uniformly dispersed in the sheet in the form of microfibrils having numerous micro voids and has hydrophilic moieties in itself. Therefore, the water contained in the sheet functions as a plasticizer not only for natural pulp but also for synthetic pulp. In addition, when the sheet is subjected to the treatment with heat and pressure, the water contained in the sheet is removed accompanying air which is filled in the micro voids, whereby an inherent clarity of the polymers which constitute the synthetic pulp are developed effectively, and accordingly an excellent transparency is obta ined .
The equilibrium moisture (at 20C, 60% RH) of the untreated sheet material of the invention varies with the mixing ratio of synthetic pulp, for example, it is about 6 % when the sheet consists of 10 parts by weight of synthetic pulp and 90 parts by weight of natural pulp, and it is about 4 % when the sheet consists of 60 % by weight of synthetic pulp and 40% by weight of natural pulp.
When it is intended to obtain a desired transparency, it is found that there is such a relation between the mixin-g -ratio of synthetic pulp and the moisture content that an increase in the amount of synthetic pulp saves the moisture content. Therefore, when the mixing ratio of synthetic pulp is 60 %, it is sufficient for achieving . .
- ', '. ~ ' ' ' ':
, . .
the effect that the moisture content is at least 5 %. When the mixing ratio of synthetic pulp is 10 %, the moisture content is preferably more than 20 %.
As is understood from the abovê descriptions, the transparent paper according to the invention has following advantages:
(a) It has a uniform and high transparency.
(b) It has excellent physical properties such as a tensile strength and a folding strength.
(c) It has an excellent stability to moisture or water, whereby the disadvantages such as curl, stretching and corrugation can be avoided.
(d) The blister phenomenon which occurs when it is heated can be avoided.
(e) It is suitable for various uses such as offset printing use and secondary processing use.
(f) It offers various advantages in preparation such as an - increase of ,the rate of paper making, a reduction of beating treatment and a simplified transparentizing treatment .
lOS7911 - :
This invention includes not only a sheet which is wholly transparentized but also a sheet which is partly transparentized .
The transparency of the resultant paper may be controlled at will according to its use. For example, it is generally controlled at more than 50 % u~hem the paper is used for a master for duplication. For a tracing paper or a paper for plotter, it is controlled at more than 60 %. And it is controlled at more than 80 % when the paper is used for a glassine paper.
The transparency is given by the following formula:
Transparency = 100 - (value of opacity) wherein the value of opacity is measured by Hunter reflectometer according to JIS P-8138.
The invention will be further illustrated by reference to the following examples, however, the invention is not limited to those examples but includes wide variations.
Unless otherwise indicated, parts and % signify parts by weight and % by weight, respectively.
: " ': -' " ' ' .. . .
10579~
Exa mple A PVA-AN graft copolymer in which the ratio of PVA to AN i6 50/50 was obtained by grafting AN to PVA having a degree of polymerization of 1400 according to a~n ordinary radical polymerization method with use of persulfate salt as a catalyst.
I
An AN-S copolymer in which the ratio of AN to styrene is 24/76, having an intrinsic viscosity of 0. 54 (determined in MEK
at 30C ) was obtained according tOa conventional suspension polyme r ization .
One part by weight of the above PVA-AN graft copolymer and 4 parts by ~veight of the above AN-S copolymer were diss`olved in 15 parts by weight of dimethyl sulfoxide (hereinafter referred to as "DMSO") to obtain a 25% spinning solution.
A wet spinning with that solution was carried out in a water/
DMSO (45/55) bath from a spinning nozzle having a diameter of 0. 08mm to obtain a continuous filament having a denier of 7 and a PVA
content of 10% . The draw ratio was 2 times. Thus obtained filament was cut into staple fibers having a length of about 10mm and the fibers were then beaten with use of a single discrefiner under the conditions of a pulp concentration of 3 % and the clearance of 50 mic:rons to obtain a synthetic pulp (A) whose CSF was 200cc. The a verage diameter of the fibrils was 8 microns, the minimum diameter in a fibril was 0. 5 microns and the ratio of the length by the average diameter was about 50.
Separately, bleached broad-leaved wood kraft pulp (L) having a CSF of 480cc, bleached needle-leaved wood pulp (N) having a CSF of 350cc, heavily beaten bleached needle-leaved wood kraft pulp (N') having a CSF of lOOcc and heavily beaten bleached broad-leaved wood kraft pulp (L') having a CSF of 120cc were prepared. The above synthetic pulp (A) and the natural pulp (L) (N) (L') (N') were formed intoa sheet witha manual paper-making sheet machine (with 80 mesh metal screen) manufactured by Toyo Seiki Co., Ltd. according to the formulations shown in the following Table 1.
As a control, a bleached needle-leaved wood kraft pulp (N') having a CSF of lOOcc and a bleached broad-leaved wood kraft pulp (L') having a CSF of 120cc were mixed with the above synthetic pulp (A) to form a sheet under the condition shown in Table 1 in the same manner as in th~ above.
The moisture contents of the thus obtained dry sheets were controlled as shown in Table 1 by applying water to the sheets with a wire wound coating rod. Then, the sheets were subjected , lOS'7911 to a transparentizing treatment in which the sheets were made to pass through a nip of a two stack pressure equipment provided with an elastic roll and a hard chrome plated metal roll (surface temperature at 150C) under the linear pressure of 135 kg/cm for four times in all, reversing the sheet upside-down. Various characteristics of the obtained transparent papers are shown in Table 1.
The transparent papers obtained according to the invention were superior in the paper making ability, the transparency, the physical properties and the secondary processability, compared with that of Control. The transparent paper according to the invention had a good balance of quality.
Example 2 Two kinds of filam~ts having PVA contents of 30% and 10%
respec~ively, were made by a conventional spinning method similarto that described in Example 1 froma 25% solution in DMSO of a mixture of one part by weight of a PVA-AN copolymer obtained by grafting AN to PVA having a degree of polymerization of 1800 according to an ordinary radical polymerization method with uæe of persulfate salt as a catalyst in which the ratio of PVA/AN
is 80/20, with 1. 67 and 7 parts respectively by weight of an AN-S copolymer having an intrinsic viscosity of 0. 65 determined 105~91~L
in MEK at 30C which is obtained by a conventional suspension polymerization method, in which the ratio of AN/styrene is 30/70. The draw ratio was 3. 5 times and each of the obtained two kinds of filaments had a denier of 5. The filamen~s were cut into staple fibers having a length of about 3 mm and the staple fibers were then beaten in the same manner as in Example 1, respectively, to obtain two kinds of synthetic pulp. One was a synthetic pulp (B) whose PVA content was 30% and having a CSF of 195 cc, and the other was a synthetic pulp (C) whose PV~ content was 10%
and having a CSF of 240 cc.
The average diameter of the fibrils having a PVA content of 30% was 2 microns, the minimum diameter in the fibril was 0. 2 microns and the ratio of the length by the average .
diameter was about 90, and the average diameter of the fibrils having a PVA content of 10 % was 4 microns, the minimum diame~er in the fibril was 0. 3 microns and the ratio of the length by the average diameter was about 70.
Separately, a bleached needle-leaved wood kraft pulp (N"~ having a CSF of 280cc and a bleached broad-leaved wood kraft pulp ~L") having a CSF of 450cc were prepared.
.
1(~5791~
A sheet was formed with use of the above synthetic pulps (B) and (C) and natural pulps (N' ')and (L' ' ) in the same manner as in Example 1 under the condition as shown in Table 2.
The moisture content of the resultant sheet was adjusted at the value shown in Table 2 in the same manner as in Example 1.
Then, the sheet was made to pass through the two stack calender which was used in Example 1 under the conditions of the surface temperature of the roll at 140C and t~e linear pressure at 220kg/cm for four times in all, reversing the sheet upside-down, to obtain a transparent paper. The properties of the resultant transparent papers are shown in Table 2.
Example 3 Two kinds of filaments having PVA contents of 7 % and 20% respective;Ly, were made by a wet spinning method similar to that disclosed in Example 1 from a 25% solution in DMSO of a mixture of one part of a PVA-AN graft copolymer obtained by grafting AN to PVA having a degree of polymerization of 1100 according to an ordinary radical polymerization method with use of persulfate salt as a catalyst in which the ratio of PVA/AN was 60/40, with 7. 57 and 2 parts, respectively, of an AN-S copolymer having an intrinsic vi scos ity ()f 0. ~5 determined in MEK at 30C which was obtained by a conventional mass polymerization method, in which the ratio ofAN/styrene was 20/80.
The obtained tWG kinds of filaments had the same denier of 10. Those filaments were cut into staple fibers having a length of about 5 mm and the staple fibers are then beaten in the same manner as in Example 1 to obtain two kinds of synthetic pulp.
One was a synthetic pulp (D) whose PVA content was 7% having a CSF of 230cc, and the other was a synthetic pulp (E) whose PVA content was 20% having a CSF of 200cc. The average diameter of the fibrils having a PVA content of 7 % was 13 microns, the minimum diameter in the fibril was 0. 8 microns and the ratio of the length by the average diameter was about 45, and the average diameter of the fibrils having a PVA content of 20 %
was 8 microns, the minimum diameter in the fibril was 0. 5 microns and the ratio of the length by the average diameter was about 55.
Separately, the same bleached needle-leaved wood kraft pulp (N) -and bleached broad-leaved wood kraft pulp (L) as in E~ample 1 were prepared. The above synthetic pulps (~) and (E) and natural pu1ps (N) and (L) were mixed in such proportions as shown in Table 3 to form a dry sheet with a Fourdrinier test machine manufactured by Mitsubishi Kakoki Co., Ltd. at the lOS7911 paper making rate of 20m/min.
The moisture content of the resultant sheets were adjusted at the value shown in Table 3 by water coating with use of a pilot coater. Then, the sheets were made to pass through 4 nips of a super calender which was provided with alternatively arranged chilled rolls having a highest surface temperature of 160C and cotton rolls under the linear pressure at 220kg/cm to obtain transparent papers. The properties of the resultant transparent papers are shown in Table 3.
Control 3 A transparent paper was obtained in the same manner as in Example 1-4 except that a commercially available pulp prepared from poly 0(-olefin fiber was used instead of the synthetic pulp (A) which was used in Example 1-4, and that the adjustment of moisture content was not carried out. The transparency of the resultant transparent paper was only 60 %. Besides, a macroscoplc unevenness of transparency was remarkably appreciated. The offset printabilities of the above transparent paper and that of the transparent paper obtained in Example 1-4 were examined, respectively. The transparent paper of Example 1-4 showed a good ink acceptability and gave a good result in printing. On the contrary, the transparent paper obtained in this control showed a poor ink acceptability due to its poor water absorbability, and microscopic white-spots were remarkably appreciated .
Example 4 A continuous filament having a denier of 7 and having a PVA
content of 7 % was prepared by a conventional spinning method similar to that in EKample 1 from a 25% solution in DMSO of a mixture of one part of a PVA-AN graft copolymer obtained by grafting AN
to PVA having a degree of polymerization of 2600 according to an ordinary radical polymerlzation method with use of persulfate salt as a catalyst, in which the ratio of PVA/AN was 30/70, with 3. 29 parts of an AN-S copolymer having an intrinsic viscosity of 0. 54 determined in ME K at 30C which was obtained by a usual suspension polymerization method, in which the ratio of AN/styrene was 24,/76.
The obtained filament was cut into staple fibers having a length of about 10 mm and then the staple fibers Iwere beaten in the same manner as in Example 1 to obtain a synthetic pulp (F) having a CSF of 280cc. The average diameter of the fibrils was 13 microns, the minimum diameter in the fibril was 0. 8 microns and the ratio of the length by the average diameter was about 45.
105791~
The bleached needle-leaved wood kraft pulp tN) and the bleached broad-leaved wood kraft pulp (L) which were used in Example 1 were mixedw~hthe above synthetic pulp (F) in such propl3rtions as shown in Table 4. The resultant mixed pulp was made into two sheets with a Fourdrinier test machine manufactured by Mitsubishi Kakoki Co., Ltd. at a rate of 20 m/min. The moisture contents of the resultant dry sheets were controlled at the value shown in Table 4 by-spraying 3 % aqueous solution of glycerin as a plasticizer with use of a spray-type damping equipment attached to a pilot coater.
Then, the sheets were made to pass through 4 nips of a super calender provided with alternatively arranged chilled rolls having a highest surface temperature of 150C and cotton rolls under the linear pressure of at most 200kg/cm to obtain a transparentized papers, The properties of the obtained transparent papers are shown in Table 4. The transparent papers obtained in Example 4 showed excelIent properties having a good balance of quality. To the contrary, the transparent paper obtained in Control 4 had an undesirable texture due to its poor dehydration property, and showed a poor ' t workability in super calendering due to its poor tear strength and folding strength and showed a bad ink acceptability in offset printing, Furthermore, the corrugation~ of the resultant transparent A
1~)5793LiL
paper were appreciated.
:E~ample 5 A continuous filament having a PVA content of 28 % was made by-a wet spinning method similar to that described in Example 1 from a 25% solution in DMSO of a mixture of one part of a reaction product obtained by grafting AN to PVA having a degree of polymerization of 1800 according to an ordinary radical polymerization method with use of persulfate salt as a catalyst, which consisted of 74 % by weight of PVA-AN copolymer (75/25), (20% by weight of unreacted PVA and 6 % by weight of a homogenous acrylonitrile polymer, with 1. 7 parts of an AN-S copolymer (havingan intrinsic visoosity of 0.71 determined in MEKat 30C) which was obtal~ned by a conventional suspension polymerization method, in which the ratio of AN/styrene . was 15/85. The obtained filament having a denier of 7 was cut into staple fibers having a length of about 5mm and the staple fibers were then beaten in the same manner as in Example 1 to obtain a synthetic pulp (G) having a CSF of 240cc. The average diameter of the fibrils was 4 microns, the minimum diameter in a fibril was 0 3 microns and the ratio of the length by the average diameter was about 70.
10~7911 Separately, a bleached needle-leaved wood kraft pulp (N"') having a CSF of 550cc a bleached broad-leaved wood pulp (L"') having a CSF of 620cc were prepared, The above synthetic pulp (G) and the natural pulps (N"') and (L"') were mixed and made into two sheets under the conditions shown in Table 5. As a Control, a sheet composed of the above natural pulps (N"') and (L"') only was prepared under the condition shown in Table 5.
The moisture contents of the resultant sheets were adjusted at the values shown in Table 5 by coating a 0. 3 % aqueous solution containing sodium chloride as an antistatic agent on one side surface of the sheet with use of a wire wound coating rod.
Then the sheets were made to pass through a two stack type calender provided with an elastic roll and a hard chrome plated metal roll (surface temperature at 150C) four times under linear pressure of 210kg/cm, reversing both sides of sheets, to obtain transparentized papers. The properties of the resultant papers are shown in Table 5.
The transparent papers obtained in this Example were superior to that obtained in Control in the respects of the transparency, the physical properties and the secondary processability. The properties of the transparent papers !
1~57911 according to the invention transcended those which the glassine paper should possess.
Example 6.
A continuous filament having a PVA content of 10%
was made by a wet spinning method similar to that disclosed in E xample 1 from 25% solution in DMSO of a mixture of one part of a PVA-AN graft copolymer obtained by grafting AN to PVA
having a degree of polymerization of 800 according to a conventional radical polymerization with use of persulfate salt as catalyst, in which the ratio of PVA/AN was 40/60, with 3 parts of AN-S
copolymer havingan intrinsic viscosity of 0.75 determined n MEK at 30C and having a ratio of AN/styrene at 20¦80, which was obtained by a common suspension polymeri zation method.
The draw ratio was 2. 0 times.
The resultant filament having a denier of 10 was cut into staple fibers having a length of about 5 mm, and the staple fibers were then beaten in th e same manner aæ in Example 1 to obtain a synthetic pulp (H) having a CSF of 260 cc. The average diameter of the fibrils was 7 microns, the minimum ,1 ~
10579~1 diamer in the fibril was 0. 5 microns and the ratio of the length by the average diameter was about 50.
The same bleached needle-leaved wood kraft pulp (N"') and bleached broad-leaved wood kraft pulp (L"') as those which used in Example 5 were prepar ed.
The above synthetic pulp and natural pulps (N"') and (L"') were mixed at the mixing ratio shown in Table 1) and then made into three sheets with use of a commercially available Fourdrinier paper machine provided with a wire cloth having a width of 1975mm, at a paper-making rate of 50 m/min.
As a control, a sheet composed of the above natural pulps (N"') and (L"') only was prepared in the same manner as the above.
The moisture contents o~ each sheet thus prepared was adjusted at the value shown in Table 6 by coating a 0. 2 %
aqueous solution containing a commercially available wax emulsion as a releasing agent with a commercially available bar coater.
Then, each sheet was made to pass 16 nips of a super calender provided with alternatively arranged chilled rolls having a highest -~6 1~)579~
surface temperature of 160C and cotton rolls under the linear pressure of at most 400 kg/cm to o'btain a transparentized paper, The properties of the resultant transparent papers are shown in Table 6.
It was clearly appreciated that the transparent papers obtained in this :Example showed an excellent transparency and excellent properties having a good balance of q uality with increasing the mixing ratio of synthetic pulp even when the moisture content was relatively low. On the contrary, the sheet composed of natural pulp only which was obtained in Control had an insufficient transparency though, it was treated at high moisture content .
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Note:
1) Talc filler (~): The amount of ash in a dry p~per determined according to Japanese . Industrial Standard JIS P-8128
2) Oxidized starch siz,e press:
The amount of coating g/m2 on dry basis
The amount of coating g/m2 on dry basis
3) Dehydration rate:
Time required for dehydration of 10~
of pulp dispersion on a 80 mesh metal screen of a manual paper-making sheet machine having a width of 20 cm and a length of 25 cm
Time required for dehydration of 10~
of pulp dispersion on a 80 mesh metal screen of a manual paper-making sheet machine having a width of 20 cm and a length of 25 cm
4) Transparéncy (~) = 100 - value of opacity by Hunter reflectometer (JIS P-8138)
5) Air permiability was measured by High Pressure Gurley Densometer (ASTM D726-58, method B)
6) Breaking length was measured according to JIS P-8113
7? Tear factor was determined according to JIS P-8116 : 8) Folding strength was measured by MIT according to . tensile strength of re~etted p~per 9) Breakinglength (Km)= (K~ xDOO
` drybasis weight (g/m2~ xpaperwidth . . wherein the tensile strength of . re`wetted pap~r.ls measured by JIS P-8135, the dry basis weight is given by.
JIS P-8111, and the paper width is 15 mm as defined in JIS P-8135.
.
. -40-1~)579~
10) Expansion in water was measured with a Fenchel expansion meter after dipping the sheet in water at 20C for 5 minutes.
The above note for each of the items in Table 1 also applied to Tables 2 to 6.
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` drybasis weight (g/m2~ xpaperwidth . . wherein the tensile strength of . re`wetted pap~r.ls measured by JIS P-8135, the dry basis weight is given by.
JIS P-8111, and the paper width is 15 mm as defined in JIS P-8135.
.
. -40-1~)579~
10) Expansion in water was measured with a Fenchel expansion meter after dipping the sheet in water at 20C for 5 minutes.
The above note for each of the items in Table 1 also applied to Tables 2 to 6.
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Claims (9)
1. Transparent paper which is obtained by moistening a fibrous matrix in the form of a sheet material so as to have a moisture content within the range of 5 to 40% and then pres-sing the thus moistened sheet material with press means having a press surface temperature of 130°C to 250°C, said fibrous matrix consisting essentially of:
a) 6 to 60 parts by weight on dry basis of synthetic pulp formed from stable fibres having a length of 1.0 to 25 mm and having a self-bondable microfibril structure of pulp fibres having a diameter of 0.01 to 5 microns at their minimum dimensions and a length at least five times their average diameter, the synthetic pulp having a freeness of 50 to 600 cc CSF and being of a blended polymer system which con-sists essentially of 5 to 40% by weight of polyvinyl alcohol-acrylonitrile copolymer comprising a polyvinyl alcohol component which has an average degree of polymerization of 500 to 3400 and is chemical-ly bonded to an acrylonitrile component, the polyvinyl alcohol component content being 20 to 80% by weight, and the polyvinyl alcohol-acrylonitrile copolymer being dispersed in 60 to 95% by weight of acrylonitrilestyrene copolymer in which the acrylonitrile component content is 5 to 45% by weight; and b) 94 to 40 parts by weight on dry basis of natural pulp.
a) 6 to 60 parts by weight on dry basis of synthetic pulp formed from stable fibres having a length of 1.0 to 25 mm and having a self-bondable microfibril structure of pulp fibres having a diameter of 0.01 to 5 microns at their minimum dimensions and a length at least five times their average diameter, the synthetic pulp having a freeness of 50 to 600 cc CSF and being of a blended polymer system which con-sists essentially of 5 to 40% by weight of polyvinyl alcohol-acrylonitrile copolymer comprising a polyvinyl alcohol component which has an average degree of polymerization of 500 to 3400 and is chemical-ly bonded to an acrylonitrile component, the polyvinyl alcohol component content being 20 to 80% by weight, and the polyvinyl alcohol-acrylonitrile copolymer being dispersed in 60 to 95% by weight of acrylonitrilestyrene copolymer in which the acrylonitrile component content is 5 to 45% by weight; and b) 94 to 40 parts by weight on dry basis of natural pulp.
2. Transparent paper as defined in claim 1, in which said blended polymer system further includes unreacted polyvinyl alcohol in an amount of 23% or less by weight.
3. Transparent paper as defined in claim 2, in which said blended polymer system further include an acrylonitrile polymer in an amount of 35% or less by weight.
4. Transparent paper as defined in claim 1, in which said polyvinyl alcohol-acrylonitrile polymer is a graft co-polymer.
5. Transparent paper as defined in claim 1, in which said fibrous matrix consists essentially of 10 to 50 parts by weight of said synthetic pulp and 90 to 50 parts by weight of natural pulp.
6. Transparent paper as defined in claim 1, in which said natural pulp is wood pulp.
7. Transparent paper as defined in claim 1, in which the pressure applied to said sheet material is within the range of 100 to 500 kg/cm.
8. Transparent paper as defined in claim 7, in which the pressure applied to said sheet material is within the range of 120 to 400 kg/cm.
9. Transparent paper as defined in claim 1, in which said sheet material after said transparentizing treatment has a transparency ratio of more than 50%.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP49103702A JPS597839B2 (en) | 1974-09-09 | 1974-09-09 | transparency paper |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1057911A true CA1057911A (en) | 1979-07-10 |
Family
ID=14361075
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA234,678A Expired CA1057911A (en) | 1974-09-09 | 1975-09-03 | Transparent paper |
Country Status (9)
| Country | Link |
|---|---|
| JP (1) | JPS597839B2 (en) |
| BE (1) | BE833164A (en) |
| CA (1) | CA1057911A (en) |
| DE (1) | DE2540069C2 (en) |
| FR (1) | FR2283991A1 (en) |
| GB (1) | GB1522854A (en) |
| IT (1) | IT1042387B (en) |
| NL (1) | NL7510609A (en) |
| SE (1) | SE7509849L (en) |
Families Citing this family (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS597840B2 (en) * | 1976-10-04 | 1984-02-21 | 三菱製紙株式会社 | Transparent paper manufacturing method |
| DE3368092D1 (en) * | 1982-07-30 | 1987-01-15 | Mishima Paper Co Ltd | Conductive film for packaging |
| DE10002576A1 (en) * | 1999-09-21 | 2001-03-22 | Heinr Aug Schoeller Soehne Gmb | Process for the production of paper and corresponding paper |
| JP2005048323A (en) * | 2003-07-29 | 2005-02-24 | Daio Paper Corp | Sheet transparentized by sensing heat |
| DE102011087742A1 (en) * | 2011-12-05 | 2013-06-06 | Papierfabrik Schoellershammer Heinr. Aug. Schoeller Söhne GmbH & Co. KG | Corrugated cardboard used for packaging food product e.g. chocolate in food processing industry, has transparent paper made cover material and shaft material which are joined together |
| CN110552234B (en) * | 2018-05-30 | 2022-02-15 | 华南理工大学 | Super folding-resistant, high-haze and high-transparency paper and preparation method thereof |
| AT525436B1 (en) * | 2022-02-11 | 2023-04-15 | Mondi Ag | TRANSPARENT PAPER |
Family Cites Families (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3101294A (en) * | 1959-12-17 | 1963-08-20 | Du Pont | Process for forming a web of synthetic fibers |
| FR2108395A5 (en) * | 1970-09-25 | 1972-05-19 | Toray Industries | |
| JPS5117608B2 (en) * | 1973-07-26 | 1976-06-03 | ||
| JPS5040803A (en) * | 1973-08-10 | 1975-04-14 |
-
1974
- 1974-09-09 JP JP49103702A patent/JPS597839B2/en not_active Expired
-
1975
- 1975-09-03 CA CA234,678A patent/CA1057911A/en not_active Expired
- 1975-09-04 SE SE7509849A patent/SE7509849L/en unknown
- 1975-09-08 BE BE159820A patent/BE833164A/en unknown
- 1975-09-08 FR FR7527478A patent/FR2283991A1/en active Granted
- 1975-09-09 DE DE2540069A patent/DE2540069C2/en not_active Expired
- 1975-09-09 NL NL7510609A patent/NL7510609A/en not_active Application Discontinuation
- 1975-09-09 IT IT27044/75A patent/IT1042387B/en active
- 1975-09-09 GB GB37151/75A patent/GB1522854A/en not_active Expired
Also Published As
| Publication number | Publication date |
|---|---|
| GB1522854A (en) | 1978-08-31 |
| JPS597839B2 (en) | 1984-02-21 |
| FR2283991A1 (en) | 1976-04-02 |
| DE2540069C2 (en) | 1984-07-05 |
| FR2283991B1 (en) | 1979-06-29 |
| SE7509849L (en) | 1976-03-10 |
| IT1042387B (en) | 1980-01-30 |
| JPS5132803A (en) | 1976-03-19 |
| AU8458475A (en) | 1977-03-10 |
| NL7510609A (en) | 1976-03-11 |
| BE833164A (en) | 1975-12-31 |
| DE2540069A1 (en) | 1976-03-25 |
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