JP6529124B2 - Evaluation method for breaking of kraft paper for heavy packaging and kraft paper for heavy packaging - Google Patents

Description

  The present invention relates to a method for evaluating the breakage of heavy duty kraft paper and the heavy duty kraft paper.

  Kraft paper is a strong, strong, tear-resistant paper made from pulp manufactured by the kraft method, and is mainly used for heavy packaging applications, corrugated board materials, envelopes, adhesive tapes and the like. In the case of heavy packaging application, it is also called heavy bag kraft paper, and is processed into a bag, for example, filled with several tens kg of various products such as cement, rice, flour, etc., and used for storage and transportation. In the case of kraft paper used for such applications, it is of course required to have high strength not to break easily. In JIS-P3401: 2000, 1 to 5 types of kraft paper are specified according to the application etc., and properties such as tensile strength and tear strength are respectively standardized at a certain level or more.

  Among kraft papers, especially kraft paper for heavy packaging applications is required to have a strength that does not break when thrown or dropped during bagging operation, storage and transportation, and kraft paper for heavy packaging applications is required. Regarding the corresponding JIS No. 5 type No. 1, “by shrinking the paper on the paper machine minutely, the stretching performance in the flow direction of the paper is given, and the impact characteristics after bag making are improved, mainly It is defined that "non-bleached kraft stretch paper used for heavy packaging paper bags". This is what is called a so-called Kurpak paper.

  In Kurpac, a web is carried between a roll and an endless rubber blanket, and while the web is compressed with a nip bar and a rubber blanket, the pre-stretched blanket is shrunk to compress the web. It is intended to shrink and increase the breaking elongation, which is the name of a device used to make the kraft paper used for heavy packaging applications have the breaking elongation. In addition, the paper (5 types 2nd) which gave the expansion | extension performance in the width direction is called fructo paper, and is not included in the paper.

Patent Document 1 (Japanese Patent No. 4803586) is composed of a single layer having a basis weight of 95 to 130 g / m ² and is measured in accordance with JIS-P8113 by creping with a Kurpaak apparatus. The kraft paper used for the decorative paper or reinforcing paper of a kraft paper bag is characterized in that the raw material pulp whose freeness is adjusted to 450 to 650 cc is used with the product of the tensile strength and the transverse elongation at break of 30 to 65. Have been described.

  By the way, as an evaluation method of heavy paper for kraft paper, there is a test method in which the contents such as actual rice are packed in a bag made of kraft paper and then dropped from a certain height (JIS Z0217: 1998 ). This evaluation method is very stressful to the bag and very severe, and may be rejected if the bag is torn at a specified number of times. In addition, since this drop test involves making a kraft paper after making it into a bag and requiring filling of the contents, it takes a lot of work steps and takes time until the result of acceptance or rejection becomes clear, and the productivity becomes worse. There is a problem of

  The above-mentioned Patent Document 1 is an invention about kraft paper used for decorative paper or reinforcing paper of kraft paper bag, and as a method for evaluating the suitability of the kraft paper, tensile strength in the transverse direction and transverse direction measured according to JIS-P8113 It has been proposed that the suitability of kraft paper be simply evaluated by setting the product with the elongation at break in the range of 30 to 65.

  However, the inventors of the present invention have found that the above-mentioned drop test is good as long as the heavy packaging kraft paper and the crupak paper satisfy the strengths such as tensile strength and tear strength specified in the above-mentioned JIS-P 3401: 2000. It is considered appropriate to obtain an evaluation, and various tests have shown that although it is actually a bag made of kraft paper for heavy packing that satisfies the above strengths such as tensile strength and tear strength, it has been performed several times. It turned out that tears often occur due to the fall of the.

Patent No. 4803586 gazette

  As described above, since the drop test is performed after making kraft paper into a bag and processing, and the contents need to be filled, it takes many work steps and takes time until the result of pass / fail is revealed, and the productivity Even if it is a kraft paper bag for heavy packaging that satisfies the strengths such as tensile strength and tear strength specified in JIS-P3401: 2000, there is a problem that the film is broken in a few times. It sometimes occurred. This means that even if only strength conditions such as tensile strength and tear strength are used as indicators for evaluation when evaluating kraft paper for heavy packaging, it means that appropriate evaluation can not necessarily be made. Do.

  The present invention has been made under such a background, and it is possible to easily predict the occurrence of breakage in a drop test, and to evaluate and select the method to obtain a bag that is difficult to tear. It is an object of the present invention to provide a kraft paper for heavy packaging.

  The inventors of the present invention have made it possible to evaluate the expected bag breakage of heavy-packed Kraft paper based on the finding that appropriate results can not be obtained by using strength conditions such as tensile strength and tear strength as indicators. As a result of intensive investigations, it was found that the occurrence of tearing in the drop test had a high correlation with the lateral elongation characteristics of the paper, and the present invention has been completed.

  That is, the present inventors observe the appearance of the bag at the time of the drop test, and the impact applied to the bag at the time of falling is that the short side direction (short side) of the bag is in the long side direction (long side). I guess it was bigger than the shock. And, in general bag-making processing of kraft paper for heavy packaging, since the short side direction of the bag corresponds to the lateral direction of the paper, tearing is expressed as the lateral direction of the paper (width direction or CD direction) In the following description, it is expressed as “horizontal direction.” Also, the direction perpendicular to this is expressed as “longitudinal direction”. By adding it, I thought that the paper was stretched in the lateral direction gradually and the bag was broken. In addition, it was confirmed in the drop test that the time for impacting the bag is as short as 1/100 second.

The present invention was made under the above findings, and the invention according to claim 1 for solving the above problems is a heavy duty packaging Kraft for predicting the occurrence of breakage in the drop test prescribed in JIS Z0217: 1998. It is a paper tear bag evaluation method, and
The tensile strength obtained from the tensile test in which the tensile test is performed until the test piece breaks at a stretching speed of 500 mm / min or more for the test piece in the transverse direction of kraft paper, and the tensile strength obtained from the single tensile test until the break Perform a tensile test that repeats the action of applying a load in the range of 50% or more of the length and returning it to the zero point until it breaks at an elongation speed of 500 mm / min or more,
Also, the amount of plastic deformation and the elongation at break shown below are each measured, and the sum of the measured amounts of plastic deformation is divided by the value obtained by subtracting 1 from the number of repetitions of the tensile test to determine the average value of the amount of plastic deformation. Then, a breaking index, which is a value obtained by dividing the breaking elongation by an average value of the amount of plastic deformation, is determined, and the breaking index is used as an index for predicting the occurrence of breakage in the drop test. Evaluation method for heavy packaging kraft paper.
Plastic deformation (mm): In a cyclic tension test, the amount by which the paper is pulled and then returned to 0, and the paper does not return as stretched at the start of the next tension and is longer than the length in the previous tension.
-Elongation at break (mm): Elongation at break in a single tensile test which is carried out until it breaks at the same speed as the cyclic tensile test.

  In one embodiment, it is determined that breakage does not occur in the drop test when the bag breakage index obtained under conditions of an elongation speed of 1,000 mm / min and a load of 2.00 kN / m is 7.0 or more. In another embodiment, no breakage occurs in the drop test if the bag breakage index obtained under the condition of an elongation speed of 1,000 mm / min and a load of 1.33 kN / m is 14.0 or more In still another embodiment, breakage occurs in the drop test when the bag breakage index obtained under the conditions of an elongation speed of 500 mm / min and a load of 2.00 kN / m is 16.0 or more. It is judged not to.

The invention according to claim 5 for solving the above-mentioned problems is a method for evaluating the breakage of heavy-packed kraft paper, which predicts the occurrence of breakage in the drop test prescribed in JIS Z 0217: 1998,
The tensile strength obtained from the tensile test in which the tensile test is performed until the test piece breaks at a stretching speed of 500 mm / min or more for the test piece in the transverse direction of kraft paper, and the tensile strength obtained from the single tensile test until the break is an operation of returning to the zero point after applying a load of 50% or more ranges subjected to tensile tests repeated at extension rate 500 mm / min or more, the number of tests to the test piece is broken as an index, before Symbol drop test It is an evaluation method of the bag breakage evaluation of kraft paper for heavy packaging characterized by predicting the occurrence of the tear in.

  In one embodiment, when the cyclic tensile test is performed under a condition of an elongation speed of 1,000 mm / min and a load of 2.00 kN / m, breakage occurs when the number of the cyclic tensile test is 6 or more. In another embodiment, when the cyclic tension test is performed under conditions of an elongation speed of 1,000 mm / min and a load of 1.33 kN / m, the number of cyclic tensile tests is 11 in another embodiment. It is judged that breakage does not occur if the number of times is more than one, and in still another embodiment, the cyclic tension test is carried out under the conditions of an elongation speed of 500 mm / min and a load of 2.00 kN / m. It is determined that no breakage occurs when the number of tensile tests is 11 or more.

The invention according to claim 9 for solving the above-mentioned problems is a method for evaluating the breakage of heavy-packed kraft paper, which predicts the occurrence of breakage in a drop test prescribed in JIS Z 0217: 1998,
Both of the bag breakage index according to claim 1 and the number of tension tests according to claim 5 are used as indexes for predicting the occurrence of breakage in the drop test. It is a bag breakage evaluation method.

Kraft paper for heavy packaging in a preferred embodiment has a bag breakage index of 7.0 or more under the conditions of an elongation speed of 1,000 mm / min and a load of 2.00 kN / m according to the method of claim 1. It is characterized in that the bag breakage index determined by the method according to claim 1 under conditions of an elongation speed of 1,000 mm / min and a load of 1.33 kN / m is 14.0 or more. Alternatively, it is characterized in that the bag breakage index determined by the method according to claim 1 under the conditions of an elongation speed of 500 mm / min and a load of 2.00 kN / m is 16.0 or more.

  The heavy duty kraft paper in a preferred embodiment is made using 15-40% high concentration refined kraft pulp.

  According to the present invention, it is possible to easily predict the occurrence of tearing in the drop test of the bag, so it is possible to enhance the efficiency of the bag making operation. In addition, according to the kraft paper for heavy packaging according to the present invention, there is an effect that it is possible to obtain a kraft paper bag for heavy packaging with excellent strength, which is less likely to be broken when paper is processed and used as a bag. .

It is a schematic diagram of the cyclic tension test performed in the evaluation method which concerns on this invention. It is a graph which shows the elongation-load curve created in the evaluation method concerning the present invention.

<Definition of terms>
Before describing the modes for carrying out the present invention, terms used in the following description are defined.
・Tensile strength (kN / m) by one tensile test : Tensile strength when breaking a kraft paper transverse direction test piece by one tensile test at the same extension rate as the cyclic tensile test ・Fracture Elongation (mm) : Elongation until the transverse test piece of kraft paper is broken in one tensile test at the same elongation speed as the cyclic tensile test Cyclic tension test : transverse test of kraft paper The test is repeated until the piece is subjected to a constant load at a constant elongation rate and then returned to the zero point. Elongation (mm) : The amount by which the test specimen is pulled and stretched in the cyclic tension test (FIG. 1b, 2b))
Plastic deformation (mm) : In a cyclic tension test, the amount by which the paper is tensioned and then returned to 0, and the paper does not return as stretched at the start of the next tension and is longer than the length at the previous tension ( Figure 1 (see 1a and 2a)
Sum of plastic deformation (mm) : Sum of plastic deformation of each time of multiple tensile tests in cyclic tension test Elastic deformation (mm) : After applying load in cyclic tensile test Amount returned when returning to 0 point (see Fig. 1 (1b-1a, 2b-2a))
・Elongation-load curve : A curve showing the relationship between load and elongation

  Subsequently, a mode for carrying out the present invention will be described with reference to the attached drawings. As described above, the present inventors have keenly found that there is a limit to the evaluation of kraft paper for heavy packaging taking into consideration only strength conditions such as tensile strength and tear strength. As a result of examination, it was found that the occurrence of breakage in the drop test is highly correlated with the lateral elongation characteristics of the paper.

  FIG. 1 is a schematic view of a cyclic tension test performed in the evaluation method according to the present invention. In the case of normal conditions (normal test method) as shown in FIG. 1A, the tensile strength and the elongation at break (A) were evaluated by one tensile operation until the test piece (paper) is broken. Measure). On the other hand, in the case of the present invention (FIG. 1B), an operation of repeating a cyclic tensile test, that is, a tensile test of applying a constant load and then returning to a zero point, is repeated several times until breakage. The test piece preferably has a width of 15 mm, and the gripping length of the test piece is 100 mm, but may be changed to the adjustable width or gripping length in the tester used.

  As shown in FIG. 1B, when such a cyclic tension test is performed, when the paper is pulled for the first time (elongation amount 1 b) and returned to 0 point, the plastic deformation does not return to the original state, and a certain amount The second tensile test starts from the length obtained by adding the plastic deformation (1a) of the first test to the original length. Then, after pulling the paper for the second time (stretching amount 2b) and returning it to the 0 point, it does not return to the state at the time of the second start, and it will be a state where it is further stretched by (2a) due to plastic deformation from there. I understand. The same result is obtained for the third and subsequent times, and assuming that the fracture occurs at the n-th time, the total plastic deformation at the start of the n-th test, that is, the sum (B) of the plastic deformations at each time is [1a + 2a + 3a + ... + ( n-1) a].

  The amount (1a, 2a, ..., (n-1) a) longer than the original length due to each plastic deformation, that is, the amount of plastic deformation (mm) is the load-elongation curve obtained in the tensile test It can be calculated from FIG. 2 shows an example of a load-elongation curve. The amount of plastic deformation is accumulated as the number of times of tension increases.

Theoretically, as shown in the following equation, a value obtained by adding the elongation amount (b) last extended in the cyclic tension test to the sum (B) of plastic deformation which is the amount not to return in the cyclic tension test It is considered that breakage occurs if it is equal to or exceeds the breaking elongation (A) which is the elongation length to break in one tensile test at the same elongation rate as the cyclic tensile test.
"Sum of plastic deformation (B)" + "Elongation (b)"「" Break elongation (A) "

  That is, it is considered that the breakage can be suppressed by suppressing the increase of (B) on the left side or increasing (A) on the right side. Therefore, in the present invention, first, the sum (B) of the amount of plastic deformation is a value obtained by subtracting the last one from the number of repetitions of the tensile test (n-1) Since the amount can not be determined, divide by n-1) to obtain the average value (C) of the amount of plastic deformation, and then divide the breaking elongation (A) by the average value (C) of the amount of plastic deformation The bag breakage index (A / C) was used as the index for the evaluation of tearing, that is, as an index for predicting the tearability in the drop test.

  In order to apply the above procedure as an evaluation of tear resistance such as heavy bag kraft paper, the elongation speed is set to 500 mm / min or more in the cyclic tensile test of the test piece in the transverse direction of the kraft paper. It has been found that the load applied to the test piece in the transverse direction of 50% needs to be 50% or more of the tensile strength in one tensile test. In addition, as a tension tester, a tension tester conforming to JIS P8113: 2006 was used.

  When the extension speed is lower than 500 mm / min, the length of time for which the paper is subjected to load in the cyclic tension test is obviously longer than the time for which the bag is subjected to impact in the drop test prescribed in JIS Z0217: 1998. As a result, it was found that the drop test could not be reproduced in the repeated tension test, and it did not function sufficiently as a method for evaluating the resistance to bag. Therefore, it is important that the extension speed be 500 mm / min or more. In addition, since it is considered that the elongation at the highest speed is suitable for evaluation among the usable range in the tensile tester used, it is a general maximum elongation rate in the tensile tester conforming to JIS P8113: 2006. Evaluation at 1,000 mm / min was considered to be preferable.

  In addition, when the load is 50% or less of the tensile strength in one tensile test, the impact on the paper is too small, and the number of repeated tensile tests is too large, so the samples have superiority and inferiority. It is thought that it becomes difficult to predict the resistance to bag growth. Therefore, it is important that the range of load / tensile strength under the above-mentioned normal conditions be 50% or more. In addition, in the case of general kraft paper for heavy packaging, by setting the load to 1.33 kN / m or more, it is possible to easily and sufficiently evaluate the tear resistance.

  Furthermore, as a standard for judging that no breakage occurs in the drop test defined in JIS Z 0217: 1998, in the cyclic tension test carried out under the conditions of an elongation speed of 1,000 mm / min and a load of 2.00 kN / m. The number of cycles of pulling until breaking is required to be 6 or more, preferably 8 or more, and more preferably 10 or more. However, in consideration of ease of measurement and workability, the upper limit is desirably less than 30 times.

  In addition, as a standard for judging that no breakage occurs in the drop test defined in JIS Z 0217: 1998, the breakage was obtained by the above evaluation method under the conditions of an elongation speed of 1,000 mm / min and a load of 2.00 kN / m. The bag index needs to be 7.0 or more. As a result of conducting various tests, the present inventors have found that it is possible to judge that no breakage occurs in the drop test prescribed in JIS Z 0217: 1998 if the bag breakage index is 7.0 or more. The

  Under the conditions of an elongation speed of 1,000 mm / min and a load of 2.00 kN / m, the tear index is preferably 10.0 or more, more preferably 14.0 or more. The upper limit is not particularly limited, but it is preferably 30.0 or less, more preferably 25.0 or less, in view of the balance with other problems such as bag-making processability, handleability, production efficiency, etc. . Therefore, it can be said that the most preferable range is 15.0 or more and 25.0 or less. The drop test is conducted by filling 30 kg of brown rice as a content and dropping it 10 times from a height of 1.2 m.

  In the evaluation method according to the present invention, heavy packaging kraft paper, in particular heavy bag kraft paper specified as five types of kraft paper in JIS P 3401: 2000 (as mentioned above, commonly known fructoco. (Not included in the paper), and is particularly suitable for the paper provided with the paper, which is specified as type 5 No. 1. The kraft paper of the present invention is based on the premise that the kraft paper satisfies various specified values including the basis weight defined in JIS P3401: 2000.

  The raw material pulp used for the kraft paper in the present invention is preferably digested by the kraft method to obtain unbleached or bleached kraft pulp, and is then refined (refined) to a pulp slurry. By the beating, the pulp is in the form of branched or swollen microfibrils along the length direction, and the strength and the lateral elongation of the paper can be enhanced. In particular, in the present invention, it is preferable to beat at a high concentration of 15 to 40% (preferably 20 to 30%). When the high concentration beating (HCR treatment) is performed as described above, the pulp is more branched or microfibrillated, and the breaking elongation, tensile energy, tear strength, burst strength and the like of the paper can be enhanced.

  In the present invention, the high concentration refined pulp may be used alone, or may be mixed with a low concentration refined pulp. When mixing, it is preferable that high concentration refined pulp is 50 weight% or more.

  The prepared raw material thus obtained is made by a known wet paper machine, for example, a long mesh paper machine, twin wire former paper machine, circular mesh paper machine, short mesh paper machine, gap former, etc. . Among them, gap formers are suitable for use in the present invention because high speed papermaking is possible and production efficiency is high. In addition, when making paper at high speed with a wide machine (for example, 5 m or more), for example, the size of the tension acting on the paper and the drying conditions are likely to be different between the both ends and the center in the paper width direction, Although there is a tendency for strength and elongation characteristics to be uneven, fiber orientation in the machine width direction or J by examining the tendency in the machine width direction (for example, the operation side of the machine to the drive side) It becomes possible to adjust machine conditions such as the / W ratio.

  In the present invention, the paper sheet is made by the gap former to change the fiber orientation in the thickness direction, and the above-mentioned adjustment of high concentration beating, concentration, J / W ratio, etc. Even with a wide paper machine, it is possible to produce kraft paper that satisfies the elongation and strength characteristics in the width direction.

  In the present invention, it is preferable to use softwood pulp as a raw material because the fiber length is long and advantageous for improving the strength. The type of softwood is not particularly limited, and examples thereof include Douglas fir, larch, spruce, radiata pine, etc. These may be used alone or in combination of two or more. The proportion of softwood kraft pulp in the raw material pulp is preferably 50% by weight or more based on the total solid weight of the raw material pulp. Examples of raw material pulp that can be used in combination with kraft pulp include waste paper pulp and mechanical pulp.

  In addition, when manufacturing high basis weight paper such as kraft paper, it is necessary to jet a large amount of raw material, and when the jet speed is slow, the raw material falls without reaching the wire. When the basis weight increases, it is necessary to slow down the machine speed to a certain extent because of the balance with the drying ability, and when conditions of a large amount of raw materials and a decrease in machine speed overlap, fibers clog in the mesh without passing through the screen. Tend to occur. Therefore, in order to eject a large amount of raw material from the head box, a jet velocity exceeding gravity is required, and it is desirable to have a flow velocity as fast as possible without causing screen clogging. Therefore, in the present invention, it is preferable to increase the velocity of the jet compared to the velocity of the wire, and the J / W ratio can stabilize the operation by setting the pressing condition, in particular, 103 to 130%. So it is preferable to do so.

Since the above-mentioned kraft paper has a relatively high basis weight, as described above, the machine speed is influenced by the drying ability in the dryer part. And when the value of the product of basis weight (g / m ² ) and machine speed (m / min) is large, the drying process in the dryer part becomes insufficient, while when the product value is small, productivity is descend. Therefore, in the present invention, it can be said that it is preferable to achieve papermaking under the condition that the value of product of basis weight and machine speed becomes 20,000 to 50,000, in order to achieve both drying property and productivity.

  The kraft paper according to the present invention is manufactured by a manufacturing method using a Kurpaak apparatus to impart longitudinal extensibility. A manufacturing method using this Kurpaak apparatus is to carry a web between a roll and an endless rubber blanket, and while the nip bar and the rubber blanket compress the web, the pre-stretched blanket is It is a method of contracting to shrink the web and increase the breaking elongation. In the Kurpaak apparatus, it is possible to adjust the breaking elongation in the longitudinal direction of the kraft paper mainly by the ratio of the manufacturing speed on the Kurupak apparatus entering side, the manufacturing speed on the Kurupak apparatus outlet side, and the pressing force by the nip bar. The Kurpaak apparatus is usually installed in the dryer group of a paper machine, and excess water is removed after the desired creping has been applied.

  Although the moisture content of the wet paper at a certain position in the dryer fluctuates due to the relationship between the speed of the paper machine and the basis weight, when installing the Kurpaak, when the moisture of the paper being fed is too low, the elongation of the paper is obtained It is difficult for the wet paper to be broken, and when it is too high, the wet paper should be allowed to pass between the Kurpaak blanket and the Kurpaak dryer cylinder in a state containing 20 to 45% of water, preferable. A more preferable water content is 30 to 45%.

  The nip pressure between the roll pack blanket and the roll pack dryer cylinder is preferably 20 kN / m or more, because if the pressure is too low, the shrinkage at the nip outlet decreases. The surface temperature of the Kurpaak dryer cylinder is preferably set to 100 to 120 ° C. in order to facilitate the development of elongation. This temperature adjustment can be performed by managing the dryer cylinder inlet steam pressure.

  The ratio of the production speed on the outgoing side to the production speed on the incoming side in the above-mentioned Kurupak apparatus is called the draw ratio, and the percentage of making the production speed on the outgoing side slower than the production speed on the incoming side is called minus draw%. In order to process the curd pack paper to obtain a heavy bag which is difficult to break, it is necessary to set the range of minus draw to -3 to -8% (preferably -4 to -7%).

  In terms of pulp raw materials, there are methods such as beating at a high concentration, moderately enhancing beating, and increasing the amount of paper strength agent added. In terms of papermaking conditions, there are methods such as adjusting the J / W ratio, reducing the fiber orientation ratio, and adjusting the draw at the time of the Kurupak process for the Kurupak paper.

  In addition, in the case of a cruppa paper, the specific tensile energy absorption amount (TEA) in the longitudinal direction specified in JIS P8113: 2006 is preferably 2.5 J / g or more, and more preferably 2.7 J / g or more. It is more preferably 2.9 J / g or more. On the other hand, the specific tensile energy absorption in the transverse direction is preferably 1.0 J / g or more, more preferably 1.2 J / g or more, and still more preferably 1.4 J / g or more.

The specific tensile energy mentioned here indicates the amount of energy per unit area required to break. It is seen that the paper tends to decrease the longitudinal tensile strength while the longitudinal elongation at break increases by the curl pack processing. However, if the specific tensile energy in the longitudinal and longitudinal directions is within the above range, the paper absorbs energy even if a large force is applied to the bag when the bag is processed and used. , Less likely to cause a bag.

  The kraft paper in the present invention preferably has a specific tensile strength in the longitudinal direction of 60 N · m / g or more, more preferably 65 N · m / g or more, as defined in JIS P8113: 2006. Preferably it is 70 N · m / g or more. On the other hand, the tensile strength in the transverse direction is preferably 28 N · m / g or more, more preferably 30 N · m / g or more, and still more preferably 32 N · m / g or more. In addition, when the breaking elongations in the longitudinal and lateral directions are respectively greater than 60 N · m / g and 28 N · m / g, sufficient strength can be obtained when using the bag, and the risk of tearing is reduced.

  Furthermore, in the present invention, the specific tear strength in the longitudinal direction specified in JIS P-8116: 2000 of kraft paper is preferably 12 mN · m 2 / g or more, preferably 14 mN · m 2 / g or more, more preferably 16 mN ·· The specific tear strength in the transverse direction is desirably 20 mN · m 2 / g or more, preferably 22 mN · m 2 / g or more, and more preferably 24 mN · m 2 / g or more.

  In the present invention, the specific tensile stiffness in the longitudinal direction specified in ISO / DIS 1924-3: is desirably 4.0 kN · m / g or more, preferably 4.2 kN · m / g or more, and more preferably Is preferably 4.4 kN · m / g or more, and the specific tensile stiffness in the transverse direction is preferably 2.8 kN · m / g or more, preferably 3.0 kN · m / g or more, more preferably 3.2 kN • m / g or more. When the specific tensile stiffness in the longitudinal and lateral directions is greater than 4.0 kN · m / g and 2.8 kN · m / g, sufficient stiffness is obtained on the paper, and the handling as paper is improved. The processability at the time of processing becomes good.

  Furthermore, in the present invention, it is preferable that the disintegration freeness measured by the measurement method specified in JIS P8121-2: 2012 is 400 to 700 ml, for the pulp that has been disintegrated according to the definition of JIS P8220-1: 2012 of kraft paper, More preferably, it is 500-650 ml. In the present invention, disaggregation freeness is freeness measured after disaggregating kraft paper, and disaggregated in accordance with JIS P 8220-1: 2012 and measured by a measuring method defined in JIS P 812 1-2: 2012. It is the value of freeness. If the disaggregation freeness is in the range of 400 to 700 ml, the air resistance of the kraft paper can be in the range of 10 to 25 seconds, and the content is more appropriate in the case of heavy packaging for grain etc. Can be stored. If the disintegration freeness is less than 400 ml, the tensile strength, tear strength and the like of the kraft paper tend to decrease.

  As described above, since the kraft paper according to the present invention is manufactured so as to have a specific strength range, it is used as, for example, a bag, and the contents are particularly grains, inorganic powder, granules, or When it is made into a bowl-like thing etc., it can fully prevent that a bag tears by moving in the load and inside.

  Examples of the present invention and comparative examples will be specifically described below, but it goes without saying that the present invention is not limited to these examples. In addition,% shows weight% unless there is particular notice.

Manufacture of kurupakaki for evaluation and heavy bags (Sample A)
A basic weight of 83 g / m ² , prepared by blending 100% of unbleached softwood kraft pulp concentrated at a high concentration of 30% as a raw material with a gap former type paper machine equipped with a Kurpaak machine at 480 m / min. It is a paper for heavy bags. In addition, the minus draw in Kurupak was -4.5%.
(Sample B)
The heavy-bag heavy-duty paper is made in the same manner as in Example 1 except that the beating concentration of the raw material is 13%.
(Sample C)
The heavy-bag heavy-duty paper is made in the same manner as in Example 1 except that the beating concentration of the raw material is 3.0%.

Drop test and measurement method of test items in Table 1 (drop test)
It evaluated according to JIS Z 0217: 1998.
○ ... No broken bags out of 10 drop tests ... ... 1 out of 10 dropped tests with a broken bag × · · 10 out of 10 dropped tests with 3 or more broken bags

(Measurement of tensile strength and elongation at break by one tensile test)
A horizontal sample (15 mm width) of kraft paper is divided into four stages of 1,000 mm / min, 500 mm / min, 200 mm / min, 50 mm / min by using the ORIENTEC Tensilon Universal Material Tester RTC-1210A. It changed and the tensile strength by one tension test and breaking elongation were measured. In addition, the elongation rate prescribed | regulated by JISP8113: 2006 is 20 +/- 5 mm / min, and the elongation rate in this invention is set higher than it.

(Measurement of the number of cycles of tension until breakage and the sum of plastic deformation by carrying out cyclic tension test)
The tensile strength of a transverse sample (15 mm width) of kraft paper was measured using the ORIENTEC Corporation Tensilon Universal Material Testing Machine RTC-1210A, and the elongation speed was 1,000 mm / min, 500 mm / min, 200 mm / min, 50 mm / min. The load is changed to three stages of 2.00 kN / m (30 N / 15 mm width), 1.33 kN / m (20 N / 15 mm width) and 1.00 kN / m (15 N / 15 mm width). The cyclic tension test was carried out to determine the number of tension cycles until breakage and the sum of the amount of plastic deformation.

(Load / tensile strength)
The load / tensile strength (%) was determined by dividing the load kN / m by the tensile strength in one tensile test.

(Breakable bag index)
The sum of the plastic deformation is divided by the value obtained by subtracting the last one from the number of repetitions of the tensile test to obtain the average value of the plastic deformation, and then the breaking elongation is divided by the average value of the plastic deformation to break The bag index was determined.

<Table 1>

  The evaluation results of the drop test of Sample A, Sample B, and Sample C were ○, Δ, and ×, respectively. From this, it is necessary to make the heavy-packing kraft paper in the present invention using high-concentration refined kraft pulp of 15 to 40%, preferably 20 to 30%.

Example 1
In each of the samples A, B, and C, the load applied at the time of breakage was tensile strength in each of Examples 1 in which the measurement was performed under the measurement conditions of an elongation speed of 1,000 mm / min and a load of 2.00 kN / m. It was 50% or more, and a correlation was found between the drop test and the number of tension cycles, and the tear index. Under the above measurement conditions, it is considered that the index of the number of repetitions of tension before breaking in the cyclic tension test which is judged not to cause breakage in the drop test is 6 or more, and the index of the breakage index is 7.0 or more. .

Example 2
The load applied at the time of breakage was 50% or more of the tensile strength in each case of Example 2 in which the measurement was performed under the measurement conditions of an elongation speed of 1,000 mm / min and a load of 1.33 kN / m. A correlation was found between the number of repetitions and the bag breakage index. Under the above measurement conditions, it was considered that the index of the number of repetitions of tension before breaking in the cyclic tension test which is judged not to cause breakage in the drop test is 11 or more, and the index of the tear index is 14.0 or more. .

Example 3
The load applied at the time of breakage was 50% or more of the tensile strength in each case of Example 3 in which the measurement was performed under the measurement conditions of elongation speed 500 mm / min and load 2.00 kN / m, and the drop test and tension repeated A correlation was found between the number of times and the bag breakage index. Under the above measurement conditions, it is considered that the index of the number of repetitions of tension before breaking in the cyclic tension test which is judged not to cause breakage in the drop test is 11 or more, and the index of the tear index is 16.0 or more. .

Comparative Example 1
In Comparative Example 1 in which the measurement was performed under the measurement conditions of an elongation speed of 1,000 mm / min and a load of 1.00 kN / m, the load was less than 50% with respect to the tensile strength, and the number of times of tensile repetition of samples A and B was More than 30 times. Although the bag breakage index calculated from the results up to 30 times was correlated with the drop test, it was judged to be unsuitable as a test condition because it is difficult to measure an accurate bag breakage index.

Comparative example 2
In Comparative Example 2 in which the measurement was performed under the measurement conditions of an elongation speed of 200 mm / min and a load of 2.00 kN / m, the load applied at the time of breakage was 50% or more of the tensile strength. The number of times of tension repetition became 30 times or more. The bag breakage index calculated from the results up to 30 times was not correlated with the drop test, so that it was difficult to measure the correct bag breakage index, and it was judged to be unsuitable as a test condition.

Comparative example 3
In Comparative Example 3 in which the elongation rate was 50 mm / min and the load was 2.00 kN / m, the load applied at the time of breaking was 50% or more of the tensile strength in each case. The tensile repetition number of C became 30 times or more. The bag breakage index calculated from the results up to 30 times was also found to have no correlation with the drop test, and was judged to be unsuitable as a test condition.

  Although the invention has been described in some detail with particular reference to its most preferred embodiments, it will be appreciated that a wide variety of different embodiments can be constructed without departing from the spirit and scope of the invention. Accordingly, the present invention is not to be limited to any particular embodiment except as set forth in the appended claims.

Claims (9)

It is a method for evaluating the breakage of heavy duty kraft paper for predicting the occurrence of breakage in the drop test prescribed in JIS Z 0217: 1998,
The tensile strength obtained from the tensile test in which the tensile test is performed until the test piece breaks at a stretching speed of 500 mm / min or more for the test piece in the transverse direction of kraft paper, and the tensile strength obtained from the single tensile test until the break Perform a tensile test that repeats the action of applying a load in the range of 50% or more of the length and returning it to the zero point until it breaks at an elongation speed of 500 mm / min or more,
Also, the amount of plastic deformation and the elongation at break shown below are each measured, and the sum of the measured amounts of plastic deformation is divided by the value obtained by subtracting 1 from the number of repetitions of the tensile test to determine the average value of the amount of plastic deformation. Then, a breaking index, which is a value obtained by dividing the breaking elongation by an average value of the amount of plastic deformation, is determined, and the breaking index is used as an index for predicting the occurrence of breakage in the drop test. Evaluation method for kraft paper for heavy packaging.
Plastic deformation (mm): In a cyclic tension test, the amount by which the paper is pulled and then returned to 0, and the paper does not return as stretched at the start of the next tension and is longer than the length in the previous tension.
-Elongation at break (mm): Elongation at break in a single tensile test which is carried out until it breaks at the same speed as the cyclic tensile test.   It is judged that a tear does not occur in the drop test when the bag breakage index obtained under conditions of an elongation speed of 1,000 mm / min and a load of 2.00 kN / m is 7.0 or more. Evaluation method of kraft paper for heavy packaging   It is judged that a tear does not occur in the drop test when the bag breakage index obtained under conditions of an elongation speed of 1,000 mm / min and a load of 1.33 kN / m is 14.0 or more. Evaluation method of kraft paper for heavy packaging   It is judged that a tear does not occur in the drop test when the bag breakage index obtained under conditions of an elongation speed of 500 mm / min and a load of 2.00 kN / m is 16.0 or more. Evaluation method for broken bags of heavy-duty kraft paper. It is a method for evaluating the breakage of heavy duty kraft paper for predicting the occurrence of breakage in the drop test prescribed in JIS Z 0217: 1998,
The tensile strength obtained from the tensile test in which the tensile test is performed until the test piece breaks at a stretching speed of 500 mm / min or more for the test piece in the transverse direction of kraft paper, and the tensile strength obtained from the single tensile test until the break is an operation of returning to the zero point after applying a load of 50% or more ranges subjected to tensile tests repeated at extension rate 500 mm / min or more, the number of tests to the test piece is broken as an index, before Symbol drop test A method for evaluating the breakage of heavy-duty kraft paper characterized by predicting the occurrence of breakage in the above.   When the cyclic tension test is carried out under conditions of an elongation speed of 1,000 mm / min and a load of 2.00 kN / m, it is judged that breakage does not occur when the number of cyclic tension tests is 6 or more. The method for evaluating the breakage of heavy duty kraft paper according to claim 5.   When the cyclic tension test is carried out under conditions of an elongation speed of 1,000 mm / min and a load of 1.33 kN / m, it is judged that breakage does not occur when the number of cyclic tension tests is 11 or more. The method for evaluating the breakage of heavy duty kraft paper according to claim 5.   In the case where the cyclic tension test is carried out under conditions of an elongation speed of 500 mm / min and a load of 2.00 kN / m, it is judged that no breakage occurs when the number of cyclic tension tests is 11 or more. 5. The method for evaluating the breakage of heavy duty kraft paper according to 5. It is a method for evaluating the breakage of heavy duty kraft paper for predicting the occurrence of breakage in the drop test prescribed in JIS Z 0217: 1998,
Both of the bag breakage index according to claim 1 and the number of tension tests according to claim 5 are used as indexes for predicting the occurrence of breakage in the drop test. Evaluation method of bag breakage.