Field of Invention

This invention is related to reoriented polyolefin foamed sheets production, particularly semi-finished products (core sheets) for following sandwich boards manufacturing during which surface top layer ensuring reinforcement and/or protection against physical and chemical external effects and/or decorative function is laminated from both sides perpendicular to thickness direction.

Current State of the Art

Generally, extruded polyolefin foam physically expanded by butane, propane, freon or CO2 in the form of film or square/rectangular profile has significantly higher compressive strength and modulus in the lengthwise (i.e. extrusion) direction than in the widthwise or thicknesswise directions. This is commonly used fact especially for multilayer lightweight sandwich boards which are composed of foamed core sheets with extrusion direction perpendicular to outer covering layers of final multilayer board.

Typical example of this technical solution is Chinese utility model CN216300437 focused on high strength polyethylene terephthalate (PET) composite boards containing core sheet made of PET foam transversely cut from PET sheet. Top frontal side of this core sheet is bonded by top hot melt layer to top layer made of nonwoven textile and further foamed sheet and finally covering surface layer is bonded to it. Bottom side of the core sheet is bonded to bottom side of nonwoven textile and further foamed sheet and finally covering surface layer is bonded to it. Covering surface layer can be film resistant to weather effects, ultraviolet light etc. Due to this fact, whole composite board is resistant to these effects. Aging resistance can be further adjusted according to specific requirements. Composite board is produced from PET materials, and due to thermal bonding of composite structure it is not susceptible to damage. However, this particular Chinese utility model as well as other openly published documents focused on similar topic have not in more detail described and thus technologically optimized method of core sheet production with extrusion direction perpendicular to outer covering layers of final the multilayer board. Summary of the Invention

Above mentioned lack can be to as great extend overcome by reoriented foamed polyolefin sheets production method according to this invention. Its basic principle consists of: aa) continual extrusion or unwind of square or rectangular lengthwise oriented and calibrated polyolefin foamed profile with thickness of 5 to 200 mm, width of 100 to 400 mm and density of 30 to 300 kg/m ³ followed by transverse cut on blanks with length of 400 to 4000 mm, ab) continual feeding of lengthwise oriented polyolefin foamed sheets with thickness of 5 to 1250 mm, width of 100 to 2600 mm, length of 400 to 4000 mm and density of 30 to 300 kg/m ³ beforehand prepared by longitudinal bonding from more elements unequivocally in direction of lengthwise orientation, ac) continual extrusion or unwind of lengthwise oriented and calibrated polyolefin foamed strip with thickness of 1 to 100 mm, width of 100 to 2600 mm and density of 30 to 300 kg/m ³ followed by transverse cut on parts with length of 400 to 4000 mm, b) blanks or sheets planar bonded by welding with the aid of residual heat from extrusion or gluing from which block with thickness of 10 to 3000 mm consisting of 2 to 200 layers of original blanks of foamed profile, strip or sheet is gradually created, c) block obtained in this way is after possible side alignment from top and other sides transversely cut on sheets with thickness of 2 to 500 mm with that da) these sheets after cut of longitudinal edges on final width of 100 to 2600 mm represents finished sheets with reoriented structure or db) in the case when side alignment of the block is not performed, these sheets are after trimming of contact edges bonded together by welding or gluing in transverse direction into infinite sheet which is then cut to individual sheets of final length of 100 to 15000 mm which after cut of longitudinal edges on final width of 100 to 2600 mm represents finished board with reoriented structure.

Planar bonding of the blanks is with benefit realized by thermo contact (fusion) heating or hot air welding or infrared welding or gluing.

Transverse cut of final block is with benefit performed by resistance wire, band saw or high-speed wire.

Contact edges of the sheets before bonding are trimmed by cutting or milling. Bonding of trimmed sheets is then with benefit performed by thermo contact (fusion) heating or hot air welding or infrared welding or gluing. Extruded physically foamed polyolefin (e.g. polypropylene) foam expanded by butane, propane, freon or CO2 in the form of film or square profile or rectangular profile can be during extrusion or just after extrusion oriented in extrusion direction.

During this orientation under higher temperature and force foamed cell is elongated in one direction and thus, cells are oriented into elongated shape. After orientation is performed, this oriented state is immediately fixed by cooling of the oriented foam.

Simplified interpretation of orientation principle is depicted in Fig. la-c. In Fig. la dimensional changes of foamed structure element in orientation direction (most often lengthwise, i.e. orientation in extrusion direction) is shown. In Fig. lb horizontal cut of discrete foamed structure cell model before and after orientation is depicted. Hereby oriented foam has significantly higher compression strength and compression modulus in direction of orientation than in other two directions (2 directions perpendicular to direction of orientation) - see scheme of discrete cell model after orientation process shown in Fig. 1c where polypropylene foam oriented in this way has mechanical parameters specified in Fig. 1c.

Compression strength and modulus in thicknesswise direction of this oriented foam can in the next step consist of additional reorientation process of the foam according to this invention significantly increase. Dependence of compression strength and compression modulus on foam density for polypropylene foam in the orientation direction is depicted in Fig. 2 and Fig. 3, respectively.

This reorientation process can be applied immediately after previous orientation process from still uncooled foam or additionally from cooled foam wound into a coil or cut. It is also possible to process foams produced in advance in the form of boards combined from several elements of foam that have undergone an orientation process (typically, for example, boards prepared by welding several layers of foam polypropylene strip on top of each other or boards prepared by welding several rectangular profiles of foamed polyolefin next to each other).

Reoriented boards from foamed polyolefin with a width of 100 to 2600 mm, length of 100 to 15000 mm and thickness of 2 to 500 mm can be prepared by below mentioned manners. These boards can have density of 30 to 300 kg/m ³ .

Reoriented boards made of foamed polyolefin (e.g. polypropylene) produced by mentioned variants of the method according to the invention are primarily intended for the production of sandwich boards laminated on both sides perpendicular to thickness direction (i.e. to the direction of orientation) with a surface layer that has a reinforcing function and/or protective function against physical and chemical external influences and/or decorative function.

Depending on the method of use, reoriented plates made of foamed polypropylene have a temperature of use between -40 to 140 °C and a processing temperature of up to 155 °C. They are characterized by chemical resistance, high resistance to moisture, high non-absorption, good thermal insulation properties, high impact strength and high resistance to fatigue stress.

Reoriented boards made of foamed polyolefin can be designed with increased resistance to UV radiation.

Reoriented boards made of foamed polyolefin can also be designed with increased fire resistance.

By using reoriented boards made of foamed polyolefin with suitable surface layers, significant weight savings in comparison to conventional board types can be achieved.

Furthermore, by using reoriented boards made of foamed polyolefin with suitable surface layers and binders, a significantly lower weight of the resulting sandwich boards can be achieved in comparison with commonly used wood boards and chipboards at similar strength and stiffness.

Brief Description of Drawings

The attached drawings used to clarify the principle of the invention in more detail are following:

Fig. la: schematic representation of the dimensional changes of the foamed structure element in the orientation direction,

Fig. lb: longitudinal section view of the discrete cell model of the foamed structure before and after orientation

Fig. 1c: schematic representation of mechanical parameters during loading of a discrete cell model of oriented foamed structure of polypropylene foam

Fig. 2: dependence of compression strength on foam density of polypropylene foam in the direction of orientation during compression,

Fig. 3: dependence of compression modulus on foam density of polypropylene foam in the direction of orientation during compression,

Fig. 4: technological scheme of the method according to the invention in the variant of reorientation by layering an endless foamed polyolefin strip into a block followed by transverse cutting and joining into the required format, Fig. 5a: technological scheme of the method according to the invention in the variant of reorientation by layering plates of foamed polyolefin into a block followed by transverse cutting and bonding into the required format,

Fig. 5b: schematic representation of the plates used in the reorientation variant according to Fig. 5a.

Fig. 6: technological scheme of the method according to the invention in the variant of reorientation by cyclic layering of foamed polyolefin into a block using residual heat after extrusion followed by transverse cutting and bonding into the required format,

Fig. 7: technological scheme of the method according to the invention in the variant of reorientation with side bonding of foamed polypropylene to the block using residual heat after extrusion followed by transverse cutting and bonding into the required format.

Examples of Invention Realization

Example 1

An exemplary embodiment of the method of manufacturing reoriented foamed polyolefin boards according to the invention, in the variant of reorientation by layering an endless foamed polyolefin strip into a block with subsequent transverse cutting and bonding into the required format is shown by the technological scheme in Fig. 4.

In this variant of the production of reoriented foamed polyolefin (specifically polypropylene) sheets, a strip of lengthwise oriented and calibrated foamed polyolefin with a thickness of 1 to 100 mm, a width of 100 to 2600 mm and a density of 30 to 300 kg/m ³ is continuously extruded or unwound and subsequently it is transversely cut on blanks of length 400 to 4000 mm, which are then welded by thermocontact (fusion) heating or hot air heating or infrared heating or gluing in plane B into a gradually formed block 4 with a thickness of 10 to 3000 mm containing 2 to 500 layers of blanks 3 of the original foamed strip 1.

The block 4_is then laterally aligned, transversely cut C into plates 5 with a thickness of 2 to 500 mm and these plates 5 after trimming D of the contact edges 6_are then bonded E by welding or gluing in the transverse direction to an endless plate 7. The transverse cutting C of the block 4 is performed by a resistance wire, band saw or high-speed wire, side alignment is performed by a resistance wire, band saw or high-speed wire or a milling cutter, trimming D of the contact edges 6 of plates 5 before bonding E is performed by cutting or milling.

The endless plate 7 is subsequently divided F into individual plates 8 of a final length of 100 to 15000 mm which then, after trimming G of the longitudinal edges 9 to a final width of 100 to 2600 mm, represent finished plates 10 with a reoriented structure. Bonding E of the plates 5 with trimmed contact edges 6 is carried out by welding based on thermocontact (fusion) heating or hot air heating or infrared heating or gluing.

Example 2

An exemplary embodiment of the method of manufacturing reoriented foamed polyolefin boards according to the invention in the variant of reorientation by layering boards from foamed polyolefin into a block with subsequent cross-cutting and bonding into the required format is shown by the technological scheme in Fig. 5a.

In this variant of the production of reoriented foamed polyolefin (specifically polypropylene) sheets, lengthwise oriented foamed polyolefin sheets 2 with thickness of 5 to 1250 mm, width of 100 to 2600 mm, length of 400 to 4000 mm and density of 30 to 300 kg/m ³ are continuously fed. These plates 2 are prepared beforehand by the longitudinal bonding of several rectangular elements 2a (1-200 elements in the h direction; 1-200 elements in the w direction) with a cross-sectional area of each element of at least 1000 mm ² with a composition unequivocally in the direction of lengthwise orientation (see Fig. 5b).

The plates 2 are then planar bonded B by welding based on thermocontact (fusion) heating or hot air heating or infrared heating or gluing into a gradually created block 4 with a thickness of 10 to 3000 mm, containing 2 to 500 layers of plates 2.

The block 4 is then laterally aligned, transversely cut C into plates 5 with thickness of 2 to 500 mm, and these plates 5 are after trimming D of the contact edges 6 then bonded E by welding or gluing in the transverse direction to an endless plate 7. The transverse cutting C of the block 4 is performed with a resistance wire, band saw or high-speed wire, side alignment is performed with a resistance wire, band saw or high-speed wire or a milling cutter, trimming D of the contact edges 6 of plates 5 before bonding E is performed by cutting or milling.

The endless plate 7 is subsequently divided F into plates 8 with a final length of 100 to 15000 mm which then, after trimming G of the longitudinal edges 9 to a final width of 100 to 2600 mm, represent finished plates 10 with a reoriented structure. The bonding of the E plates 5 with trimmed contact edges 6 is carried out by welding based on thermocontact (fusion) heating or hot air heating or infrared heating or gluing. Example 3

An exemplary embodiment of the method of manufacturing reoriented foamed polyolefin boards according to the invention in the variant of reorientation by cyclic layering of foamed polyolefin into a block using the residual heat after extrusion with subsequent transverse cutting and bonding into the required format, is shown in the technological scheme in Fig. 6.

In this variant of the production of reoriented foamed polyolefin (specifically polypropylene) sheets, a foamed polyolefin strip 1 with a thickness of 1 to 100 mm, a width of 100 to 1500 mm and a density of 30 to 300 kg/m ³ is continuously extruded and lengthwise oriented, calibrated K and subsequently divided transversely A for blanks 3 with a length of 400 to 4000 mm.

The welding of blanks 3 using the residual heat after extrusion is based on planar bonding B into a gradually created block 4 with a thickness of 10 to 3000 mm, containing 2 to 500 layers of blanks 3 of the original foamed strip 1 during which they are taken from storage conveyor of the extrusion line and cyclic layered by layering applicator Bl to block 4. Hot air or infrared heating B2 is used to warm up the blanks before bonding B.

The block 4 is cooled and then laterally aligned by cutting with a resistance wire, band saw or high-speed wire or milling with a milling cutter, cross-cut C with a resistance wire, band saw or high-speed wire into plates 5 with a thickness of 2 to 500 mm, and these plates 5 are then after trimming D of contact edges 6 trimmed D by cutting or milling and bonded E by welding based on thermocontact (fusion) heating or hot air heating or infrared heating or gluing in the transverse direction to the endless plate 7.

The endless plate 7 is subsequently divided F into plates 8 with a final length of 100 to 15000 mm which then, after trimming G of the longitudinal edges 9 to a final width of 100 to 1500 mm represent finished plates 10 with a reoriented structure.

Example 4

An exemplary embodiment of the method of manufacturing reoriented foamed polyolefin boards according to the invention in the variant of reorientation with lateral bonding of foamed polypropylene to the block using the residual heat after extrusion with subsequent transverse cutting and bonding to the required format is shown in the technological diagram in Fig. 7.

In this version of reoriented foamed polyolefin production (specifically polypropylene) sheets, a rectangular profile 1 of foamed polyolefin with thickness of 5 to 100 mm, width of 50 to 1000 mm and density of 30 to 300 kg/m ³ is continuously extruded and lengthwise oriented, calibrated K and transversely divided A into blanks 3 with a length of 400 to 4000 mm.

The blanks 3 are welded by using residual heat after extrusion and further they are planar bonded B into a gradually created block 4 with thickness of 50 to 1000 mm, containing side by side 2 to 500 layers of blanks 3 of the original foamed profile 1. During this, they are taken from stock conveyor of extrusion line, heated by hot air B2 or infrared heated, positioned and bonded to a continuous block 4a when passing through the input bonding conveyor B3 and compression conveyor B4 which is then cut B6 into individual blocks 4 after cooling on the cooling conveyor B5.

Each of the blocks 4 prepared in this way is then laterally aligned by trimming with a resistance wire, band saw or high-speed wire or by milling with a milling cutter, cross-cut C with a resistance wire, band saw or high-speed wire into plates 5 with thickness of 2 to 500 mm and these plates 5 are after trimming D of contact edges 6 by cutting or milling, bonded E by welding based on thermocontact (fusion) heating or hot air heating or infrared heating or gluing in the transverse direction to an endless plate 7.

The endless plate 7 is subsequently divided F into plates with a final length of 100 to 15000 mm which then, after trimming G of the longitudinal edges 9 to a final width of 100 to 2600 mm, represent finished plates 10 with a reoriented structure.

Example 5

An exemplary embodiment of the method of manufacturing reoriented foamed polyolefin boards according to the invention is a variant of reorientation by layering an endless foamed polyolefin strip into a block followed by cross-cutting and bonding into the required format according to the technological scheme in Fig. 4.

In this variant of the production of reoriented foamed polyolefin (specifically polypropylene) sheets a strip la of lengthwise oriented and calibrated foamed polyolefin with thickness of 1 to 100 mm, width of 100 to 2600 mm and density of 30 to 300 kg/m ³ is continuously extruded or unwound, and subsequently transversely divided into blanks 3 with length of 400 to 4000 mm, which are then planar bonded B by welding based on thermocontact (fusion) heating or hot air heating or infrared heating or gluing into a gradually produced block 4 with a thickness of 10 to 3000 mm, containing 2 to 500 layers of blanks 3 of the original foamed strip 1. Block 4 is then laterally aligned, cross-cut C into plates 5 with thickness of 2 to 500 mm, and contact edges D of these plates are trimmed. Cross-cutting C of block 4 is done with a resistance wire, band saw or high-speed wire, side trimming is done with a resistance wire, a band saw or a high-speed wire or a milling machine, the trimming D of contact edges 6 of the plates 5 is performed by cutting or milling. The bonding E of the plates 5 with the trimmed contact edges 6 is then no longer performed in this variant.

The resulting plates 8 with a final length of 10 to 3000 mm then, after trimming G of the longitudinal edges 9 to a final width of 100 to 2600 mm, represent finished plates 10 with a reoriented structure.

Industrial Applicability

The method of production of reoriented foamed polyolefin boards according to the invention is mainly intended for the preparation of semi-finished products (core boards) for the following production of sandwich boards. In them, core plate is laminated from both sides perpendicular to the thickness direction by a surface layer that has a reinforcing function and/or a protective function against physical and chemical external influences and/or a decorative function corresponding to its specific application.