Patent Description:
The prior expanded slit sheet paper was non-extensible and was primarily made from Kraft paper. The prior expanded slit sheet paper was expanded using manual or powered expansion systems. See: <CIT>, <CIT>,<CIT>, and <CIT>, and <CIT>.

For decades, the prior expanded slit sheet paper persisted in the marketplace despite limitations of the existing technology without any contemplation of the present invention or the potential advantages therefrom.

The preferred embodiments of the present invention are described by a way of example, and not limitation, in relation to the accompanying figures, in which:.

For the purposes of the present invention, the term "expandable" as applied to paper sheets, means a paper having a slit pattern that enables the paper to be expanded by opening of the slits upon applying a force in a longitudinal direction of the paper sheet. Illustrative expandable paper sheets are disclosed in <CIT>, <CIT>,<CIT>, and <CIT>, and International Application No. <CIT>. The slit pattern enables the paper to be expanded in length, with a related decrease in width due to the nature of the slit pattern. The slit pattern produces an increase in length due to the slit pattern when processed in an expander as taught in <CIT> pending <CIT>, <CIT>, and <CIT>.

For the purposes of the present invention, the term "extensible" as applied to paper sheets, means a paper sheet that is able to stretch in a longitudinal direction of the paper sheet upon applying a force in the longitudinal direction of the paper sheet. Illustrative extensible sheets are disclosed in <CIT>, <CIT> (<CIT>), International Application No. <CIT>, <CIT>, <CIT> (<CIT>), and <CIT>, <CIT>, <CIT>, <CIT>, <CIT>, <CIT>, <CIT>, and <CIT>. It should be understood that the stretching of an extensible paper must be measured in an unslit sheet of paper. As disclosed in <CIT>, the test and characterization procedures employed in measuring elongation (extensibility) properties can be in accordance with standard TAPPI test Elongation T457. In addition, as disclosed in <CIT>, the expression "extensible papers" means a paper having an increasable elongation in the machine direction as compared to standard, non-extensible Kraft paper.

For the purposes of the present invention the term "extensible slit sheet paper" means a paper that is both extensible and expandable.

While the present invention may be embodied in many different forms, the illustrative embodiments are described herein with the understanding that the present disclosure is to be considered as providing examples of the principles of the invention and that such examples are not intended to limit the invention to preferred embodiments described herein and/or illustrated herein.

The disclosures of <CIT>, <CIT>, <CIT>, and <CIT> and <CIT> describe expandable slit sheet papers.

A crepe paper type, as found in <CIT> (<CIT>) teaches the creation of an extensible sheet that is not usable within the present invention. In this case the manufacturing of the slit sheet material is not possible since the crepe paper would easily stretch through the expanded slit sheet manufacturing process. This type of extensible paper is not usable in the present invention because it has too much stretch and creates a distorted expanded slit sheet. The sheet then becomes very narrow as the hexagonal cells stretch to their limit and virtually close.

Pending <CIT> describes an expansion device that varies the tension directly to the extended paper core attached to the unexpanded slit sheet material. Surprisingly, the present inventor has discovered as set forth in the present application that substantial benefits are created as a result of using a minor to moderately extensible type paper that provides a stretch to the paper, which, e.g., greatly facilitates and reduces the force required to expand the expanded slit sheet material. Notably, the prior expanded slit sheet paper persisted in the marketplace for decades despite limitations of the existing technology without any contemplation of the present invention or the potential advantages therefrom.

In some preferred embodiments, extensible paper can be produced by varying the accumulation of paper fibers by essentially slowing the paper feeding process during the drying method to trap extra fibers that make the paper appear to have microscopically sized rows of paper that you would see if one were to pleat the paper. The difference is that extensible paper's microscopic rows are adhered to each other through the use of binders and other types of adhesives in conjunction with the drying process. Reference is made to patent <CIT> (<CIT>) where the purpose is to create a non-creped extensible paper that does not easily disconnect from itself. In addition, the surface of the extensible paper is still fairly flat.

In the preferred embodiments of the present invention, the extensible paper that is employed has low extensible properties as compared to other types of extensible papers. In this regard, an optimal extensible paper enables a smooth transition from an unexpanded to the expanded slit sheet by providing a small amount of stretching at the very start of expansion of the extensible slit sheet paper material.

In some exemplary constructions, during expansion of a slit sheet, the force required to initiate expansion is substantially higher than the force required to continue expansion. For example, once the paper initially starts to bend at the slits, the expansion continues more easily during continued bending at the slits. The force required to continue the expansion of the slit sheet during this continued bending is dramatically reduced beyond the above-noted initial expansion. In some preferred embodiments, the extensible slit sheet paper substantially reduces the force required to initiate expansion. On the other hand, in some preferred embodiments, during the above-noted continued expansion, the extensible paper does not substantially stretch simultaneously with the process of expanding the slit sheet paper; otherwise, the expanded sheet might not optimally be made into a cushioning wrap.

It should be noted that in this application, all theories related to functioning of the invention are provided to facilitate appreciation of concepts of the invention, rather than by way of limitation. Extensible paper, as designed, stretches as part of an increase in paper strength. In some embodiments, the functioning of the invention involves that the extensible slit sheet paper substantially utilizes the extensible property to ease the rotating the cells into the stretched shape and to resist tearing of the slit sheet during the expansion step. This means that at the initial point at which the cell rotates (i.e., initiating rotation between legs 38a and 38b on each side of the slit and land <NUM>) the extensible slit sheet paper is substantially enhanced by the extensible paper's ability to stretch. In some embodiments, the functioning of the invention, thus, involves that extensible papers' properties are substantially utilized at this initial point and substantially finished as soon as the cell begins to rotate into its three dimensional shape (i.e., after this initial point, the reliance on the extensible nature of the paper may be less substantial or even non-existant). After that initial point, the slit pattern properties, regardless of paper type, opens with greater ease to the point at which it forms a hexagon. Accordingly, in some embodiments, the extensible property substantially merely comes into play at the initial moment of expansion. In some other embodiments, while the extensible features of the paper comes into play most substantially at this initial point of rotation, the extensible features of the paper can have some affect during further expansion of the paper, whereby the initial point of expansion can be substantially facilitated due to extensibility and further expansion can also be, at least, somewhat facilitated due to extensibility.

In some of the preferred embodiments, preferable extensible papers that can be employed include extensible papers where the purpose of the extensible nature is to provide the type of stretching found for the use of multi-wall bags for heavy weight items like cement, or seed and the like. <CIT> (<CIT>) and <CIT> and <CIT> teach the manufacture and properties of this form of extensible paper. Further teachings can be found in "<NPL>).

The prior expanded slit sheet art (See, e.g., <CIT>, <CIT>,<CIT>, and <CIT>) focused on paper strength to inhibit tearing during the expansion process and Kraft paper was satisfactory because the strength required coincided with the thickness required to make a satisfactory wrapping product. The increased strength of an expandable sheet does not contribute to or increase the value/performance of the expansion of the slit sheet material. It has now been found by the present inventor that an expandable slit sheet paper can be substantially improved by the use of an extensible sheet. In the preferred embodiments, this use of an extensible slit sheet paper advantageously provides a reduction in force required to open the slit sheet and therefore provides a faster and easier expanding process for the user of the expanded slit sheet. The unexpected benefit resulting from the reduction in force at the very start of the expansion of the slit sheet provides an unexpected improvement to the slit sheet packaging product and renders the employment of the extensible paper highly unique. Notably, the prior expanded slit sheet paper persisted in and was widely used in the marketplace for decades without the contemplation of the present invention or the potential advantages therefrom.

As set forth in this application, the present inventor has discovered that the force needed to expand an expandable slit sheet paper is far greater than the force required to expand an extensible slit sheet paper. By way of example, a <NUM> (<NUM> pound) Kraft paper expandable slit sheet that is <NUM> (<NUM>") wide prior to expansion requires approximately <NUM> - <NUM> (<NUM>-<NUM> pounds) or <NUM> Newton per meter (<NUM> pounds per inch), whereas the force required to expand an extensible slit sheet of the same paper weight is <NUM> to <NUM> Newton per meter (<NUM> - <NUM> pounds per inch). This is a marked difference between the papers. Kraft paper has the strength to provide an acceptable expandable slit sheet. However, unexpectedly, the extensible slit sheet imparts an ease of expansion that greatly reduces the force required to expand the slit sheet, not based on the main purpose for extensible paper which is to increase its tensile strength but, rather, its capability to stretch. Since extensible paper is higher in cost and Kraft paper was strong enough, it was not previously known that extensible paper could be of benefit for making slit paper sheets of the types found in, e.g., <CIT>, <CIT>, <CIT>, and <CIT>, and <CIT>. For example, it was not appreciated that an extensible slit sheet could have provided an equivalent strength to light weight, thin papers that previously had no applicability as a wrapping product. Light weight Kraft paper tears more easily than heavier weights of Kraft paper. It has now been found that the extensible paper enables the use of the lighter weight expanded slit-sheet papers that also advantageously provide gentler cushioning required by fragile items when a slit sheet is expanded, in contrast to the more rigid cushioning provided by heavier weight expanded slit-sheet papers.

Reference is particularly made to the graph of Table <NUM> on page <NUM> of <CIT> (now <CIT>) as if recited in full, that describes paper strength based on certain manufacturing techniques. Within the graph is a column describing elongation at the point of paper break (or tearing of fibers) separated into two sub columns of the machine direction (MD) and cross direction (CD), also referred to as transverse direction. The elongation percentage of Table <NUM> ranges from <NUM>% to <NUM>% in the cross direction (CD) and <NUM>% to <NUM>% in the machine direction (MD).

Reference is also made to <CIT> within Table III of column <NUM> which references elongation in the percentage range from <NUM>% to <NUM>% in the CD or cross direction and <NUM>% to <NUM> % in the machine direction.

In both `<NUM> and `<NUM>, the variations are based on the manufacturing process that places an emphasis on tensile strength and stretch in either the cross direction or machine direction accordingly.

The present inventor has discovered that for the purposes of expanding an extensible slit sheet paper for use as a packaging wrap and/or void fill, machine direction extensible ranges from <NUM>%-<NUM>% provide an adequate extensibility, with <NUM>% to <NUM>% preferred, and <NUM>% to <NUM>% most highly preferred. The lower the extensibility coincides with lower costs of the paper per square foot. As indicated above, it should be understood that extensibility is measured on unslit paper.

Machine direction extensibility ranges of the extendible slit sheet paper have ranges from <NUM>%-<NUM>%, or more preferably from <NUM>% to <NUM>% preferred, or even more preferably from <NUM>% to <NUM>%.

For the purposes of expanding the slit sheet paper for use as a packaging wrap and/or void fill, it has been found that cross direction extensible ranges from <NUM>%-<NUM>% provides an adequate extensibility with <NUM>% to <NUM>% preferred, and <NUM>% to <NUM>% most highly preferred.

In some alternative embodiments, cross direction extensibility ranges of the extendible slit sheet paper can have ranges of: a) from <NUM>%-<NUM>%, or more preferably from <NUM>% to <NUM>%, or even more preferably from <NUM>% to <NUM>%; or b) from <NUM> %-<NUM>%, or more preferably from <NUM>% to <NUM>%, or even more preferably from <NUM>% to <NUM>%.

In combination with the extensible paper, a smaller, lighter weight, and recyclable version of an expander can be employed (such as, e.g., made entirely or substantially entirely with recyclable cardboard in some illustrative embodiments). This expands the market to customers that use a very small amount of wrap as compared to the industrial market. It also provides for a less expensive expansion device to be employed for expanding the slit paper. Additionally, it enhances the ease of use by the packer by providing for less ripping during the wrapping process that occurs when the tension is not properly set. This occurs as the roll, during its continued use, becomes smaller and lighter in weight. As the roll of expanded slit sheet becomes lighter the tension required increases. Thus, there need for a varying tensioning method. With the use of the extensible paper, the tension required is significantly decreased and the strength of the paper is increased. Both benefit the person wrapping by making the tensioning required much less precise to the point at which, a single tension setting can be used with little or no adjustment. If the tension is set higher than necessary, the increase in strength from the extensible paper keeps the product from tearing and therefore makes it easier for the packer to use. Therefore, the packer can make fewer adjustments as the slit sheet roll becomes smaller and smaller.

The reduction in the force required to expand the slit paper enables a new product to be created using lighter weight papers. In the past, expanded slit sheet paper is primarily used as a wrapping product whereas its use as a void fill would be in limited circumstances due to void fill being typically the cheapest, that is, the lowest cost of all packaging products. The increased strength of the extensible sheet enables the use of a thinner and lighter weight slit sheet paper as a void fill product. If the expanded slit sheet is not being used as a wrap, then the thicker <NUM> (<NUM>"), <NUM> pounds per <NUM>,<NUM> square feet paper and above is not required and a lighter weight <NUM> - <NUM> (<NUM>-<NUM>") thick, <NUM> - <NUM> gram per square meter (<NUM>-<NUM> pounds per <NUM>,<NUM> square feet) paper can be used as void fill. It can also be used to provide cushioning that other paper void fill products have not been able to provide. It has now been found that even though the extensible paper has a <NUM>% higher price, the use of a thinner paper provides much more square footage per ton and more than compensates for the increased cost of the extensible paper as compared to Kraft paper.

The use of the slit sheet expanded paper as a void fill is described in <CIT>, at column <NUM>, and illustrated in <FIG> and <NUM>. However, in the present invention, a separator sheet is preferably not required as disclosed in co-pending patent applications <CIT>, <CIT>, <CIT>, and <CIT>.

The accompanying figures set forth details in relation to some preferred, and non-limiting, embodiments of the invention.

<FIG> is the perspective view of an illustrative expander according to some illustrative embodiments, wherein the expander is employed to expand extensible slitted sheet matter that is wound in a roll and supported on the expander. As shown in <FIG>, element <NUM> is a corrugated carton frame that houses and is adhered to corrugated yokes <NUM> and <NUM> at sides of the carton. The two yokes <NUM> and <NUM> have receiving openings that support opposite ends of a cylindrical paper core <NUM> that supports a roll <NUM> of unexpanded slit sheet paper that is wound around the core (i.e., having multiple windings or layers around the core). In some preferred embodiments, an optional roll holder <NUM> is mounted to one of the yokes (e.g., yoke <NUM> as shown) and adapted to apply a clamping force against the outer surface of the paper core <NUM> through the use of the setscrew <NUM> that passes through the spring <NUM> and the roll holder <NUM> into a threaded fixture <NUM> of the yoke <NUM> as described in co-pending non-provisional application <CIT> of the present inventor. By adjusting the setscrew <NUM>, the clamping force on the core <NUM> can be adjusted, whereby the tension force applied to the roll <NUM> upon pulling of the paper from the roll during operation can be adjusted.

<FIG> is perspective view of the expander shown in <FIG> in a ready-to-ship configuration including upper corrugated box cover <NUM> fitted over and hiding the lower corrugated box <NUM> shown in <FIG> that supports the corrugated expansion device. In this illustrative example, straps <NUM> secure the upper corrugated box <NUM> to the lower corrugated box.

<FIG> is an illustration of an exemplary slit pattern in an illustrative expanded slit sheet. In preferred embodiments, the extensible slit sheet paper includes a slit pattern similar to that shown in <FIG>. The expandable slit sheet paper shown in <FIG> operates as an expandable cell-forming paper that can be expanded to an expanded state as shown in <FIG> (discussed below). <FIG> shows an illustrative section of an expandable slit sheet <NUM> in an unexpanded (unopened) state, with staggered rows of slits <NUM> and <NUM> that extend entirely through the width of the sheet <NUM>, and land portions <NUM> extending between adjacent slits within rows <NUM> and <NUM>. As shown in <FIG>, in the preferred embodiments, the slit lengths <NUM> and <NUM> are uniform across the face of the sheet <NUM>; similarly, the distance and area of each row spacing <NUM> (i.e., between adjacent rows) and each slit spacing <NUM> (i.e., between adjacent slits) are also uniform. Although an extensible slit sheet can be formed with a variety of slit patterns, the illustrative example shown in <FIG> and <FIG> depicts an illustrative example to scale with illustrative lengths of slits, spacing between slits, proportional relationships of sizes of created hexagonal cells, land portions and leg portions, etc., according to some illustrative examples with such as drawings being to scale in some illustrative and non-limiting embodiments.

In <FIG>, the sheet <NUM> shown in <FIG> has been pulled in the direction of arrows B and C and opened to its optimum cell formation. In that regard, the optimum cell formation results in hexagonal shaped cells as shown in <FIG>. In particular, as depicted, the slits <NUM> and <NUM> are in an opened state in which the sheet <NUM> is oriented to have an array of three-dimensional hexagonal cells <NUM>, with substantially rectangular land portions <NUM> within the slit spacings <NUM> situated at an inclined angle (i.e., such as to be transverse to the original plane of the sheet <NUM>), and the leg portions 38a and 38b connecting the land portions between the row spacings having been warped to, e.g., slightly less than a <NUM>° angle to the original plane of the sheet. The leg portions 38a and 38b are basically mirror images of one another and connect the land portions <NUM> such as to form the three dimensional hexagonal cells.

<FIG> is a schematic diagram that illustrates a roll <NUM> of the extensible slit sheet paper, with a length LL of paper unrolled from the roll <NUM>. In this unrolled state, the extensible slit sheet paper is not in an expanded state unless an expanding force has been applied to the paper. Towards that end, in some preferred embodiments, the expanding force is applied by having an operator grasp a forward end of the length LL with the operator's hands HH and pulling the length LL along the longitudinal direction MD (also referred to herein as the machine direction) which extends parallel to the plane of the extensible slit sheet material. In this manner, in the illustrative embodiment shown in <FIG>, a force will be applied to the sheet in the direction MD due to the opposing forces of pulling by hand and resistance of rotation at the roll <NUM>. Notably, as indicated above, this resistance of rotation can preferably be adjusted by the operator to a desired force via the setscrew <NUM> discussed above. With reference to <FIG>, the machine direction MD is perpendicular to the transverse direction CD (also referred to herein as the cross direction) which extends perpendicular to the longitudinal direction MD along the plane of the extensible slit sheet material. As also shown in <FIG>, the machine direction MD and the cross direction CD are both perpendicular to the thickness direction TD which extends substantially vertically in the illustrated example shown in <FIG>.

<FIG> is an explanatory schematic diagram that helps to describe functionality of the present invention according to some preferred embodiments of the invention. This diagram is for explanatory purposes and should not be construed as restricting or otherwise limiting embodiments of the present invention.

Towards this end, <FIG> is a schematic diagram comparing a hypothetical illustrative background expandable slit sheet product (see left side) with an illustrative and non-limiting exemplary extensible slit sheet product (see right side). In this figure, it should be appreciated that the force axis values illustrated are not an admission of values in the prior art (i.e., the representation of the expandable slit sheet example is not to scale or proportional and does not suggest or imply any particular values). Similarly, the force axis values illustrated should not be improperly construed as limiting any embodiments of the present invention, as such are depicted for illustrative purposes and not by way of limitation.

<FIG> schematically illustrates that with respect to the existing expandable slit sheet paper, the force required to tear the sheet (i.e., Tear Force shown at the left side of the figure) is substantially lower than the force required to tear a sheet (i.e. Tear Force shown at the right side of the figure) of an extensible slit sheet paper according to some illustrative embodiments of the invention. On the other hand, <FIG> also schematically illustrates that that with respect to the existing expandable slit sheet paper, the force required to initially begin to expand or open the slits (i.e., T1 at the left side of the figure) is a) substantially closer to the Tear Force required to tear the expandable slit sheet and b) substantially higher than the force required to initially begin to expand or open the slits (i.e., T1 at the right side of the figure) of an extensible slit sheet paper according to some illustrative embodiments of the present invention.

In addition, <FIG> also schematically illustrates that after the initial opening of the expandable slit sheet example at the point T1 at the left side of the figure, the continued expansion of the slits to a fully expanded state is at a lower force value in the extendable slit sheet example (i.e., T2 at the left side of the figure). Similarly, in this illustrative example, <FIG> also schematically illustrates that after the initial opening of the illustrative extensible slit sheet at the point T1 at the right side of the figure, the continued expansion of the slits to a fully expanded state is at a lower force value in the extensible slit sheet example (i.e., T2 at the right side of the figure). However, <FIG> illustrates that the range between the values T1 and T2 of the extensible slit sheet example is substantially narrower than the range between the values T1 and T2 of the extendable slit sheet shown in <FIG>.

Among other things, <FIG> helps to highlight a number of substantial advantages that can be achieved in some illustrative and non-limiting embodiments of the present invention. First, the use of the extensible slit sheet material substantially lowers the Tear Force that leads to failure of the sheet. Among other things, this means that in some embodiments the sheet can be readily expanded manually by a user with less risk of inadvertently tearing the sheet. Second, the use of the extensible slit sheet material substantially lowers the initial force T1 required to initiate opening which renders expansion of the slit sheet material to be substantially facilitated, which, e.g., also facilitates manual expansion. Third, the narrowing of the values between T1 and T2 in the extensible slit sheet example facilitates control and operation by, e.g., requiring a more consistent force during the range of opening of the slits from T1 to T2 in the extensible slit sheet example, which, e.g., also facilitates manual expansion.

Fourth, the increased Tear Force of the extensible slit sheet example also leads to other substantial advantages that facilitate use and operation, such as, e.g., in manual examples. By way of example, the increased Tear Force of the extensible slit sheet example facilitates manual grasping of the paper (e.g., as shown in <FIG>) with reduced risk of tearing of the sheet in some embodiments (e.g., a user can be more flexible in how the paper is grasped without as substantial worry about causing the paper to tear, such as e.g., grasping with paper with one hand or otherwise varying one's grasp). By way of another example, after the extensible slit sheet paper is fully expanded, there is a lower risk of inadvertently causing the expanded paper to tear by further pulling. As a result, the use of the extensible paper in an extensible slit sheet example can have a number of substantial advantages over prior expanded slit sheet products.

In some illustrative and non-limiting extensible slit sheet embodiments, the force value T1 is substantially closer to the force value T2 such that the force applied throughout expanding of the slits from closed to fully opened hexagons is substantially more consistent during the entire range of expansion. In some illustrative and non-limiting examples, the force T1 is less than <NUM> times the force T2; in other illustrative embodiments, the force T1 is less than <NUM> times the force T2; in other illustrative embodiments, the force T1 is less than <NUM> times the force T2; in some other illustrative embodiments, the force T1 is approximately equal to the force T2.

It should also be appreciated that the force T2 represents the force required to reach a fully opened state of the cells in the paper, and that the force from initial opening at T1 to full opening at T2 may vary slightly in some embodiments. In many exemplary embodiments, the force would initially be greatest at T1 and lowest at T2. Thus, the force through the entire opening to achieve full expansion can be maintained within such ratios in some exemplary embodiments. In addition, in some embodiments the force between T1 to T2 (at the end of fully opening) may be lower than T2. However, in some illustrative embodiments the entire breadth of forces (e.g., closeness of values and ratios between maximums and minimums) required from initial opening to achieving full expansion would fall within such ranges described above. It should be understood that these are illustrative embodiments and do not limit other embodiments with different force ratios.

Heavy-duty Clupak paper having a basis weight of <NUM>/m2 was made using a gap-former paper-making machine equipped with a Clupak system, at a paper-making speed of <NUM>/min and using, as material, <NUM>% unbleached softwood Kraft pulp that had been beaten at high concentration of <NUM>%. The negative draw on the Clupak was set to -<NUM>%.

Heavy-duty Clupak paper was made in the same manner as in Example <NUM>, except that the paper had a basis weight of <NUM>/m<NUM> and the negative draw on the Clupak was set to -<NUM>%.

Heavy-duty Clupak paper was made in the same manner as in Example <NUM>, except that the paper had a basis weight of <NUM>/m<NUM>, the negative draw on the Clupak was set to -<NUM>%, and the pulp blend consisted of <NUM>% unbleached softwood Kraft pulp and <NUM>% unbleached hardwood Kraft pulp.

Heavy-duty Kraft paper was made in the same manner as in Example <NUM>, except that the paper had a basis weight of <NUM>/m2 and the Clupak process was not performed.

Measured by the method specified in JIS P8113: <NUM>.

Measured by the method specified in JIS P8116: <NUM>.

Measured by the method specified in JIS P8112: <NUM>.

Measured by the method specified in ISO/DIS <NUM>-<NUM>.

Measured by the method specified in JIS P8220: <NUM> and JIS P8121: <NUM>.

Looking at the properties of the Clupak papers in Examples <NUM> to <NUM> and Comparative Examples <NUM> and <NUM> as well as those of the Kraft paper in Comparative Example <NUM>, as shown in Table <NUM>, the Clupak papers described in Examples <NUM> to <NUM> exhibit a good balance of various strengths and elongation and have excellent strength overall; on the other hand, the Clupak papers described in Comparative Examples <NUM> and <NUM> and Kraft paper described in Comparative Example <NUM> exhibit a poor balance of various strengths and elongation and cannot be said to have excellent strength overall.

The following are Citations from "<NPL>):
Tensile strength and extensibility or stretch are two important failure properties of paper. They are defined by the end-point of the sheet's load-elongation curve (<FIG>). Individually and together, they are important for many product performance properties. For example, TEA, the tensile energy absorbed by the sheet before failure is proportional to the area under the load-elongation curve. Thus, it depends on both the tensile strength and extensibility of the sheet. A high TEA is desired in sack papers [<NUM>]. The bursting strength of paper has been shown to be proportional to the product of tensile strength and the square-root of stretch [<NUM>]. The fracture toughness of paper has been found to depend strongly on the sheet's tensile strength and stretch [<NUM>, <NUM>]. Sheet stretch has also been regarded as important for paper runnability both at the paper machine's dry-end and in the pressroom [<NUM>-<NUM>]. Papers with high stretch also seem to have a somewhat higher tearing resistance [<NUM>], and folding endurance; they are found to be more dimensionally unstable as well [<NUM>]. The factors that control sheet tensile strength are fairly well understood [<NUM>]. The tensile strength is high if fibres are strong, long, fine and thin-walled. The fibres should be conformable and have a high fibre-fibre bond strength. The sheet tensile strength is also high if fibres are straight, free from deformations and the sheets are well formed. Otherwise, the stress is unevenly distributed when the sheet is strained, leading to premature failure.

This report deals with the factors that control sheet stretch.

A specimen under tensile load extends more, the longer it is. Therefore, extensibility or stretch or strain at failure as a material property, is expressed as a percentage of the original specimen length (<FIG>).

Regardless of how bonding between the fibres is increased -- by wet pressing, beating or refining, or additives, the sheet stretch of a furnish generally increases with increased fibre-fibre bonding. This is observed for almost all papermaking fibreschemical, mechanical, wood, non-wood, or recycled. The reasons are as follows. Fibres have a certain "stretch-potential". However, this potential is realized in paper only when fibres form a bonded network. If the bonding is weak, the network fails before the stretch-potential is realized; the sheet stretch is low. As bonding in the network is increased, the stretch-potential of fibres is increasingly realized, the sheet stretch increases. Since increased inter-fibre bonding also increases sheet tensile strength, an increase in stretch with tensile strength is often observed for handsheets (<FIG>). The stronger the sheet, the more the fibres' stretch-potential is utilized. Because of this relationship between tensile strength and stretch, factors such as sheet grammage or formation that tend to affect tensile strength also affect sheet stretch [<NUM>]. A comparison of handsheet stretch values at similar tensile strengths provides a meaningful comparison of the stretch-potential of various furnishes.

Extensible paper is a known paper which, because of special treatment during its production, presents considerable extensibility both in the longitudinal direction (i.e. in the direction of its advancement along the production line) and in the transverse direction (i.e. in the direction perpendicular to the preceding). This treatment consists essentially of passing the paper web not yet formed and presenting a moisture content of about <NUM>%/<NUM>% between two rollers rotating at different speeds. One of these rollers, generally the lower roller, is made of rubber and is rotated at lower speed, while the upper roller is made of steel and comprises in its cylindrical surface a continuous spiral-shaped groove. The different material nature and the different speed of the two rollers results in a sort of longitudinal accumulation of the paper forming material and prepares it for longitudinal extensibility, by an amount which can reach <NUM>-<NUM>%. At the same time, the spiral groove performs a double function: on the one hand it causes a sort of transverse accumulation of the material forming the paper to prepare it for transverse extensibility. By an amount which can reach <NUM>-<NUM>%. On the other band the spiral groove contributes to maintaining longitudinal advancement of the processed paper web along the machine.

The tensile test is used for measuring force versus percent elongation properties. The tests are performed on a Thwing Albert Intellect II-STD Model No. <NUM>-24PGB, available from the Thwing-Albert Co. of Philadelphia, Pa.

The samples used for this test are <NUM> (<NUM> ") wide x <NUM> (<NUM>") long with the long axis of the sample cut parallel to the direction of maximum extensibility of the sample. The sample should be cut With a sharp Exacto knife or some suitably sharp cutting device design to cut a precise <NUM> (<NUM>") wide sample. (If there is more than one direction of extensibility of the material, samples should be taken parallel to representative direction of elongation). The sample should be cut so that an area representative of the symmetry of the overall pattern of the deformed region is represented. There will be cases (due to variations in either the size of the deformed portion or the relative geometries of regions <NUM> and <NUM>) in which it will be necessary to cut either larger or smaller samples than is suggested herein. In this case, it is very important to note (along with any data reported) the size of the sample, which area of the deformed region it was taken from and preferably include a schematic of the representative area used for the sample. Three samples of a given material are tested.

The test and characterization procedures employed in measuring various properties reported herein are listed in Table I below. Unless otherwise indicated the code letter numerals indicate standard TAPPI tests.

By the expression "extensible papers" is meant a paper having an increased elongation (generally a minimum of about <NUM>%) in the machine direction.

In runs IA and IB of this example, rosin size (<NUM>% by weight based on the weight of pl up) is added at the beater and the pH is adjusted to <NUM> with alum. The stock, having a consistency of <NUM>% is dropped to the beater chest and is then pumped to a second chest, passed through a Jordan and continuously diluted with "white water" at the Fourdrinier headbox to a consistency of <NUM>%. Properties measured on the various papers is reported in Table III. Each paper has a basis weight of from <NUM> to <NUM> (<NUM> to <NUM> pounds) per ream.

These and other objects which will be apparent from the ensuing description are attained according to the invention by a multilayer papery material comprising at least one first three dimensional structure sheet exhibiting reliefs having maximum sizes which are lower than the width of the original sheet, said reliefs being obtained through localized stretching of said first sheet which has an original degree of extensibility of not less than <NUM>% in all the directions, and at least one second sheet made of papery material coupled to said first structure sheet and defining empty spaces with the reliefs thereof.

As it can be seen from the figures, in the embodiment shown in <FIG> the multilayer material of the invention consists of two layers <NUM>, <NUM> of paper presenting extensibility characteristics of not less than <NUM>% both in a longitudinal and in a transverse direction, and preferably not less than <NUM>%.

Claim 1:
An extensible slit sheet paper product for wrapping and cushioning an object, said slit sheet paper having a slit pattern that forms open cells upon expansion of said paper product, said paper product further being extensible and having an extensible range as measured on unslit paper from <NUM>-<NUM>% in a machine direction and <NUM>-<NUM>% in a cross direction.