Patent Application
20060037724
The present invention relates to a bulky, water-disintegratable cleaning article and a process of producing bulky, water-disintegratable paper.
Applicant has previously proposed a water-disintegratable cleaning sheet having water-disintegratable paper impregnated with an aqueous cleaning agent (see JP-A-2-149237), in which the water-disintegratable paper is made by wet papermaking and contains a water soluble binder having a carboxyl group, and the aqueous cleaning agent contains a polyvalent metal ion and an organic solvent as essential ingredients. Applicant has also proposed a water-disintegratable cleaning article having water-disintegratable paper impregnated with a boric acid aqueous solution containing a water soluble solvent (see JP-A-3-292924), in which the water-disintegratable paper is made by wet papermaking and contains polyvinyl alcohol as a binder. These water-disintegratable cleaning articles have strength withstanding cleaning operation and good water disintegratability making them flushable. The water-disintegratable paper, i.e., a fibrous base sheet, of these water-disintegratable cleaning articles is made of non-heat-fusible and biodegradable cellulosic materials such as pulp to develop post-disposal water disintegratability.
In order to secure post-disposal biodegradability of water-disintegratable paper for applications inclusive of the cleaning articles, it is difficult to use heat fusible fiber that is generally non-biodegradable. Although fiber of biodegradable polylactic acid, etc. is among heat fusible fibers, such biodegradable fiber is expensive and not economical. Pulp is typical of biodegradable and inexpensive fibers.
Means for making paper made mainly of pulp bulky for applications inclusive of the cleaning articles include embossing between engraved rolls. Paper embossing techniques are roughly divided into dry embossing effected on dry paper and wet embossing effected on a wet fiber web on a papermaking machine before drying (see JP-A-8-260397). JP-A-8-260397 mentions that an embossed wet fiber web is dried in a drying step. In order to remove a quantity of water from a wet fiber web from a papermaking step, it is necessary to bring the wet web in contact with a yankee dryer or a multi-cylinder dryer to achieve high thermal efficiency. When such a drying method is adopted, it has been impossible to highly emboss the wet web to create high bulk. On the other hand, dry embossing, which is most commonly practiced, is effected on paper obtained by drying a wet fiber web from a papermaking step. When paper made primarily of non-heat-fusible fiber such as pulp is embossed, paper undergoes destruction of the fiber-to-fiber bonds (including hydrogen bonds and bonding via a binder), or fibers break. This results in reductions of paper strength and embossed shape retention (bulk retention). In applications as water-disintegratable cleaning articles, the dry embossed paper is subject to various external forces while it is processed into a final product, such as folding, cutting, impregnation with a cleaning solution, packaging, and container filling. In the meantime, the bulk created by the embossing is reduced. The tendency to the reductions in paper strength and bulk during post-embossing processings and cleaning operation is conspicuous where paper is highly embossed.
The present invention provides a bulky, water-disintegratable cleaning article including water-disintegratable paper and an aqueous agent impregnated in the water-disintegratable paper. The water-disintegratable paper has a basis weight of 30 to 150 g/m2 and a substantially water dispersible fibrous sheet which contains at least one of a water soluble binder and a water swellable binder. The water-disintegratable paper has a number of protrusions and depressions formed by embossing. The amount of the aqueous agent impregnating the water-disintegratable paper is 100% to 500% by weight, based on the dry weight of the water-disintegratable paper. The cleaning article has a thickness T1 of 1.0 to 3.0 mm under a load of 0.3 kPa and a thickness T2 of at least 0.9 mm under a load of 1.0 kPa.
The present invention also provides a process of producing water-disintegratable paper including the step of embossing a substantially water dispersible fibrous sheet containing a water soluble or swellable binder and having a basis weight of 30 to 150 g/m2 while the fibrous sheet has a water content of 10% to 200% by weight and the step of drying the fibrous sheet simultaneously with or immediately after the embossing.
The present invention also provides a process of producing water-disintegratable paper including the steps of adding an aqueous solution of a water soluble binder to a sheet containing a substantially water dispersible fiber and containing no water soluble binder to provide a fibrous sheet having a water soluble binder content of 1% to 30% by weight and a water content of 10% to 200% by weight based on the dry weight of the sheet, embossing the resulting fibrous sheet, and drying the fibrous sheet simultaneously with or immediately after the embossing.
The present invention relates to a bulky, water-disintegratable cleaning article the strength of which has not been reduced by embossing and the bulk of which has not been reduced by post-embossing processings and will not be reduced when used as a wipe, etc., that is, a bulky, water-disintegratable cleaning article having satisfactory shape retention. The present invention also relates to a process of producing water-disintegratable paper including the step of embossing without involving reduction in bulk and strength accompanying embossing.
The present invention will be described based on its preferred embodiments with reference to the accompanying drawings. The premise of the present invention resides in that a substantially water dispersible fibrous sheet containing a water soluble or swellable binder is embossed to increase its thickness or bulk. The water-disintegratable paper obtained by embossing the fibrous sheet has a basis weight of 30 to 150 g/m2, preferably 50 to 120 g/m2, in its dry state. Impregnating the water-disintegratable paper with 100% to 500% by weight, preferably 100% to 300% by weight, of an aqueous agent gives the bulky, water-disintegratable cleaning article of the present invention. The bulky, water-disintegratable cleaning article has a thickness T1 of 1.0 to 3.0 mm under a load of 0.3 kPa, which is a primary criterion representing increased bulk as aimed in the present invention.
As stated, the cleaning article 1 is characterized by its high bulk. The thickness T1 of the cleaning article 1 (i.e., the distance from the apices of protrusions 2 on the first side 1a to the apices of protrusions 2 on the second side 1b) under a load of 0.3 kPa is 1.0 to 3.0 mm, preferably 1.2 to 2.5 mm, more preferably 1.3 to 2.0 mm. Within that range of thickness T1, the cleaning article 1 feels bulky like dustcloth and retains satisfactory strength. With a thickness T1 smaller than 1.0 mm, the cleaning article 1 would not be felt noticeably bulkier than conventional cleaning sheets. It may be slightly inconvenient to use as a wipe and make a user feel insecure about dirt's striking therethrough. A cleaning article having a thickness T1 exceeding 3.0 mm may have insufficient strength, and a packet of such thick cleaning articles would be bulky, which is uneconomical for disposable applications. The 0.3 kPa load under which thickness T1 of the cleaning article 1 is measured is very light so that thickness T1 approximates the apparent thickness of the cleaning article 1.
Besides being bulky, the cleaning article 1 should have thickness retention when a user holds her or his hand against the cleaning article 1 in a wiping operation. In the present invention, the force of a hand against the cleaning article is estimated at 1.0 kPa. When the bulky, water-disintegratable cleaning article (impregnated with an aqueous agent) has a thickness T2 of 0.9 mm or larger measured under a load of 1.0 kPa, the cleaning article can be said to meet the above-described requirement for thickness retention. To ensure ease in wiping with a hand to give a thorough cleaning and to prevent dirt striking through, the thickness T2 is preferably 1.0 mm or larger, more preferably 1.2 mm or larger. Understandably, T2 does not exceed T1.
It is preferred for embossed shape retention that the thickness ratio of T2 to T1 of the cleaning article 1 be 0.8 or greater, more preferably 0.85 or greater. With that thickness ratio being smaller than 0.8, desired embossed shape retention is not secured, and the bulk is collapsed easily when pressed with the hand, failing to give cloth-like is softness or a sense of security. The T2/T1 thickness ratio is preferably 0.85 or greater with no particular upper limit. The closer the ratio to 1, the higher the bulk retention.
The T1 and T2 values are not greatly affected by the amount and the composition of the impregnating aqueous agent so that the aqueous agent content is not included in the conditions of measuring T1 and T2. If the amount of the aqueous agent is to be included in the measuring conditions, double the dry weight of the water-disintegratable paper, which is typical in the present invention, would be a suitable condition.
The fibrous sheet contains a substantially water dispersible fiber and a water soluble or swellable binder. This is indispensable to provide a bulky, water-disintegratable cleaning article and water-disintegratable paper which retain high bulk and exhibit satisfactory wet strength. The water soluble or swellable binder contributes to development of wet strength in the presence of the aqueous agent, embossed shape retention, and water disintegratability (flushability).
The substantially water dispersible fiber used in the fibrous sheet preferably has a fiber length of 15 mm or shorter, more preferably 10 mm or shorter, even more preferably 5 mm or shorter. For ease of obtaining both water disintegratability and wet strength, it is desirable to use primarily pulp fiber having a weight average fiber length of 0.5 to 3.0 mm. Rayon fiber or synthetic fiber having an average length of about 4.0 to 7.0 mm may be used in combination to improve the hand. Biodegradable fibers are preferably used, typically exemplified by cellulosic fibers including natural fibers such as pulp and cotton and semisynthetic fibers such as rayon. These fibers can be used either individually or as a combination of two or more thereof. Fibrillated fibers obtained by beating to an increased degree are also usable. Useful pulps include bleached wood pulps such as Nadelholz (needle-leaf) bleached kraft pulp (NBKP) and Laubholz (broad-leaf) bleached kraft pulp (LBKP); other pulps such as hemp pulp; mercerized pulp (alkali-swollen pulp); chemically crosslinked pulp having a helical structure; and microfibrous cellulose. Synthetic fibers having no biodegradability including polyolefin fibers such as polyethylene and polypropylene and polyester fibers are also employable. Biodegradable synthetic fibers such as polylactic acid fiber are preferably used. It is preferred for the fibrous sheet to contain cellulosic fiber in a proportion of 70% to 100%, more preferably 80% to 100%, based on the total fiber weight.
The water soluble binder includes natural polysaccharides, polysaccharide derivatives, and synthetic polymers. Examples of the natural polysaccharides include sodium alginate, gum tragacanth, guar gum, xanthan gum, gum arabic, carrageenan, galactomannan, gelatin, casein, albumin, and pullulan. Examples of the polysaccharide derivatives include carboxymethyl cellulose, carboxyethyl cellulose, carboxymethylated starch and its salts, starch, methyl cellulose, and ethyl cellulose. Examples of the synthetic polymers include polyvinyl alcohol, polyvinyl alcohol derivatives, unsaturated carboxylic acid polymer or copolymer salts, and salts of copolymers of an unsaturated carboxylic acid and a monomer copolymerizable with the unsaturated carboxylic acid. The unsaturated carboxylic acids include acrylic acid, methacrylic acid, itaconic acid, crotonic acid, maleic anhydride, maleic acid, and fumaric acid. The amount of the water soluble binder to be used is subject to variation depending on the use of the final product and the kind of the binder. From the viewpoint of bulk retention, wet strength, water disintegratability, and economy, a preferred amount of the water soluble binder usually ranges from 1% to 30%, more preferably 2% to 15%, by weight based on the weight of the fibrous sheet. It is preferred that the water soluble binder be temporarily insolubilized in the presence of the aqueous agent having a high water content to function as a binder maintaining the fiber-to-fiber bonds thereby serving for retaining the bulk and strength during cleaning. The water content in the aqueous agent is preferably in a range of from 30% to 95%, more preferably 50% to 95%, even more preferably 60% to 95%, by weight, to secure ability of removing dried urine stains and to minimize possible irritation to the skin.
The above-mentioned temporary insolubilization of the water soluble binder is achieved by a sufficient amount of the aqueous agent impregnating the water-disintegratable paper and the presence of a binder-insolubilizing component in the water-disintegratable paper or the aqueous agent. While the amount of the aqueous agent to be infiltrated into water-disintegratable paper cannot be specified quantitatively as it depends on the kind, the molecular weight and the content of the binder in the water-disintegratable paper, it is preferably such that the most of the binder cannot dissolve. The binder insolubilizing component includes water soluble organic solvents and specific acids or electrolytes.
The water soluble organic solvents include monohydric alcohols, such as methanol, ethanol, and isopropyl alcohol; glycols, such as ethylene glycol, diethylene glycol, polyethylene glycol, propylene glycol, dipropylene glycol, butylene glycol, hexylene glycol, and 3-methyl-1,3-butanediol; mono- or diethers between these glycols and lower alcohols, e.g., methanol, ethanol, propanol, and butanol; esters between the glycols and lower fatty acids; and polyhydric alcohols, such as glycerol and sorbitol. The water soluble organic solvents can be used either individually or as a combination of two or more thereof. The concentration of the water soluble organic solvent in the aqueous agent is preferably 30% to 70% by weight, more preferably 30% to 60% by weight, even more preferably 30% to 50% by weight. Where used in combination with an acid or an electrolyte described below, the water soluble organic solvent is preferably used in a concentration of 1% to 50% by weight, more preferably 5% to 40% by weight, even more preferably 10% to 30% by weight.
The acid and the electrolyte that can be used as a binder insolubilizing component typically include those capable of temporarily insolubilizing water soluble binders through salting-out or crosslinking. Various salts can be used for salting-out as far as they are water soluble. Salts for crosslinking should be selected according to the kind of the binder. In using, for example, carrageenan or guar gum as a water soluble binder, a water soluble salt that releases a potassium ion in an aqueous agent and crosslinks with the binder to gelatinize the binder is chosen. In using a carboxylic acid-based binder, a water soluble salt that releases a divalent metal ion in an aqueous agent and crosslinks with the carboxylic acid-based binder in the presence of a small amount of a water soluble solvent is chosen. In using polyvinyl alcohol as a water soluble binder, boric acid or a borate such as sodium tetraborate that crosslinks with the binder to gelatinize the binder is chosen. While the concentration of the acid or electrolyte in the aqueous agent cannot be specified because it is subject to variation depending on the kind and the content of the binder in the water-disintegratable paper, it preferably ranges from 1% to 10% by weight, more preferably 1% to 5% by weight, taking the cleaning finish and irritation to the skin into consideration.
The aqueous agent is a composition containing the aforesaid binder insolubilizing component dissolved in a water medium. According to necessity, the aqueous agent may further contain various compounding ingredients, such as surfactants, sterilizers, chelating agents, bleaches, deodorants, and perfumes, to enhance the cleaning ability of the aqueous agent. The surfactants include anionic ones, nonionic ones, cationic ones, and amphoteric ones. To secure both cleaning action and finish, it is recommended to use nonionic ones such as polyoxyalkylene (number of moles of alkylene oxide added: 1 to 20) alkyl (straight-chain or branched, containing 8 to 22 carbon atoms) ethers, alkyl (straight-chain or branched, containing 8 to 22 carbon atoms) glycosides (average sugar condensation degree: 1 to 5), sorbitan fatty acid (straight-chain or branched; containing 8 to 22 carbon atoms) esters, and alkyl (straight-chain or branched, containing 6 to 22 carbon atoms) glyceryl ethers; or amphoteric ones, such as alkylcarboxybetaines, alkylsulfobetaines, alkylhydroxysulfobetaines, alkylamidocarboxybetaines, alkylamidosulfobetaines, and alkylamidohydroxysulfobetains, each having 8 to 24 carbon atoms in the alkyl moiety thereof.
The aqueous agent is infiltrated into the water-disintegratable paper in an amount of 100% to 500% by weight, preferably 100% to 300% by weight, based on the dry weight of the water-disintegratable paper.
The water swellable binder includes a fibrous carboxyl-containing cellulose derivative, a fibrous starch derivative, a fibrous hydroxyl-containing polyvinyl alcohol or a fibrous hydroxyl-containing polyvinyl alcohol derivative. More specifically, the water swellable binder includes fibrous polyvinyl alcohol, fibrous carboxymethyl cellulose, and fibrous carboxyethyl cellulose. Such a water swellable binder is usually mixed into a stock of pulp fiber, etc. for making a fibrous sheet. The content of the water swellable binder in the fibrous sheet is preferably 5% to 40% by weight, more preferably 8% to 30% by weight, even more preferably 10% to 25% by weight, in view of bulk retention, wet strength, water disintegratability, and economy. Similarly to the water soluble binders, it is preferred that the water swellable binder be temporarily suppressed from swelling in the presence of the aqueous agent having a high water content to function as a binder maintaining the fiber-to-fiber bonds thereby serving for retaining the bulk and strength during cleaning. Such temporary suppression of swell of the binder is achieved by the presence of a swell suppressing component. Swell suppressing components for fibrous polyvinyl alcohol include boric acid and boric acid salts, e.g., sodium tetraborate, and those for fibrous carboxyethyl cellulose include water soluble salts releasing divalent metal ions, such as a magnesium ion, a calcium ion, and a zinc ion.
There are various useful combinations of a water soluble or swellable binder and an insolubilizing component or a swelling suppressing component. Inter alia, a combination of a carboxylic acid-based water soluble binder and an aqueous agent containing a divalent metal ion and a water soluble organic solvent is suitable.
Of the carboxylic acid-based water soluble binders particularly preferred is an alkali metal salt of carboxymethyl cellulose (hereinafter abbreviated as CMC). CMC preferably has a degree of etherification of 0.8 to 1.2, more preferably 0.85 to 1.1, to exhibit satisfactory binding performance and good affinity to a crosslinking agent hereinafter described. Considering handling properties in applying the binder to paper by spraying or like means, CMC preferably has a viscosity of 10 to 40 mPa·s, more preferably 15 to 35 mPa·s, in a 1% by weight aqueous solution at 25° C., of 2500 to 4000 mPa·s, more preferably 2700 to 3800 mPa·s, in a 5% by weight aqueous solution at 25° C., and of 1200 mPa·s or lower in a 5% by weight aqueous solution at 60° C.
The aqueous agent that is preferably combined with water-disintegratable paper containing a carboxylic acid-based water soluble binder is a composition containing 60% to 90% by weight of water, 8% to 35% by weight of a water soluble organic solvent, and 1% to 5% by weight of a water soluble divalent metal salt releasing at least one metal ion selected from the group consisting of alkaline-earth metals, e.g., calcium, magnesium, strontium, and barium, manganese, zinc, cobalt, and nickel. That formulation of the aqueous agent is preferred because of its ability to temporarily insolubilize the binder to develop sufficient wet strength and in view of its good water disintegratability. The water soluble divalent metal salt includes hydroxides, chlorides, sulfates, carbonates, formates, and acetates. Calcium chloride and zinc sulfate are particularly preferred of them.
The aqueous agent-impregnated water-disintegratable paper, namely the water-disintegratable cleaning article 1 preferably has a wet strength of 300 cN/25 mm or more in the machine direction (MD) and of 100 cN/25 mm or more in the cross direction (CD) from the standpoint of strength required for wiping. The MD wet strength is more preferably 400 cN/25 mm or more, even more preferably 500 cN/25 mm or more. The CD wet strength is more preferably 150 cN/25 mm or more, even more preferably 200 cN/25 mm or more.
Returning to
The embossing pattern is not limited as long as the fibrous sheet becomes bulky by embossing. Embossing using matched steel embossing rolls is suitable to give high bulk, in which two engraved rolls having elevations and recesses aligned in a regular pattern on their surface are fully engaged with each other along the nip line. The elevations and recesses (see
The average number of the protrusions 2 formed on one side of the cleaning article 1 and the water-disintegratable paper is preferably 50 to 850, more preferably 100 to 600, per 10 cm square at any site on that side. With the density of the protrusions 2 falling within that range, the cleaning article 1 and the water-disintegratable paper have protrusions 2 and depressions 3 arranged in good balance and therefore exhibit still superior performance in removing dirt.
As will be understood from preferred processes of producing water-disintegratable paper described infra, the shape and arrangement of the protrusions 2 and the depressions 3 can be freely designed by designing the engraving pattern on an engraved roll used in the production.
Preferred processes of producing water-disintegratable paper serving as a base material of the cleaning article 1 will then be described. The water-disintegratable paper is produced by the step of embossing a substantially water dispersible fibrous sheet containing a water soluble or swellable binder and having a basis weight of 30 to 150 g/m2 while the fibrous sheet has a water content of 10% to 200% by weight and the step of drying the fibrous sheet either simultaneously with or immediately after the embossing. The water-disintegratable paper is also produced by the step of adding an aqueous solution of a water soluble binder to a sheet containing a substantially water dispersible fiber and containing no binder to provide a fibrous sheet having a water soluble binder content of 1% to 30% by weight and a water content of 10% to 200% by weight based on the dry weight of the sheet and the step of embossing and drying the resulting fibrous sheet simultaneously.
The water soluble binder-containing, water dispersible fibrous sheet can be prepared in various methods. For example, it is known that water-disintegratable paper containing a predetermined amount of a water soluble binder is obtained from a pulp dispersion, namely, a pulp stock containing a water soluble binder and a fixative for fixing the water soluble binder to the pulp fiber (see JP-A-3-193996). It is possible to prepare water-disintegratable paper containing a predetermined amount of a water soluble binder by forming a sheet from a pulp stock, press dewatering or half drying the sheet, and applying the water soluble binder with a spray or like means, followed by drying. A pre-drying system using a hot air blow-through dryer is preferred to press dewatering to give low-density paper having higher water disintegratability. It is also possible to produce a fibrous sheet by dispersing and laying pulp fibers in a dry process (without using water) to form a web, applying a water soluble binder with a spray or like means, and drying (i.e., air laying process).
Water of the finished stock fed from the former 4 is drained through the wire 5 to form a wet fiber web on the wire 5, which is dewatered to reduce its water content to a predetermined level by means of suction boxes 6 placed under the wire 5. The wet web is introduced into the first dryer part 7 and dried. The first dryer part 7 has a through-air dryer (hereinafter abbreviated as TAD), which has a perforated rotary drum 8 and a hood 9 covering the drum 8 almost hermetically. Hot air at a prescribed temperature is fed into the hood 9 and enters into the inside of the rotating drum 8. The wet web is wrapped around the drum 8 rotating in the direction indicated by the arrow in
The paper obtained in the first dryer part 7 is sprayed with an aqueous solution of a water soluble binder in the spray part. The spray part is located between the first dryer part 7 and the second dryer part 14, which are linked via a conveyor.
The conveyor has an upper conveyor belt 10 and a lower conveyor belt 11 running in the respective directions indicated by the arrows. The conveyor is configured to held the paper dried in the TAD of the first dryer part 7 between the lower run of the upper conveyor belt 10 and the upper run of the lower conveyor belt 11 and carry the paper to the second dryer part 14. At the downstream end of the upper conveyor belt 10 is provided a vacuum roll 12, which is configured to suck the paper to the surface of the upper conveyor belt 10 and carry the paper on the upper run of the upper conveyor belt 10.
As shown in
After addition of the binder, the wet paper form the spray part is transferred to the second dryer part 14 having a yankee dryer. The yankee dryer has a rotary drum and a hood 16 covering the drum 15. The wet paper is wrapped around the rotating drum 15 and dried while rotating.
At the outlet of the yankee dryer is provided a doctor blade 17, which is configured to scrape the paper off the rotating drum 15 while creping the paper. The paper coming off the second dryer part 14 of the paper machine is wound into roll in a winder (not shown).
The water swellable binder-containing, water dispersible fibrous sheet can be prepared in various methods. For example, it is known that a fibrous sheet is obtained by forming a sheet from a pulp stock containing a prescribed amount of a water swellable fibrous binder and drying the resulting wet web (see JP-A-4-370300 and JP-A-2-74694). Such a fibrous sheet can also be produced by a dry papermaking process, in which a mixture of pulp fiber and a water swellable fibrous binder is air laid to form a web, which is then dried.
It is also possible to produce a water dispersible, fibrous sheet containing both a water soluble binder and a water swellable binder by combining the above-described techniques. The water dispersible fibrous sheet containing a water soluble binder and/or a water swellable binder will hereinafter be referred to as base paper.
The base paper, either as obtained or after once stored in roll form, is given water again, embossed to gain bulk in the presence of the water content, and dried simultaneously with or immediately after the embossing to become bulky water-disintegratable paper with a great number of protrusions and depressions. These processing steps can be carried out on, for example, a heat embossing apparatus shown in
As illustrated in
If the base paper is shaped between the nip of the embossing rolls 18 in its dry state as commonly practiced, the base paper undergoes large deformation in its thickness direction while maintaining the interfiber hydrogen bonds. It will follow that the interfiber bonds are destroyed or the fibers per se break as depicted in
In order to carry out the embossing successfully, it is necessary to spray water to the base paper to be introduced into the nip between the embossing rolls 18 to give the base paper a water content of 10% to 200% by weight based on the dry weight of the base paper. The water content of the base paper to be embossed is preferably 10% to 130% by weight, more preferably 10% to 50% by weight, even more preferably 10% to 40% by weight. The base paper usually has an original water content of about 5% to 10% by weight. A water content (the original water content plus water sprayed) smaller than 10% by weight is too small to weaken the fiber-to-fiber hydrogen bonds and to swell or dissolve the binder sufficiently, resulting in a failure to induce re-arrangement of the fibers along the embossing pattern. A water content larger than 200% by weight demands wasteful burden of drying. The embossing rolls 18 are preferably heated to 150° to 250° C. to thoroughly dry the base paper. The degree of drying of the base paper often depends on the moving speed of the base paper. As the moving speed increases, it is more likely that only the heat of the embossing rolls is insufficient to dry the base sheet thoroughly. For such a case, the contact time of the base paper with a heat embossing roll 18 can be increased by increasing the diameter of the heat embossing roll about which the embossed sheet is wrapped as shown in
Another preferred process of producing water-disintegratable paper serving as a base material of the cleaning article 1 includes the steps of providing a sheet containing a substantially water dispersible fiber and containing no water soluble binder by a wet papermaking method or an air laying method, adding an aqueous solution of a water soluble binder with a spray or like means in the line of the wet papermaking method or air laying method to provide a damp fibrous sheet containing a water soluble binder and having a specific water content, embossing the resulting damp fibrous sheet, and drying the fibrous sheet simultaneously with or immediately after the embossing. According to the system shown in
Water disintegratable paper can also be produced by processing the sheet containing no water soluble binder by use of the heat embossing apparatus shown in
It is preferred that the water-disintegratable paper satisfy the following thickness relationship between Td and Tw. Thickness Td is the thickness of the water-disintegratable paper in its dry state immediately after being embossed measured under a load of 0.3 kPa. The thickness Tw is the thickness of the water-disintegratable paper in the state impregnated with an aqueous agent (i.e., the bulky, water-disintegratable cleaning article) measured under a load of 2.2 kPa. In the manufacture of a water-disintegratable cleaning article, the embossed paper is usually subjected to various processings such as folding, cutting, impregnation, and stacking. The external forces that would be imposed to the embossed paper during these post-embossing processings is estimated at about 2.2 kPa, under which load the Tw measurement is taken. The thickness ratio Tw/Td is a measure of shape retention, i.e., bulk retention. The closer Tw/Td to 1, the higher the shape retention. When the production process of the present invention is followed, the thickness ratio Td/Tw reaches preferably 0.7 or greater, more preferably 0.75 or greater, even more preferably 0.8 or greater. A Tw/Td smaller than 0.7 means that the water-disintegratable paper (i.e., embossed dry paper) has low embossed shape retention against post-embossing processings, showing no noticeable difference from those obtained by conventional embossing techniques.
The Tw value is not significantly affected by the amount of the impregnating aqueous agent within the impregnation ratio of 100 to 500% by weight so that the aqueous agent content is not included in the conditions of measuring Tw. If the amount of the aqueous agent is to be included in the measuring conditions, double the dry weight of the water-disintegratable paper, which is typical in the present invention, would be a suitable condition.
As described above, embossing a fibrous sheet in the presence of a specific water content simultaneously with, or followed by, drying results in formation of a large number of protrusions and depressions without developing a tear nor reducing the strength of the fibrous sheet. By properly choosing embossing rolls, sufficiently high bulk can be attained. The embossed fibrous sheet (i.e., the water-disintegratable paper) exhibits high retention of its three-dimensional profile.
The water-disintegratable cleaning article 1, which is the water-disintegratable paper impregnated with an aqueous agent, does not disintegrate as it is but, when flushed, it disintegrates quickly into fibers. Water disintegratability of a water-disintegratable cleaning article is measured in terms of time required for disintegration specified in JIS P4501-1993 (toilet paper). The shorter the time, the higher the water disintegratability. The time is preferably 100 seconds or shorter, more preferably 60 seconds or shorter.
The cleaning article 1, which is the water-disintegratable paper impregnated with an aqueous agent, is suitable to applications including housekeeping, such as cleaning bathrooms and kitchens; and skin care such as baby wipe, body wipe for nursing and make-up removal. After use, the cleaning article can be flushed for disposal because it disintegrates rapidly in flush water and does not clog pipes.
The present invention is not limited to the above-described embodiments. For instance, the water-disintegratable paper is not limited to a single-layer structure and may be a multi-ply structure. In the latter case, it is preferred that the water soluble or swellable binder be present in at least one of the outermost plies.
The present invention will now be illustrated in greater detail with reference to Examples, but it should be understood that the invention is not deemed to be limited thereto. Unless otherwise noted, all the percents and parts are given by weight.
The apparatus shown in
The base sheet was unrolled and sprayed with a varied amount of water through the spray nozzle 19 shown in
The thickness Td of the water-disintegratable paper (in a dry state) under a load of 0.3 kPa was measured. The water-disintegratable paper was impregnated with twice the dry weight of an aqueous agent A described below. The water-disintegratable paper impregnated with the aqueous agent A was measured for thickness Tw under a load of 2.2 kPa and wet strength. Separately, the resulting water-disintegratable paper was folded, cut, impregnated with the aqueous agent A, and packaged into a commodity on a processing machine possessed by the applicant company under the same conditions as ordinarily used. The resulting, commodity-processed water-disintegratable cleaning article was measured for thickness T1 under a load of 0.3 kPa and thickness T2 under a load of 1.0 kPa.
A three-ply base paper having a structure of CMC-containing paper/CMC-free paper/CMC-containing paper and having a basis weight of 90 g/m2 was prepared in the same manner as in Example 1. Without being sprayed with water, the base paper was embossed between a pair of the embossing rolls 18 that were not heated. The embossed paper was impregnated with the aqueous agent A in the same manner as in Example 1 to obtain a water-disintegratable cleaning article.
A wet fiber web was formed on a wet paper machine using a stock containing NBKP and fibrous PVA (Kuraron KII, available from Kuraray Co., Ltd.) at a weight ratio of 90:10 and dried on a yankee dryer to make a sheet having a basis weight of 33 g/m2. Two plies of the sheet were stacked to prepare a fibrous sheet as base paper. The base paper was processed in the same manner as in Examples 1-8, except for using an aqueous agent B having the following composition, to obtain a water-disintegratable cleaning article.
A water-disintegratable cleaning article was obtained in the same manner as in Examples 9 and 10, except that water was not applied to the base paper to be embossed and that the embossing rolls 18 were not heated.
Evaluation of Performance:
Thickness Td (under 0.3 kPa load) of the water-disintegratable paper obtained in Examples and Comparative Examples, and thickness Tw (under 2.2 kPa load) of the aqueous agent-impregnated water-disintegratable paper obtained in Examples and Comparative Examples were measured. Further, a thickness ratio Tw/Td was calculated based on the respective values of Td and Tw. Thicknesses T1 (under 0.3 kPa load) and T2 (under 1.0 kPa load) of the post-treated water-disintegratable cleaning articles obtained in Examples and Comparative Examples were measured to calculate a thickness ratio, T2/T1. Furthermore, the wet strength (breaking strength) and water disintegratability of the water-disintegratable cleaning articles were determined according to the following methods. The results obtained are shown in Table 1.
1) Wet Strength (Breaking Strength)
A specimen measuring 100 mm in the MD and 25 mm in the CD was cut out of a sample cleaning article and set on a tensile tester (Tensilon RTA-100, supplied by Orientec Co., Ltd.) at a chuck distance of 50 mm. The specimen was pulled at a rate of 300 mm/min. The strength at break is an MD wet strength. A CD wet strength was measured in the same manner, except that the specimen measured 100 mm in the CD and 25 mm in the MD.
2) Water Disintegratability
Water disintegratability of the water-disintegratable cleaning article was measured in accordance with the method specified in JIS P4501 using a square specimen the size of which was such that the paper per se (exclusive of the aqueous agent) weighed 0.3 g.
As is apparent from the results shown in Table 1, the bulky, water-disintegratable cleaning articles of the present invention even after commodity-processed into a finished item keep their thickness T2 (under 1.0 kPa) above 0.9 mm at a high ratio to the thickness T1 (under 0.3 kPa), which means excellent embossed shape retention, and also retain the strength. In contrast, the comparative articles undergo considerable thickness reduction when commodity-processed. The comparative articles have low strength. It is seen from the results of Examples that embossing in the presence of a higher water content (as a result of a metered water spray) results in improved embossed shape retention (represented by the thickness ratio after commodity-processing into a finished product, T2/T1) and improved wet strength.
While not shown in Table 1, each of the bulky, water-disintegratable cleaning articles of Examples was thicker and stronger and fitted in user's hand more comfortably while being used to wipe toilets, etc. clean. as compared with the comparative cleaning articles. The cleaning articles of Examples were capable of scrubbing off dirt and stains easily due to their wet strength. The thickness of the cleaning articles gives a user a sense of security (a sense of distance between the hand and the dirt). Since the sheet thickness is maintained during a wiping operation, a wider area could be wiped clean with a single sheet. From all these considerations, the bulky, water-disintegratable cleaning articles of Examples are proved to be more convenient to use than the comparative ones.
Additionally, the water-disintegratable papers of Examples have a thickness ratio Tw/Td of 0.7 or greater, which indicates shape retention under load, and exhibit higher dry and wet strengths than the comparative ones.
As described above, the bulky, water-disintegratable cleaning article according to the present invention has high bulkiness and, in spite of its wetness, satisfactorily retains the bulk and hardly tears against physical loads such as compression and tension. The embossed shape is retained even after post-embossing steps including cutting, folding, impregnation with a cleaning agent, stacking, and packaging.
The production process according to the present invention provides highly bulky, water-disintegratable paper. Even in a state wetted with an aqueous agent, the water-disintegratable paper produced by the process of the invention retains the embossed shape and hardly tears under physical loads such as compression.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2004-241481 | Aug 2004 | JP | national |
| 2004-342876 | Nov 2004 | JP | national |
| 2004-342961 | Nov 2004 | JP | national |
