Packaging element

0001The invention relates to a method for splicing inhibition of a band-shaped packaging element, in particular a strapping band or a harvest binding yarn, made of a polyester-based plastic band, a PET being used as the polyester, the PET being compounded with at least one styrene-based polymer as a splice inhibitor in the extrusion process.

0002Strapping tapes are usually made from polyester or polyolefins using an extrusion process with subsequent stretching. Due to the alignment of the molecules during the stretching process, they tend to splice, ie to form cracks in the direction of the tape. The brittleness of plastics at low temperatures, especially below 5°C, increases the tendency to splice. To reduce the tendency to splice, splice inhibitors are usually added to the compounds used to produce strapping. However, the splicing inhibitors used so far do not provide sufficient help against embrittlement at low temperatures.

0003From the<patcit id="pcit0001" dnum="US2005238897A1"><text>US 2005/238897 A1</text></patcit> a packaging tape is known which consists of more than 92% by weight of a polyester and a total of less than 8% by weight of a polyolefin-based additive and other additives, the polyolefin additive content being less than 3% by weight. Other additives mentioned include polystyrene-based elastomers in a proportion of between 0.5% by weight and 2% by weight. The addition of polyolefin is intended to reduce the tendency to splice longitudinally. The styrene elastomers should also contribute to reducing this tendency to splice.

0004The use of styrene-butadiene rubber in proportions of up to 25% by weight in a polyethylene tape is also from the<patcit id="pcit0002" dnum="DE2037398A1"><text>DE 20 37 398 A1</text></patcit> known, although the purpose of the addition is not stated in this document.

0005The<patcit id="pcit0003" dnum="DE2727356A1"><text>DE 27 27 356 A1</text></patcit> describes a binding tape formed from a thermosetting and a thermoplastic resin, the resins being derived from the same monomers such that the two resins have a chemical affinity for each other, and the thermosetting resin being an unsaturated polyester resin cross-linked with styrene. The thermoplastic resin may be an acrylonitrile-butadiene-styrene copolymer or an acrylonitrile-styrene copolymer. The aim is to provide a binding band of sufficient strength, comparable to a steel band, which shows high tensile strength and low elongation as well as low creep behavior, and which can be easily and firmly connected to one another at the ends. For this purpose, the thermoplastic resin forms the outer layer of the binding tape and the thermosetting resin forms the core.

0006The object of the present invention is to create a band-shaped packaging element which has reduced splicing even at low temperatures.

0007This task is solved on the one hand by using the method mentioned at the beginning, in which a thermoplastic, non-elastomeric, styrene-based polymer is added as the splice inhibitor, and the compounding is processed at a temperature between 250 ° C and 310 ° C, so that the splice inhibitor is unbound in the plastic tape is present, and independently of this, through the use of a non-elatomeric styrene-based polymer in an extrusion process as a splice inhibitor for a polyester-based strapping or harvest twine, the polyester being a PET.

0008Surprisingly, it was found that the use of thermoplastic styrene polymers, i.e. non-elastomeric polymers, as embrittlement inhibitors to reduce the splicing sensitivity of packaging tapes, in particular strapping tapes or harvest binding twines, not only reduces this property, but also their use at low application temperatures is improved by reducing the tendency of the band-shaped packaging element to break brittle. The term “low application temperature” means a temperature of below 5 °C, although there is naturally a limit to low temperatures due to the material.

0009Polymers are particularly suitable as splicing inhibitors in this context. Copolymers are highlighted, which are selected from a group comprising or consisting of polystyrene homopolymer, acrylonitrile-butadiene-styrene copolymer (ABS), methyl methacrylate-acrylonitrile-butadiene-styrene copolymer (MABS), styrene-acrylonitrile copolymer (SAN ), acrylonitrile-styrene-acrylate copolymer (ASA), styrene-maleic anhydride copolymer (SMA), methyl methacrylate-butadiene-styrene (MBS) and mixtures thereof. The reason for their particular suitability has so far only been verified through tests. An explanation at the molecular level is not yet available.

0010The proportion of styrene-based polymer in the plastic tape is preferably selected from a range with a lower limit of 0.2% by weight and an upper limit of 20% by weight, in particular 5% by weight. Below 0.2% by weight, the reduction in splicing is too low. Above 20% by weight, the proportion of the base polymer is reduced to such an extent that the packaging tape has poorer tensile strength properties.

0011According to one embodiment variant of the method, it is provided that it is completely polyolefin-free or contains less than 0.2% by weight of polyolefin(s). This also avoids a reduction in the tensile strength and hardness of the plastic tape.

0012It can also be provided that, in addition to the styrene-based splice inhibitor, the packaging element contains at least one further different splice inhibitor in the plastic tape, which is in particular selected from a group comprising or consisting of olefin-acrylate copolymers, thermoplastic polymers (TPE), low density polyethylene ( LDPE), linear LDPE (LLDPE), polyethylene, polypropylene, butadiene rubber (BR), and mixtures thereof. This allows the property profile of the packaging element to be better and more finely tailored to the respective area of ​​application.

0013It has proven to be advantageous if the further splicing inhibitor is contained in a proportion such that the quantitative ratio of the styrene-based splicing inhibitor to the further splicing inhibitor is selected from a range of 80:20 to 20:80, in particular 60:40 to 40:60. This avoids a reduction in the effect of the styrene-based splice inhibitor with a high degree of certainty, which is particularly important with regard to the manufacturing process of the band-shaped packaging element under changing production conditions.

0014With regard to the reduction of brittle fracture, the styrene-based polymer is unbound in the plastic tape, in particular in the shape of a domain, it being preferred if the domains are designed to be stretched in at least one spatial direction and, in particular, have an at least approximately elliptical cross section in at least one spatial direction. In particular, according to one embodiment, the binding forces between the domain and the surrounding matrix are weaker than the binding forces within the matrix and within the domain. By avoiding the chemical crosslinking of the base polymer with the molecules of the splice inhibitor, whereby these are unbound in the sense of the invention, a change in the tensile strength is avoided, with the domain-shaped design acting as an area in which cracks "run dead". The elongated, in particular at least approximately elliptical, design of the domains has a positive effect in terms of maintaining the anistropic properties of the plastic tape. The term “domain” is understood to mean a discrete, delimited area in the plastic tape.

0015For a better understanding of the invention, it will be explained in more detail using the following figures.

0016Show it:<dl id="dl0001"><dt>Fig. 1</dt><dd>a scanning electron microscope image of a cross section through a polyester-based strapping tape with 2% by weight of polystyrene;</dd><dt>Fig. 2</dt><dd>a scanning electron microscope image of a cross section through a polyester-based strapping band without the addition of a thermoplastic styrene polymer according to the invention;</dd><dt>Fig. 3</dt><dd>a graphical representation of the splicing tendency of different strapping tapes at -5 °C;</dd><dt>Fig. 4</dt><dd>a graphic representation of the splicing tendency of various strapping tapes at -15 °C.</dd></dl>

0017As an introduction, it should be noted that individual features or combinations of features from the different exemplary embodiments described can represent independent solutions according to the invention.

0018The strip-shaped packaging element according to the invention is a plastic band and in particular a strapping band or a harvest twine.

0019The packaging element is preferably made from polyester. For the purposes of the invention, polyester-based means that the strapping band or the harvest binding twine or the packaging element consists of a base material or matrix material made of at least one polyester, i.e. the polyester is contained as the main component in a proportion of at least 50% by weight in the packaging element . The band-shaped packaging element preferably contains a polyester content of at least 75% by weight, in particular at least 85% by weight or at least 90% by weight.

0020The polyester used is polyethylene terephthalate (PET).

0021In addition to the polyester base material, the packaging element can also contain other additives, such as colorants, as are known from the prior art, and/or inorganic fillers, such as talc or chalk. In the preferred embodiment of the invention, the polyester-based packaging element does not contain any other ingredients or additives apart from the polyester, the thermoplastic, styrene-based polymer and a colorant.

0022The band-shaped packaging element made of the polyester base material preferably contains no polyolefins.

0023In the two embodiment variants of the band-shaped packaging element as a strapping band or as a harvest binding twine, the respective base material contains at least one thermoplastic, styrene-based polymer as a splice inhibitor. A styrene-based polymer is understood to mean a polymer that is either a homopolymer or a copolymer or a copolymer, in which case a styrene monomer was used to produce it.

0024The styrene-based polymer used is preferably a polymer which is selected from a group comprising or consisting of polystyrene homopolymer, acrylonitrile-butadiene-styrene copolymer (ABS), methyl methacrylate-acrylonitrile-butadiene-styrene copolymer (MABS), styrene -Acrylonitrile copolymer (SAN), acrylonitrile-styrene-acrylate copolymer (ASA), styrene-maleic anhydride copolymer (SMA), methyl methacrylate-butadiene-styrene (MBS) and mixtures thereof.

0025These are preferably commercially available products, just like the polyesters and polyolefins as well as the other ingredients of the packaging element.

0026The proportion of the styrene-based polymer in the plastic tape is selected from a range with a lower limit of 0.2% by weight, preferably 0.5% by weight, and an upper limit of 20% by weight, preferably 15% by weight. -%, in particular 3.5% by weight.

0027However, a proportion of up to and including 80% by weight, in particular 50% by weight, preferably 20% by weight, of this styrene-based polymer can also be replaced by a further splice inhibitor that has previously been commonly used as a splice inhibitor in such band-shaped packaging elements, which is different to the styrene-based splice inhibitor. In particular, this further splicing inhibitor is selected from a group comprising or consisting of olefin-acrylate copolymers, thermoplastic polymers (TPE), low density polyethylene (LDPE), linear LDPE (LLDPE), polyethylene, polypropylene, butadiene rubber (BR), and mixtures from it. The further splicing inhibitor is preferably contained in a proportion such that the quantitative ratio of the styrene-based splicing inhibitor to the further splicing inhibitor is selected from a range of 80:20 to 20:80, in particular 60:40 to 40:60.

0028For experimental purposes, the following compositions were processed into tapes or yarns using the extrusion process, with the tapes having a bandwidth of 9 mm to 19 mm and the yarns having a running length of 400 m/kg. Since the manufacturing process for such band-shaped packaging elements is known from the prior art, the person skilled in the art is referred to the relevant literature.

0029In the tables mean:<tables id="tabl0001" num="0001"><table frame="all"><tgroup cols="5"><colspec colnum="1" colname="col1" colwidth="28mm" /><colspec colnum="2" colname="col2" colwidth="38mm" /><colspec colnum="3" colname="col3" colwidth="31mm" /><colspec colnum="4" colname="col4" colwidth="33mm" /><colspec colnum="5" colname="col5" colwidth="37mm" /><thead valign="top"><row><entry>Attempt</entry><entry>Dimension [mm]</entry><entry>SP additive</entry><entry>Share SP [%]</entry><entry>Std additive [%]</entry></row></thead><tbody><row><entry>tape</entry><entry>9x0.55</entry><entry>P.S</entry><entry>2,5</entry><entry>0</entry></row><row><entry>tape</entry><entry>15x0.55</entry><entry>P.S</entry><entry>0,5</entry><entry>0</entry></row><row><entry>tape</entry><entry>15x1</entry><entry>P.S</entry><entry>0,01</entry><entry>0</entry></row><row><entry>tape</entry><entry>15x1</entry><entry>P.S</entry><entry>0,02</entry><entry>0</entry></row><row><entry>tape</entry><entry>15x1</entry><entry>P.S</entry><entry>0,04</entry><entry>0</entry></row><row><entry>tape</entry><entry>15x1</entry><entry>P.S</entry><entry>1</entry><entry>0</entry></row><row><entry>tape</entry><entry>15x1</entry><entry>P.S</entry><entry>2</entry><entry>0</entry></row><row><entry>tape</entry><entry>16x0.9</entry><entry>P.S</entry><entry>2</entry><entry>0</entry></row><row><entry>tape</entry><entry>16x1.0</entry><entry>P.S</entry><entry>2</entry><entry>0</entry></row><row><entry>tape</entry><entry>16x1.0</entry><entry>SECTION</entry><entry>0,5</entry><entry>0</entry></row><row><entry>tape</entry><entry>16x1.0</entry><entry>SECTION</entry><entry>1</entry><entry>0</entry></row><row><entry>tape</entry><entry>16x1.0</entry><entry>SECTION</entry><entry>1,5</entry><entry>0</entry></row><row><entry>tape</entry><entry>16x1.0</entry><entry>SECTION</entry><entry>2</entry><entry>0</entry></row><row><entry>tape</entry><entry>16x1.0</entry><entry>SECTION</entry><entry>2,5</entry><entry>0</entry></row><row><entry>tape</entry><entry>16x1.0</entry><entry>SAN</entry><entry>0,5</entry><entry>0</entry></row><row><entry>tape</entry><entry>16x1.0</entry><entry>SAN</entry><entry>1</entry><entry>0</entry></row><row><entry>tape</entry><entry>16x1.0</entry><entry>SAN</entry><entry>1,5</entry><entry>0</entry></row><row><entry>tape</entry><entry>16x1.0</entry><entry>SAN</entry><entry>2</entry><entry>0</entry></row><row><entry>tape</entry><entry>16x1.0</entry><entry>SAN</entry><entry>2,5</entry><entry>0</entry></row><row><entry>tape</entry><entry>19x1.0</entry><entry>P.S</entry><entry>0,5</entry><entry>0</entry></row><row><entry>tape</entry><entry>19x1.0</entry><entry>P.S</entry><entry>2</entry><entry>0</entry></row><row><entry>tape</entry><entry>19x1.27</entry><entry>P.S</entry><entry>1</entry><entry>0</entry></row><row><entry>tape</entry><entry>19x1.27</entry><entry>P.S</entry><entry>2</entry><entry>0</entry></row><row><entry>tape</entry><entry>19x1.27</entry><entry>P.S</entry><entry>3,5</entry><entry>0</entry></row><row><entry>tape</entry><entry>19x1.27</entry><entry>P.S</entry><entry>1</entry><entry>1</entry></row><row><entry>tape</entry><entry>19x1.27</entry><entry>P.S</entry><entry>1,5</entry><entry>0,5</entry></row><row><entry>tape</entry><entry>19x1.27</entry><entry>P.S</entry><entry>2,25</entry><entry>0,75</entry></row></tbody></tgroup><tgroup cols="5" rowsep="0"><colspec colnum="1" colname="col1" colwidth="28mm" align="justify" /><colspec colnum="2" colname="col2" colwidth="38mm" /><colspec colnum="3" colname="col3" colwidth="31mm" /><colspec colnum="4" colname="col4" colwidth="33mm" /><colspec colnum="5" colname="col5" colwidth="37mm" /><tbody><row><entry namest="col1" nameend="col5">SP ... styrene polymer, Std. additive ... a common additive corresponding to the state of the art, as stated in the introduction, [%] ....% by weight.</entry></row></tbody></tgroup></table></tables><tables id="tabl0002" num="0002"><table frame="all"><tgroup cols="4"><colspec colnum="1" colname="col1" colwidth="17mm" colsep="0" /><colspec colnum="2" colname="col2" colwidth="29mm" /><colspec colnum="3" colname="col3" colwidth="21mm" /><colspec colnum="4" colname="col4" colwidth="23mm" /><thead valign="top"><row><entry colsep="1">Attempt</entry><entry>Running meter [m/kg]</entry><entry>SP additive</entry><entry>Share SP [%]</entry></row></thead><tbody><row><entry colsep="1">yarn</entry><entry>400</entry><entry>P.S</entry><entry>1</entry></row><row><entry colsep="1">yarn</entry><entry>400</entry><entry>P.S</entry><entry>2</entry></row><row><entry colsep="1">yarn</entry><entry>400</entry><entry>P.S</entry><entry>5</entry></row></tbody></tgroup></table></tables>

0030At least a proportion of 90%, in particular 95%, preferably 99%, of the total proportion of the styrene-based splice inhibitor, preferably at least approximately 100%, is unbound in the plastic tape and, according to one embodiment variant, in a domain shape, as shown<figref idref="f0001">Fig. 1</figref> It can be seen that a strapping band with the composition 98% by weight of PET and 2% by weight of PS is shown. This is achieved by processing the compounding to produce the packaging element at a temperature between 250 °C and 310 °C, in particular between 270 °C and 300 °C.

0031In contrast to this shows<figref idref="f0001">Fig. 2</figref> A scanning electron microscope image of a PET tape without the addition of a thermoplastic, styrene-based splice inhibitor. This is intended to clarify the difference to the packaging element according to the invention. It can be seen that in this case domains are also formed (white dots), but these are due to semi-crystalline areas of the PET.

0032Particularly preferred is an embodiment in which the domains are designed to be stretched in one direction, as shown<figref idref="f0001">Fig. 1</figref> is visible. For this purpose, the stretching in at least one spatial direction of the domains was achieved by stretching using stretching units and a stretching oven. The domains are preferably stretched in a spatial direction to an at least approximately elliptical cross section.

0033For the representations in the<figref idref="f0002">3 and 4</figref> was carried out on various polyester-based strapping tapes with different proportions of polystyrene or without such splicing inhibitors or with commercially available standard additives (the information below the bars on the abscissa are again to be understood as % by weight, where the abbreviations "STD" stand for a commercially available standard additive and "Sty" stands for polystyrene) due to mechanical pressure load transverse to the splice stretching direction at a temperature of -5 °C (<figref idref="f0002">Fig. 3</figref>) or - 15 °C (<figref idref="f0002">Fig. 4</figref>) provoked. This was done multiple times on each band (40-60 times). The proportion of those stress cases in which splicing actually occurred was rated as “poor”.

0034In<figref idref="f0002">Fig. 3</figref> In addition to pure additives, combinations of commercially available splicing inhibitors and PS were added to the PET<figref idref="f0002">Fig. 4</figref> exclusively pure additives.

0035How out<figref idref="f0002">Fig.3</figref> As can be seen, an addition of 1% by weight of PS causes a significantly better splice-inhibiting effect than an addition of 2% by weight of the prior art splice inhibitor. In the tapes with combinations of prior art additive and PS, the resistance to splicing under these environmental conditions increases with increasing PS content.

0036<figref idref="f0002">Fig. 4</figref> shows that at the very low temperature of -15°C for this application, the tendency to splice can be significantly reduced with 2% by weight of PS. The state of the art additive, however, no longer has any effect under these conditions.