Snap fastener and packaging bag with the same

Abstract: A snap fastener 11 having a base section 14, 17 to be welded to a bag body 22 which is made of a liner chain low-density polyethylene (L-LDPE) or a compound resin of the liner chain low-density polyethylene and a low-density polyethylene (LDPE) as a sub-ingredient. A packaging bag fabricated with the snap fastener from the bag body 22 and the pair of snap faster half-members. When the snap fastener 11 is made of a compound resin of L-LDPE and LDPE, the composition ratio between them is set in 95-60wt% : 5-40wt%. The melt index (MI) of the compound resin is set in a range of 1-15g/10minutes. The packaging bag body 22 is adapted to have an inner side layer made of L-LDPE. An outer side layer adhered to the inner side layer may be made of Nylon so as to form the multilayered bag body.

Description: BACKGROUND OF THE INVENTION 1. FIELD OF THE INVENTION This invention relates to a snap fastener and a packaging bag having the snap fastener and, more particularly, is applicable to several fields such as the food industry, pharmaceutical preparations, and haberdashery. 2. DESCRIPTION OF THE RELATED ART Several packaging bags which have, on an opening side thereof, a web-like snap fastener consisting of a male snap fastener half-member (herein after referred to as "male half-member") and a corresponding female snap fastener half-member (herein after referred to as "female half-member) capable of intermeshing each other so that the opening side of the packaging bag can be shut and opened repeatedly have been used in the food industry, pharmaceutical preparations, and haberdashery. It is noted that there have been some proposed methods for producing such a packaging bag. One of the known general methods to produce the packaging bag is to extrude a cylindrical film with the male half-member as well as the corresponding female half-member through an extruding die, and the other is to preliminary produce a two-piece type snap fastener tape of which one is used as the male half-member and the other is used as the corresponding female half-member and to adhere/weld the tape on a base film as the packaging bag body by means of a thermal adhesion method or an adhesive agent. The former method involves some problems such as there is a limit to variety of applicable resins, it is inapplicable to laminated films, it can not be adapted to required sizes of packaging bags, and it can not be printed easily, so that this method is restricted to produce general-purpose packaging bags. The latter method has some advantages in applications to various size bags, dealing and cost, and because the packaging bag can be produced by a combination of a tape with snap fastener and a base film, this method is more popular than the former method. The qualities of the material for the snap fastener are preferably low-density polyethylene (LDPE), polypropylene (PP) or the like so that the snap fastener can be adhered to the base film made from the same resin. Therefore, if the outer layer of the base film where the snap fastener is attached is made from LDPE, the snap fastener should be produced from LDPE too. However, the snap fastener made from LDPE or PP tends to have insufficient adhesion to the bag body at a low heating temperature. When the packaging bag with the snap fastener made from LDPE is sterilized by boiling, some problems will arise. EP-A-0371402 discloses a snap fastener for a packaging bag, and a bag having said fastener attached thereto, the fastener comprising a pair of elements capable of engaging one another to close the bag, and wherein the portion of the fastener that is to be welded to the bag body consists mainly of an ethylene vinyl acetate copolymer resin containing vinyl acetate in an amount of 1 to 9% and having a melt index of 0.5 to 6.0 g/10 minutes. Accordingly, it is an object of the present invention to provide an improved snap fastener and packaging bag with the same, in which a reliable adhesion at a low temperature and a greater heat-resistance can be obtained. SUMMARY OF THE INVENTION A snap fastener according to the present invention comprises a welding portion to be welded to an object to be provided with the snap faster, the welding portion of said snap fastener being made of a linear-chain low-density polyethylene. The welding portion of the snap fastener may be made of a compound resin of linear-chain low-density polyethylene (L-LDPE) and a low-density polyethylene (LDPE) as a sub-ingredient. The compound resin of the linear-chain low-density polyethylene and the low-density polyethylene is set in a ratio of 95-60wt% : 5-40wt%. The resin forming the welding portion has a melt index (MI) of from 1-15g/10minutes, preferably from 2-8g/10minutes. The MI beyond this range causes a poor shape of the snap fastener after boiling so that the performance of open-and-close function becomes bad. The recommended thickness of the welding portion is 80-220 micrometers, preferably 130-170 micrometers because the hot-welding temperature tends to fall upon a decrease of the thickness of the welding portion. A method of producing the snap fastener is not limited particularly to a certain one, but can be conducted by being molded by means of a corresponding die and cooling the molded article in water. The original shape of the snap fastener according to the present invention need not only be limited to one shape formed of a pair of half-members intermeshing each other, but may also have a known shape having portions capable of intermeshing to each other. A packaging bag capable of opening-and-closing repeatedly according to the present invention is characterized to have: a bag body heat-sealed at three side portions thereof; and a snap fastener having a welding portion to be welded to one side portion other than the three side portions of the bag body, the welding portion of said snap fastener being made of a linear-chain low-density polyethylene. The welding portion of the snap fastener may be made of a compound resin of a linear-chain low-density polyethylene and a low-density polyethylene as a sub-ingredient. Incidentally, the hot-welding between the snap fastener and the bag body can be conducted by means of a heat, high-frequency, ultrasonic waves energy, or the like. The preferable resins for the inner side layer of the bag body are made of, for example, LDPE, ethylene-vinyl acetate copolymer (EVA), ethylene-methacrylic acid copolymer (EMAA), ionomer (IO), L-LDPE or the like. The most preferable material is L-LDPE considering thermal properties. The outer side layer contacting with the inner side layer is preferably Nylon, Polyethylene terephtthalate (PET), PP, Biaxially oriented nylon finished with vinylidene chloride (KON) and Biaxially oriented polypropylene finished with vinylidene chloride (KOP), or the like. Furthermore, the snap fastener can add thereon with a general compounding ingredient, if necessary, for instance, a coloring agent, stabilizing agent, anti-oxidizing agent, slipping agent, chemical destaticizer, or the like. The slipping agent as one of the known compounding ingredients should be added to the materials to produce the snap fastener in an amount of 0.05-0.5wt%, in order to obtain smooth intermeshing between the male half-member and the female half-member. Examples of slipping agents are oleic acid amide, erucic acid amide, stearic acid amide, behenic acid amide, oleyl palmitamide, calcium stearate, talc, kaolin, silica, polysiloxane, and so on, but oleic acid amide and erucic acid amide are preferred. When either oleic acid amide or erucic acid amide is used, the mentioned addition ratio should be maintained to obtain a preferable performance of open-and-close. As the anti-oxidizing agent, a phenolic, phosphorus, or sulfur type can be applied. As the chemical destaticizer, 0.05-0.5wt%, preferably 0.1-0.2wt%, of compound consisting of stearic acid monoglyceride and palmitinic acid monoglyceride is preferable. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a sectional view of a pair of male and female half-members capable of intermeshing according to the first embodiment of the present invention. Figure 2 is a sectional view of the snap fastener in an intermeshing state. Figure 3 is the front view of a packaging bag with the snap fastener according to the first embodiment. Figure 4 is a sectional view of the packaging bag with the snap fastener depicted in Figure 3. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S) The preferred embodiment of the present invention will now be described with reference to the drawings. 1ST EXPERIMENTAL EXAMPLE A male half-member 12 and a female half-member 13 formed into shapes as shown in Figures 1 and 2 according to the present invention can be manufactured from a linear-chain low-density polyethylene (L-LDPE) as a feed stock, while extruding and cooling successively the L-LDPE through an extruder. Incidentally, the L-LDPE has a melt index; 6 g/10 minutes. A snap fastener 11 in this experimental example can be fabricated with the male half-member 12 and the female half-member 13. The male half-member 12 is integrated with a web-like base section 14 as a welding portion to be welded to a bag body, a sectionally heart-shaped head section 15 and a joint section 16 to connect both sections 14 and 15 with each other. The female half-member 13 is integrated with a web-like base section 17 to be welded to a bag body, a semi-circular first hook 18 fixed in relation to the base section 17 and a second hook symmetrical to the first hook 18. There is provided an interval 21 between edges 18A and 19A of both hooks 18 and 19. Incidentally, the bese sections 14 and 17 have a thickness of 150 micrometers. An intermeshing between the male and female half-members 12, 13 can be performed by moving both half-members 12, 13 towards each other so that the head portion 15 of the male half-member 12 is held at the interval between the edges 18A and 19A of the female half-member 13, and continuously moving the two members towards each other while parting the hooks 18, 19 to the right and the left until the head section 15 is completely located in the space between the hooks 18, 19. Figures 3 and 4 are related drawings depicting a packaging bag 24 with the above-mentioned snap fastener 11 consisting of the male half-member 12 and the female half-member 13. The packaging bag 24 can be fabricated by heat-welding both base sections 14 and 17 of the male and female half-members 12 and 13 to a base film 23 forming a bag body 22 by means of a heat seal bar at a temperature of 143 degrees and further heat-sealing three sides of the bag body 22 except for an opening side where the snap faster 11 is lain. The base film 23 has two layers; a nylon-6 layer(15 micrometers)/a L-LDPE layer(120 micrometers), wherein the L-LDPE layer is used as an inside layer of the bag body 22 and adapted to be heat-welded with the male half-member 12 or the female half-member 13. The applicant conducted several experimental examples and control examples to confirm the thermal properties of the produced packaging bag with the snap fastener 24 under a boiling temperature of 90, 95 or 99 degrees for 45 minutes. Each result of the experimental examples and control examples is shown in an attached Table 1. At a thermal properties evaluation column in this table, a legend "Circle" explains a state of the bag with no problem after boiling, a legend "Cross" explains a presence of tear and/or abnormal appearance in the bag after boiling so that a preferable performance of open-and-close on the opening side of the bag became worse. The presence of "Tear" means, when opening the packaging bag, a state in which there is a break on the bag where the heat seal bar acted to the base sections 14, 17 so as to heat-weld the base sections 14, 17 and the inside layer of the bag body 22. The "Abnormal appearance" means a malfunction of the snap fastener 11 because of its thermal deformation, or a state in which the packaging bag looks unattractive because of creases thereon which is caused by the heat contraction gap between the snap fastener 11 and the base film 23. Furthermore, at a column for the evaluation on shape retainment of the snap fastener in Table 1, a legend "Double-circle" explains a preferable shape of the both half-members, a legend "Circle" explains a state in which unfavorable deformation of the half-members can be seen, but which can be still put to practical use, and a legend "Cross" explains a state in which the deformation of the both half-members is too big to intermesh to each other. However, it should be noted, in Table 1, that a description of 100 wt% of L-LDPE may not mean its pure state for making the snap fastener 11 but can contain a very little and general formulating ingredient. According to the result of Table 1, the snap fastener 11 of the present invention can be preferably heat-welded with the bag body 22 at a low temperature of 143 degrees, which affects high productivity of the packaging bag with the snap fastener. Since the manufactured packaging bag with the snap fastener 24 according to the present invention has an excellent high-temperature resistance at 99°C, the preferable open-and-close condition of the bag can be maintained and the appearance of the bag will not be deteriorated. The user can expect wide application of the packaging bag with a fine shape of the packaging bag, because of wide range of temperature when boiling and cooking. 2ND-6TH EXPERIMENTAL EXAMPLES The 2nd-6th experimental examples in Table 1 have been conducted to confirm whether other snap fastener compounded L-LDPE and LDPE by various composition ratios are useful. Respective composition rations in the 2nd-6th experimental examples are as follows; L-LDPE:LDPE=95wt%:5wt% in the experimental example 2, L-LDPE:LDPE=90wt%:10wt% in the experimental example 3, L-LDPE:LDPE=80wt%:20wt% in the experimental example 4, L-LDPE:LDPE=70wt%:30wt% in the experimental example 5, and L-LDPE:LDPE=60wt%:40wt% in the experimental example 6. First, the each snap faster 11 in respective experimental examples is prepared as in the mentioned 1st experimental example. The test packaging bags with the thus prepared snap fasteners 24 can be prepared for each experimental example. The hot-welding temperature is set at a temperature of 142 degrees in the 2nd experimental example and 140 degrees in the 3rd-6th experimental examples. The shown results in Table 1 are obtained in the same way as the 1st experimental example. An observation of the test packaging bags used in the 2nd-6th experimental examples is that the enough hot-weldability can be obtained at a temperature of from 140-142 degrees which is lower than that in the 1st experimental example and that the thermal properties when boiling reaches at a extremely good temperature of 99 degrees. Furthermore, each of the test packaging bags used in the 2nd-6th experimental examples shows a good property to keep its original shape as in the 1st experimental example. 7TH-11TH EXPERIMENTAL EXAMPLES A packaging bag used in the 7th-11th experimental examples has a snap fastener 11 made of L-LDPE and having a different value of Melt Index (herein after referred to as MI). The MI of L-LDPE is set as follows; 2g/10minites in the 7th experimental example, 8g/10minites in the 8th experimental example, 1g/10minites in the 9th experimental example, 9g/10minites in the 10th experimental example, and 15g/10minutes in the 11th experimental example. First, the each snap fastener 11 in respective experimental examples in prepared as in the mentioned 1st experimental example. The test packaging bags with the thus prepared snap fasteners 24 can be prepared for each experimental example. The hot-welding temperature is set at a temperature of 143 degrees in the 7nd-9th experimental examples and 142 degrees in the both 10th and 11th experimental examples. The shown results in Table 1 are obtained in the same way as the 1st experimental example. An observation of the test packaging bags used in the 7th-11th experimental examples is that the thermal properties when boiling reaches at a extremely good temperature of 99 degrees. Furthermore, each of the test packaging bags used in the 7th-8th experimental examples shows a good property to keep its original shape as in the 1st experimental example so that the good open-and-close performance is not damaged. The packaging bags in the 7th and 8th experimental examples does not show a perfect shape of the snap faster but such state will not be a problem in view of the actual performance of open-and-close. 12TH-14TH EXPERIMENTAL EXAMPLES The 12th-14th experimental examples in Table 1 have been conducted to confirm whether other snap fastener compounded L-LDPE and LDPE by various composition ratios are useful. Incidentally, the values of MI in the respective experimental examples are also varied. Respective composition rations in the 12th-14th experimental examples are as follows; L-LDPE:LDPE=95wt%:5wt% in the experimental example 12, L-LDPE:LDPE=80wt%:20wt% in the experimental example 13, and L-LDPE:LDPE=60wt%:40wt% in the experimental example 14. The MI of L-LDPE is set as follows; 1g/10minites in the 12th experimental example, 9g/10minites in the 13th experimental example, and 15g/10minites in the 14th experimental example. First, the each snap fastener 11 in respective experimental examples in prepared as in the mentioned 1st experimental example. The test packaging bags with the thus prepared snap fasteners 24 can be prepared for each experimental example. The hot-welding temperature is set at a temperature of 142 degrees in the 12th experimental example and 140 degrees in the both 13th and 14th experimental examples. The shown results in Table 1 are obtained in the same way as the 1st experimental example. An observation of the test packaging bags used in the 12th-13th experimental examples is that the thermal properties when boiling reaches at a extremely good temperature of 99 degrees. The test packaging bag used in the 14th experimental example has the thermal properties when boiling reaches at a temperature of 95 degrees. Furthermore, each of the packaging bags in the 12th-14th experimental examples does not show a perfect shape of the snap faster compared with that in the 2nd-6th experimental examples but such state will not be a problem in view of the actual performance of open-and-close. 15TH EXPERIMENTAL EXAMPLE The snap fastener 11 used in this experimental example is made of L-LDPE and the thickness of the base film 23 forming the bag body 22 is varied. The base film 23 consists of two layers, one being of the nylon-6 layer having 15 micrometers thickness and the other being of the L-LDPE layer having 100 micrometers thickness which is thinner than the L-LDPE layer in the 1st experimental example by 20 micrometers. First, the snap faster 11 is prepared as in the mentioned 1st experimental example. The test packaging bag with the thus prepared snap fastener 24 can be prepared. The hot-welding temperature is set at a temperature of 141 degrees. The shown result in Table 1 is obtained in the same way as in the 1st experimental example. An observation in this experimental example is that the heat-welding temperature is lower than that in the 1st experimental example by 2 degrees but other results are almost same as in the 1st experimental example. 16TH-19TH EXPERIMENTAL EXAMPLES The 16th-19th experimental examples are conducted to confirm whether the packaging bags compounded with other ingredients making the base film 23 are useful or not. Respective ingredients of the base film 23 are as follows; the two layers with the 12-micrometer thickness polyethylene terephthalate (PET) layer and the 60-micrometer thickness LDPE layer in the 16th experimental example, the two layers with the 15-micrometer thickness nylon-6 layer and the 60-micrometer thickness LDPE layer in the 17th experimental example, the two layers with the 20-micrometer thickness biaxially oriented polypropylene finished with vinylidene chloride (KOP) and the 40-micrometer thickness LDPE layer in the 18th experimental example, and the three layers with the 15-micrometer thickness biaxially oriented nylon finished with vinylidene chloride (KON), 15-micrometer thickness LDPE and the 50-micrometer thickness ethylene-vinyl acetate copolymer (EVA) in the 19th experimental example. Incidentally, the respective inner layers of these base films 23 are the LDPE layer in each of the 16th-18th experimental examples and the EVA layer in the 19th experimental example. First, the each snap fastener 11 in respective experimental examples is prepared as in the mentioned 1st experimental example. The test packaging bags with the thus prepared snap fasteners 24 can be prepared for each experimental example. The hot-welding temperature is set at a temperature of 135 degrees in the 16th and 17th experimental examples, 133 degrees in the 18th experimental example, and 126 degrees in the 19th experimental example. The shown results in Table 1 are obtained in the same way as the 1st experimental example. An observation in the 16th-19th experimental examples is that the hot-welding temperature is lower than in the 1st experimental example and the state of the snap fastener shape is fine as in the 1st experimental example but the thermal properties shows a temperature of 95 degrees inferior to 99 degrees in the 1st experimental example by 4 degrees. 1ST-3RD CONTROL EXAMPLES First, the each snap faster in respective control examples is prepared as in the mentioned experimental examples. The comparative packaging bags with the thus prepared snap fasteners can be made for the following control examples. It will be mentioned, however, that material resins for the snap faster and a temperature of hot-welding in these control examples are varied. The used material resins are as follows; the compound resin with the 40wt% L-LDPE and the 60wt% LDPE in the 1st control example, the LDPE in the 2nd control example, and the EVA in 3rd control example. The respective set temperature for hot-welding are 140 degrees in the 1st control example, 145 degrees in the 2nd control example, and 128 degrees in the 3rd control example. The shown results in Table 1 are obtained in the same way as the 1st experimental example. An observation in the 1st control example is that the sort of resin for the snap fastener is included in the scope of the present invention but does not have L-LDPE as a main ingredient, so that the hot-weldability at a low temperature is fine but the thermal properties when boiling is poor. The snap fastener according to the 2nd control example does not made of the same resin in this invention, whereby the thermal properties when boiling is limited at a temperature of until 90 degrees, which is poor in view of the actual use. The snap fastener according to the 3rd control example does not made of the same resin in this invention, so that the hot-weldability at a low temperature is fine but the thermal properties when boiling is limited at a temperature of until 90 degrees, which is poor in view of the actual use. 4TH CONTROL EXAMPLE The used material resin for the snap fastener 11 is PP in this control example, but when preparing the packaging bag with this snap fastener can not be obtained as the snap faster 11 is not hot-welded to the base film 23. 5TH AND 6TH CONTROL EXAMPLES The snap fasteners used in these control examples are made of L-LDPE and the value of MI are varied. First, the snap fastener 11 is prepared as in the mentioned 1st experimental example. The control packaging bag with the thus prepared snap fastener can be prepared. As can be seen from Table 1, the MI value of L-LDPE is 16g/10times in the 5th control example and 25g/10minutes in the 6th control example. The fine hot-welding state can be obtained in the control examples 5, 6 at a temperature of 143 degrees. The shown result is Table 1 is obtained in the same way as in the 1st experimental example. According to the 5th and 6th control examples, it is noted that the thermal properties when boiling the packaging bag can be obtained at a temperature of until 99 degrees as in the 1st experimental example, but the shape of the snap fastener is deformed so that the preferable performance of open-and-close is spoiled. 7TH AND 8TH CONTROL EXAMPLES In these control examples, a compound rate of L-LDPE and LDPE is changed as 60wt%:40wt% and the MI values are also changed, respectively. The MI value is 16g/10minutes in the 7th control example and 20g/10 minutes in the 8th control example. First, the snap fastener is prepared as in the mentioned 1st experimental example. The control packaging bag with the thus prepared snap fastener can be made. The hot-welding can be conducted preferably at a temperature of 140 degrees in both control examples. The shown result in Table 1 is obtained in the same way as in the 1st experimental example. When reviewing these control examples 7 and 8, it is noted that the fine thermal properties when boiling can be obtained at a temperature of until 95 degrees which is similar level to that in the 1st experimental example. However, the shape of the snap faster is not kept in its original state, so that the performance of open-and-close is poor. According to the above-mentioned experimental and control examples, the following results can be understood. The snap faster 11 made of L-LDPE or the composition of L-LDPE and LDPE can achieve fine hot-welding condition at a lower temperature than that in the 2nd control example by from 2-5 degrees. The snap faster compounded with independent L-LDPE or L-LDPE and LDPE at a composition ratio of 95wt%-60wt%:5wt%-40wt% can obtain the practical thermal properties at a temperature of at least 95 degrees. When the inner layer of the bag body uses L-LDPE, the thermal properties at a temperature of until 99 degrees can be expected. While, if the mixing ratio of L-LDPE and LDPE to produce the snap faster is beyond the mentioned range, the thermal properties at a temperature of 95 degrees can not be expected as shown in the 1st control example. When the value MI is set at from 1g/10minutes-15g/10minutes, the shape of the snap fastener can be kept in its original state, and particularly, from 2g/10minutes-8g/10 minutes, the shape can be kept in an extremely good state. While, as in the 5th-8th control examples, when the value MI is beyond 15g/10minutes, the shape of the snap fastener can not be kept in an ideal state. As shown in the 1st and 15th experimental examples, the thinner L-LDPE layer is effective to lower the hot-welding temperature. As has been mentioned, the snap fastener according to the present invention is superior to the hot-welding to the bag body at the lower temperature than the conventional fastener and to the thermal properties. The packaging bag produced according to the present invention has the fine thermal properties and maintain good state of the performance of open-and-close. Composition of Snap Fastener (wt%) Composition and Thickness (µm) of Bag Body Outer Layer/Inner Layer °C Thermal Properties °C MI State of Shape 90 95 99 Ex. Exam. 1 L-LDPE(100) NY6(15)/L-LDPE(120) 143 ○ ○ ○ 6 o ○ Ex. Exam. 2 L-LDPE(95)+LDPE(5) " 142 ○ ○ ○ 8 o ○ Ex. Exam. 3 L-LDPE(90)+LDPE(10) " 140 ○ ○ ○ 5 o ○ Ex. Exam. 4 L-LDPE(80)+LDPE(20) " 140 ○ ○ ○ 4 o ○ Ex. Exam. 5 L-LDPE(70)+LDPE(30) " 140 ○ ○ ○ 8 o ○ Ex. Exam. 6 L-LDPE(60)+LDPE(40) " 140 ○ ○ ○ 2 o ○ Ex. Exam. 7 L-LDPE(100) " 143 ○ ○ ○ 2 o ○ Ex. Exam. 8 " " 143 ○ ○ ○ 8 o ○ Ex. Exam. 9 " " 143 ○ ○ ○ 1 ○ Ex. Exam. 10 " " 142 ○ ○ ○ 9 ○ Ex. Exam. 11 " " 142 ○ ○ ○ 15 ○ Ex. Exam. 12 L-LDPE(95)+LDPE(5) " 142 ○ ○ ○ 1 ○ Ex. Exam. 13 L-LDPE(80)+LDPE(20) " 140 ○ ○ ○ 9 ○ Ex. Exam. 14 L-LDPE(60)+LDPE(40) " 140 ○ ○ ○ 15 ○ Ex. Exam. 15 L-LDPE(100) NY6(15)L-LDPE(100) 141 ○ ○ ○ 6 o ○ Ex. Exam. 16 " PET(12)/LDPE(60) 135 ○ ○ X 6 o ○ Ex. Exam. 17 " NY6(15)/LDPE(60) 135 ○ ○ X 6 o ○ Ex. Exam. 18 " KOP(20)/LDPE(40) 133 ○ ○ X 6 o ○ Ex. Exam. 19 " KON(15)/LDPE(15)/EVA(50) 126 ○ ○ X 6 o ○ Con. Exam. 1 L-LDPE(40)+LDPE(60) NY6(15)/LDPE(120) 140 ○ X X 7 o ○ Con. Exam. 2 LDPE(100) " 145 ○ X X 2 o ○ Con. Exam. 3 EVA(100) " 128 ○ X X 3 o ○ Con. Exam. 4 PP(100) " - - - - 7 o ○ Con. Exam. 5 L-LDPE(100) " 143 ○ ○ ○ 16 X Con. Exam. 6 L-LDPE(100) " 143 ○ ○ ○ 25 X Con. Exam. 7 L-LDPE(60)+LDPE(40) " 140 ○ ○ X 16 X Con. Exam. 8 L-LDPE(60)+LDPE(40) " 140 ○ ○ X 20 X NOTE: Ex. Exam. = Experimental Example Con. Exam. = Control Example

Claims: A snap fastener (11) comprising a welding portion (12) capable of being welded to an object to be provided therewith, characterised in that the welding portion comprises a linear-chain low-density polyethylene. A snap fastener according to claim 1, wherein the welding portion comprises a compound of the linear-chain low-density polyethylene and a low-density polyethylene as a sub-ingredient. A snap fastener according to claim 2, wherein the compound comprises the linear-chain low-density polyethylene and the low-density polyethylene in a weight ratio of 95:5 to 60:40. A snap fastener according to claim 2 or claim 3, wherein the compound has a melt index of from 1 to 15 g/10 minutes. A snap fastener according to any preceding claim, wherein the linear-chain low-density polyethylene has a melt index of from 1 to 15 g/10 minutes. A packaging bag capable of opening-and-closing repeatedly, comprising: a bag body (22) heat-sealed at three side portions thereof; and a snap fastener (11) whose welding portion is welded to one side portion, other than the said three side portions, of the bag body, characterised in that the snap fastener is as defined in any preceding claim. A packaging bag according to claim 6, wherein the bag body has, welded to the snap fastener, an inner side layer comprising a linear-chain low-density polyethylene. A packaging bag according to claim 7, wherein the bag body comprises plural laminated layers of which an outer side layer, adhered to the inner side layer, is made of a nylon.

Inventors: TAKUBO TOYOKAZU, YAMAMOTO SHIGEZO, TAKUBO, TOYOKAZU, YAMAMOTO, SHIGEZO, Takubo, Toyokazu, c/o Idemitsu Petrochem. Co. Ltd., Yamamoto, Shigezo, c/o Idemitsu Petrochem. Co. Ltd
Applicants: IDEMITSU PETROCHEMICAL CO, IDEMITSU PETROCHEMICAL CO. LTD.
Application year: 1993
Main classification: A44B19
IPC codes: B65D33, A44B19