WO1992003614A1

WO1992003614A1 - Method for reducing amount of linting

Info

Publication number: WO1992003614A1
Application number: PCT/US1991/005222
Authority: WO
Inventors: Theodore G. Waech
Original assignee: Beloit Corporation
Priority date: 1990-08-22
Filing date: 1991-07-24
Publication date: 1992-03-05
Also published as: AU8394891A

Abstract

A method is disclosed for reducing the amount of linting generated by newsprint during printing thereof. The method includes the steps of ejecting a slurry of papermaking stock (10) onto a forming wire (12) of a papermaking machine (14). A first portion of water is drained through the forming wire (12) such that a web (W) is formed and supported on the forming wire (12). The formed web (W) is removed from the forming wire (12) onto a press felt (16) where the formed web (W) passes through a press nip (18) for removing a second portion of water from the formed web (W). The pressed web (W) is transferred to a dryer felt (20) of a drying section (22) where the web (W) extends around a plurality of rotatable heated cylinders (24, 25) for removing a third portion of water from the pressed web (W). The dried web (W) is guided through a calender (26) which includes a roll (28) and a further roll (30) counter-rotating relative to each other. The rolls (28, 30) define therebetween a calendering nip (36) for the passage therethrough of the dried web (W). At least one of the rolls (28) is heated to a temperature above 200 °C such that at least one of the surfaces (38) defined by the web (W) include strongly bonded fibers due to thermoplastization and flow of fibers within the web (W) so that during printing, the amount of linting by the web (W) is reduced. The disclosure also includes newsprint produced by the aforementioned method.

Description

TITLE: METHOD FOR REDUCING AMOUNT OF LINTING

BACKGROUND OF THE INVENTION

FIELD OF THE INVENTION

The present invention relates to a method for reducing the amount of linting generated by newsprint during printing thereof. The invention also includes a product by the aforementioned method.

INFORMATION DISCLOSURE STATEMENT

A large proportion of the world's production of paper is in the form of newsprint for use in the production of newspapers and the like. However, during printing, when a web of paper progresses through a printing machine, surface fibers of the web become detached from the web, and these detached fibers contaminate ink supplies and the printing blankets of the printing machine. The aforementioned problem is known in the printing art as "linting".

Particularly, in the printing art, it is essential that the printing presses operate at high speed and without any unnecessary shutdowns.

Typically, most of today's newspapers are produced by offset lithographic printing machines in which treated plates are developed such that the printing areas have an affinity to printing ink while the non-printing areas are hydrophilic. Therefore, the rotating lithographic plates are exposed in succession to water and ink fountains.

Some water on the lithographic plate transfers to the blanket which comes into intimate contact with the surface of the web being printed and has the tendency to loosen surface fibers therefrom. Additionally, the relatively viscous, tacky printing ink also tends to detach surface fibers from the printing areas. Due to increased color printing, paper is often exposed to water and ink several times in succession.

Accordingly, such detached fibers tend to accumulate on the blanket, in the ink train, and in the supply of printing ink. Such linting is a very expensive problem for manufacturers of newspapers due to the time required to stop and clean lint from the printing presses.

Also, much paper is wasted in the restart operation of the printer, and inherently, the quality of the printing deteriorates as a result of such linting.

The economic considerations of linting have at least been equated to those of runnability.

Although the particular printing conditions and the type of paper fibers being used do affect the amount of linting, it is understood by Applicant that the amount of linting can be controlled to a significant degree by the type of machinery used in the manufacture of such paper. For example, certain papermaking machines designed for the production of newsprint include relatively expensive gate roll sizing presses for applying a thin coating of size to the dried web in an attempt to decrease linting of the web in subsequent newsprinting operations.

Those skilled in the art had previously concluded that calendering of newsprint caused an increase in subsequent linting. Generally, it was understood that during calendering, the web is crushed and weakened, thereby loosening surface fibers to cause linting.

However, the unexpected discovery has been made that by heating at least one of the calendering rolls to a very high temperature, such linting is reduced. Applicant is of the opinion that this reduced tendency to lint is due to thermoplastization and flow of fibers to form a more strongly bonded surface.

Therefore, it is a primary objective of the present invention to provide a method of producing newsprint which overcomes the aforementioned problems associated with prior art methods of reducing linting.

Another object of the present invention is to provide a method of producing newsprint in which at least one of the calender rolls is heated above 150°C such that linting in a subsequent printing operation is substantially reduced.

Another object of the present invention is the production of newsprint by the aforementioned method.

Other objects and advantages of the present invention will be readily apparent to those skilled in the art by a consideration of the detailed description contained hereinafter taken in conjunction with the annexed drawings and as exemplified in the description of various laboratory experiments as stated hereinafter.

SUMMARY OF THE INVENTION

The present invention relates to a method for reducing the amount of linting generated by newsprint during printing thereof. The method includes the steps of ejecting a slurry of papermaking stock onto a forming wire of a papermachine and then draining a first portion of water through the forming wire such that a web is formed and supported on the forming wire. The formed web is removed from the forming wire onto a press felt, and the formed web is then passed through a press nip while supported on the press felt for removing a second portion of water from the formed web. The pressed web is transferred to a dryer felt where the web supported by the dryer felt is trained around a plurality of rotatable heated cylinders such that a ^"third portion of water is removed from the pressed web. The dried paper web is guided through a calender which includes a roll and a further roll which counter-rotate relative to each other.

The rolls define therebetween a calendering nip for the passage therethrough of the dried web. At least one of the rolls is heated to a temperature above 150°C such that at least one of the surfaces defined by the web develops strongly bonded fibers due to thermoplastization and flow of fibers within the web so that during subsequent printing, the amount of linting by the web is reduced. A similar second nip, or even several more nips, may be used to reduce linting from both sides of the web.

In a more particular method for reducing linting, according to the present invention, the step of heating is carried out with one of the rolls being heated to at least 230°C.

A preferred embodiment of the present invention includes guiding the web through a soft calender in which the roll has a smooth metallic surface and the further roll has a resilient cover.

The present invention also includes newsprint for reducing the amount of linting generated during printing thereof, the newsprint being produced by the method as stated hereinbefore.

Many modifications and variations of the present invention can be made without departing from the spirit and scope of the present invention as defined by the appended claims. In the present invention, as described in the subject application, it is to be understood by those skilled in the art that newsprint, as used in this application, includes other uncoated wood containing paper grades and mechanical grades.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a side-elevatioηal view of a papermaking machine for carrying out the method according to the present invention;

Figure 2 is a side-elevational view of a soft calender used for the method according to the present invention in which at least one of the rolls is heated;

Figure 3 is a bar graph showing the dramatic drop in linting achieved with newsprint produced by hot calendering according to the present invention and shows the percentage of linting that was generated from three samples of newsprint;

Figure 4 is a diagrammatic representation of the production of six sample rolls from an uncalendered roll;

Figure 5 is a bar graph showing the amount of linting from side 1 and side 2 originating from newsprint "A";

Figure 6 is similar to that shown in Figure 5 but shows the results obtained from newsprint "B";

Figure 7 is similar to Figure 5 but shows the results from newsprint "C";

Figure 8 is similar to Figure 5 but shows the results from newsprint "D"; Figure 9 is a graph showing the amount of linting relative to the calender loading at 230°C;

Figure 10 is a graph showing the amount of linting relative to calender loading at 18°C;

Figures 11-14 show graphs for linting relative to the number of calender passes at 21°C, 100°C, 155°C and 220°C respectively.

Similar reference characters refer to similar parts throughout the various figures of the drawings.

DETAILED DESCRIPTION OF THE DRAWINGS

Figure 1 diagrammatically represents a method for reducing the amount of linting generated by newsprint during printing thereof. The method includes the steps of ejecting a slurry of papermaking stock 10 onto a forming wire 12 of a papermaking machine generally designated 14.

A first portion of water is drained through the forming wire 12 such that a web W is formed and supported on the forming wire 12. The formed web W is removed from the forming wire 12 onto a press felt 16.

The formed web supported by the press felt 16 is passed through a press nip generally designated 18 for removing a second portion of water from the formed web W.

The pressed web W is transferred to a dryer felt 20 of a drying section generally designated 22.

The pressed web W supported by the dryer felt 20 is trained around a plurality of rotatable heated cylinders 24 and 25 such that a third portion of water is removed from the pressed web. The dried web W is guided through a calender, generally designated 26 which includes a roll 28 and a further roll 30 which counter-rotate relative to each other as indicated by the arrows 32 and 34. The roll 28 and further roll 30 define therebetween a calendering nip 36 for the passage therethrough of the dried web W.

At least one of the rolls 28 is heated to a temperature above 200°C such that at least one of the surfaces 38 defined by the web W includes strongly bonded fibers due to thermoplastization and flow of fibers within the web W so that during subsequent printing, the amount of linting by the web is reduced.

Figure 2 is an enlarged sectional view of the calender 26 and shows the roll 28. The roll defines a smooth metallic surface 40 which, in a preferred embodiment of the present invention, is heated to at least 230°C.

The further roll 30 is either a rubber covered roll or a metal roll.

Figure 3 is a bar graph showing the percentage of linting that was generated from three samples of newsprint.

More particularly, Figure 3 shows raw stock 42C, which is an uncoated, uncalendered web as having generated approximately 12% linting during subsequent printing thereof.

When the same type of raw stock was calendered at approximately 21°C, as indicated on the graph at 44C, the amount of linting increased to approximately 13%.

When a raw stock sample from the same source was subjected to hot calendering at 230°C, as shown at 46C, the linting dramatically decreased to approximately 2%. From the aforementioned experimentation, it was clearly demonstrated that hot calendering greatly reduced the amount of linting in any subsequent printing operation.

Also, in the aforementioned method of hot calendering, it was determined that such treatment of raw stock had a considerable cost advantage over the prior art sizing procedures. In fact, such high temperature calendering typically decreases the linting by a factor of about 4.

The aforementioned discovery was made during various experiments in the application of heat during the calendering process in an attempt to reduce linting. The results of such experiments are stated hereinafter.

Experiment I, II and III;

Three different experiments were carried out to determine the effect that calendering would have on linting. All three experiments involved the use of 46 cm (18 in) wide commercial newsprint rolls 48, as shown in Figure 4, which were obtained in an uncalendered state. These rolls 48 were calendered on a pilot calender with the paper going through one nip each time it was rewound, as shown in Figure 4. Generally, only the side of the paper contacting the variable temperature metal roll was tested. The rolls of paper produced were slit into two sets of rolls generally designated 50 and 52 respectively and rewound. These rewound rolls 54,55 and 56 of set 50 and 57,58 and 59 of set 52 were then stored after being wrapped. The temperature of such rolls was acclimated to that of the laboratory. Subsequently, the rolls of paper were printed using an Apollo offset press shortly after being unwrapped.

Table 1 summarizes the experimental conditions used for the three experiments as follows: Table I: Calendering Conditions

1 Soft 21 and 175 305 230

II 1 Soft 18, 100, 70,141, 305 and 230 211, 263

III 0-4 Metal 21, 100, 175 610 155, 220

The printing press procedure for measuring lint involves a printing of 500 impressions, and the removal of lint from the offset blanket with transparent tape. Such procedure is followed by the measurement of the lint area by image analysis. Subsequently, the percentage of the offset blanket covered by lint is reported.

Experiment I:

More particularly, experiment No. 1 was carried out utilizing the following procedures. An uncalendered commercial newsprint "A" was soft calendered with the paper going through the nip only once. Part of the large roll 48 was calendered at room temperature, that is, 21°C and part at 230°C. These conditions were repeated with the other side of the web in contact with the heated queen roll 28. With the raw stock sample 48, the aforementioned procedure gave six small rolls 54,55,56,57,58 and 59 as shown in Figure 4 for print testing from the newsprint 48 with the results shown in Figure 5. Care was taken that all six rolls 54-59 came from the same large roll 48 so that paper property variations would be minimal. The aforementioned procedure was repeated with another three newsprints "B", "C" and "D" from different furnishes as shown in Figures 6, 7 and 8. It is to be noted that room temperature calendering generally increased the amount of linting when compared to uncalendered raw stock, but high temperature calendering, as demonstrated by the subject experiments, decreases the amount of lint by a factor of 1.9 to 6.5.

The aforementioned results are similar to the reductions that occur due to the application of starch from a gate roll size press, which applies a size coating to the newsprint.

As shown in Figures 5-8, the three bar graphs on the left show the percentage of linting from uncalendered, cold calendered and hot calendered first sides of the web. The three bar graphs on the right show the percentage of linting from uncalendered, cold calendered and hot calendered second sides of the web.

More specifically, in Figure 5, for the newsprint "A", the uncalendered raw stock 42A from roll 54 showed linting of approximately 9%. For newsprint "A", the linting, when cold calendered at 21°C, was approximately 7% as shown by the block graph 44A from roll 55. However, when newsprint "A" from roll 56 was calendered at 230°C, as shown by the bar graph 46A, the linting decreased to approximately 3%.

For the second side of the samples, roll 57, as shown in Figure 4, was not calendered and, subsequently, resulted in 10% linting as indicated by the bar graph 60A.

Roll 58 was cold calendered at 21°C and the percentage of linting therefrom, as indicated by the bar graph 62A, was approximately 12%. When roll 59 was hot calendered, the linting results, as indicated by bar graph 64A, was in the region of 4%.

Similar experiments were carried out for newsprint "B", "C" and "D" as shown in Figures 6-8 with the linting results shown by the same numerals as those shown in Figure 5 but with different suffixes, B, C and D, added thereto. As can be seen from &the results shown in Figures 5-8, the hot calendering of the web in each instant caused a dramatic decrease in the amount of linting occurring during subsequent printi g.

Experiment II:

Six large uncalendered rolls were obtained from one source, and all were obtained from the same furnish. For a given large roll, single nip calendering was done at four different loads. The six rolls were run at three temperatures with two different sides contacting the variable temperature metal roll (that is, a raw stock 5 3 x 2 factorial design) .

Figure 9 shows how the lint from one side, that is the top side, decreased to approximately 3% as shown by graph 66 when heated to 230°C with a calender load of 210kN/m. Another roll was calendered at 18°C, and the lint generated therefrom increased as shown in Figure 10. The linting increasing from 10% at zero loading to 15% at a loading of 60 kN/m as indicated by the graph 68.

Experiment III:

Rolls from one reel of non-calendered newsprint were put through the calender up to four times with the bottom side always contacting the variable temperature roll. Although there are duplications of many of the experimental conditions, it is to be noted that since two different raw stock rolls were used at each temperature, the results were not always identical. The uncalendered raw stocks all tested at 10% to 15% lint, but the results after calendering were not always the same for the same experimental condition shown in Figures 11-14.

Besides the variations in calendering response, it is to be noted that 1) for the subject furnish, even low temperature calendering reduces lint somewhat; and 2) calendering at high temperature reduces linting even more. The conclusion is that due to thermal expansion and possible uneven nip pressure, calendered paper surface data is often plotted versus paper density. In this case, one gets the same conclusions as for those shown in Figures

11-14. It was noted that the results varied, suggesting that each individual roll varies in its response to calendering but that higher temperatures did, in fact, decrease linting.

From the aforementioned three experiments, the following conclusions were made:

Two observations were made based on multiple tests as follows:

1. High temperature calendering can be used to decrease linting of newsprint by a factor of four or more.

2. Calendering at low temperatures may increase linting.

Although from the aforementioned observations it would appear that thermoplastization of fibers occurs at high temperature and that conversely, there exists relative brittleness of fibers or bonds at low temperatures, such a conclusion is not proved by means of the aforementioned experiments. It is suggested that wet end pressing or drying variables can greatly affect the linting.

The present invention provides_. a method of producing newsprint which greatly reduces the amount of linting in subsequent printing operations, thereby reducing costs over prior art procedures.

Claims

What is claimed is:

1. A method for reducing the amount of linting generated by newsprint during printing thereof, said method comprising the steps of: ejecting a slurry of papermaking stock (10) onto a forming wire (12) of a papermaking machine (14); draining a first portion of water through the forming wire (12) such that a web (W) is formed and supported on the forming wire (12); removing the formed web (W) from the forming wire (12) onto a press felt (16); passing the formed web (W) supported by the press felt (16) through a press nip (18) for removing a second portion of water from the formed web (W) ; transferring the pressed web (W) to a dryer felt (20) of a drying section (22); drying the pressed web (W) supported by the dryer felt (20) by training the web (W) around a plurality of rotatable heated cylinders (24,25) such that a third portion of water is removed from the pressed web (W) ; guiding the dried web (W) through a calender (26) which includes a roll (28) and a further roll (30) which counter-rotates relative to the roll (28), the roll (28) and further roll (30) defining therebetween a calendering nip (36) for the passage therethrough of the dried web (W) ; and heating at least one of the rolls (28) to a temperature above 150°C such that at least one of the surfaces (38) defined by the web (W) includes strongly bonded fibers due to thermoplastization and flow of fibers within the web (W) so that during printing, the amount of linting by the web (W) is reduced. 2. A method for reducing linting as set forth in claim 1 wherein the step of heating is carried out with one of the rolls being heated to at least 200°C.

3. A method for reducing linting as set forth in claim 1 wherein the step of guiding the dried web through a calender includes: guiding the web (W) through a soft calender (26), in which the roll (28) has a smooth metallic surface

(40) and the further roll (30) has a resilient cover.

4. A method for reducing linting as set forth in claim 1 wherein the step of guiding the dried web (W) through a calender (26) includes guiding the dried web (W) through the calendering nip (36) and then passing the web (W) through at least one further calendering nip for maximum reduction of linting on both sides of the web (W) .

5. Newsprint for reducing the amount of linting generated during printing thereof, the newsprint being produced by the method as set forth in claim 1.