JPH0119338B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field) The present invention relates to a polypropylene packaging band suitable for automatic packaging machines that generates little abrasion powder, and a method for manufacturing the same.

(Prior Art and Its Disadvantages) Polypropylene bands are widely used as packaging bands because they are light, strong, hard to be attacked by chemicals, easy to heat-seal, and inexpensive.

However, when conventional polypropylene bands are applied to an automatic packaging machine, they rub against the packaging machine's band feed rollers, guides, tightening rollers, etc., producing abrasion powder that tends to accumulate inside the packaging machine. When this abrasion powder adheres, it causes various troubles such as roller slippage and limit switch malfunction, which impedes the smooth operation of the automatic manufacturing and packaging line. Therefore, cleaning must be carried out frequently.

However, as a countermeasure, hardening the surface of the polypropylene band or using a polypropylene copolymer is expensive. Therefore, in the past, attention was focused on improving the Young's modulus, elongation, tensile strength, longitudinal cracking resistance, etc. of the band, since the generation of abrasion powder was unavoidable.

(Problem or objective of the present invention) While comparatively studying various physical properties of various commercially available bands in order to improve the performance of polypropylene bands, the present inventors discovered the wear resistance of polypropylene bands and the crystal grain size of the bands. It has been found that there is a large relationship between the size of the width and that one-stage stretching at a high stretching rate under high heat conditions, which is not normally carried out, is effective in obtaining a product with less generation of abrasion powder.

That is, the first object of the present invention is to obtain a polypropylene band with significantly improved wear resistance compared to conventional products, and the second object is to obtain a new manufacturing method for making this band.

(Structure of the present invention, etc.) The structure of the invention of the product for achieving the first object is as stated in claim 1, ``The main component is polypropylene, uniaxially stretched at a stretching ratio of 11 times or more. "Wear-resistant packaging band with embossed surface irregularities with crystal orientation in the longitudinal direction, crystallinity of 41% or more, and crystal grain width of 60 Å or more." In addition, the structure of the method invention for achieving the second object is as described in claim 2, ``A band material mainly made of polypropylene is melted and extruded, and a band material obtained by rapidly cooling is dried. After being introduced into a heat chamber and subjected to one-step uniaxial stretching at a stretching ratio of 11 times or more in an atmosphere exceeding the crystal melting point of polypropylene to orient the crystals in the longitudinal direction, the material is embossed with a pair of pressure rollers having surface irregularities. , a method for producing a wear-resistant packaging band having a crystallinity of 41% or more and a crystal grain width of 60 Å or more.

A supplementary explanation of the wear-resistant packaging band according to the present invention is as follows.

This band has a known composition in which the main material is crystalline polypropylene with an MI value in the range of 0.5 to 4 g/10 minutes, and various stabilizers, inorganic fillers, and coloring pigments are added and mixed therein. Bands are melt extruded, quenched,
As a result of polypropylene, it is formed into a band shape by one-step stretching in the uniaxial direction at a high stretching rate of 11 times or more under dry heat at a high temperature above the melting point, and crystal orientation in the longitudinal direction occurs. Similar to conventional products, the front and back sides of the band are embossed with a certain pattern of irregularities of appropriate size, shape, and depth for the purpose of preventing vertical cracking, improving apparent thickness and stiffness, and increasing surface friction resistance. It is distributed as follows. Its thickness is 0.3
~1.5mm, and the width is generally in the range of 5 to 25mm,
It is not necessarily limited to this range.

As described in claims 1 and 2, this band must have a microscopic structure in which the width of crystal grains is 60 Å or more.

Here, the term "the width of the crystal grain is 60 Å or more" refers to a measured value obtained by the following measurements and calculations. That is, six samples were taken from a small piece of the band, and using an XD-3A X-ray diffractometer manufactured by Shimadzu Corporation, they were measured in the long axis direction of the band using the transmission method, with the Bragg angle set as θ on the equator line, and 2θ = 8 to 25°. Scan the area with X-rays,
Obtain a diffraction intensity curve from the pattern of diffraction intensity on the equator line, draw a baseline along the diffraction angle 2θ = 11~24°, and calculate the Miller index (110), that is, the diffraction angle 2θ
= 14.2° The apparent half-value width (β°) of the diffraction intensity curve was measured, and from the half-value β°, Sierra's formula β = Kλ/
The average D value calculated by D cos θ is defined as the width Å of the crystal grain according to the present invention. However, constant K=
0.92, wavelength λ=1.54 Å. Note that, for example, the VD manufactured by Shimadzu Corporation has a lower resolution than the measuring device described above.
When measured using a -1 type X-ray diffractometer, the numerical value of the crystal grain width is several angstroms lower. The numerical values in the claims are based on the high resolution
It should be noted that the values are measured using the XD-3A model.

A band with a crystallinity of 41% or more and crystals with a large grain width that has been uniaxially stretched at a high draw ratio in such a high-temperature dry heat chamber will generate abrasion powder when placed in an automatic packing machine as described below. are extremely rare.

Next, we will explain how to create this band.

Belt-shaped melt extrusion of polypropylene may be carried out under commonly used method conditions. In the method of the present invention, the band-shaped extrudate is once rapidly cooled. The quenching method may be a conventional method of passing through a water tank. Next, the cooled strip is sent into a heating chamber several meters long in which the atmosphere near its surface is maintained at a temperature between the melting point of polypropylene and 300°C, and the stretching ratio is increased to 11 times or more at once. Perform stepwise stretching. The minimum temperature in the heating chamber must be above the crystalline melting point of polypropylene. Otherwise, even if the polypropylene strip is attempted to be stretched at a high stretching ratio of well over 10 times, the polypropylene strip will break. Note that if the ambient temperature near the strip in the heating chamber is raised sufficiently above 300° C., the side edges of the strip tend to melt, so it is desirable to keep the upper limit of the temperature at about 300° C. as much as possible. This stretching can be carried out by significantly increasing the speed ratio of the stretching rollers at the entrance and exit of the heating chamber compared to conventional stretching methods.

The approximate crystal melting point of polypropylene is usually
Although the temperature is said to be around 170℃, one-step stretching of packaging bands exceeding 10 times in a heating chamber, which significantly exceeds this crystal melting point, has never been attempted before, and the crystallinity of conventional products is in the 30% range. and the width of the crystal grain is 60
Nothing reached that level. In the conventional method, polypropylene is stretched in a hot water bath maintained at a temperature above its secondary transition point and below its crystal melting point. Comparing the width of the particles with the width of the particles after leaving the tank, the latter tends to be smaller. However, according to the method of the present invention, it has been found that the width of the crystal grains of the strip on the heating chamber inlet side remains approximately the same or is improved on the same chamber outlet side.

In this way, a stretched band with a high degree of crystallinity and a large width of crystal grains, which is stretched by a high stretching rate under high temperature dry heat, has significantly improved wear resistance compared to conventional products, as shown in Figure 3. As per the particle width
When the thickness is 60 Å or more, the amount of wear debris generated is drastically reduced to less than half of that at 50 Å. The reason for this is not clear at present, but it is a fact that the larger the particle width of dense microcrystals, the greater the abrasion resistance against scratches.

(Examples and Comparative Examples) Examples of the present invention will be described below with reference to FIG. 2, including the manufacturing method and the order of the products obtained.

In the following descriptions of Examples and Comparative Examples, the band thickness t ₀ refers to the thickness before forming with a textured roll after stretching, the apparent thickness t refers to the thickness after forming, and the degree of crystallinity refers to Rigaku Denki Co., Ltd. From the melting curve Q obtained using a differential scanning calorimeter (DSC) manufactured by Manufacturer Co., Ltd. under the conditions of a temperature increase rate of 10°C/min, a chart paper feed rate of 10 mm/min, a DSC range of 4 ± mcal/sec, and a sample amount of 8 to 10 mg. , the amount of thermal melting of a perfect crystal of polypropylene is
This is a value measured using the following formula at 62 cal/g.

Crystallinity (%) = (Measured heat of fusion / 62.0) × 100 In addition, the degree of selective plane orientation R is the Miller index (110) and (040) in the above-mentioned X-ray diffraction test, that is, the diffraction angle 2θ = 14.2 The intensity of the diffraction peaks corresponding to 16.5° and 16.5° is R = (110)/(040).

Example 1 Crystalline polypropylene (manufactured by Ube Industries: E103,
M13) A raw material resin prepared by adding 3 parts by weight of calcium carbonate to 100 parts by weight is supplied to the extruder 1, and extruded into a belt shape from the die 2 at 230°C with a drawing ratio of 1.7.
A box-shaped water fountain 4 that leads to a cooling tank 3 at 20°C and has a large number of pores facing each other on both the front and back sides of the strip.
Water is jetted out from the band and the band is cooled and solidified to obtain an unstretched band. Use an infrared heater as the heat source to measure the length of this band.
Three 1.4m heating tanks are connected, and the set temperature of the heater in each tank is 400°C, and the ambient temperature of the band running part in the center of each tank is 230°C in the first tank 6a, and 230°C in the second tank 6.
The temperature of the third tank 6 is 260°C and the heating tank 6 is 290°C, and uniaxial stretching is performed with the speed ratio of the stretching rollers 5 and 7 being 12 times to obtain a band with a thickness t ₀ = 0.325 mm. When the surface temperature is 140℃,
A pair of embossing rollers 8 having a continuous pattern of diagonal diamond-shaped recesses on the surface are used to form a large number of irregularities on both the front and back surfaces of the band, and then the band is cooled by being guided into a cooling tank 9. Winding machine 1
Width 15.5mm when rolled up by 0, apparent thickness t=0.64
A band of mm was obtained.

Regarding this band, the above-mentioned Shimadzu XD-3A
When the crystal grain width defined in the present invention was determined using a type X-ray diffractometer and calculated as described above, the crystal grain width of 6 samples was 63 to 70 Å, and the average
67 Å, crystallinity 43%, selective plane orientation R=
1.56 (However, the above-mentioned Shimadzu VD with low resolution
The width of the crystal grains measured and calculated using a Type-1 X-ray diffractometer was 57 to 65 Å (61 Å on average).

This band is wrapped in an automatic packing machine (manufactured by Ikegai Tekko Co., Ltd.).
By repeatedly packing 400 x 400 square wooden boxes using FHI), one roll of 2,500 m is consumed, and the abrasion powder generated due to friction between the band and each part of the packing machine is removed. The result of suction collection and weighing was 0.2g/2500m.

Example 2 The set temperature of the heating tank is 310°C, and the ambient temperature of the band running part is 180°C in the first tank, 220°C in the second tank, and 220°C in the third tank.
Example 1 except that the temperature was 250°C, the stretching ratio was 11 times, and the band surface temperature before embossing was 120°C.
A band was manufactured under exactly the same conditions. This band has a crystallinity of 41% and an average width of crystal grains defined in the present invention of 62 Å (however, the value measured and calculated using the aforementioned low-resolution X-ray diffractometer is an average of 56 Å).
), and the degree of selective plane orientation R was 1.51. Also,
The amount of wear powder generated by the same test as Example 1 is as follows:
It was 0.4g/2500m.

Comparative Example 1 Compared to Example 1, the set temperature of the heating tank was 250
℃, the ambient temperature of the band running part is 160℃ in the first tank,
The conditions were exactly the same as in Example 1, except that the second tank was 200°C, the third tank was 220°C, the stretching ratio was 10 times, and the band surface temperature before embossing was 110°C.
A band with a thickness of t0.6 mm was obtained. This band has a crystallinity of 39% and a crystal grain width of 58 Å defined in the present invention.
(However, the values measured with the low resolution device mentioned above are
53 Å), and the degree of selective plane orientation R was 1.32.

Further, the amount of abrasion powder generated by this band in the same test as described above was 0.9 g/2500 m.

Comparative Example 2 The same raw materials as in Example 1 were used, and the material was melt-extruded at the same temperature as in Example 1, then introduced into a water bath to cool and solidify, and then passed through a hot water bath at 95°C and stretched 7 times. Embossing was performed in the same manner as in Example 1 to obtain a band with an apparent thickness of 0.6 mm and a width of 15.5 mm. The band obtained by this conventional general production method had a crystallinity of 39%, a crystal grain width of 51 Å (however, the value measured with the low resolution device mentioned above was 41 Å), and a degree of selective plane orientation R=1.21. In addition, the amount of wear powder generated is 1.2g/2500
It was m.

Reference Example 1 For reference, a polypropylene embossed packaging band manufactured by Company A with a width of 15.5 mm and an apparent thickness of 0.62 mm was measured, and the crystallinity was 38.1%, the degree of selective plane orientation R was 1.3, and the crystal grain Width is 57Å
(However, the value measured with a low resolution device is 51.9
Å) It was.

When this band was tested using the same packaging machine as before, the amount of abrasion powder generated was 0.9g/2500m.

Reference Example 2 In addition, when we measured a commercially available band made by Company B with a width of 15.5 mm and an apparent thickness of 0.64 mm, the crystallinity was 39.4% and the width of the crystal grains was 51 Å (however, with a low resolution device 45.4 Å)
However, when we performed the same wear test on this band as before, the amount of wear powder generated was 1.1g/
It was 2500m.

(Operation and Effect) Although the main items during many tests have been described above, the amount of abrasion powder generated is not determined by the size and shape of the band, such as width and thickness. In addition, the stretching temperature, stretching ratio, and embossing molding conditions affect the strength, strength, elongation, tensile modulus, etc. of the band.
It is not thought that these physical properties affect the amount of wear. The value of the degree of selective surface orientation, which depends on the embossing conditions, is also not related to the amount of wear.

In the end, the primary influence on the amount of wear is
This is a difference in crystalline state caused by stretching conditions, particularly one-step stretching at a large stretching ratio in an atmosphere at a high temperature above the melting point of polypropylene. In other words, the width of the crystal grains has a large influence on the amount of wear, and the degree of crystallinity may also have an effect on the amount of wear.

In commercially available products manufactured by ordinary stretching, the width of crystal grains is generally on the order of 50 Å, but products with grain widths of this order cannot significantly reduce the amount of wear. For example, please refer to Comparative Example 1 and Reference Example shown in FIG. However, when the stretching ratio is increased to 11 times or more at a sufficiently high temperature, crystal grains with a width of at least 60 Å can be obtained.
This material exhibits excellent wear resistance. When going through a general stretching process, the width of the crystal grains tends to be somewhat reduced compared to before stretching, but according to the stretching conditions of the present invention, the width of the crystal grains tends to become slightly larger.

Therefore, the packaging band according to the present invention exhibits extremely good abrasion resistance when used in an automatic packaging machine, and the one-step stretching at high temperature and high magnification of the present invention
This method is extremely useful because it allows a band with excellent properties as described above to be obtained.

[Brief explanation of drawings]

FIG. 1 is a plan view of a band according to the present invention. FIG. 2 is a schematic diagram showing the method of the present invention, in which 1 is an extruder, 2 is a die opening, 3 is a cooling tank, 4 is a water fountain,
5 is a stretching roller, 6 is a first tank 6a, a second tank 6b,
A heating tank consisting of a third tank 6c, 7 a stretching roller, 8
1 is an embossing roller, 9 is a cooling tank, and 10 is a winding machine. Figure 3 shows the tests of Examples 1 and 2 of the present invention, Comparative Examples 1 and 2, and Reference Examples 1 and 2 on rectangular coordinates with the width of the crystal grain on the X axis and the amount of wear powder generated on the Y axis. This is a diagram showing the results.

Claims (1)

[Scope of Claims] 1 The main component is polypropylene, and the crystals are oriented in the longitudinal direction by uniaxial stretching at a stretching ratio of 11 times or more,
A wear-resistant packaging band with an embossed surface roughness with a crystallinity of 41% or more and a crystal grain width of 60 Å or more. 2. Melt and extrude a band material whose main material is polypropylene, and then introduce the resulting band into a dry heat chamber and perform one-step uniaxial stretching at a stretching ratio of 11 times or more in an atmosphere exceeding the crystalline melting point of polypropylene. After the crystals are oriented in the longitudinal direction, they are embossed using a pair of pressure rollers with uneven surfaces to produce a wear-resistant packaging band with a crystallinity of 41% or more and a crystal grain width of 60Å or more. how to.