US2001023A - Creped paper - Google Patents

Description

May 14, 1935.

c. M. HOWELL ET A1. 2,001,023

CREPED PAPER Filed 001. 2s, 1954 v (QQ 1 i 2 Patented Mey 14, 1935 2,0%,023

UNITED STATES PATENT oFFic Caspian PAPER Charles M. Howell, Springfield, and James dA. Clark, Swarthmore, Pa., assignors to Scott Paper Company, Chester, Pa., a corporation of Pennsylvania Application October 23, 1934, Serial No. 749,648

6 Claims. (Cl. 154-55l This invention relates to the manufacture of of finished tissue for similar use at a rate of up creped paper products 'more particularly those to one thousand feet per minute. used for personal purposes' such as towels and It is known that the lightest weight issues toilet tissue. which are virtually dried before creping, are One of the principal objects'of the invention is specifically softer than the heavier weight tis- 5 to provide a. soft absorbent paper which is at the sues. By specific softness is meant the inherent same time particularly resistant to fracture in softness of the paper after allowing for the effect use. of the greater substance. By experiment it was Another object of the invention is to provide a found that the specific softness of the tissue was 10 paper which has a superior degree of softness and proportional to (a) the degree of dryness rat the 10 absorbecy. creping doctor and (b) the extent which the Other objects. and advantages of the invention tissue was dried in cohtact with the creping will be apparent from the description thereof cylinder. It was further found that the funcset out below and from the claims. tion of the creping doctor is to disturb the co- As is well known in the manufacture of creped hesion between the bres comprising the sheet 15 paper the web is formed from -a fibrous suspenfand that the dryer the sheet at that point, the sion on a suitable forming cylinder or Fourdrinier less the tendency for the libre bonds to reform machine, then picked olf the forming wire by during the subsequent drying operation; furmeans of a felt, passed between rollers to express thermore an increased degree of drying on the the surplus water and pressed against a heated cylinder causes a greater adhesion between the drying cylinder and then creped thereoi by means moist web and the surface of the cylinder which of a scraper or doctor placed at an angle to and results in a greater resistance to the edg of the in contact with the face of the cylinder. The doctor` blade and henceV a more complete discreped web is then dried, calendered and reeled ruption of the fibrous structure. It is clear up, During the crepingvv step there are two disthat this disruption of the bonds between the 25 tinct and separate methods employed for combres not only leads to enhanced softness and pletine the manufacture depending on whether absorbency but at the same time tends to dethe tissue is, of the lightest weight for example stroy the specific strength of the sheet. Further about 6 lbs. but usually below 10 pounds per 3000 experiments disclosed that the numerical prodsquare feet (24"X36"-500) which is used for uct of the specific tensile strength and specific 30 facial tissue and the like, known technically asv softness of a creped sheet of tissue prepared.

cellulose wadding or if the tissue is of a heavier from different ingredients. and in different ways basis weight between l0 and l5 pounds per 3000 is approximately a constant quantity. In adsquare feet used for example for toilet paper and dition to softness and absorbency another irnthe like, and the heaviest tissue of over twentyportant fundamental requirement of tissues and 35 five pounds per 3000 square feet used for example towels is that they should possess a high degree for toweling and the like. In the case of the wadof strength when in use, and4 as these experidine or lightest weight tissue, it is made by pressments indicate, itis possible to obtain increased ing the moist Web against a large diameter heated softness and absorbency only at the expense of creping cylinder, and made at a speed not above specific strength. Y 4,0 that which allowsthe web to be virtually dry as A hitherto unknown fact was discovered; that it issues from the creping doctor when it is next the property of both towels and tissues which wound up onto a reel for packaging operations. gives them strength in practice, is not tensile In the case of the tissues heavier than 10 pounds and bursting strength, as required for example in per 3000 square feet with a cylinder of a normal U. s. Government specifications for such prcd- 45 size and at commercial speeds for these tissues ucts, but the property of stretch, which as far the web issues from the creping doctor not 'very as we are aware, has not been there or elsewhere much drier than when pressed against the drying mentioned in this connection. cylinder because it will be readilyappreciated Iii is well known that any paper made from that as the point of contact with the cylinder the cellulose without the addition of a special water- 50 web contains at least 65 percent of moisture and proof binding agent, however strong it might be is at a temperatule usually not in GXCSSS 0f 100 when dry, becomes extremely weak when moist- F., it requiresa substantial time vin contact with ened, more especially so with soft absorbent; pathe heated cylinder to raise the temperature to -pers made from pulp which has been relatively where evaporation can take placefreely and to lightly beaten or otherwise processed; for ex- 55 supply thenecessary latent heat for evaporation. ample all untreated paper towels have their dry Consequently the time necessarily required -to-tensilestrength Areduced to the order of only effect much drying of the heavier tissues has not about ten ounces per inch of Awidth when moistbeennconsidered hitherto commercially available fenedand it will be appreciated that this is an as modern large paper machines produce a web insignificant amount compared to the relatively large forcesimposed by the knuckles upon a moist paper towel when used for drying of the hands. If in place of a towel, a piece of extremely thin rubber sheeting were used similarly to a towel to wipe the hands, even if the ultimate tensile strength of the sheeting *vere considerably less than that of a moist paper towel, it would not disintegrate during such use. Accordingly, as will be described, paper towels were then made having a stretch many times greater than hitherto deemed necessary for imparting softness and absorbency and it was discovered that the similarity with the rubber sheeting held good; and in addition to providing a towel with a marked resistance to disintegra-- tion during use, the properties of absorbency and softness were improved and a paper towel of markedly superior and hitherto unknown characteristics was obtained. Similarly toilet tissue was made with a high degree of stretch incorporated which proved much more resistant to fracture in practice than hitherto available.

It is clear that a considerable amount of stretch must be potentially available to such tissues before reasonable protection is provided other than from mere numbers of sheets used together, and it was found by experiment that a degree of potential stretch of much less than percent yields a wholly inadequate protection to fracture when the tissue becomes moist.

For the purposes of description and as setting outa form of mechanism which will operate in a very satisfactory and economical manner for producing anew soft paper product having a high potential stretch, the drawing illustrates a preferred form. In the gure, l indicates means of forming the paper web, shown as a Fourdrinier but it may take the form of a cylinder machine. 3 indicates the carrying felt and 2 the press section where excess water is expressed from the wet web in a well known way. 5 indicates the large heated receiving or creping cylinder onto which theweb is pressed by means of the roll 4 and the Wet web of paper is creped off by the doctor 6, the web being shown at 1, and the web is passed to a series of dryer rolls 8 from which the web goes through pair of calender rolls 9 and is finally reeled up at I0 where it is ready to be cut into the finished form.

With the diameter of the receiving dryer 5 about the same as that of the succeeding dryers 8, it was found in practice when retaining the same speed of production and attempting to substantially increase the amount of crepe given hitherto so as to be in accordance with the invention by improving the drying effect of the receiving dryer by raising its temperature, when the surface temperature of the receiving (or creping) drier approached that of boiling water, the web blistered while in contact with this dryer and uneven and unsatisfactory creping resulted. To overcome this difficulty without having to slow down considerably the whole paper machine and so add greatly to the costs of production, it was found necessary to substantially increase the size of the receiving drier 5 preferably to'at least ten feet or sa'y double that of the normal size remaining driers 8 so as to effect the necessary amount of drying at a temperature well below 212 F. at the' same production speed as heretofore.

The dryer section 8 is driven at a peripheral speed lower than the receiving dryer 5, by about 10 percent or over, the maximum possible dii.'- ference being governed by the ability of the creped web to retain its crepe without being pulled out by,V its own weight and the tension imposed upon it, and its inherent strength to resist being pulled out. Its inherent strength is found to be governed by the dryness of the web after leaving the creping doctor, which should preferably be over 40 percent of its moist weight and also by its uncreped bulk, the bulkier the moist sheet, the more rigid it is and the better it resists beingl stretched While moist. The composition of the fibrous furnish is preferably selected so as to be inherently as bulky as possible. To further preserve the resulting crepe from being drawn out by the natural shrinkage of the web during drying, it is also desirable to graduv ually reduce the peripheral speed of the driers 8 towards the calenders, for example by slightly reducing their diameters successively or in successive groups.

By these means it is possible to produce a soft creped tissue of substantial substance and having a high degree of potential stretch. It will be understood that the potential stretch in a creped paper is made up of two components, first the stretch available through the imparted crepe and secondly the stretch available by the elasticity and length of the component fibres which amounts usually to about two to three percent but has been found in the case for example of certain pulps prepared by an alkaline process to give an elongation of as high as six percent before fracture. It is, therefore, possible to produce a creped tissue having a potential stretch of fifteen percent according to this invention with only nine percent of crepe being added.

For the purpose of definition the softness of the products is determined .by the following method:

Cut parallel strips of paper in the machine and cross directions about one or two inches wide, insert the end of each strip in turn between a diametrically split horizontal spindle preferably about 1/2 inch in diameter, and adjust thev overhanging length so that on rotating the spindle through 90 degrees the strip just flops over in the direction in which the spindle is being rotated as it is turned back and forth through 90 degrees. The overhanging lengths are then measured in inches for both the machine and cross directions. If the average overhanging length so found is lm inches for the machine direction and lc inches for the cross direction'and the thickness of the strip is t thousandths of an inch, the average softness factor is calculated according to the following empirical formula:

"l being either "l or lm, whichever is the greater. The test is carried out at 65% relative humidity and '70 F.

According to this method the values for the softness of commercial soft absorbent tissues range from 5.0 to over 10.0.* A tissue having an average softness factor of over 5.0 is considered as soft.

For the purposes of denition the absorbency is determined by the following method:

Place one thickness of the tissue on a 4 mesh per inch wire screen and allow 0.1 millimeter of water to flow on to the tissue. The absorbency is the time in seconds from the contact of the water with the tissue until the drop is completely absorbed, as indicated by no further reflection decorative purposes and the like.

of light from it. The test is carried out at 65% relative humidity and '740 F.

If the drop is absorbed. in'less than 600 seconds (10 min.) the tissue is considered absorbent.

For the purposes ofdefinition stretch means the percentage increase of the original length of a parallel strip of paper at the instant of rupture, when subjected to a slowly increasing tensile strain and is determined by well known means at a temperature of 70 F. and a relative humidity of 65%.

The relative proportions of the stretch due to the added crepe and the inherent potential stretch of the fibrous structure may be determined by reference to the stress strain diagram when drawn by a recording extensometer in a well known manner. f

We are aware that various non-absorbent creped papers having a high degree of crepe or stretch are known which are commonly used for 'I'he process for producing them is confined to a separate machine from that on which the paper is formed and dried, and is applied to the dried web` of paper by causing it to be stuck, by means of an added adhesive, to a creping cylinder and creping therefrom. As the adhesive used invariably detracts from its absorbency, as well 'as the fact that the fibrous structure of the paper is not disturbed as it is when creping just after its formation and while still moist, the resulting product is neither soft nor absorbent according to the stated tests and no claims are directed towards such a product.'

We are also aware that creped soft absorbent multiply tissues are known, such products being made from highly creped tissues, the web of which has been substantially fully dried on the 'creping cylinder before creping and in consequence of which the use of a relatively light substance, usually between six and ten pounds per 3000 square feet, is necessary and the separate sheets of wadding are combined into a multiply sheet of'any desired composite substance by superimposing a number of webs together ,with or Without embossing. This type of construction gives an extremely soft product and also an abrubbed, the top or individual layer breaks and rolls`up, followed by the successive layers and the whole product rapidly disintegrates. Conseqently a product made from multiple thicknesses of sheets having individually a low basis weight, even though they may have a high degree of stretch, in practice proves more unsatisfactory as regards disintegration than a single ply sheet possessing a low degree of stretch and of the same basis weight as the composite multiply sheet. We make no claim for such a multiply product unless the outer plies areV composed of tissue made in accordance with this invention when the objection cited becomes less valid.

In the appended claims, the term towel refers to a paper article, the basis weight of such article being in excess of approximately twentyve pounds per 3000 square feet. Further, the term toilet tissue refers to a paper article the basis Weight of which \exceeds approximately twelve pounds per 3000 square feet. Further,

the term cellulose wadding refers to a paper article the basis weight of which is usually considerably less than that of toilet tissue and which has been substantially fully dried before creping and is characterized by softness and 4flimslness in the lighter weights and by the greater gloss or polish imparted to one surface by such drying, such gloss being especially noticeable in Athe heavier weights. A

While this invention may be carried into effect with any paper machine adapted to the manufacture of tissue we are not aware that anyone has hitherto recognized the novel and unexpected results of imparting a high degree of crepe to the heavier classes of tissues mentioned lnor are f we aware of any paper towel or similar tissue except when made of cellulose wadding having a potential stretch in excess of ten percent. Indeed we have found that the great majority. have a much lesser percentage of stretch than ten available, being commonly between three and six percent. Furthermore, to produce such a product on a paper machine without the large receiving dryer which hitherto has not been used for such tissues would severely limit the speed at which the products could be made and so make their production uneconomical.

It will be obvious that the invention may be applied to any paper products of which the desirable characteristics of softness and/or absorbency and the possession of a sufcient degree .of stretch to give effective resistance to fracture or disintegration during use, for example paper for l/table napkins and the like, but for these particular.

products high degree of absorbency is undesirable and sizing materials may accordingly be added to the paper.

We claim:

1. As a product of manufacture, a soft creped multiply towel or toilet tissue paper whereof any ply is madeof paper other than cellulose wadding,

said product having a potential stretch of not' less than fifteen percent. l v 2. As an article of manufactlure, a single ply paper towel having a potential stretch of not less than fifteen percent.

3. As an article of manufacture, a single ply sheet of soft toilet tissue paper other than cellulose wadding having a potential Vstretch of not less than fifteen percent.

4. As a product of manufacture, a soft towel f or toilet tissue paper other than cellulose wadding having an additional percentage' of stretch incor- CHARLES M. HOWELL. JAMES DA. CLARK.

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