FR2715051A1 - Paper towel material - Google Patents

Abstract

The paper material is dried laterally without creping, and has a dry thickness independent of the paper weight of 0.4 mm or more, a fluid absorption of 500% or more and a stretch of 10% or more along the machine line.

Description

 In the manufacture of many paper products, such as towels, wiping cloths and the like, attention must be paid to a wide variety of product characteristics to obtain a final product with the appropriate combination of suitable attributes. the goals of the product. Among these various attributes, resistance, absorbability, thickness and improved extensibility have always been major objectives, in particular for products sold and used in the service and industrial sectors.

Traditionally, many of these paper products have been made using a wet pressing process in which a significant amount of water is removed from a wet spread sheet by pressing or clamping the sheet to expel water before drying final. In particular, while it is supported on an absorbent paper felt, the web is clamped between the felt and the surface of a heated rotary cylinder (friction dryer) using a pressure roller while the web is transferred to the surface. of the friction dryer. The sheet is then separated from the friction dryer using a doctor blade (creping) which is used to partially untie the sheet by breaking many of the bonds previously formed during the wet pressing steps of the process. The tablecloth can be creped dry or wet. Creping generally improves the flexibility of the web, but at the expense of a significant loss of strength.

 More recently, cross-blowing drying has become a more common means of drying paper webs. Cross blowing drying provides a relatively non-compressive process of removing water from the web by passing hot air through the web until it is dry. More specifically, a wet spread sheet is transferred from the forming fabric to a fabric for coarse and highly permeable blowing drying, and the web is retained on the fabric for transverse blowing drying until it is dried. The resulting dried web is softer and thicker than an uncrimped, traditionally dried sheet, because fewer bonds are formed and the web is less compressed. The dewatering of water from the wet sheet is eliminated although the use of a pressure roller to subsequently transfer the sheet to a friction dryer can still be used for creping purposes.

 Although this is an incentive to remove the Yankee dryer and make a non-creped cross-blown dried product, the non-creped cross-blown dried leaves are usually stiff and, if not calendered, they are rough to the touch compared to their crepe counterparts. This is partly due to the inherent high stiffness and resistance of the non-crepe sheets, but also partly to the coarseness of the fabric for drying by transverse blowing on which the wet sheet is shaped and dried. As a result, the use of non-creped cross-blown sheets has been limited to applications where the important thing is that the sheet has high strength. These products have moderate absorption properties.

 There is therefore a need for a non-creped, cross-blown paper product offering an improved combination of properties to allow its use as a wiping cloth or paper towel.

 It has now been discovered that, for some non-creped cross-blown base sheets, particularly non-creped cross-blown base sheets of relatively low base weight, the size of the base sheet is surprisingly , substantially independent of the base weight of the sheet. (As used herein, the term base sheet refers to the dry sheet exiting the paper machine, prior to any post-processing, such as calendering, embossing or the like.) By producing towels or multi-jet cloths from jets of blown-dried base sheets, uncrimped, individual, relatively light, rather than making the products from a single uncrimped sheet of high base weight, for example, improved properties can be obtained in relation to the quantity of fibers used, in particular with regard to the absorption capacity and the size for a given level of resistance. As a result, it is possible to produce multi-jet towels and rags having a higher gauge in the wet and dry state than the current commercial products, while possessing a combination of properties which correspond or exceed those of the best products to multiple jets creped, and surpass those of previous products dried by cross-blowing, not creped.

It has also been discovered that the aqueous absorption capacity of certain non-creped cross-blown base sheets is also independent of the sheet size imparted by dry aftertreatments, such as creping, embossing or calendering. . Unlike conventional tablecloths of wet and crimped pressed paper, which flatten when exposed to water, the uncrimped sheets, according to certain embodiments of the invention, increase substantially in thickness when '' they are exposed to water, so that the ratio of Wet Caliber to
Dry Caliber (as defined below) is approximately 1.5 or more. For product uses in which it is important to be able to wipe away water or spilled aqueous liquids, it is preferred that the fiber-making composition used to make the sheet contain a resin promoting wet strength because a such resin increases the wet "memory" of the sheet to allow the sheet, when wet, to return to the state it was in before the dry post-treatment. However, the presence of a resin promoting wet strength is not necessary for products which are only used to wipe off oil or other non-polar liquids, such as certain industrial rags.

Therefore, in one aspect, the invention relates to a method of manufacturing a non-creped cross-blown sheet, comprising: (a) depositing an aqueous suspension of paper fibers on a porous forming fabric which retains fibers and allows water to pass through to form a wet sheet; (b) dewatering the web to a consistency ranging from about 10 to about 30 W; (c) the transfer of the dehydrated sheet to a fabric for drying by transverse blowing having a three-dimensional surface contour such that the dimension in the z direction, or depth of the surface contour, is substantially greater than the thickness of the wet sheet, and the conformation of the wet web to the surface contour of the fabric for drying by transverse blowing using a positive and / or negative pressure and (d) the drying by transverse blowing of the web, the
Dry gauge of the dried web being substantially independent of the base weight of the web.

According to another aspect, the invention provides a base sheet dried by cross-blowing, not creped, having a Dry Size which is independent of the base weight of the base sheet, said base sheet having a Size
Dry about 0.4 mm or more, Absorption Capacity
Aqueous of approximately 500 Oo or more and an extensibility in the machine direction of approximately 10 W or more.

 In another aspect, the non-creped blown-dry jet has a basis weight of between about 10 and about 30 or 50 g / m2, a tensile strength in the machine direction of about 1000 g or more , and a Dry Caliber and / or a Wet Caliber in the uncalendered state of approximately 0.4 mm or more.

 These and other aspects of the invention will be described later in more detail.

 The cellulosic fibers suitable for the implementation of the present invention include secondary (recycled) paper fibers and virgin paper fibers, in all proportions. Such fibers include, without limitation, hardwood and resinous wood fibers, as well as non-wood fibers. Part of the manufacturing composition may also contain non-cellulosic synthetic fibers. It has been found that a high quality product with a unique balance of properties can be made using only, or predominantly, secondary fibers.

 The finished basis weight of the individual cross-blown sheets or jets according to the invention may preferably be between about 10 and about 30 g / m2, more particularly between about 15 and about 25 g / m2 and better be '' about 20 g / m2. These cross-dried sheets can be joined together to form a multi-jet product having two, three, four or more jets. These multi-jet products unexpectedly have a high caliber and absorption characteristics in relation to the quantity of fibers involved. The basic weight of the multi-jet products depends on the number of jets according to the invention and on the basic weight of each jet.

Suitable training methods include the flat table method and other conventional training methods well known in the paper industry. Double cloth formers are particularly suitable for the relatively low base weights encountered in the case of towels and rags according to the invention. The forming fabrics may also be conventional, with fine weavings which provide greater support for the fibers being preferred for producing a smoother sheet or web. Suitable training fabrics include those made by Asten Forming Fabrics Inc., Appleton,
Wisconsin (USA) and which are designated by 856A or 866A.

Also suitable for stainless steel or monofilament fabrics with 100 mesh opening.

 The drying process can be any non-compressive drying process which tends to increase the caliber or thickness of the wet web, including, but not limited to, drying by transverse blowing, infrared radiation , microwave drying, etc. Due to its commercial availability and convenience, cross-blowing drying is a well-known and preferred means for performing non-compressive drying of a web.

The transverse blowing drying process can be conventional, as is well known in the paper industry. Suitable methods of transverse blowing drying are described in US-A-5,048,589 in the name of Cook et al. (1991) entitled "Non-Creped Hand or Wiper Towel" and
US-A-4,440,597 to Wells et al. (1984) entitled "Wetmicrocontracted Paper and Concomitant Process".

A high degree of sheet extensibility is desirable, such as - in the machine direction - from about 10% or more, preferably from about 15 to about 30%, and conveniently from about 20%, and it can be obtained by using differential speed transfers between the forming fabric and the fabric for cross-blowing drying, as described in the aforementioned Wells patent, or between any other fabrics used at the wet end of the process. The use of one or more transfer fabrics between the forming fabric and the fabric for drying by transverse blowing, as described in the co-pending American patent application No. 08/036 649 entitled "Method For Making Smooth
Uncreped Throughdried Sheets "filed March 24, 1993 on behalf of Steven A. Engel et al. Can also be used to provide increased extensibility and to produce a smoother sheet. It is preferred that the degree of extensibility be between about 5 and about 40%, and better between about 15 and about 30% in the dried non-crepe leaf.

The fabrics suitable for drying by transverse blowing include, without being limiting, the products Asten 920A and 937A and the products Velostar P800 and 103A also manufactured by Asten. These fabrics offer sufficient three-dimensionality to provide a size independent of the base weight of the tablecloth. The three-dimensionality of the fabrics can be quantified by the distance in the z direction between the warp joints and the weft joints of the canvas. In the aforementioned fabrics, this distance ranges from approximately 0.17 mm to approximately 0.38 mm. It is believed that multi-layered fabrics can have an even greater three-dimensionality. By way of example, if a fabric for cross-blowing drying Asten Velostar P800 according to the present invention is used, and manufactures sheets which are dried by cross-blowing, non-crepe, having base weights of approximately 14, 18, 21, 27, 30 and 32 g / m2, it is found that they have substantially the same dry size of approximately 0.5 mm as determined by a different but similar method of measuring the size.

 The junction between jets of the different jets dried by transverse blowing, not creped, according to the invention, can be carried out by any means of jetting assembly as is well known in the paper industry. Crimping is one of the preferred means of joining jets. The multi-jet products, described below in the examples, are joined together with the smoother side of the exterior jets facing outward. The smoother side of the jet is the side which is not in contact with the fabric for drying by transverse blowing during drying, a side often called "air side" of the sheet. The side of the sheet which is in contact with the fabric for blowing drying during drying is often called the "dryer side" of the sheet. It is believed that multi-jet products having an even greater size can be obtained by joining the air sides of neighboring jets together.

 The jets according to the invention may individually have a tensile strength in the machine direction of approximately 1000 g or more, preferably approximately 2000 g or more, depending on the shape of the product.

 The Aqueous Absorption Capacity of the products formed from the jets according to the invention is at least about 500% by weight, preferably about 800% by weight or more, and better still about 1000% or more. This concept refers to the ability of a product to absorb water over a period of time and is related to the total amount of water retained by the product at its saturation point. The specific procedure used to measure "Aqueous Absorption Capacity" is described in US Federal Standard No. UU-T-595C and is expressed, as a percentage, as the weight of absorbed water divided by the weight of the sample. Advantageously, the Aqueous Absorption Capacity is independent of the Dry Caliber of the product.

The products formed from the jets according to the invention can also have an aqueous absorption speed of about one second or less. The "Speed of Absorption
"Aqueous" is the time required for a drop of water to penetrate the surface of a towel or cloth according to the US federal standard UU-P-3lb.

 The Oil Absorption Capacity of the products formed from the jets according to the invention can be approximately 300% by weight or more, preferably approximately 400% or more, and conveniently approximately 400 to approximately 550 % in weight. The "Oil Absorption Capacity" is measured according to the procedure described in the US federal standard UUT 595B.

 The products formed from the jets according to the invention offer an Oil Absorption Speed of approximately 20 seconds or less, preferably of approximately 10 seconds or less, and better still of approximately 5 seconds or less. The Oil Absorption Speed is measured according to the US federal standard UU-P-3lb.

The Dry Size of the individual base sheets or uncalendered jets is about 0.4 mm or more, preferably about 0.6 mm or more, and conveniently about 0.4 to about 0.8 mm . Dry Caliber is the thickness of a product or a dry jet measured under a controlled load. The dry caliber determination method uses a Starrett graduated gauge (model 2320 available from Mitutoyo
Corporation, Landic Mita Building, 31-19 Shiba, 5-Chome,
Minato-Ku, Tokyo 108, Japan) and a plastic block (LUCITER) measuring 100 mm x 100 mm. The center of the LUCITE block is marked to allow the tip of the gauge to be centered on the block. The thickness of the block is such that the total force exerted on the sample by the weight of the block and the gauge spring is 225 g. A sample of material to be measured is cut to a size of 100 mm x 100 mm.

The sample must have no wrinkles, ripples, or creases. The sample is placed under the block of LUCITE and the block and the sample are placed under the tip of the gauge with the tip of the gauge centered on the block. The tip of the gauge is gently released and the Dry Caliber is read to the nearest 0.01 mm after 15 to 20 seconds. The procedure is repeated on four additional representative samples and the results of the 5 samples are averaged.

The Wet Caliber of the individual jets can be about 0.4 mm or more, preferably about 0.6 mm or more and conveniently from about 0.4 to about 0.8 mm. The
Wet Caliber is measured similar to the method described above for Dry Caliber, except that the sample is immersed in a water bath until it is completely saturated. The sample is removed from the water by carefully holding it by two of its neighboring angles and removing excess water by letting the sample drag against the edge of the container of the water bath while it is being removed of said bath. The sample is lowered on the underside of the LUCITE block from an edge (not at an angle) to avoid the formation of bubbles, folds or ripples. We then measure the Caliber
Wet as shown above for Dry Caliber.

 These and other aspects of the invention will be described in more detail in the following examples.

EXAMPLE 1
An aqueous suspension formed from 100 W of secondary paper fibers containing approximately 0.2 W by weight of fibers was prepared. The fiber suspension was supplied to a double canvas arrival box (head box) and placed on a training canvas. The formation fabric was an Asten 866 fabric with a void volume of 64.5 W. The speed of the formation fabric was 681 m (2234 feet) per minute. The newly formed web is stripped of its water to a consistency of about 20 W by weight using a suction box located below the forming fabric before being transferred to a transfer fabric which moves at a speed of 567.5 m (1862 feet) per minute (20 W speed difference). The transfer fabric was an Asten 937 fabric with a void volume of 61.6 Oo.

The fabrics were positioned so that the forming fabric was in close proximity to the transfer fabric. The transfer shoe was disposed behind the transfer fabric and it moved into the formation fabric, so as to move the transfer fabric but not the formation fabric. In the papermaking art, this positioning is called tangential contact or touch of contact between the fabrics. The vacuum shoe drew a 127 mm (5 inch) vacuum of mercury to effect the transfer without compacting the web. The web was then transferred to the fabric for cross-blowing drying Asten Velostar 800 moving at a speed of 567.5 m (1862 feet) per minute. The tablecloth was transported on a Honeycomb transverse blowing dryer at a temperature of approximately 1770C (3500F) and dried until the final dry state (approximately 2 W of humidity). The resulting base sheet was rolled up into a flexible roll and then joined with a similar base sheet by crimping the edges to produce a two-jet towel.

EXAMPLE 2
A two-jet towel was made as in Example 1, except that the resulting two-jet product was lightly calendered under a pressure of 0.45 kg per 25.4 mm linear (approximately 1 pound per linear inch).

EXAMPLE 3
A two-jet towel was made as in Example 2, except that the calendering pressure was about 26.1 kg per 25.4 mm (58 pounds per linear inch).

EXAMPLE 4
A two-jet towel was made as in Example 2, except that the calendering pressure was about 50.4 kg (112 pounds per linear inch).

EXAMPLE 5
A three-jet towel was made by curling together three jets of a base sheet made according to Example 1 and lightly calendering the three-jet product.

EXAMPLE 6
A four-jet towel was made by curling together four jets of a base sheet made according to Example 1 and lightly calendering the four-jet product.

The physical properties of the products manufactured as indicated above were measured and the results are reported in Table I below. For comparison, the properties of certain commercially available towels and rags are shown in Table II. As used in Tables I and II, "Technology" refers to the process by which the product was manufactured "STNC" means non-creped cross-blown dried "STC" means creped cross-blown dried; and "PHC" means wet pressed crêpe. Other terms used in the Tables and their meanings are as follows: "Base weight" is the basic weight of the product expressed in grams / m2; "Jets" means the number of jets in the product; "Traction SM" is the tensile strength in the machine direction expressed in grams per 7.62 cm (per 3 inches); "Traction ST" is the tensile strength in the cross direction, expressed in grams per 7.62 cm (per 3 inches); "Aqueous Abs. Cap" is the Aqueous Absorption Speed expressed as a percentage by weight; "Aqueous Abs. Speed" is the Absorption Speed
Aqueous expressed in seconds; "Cap Abs. Huile" is the
Oil Absorption Capacity expressed as a percentage by weight; "Oil Abs. Speed" is the Oil Absorb Speed expressed in seconds; "Dry Cal" is the Dry Caliber expressed in mm; "Cal Hum." is the Wet Caliber expressed in mm; and "Extens." is the machine direction extensibility, expressed as a percentage of elongation.

TABLE I
(Products prepared from jets according to the invention)
Product Ex.l Ex.2 Ex.3 Ex.4 Ex.5 Ex.6
STNC Technology STNC STNC STNC STNC STNC
Base weight 44.70 43.85 42.41 42.50 65.4 84.5
Jets 2 2 2 2 3 4
Traction SM 4122 4012 3970 3959 5470 7630
Traction ST 4244 4098 3870 3885 5570 5460
Cap. Abs. Aqueous 1060 1084 1104 1000 1060 1235
Abs Speed

Aqueous 0.62 0.64 0.66 0.68 0.70 0.70
Cap Abs. Oil 435 430 395 300 445 445
Abs Speed

Oil 2.3 2.3 7.0 11.5 3.0 2.5
Cal Sec 0.91 0.63 0.41 0.31 1.01 1.25
Cal Hum. 0.82 0.71 0.62 0.57 1.09 1.37
Extens. 20.5 19.1 16.3 16.8 18.0 17.0
TABLE II
(Commercially available products)
Product BOUNTYR SURPASSR KLEENEXR KLEENEXR
STC STNC Technology PHC STNC
Base Weight 49.00 47.4 47 49
Jets 2 1 2 1
Traction SM 2415 6460 3145 3615
Traction ST 1810 4180 3305 3515
Cap. Abs.

Aqueous 1015 360 425 470
Abs Speed

Aqueous 0.5 3.9 1.70 1.70
Cap Abs. Oil 550 305 275 275
Abs Speed

Oil 3.6 85.0 12.3 100.0
Cal Sec 0.66 0.49 0.29 0.35
Cal Hum. 0.66 0.44 0.29 0.48
Extens. 15.0 5.0 24.0 5.0
These results show that the non-creped products with multiple jets prepared from the jets according to the invention have a higher size (not calendered) than any of the commercial products in Table II owing to the fact that the size is independent. base weight, and a better balance of properties, including strength and absorbency.

Claims (7)

 1- Base sheet dried by cross-blowing and not creped having a Dry Size which is independent of the base weight of the base sheet, said base sheet having a Dry Size of about 0.4 mm or more, a Aqueous Absorption capacity of approximately 500 W or more, and machine-directional extensibility of approximately 10 W or more.  2- Method of manufacturing a sheet dried by cross-blowing and not crepe comprising  (a) the deposition of an aqueous suspension of paper fibers on a porous forming fabric which retains the fibers but allows water to pass through to form a wet sheet  (b) dewatering the sheet to a consistency of about 10 to about 30 Oo  (c) transferring the dehydrated web to a fabric for transverse blowing drying having a three-dimensional surface contour such that the depth of the surface contour is substantially greater than the thickness of the wet web, and the conformation of the wet web to the surface contour of the fabric for drying by transverse blowing; and  (d) drying by transverse blowing of the ply, the Dry Caliber of the ply being substantially independent of the basic weight of the ply.  3- The method of claim 2, wherein the Dry gauge of the tablecloth is approximately 0.4 mm or more.  4- The method of claim 2, wherein the tensile strength in the machine direction of the web is about 1000 g or more.  5- The method of claim 2, wherein the basic weight of the web is between about 10 and about 50 g / m2.  6- The method of claim 2, wherein the Wet gauge of the tablecloth is approximately 0.4 mm or more and is substantially independent of the basic weight of the tablecloth.  7- The method of claim 2, wherein the web has a basis weight between about 10 and about 30 g / m2.