JPS6119494B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a coated baling band. Currently, packing bands are generally manufactured and used by melt-extruding a crystalline polyolefin resin such as polypropylene or high-density polyethylene and stretching the resulting product in the longitudinal direction. Among these, polypropylene bands are most commonly used because they are inexpensive and have high strength. As methods for tightening the band, there are generally used methods such as using metal fittings, heat fusing in which the joint surfaces are heated to around the melting point and then pressed with a constant pressure, and a method using a plastic tightening tool. Of these methods, the method using heat fusion is the most widely used because of its speed and ease of tightening. The performance of such a band is not only that the tensile strength in the longitudinal direction of the band (hereinafter referred to as linear strength) is high, but also that the tensile strength of the fused part after the bands are stacked and heat fused (hereinafter referred to as fusion strength) is high. ) is desirable. This is especially true since fusion strength is generally smaller than linear strength. However, with conventional oriented single-layer polypropylene bands, if the welding temperature is increased or the heating time is increased in an attempt to obtain greater welding strength, the welded part deforms and the appearance is impaired, as shown in Figure 4. As shown, if the ends of the band are misaligned, a notch will be formed at the ends 4, 4' of the mating surfaces, and the tensile strength of the band will be extremely reduced. There were other inconveniences. Therefore, the appearance of a band that can be firmly fused at low temperatures is desired.
Furthermore, the fusion strength of the band increases as the degree of stretch orientation increases in a range where the degree of stretch orientation is low, but at a certain degree of stretch orientation, for example, for crystalline propylene homopolymer (hereinafter abbreviated as PP), 8～
It reaches a peak at a draw ratio of 9 times, and if the degree of draw orientation is increased further, delamination tends to occur at the fused part despite the increase in direct strength, and as a result, the fused bond strength begins to decrease. . Therefore, there is a certain limit to the ability to increase the fusion strength by increasing the degree of stretching orientation. Furthermore, the present inventors found that the band fusion strength is greater for resins with lower melt fluidity even if they are the same type of resin, but low melt fluidity reduces the power consumption of melt extrusion. It has the disadvantage of having great influence and making it big. On the other hand, conventional packing bands made from polypropylene are highly stretched and oriented in the longitudinal direction, making them prone to vertical cracking and, furthermore, being prone to fuzzing. This caused the inconvenience of the objects getting wrapped around each other. An object of the present invention is to provide a polypropylene packing band that has high fusion strength and is resistant to longitudinal cracking. The present invention comprises a base material layer made of a resin mainly composed of a crystalline propylene polymer that is stretched and oriented in the length direction by a factor of 6 or more, and a crystalline propylene polymer that is present at the outermost part and is stretched and oriented in the length direction. and a coating layer consisting of a resin whose main component is a resin having a melting point lower than the melting point of the resin of the base material layer, and each layer is bonded to each other by overlapping and stretching. The lengthwise stretching of the base layer is defined as W _{1 ≧W 2 ≧0.5, where W 1 is the width of this layer in an unstretched state and W 2 is the width} after stretching. The gist is a packing band which is formed in the orientation temperature range of this layer by limiting the shrinkage in the width direction to a range of _W1 . The crystalline propylene polymer of the base layer and the coating layer is a crystalline copolymer of PP or propylene as the main component and one or more other olefins, or a mixture thereof as the main component. can be mentioned. When using PP or propylene-based crystalline copolymer of propylene and other olefins for the base layer and PP for the coating layer, the coating layer
EPR (ethylene-propylene rubber) may be blended in an amount of 2 to 25% by weight based on PP. This increases the band's fusion strength. The band is firmly fused at a relatively low fusion temperature, and the melting point of the covering layer is lower than that of the base material layer in order to increase the fusion strength. For this purpose, a resin having a lower melting point than that of the resin of the base material layer may be selected as the resin for the coating layer, or even if the resin is of the same type, the melting point may be lowered by making it weakly oriented. Block copolymers generally have two melting points,
In the present invention, the lower melting point is the standard. Stretching for orientation of the base layer and the covering layer can generally be 6 to 20 times. Furthermore, if a resin with lower melt flowability than that of the base material layer is used as the resin for the coating layer, a band with even greater fusion strength can be obtained. An example of such a band is MFR (condition 14 in Table 1 of JISK 7210-1976).
(230℃, 2.16Kgf). ) A highly oriented (stretching ratio usually 6 to 20 times, preferably 9 to 15 times) base material of a crystalline copolymer of 1.5 to 10 PP or propylene as the main component and other olefins. layer, and a crystalline copolymer of this and other olefins containing PP or propylene as a main component with an MFR of 0.1 to 2.5 and lower than the MFR of the resin of the base layer (propylene content is usually 80 to 2.5).
99.5%, including block copolymers and random copolymers). This outermost layer is preferably stretched 5 to 15 times. The base material layer and the covering layer may be directly adhered to each other as shown in FIGS. 1 and 2, or may be adhered to each other through another synthetic resin layer as shown in FIG. 3. In order to bond these layers together, the resin webs forming each layer may be stretched in a superimposed state.
The means for overlapping the webs include co-extruding the resins forming each layer, extrusion coating a web of one resin that has been unstretched or stretched at a low ratio with another resin, and adding the solidified webs that form each layer. An example of this is heating and overlapping preformed products. The stretching temperature of the base layer and the coating layer is preferably within a range known as the orientation temperature range of these resins. After stretching, the band may be annealed in order to reduce its shrinkage during fusion bonding. When stretching the base material layer in the vertical direction, the width of the unstretched material is
W ₁ , W ₂ is the width after stretching, W ₁ ≧W ₂ ≧
The shrinkage in the width direction is limited to a range of 0.5W ₁ .
Generally, when an unstretched original fabric is stretched, the width and thickness of the original fabric decrease depending on the stretching ratio. In the conventional stretching of a band, the width and thickness are reduced at approximately the same rate as a result of stretching. That is, when the width of the original fabric before stretching is W ₁ and the stretching ratio is SR, the width W ₂ of the original fabric after stretching is expressed as W ₂ =(1/√)W ₁ . Therefore, if the stretching ratio is 4 times, the width W ₂ of the original fabric after stretching is 1/2 of the width W ₁ of the original fabric before stretching.
In addition, if the stretching ratio is 9 times, W ₂ is usually reduced to 1/3 of W ₁ . If the reduction in width due to stretching is not suppressed in this manner, the molecular orientation of the stretched product progresses in the stretching direction, and vertical cracks become more severe as the stretching ratio increases. In the case of the present invention, the base material layer has 6 to 6
The stretching ratio is 20 times, but in this case,
In a normal band, the width W ₂ after stretching is (1/√6) W ₁ ~ (1/ _√20 ) W ₁ ≒ 0.41 ~ with respect to the original width W 1
_However , in the band of the present invention, shrinkage in the width direction is suppressed to W ₁ ≧W ₂ ≧0.5W ₁ in the base material layer, regardless of the stretching ratio. By stretching while suppressing shrinkage in the width direction, molecular orientation in the longitudinal direction progresses, and some molecular orientation also occurs in the transverse direction. As a result, longitudinal cracking resistance is significantly improved compared to conventional synthetic resin bands. In addition, when adhering layers by overlapping them and stretching them in the vertical direction, stronger adhesive strength can be obtained than when shrinkage in the width direction is not restricted, and the surface smoothness is very excellent. , suitable for printing. Note that stretching in the vertical direction while limiting shrinkage in the width direction is achieved by making the part of the web that does not contact the rolls between the delivery nip roll and the take-up nip roll for stretching as short as possible, and widening the width of the other webs. This can be achieved by increasing the force between the roll and the web as much as possible. The web can then be slit to a predetermined width to obtain a band. Using a wide web in this way allows high-speed multi-web production, and also has the advantage of greatly improving production efficiency. In the present invention, an ultraviolet absorber or an antistatic agent may be added only to the coating layer. This reduces the use of these chemicals and provides the band with the desired UV degradation resistance and antistatic properties. The packing band of the present invention may be so-called wrinkled. The present invention will be explained below with reference to the drawings. FIG. 1 shows an example in which a coating layer 2 is provided on one side of a base layer 1. 2 and 3 show an example in which the base layer 1 has coating layers 2 and 2' on both sides. The types of resins in one coating layer 2 and the coating layer 2' on the opposite side may be different, but it is preferable that they be the same. Although 3 in FIG. 3 is a third layer that is neither a base layer nor a covering layer, such a layer may be required as a binder for the layers on both sides thereof. EXAMPLES The present invention will be explained below using Examples, but the present invention is not limited thereto. Example 1 Crystalline polypropylene (Chitsuso Polypro A5012 [trademark]) with an MFR of 1.8 and a melting point of 163°C as measured by a differential scanning calorimeter (DSC) (the same applies hereinafter) was used as a base material.
Extruded from mmO/extruder (L/D=25; CR=3.5) (thickness approx. 3mm), and on both sides of it from another extruder (40mmO/;
Width 60mm thickness manufactured with L/D=25; CR=3.8)
0.3mm film (raw material MFR = 2.5; melting point 120℃
and 163°C crystalline propylene ethylene block copolymer (Titsopolypro K7014 [trademark]) or MFR = 0.5; The unstretched original fabric is led in-line to a nearby roll stretching machine, and the roll surface temperature is 125℃.
The film was stretched 8 times. The distance between the stretches during stretching was varied to obtain a stretched product with a width retention rate of 45 to 100% (width of the stretched product, 27 to 60 mm), and this was slit to obtain a band with a width of 15.5 mm. The properties of this band are shown in Table 1. Next, for comparison, Chitsuso Polypro A5012 [trademark]
A single-layer band was made in the same manner. This property is shown in Table 1.

[Table] As is clear from Table 1, Comparative Example 1 has good cracking prevention, but the fusion strength is low, and even a multilayer band is easy to crack at a width retention rate of 45%. Products with a width retention rate of 50% or more and a copolymer coating layer have excellent crack prevention and fusion strength. Example 2, Comparative Examples 2 and 3 Block copolymer (Chitsuso Polypro K7014 [trademark]) was used as the raw material for the coating layer, and the width retention rate was 70.
A band was obtained in the same manner as in Example 1 and Comparative Example 1 except that the stretching ratio was kept constant at % and the stretching ratio was changed (Example 2, Comparative Example 2). The properties of this band are shown in Table 2. In addition, according to the conventional method, the above-mentioned Chitsuso Polypro A5012
[Trademark] to 65mmO/extruder (L/D=25; CR=
3.5) was melted and extruded from the T-die, cooled and solidified to produce a 40 mm wide original fabric, which was introduced in-line to a steam heated stretching tank and stretched 7 times at 115°C to obtain a 15.5 mm wide band (Comparative Example 3) The properties of this band are shown in Table 2.

[Table] From Table 2, as the stretching ratio increases for multi-layer bands, the fusion strength also increases accordingly, whereas for single-layer bands, as the stretching ratio increases, the linear strength increases, but the fusion strength does not. The band produced by the conventional method (Comparative Example 3) has severe cracking and low fusion strength. Example 3, Comparative Examples 4 and 5 Crystalline polypropylene (Chitsuso Polypro A5012) with an MFR of 1.8 and a melting point of 163°C was used as the base layer, and in Example 3, crystalline propylene with an MFR of 7.0 and a melting point of 138°C was used as a raw material for the coating layer. Ethylene-butene-1 random copolymer (Chitsuso Polypro A3132) was used as the raw material for the coating layer in Comparative Example 4, with an MFR of 0.8 and a melting point of 163.
°C crystalline polypropylene (Chitsuso Polypropylene)
A band was obtained in the same manner as in Example 1, except that the width retention rate was kept constant at 70% and the stretching ratio was changed. In Comparative Example 5, a single layer band of Chitsuso Polypro A5012 was made in the same manner. These properties are shown in Table 3.

【table】

[Table] As is clear from Table 3, the present invention, that is, the resin for the coating layer that has PP with a lower melting point than the base layer even though the molecular weight is small (Example 3), the coating layer has the same melting point as the base layer. The fusion strength is significantly superior to that of the resin having a large molecular weight (Comparative Example 4). It can be seen that the single layer one (Comparative Example 5) is the most inferior.

[Brief explanation of the drawing]

Figures 1, 2, and 3 are cross-sectional views in the width direction of a packing band showing a specific example of the present invention, and Figure 4 is an overlapping of the ends of a conventional single-layer oriented crystalline thermoplastic resin band. FIG. 4 is a perspective view of the overlapping portion showing a case where the two parts are shifted. In these figures, 1 is the base material layer;
2, 2' are coating layers, 3 is a layer such as a binder, 4,
4' is the edge of the mating surface.

Claims (1)

[Scope of Claims] 1. A base material layer consisting of a resin mainly composed of a crystalline propylene polymer that is stretched and oriented six times or more in the length direction; It has a multi-layer structure comprising a crystalline propylene polymer as a main component and a coating layer made of a resin having a melting point lower than the melting point of the resin of the base layer, and each layer is formed with or without another synthetic resin layer. The base material layer is stretched in the length direction so that the width of this layer in an unstretched state is W ₁ and the width after stretching is W ₂ . When, W ₁ ≧
A packing band characterized in that the shrinkage in the width direction is limited to a range of W ₂ ≧0.5W ₁ in the orientation temperature range of this layer. 2 of the crystalline propylene polymer of the base layer
The packing band according to claim 1, wherein the MFR of the crystalline propylene polymer of the coating layer is 0.1 to 2.5 and lower than the MFR of the resin of the base material layer. . 3. The packing band according to claim 2, wherein the base material layer is stretched 6 to 20 times. 4. The packing band according to claim 1, wherein the coating layer is a crystalline propylene homopolymer containing 2 to 25% by weight of EPR. 5. The packing band according to any one of claims 1 to 4, wherein the base layer and the covering layer are directly bonded to each other. 6. The packing band according to any one of claims 1 to 5, wherein an ultraviolet absorber or an antistatic agent is added only to the coating layer. 7. The packing band according to claim 1, 2, 3, 5 or 6, wherein the crystalline propylene polymer of the coating layer is a crystalline propylene homopolymer.