JPH026866B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a facing that coats at least the surface side (skin side) of liquid-absorbing sanitary products such as sanitary napkins and diapers, and a method for manufacturing the same. Although it is a facing made of non-woven fabric mainly made of polypropylene threads joined by some softening, it has a basis weight of 15 to 40 g/m ² and a relatively high longitudinal and transverse tear length. The present invention relates to an ideal facing that has excellent flexibility and has a well-balanced combination of strength and flexibility. The present inventors have discovered that facings can be obtained that are highly flexible and have excellent liquid absorption properties, and that also satisfy the strength requirements required for actual use. Conventionally, various fiber materials have been used for this type of non-woven fabric facing, but the characteristics required for this type of facing are that since it comes into contact with the skin, even if the facing has fiber fuzz, it should not be fuzzed during use. It should not adhere to the skin, it should not tear during use, its liquid absorption properties should not decrease due to the provision of a facing, and the absorbed liquid should not return to the skin in a significant amount ( It is said that it is desirable to have less wet bag), as well as something that is flexible and bulky. In addition, even in the case of facings using polypropylene threads as in the present invention, it is possible to use only ordinary drawn polypropylene threads, or a nonwoven fabric made of partially joined polypropylene threads mainly by mixing them with partially drawn or partially drawn polypropylene threads. Facings made of
Increasing the strength requires sacrificing flexibility, so in any case, facings made of partially bonded nonwoven fabrics mainly made of drawn polypropylene threads are unsuitable. Furthermore, as an invention similar to the present invention, a nonwoven fabric with highly oriented polypropylene fibers having a fabric weight of 68 to 170 g/m is strongly bonded by fusion of low oriented or unoriented polypropylene fibers described in Japanese Patent Publication No. 50-30747. There are inventions related to carpet base fabrics such as ^{No. 2} . As described above, there have been attempts to obtain nonwoven fabrics using undrawn or partially drawn polypropylene threads as adhesive fibers, but as in the present invention, the threads can be used alone or in an amount of 70% by weight, preferably 90% by weight.
There has been no attempt to face sanitary products with a low basis weight such as 15 to 40 g/m ² using more than 1% by weight, and it is also known that by doing so, all of the performance requirements for facings as described above can be satisfied. Not yet. The present invention mainly uses such undrawn or partially drawn polypropylene yarns, generally 70%
A web containing preferably 90% or more by weight,
Nip cotton at a pressure of 5 kg/cm or more between a pair of upper and lower calender rolls or a pair of left and right rolls, one or both of which are heated to a temperature of 130°C or higher that does not melt the yarn.
Preferably, the upper limit is at most 20 kg/cm, and the web running speed is 20 m/min or more, which is preferable for operational reasons.
By running at a speed of 50 m/min or more, the undrawn or partially drawn polypropylene thread is not melted, but at least a portion of the thread is softened and bonded to other threads forming the nonwoven fabric. The undrawn or partially drawn polypropylene thread used in the present invention has the property of being more easily softened and melted than ordinary drawn polypropylene thread, and its softening point is about 150° C. or lower. Such yarns do not shrink or substantially do not shrink when subjected to the above-mentioned calender roll treatment, and therefore do not deteriorate the surface condition of the nonwoven fabric.
The fabric weight of the web is 15 when used as a product.
It must be pre-designed to be like ~40g/ ^m2 . If it is less than 15g/ ^m2 , it will not be useful as a facing even if it is coated on sanitary products.
On the other hand, if it exceeds 40 g/m ² , the liquid absorbency generally decreases, which is not desirable. In the present invention, the web, particularly the parallel web, as described above is run at a running speed of 20 m/min or more, preferably 50 m/min or more, and is preferably nipped heated by a pair of upper and lower heating rolls to form the web. This method softens at least a part of the undrawn or partially drawn polypropylene yarn, but in order to obtain a nonwoven fabric that has the desired properties without softening at the speed,
The temperature of the upper and lower pair of rolls is 130℃ or higher, and the nip line pressure is 5Kg/cm or higher, preferably 5 to 20Kg/cm.
It has been discovered that this can be achieved by doing the following, and this point is also a feature of the present invention. Here, the pair of rolls can both be flat rolls or embossed rolls,
One side may be a flat roll and the other side may be an embossed roll with an arbitrary pattern. The temperature of the roll should be 130° C. or higher; if it is lower than this, the softening will not be sufficient in terms of operation, so it is not suitable. Note that the upper limit of the roll temperature is determined by the correlation with the running speed of the web; for example, when the running speed is 50 m/min, the roll temperature may be 170°C. In short, the temperature may be any temperature at which the undrawn or partially drawn polypropylene thread is softened without melting. Also,
The same objective can also be achieved by setting the nip line pressure of the rolls at that time to, for example, 50 kg/cm for the same reason as the roll temperature. In this way, the facing, which is the object of the present invention, can be obtained, and at the time of manufacture, the composition of the starting web, its running speed, and heating roll treatment conditions are set within specific ranges. When the facing of the present invention is observed under a microscope, the polypropylene polymer is partially softened and bonded in the nonwoven fabric, and when touched with the hand, it has drapability (flexibility) and has a basis weight of 15 to 40 g/ ^m2. Then, the average of the longitudinal and transverse fracture lengths, that is, y (Km) = (longitudinal fracture length + transverse fracture length) /
When I looked at 2, I found that it was very flexible, even though it was relatively high-ranking. The present invention has actually measured the characteristics of such facings, particularly their strength and flexibility, and found that such facings have similar strength and flexibility characteristics to facings made from ordinary stretched polypropylene soft bonded nonwoven fabric. It turned out that there was a clear difference. This can be understood by referring to the accompanying drawings. That is, in FIG. 1, the horizontal axis is x for the nonwoven fabric facing A of the present invention and the conventional soft bonded nonwoven fabric facing B made of stretched polypropylene.
(Km), that is, (longitudinal tear length + transverse tear length)/2, which shows the mutual relationship between both facings, with the vertical axis representing the degree of flexibility y(g). As is clear at first glance from the figure, the facing A of the present invention has a higher degree of flexibility than the control facing B at the same strength. In other words, it can be seen that it is soft. It was found that area A in the figure is surrounded by four straight lines of 0.3Km≦x≦3.0Km, y=-77.5x+98.5 and y=-7.75x+93.5. More preferably x≦
It is 2.5km. The plot in the figure is based on the phasing test results shown in Tables 1 and 2 below, and the facings of the present invention (black plots) and the control facings (white plots) have different characteristics. It turns out that they can be almost completely separated. This point is the greatest finding of the present invention. As is clear from FIG. 1, the facing of the present invention is well-balanced with flexibility, with a lower limit of 70 g and more preferably a target of 75 g or more. The method for measuring the degree of flexibility y(g) here is as follows. Take three 21.5 cm x 21.5 cm sample pieces from the nonwoven fabric and place them on the sample stand of a handle-o-meter measuring machine manufactured by THWING ALBEST INSTRUMENT so that the longitudinal direction of the test pieces is perpendicular to the slots (8 mm intervals). Place it like this. Next, lower the penetrator blade at a position of 10.7 cm (1/2 of the test width),
Read the maximum value (g) indicated by the microammeter when pressing the test piece, subtract that value from 100, define this as the degree of flexibility y (g), and express it as the average value of 4 samples. The partially joined facing of the present invention obtained by the manufacturing method described above has the above-mentioned flexibility of 70 g, particularly 75 g or more, and (longitudinal tear length + transverse tear length)/2 as required performance in practical terms. It was found that one that satisfies the requirement of 0.3 km, especially 1 km or more, can be easily obtained. In addition, it has excellent liquid absorption properties and has little wet baggage, and there is no fiber fuzz, and even if a small amount of fuzz is found on the surface, it will not fall off and get on the skin because it is bonded. It does not tear during use, dries more easily than conventional polyester nonwoven facings, and is smooth to the touch. In this respect, as is clear from the comparison in Tables 1 and 2, the facing of the present invention is clearly different from the facing of the control. The present invention will be explained below with reference to Examples and Comparative Examples. Examples 1 to 10 and Comparative Examples 1 to 11 The nonwoven fabric forming fibers used in the examples were 100% unstretched polypropylene staples, and the fibers used in the comparative examples were fully oriented polypropylene staples 100%.
%. Regarding the conditions adopted in the experiment and the physical properties of facings obtained, those of Example 1 are as follows.
Comparative examples are summarized in Table 2.
Here, the flexibility of facings with a basis weight of 30 g/m ² and 40 g/m ² is a value converted to a basis weight of 20 g/m ² . The nip linear pressure of the rolls is 7Kg/cm, and the running speed is
The speed was 30 m/min, and the roll combination consisted of a flat roll and an embossing roll, each of which was heated. Also,
The measurement of fiber fuzz here was carried out as follows. First, the principle consists in measuring the amount of fibers removed from the nonwoven surface by friction. 30cm (length direction) of the nonwoven fabric to be measured
Cut into 14cm (widthwise) pieces. Place this on the fixing plate and secure both ends with fixing metal fittings.
At this time, it is necessary that the nonwoven fabric does not sag. On the other hand, prepare a metal rod, tightly wrap felt around the surface of the metal rod, and slide the felt around the surface of the nonwoven fabric smoothly 10 times. At this time, the fluff of the nonwoven fabric adhering to the felt wrapped around the surface of the metal rod was carefully removed using tweezers, and this was weighed in mg. Measured values are the average of n=5.

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【table】 [Brief explanation of drawings]

Figure 1 shows facing A of the present invention and facing B as a control (longitudinal tear length + transverse tear length)/
2=x (Km) on the horizontal axis and flexibility y (g) on the vertical axis to show the difference in characteristics between the two facings.

Claims (1)

[Scope of Claims] 1. A facing made of a non-woven fabric mainly made of unstretched or partially stretched polypropylene threads, which facings are joined by softening of the polypropylene threads, and have a basis weight of 15 to 40 g/m. ² , x (Km)
= (longitudinal tear length + transverse tear length) / 2, when y (g) is the flexibility, 0.3≦x≦3.0, y = -7.75x +
98.5 and y=-7.75x+93.5. 2. A facing for sanitary products as set forth in the preceding item, characterized in that it contains 70% by weight or more of undrawn or partially drawn polypropylene thread. 3 Facings for sanitary products characterized by 0.3≦x≦2.5 in any of the preceding items.