JPS637153B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to wrap packaging materials that can be heat sealed at relatively low temperatures. More particularly, the present invention relates to a wrap packaging material having a non-stick overcoat layer that can be heat sealed at relatively low temperatures. Flexible packaging sheets having a base sheet coated with compositions of petroleum-based waxes, such as paraffin and microcrystalline waxes, have been used in the packaging industry for many years. This is because this sheet not only has excellent properties such as good content protection properties, tasteless and odorless properties, heat sealability, gloss and shine, but also is available at low cost. Depending on the use of the sheet, the wax may be formulated with modifiers such as natural and synthetic rubbers, resins, polymers, etc. for example,
A composition of microcrystalline paraffin wax with a small amount of elastomer (e.g., 3-20 wt%) is applied to one side of a flexible base sheet such as paper, cellophane, metal foil, and other sheet materials. The wrap material obtained by this process can be heat-sealed and has excellent protective properties as a food packaging material. However, the surface of the wax elastomer layer is somewhat sticky at room temperature, so cut sheets of this wrap material may be piled up on top of each other, or
Wraps tend to stick together when stored in a continuous roll. Such sticking phenomenon poses a serious problem when using the wrap material. Therefore, conventionally, a release agent-treated sandwich paper sheet,
Applications of solid, finely divided anti-blocking agents (such as starches or salts) or overcoats of non-stick compositions in volatile organic solvent solutions or suspensions have had to be applied. Such measures have had some success in alleviating sticking problems. However, the use of sandwich paper is inconvenient and expensive. In addition, the use of starch impairs the transparency of the lap material and also pollutes the area around the work area. Furthermore, starch may migrate to the food surface, giving the food a whitish appearance. Non-blocking overcoats containing salt crystals tend to generate water droplets on the food surface adjacent to the salt due to the deliquescent nature of the salt, resulting in an undesirable appearance to the food product. Overcoating with a non-adhesive composition in the form of a solution or suspension in a volatile organic solvent was published in 1973.
-Disclosed in Publication No. 44000. This overcoat is formed from a solution of polyamide in isopropyl alcohol. Polyamides simply impair the adhesion of the wax/elastomer layer and can only be heat sealed at high temperatures. Also,
The polyamide overcoat had the drawback of poor adhesion to the food contents, and air bubbles. Therefore, an object of the present invention is to exhibit excellent non-blocking properties without impairing the low-temperature heat-sealability of the wax elastomer layer, and to further improve transparency and
An object of the present invention is to provide a flexible packaging sheet material that is satisfactory in terms of contents protection properties, glossiness, and low cost. The present inventor has continued extensive trial production, experimentation, and research for many years. As a result, we unexpectedly found that by using an isopropyl alcohol solution of a mixture of shellac resin of more than 50 wt% and less than 70 wt% and urethane resin of more than 30 wt% and less than 50 wt%, overcoating almost eliminated the drawbacks associated with the conventional technology. It has been discovered that a composition can be obtained. Thus, in accordance with the present invention, (a) a flexible base sheet, such as paper, cellophane or a composite laminate web, is coated on one side with (b) a composition consisting of a heat-sealable thermoplastic wax and an elastomer, and (c) applying an isopropyl alcohol solution of a mixture consisting of more than 50 wt% of a shellac resin and less than 70 wt% of a shellac resin and more than 30 wt% but less than 50 wt% of a urethane resin as a non-adhesive overcoat on the surface of the heat-sealable wax composition; A flexible packaging sheet material is provided. When using an isopropyl alcohol solution of shellac resin alone, a completely uniform overcoat could not be formed, and cracks occurred at low temperatures. That is,
It was confirmed that when shellac resin was used alone, film-forming properties and flexibility were poor. The inventor of the present invention has discovered that the drawbacks of shellac resin can be completely overcome by using urethane resin in combination, and have completed the present invention. There is no known literature that suggests or teaches that an overcoating composition with excellent blocking resistance can be obtained by using a shellac resin and a urethane resin in combination. Furthermore, the blending ratio of shellac resin and urethane resin is also new. The amount of coating of isopropyl alcohol solution of shellac resin/urethane resin is not necessarily an absolute requirement of the present invention. However, in general, the weight of the shellac resin/urethane resin layer formed after evaporating the solvent is 5 to 15 g/m ² , preferably 7 to 10 g/m 2 .
Good results can be obtained by coating at g/m ² . Even if oil-based foods are packaged using the packaging sheet material of the present invention, the overcoat surface will not be adversely affected at all. That is, the overcoated surface has excellent oil resistance. In other words, there is no adverse effect on oil-based foods. The shellac resin/urethane resin mixture has better adhesion to the contents than polyamide and does not contain air bubbles. Shellac resin/urethane resin mixtures can be heat sealed at relatively low temperatures compared to polyamides. The flexible packaging sheet material of the present invention can be used in a wide range of applications. Particularly suitable for food packaging. Among food products, it is most suitable for packaging cheese. However, it can also be used to package not only cheese but also block-shaped meat, ham, sausages, minced meat, sliced ham, sausages, etc. Hereinafter, the present invention will be explained in more detail with reference to Examples. Example 1 A tacky wax composition consisting of 75% microcrystalline wax, 15% polyisobutylene and 10% petrolatum was applied to a cellophane sheet. On the surface of this wax layer, a predetermined proportion of 60wt% of shellac resin is applied.
A solution prepared by dissolving a mixture of urethane resin and 40 wt% urethane resin in isopropyl alcohol was overcoated. This solution was applied to the surface of the wax composition from a gravure printing cylinder without heating, and excess solution was removed by a conventional method.
The solvent was then evaporated to leave a uniform thin continuous film of shellac/urethane resin on the surface of the wax composition. The dry coating amount of the shellac resin/urethane resin was 7 g/m ² . The weight of the coating can be controlled freely by adjusting the concentration of the solution or the shape and depth of the cylinder. The sheet material obtained was satisfactory in terms of transparency and gloss. This sheet material was tested for blocking resistance and heat sealability. Blocking resistance was evaluated using a 10 x 10 cm sample of the sheet material, combining the overcoated surface and the non-coated surface of the base sheet, and then applying a specified load for 1 hour at an ambient temperature of 20°C. . Furthermore, in order to observe changes in blocking resistance due to temperature, an operation was performed at each temperature in which a constant load of 3 kg/100 cm ² was applied for 1 hour. Blocking resistance was evaluated in four stages. The ◎ mark indicates that when both sheets are lifted, the sheets separate and fall.
Indicates that there is no adhesion at all, and the ○ mark indicates that there is only very small adhesion between the sheets and no adhesion.
A △ mark indicates that the sheets can be easily separated by peeling and there is no adhesion and can be used, while an × mark indicates that it is difficult to separate the sheets or the sheets are completely adhesive and cannot be used. Show that something is true. Heat sealability was determined by placing the overcoated surfaces of the sheets facing each other, and applying 2 kg/kg at each test temperature.
A sealing pressure of cm ² was applied for 1 second and the sealed sheet piece was then cooled to room temperature. The seal strength of the sealed portion was measured using a rheometer according to the 180° peel test method. The pulling speed is 6
cm/second. The heat sealability was also evaluated in four stages. Items with a sealing strength of less than 200g/15mm width and unusable are marked with an "X", items that can be used with a seal strength of 200g to 300g are marked with a △, and sealing strength is used with a width of 300g to 400g. Items that are in good condition are marked with an ○ mark, and items that weigh more than 400g and can be used satisfactorily are marked with an ◎ mark. The results of these tests are shown in Tables 1 and 2 below. Table 1 Tests related to blocking resistance (A) Blocking resistance test load (Kg/100cm ² ) evaluation by load 2 ◎ 5 ◎ 7 ◎ 10 〇 (B) Blocking resistance test by temperature Temperature (℃) evaluation 20 ◎ 40 ◎ 60 〇 80 × Table 2 Test sealing temperature (°C) evaluation regarding heat sealability 60 × 70 △ 80 〇 90 ◎ 100 ◎ Blocking resistance is generally considered to be good if it can withstand a load of 3Kg/100cm ² . The test results fully meet this requirement. Also, 3Kg/
No stickiness occurs even when stored at room temperature (20-40℃) under a load of ^100cm2 . Furthermore, regarding the seal strength, a value of 250 g/15 mm width or more is said to be acceptable for normal use, and the overcoat of the present invention is also satisfactory in this respect. Example 2 The procedure was as described in Example 1, except that the coating amount of shellac resin/urethane resin was varied. Each sheet obtained was tested for blocking resistance, heat sealability, and oil resistance. The blocking resistance test was carried out by applying a load of 3 kg/100 cm ² for 1 hour at 40°C. The heat sealability test was conducted by applying a sealing pressure of 2 kg/cm ² for 1 second at 90°C. The oil resistance test was conducted by using n-heptane as the oil, directly contacting the overcoated surface of a 10 x 10 cm sample, and observing the condition of the coated surface after leaving it at 20°C for 60 minutes. Summer. Oil resistance was evaluated in four stages. If there is no change at all on the overcoat surface, it is marked ◎, if some spots appear, it is marked ○, if it becomes slightly cloudy or there is no problem with the coating, it is marked △, and if the overcoat surface is immersed, it is marked △. Items that fall apart are marked with an x. The results are shown in Table 3 below.

[Table] From the above results, it is understood that in order to satisfy each performance, shellac resin/urethane resin should be applied at a dry weight of 5 to 10 g/m ² , preferably 7 to 10 g/m ² . Ru. Example 3 The procedure was as described in Example 1 except that the proportions of shellac resin and urethane resin in the overcoat solution were varied. Each sheet obtained was tested for blocking resistance, heat sealing resistance, and oil resistance as described in Example 2. The results are shown in Table 4 below.

[Table] As is clear from the above results, the preferred blending ratio of shellac resin/urethane resin is 50 to 70/
50-30. Food Shelf Life Testing In a number of experiments in which cheese was packaged in the sheet material of the present invention coated with the heat-sealable wax composition described above and overcoated with a non-stick coating, When the cheese was vacuum packaged and stored under refrigerated conditions at about 4° C. for 6 months, the package was unpacked, the overcoat did not transfer to the surface of the cheese, and there were no foreign substances on the surface of the cheese. All packages maintained satisfactory vacuum levels during the test period. The protective properties of the sheet coated with the wax composition are not impaired;
The sheet material also exhibited low surface friction and excellent workability during mechanical packaging operations. Furthermore, as fully demonstrated in the examples above, the non-adhesive composition of the present invention can be applied to papers, cardboards, metal foils, and synthetic plastic films used for labels and packaging in various applications. It can be applied to various types of base sheets made of composites.

Claims (1)

[Claims] 1 a flexible base sheet, a heat-sealable wax coated on one side of the base sheet;
a layer of an elastomer composition, and said wax/
Shellac resin on the surface of the elastomer composition layer
More than 50wt% and less than 70wt% and urethane resin more than 30wt%
A blocking-resistant packaging sheet material comprising a non-adhesive layer formed by overcoating an isopropyl alcohol solution of a mixture containing less than 50 wt% and evaporating the solvent.