FOR INCREASING MATTRESS SHAPE STABILITY

Technical Field

5 The present invention relates to a mattress spring core, and more specifically to improvements for stabilizing the shape and size of such a mattress spring core.

Background

Spring core mattresses are a common type of mattresses, where, most often,

10 coil springs are arranged in fabric material pockets forming elongated strings comprising a plurality of interconnected spring pockets. The strings are then arranged side by side thereby providing a mattress with individual springs being held together by the fabric normally made from a nonwoven material. As the techniques for manufacturing mattresses improve, customers have come to expect ever improving

15 performance from new mattresses which are made available on the market. For instance, mattresses are available with zones having varying stiffness to suit the needs of different users.

To provide a mattress having an improved shape and size stability, mattresses are commonly designed with a frame or other type of reinforcement around the edges of

20 the mattress. One known example of such frames is for instance a foam box construction, where a polyurethane frame is used to reinforce the edges. Another example is a steel frame construction where a metal rail is stapled to the coil springs. The use of such reinforcements provide shape stability when the mattress spring core is arranged in a mattress cover, as the reinforcement will urge the mattress spring core

25 towards the corners. The rectangular shape of the mattress spring core is thus maintained due to the reinforcement. However, these solutions comprise non- sustainable materials and additional components which complicates recycling and production. A further drawback with the foam box construction and the steel frame construction is that both of them require manual handling in the production, which

30 makes them costly.

To reduce cost during transport and storage of the mattress, it is preferred that the mattresses can be vacuum pressed. To further reduce cost, it is also preferred that the vacuum pressed mattress can be rolled up. Thereby each mattress will require much less space during transport and storage, before it reaches the customers. However,

35 especially when producing mattresses with the above-mentioned steel frame, the mattress cannot be vacuum pressed and rolled up for storage and transport without damaging the frame.

An improved shape and size stable mattress is therefore sought after, which provides improved performance at a lower cost, which allows for vacuum and roll packaging and which is more environmentally friendly. Especially, it would be desired to provide an improved mattress spring core with the above-listed advantages and which is capable of allowing a rectangular shape when the mattress spring core is arranged in a mattress cover.

Summary

It is an object of the invention to at least partly overcome one or more of the above-identified limitations of the prior art. In particular, it is an object to provide a mattress which costs less to produce, a method for manufacturing the mattress, and a machine configured to perform the method for manufacturing the mattress.

According to one aspect of the invention a mattress spring core is provided. The mattress spring core comprises a plurality of spring pockets arranged in longitudinal columns and transverse rows, wherein at least one comer spring pocket projects longitudinally from an adjacent column end spring pocket.

Preferably the longitudinal columns are extending in the intended head-to-toe direction of a person using the mattress.

The spring pockets may be arranged in a plurality of parallel central spring strings forming a rectangular central part, and in at least two outermost spring strings arranged on opposite sides of the central spring strings. Preferably, the outermost spring strings are arranged immediately next to the rectangular central part. Further, it is preferred that the central spring strings of the rectangular central part all have the same length and/or the same number of spring pockets.

At least one of the outermost spring strings is longitudinally displaced relative the central spring strings. This provides an efficient means for ensuring the longitudinal projection of the corner spring pocket. Preferably, each outermost spring string comprises one additional spring pocket as compared to the central spring strings. In such embodiment each end spring pocket of the outermost spring string will protrude longitudinally by half a spring pocket from the end spring pockets of the central spring strings. A width of the spring pockets of the outermost spring string may be smaller or greater than the width of the spring pockets in a central spring string. Different firmness of different areas of the mattress may thus be achieved.

The spring strings may be attached to each other side by side by means of an adhesive, preferably a hot melt adhesive, or by ultra-sonic welding. This further ensures size stability of the mattress spring core.

The spring pockets of each central spring strings may be aligned centre-to- centre with the spring pockets of each adjacent central spring string. The central spring strings will thereby form a perfectly rectangular shape, thereby allowing for a linear head and foot edges of the mattress spring core.

The central spring strings may comprise fewer spring pockets than the outermost spring strings, preferably each of said central spring strings comprises one spring pocket less than each of the outermost spring strings. The outermost spring strings can then be arranged in an overlap configuration with the central spring strings, ensuring the longitudinal projection of the corner spring pockets.

Preferably, the spring pockets of each outermost spring string are aligned off centre with the spring pockets of each adjacent central spring string. The outermost spring pockets can thus be fit inside a cavity formed by the distance between adjacent central spring pockets, which thereby assists in maintaining the longitudinal position of the outermost spring pockets.

The corner spring pockets may project longitudinally by at least one third of a spring pocket width, preferably said corner spring pockets project longitudinally by half of the spring pocket width. This has proven to provide effective comer filling when the mattress spring core is arranged in a mattress cover, thereby ensuring a rectangular shape of the mattress with well-defined corners.

The plurality of spring pockets may have the same width or diameter. This facilitates manufacturing and production of the mattress spring core.

The mattress spring core may comprise four corner spring pockets, each projecting longitudinally from an adjacent column end spring pocket. Each corner of the rectangular mattress spring core will thus fill out the corner of an associated mattress cover.

The mattress spring core may comprise eight corner spring pockets arranged in pairs, wherein each pair of spring pockets project longitudinally from an adjacent column end spring pocket. Hence, each comer of the mattress spring core will have two comer spring pockets. The mattress spring core may comprise one or more layers of spring pockets, preferably one or two layers of spring pockets. It is thus possible to produce mattress spring cores of different properties and behaviour, still benefiting of shape stability and well-defined corners.

A fabric material of the spring pocket may be a nonwoven fabric material comprising thermoplastic material.

A spring constant of the spring of the corner spring pocket may be higher than a spring constant of the spring of the adjacent column end spring pocket.

According to a second aspect, a mattress is provided. The mattress comprises the mattress spring core according to the first aspect, and a mattress cover enclosing said mattress spring core.

According to a third aspect, a method for manufacturing a mattress spring core is provided. The method comprises the step of providing a plurality of spring pockets arranged in longitudinal columns and transverse rows, and arranging at least one comer spring pocket such that it projects longitudinally from an adjacent column end spring pocket.

Further objects and advantages of the present invention will be obvious to a person skilled in the art when reading the detailed description below of different embodiments.

Brief Description of the Drawings

The present invention will be described further below by way of example and with reference to the enclosed drawings. In the drawings:

Fig. la is a top view of the mattress spring core according to one embodiment;

Fig. lb is a top view of a mattress spring core according to another embodiment;

Fig. 2 is an enlarged portion of a portion of a spring string comprised in said mattress spring core;

Fig. 3 is a cross-sectional view of a plurality of spring pockets of a spring string;

Fig. 4 is a perspective view of a mattress, including a mattress spring core according to one embodiment; and

Fig. 5 is a flowchart showing a method of producing a mattress spring pocket.

Detailed Description of Embodiments In the following a mattress spring core will be described, as well as a mattress having such mattress spring core, and a method for producing the mattress spring core. As used in this description the expression “longitudinal” refers to the direction of the length of the mattress, i.e. the normal feet-to-head direction of a person lying on the mattress comprising the mattress spring core. The expression “transverse” refers to the direction of the width of the mattress spring core. The longitudinal and transverse directions are consequently perpendicular to each other.

Preferably, the mattress spring core has a substantially rectangular form as seen from above (shown in Figs, la-b and 4). Thus, the length of the mattress spring core corresponds to the longer sides of the rectangle and the width of the mattress spring core corresponds to the shorter sides of the rectangle. It is for instance common to have mattresses with a length of 200 cm and a width of 90 cm, as one example only. The terms “upper” and “lower” are used to define the normal position of the mattress, i.e. having an upper side onto which the person using the mattress is intended to rest upon, and a lower side forming the underside of the mattress during normal use.

Fig. la shows a mattress spring core 1 as seen from above. The mattress spring core 1 comprises a plurality of spring pockets 8 arranged in longitudinal columns and transverse rows. The spring pockets 8 are preferably distributed in a plurality of longitudinally extending spring strings 3, 4.

The spring strings 3,4 are arranged side by side, which together form the mattress spring core 1. The spring strings 3,4 are central spring strings 3 or outermost spring strings 4. The two outermost spring strings 4 are arranged along the outer longitudinal edge of the mattress spring core 1, on an external side of the last central spring strings 3. The outermost spring strings 4 are in direct contact, or immediately next to, the central spring strings 3.

As can be seen in Fig. lb, another embodiment of a mattress spring core 1 is shown where two outermost spring strings 4 are arranged on each side of the central spring strings 3. Also in this embodiment the inner ones of the outermost spring strings 4 are in direct contact, or immediately next to, the central spring strings 3.

Referring to both Fig. la and Fig. lb, each spring string 3,4 comprises a fabric material 6 forming pockets or cavities configured to hold springs 7 (see Fig. 3). Hence, a spring pocket 8 comprises a spring 7 and a fabric material 6 enclosing the spring 7. The fabric material 6 may e.g. be a nonwoven fabric material, preferably a material comprising thermoplastic material or another material which is suitable for ultrasonic welding or friction welding. The springs 7 are preferably coil springs (as shown in Fig. 3), but other spring types are also conceivable.

In the embodiment of Fig. la the mattress spring core 1 comprises four corner spring pockets 8’. In the embodiment of Fig. lb the mattress spring core 1 comprises eight corner spring pockets 8’.

These corner spring pockets 8’ are the end spring pockets of the outermost spring strings 4. The last central spring strings 3 have end spring pockets 8”, arranged adjacent to the comer spring pockets 8”. As will be explained further in the following, the corner spring pockets 8’ project longitudinally relative the adjacent end spring pockets 8”.

With reference to Fig. 2, an enlarged portion of a spring string 3,4 is shown. The spring pockets 8 are made from the fabric material 6, and are separated from each other by a welded edge seam 10, formed when manufacturing the spring pockets 8. The portion of the spring string 2 in Fig. 2 comprises two spring pockets 8, each having a diameter or width WSP.

As shown in Fig. la and Fig. lb each central spring string 3 is arranged as an array of spring pockets 8, where the central spring strings 3 are aligned in both the transversal and the longitudinal direction such that adjacent spring pockets 8 are aligned centre-to-centre. Together, the central spring springs 3 are connected to each other form a central part 30 of the mattress spring core 1. The central part 30 has a rectangular shape. However, in other embodiments of the disclosed mattress spring core 1, the central part 30 may have a square or more elongate shape than shown in Fig. la and Fig. lb.

As opposed to the central spring strings 3, the outermost spring strings 4 are not centre-to-centre aligned with respect to the central spring strings 3. This achieves protruding corners on the mattress spring core 1 by means of the corner spring pockets 8’.

The outermost spring strings 4 in Fig. la and Fig. lb are all arranged offset in the longitudinal direction with respect to the central spring strings 3. The displacement of the outermost spring strings 4 is about half a spring pocket 8, i.e. half a width WSP of the spring pocket 8. Therefore, as shown in Fig. la and Fig. lb, each corner spring pocket 8’ project by approximately a half spring pocket width WSP from the short, or longitudinal end of the central part 30 of the mattress spring core 1. Hence, the outer spring strings 4 comprise one additional spring pocket 8 compared to the central spring strings 3. The arrangement of the outer spring strings 4 as described above creates additional material at the comers and thus minimizes the space which otherwise may exist between the corners of the mattress spring core 1 and an internal corners of a mattress cover. Therefore, the problem of collapsing mattress corners is mitigated and prevented. A size and shape stable mattress spring core 1 is achieved by the addition of one extra half spring in each corner of the mattress spring core 1.

Furthermore, the concept of using longer and offset outermost spring strings 4 as disclosed herein enables an automated production, since the outermost spring strings 4 may be manufactured in the same way and by the same materials as the central spring strings 3.

Moreover, the mattress spring core 1 disclosed herein provides a more sustainable solution against collapsing mattress corners, since less and/or more sustainable materials are used compared to the use of a supporting metal rail or the use of stuffed polyurethane foam glued to the spring coil, which are common methods used in the art today.

In addition, the solution presented herein provides a less labour intense manufacturing process, since the solution enables a lean and automated production. The mattress spring core 1 comprising the outermost spring strings 4 with corner edge spring pockets 8’ is formed directly during the production of the mattress spring core 1 as such.

Further, the mattress spring core 1 may be produced with varying sizes since the reinforcement for the mattress comers merely comprises displacement of the outermost spring strings 4 in relation to the central spring strings 3. A metal rail frame embedding the edges of a mattress spring core, on the other hand, would need to be manufactured specifically for each mattress size.

A further effect of the mattress spring core 1 as disclosed herein, is that the mattress spring core 1, and later a mattress 20 (see Fig. 4) comprising the mattress spring core 1, can be packed by vacuum pressing and roll-up for space savings and easier transports.

Also, the stiffness and/or softness and zones of different stiffness/softness of the mattress spring core 1 can easily be adjusted during the manufacturing process since the resilience of the springs 7 within a central or outermost spring string 3, 4 may be altered during manufacturing, or the resilience of the strings 7 in the central spring strings 3 and the outermost spring strings 4 can be different. Alternatively, the central part 30 is formed by central spring strings 3 having springs 7 of various resilience. Optionally, the diameter of the spring pockets 8 may vary between the outermost spring strings 4 and the central spring strings 3, such that the width WSP of the spring pockets 8 of the central spring strings 3 is smaller than the width WSP of the spring pockets 8 of the outermost spring strings 4, or such that the width WSP of the spring pockets 8 of the outermost spring strings 4 is smaller than the width WSP of the spring pockets 8 of the central spring strings 3.

In Fig. la and Fig. lb, a spring string 3,4 forms one column of the mattress spring core 1. The spring strings 3,4 have a longitudinal extension along the length of the mattress spring core 1. In other embodiments, the spring strings 3,4 may be arranged in a transverse direction, extending along the short or longitudinal sides of the mattress spring core 1.

The spring strings 3,4 may be attached to each other by means of an adhesive, such as a hot melt adhesive, by sewing, or by stapling. Other adhesives are also feasible, as well as other feasible fastening techniques known in the art.

Further, the spring constant of the springs 7 may vary and the mattress spring core 1 may comprise reference springs and stiffer springs compared to reference springs comprised in the mattress spring core 1. For instance, the stiffer springs have a spring constant in the range of 15% to 30%, more specifically 20% to 25%, and preferably approximately 25% higher than the reference springs. In addition, the diameter of the springs 7 can be of varying size.

An increased spring constant can be achieved for instance by increasing the wire gauge of the springs 7. An exemplary diameter for stiffer frame springs may be approximately 1.9 mm whilst reference springs may have a diameter of approximately 1.7 mm.

Alternatively, an increase in spring constant of the springs 7 could be achieved by removing one convolution on each of the springs 7. The exact use of stiffer springs can of course be varied; in one embodiment each of the outermost spring strings 4 comprises stiffer springs 7 than the central spring strings 3. Optionally, the comer spring pockets 8’ are enclosing stiffer springs 7 than the remaining spring pockets 8 of the mattress spring core 1.

In Fig. la and Fig. lb, the mattress spring core 1 is comprised of a monolayer of spring strings 3,4. It is to be realized that combinations of several layers of spring strings 3,4, such as two, three or four layers, are also feasible to form a mattress spring core 1. In such case, additional combinations of springs 7 having varying stiffness and/or diameter is possible. For instance, when combining two layers of spring strings 2, three outermost rows can be made of stiffer frame springs in the upper and/or the lower layer along the longitudinal edges of the mattress spring core 1 and two outermost rows of stiffer frame springs in the upper and/or the lower layer along the transversal edges.

Each spring string 3,4 may comprise between 8 and 30, such as between 12 and 16 spring pockets 8 per meter. In one particular embodiment each spring string 3, 4 comprises 25 spring pockets 8 per two meters, i.e. 12.5 spring pockets 8 per meter. A mattress spring core 1 of a typical length of 200 cm may for example comprise between 16 and 60, preferably between 20 and 32 spring pockets 8 in the longitudinal direction. Hence, if the spring strings 2 are arranged in a transverse direction, along the short edge of the mattress spring core 1, each spring string 3,4 comprises fewer spring pockets 8 than when the spring strings 3,4 are arranged along the length of the mattress spring core 1.

Each spring string 3,4 is attached by means of an adhesive, preferably hot melt adhesive, side by side to another spring string 3,4. Between 10 to 25 spring strings 3,4, preferably approximately 13 to 15 spring strings 3,4 (as shown in Fig. la) together form a mattress spring core 1 with a width of 90 cm. However, fewer or more spring strings 3,4 may be used to decrease or increase the width of the mattress spring core 1, or to decrease or increase the length of the mattress spring core 1 if the spring strings 3,4 are arranged along the width of the mattress spring core 1 (as opposed to the extension direction of the spring strings 3,4 shown in Fig. la and Fig. lb).

In Fig. 3 a cross-sectional view taken from the side of a part of a mattress spring core 1 is shown. The mattress spring core 1 has a number of spring pockets 8 enclosing respective springs 7. Although shown as barrel-shaped, the springs 7 may have other configurations. The mattress spring core 1 further has a foam cover 11 arranged on top of the spring pockets 8. The foam cover 11 further stabilizes the rectangular shape of the mattress spring core 1. While many different materials and dimensions for the foam cover 11 may be considered, in one embodiment the foam cover 11 is made of polyurethane foam at a density of 20-30 kg/m3. The thickness of the foam cover 11 may be in the range of 1-25 cm, such as in the range of 3-10 cm.

Now turning to Fig. 4, a mattress 20 is shown. The mattress 20 comprises a mattress spring core 1, a foam cover 11, and a mattress cover 22. The mattress cover 22 may e.g. comprise waddings, linings, and tickings, as is well known in the art. Preferably, the mattress cover 22 is robust enough to maintain the size and shape of the mattress spring core 1. It should be noted that the foam cover 11, as well has the mattress cover 22, has been cropped. For a final mattress 20, the foam cover 11 and the mattress cover 22 will cover the entire mattress spring core 1. As has been explained above, the protruding corner spring pockets 8’ of the mattress spring core 1 will fill the interior corners of the mattress cover 22 such that the entire mattress 20 will exhibit a rectangular shape with well-defined corners. For the sake of completeness, also the adjacent end spring pockets 8” are indicated in Fig. 4.

A method 100 for manufacturing a mattress spring core 1 is schematically shown in Fig. 5. The method 100 may comprise a step 102 of providing a plurality of spring pockets 8 arranged in longitudinal columns and transverse rows, and a step 204 of arranging at least one comer spring pocket 8’ such that it projects longitudinally from an adjacent column end spring pocket 8”. The method 100 may further comprise an additional step 106 of arranging the mattress spring core 1 in a mattress cover 22, thereby extending the scope of the method 100 to actually produce a mattress 20.

The spring strings 3, 4 (both the central spring strings 3 and the outermost spring strings 4) may be manufactured according to the following. Each spring 7 is manufactured from a metal wire. Each spring 7 is positioned in a spring pocket 8 made of a fabric material 6 whereafter the spring pockets 8 are sealed, preferably by means of welding.

If the mattress spring core 1 comprises double layers of spring strings simultaneous manufacturing of the springs 7 for an upper layer and a lower layer may be performed, while enabling the alternation of two separate wires with different characteristics for each of the layers of the spring string 3, 4. Each spring string 3,4 can be varied in a large number of ways. For instance, stiffer springs may be placed in the upper layer, the lower layer or in both layers.

To form the mattress spring core 1 the spring strings 3, 4 are preferably cut when a sufficient number of spring pockets 8 are formed, for instance around 25 spring pockets 8 for a typical mattress length of 200 cm.

Further, each spring string 3,4 is attached side by side to another spring string 3, 4 by means of an adhesive, such as a hot melt adhesive.

It is also to be realized that the spring pockets 8 may be partially or completely formed before and/or after the springs 7 are positioned therein. A spring pocket 8 is usually formed by folding an elongate piece of fabric material 6 along its length, and welding the folded fabric material 6 to form a tube. A plurality of springs 7 are arranged within the tube, and welds are provided between the springs. The welding is performed orthogonally with respect to the longitudinal length of the folded fabric material, such that a plurality of connected spring pockets 8 are formed.

Again referring to Fig. 5, the method 100 may be performed by an additional step 108 in which the mattress 20 is vacuum packed and optionally rolled up and wrapped such that a very compact and space-reducing packaging is obtained. Once unpacked, the mattress 20 will return to its desired and planar shape while comer spring pockets 8’ ensures the rectangular shape of the mattress. Optionally, step 108 may be performed directly on the mattress spring core 1. In such embodiment the advantages of the corner spring pockets 8’ are even more evident, as there is no ticking or other additional layers or foam cover to assist in maintaining the desired rectangular shape of the mattress spring core 1.

The present disclosure thus presents a mattress spring core 1 comprising a plurality of spring pockets 8 arranged in longitudinal columns and transverse rows by a plurality of parallel central spring strings of the same length and forming a rectangular central part, and by at least two outermost spring strings arranged on opposite sides of and immediately next to the central spring strings. At least one corner spring pocket 8’ projects longitudinally from an adjacent column end spring pocket 8”.

It should be mentioned that the inventive concept is by no means limited to the embodiments described herein, and several modifications are feasible without departing from the scope of the appended claims. In the claims, the term “comprises/comprising” does not exclude the presence of other elements or steps. Additionally, although individual features may be included in different claims, these may possibly advantageously be combined, and the inclusion in different claims does not imply that a combination of features is not feasible and/or advantageous. In addition, singular references do not exclude a plurality. The terms “a”, “an”, “first”, “second” etc. do not preclude a plurality. Reference signs in the claims are provided merely as a clarifying example and shall not be construed as limiting the scope of the claims in any way.