WO2023275613A1 - Method for generating predetermined break lines in oblong elements in thermoplastic polymers - Google Patents

Abstract

The invention relates to a method for generating predetermined break lines in flat or slab-like or oblong elements made of thermoplastic polymers such as polyester or the like and/or derivatives thereof, said element comprising at least two faces which are opposite to each other and which are spaced apart by a predetermined thickness, and which method involves making a pre-cut by means of a cutting tool wherein said pre-cut is made so as to create a sharp slit while maintaining or generating a glassy phase of the material in the area of the remaining material thickness beyond the sharp end of said pre-cut slit.

Description

Method for generating predetermined break lines in oblong elements in thermoplastic polymers DESCRIPTION -

- INTRODUCTION -

The invention relates to a method for generating predetermined break lines in in flat or slab-like or oblong elements or portions of material, deviating from a rectangular, square, circular, or spherical form by elongation in one dimension, made from where at least one dimension is greater than the others, in thermoplastic polymers such as polyester and the like and/or derivatives thereof.

The invention applies in particular, both to elements such as panel sheets or the like and to oblong elements, such as fibers, or tapes, cables or the like.

International environmental policies are giving strong impetus to ecological transitions of production activities that generate fewer and fewer loads of pollutants on the environment.

Plastics are a critical factor in pollution, and the development trend points toward replacing materials that are difficult to recycle with recyclable materials, possibly to a high degree of circularity of the raw material. Future regulations coming into effect in the next few years will have as their object increasingly stringent restrictions on the use of certain materials that are difficult to dispose of and thus represent a high ecological burden.

One technical field particularly affected, but not the only one, by these future developments is packaging for it is a high plastics consumption sector because of the large amount of waste it generates. This is due both to the fact that packaging pertains to mass-produced products and to the fact that packaging has a very short life span, namely the time from leaving the production site to consumption by the end user.

One plastic material that exhibits characteristics of high recyclability and thus lends itself greatly to avoiding an excessive burden on the environment is polyester or similar and/or derivatives. This material makes it possible to make containers and/or other types of packaging for food use as well. Despite the undoubted qualities of mechanical strength, formability, high transparency, compatibility with food products and high recyclability, this plastic material has some characteristics that make it unsuitable for conditions in which it is necessary to provide predetermined separation lines between adjacent and interconnected parts of the said plastic material along which, thanks to an action, for example, only manual and requiring little force commitment, it is possible to implement the separation. Today's market products need the use of scissors or cutters for the separation, which is uncomfortable and possibly dangerous. This drawback makes the use of virgin and/or recycled polyester as an unattractive alternative material whenever the need for product handling requires the presence of predetermined breaking or sectioning lines and separation along said lines by a purely manual action.

- STATE OF THE ART -

Separation behavior along predetermined break lines of polyester or similar products and/or derivatives also finds drawbacks in the non-manual execution of such operations, as it is difficult to obtain a clear and well-defined line of separation.

Several state of the art patents such as W02011119639, W020200055274, WO 20200055275 attempt to solve this problem by providing multilayer materials in which the layers are composed of polymers having different stoichiometric charge of polyester and additives to allow the possibility of presenting ruptures by fractures or splits along clean, neat lines of separation.

Other attempts such as EP3722217 and EP3566832 require a complex combination of different notches that make the process expensive and complex.

Still others [EP3766799) claim, in combination with several notches, the need for cooling heat treatments to stiffen the material with viscoelastic properties and thus prevent crushing during cutting.

Therefore, the current state-of-the-art solutions are not satisfactory and have several drawbacks. In the case of multi-material elements, the high recyclability rate of polyester or similar and/or derivatives is lost, so the materials do not meet future ecological standards that will be imposed on users for the post consumer phase, both consumers [selective disposal) and companies [EPR- Extended Producer Responsibility policy approach).

In relation to processes involving pre-cuts or combined weakening zones, a first drawback is the high maintenance cost of cutting tools, which are more expensive than techniques used with other materials. A further drawback is related to the complexity and thus higher cost of devices to perform pre-cuts and thus the increased susceptibility of the machines to breakage and malfunction. In addition, the processes claimed so far are often energetically inefficient and do not take into account industrial issues such as the high degree of degradation of cutting edges when cutting thermoplastic polymer materials such as polyester or similar and/or derivatives and the consequent high maintenance of equipment. In all cases, the solutions do not provide separation lines that are clean and neat.

It is important to consider that a jagged parting line in a relatively rigid material may have a higher cutting efficiency on soft materials and therefore may present a greater hazard to users than a clean, sharp parting line that extends without spikes or ridges throughout the thickness of the material and the length of the parting line.

Therefore, there is a need to provide machining processes that allow for predetermined break lines in flat or slab-shaped elements in thermoplastic polymers such as polyester or similar and/or derivatives, by which two parts can be separated along said lines without the use of cutting tools.

A further purpose is to realize machining processes of the aforesaid type in which, by means of predetermined break lines between two parts made of thermoplastic polymers such as polyester or the like and/or derivatives, it is possible to separate said parts from each other by means of a manual bending action or mechanical stress by relative movement of the two parts to be separated.

A further problem that the invention sets out to overcome is that of being able to realize solutions for making pre-cuts, that is, incisions of a depth corresponding to a portion of an overall dimension of the thickness of the material, which allow an effective separation of the parts of material divided by the pre-cut at later times, even distant times, and yet allow pre-cuts to be made under most different conditions of said thermoplastic materials determined by pre-processing and/or co-processing with the execution of the pre-cut and/or determined by a storage conditions of the parts to be pre-cut and made of said thermoplastic materials.

Last but not least, from an industrial and ecological point of view, solutions should be found that consider the problems cutting tools maintenance by effectively suppressing the toughness and ductility of the material under certain environmental and stress conditions.

- SUMMARY OF THE INVENTION -

According to a first, more general embodiment, a method for generating predetermined break lines in oblong or slab-shaped elements made of thermoplastic polymers, such as polyester or the like and/or derivatives thereof, said element comprising at least two faces or surfaces which are opposite to each other and which are spaced apart by a predetermined thickness, provides the execution of a pre-cut by means of a cutting tool in which said pre-cut is made so as to create a sharp slit while maintaining or generating an amorphous phase of the material in the area of the remaining material thickness beyond the sharp end of said pre-cut slit.

The term pre-cut refers to an in depth incision having dimensions corresponding to only part of the total thickness between said two opposite surfaces.

In an executive form, the cutting tool is configured to be thin with a cutting edge radius close to zero at the apex. It should be noted that in the presence of a mechanical blade, the blade thickness tapers toward the apex at a constant angle below a maximum of 20 degrees, preferably by a maximum of a few degrees. The final blade footprint is further narrowed by the relaxation of elastic tension after the blade is removed from the slit. In the case of ultrasonic actuation of the aforementioned blade, the final impression of the slit will conform as closely as possible to the negative of the cutting edge because the lateral compression of the plastic will be thermally relaxed during penetration due to the friction between the vibrating body and the substrate.

When it comes to cutting tools such as ultrafast pulsed cold lasers, the focusing of the tools is such, that the energy front is as thin as possible i.e., it has the smallest possible aperture [about one micron) in the direction transverse to the extension of the cutting line. The material is removed by ablation without transmitting heat to the area surrounding the exposed one, also called cold ablation.

According to one characteristic, the above method involves alternative combinations of steps: a first alternative involving an impulsive and essentially adiabatic actuation and penetration of the cutting tool into the material; a second alternative involving the actuation of the cutting tool in the direction of penetration of the cutting tool into the thickness of the material and optionally also in the direction of sliding along a predetermined partial cutting or breaking line, and at the same time optionally a temperature difference between the temperature of the material and the temperature of the cutting tool; a third alternative involves performing the cutting by means of a rolling blade, i.e., a rotating circular blade that is advanced along the path provided for the predetermined partial cutting or scoring line, optionally with a temperature difference between the temperature of the material and the temperature of the cutting tool. With reference to the first alternative, a first executive form provides that the impulsive actuation of the knife that results in said adiabatic penetration into the material can be achieved by a single ideally point-shaped 1-10 Joule pulse or alternatively by an ultrasonic vibration having a frequency between 20000Hz and 50,000Hz, preferably around about 30,000Hz.

An executive variant of the said first alternative involves mechanically generating the pulse by means of a beating mass striking the cutting tool blade with the kinetic energy indicated above and for the duration of the pulse, generally under a millisecond.

Alternatively, instead of a beating mass, adiabatic impulsive penetration can be achieved by means of an ultrasonic cutting tool, which ultrasound is commanded to emit cutting pulses with a frequency in the range described above.

With regard to the first alternative and variants thereof the term adiabatic penetration or adiabatic notching means in the present description a pulse penetration in which the pulse duration characteristics are such as to prevent to a large extent a transformation and/or transfer of energy from the cutting tool to the material underlying the cut and/or vice versa, which energy can be absorbed in the form of thermal energy by the material itself and/or the cutting tool through permanent deformation.

In this way, a transformation of the material is avoided for the residual thickness below the bottom of the crack or notch by which the material takes on characteristics of flexibility and elasticity that oppose rupture due to a relative oscillation along the said pre-cut line of the two parts of material divided by the said pre-cut line, assuming a behavior similar to that of a film hinge.

With reference to the second alternative, the method involves heat treating an area of material along the path where a pre-cut incision or crack is provided.

According to an executive variant, the material has a higher temperature, at least along the line along which the notch is made, being this temperature chosen in dependence on the material so as to facilitate the penetration of the blade of the cutting tool into the material itself avoiding structural changes in the material due to crushing or compression of the material by the cutting tool.

According to a further executive variant, which can be provided alternatively or in combination with the previous one, it is planned to cool the temperature of the cutting tool with respect to the material, so as to increase the resistance of the cutting tool to wear and, in particular, to limit the loss of cutting edge sharpness. According to an executive form, the temperature of the material and/or cutting tool is such that the glass phases are preserved, and a sharp crack is created subsequently and/or concurrently with said heat treatment by the intervention of a cutting element.

According to an embodiment, the two alternatives afore described can also be applied in combination with each other whereby the method for generating predetermined break lines in oblong, flat or slab-shaped elements made of thermoplastic polymers such as polyester or the like and/or derivatives thereof, said element comprising at least two faces which are opposite to each other and which are spaced by a predetermined thickness involves the following steps: the establishment of a path of said predetermined break line along at least part of the extent of said faces; the making of an incision or notch from at least one of said faces and along said path which incision is made with a depth corresponding to part of the total thickness of said element, that is, part of the distance of said two faces from each other; and wherein the incision for making the pre-cut can be achieved by different methods of penetration into the material [guillotine or knife) and by different types of loading [progressive or impulsive) depending on the simplicity of application or the choice of the material to be cut; at least during scoring, perform temperature control of the cutting tool and/or material at least along the said incision or notch, that is, at least along the side walls of the said notch and along the material bridge of the part of element thickness where the incision or notch is not present; temperature control consists of maintaining a temperature difference between the cutting body of the cutting tool and the substrate, the glass transition temperature of the constituent polymer having to be between those of the two elements;

According to an executive form, the said temperature difference can be achieved by thermal conditioning of one or both elements before contact and notching. According to one feature a step of thermal stabilization by cooling can be carried out after the execution of the scoring to faithfully preserve the realized topography and/or to bring the cutting edge back to the predetermined working temperature.

The aforementioned thermal stabilization step can be provided in combination with both of the above alternatives and/or with the third alternative involving the combination of the above alternatives.

With regard to thermal conditioning, several executive forms of the method are possible.

In a first executive form, temperature control takes place by heating to a temperature below the glass transition temperature, prior to the execution of the scoring or notching and/or during the execution of the scoring or notching, at least a portion of the material, at least along the path along which the scoring or notching is performed and for a certain extent in width straddling said path and a certain depth, enough to ease tool penetration by reducing surface tension.

One embodiment may in combination or alternatively provide for cooling at least the cutting edge of the cutting tool blade and/or the entire blade to a temperature largely below the glass transition temperature of the polymer constituting the substrate.

Advantageously, the cutting edge of the blade can become stronger as a result of the cooling of the blade thus implying less wear of the cutting body and consequently a longer life time, this results in reduced maintenance of the device designed to put this cutting principle into practice.

Equally advantageously, material at a temperature close to or above the glass transition temperature reduces its hardness and facilitates the penetration and/or sliding of the cutting edge during the execution of the scoring or notching. This phenomenon further reduces the wear of the cutting edge as well as the force required and the resulting pressure on the tool, this results in further energy savings and possibly lighter and cheaper machinery. The temperature of the blade, possibly altered by contact with the substrate during cutting, can be reestablished following the incision phase in combination with or parallel to the process of thermal stabilization of the substrate.

According to yet another executive form, scoring or notching can be performed using as an alternative to a knife, ultra-fast cold ablation lasers.

One executive form may provide for the blade or at least the cutting edge to be under the influence of heating units [by contact, induction, or convection) during the entire step of performing the scoring or notching.

This form of execution can be provided in combination with a thermal conditioning step of the material itself prior to the execution of the scoring or notching step or during the execution of the said scoring or notching step if the substrate is at a temperature higher than the glass transition temperature of the constituent polymer. According to this execution form, the hot cutting edge brings the substrate into rubbery or molten phase contact during the scoring or notching step. This mechanism generates a self-lubricating effect of the cutting edge by reducing the friction and consequently the wear of the cutting unit.

Material in the rubbery or molten phase [in any case above the glass transition temperature) reduces its hardness and facilitates penetration and/or sliding of the cutting edge during the execution of the scoring or notching. This phenomenon further reduces the wear of the cutting edge as well as the force required and the resulting pressure on the tool, this results in further energy savings and possibly lighter and cheaper machinery. These attentions ensure easier blade penetration and/or sliding and/or a better preservation of the blade, resulting in reduced maintenance of the cutting equipment and less energy expenditure due to the lower force required and, if strategically placed in the material processing, also ensures thermal optimization compared to other seemingly similar processes.

According to a further executive form, the cutting edge is made from a thin blade with a cross-sectional shape such that the radius at the apex tends to the zero value.

To accentuate the effect of sharp apex of the cutting edge, the scoring can be carried out through an impulsive load to facilitate the creation of a crack that germinates from the base of the notch in the direction of the face opposite to the scored one.

According to the execution form involving impulsive loading, the stressing mode also allows the apparent stiffness of the material to be increased following its viscoelastic behavior to deformation, all without acting on the temperature of the material, thus allowing mechanically adiabatic cutting.

The invention further provides a method for line-assisted rupture, scoring or notching of predetermined rupture of an oblong or slab-shaped element made of thermoplastic polymers such as polyester or the like and/or derivatives thereof and which element comprises at least two faces which are opposite to each other and which are spaced apart by a predetermined thickness, which method involves the making along the path of a predetermined break line of an incision or notch in accordance with the steps of any of the above-mentioned execution forms of the method for generating predetermined break lines in flat or slab-like elements or in oblong elements made of thermoplastic polymers such as polyester or the like and/or derivatives thereof or any combination or sub-combination of said execution forms of the said method for generating predetermined break lines in oblong elements, flat or slab-like in thermoplastic polymers such as polyester or the like and/or derivatives and involves, in combination with said steps, the step of bendingthe two parts of said element separated by said predetermined break line, about an axis of bending coincident with said line and in the direction of mutual approach of the surfaces of said two parts corresponding to the face opposite to that from which the incision, scoring or notch was made.

- UNDERLYING MECHANISMS -

In summary, the present assisted fracture procedure along predetermined fracture lines involves the making of a notch in the thickness of the material, which notch has a partial depth with respect to the overall thickness and which notch is made according to one of the forms of execution or variants afore fully described, the bending of the flat or slab-like element from the side opposite the said notch causing the sudden relaxation of elastic energy and the sudden propagation of the fracture from the germination point at the bottom of the notch through the body, along the thickness of the said element not affected by the notch up to the next surface.

This one-degree-of-freedom bending results in a propagating cracking of the bridge of material corresponding to the part of the thickness of the element that has not been traversed by the scoring or notch, which cracking takes place according to characteristics typical of the fracture mechanics of materials with glassy characteristics. The cracking is a split that extends predictably and without slabbing along the predetermined fracture line defined by the incision, scoring or notching, whereby the edge of the two parts along the said line remains clean and homogeneous throughout the thickness of the material without forming cusps or even jagged apexes that may constitute cutting edges capable of cutting softer materials [i.e. hurting the user).

Regarding the scientific mechanisms behind the effectiveness of the above method, the holder assumes the following:

Polymers are materials generally endowed with high toughness and ductile behavior that favors the formation of plastic deformation zones [G. R. Irwin). Plastic deformation can induce yielding [a form of local crystallization) in the studied structure and is concentrated around the apex of the crack.

In contrast, brittle materials such as mineral glass tend to crack by fracture mechanics [Griffith) without creation of plastic dissipation zone.

Thus, the energy required to cause crack propagation depends essentially on two factors, the elastic energy of a body under tension trying to grow its surface, called surface energy [or tension), and the thermally dissipated energy in deforming the area bordering the crack, the latter offering resistance to propagation.

Figure 1 shows an example of a fracture mode that applies to the present method [mode 1 of fracture mechanics: opening).

In a situation similar to the one in the figure, the crack will tend to open if the applied stress resolves into a normal stress, that is, a stress perpendicular to the crack surface, such as in the case of planar stress or convex bending with respect to the notch. The thickness of the bridge of material unaffected by the notch must be thick enough to ensure a high moment of inertia of the section and have enough leverage not to confuse the neutral line of bending with the ends of the bridge, so as to allow local concentration of stress and accumulation of elastic energy that will be suddenly released during fracture.

The factors therefore determinant to the cracking process are the shape of the notch, i.e., a tip radius tending to zero that provides the maximum stress concentration, and the toughness of the material i.e., the ability to withstand deformation.

While the cutting of mineral glass by cracking is in common use because of the purely brittle behavior of ceramics, with regard to polymers the unsuitability for cracking depends almost exclusively on their plastic behavior. For this reason, some plastics referred to as rigid plastics can respond to cracking similarly to glass while others, such as thermoplastic polymers, can manifest yielding and dissipate elastic energy in deformation, crystallization and subsequent heating of the element under stress.

It has been found experimentally that, as an example for polyester and/or derivatives, the thermoplastic nature of, for instance, PET does not unconditionally lend itself to assisted cracking, i.e., as a result of simple pre cutting, and that it requires instead a particular mode of performing the pre-cutting incision.

One working praxis involves precisely the above described impulsive adiabatic penetration possibly with a subsequent thermal conditioning step to compensate for any heating of the material and/or cutting tool; a second mode involves a temperature difference between cutting edge and material, a third mode involves a combination of the above two modes, in which there is thermal conditioning of the material and/or cutting tool to preserve local glassy phases in order to reduce toughness and brittle up the material in the notch crack area. In the case of light induced matter thermalisation and subsequent notching such as a pulsed laser with long pulses or a continuously operated laser, the thermally affected zone [TAZ) around the cut tends to reduce the stress concentration near the cut. In addition, fully thermal treatment induces local microstructuring, for example blunting of the apex of the crack by coalescence, a morphology that is not congenial to crack propagation.

The temperature of the material during processing is therefore irrelevant, if proper precautions are taken as outlined in the illustrated forms of execution, as long as the topography achieved through notching or scoring is preserved until fracture and that fracture occurs when the zone of crack propagation is in a brittle stage, i.e., below the glass transition temperature and devoid of crystalline phases. Preservation of morphology can therefore be forced through a thermal stabilization phase of cooling as soon as possible after notching.

Following other experimental investigations, the influence of the incision method on the fractureability of the notched element was established. Different modes of penetration of the cutting element into the plastic material are possible. The kinematics of notching can be essentially of three types [or a combination of the three types): normal to the surface [guillotine), translated over the surface [knife) and translated over the surface [wheel).

The dynamics of cutting also can vary from slow continuous or progressive to rapid and impulsive.

While it is in common sensibility that there is a difference in "crushing" or "sliding” or "rolling" cutting, the behavior of viscoelastic materials in reaction to different stress dynamics is surprising. In fact, while in purely elastic materials, such as glass, the material never goes into deformation and fractures when stress exceeds its elastic limit, thermoplastic polymers in the glassy ["cold") phase are elastic but tend to buckle when the elastic limit is exceeded to achieve permanent deformation. The rheological behavior of viscoelastic materials appears as a property derived from thermoplasticity and adds a dependence of stiffness not only on temperature but also on stress dynamics. Microscopically, polymers need an adaptation time to move the polymer chains under stress and rearrange them to relax the stresses; failure to allow rearrangement time can result in overloading of individual chains that begin to tear even with little elongation of the material. Another consequence of the viscoelastic effect is viscous creep: according to this phenomenon, a body under load tends to relax its stress following the rearrangement of the order of the molecules to dissipate tension or compression, this can induce permanent deformations over the long term even with moderate loads relative to the nominal elastic limit of the material. The consequence is that the harmonic [vibrational) response to stress is nonlinear and strongly depends on the amplitude and frequency of mechanical excitation thus resulting in a non-adiabatic hysteresis loop due to the innate absorption of the system. The material thus behaves purely elastically [or mechanically adiabatically) for high excitation frequencies and/or small amplitudes. To resolve the question of what type of load to use to exploit an adiabatic response, the stress must have a rich frequency spectrum in the high frequencies. A Dirac delta [or pulse) [mathematical model for an impulsive load) is a discontinuous, nonharmonic function that has by definition as its Fourier transform a "white," i.e., "infinite band" spectrum. In other words, to compose an impulse one must sum all excitation frequencies resolving into a theoretically immediate or prompt excitation, with no ripple except in the impulsive harmonic response of the stressed material, a high-frequency, evanescent shock wave that can sprout cracks from stress concentration zones. By extension, this relative and dynamic behavior of the components involved in the incision can be achieved alternately through cyclic and rapid stress caused by the effect of a cutting element provided with an ultrasonic actuator acting on one or two axes resting on the plane of blade penetration.

This dependence on the speed of loading means that the cutting system can benefit from impulsive loading to dramatically increase the apparent stiffness of the material, without the need to alter its temperature and indeed allowing it to manifest stiff and brittle behavior even in a material in the rubbery phase, above the glass transition temperature. Therefore, a sudden stress does not cause the incision zone to deform vertically under the load of the cutting edge but allows a clean severing of the polymer chains and thus a clean cut. In case it is in the glassy phase [below the glass transition temperature), such an impulsive load can sprout a crack from the bottom of the notch bringing the crack angle even closer to zero.

The invention considers industrial maintenance optimization issues neglected by similar solutions for facilitated cracking of thermoplastic polymers. These considerations have direct economic, energy and logistical benefits, influential parameters in industry and adjuvant to the ecological balance of a processing site.

Synergistically, the strategic placement of such an invention within a processing line can take advantage of the thermal conditioning inherent in prior or subsequent methods in the line to avoid one or more of the active conditioning steps, prior or subsequent to notching or scoring. A particular placement in the processing line can thus further reduce the plant's carbon footprint and simplify its implementation.

The tribological effect of shear self-lubrication is only achievable if at least one of the contacting bodies is above the glass transition temperature of the polymer because thermoplastics are by nature ductile in the rubbery or molten phase as viscosity drops with temperature. In this thermal situation, the polymer chains gain mobility and align the severed bandoles in the direction of the blade sliding direction, creating a surface suitable for sliding [smoother and with a reduced sliding friction coefficient). In the case where the polymer at the interface with the cutting edge is at this stage, the relative coefficient of friction is lowered because the neighboring area, which is extremely ductile due to the increased mobility of the polymer chains, behaves like a lubricating gel, and in the case of sufficiently rapid action the bodies come into elastohydrodynamic or even hydrodynamic contact for high speeds and temperatures. In addition, as the elastic modulus decreases, the lateral pressure reacting to the penetration of the cutting edge into the substrate is reduced. Consequently, as the frictional force depends on the coefficient of friction and the force normal to the contact surface, the resistance to penetration and slipping drops.

The self-lubricating effect is therefore most effective for a "knife" notching or scoring with a sliding motion or by means of a rotating knife, while the effect of apparent hardening and "cracking" is most noticeable in a "guillotine" cut, i.e., an impulsive notching or scoring.

The invention also relates to a system for implementing the method according to one or more of the preceding embodiments and variations.

According to a first form of implementation, said system may comprise: a cutting tool having a cutting edge, which cutting tool is movable for a predetermined travel in a direction perpendicular to the cutting edge toward the surface of a workpiece in which is desired to generate, by partial penetration, a notch and which cutting tool is actuated by a beating body which is accelerated in the direction of penetration against said cutting tool and which transfers, by impact against said cutting tool, kinetic energy in an impulsive manner; a mechanism for returning the tool and/or the striking tool to the retracted position with respect to the surface of said workpiece.

According to a second executive form, the said system may include: a thermal conditioning unit of a workpiece at least along a zone of material coincident with a predetermined path of execution of a notch or scoring extending through part of the thickness of said workpiece; and/or a thermal conditioning unit of a cutting organ; said cutting organ being movable, in the direction of penetration into said workpiece and/or in the direction of relative sliding along a predetermined path defined by the notch to be made, for the execution of said notch or scoring starting from a face of said element and with said extension in depth corresponding to a part of the total thickness of the material; a unit of precise measurement and adjustment of the temperature or temperatures of the material of the element being processed and/or of said cutting blade at a temperature below or above the glass transition temperature of said material.

According to one embodiment, it is possible to provide a stabilizing station with a said cooling unit downstream of a material scoring and/or notching station made according to one of the above two variants.

According to a further embodiment variant, it is possible to provide alternatively or in combination a material stabilization station integrated with the scoring and/or notching unit and/or with the supporting and beating counterpart, the stabilization by cooling of the material being performed following the execution of the scoring or notching.

The invention relates to further refinements which are the subject matter of the dependent claims.

- DESCRIPTION OF THE ADVANCED DESIGNS AND EMBODIMENTS -

The features of the invention and advantages will result with more detail from the following description of some non-limiting examples of execution illustrated in the accompanying drawings in which:

Figure 1 shows schematically an example of notching and stressing the two parts separated by the notch for the purpose of their separation by notch-assisted rupture or cleavage.

Figure 2 shows in an enlarged image a notch extending through part of the total thickness of a flat or slab-like element, starting from one face of said flat or slab-like element.

Figures 3 to 7 schematically show the steps of an implementation form of the method according to the present invention.

Figure 8 schematically shows an executive example of a facility for implementing the method according to an example of the method of the present invention. Figure 9 schematically shows an implementation form in which the cutting tool performs a combined movement of penetration into the thickness of the material for a predetermined depth and a translation along the path of the pre-cutting line.

Figure 10 schematically shows an executive form in which the cutting tool performs notching for a depth corresponding to part of the thickness by means of adiabatic impulsive penetration of the tool along a guillotine path and in which the actuation of the impulsive cutting tool is indicated by means of a schematic example reporting the useful frequencies of an impulse transmitted to the tool itself and/or from it to the material as in the case of a smitten blade or knife or as in the case of an ultrasonic cutting tool tuned around those frequencies.

What is illustrated in the figures is only an example of the method according to the present invention, which has no limiting purpose with respect to the more general technical concept that is the subject of the claims.

In this description and in the claims, the term notching is used synonymously with the term scoring and slotting.

Figure 3 shows a flat or slab-like element that is made of a thermoplastic polymer such as polyester or the like and/or derivatives thereof.

The term flat or slab-like means an element having at least two faces opposite each other, the extent of which is greater than the distance of said two faces, which distance is defined as the thickness in this description and the claims.

Alternatively, the term flat may also include oblong elements having also a substantially rounded or cylindrical or polygonal cross-section.

Thus, element 1 has a thickness D and two opposite faces 101, 201 that are spaced apart to the extent of said thickness D.

By 2 is shown a virtual line along which element 1 is to be separated into two parts 1.1 and 1.2, respectively.

According to an executive form of the method of the present invention and as shown schematically in Figure 2, the procedure involves subjecting element 1 to an initial cooling step at a temperature well below the glass transition temperature of the constituent polymer.

Shown with 3 is a cooling device operating, for example, on the basis of conveying a flow of cold gas or air 103 at least against a zone 301 of element 1 coincident with the virtual line 2 separating the two parts 1.1 and 1.2 from each other.

In relation to the solution shown in Figure 4, the depth and extent of zone 103 may vary from what is shown. The cooling unit may also be different and not operate by conveyance of cold gas over zone 301, but for example cooling may be achieved by thermal conduction through direct contact between a cooling body and element 3 or in some other way. Such cooling preferably takes place during and/or immediately after cutting in order to stabilize the material in which the incision was made.

Furthermore, as will be seen below, the step of cooling to a temperature below the glass transition temperature of the constituent polymer, at least of the zone 301 containing the virtual line 2 that traces the path of the predetermined break line can also be omitted and performed at the same time as the step of performing the scoring along the trace defined by the virtual line 2.

This possibility is made evident in Figure 5 where unit 3 cooling by conveying a flow 103 of gas or cold air is illustrated with discontinuous lines.

In figure 5, the step of performing a notch using a die or cutting tool is shown schematically, of which only the cutting edge area of the blade is shown, which is indicated by 4.

In Figure 5, an embodiment is shown explicitly, albeit schematically, in which said blade or at least said blade cutting edge 4 is subjected to cooling to a working temperature also well below the glass transition temperature of the constituent polymer. A cooling unit 5, like a cryogenic unit is in thermal contact with blade 4, which is thus maintained at a working temperature lower to the predetermined extent of the glass transition temperature of the constituent polymer and ideal for blade storage.

The cooling action of the blade 4 may occur in a step upstream of the notch processing in element 1 or such cooling action may continue even during the execution of the notch or alternatively cooling may take place only during the execution of the notch.

In Figure 5, the notch execution action is schematically represented by arrow I.

Figure 6 shows the condition of element 1 after the execution of notching along virtual line 2 and in zone 301 of element 1. This zone has been subjected to cooling according to one or more of the previous variants that alternately or in combination provide for a thermal conditionning step of cooling the element 1 and in particular the zone 301 before the execution of the scoring and/or a cooling step during the scoring of the element 1 that may take place directly by means of a cooling unit 3 thermally acting directly on the element or alternately indirectly by cooling the cutting unit, i.e., the blade, or a combianation of the two methods. The notch is shown schematically and dimensionally unrealistically for illustration purposes only and is indicated by reference number 7.

Depending on the embodiment by which the temperature of the material is cooled and thus controlled so that it always remains definitely and abundantly below the glass transition temperature of the constituent polymer, the temperature at which the element is to be cooled directly and the temperature at which the cutting tool is to be cooled must be such that the thermal energy generated during notching does not heat up even locally part of the material of the remaining thickness bridge not affected by the notch and which is identified in Figure 2 as D2.

In this way, the thermal energy generated by the notching action is largely compensated by preventing it from reaching values above the glass transition temperature of the constituent polymer and inducing microstructural changes in the area close to the notch by coalescence and/or local crystallization making it plastically ductile.

Due to this condition, the separation of the two parts 1.1 and 1.2 of element 1 along track 2 of notch 7 can be done simply by angular displacement of the two parts 1.1 and 1.2 against each other in the direction of approaching the semi-surfaces opposite to the one where notch 7 was made as indicated by the S arrows in Figure 6 and 7.

Notching performed according to one or more of the variants described above makes it possible to generate a predetermined fracture line, which assists separation by cracking [cleavage) or fracture of the material even along the part of the thickness that was not affected by the notch itself [see part identified with D2 in Figure 2). The surface of separation indicated by 8 in Figure 7 and along which the cracking or fracture of the material occurs takes on a continuous, sharp, non-jagged shape devoid of sharp indentations or cusps.

In relation to the depth of the notch D1 with reference to the overall thickness D of element 1, this depth may vary between about 10 and 90 percent of the overall thickness and consistent with the functional needs required for element 1, i.e., the conditions under which it is desired to allow the two parts 1. 1 and 1.2 of element 1 until the bending step is exerted around the predetermined break line defined by notch 7 and the force conditions required to perform this bending operation around the predetermined break line, i.e., the notch or scoring.

Note that the force with which the blade is pushed against the material varies depending on the overall thickness of the material and/or the desired depth of cut, the width of the element to be broken, the quality of the cutting edge used as well as also the temperature and stress conditions of the material. For relatively thin sheets, i.e., under a centimeter, particularly one or two millimeters, the energy applied to exert this thrust may be on the order of a few joules, at most a few tens of joules.

The penetration force or actuation energy of the cutting tool can easily and quickly be determined empirically by experiment in the pre-cutting system setting stages.

The executive example shown above and the different variations described refer to the use of a blade to perform the notching. Temperature control takes place by precooling the substrate and/or by cooling the cutting blade.

A possible alternative form of execution involves, instead of the use of a notching blade, the use of an ultrafast laser of the femto-second type for cold ablation. Also in this case, prior to the execution of the notching and/or even during said execution by means of said cold laser, a cooling step of the material of element 1 and in particular of the zone 301 where the notching 7 will be or is being practiced according to one or more of the variants described above can be provided.

A cold laser that has been shown to be functional for performing the method according to the invention is, for example, the laser device called SATSUMA and marketed by Amplitude.

Figure 8 shows schematically and as a non-limiting example a system or facility for implementing the steps ofthe method according to one of the forms of execution ofthe present description.

The figures are to be regarded as iconic symbols of operating units that essentially show the layout of the system and its correspondence with the sequence of method steps, as well as the essential functionality of the operating units.

A conveyor 800 transports an element 1 from one processing station to the next. A first processing station consists ofthe temperature control station of element 1 or at least of said zone 301. Such a station is referred to as a pre-cooling station and is denoted 801. The station includes a thermal conditioning unit 811 of element 1 that operates according to one or more different modes of heat generation and heat transfer to maintain the temperature of said element 1 at a predetermined working temperature. In particular, said temperature is less than the glass transition temperature ofthe polymer constituting the substrate to be scored.

A subsequent station 802 provides the scoring or notching unit, which can be made according to one of the variants described above. In combination with scoring unit denoted 812, said station 802 may comprise a temperature control unit that is intended to control the temperature ofthe cutting tool and/or also a temperature control unit that is intended to further control the temperature of the material at least in the zone 301. Temperature control unit[s) are shown with a discontinuous line and are denoted by 813 whether both are present or only one of the two alternatives is present.

When, for example, an ultra-rapid laser is used instead of a cutting blade, the blade temperature control unit is not necessary and is equivalently replaced, with regard to the technical effect of keeping the material temperature controlled, by the laser setting parameters that affect heat dissipation in the cutting zone and by the light-matter interaction regime that must remain in adiabatic ablation of the substrate in the 301 zone.

According to one variant, it is possible that station 801 may not be provided and only station 802 may be provided in one or more of the variants described for it.

In the example in Figure 8, the system shown also includes automatic means for separating the two parts 1.1 and 1.2 of element 1. Although such means shown at stations 803 and 804 are illustrated on the line this solution is only optional, the preferred solution being to provide for said automatic means in a separate device that is used at different times from the time of execution of the predetermined break line at stations 801 and/or 802.

Obviously, the separation steps putin place at stations 803 and 804 can and normally are also performed by manual action by human people.

The operating units of the different stations 801, 802, 803, and 804 are controlled by a central control unit 805 which operates according to a control software 806. The control software processes data obtained from sensors 807, particularly from temperature sensors regarding the substrate and/or cutting blade and/or cold laser temperature control units, to generate the control signals of the said individual operating units. A data acquisition unit 808 receives signals from the sensors 807 and provides them to the control unit 805.

The control software 806 includes the encoding of the instructions and settings required to execute the method steps according to one or more of the executive forms and variants set forth above.

Figure 9 schematically shows an embodiment in which, in the presence of a temperature difference between knife and material, either pre-existing or induced by conditioning either side, as shown with dashed elements 3, 103 and 5, the cutting tool 4 performs both movement in the penetration direction, i.e., normal to the cutting edge, and a sliding displacement along the path provided for notch 2.

Figure 10, on the other hand, shows the operation of the notch with partial depth of thickness exerted by an adiabatic impulsive penetration of the cutting tool into the material. Since a variety of execution forms of such a cutting system are possible, mechanical, by ultrasonic, electromagnetic and others, this type of cutting tool actuation is shown generalized by means of a blade 4 and an impulsive motion application mechanism of the same blade 4 showing the energy pulse transmitted to the blade in a graph.

This pulse is of the order, 2 to 20N*s, between 1 and 10J of kinetic energy and a duration of 0.1-0.5ms.

A mechanical actuation system may involve a gravity actuation with an active return [ex. motor-driven) or passive [spring elements).

An alternative may provide for a mechanically actuated striking mass along a stroke toward and against the blade and back.

An electromagnetic alternative may provide for a beating mass whose travel in the direction of impact against the blade and back is controlled by an electromagnet, analogous, for example, to electromagnetically actuated dental hammers.

An ultrasonic alternative can take advantage of the pulsed penetration effect, which essentially consists of the rapid repetition of minor addressable pulses in a vertical direction or parallel to the surface at a frequency between 20kHz and 40kHz and a power between 20W and 100W.

- EXPERIMENTAL EXAMPLES -

The method according to the present invention has been tested in some simple experiments in the following examples:

EXAMPLE 1

A PET sheet was subjected to the execution of the three notches by means of a cutter each with a different pressure exerted on the blade namely light, medium and strong as in the previous example and by combined drive in the penetration and sliding direction of the blade.

Before notching, the cutter blade was cooled each time by cold gas to a temperature close to 0°C in order to generate the temperature difference between blade and material. Notching was immediately performed before the blade heated up.

The three samples with the three different types of notching were manipulated by bending as for the samples described above. In all three cases, upon reaching an angle of the order of magnitude of about 90°, the two parts separated by fracturing the bridge of material in the area of the thickness not affected by notching. The separation was sharp for all three specimens, and the fracture face on both sides of the slab was a sharp surface with no roughness, indentations or other deformation. The force and/or inclination required was inversely proportional to the depth of cut, the blade in its ideal preserved condition.

EXAMPLE 2.

The same type of slab was subjected to the execution of the three notches using cutters each with a different pressure exerted on the blade, namely light, medium and strong as in the previous example.

In this example, the area where the scoring was to be made was subjected to cooling by exposure to an expanding gas. The temperature of the material along the area intended to be scored was about 0°C. Immediately after cooling, the scoring was performed.

Notching was performed immediately after cooling to avoid heating of the material.

The three specimens with the three different types of notching were handled by bending as for the specimens described above. In all three cases, upon reaching an angle of the order of magnitude of about 90°, the two parts separated by fracturing the bridge of material in the area of the thickness not affected by the notch.

The separation was clean for all three specimens, and the fracture front on both sides of the slab was a clean surface with no roughness, indentations or other deformation.

EXAMPLE 3

The same type of slab was subjected to the execution of the three notches using cutters each with a different pressure exerted on the blade and that is light, medium and strong as in the previous example.

In this example, the area where the incision was to be made was subjected to heating by exposure to a stream of gas heated by a heating element. The temperature of the material along the area intended to be scored was such that the material was softened. Immediately after heating, the notching was performed.

In addition, the cutter blade was cooled each time with a similar treatment and to a temperature of about 0°C.

Scoring was performed immediately after material heating [substrate) and cooling [blade) to avoid heating of the blade by contact with the substrate. The plate material was cooled below its glass transition temperature following notching to fix and preserve the obtained morphology. The cut thus made required considerably less effort to penetrate and/or translate into the material, the blade will be preserved even longer. The cut is particularly clean, the incision is almost invisible.

EXAMPLE 4

The same plate was subjected to scoring by adiabatic impulsive penetration of the tool.

A blade was placed on the surface of the material with the cutting edge of the blade resting against said surface. A vertically guided beating mass was dropped from different heights against the side of the blade opposite the cutting edge.

By means of tests, a height value was established from which to drop the beating mass such that the slab was not severed completely, that is, such that penetration of the blade occurred only for part of the thickness of the slab.

Three notches were made lifting the beating mass at different heights, less than the maximum limiting height beyond which complete cutting of the material was achieved.

Three specimens were obtained each with a notch of different depth. The three different types of notches were manipulated by bending as for the samples described above. In all three cases, upon reaching an angle of the order of magnitude significantly less than 90°, the two parts separated by fracturing the bridge of material in the area of the thickness not affected by the notch. The separation was clean with a neat fracture that for all three samples had a fracture front on both sides of the slab that presented a clean surface with no roughness, indentations or other deformation.

The same experiment was performed by combining prior thermal conditioning of the knife and/or the material in order to generate a temperature difference between them, and the ease of fracture along the notch was verified similarly to that described above for the other experiments. Again, the separation was clean with a neat fracture that for all three samples had a fracture front on both sides of the slab that presented a clean surface with no roughness, indentations or other deformation. The ease of fracture is not determined by thermal conditioning of the material before and during cutting. The height of the striking mass was reduced to achieve behavior similar to the mode without heat treatment, the purpose of prior or concurrent conditioning is to reduce the effort required to notch and reduce tool maintenance.

In a further experimental test, for making a notch with partial depth compared with the overall thickness of about 2mm of a slab and with a notch length of about 2.5cm, the partial notch was made by impulsive penetration with an energy of about 0.2 to 0.6Joule. Following this, bending in the direction opposite to the side where the notch is made of the two parts separated by the notch resulted in a sharp and decisive break whose edges are smooth and free of serrations or other surface irregularities. In the schematic figures, the mode of execution of the scoring by means of a blade is shown only for the impulse execution variant, in which the notching is generated by a movement of the knife only in the direction of penetration, and for an execution variant in which the knife slides along a predetermined path that defines the position of the notch. An initial penetration action is followed by translation of the knife along said path, maintaining the penetration position.

An alternative not shown involves the blade being in the form of a rotating disc that has a cutting edge along its peripheral edge. Notching takes place by initial penetration to the predetermined extent into the thickness of the material and then translation along the path defining the position of the notch, during which translation, the circular blade rotates on itself, always bringing a new part of the cutting edge to penetrate the material. Alternatively to a constant depth relative travel, a constant force can be applied on the substrate, adjusting force following material properties and temperature, to obtain a constant depth incision.

In this embodiment, cooling of the blade can occur during the making of the notch by one of the alternatives described above and in which the part of the cutting edge that has not yet come to penetrate the material is properly cooled to increase its strength and durability.

This concept also applies when as an alternative to the variant involving blade cooling, the variant involving blade heating is used. In this case, only the part of the cutting edge that is yet to come to penetrate the material, immediately before notching, may be heated to working temperature.

Claims

- CLAIMS -

1. A method for generating predetermined break lines in flat or slab-like or oblong elements made of thermoplastic polymers such as polyester or the like and/or derivatives thereof, said element comprising at least two faces which are opposite to each other and which are spaced apart by a predetermined thickness, and wherein said method comprises making a pre-cut by means of a cutting tool wherein said pre-cut is made so as to create a sharp slit while maintaining or generating a glassy phase of the material in the area of the remaining material thickness beyond the sharp end of said pre-cut slit.

2. A method for generating predetermined break lines in flat or slab-like elements made of thermoplastic polymers such as polyester or the like and/or derivatives according to claim 1, said method consisting in alternative combinations of steps as following: a first alternative comprising an impulsive and essentially adiabatic actuation and penetration of the cutting tool into the material; a second alternative involving an actuation of the cutting tool in the direction of penetration of the tool into the thickness of the material and optionally also in the direction of sliding along a predetermined cutting line, and at the same time a temperature difference between the temperature of the material and the temperature of the cutting tool; a third alternative involves performing cutting by means of a rolling blade, i.e., a rotating circular blade that is advanced along the planned path for the predetermined cutting or scoring line, optionally providing for a temperature difference between the temperature of the material and the temperature of the cutting tool.

3. A method according to claim 2, wherein the impulsive actuation of the knife resulting in said adiabatic penetration into the material occurs with pulses having a duration of less than one millisecond and an energy of between 0.1 and 10J per cm of cut or alternatively with a cyclic repetition of the stress at a frequency of between 20kHz and 50kHz, preferably around about 30kHz.

4. A method according to claim 2 or 3, wherein the impulsive actuation is generated mechanically and/or electromechanically and/or electromagnetically by actuation of a beating mass that strikes the blade of the cutting tool for the duration of the impulse and with a predetermined and preset energy, or the adiabatic impulsive penetration is achieved by an ultrasonic cutting tool.

5. A method according to one or more of the preceding claims, wherein the method comprises the step of thermally treating an area of material along the path along which an incision or pre-cutting notch is provided or expected.

6. A method according to anyone or more of the preceding claims, wherein the method involves the cooling of the temperature of the cutting tool relatively to the material in order to increase the resistance of the cutting tool to wear and in particular to limit the loss of cutting edge sharpness and/or to bring the material to a higher temperature than the temperature of the cutting tool, at least along the line along which the notch is performed being such temperature chosen in dependence of the material in order to facilitate the penetration of the blade of the cutting tool into the material itself avoiding structural and microstructural modifications of the material due to crushing or compression of the same by the cutting tool and consequent possible inaccuracies on the actual depth of the notch, shape of the apex and/or unsuitability to breakage.

7. A method according to one or more of the preceding claims in which the temperature of the material and/or cutting tool is such that the glassy phases of said material are preserved, and a sharp crack is created subsequently and/or concurrently with said thermal treatment by the intervention of the cutting tool.

8. A method according to one or more of the preceding claims that consists in a combination of the alternatives described in claim 2 and in which the following steps are provided: the establishment of a path of the aforementioned predetermined break line along at least part of the extent of said faces; the making of an incision or notch from at least one of said faces and along said path, which incision is made with a depth corresponding to part of the total thickness of said element; and the incision for making the pre-cut being obtained by guillotine or sliding or rolling penetration into the material and by progressive, constant or impulsive loading; at least during the scoring, perform a temperature control of the cutting tool and/or material at least along said scoring or notch, i.e., at least along the side walls of said notch and/or along the material bridge corresponding to portion of the thickness of the element in which the scoring or notch is not present, which temperature control consists of maintaining a temperature difference between the cutting tool and the material that includes the glass transition temperature of the polymer constituting the substrate.

9. A method according to one or more of the preceding claims in which temperature control takes place according to one or more of the following combinations: by cooling and/or heating during and/or after the cutting or notching is performed, at least a portion of the material, at least along the path along which the cutting or notching is performed and for a certain extent in width straddling said path and a certain depth, preferably the entire thickness of the element, at a temperature below the glass transition temperature; cooling and/or heating at least the cutting edge of the cutting tool blade and/or the entire blade to a temperature below the glass transition temperature.

10. A method according to one or more of the preceding claims, wherein the notching is performed by means of a guillotine or knife blade or by means of ultra-fast lasers or by means of ultrasound.

11. Method according to one or more of the preceding claims in which a thermal conditioning step, preferably cooling of the material and/or cutting tool, is provided at the end of the execution of the notching to fix the morphology of the cut.

12. A method for assisted fracture, scoring or notching along a predetermined breakage line of a flat or slab-like or oblong element made of thermoplastic polymers such as polyester or the like and/or derivatives thereof and which element comprises at least two faces which are opposite to each other and which are spaced apart by a predetermined thickness, wherein the method comprises the action of making along the path of a predetermined break line a trench or notch according to the steps of any one of the above-mentioned embodiments of the method for generating predetermined break lines in flat or slab or oblong elements made of thermoplastic polymers such as polyester or the like and/or derivatives according to one or more of claims 1 to 11, comprising in combination with said steps, the step of bending the two parts of said element separated by said predetermined break line, about an axis of bending coincident with said line and in the direction of mutual approach of the half-surfaces of said two parts corresponding to the face opposite to the face from which the incision or notch was made.

13. A system for implementing the method according to one or more of the preceding claims 1 to 12, wherein said system comprises: a cutting tool having a cutting edge, which cutting tool is movable for a predetermined travel in a direction perpendicular to the cutting edge toward the surface of a workpiece in which to generate by partial penetration a notch and which cutting tool is actuated by a beating body which is accelerated in the direction of penetration against said cutting tool and which transfers by impact against said cutting tool kinetic energy in an impulsive manner; a mechanism for returning the tool and/or the striking body to the retracted position relative to the surface of said workpiece.

14. A system for implementing the method according to any one or more of the preceding claims 1 to 12, wherein said system comprises: a cutting organ displaceable in the direction of penetration into said workpiece and/or in the direction of relative sliding along a path defined by the path of longitudinal extension of the notch to be made for performing said etching or notching starting from a face of said element and with said extension in depth corresponding to apart of the total thickness of the material.

15. A system for implementing the method according to any one or more of the preceding claims 1 to 12, wherein said system comprises: a thermal conditioning unit of a workpiece at least along a zone of material coincident with a predetermined path of performing a precut or notch extending through part of the thickness of said workpiece, and/or a thermal conditioning unit of a cutting organ; a unit of precise measurement and regulation of the material temperature(s) of the workpiece and/or of said cutting blade at a temperature below or above the glass transition temperature of said material.

16. A system according to any one or more of claims 13 to 15, characterized by alternatively or in combination including a material stabilization cooling station integrated with the cutting tool and/or with the support and anvil counterpart, the material cooling stabilization being performed simultaneously with and/or following the execution of the scoring or notching.

17. A system according to any one or more of claims 13 to 16, wherein optional cooling of at least the blade or the cutting edge zone only takes place during or after the execution of the scoring or notching being provided a cryogenic unit in thermal contact with said blade and/or at least said cutting edge zone, which cryogenic unit is operable before and/or during and/or after the operation of the cutting unit for the execution of the scoring or notching.