JP3324909B2 - Food packaging materials for microwave heating - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a food packaging material constituting a food packaging bag for heating a microwave oven, and more particularly to a bonding strength between an inner melt blown layer and an intermediate pulp fiber sheet layer constituting the packaging material. The present invention relates to a food packaging material which is excellent, has an excellent processing speed when forming and processing a food packaging bag by a heat sealing method using the packaging material, and has a low breakage rate as the obtained food packaging bag. .

[0002]

2. Description of the Related Art In recent years, with the development of food packaging technology and the spread of microwave ovens, once-prepared foods, such as foods such as hot dogs, hamburgers and croquettes, Chinese steamed buns and shomai, and even yakitori and grilled fish are packaged. Enclosed in a bag and re-heated for use in eating or drinking, or thawing frozen rice such as pilaf or fried rice in its packaging bag, warming it, and serving it for eating or drinking at home or at restaurants It has become a means of being done.

When it is assumed that non-frozen foods such as hot dogs and hamburgers are heated in a microwave oven and served for eating and drinking, the contents are stored in a bag made of film so that the contents do not leak out. At the time of eating and drinking, it is heated in a microwave oven while being kept in the film bag, and is served for eating and drinking. In addition, the above-mentioned frozen cooked rice is also supplied by being sealed in a film bag having strong bonding, generally a bag made of a polyethylene, polyester, or vinyl acetate film.

[0004] However, these films do not have a moisture absorbing function or a water absorbing function themselves, so that when a heated solid food is packaged, dew condensation occurs inside the solid food, thereby impairing the flavor of the food. Further, in the case of a packaging bag in which refrigerated or frozen solid food is packaged, if it is heated in a microwave oven as it is, the internal pressure increases due to the generated steam, which eventually breaks the bag and the food is scattered. Even when a small hole is made in the bag to prevent the bag from breaking, dew condensation occurs inside the bag, which impairs the flavor of the food. For this reason, it is generally transferred to a vessel, wrapped and heated, but even in this case condensation still occurs.

[0005] Therefore, in order to overcome the inconvenience of causing such internal dew condensation, for example, the present applicant has firstly constructed an air-impermeable sheet as an outer layer and a water-absorbent fiber sheet as an intermediate layer.
A food package for a microwave oven using a composite sheet composed of three layers in which a hydrophobic sheet made of a melt-blown nonwoven fabric of a polyolefin resin having required water resistance and air permeability is disposed as an innermost layer was proposed (Japanese Utility Model Application No. 5- 19171
issue). The food package proposed in this proposal is such that even when food is heated by a microwave oven and steam is generated, one of the generated steam is generated between the outer layer and the intermediate layer and / or between the intermediate layer and the inner layer in the sealed portion. Part of the package to prevent rupture of the package, and the innermost hydrophobic sheet has air permeability, and a water-absorbing intermediate layer exists on the outside, so that steam passes through the hydrophobic sheet to the water-absorbing sheet. It is devised so that it will not be absorbed and accumulated inside the innermost part, so that dew condensation will not occur inside.

However, in such a proposed combination material of the innermost layer made of a water-resistant and air-permeable melt-blown nonwoven fabric and the intermediate layer of a water-absorbing fiber sheet as its outer layer, the innermost layer is When a polypropylene melt-blown nonwoven fabric and a pulp fiber are used for the intermediate layer, the heat bonding between them is not sufficient, and improvement thereof has been desired. That is, when a polypropylene meltblown nonwoven fabric layer is heat-sealed and joined to a pulp fiber layer by a heat sealer to form a packaging bag, the joining strength between the two is weak, and if the joining process takes a sufficient time, it is somewhat satisfactory. Although the bonding can be performed slowly, it is not possible to spend a sufficient processing time for the bonding on the premise that the forming speed of the packaging bag is required. In addition, if the joining temperature is increased, the melt blown nonwoven fabric will be damaged, and its characteristics will be impaired. Therefore, there has been a demand for an improvement such that the joining process for forming the packaging bag can be performed at a higher speed or the joining temperature can be further reduced. In addition, in the case of using both of the above, not only the problem of the forming and processing speed of the above-mentioned packaging bag, but also a defective product whose intended purpose cannot be achieved due to breakage of the melt-blown nonwoven fabric layer due to peeling of both bondings occurs. There has been a demand for an improvement that can further reduce the breakage rate of such a packaging bag.

[0007]

SUMMARY OF THE INVENTION Accordingly, the present invention is to solve the above-mentioned problems in food packaging materials. That is, the present invention is to provide an improved food packaging material capable of obtaining a food packaging bag in which no dew condensation occurs even when heated in a microwave oven, the strength of the heat seal portion is high, and the food packaging bag is less damaged. Another object of the present invention is to provide an improved food packaging material that can heat seal a packaging bag at a higher speed or a lower temperature.

[0008]

Means for Solving the Problems The present inventors have made intensive studies to overcome the above-mentioned problems, and as a result, have reached the present invention. That is, the present invention, the outer layer impermeable sheet layer,
A food packaging material in which a pulp fiber sheet layer having water absorbency is disposed as an intermediate layer, and a melt-blown non-woven fabric layer having a moisture-permeable, air-permeable and waterproof function as an inner layer, wherein the melt-blown non-woven fabric layer has an ethylene content in all resins. 2-10%
A food packaging material for heating a microwave oven, characterized in that the food packaging material comprises an ethylene-polypropylene random copolymer resin or a mixed resin of a polypropylene resin and an ethylene resin.

[0009]

The packaging bag made of the food packaging material of the present invention can be heated by microwave heating by a combination structure of a melt-blown nonwoven fabric layer having a moisture-permeable and waterproof function and a water-absorbing pulp fiber sheet layer on the outer side. The melt-blown nonwoven fabric layer is made of an ethylene-polypropylene random copolymer resin or a mixed resin of a polypropylene-based resin and an ethylene-based resin without causing condensation to occur without retaining generated steam inside. Since there is, the heat sealing strength with the pulp fiber sheet layer on the outer side is high, the processing speed of heat sealing to the packaging bag is high,
Alternatively, the heat sealing temperature can be low, the productivity of the food packaging bag is high, and the damage resistance of the packaging bag is also high.

FIG. 1 is a sectional view of a food packaging material according to the present invention. In FIG. 1, the layer denoted by reference numeral 1 is the innermost layer when configured as a packaging bag, performs heat sealing, and has a moisture permeable ventilation and waterproof function. Even if the food is heated, water vapor escapes and the food is removed. A melt-blown nonwoven fabric layer for keeping the inner side of the layer, reference numeral 2 denotes a water-absorbing pulp fiber sheet layer that absorbs water formed by cooling water vapor generated from food, and reference numeral 3 denotes an air-impermeable pulp fiber layer. Reference numeral 4 denotes a waterproof film layer, which is an outer layer for makeup and printing.

FIG. 2 (a) shows a long food packaging material composed of the four layers so that the melt blown nonwoven fabric layer 1 is placed on the innermost layer side of the package, and both ends are formed into a cylindrical shape. FIG. 2B is a perspective view showing an example of a food packaging bag in which food is inserted and the upper end portion is not sealed, and FIG. It is a perspective view which shows the state before bending a part and setting it to a microwave oven. FIG. 3 is a cross-sectional view of the packaging bag of FIG.

The melt-blown nonwoven fabric layer 1 used in the packaging material of the present invention is made of a material having a breathable and moisture-permeable and water-proof function without using additives or treating agents from the viewpoint of food safety. From the viewpoint of heat resistance to heating, a melt-blown nonwoven fabric made of polypropylene is used as the main component resin.Here, in the present invention, ethylene as a minor auxiliary component is randomly added to polypropylene as the main component resin. It is used after being copolymerized or mixed with a polyethylene resin. By using a melt-blown non-woven fabric of such a resin component, the heat-sealing speed of the melt-blown non-woven fabric layer 1 and the pulp fiber sheet layer 2 can be reduced by about 50 to 50, compared to the case of using a melt-blown non-woven fabric of a polypropylene-based single resin. It can be increased by 100% and the processing temperature of the heat sealer can be reduced by more than about 10 ° C. Further, as shown in the examples described later, the heat sealing strength with the pulp fiber sheet layer 2 can be more sufficiently increased.

The ethylene as an auxiliary component resin to be combined with the polypropylene as the main component resin may be a state in which ethylene is randomly copolymerized with the polypropylene, or a state in which polyethylene is simply mixed with the polypropylene.

In any of the above cases, it is important that ethylene as an auxiliary component be present in an amount of 2 to 10%, more preferably 3 to 6%. If the ethylene content is less than 2%, the above effects cannot be exhibited. If the amount exceeds 10%, the production of shots (polymer balls) cannot be avoided during the production of the melt blown nonwoven fabric,
As a result, it is difficult to produce a melt-blown nonwoven fabric having appropriate water resistance, which is not preferable.

The non-woven fabric melt-blown using the above resin has an average fiber diameter of 10 μm or less and a basis weight of 3
To 30 g / m ^2, more preferably having 5 to 15 g / m ² is used. The basis weight of the melt blown nonwoven fabric layer is 3
If it is less than g / m ^2, it is difficult to obtain sufficient water resistance to block water from food, and if the basis weight is more than 15 g / m ² , steam permeability will be small, and the intended purpose will be exhibited. Is difficult and uneconomical.

The water-absorbing pulp fiber sheet layer 2 serving as the outer layer of the melt blown nonwoven fabric layer 1 can prevent water vapor generated by heating the food from staying around the food.
It passes through the meltblown nonwoven fabric layer 1 to be in a separated state from food, and even if the separated water vapor cuts its passage in the outer film layer 3 and cools and condenses, it contacts the inner surface of the film layer 3. The absorption by the pulp fiber sheet layer 2 prevents the water vapor from condensing in the melt blown nonwoven fabric layer 1 to impair the flavor of the food.

For this purpose, the pulp fiber sheet layer 2 is preferably made of an absorbent fibrous nonwoven fabric sheet, and natural pulp fibers are most excellent. The use of No. 2 is a premise of the invention, and therefore, the present invention aims to improve the poor heat sealing property between the pulp fiber sheet and the polypropylene nonwoven fabric. However, the pulp fiber sheet layer 2 is not limited to the use of 100% pulp fibers, but in order to further increase the adhesive strength with the melt blown nonwoven fabric layer 1 and within a range that does not impair the effect of the pulp fibers. For example, a non-woven fabric (paper) made of pulp fibers mixed with a small amount of polyethylene fibers may be used. The nonwoven fabric made of such fibers may be manufactured by either a dry method or a wet method.

The basis weight of the pulp fiber sheet layer 2 is 5 to 5.
50 g / m ² is preferred. If the basis weight is less than 5 g / m ² , sufficient water absorption capacity cannot be obtained, and if the basis weight is more than 50 g / m ² , the whole sheet becomes too thick, and undesirably easily peels in the layer.

The melt-blown nonwoven fabric layer 1 and the pulp fiber sheet layer 2 are usually heat-bonded to each other with a heating roll having a concavo-convex pattern having a pressing area of 5 to 50% to form a two-layer body in advance. Although easier, this approach is not limited.

The air-impermeable and waterproof film layer 3 on the outside of the pulp fiber sheet layer 2 transfers the moisture absorbed by the pulp fiber sheet layer 2 to the outer decorative or printing sheet layer 4. This is a layer for preventing migration, and a single or laminated film of polyethylene, polypropylene, polyester or the like is used. However, the material is not limited to those described. This film layer 3 is usually
The outer layer is used by laminating it to the decorative or printing sheet layer 4 by an extrusion lamination method. Such a form is easy in processing and economical, but is not necessarily limited to this. Absent.

The outermost cosmetic or printing sheet layer 4 is a cosmetic or printing sheet layer relating to the content food product and the package, and is made of paper or film.

The food packaging material composed of the composite layers of the sheet layers 1 to 4 has a structure in which each sheet layer is simply overlapped, and has poor handleability before being formed into a bag as the package. Not only is there any point, but it is not so preferable from the point of easily causing damage as a packaging bag,
It is preferable that the respective sheet layers are also partially laminated and integrated.

Here, the term "integration" means that each sheet layer is in close contact with the entire surface, except for the integration of the film sheet layer 3 with the decorative or printing sheet layer 4. However, it is not preferable for the purpose of the present invention, and it is rather preferable to partially join in the form of a point, a line, or an intermittent line. That is, it is possible to maintain the shape of the melt-blown nonwoven fabric layer 1 and its characteristics such as moisture permeability and water resistance without changing the shape by partial bonding.

[0024] It is generally preferred that this partial bonding be such that the bonded portion is kept within the range of 1 to 50% of the whole. Further, it is preferable that the adhesive portions are widely distributed as far as there is no hindrance and are uniformly distributed. Further, it is preferable that the sheets are joined only by a surface layer that contacts as much as possible. In particular, the pulp fiber sheet layer 2 should be bonded to the sheet layers 1 and 3 on both sides of the layer 2 only on the surface so that the layer 2 has a function of degassing as described later. It is important to adjust.

In the packaging bag of the present invention, it is placed in a microwave oven and heated, the water in the food becomes steam, and the sealed body expands due to the expansion of the sealed air. When the food insertion end is simply bent as shown in (b), the expanded gas body easily escapes from the bent portion and the packaging bag does not burst, but the food insertion end is heat-sealed. That is, even if the whole is in a heat-sealed state, the bonding strength between the pulp fiber sheet layer 2 and its inner and outer layers,
And the pulp fibers are originally weak in bonding force, and although the sheet layer 2 is bonded on both sides thereof, the airtightness inside and outside the sheet layer 2 is relatively weak. Since the pulp fiber sheet layer 2 enters the pulp fiber sheet layer 2 through the nonwoven fabric layer 1 and escapes from the inside of the sheet layer 2 in the sealed portion to the outside of the packaging bag, the packaging bag does not burst. Moreover, the food, which is the content, is sealed by the meltblown nonwoven fabric layer 1 and does not move to any further outer layers, that is, does not leave the packaging bag.

[0026]

EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. Example 1 Ethylene-propylene copolymer (MFR 200 g / 10 min, melting point 138.7) obtained by random copolymerization with polypropylene so that the ethylene content becomes 4%.
° C) as a raw material resin, which is heated to 290 ° C and melted, melt-blown by a conventional method, and has a basis weight of 7 ° C.
g / m ² , air permeability 153 cc / cm ² / sec, water pressure resistance 2
It was prepared 70mmH ₂ O nonwoven.

The melt-blown nonwoven fabric 1 and a pulp paper 2 having a basis weight of 15 g / m ² obtained by making wood pulp were laminated and subjected to hot embossing to obtain a laminated composite A. The laminating conditions at this time were as follows: a pattern roll at 115 ° C. on the melt-blown nonwoven fabric side, a flat roller at 135 ° C. on the pulp paper side, and a linear pressure of 30 k.
g, at a speed of 80 m / min, and the area of the bonded portion by embossing was about 20% of the sheet area.

Further, by adding a homopolypropylene resin to the above-mentioned ethylene-propylene copolymer resin having an ethylene content of 4%, the ethylene content in all the resins is adjusted to 2% and 1%. A resin is used to produce a melt-blown nonwoven fabric in the same manner as described above, and further, under the same conditions as in the above, each of the laminated composites B (when the ethylene content is 2%) and C (the ethylene content is 1%).
%).

Furthermore, homopolypropylene was used as a raw material resin, and this was subjected to melt blow spinning according to a conventional method in the same manner as described above to give a basis weight of 7 g / m ² and an air permeability of 137 c.
A nonwoven fabric having a c / cm ² / sec and a water pressure resistance of 320 mmH ₂ O was produced. This melt blown nonwoven fabric 1 and the pulp paper 2 having a basis weight of 15 g / m ² used above were laminated, and subjected to hot embossing under the same conditions as above to obtain a laminated composite body D.

With respect to the laminated composites A to D, the peeling strength between the bonded melt-blown nonwoven fabric and the pulp paper was measured. This measuring method is based on JIS L-1086. A rectangular sample having a width of 5 cm and a length of 20 cm is formed, and the melt-blown nonwoven fabric-pulp paper 3 of the sample is peeled off by about 5 cm, and the peeling is performed. Each layer was sandwiched between clamps of a tensile tester, peeled at a speed of 100 m / min, and the stress at that time was determined. The value is an average value when the number of samples is n = 3. Table 1 shows the results.

[0031]

[Table 1]

As shown by the results in Table 1, when the homopolypropylene meltblown nonwoven fabric is used as the meltblown nonwoven fabric (D), the modified polypropylene meltblown nonwoven fabric obtained by copolymerizing ethylene is used (A to C). It is shown that the peel strength increases with an increase in the ethylene content, and in particular, when the ethylene content is 2% or more, the processing speed is greatly improved in the example of the present processing speed.

Further, using each of the laminated composites A to D,
The melt-blown nonwoven fabric layers of each of A to D were overlapped with each other so as to be on the inner surface, and the heat-sealing strength of each of the melt-blown nonwoven fabric layers was measured. The heat sealing strength is such that each of the laminated composites A to D has a width of 5 cm and a length of 20 c.
m, and leave each sample so that the melt-blown nonwoven fabric layers become inner surfaces (overlapping both ends in the longitudinal direction thereof) so that both ends can be used as respective gripping portions. Then, the sample was heat-sealed in the width direction, cooled at room temperature for 5 minutes, and then gripped at both ends with a tensile tester to measure the stress when the adhesive portion was peeled off. Table 2 below shows the results.

[0034]

[Table 2]

As shown in Table 2, as in the case of the peel strength, when a modified polypropylene meltblown nonwoven fabric obtained by copolymerizing ethylene is used as the meltblown nonwoven fabric (A to C), a homopolypropylene meltblown nonwoven fabric is used. Compared with the case (D), the heat sealing strength increases as the ethylene content increases, and particularly when the ethylene content is 2% or more, the strength is sufficient and greatly improved.

Example 2 As a sheet material for an inner layer and an intermediate layer of a food packaging material, a melt blown nonwoven fabric layer 1 and a pulp fiber sheet layer 2 composed of the modified polypropylene (ethylene content 4%) described in Example 1 were used. Was prepared. On the other hand, the content display was printed 12 μm
Is prepared, and the above-mentioned laminated composite A is prepared.
The molten polyethylene film 3 adjusted to have a thickness of 10 μm was extruded between the pulp paper side and the printing surface of the polyester film 4 to form a laminated four-layer composite sheet.

Both ends are overlapped at the center in the width direction so that the melt-blown nonwoven fabric layer 1 of the four-layer composite sheet becomes the innermost layer to form a tubular shape having upper and lower ends opened. The parts are heat-sealed with a pair of metal rolls at a temperature of 150 ° C., a pressure of 2 kg / cm ² and a speed of 12 m / min (contact time 1 second), and the lower end is also heat-sealed with a pair of metal bars. Then, a packaging bag having a width of 12 cm and an upper and lower length of 20 cm with only the upper end opened was prepared.

The sheet layer on the open end side of the bag is gripped at four points with the mouth open, a hamburger is charged in that state, and the open end is then closed with a pair of metal as described above. The hamburger was heat-sealed with a heating bar made of the hamburger to form a packaging bag. In this packaging bag, even if the hamburger cooled, no internal condensation occurred.

When the packaging bag is placed in a microwave oven and heated, the packaging bag expands to a certain extent after the start of heating. However, even after the heating, the pulp paper portion in the heat-sealing portion and the pulp paper and the inner and outer layer sheet layers can be formed. The inflation gas was discharged by the partial peeling, and the package did not burst. In addition, even after being taken out of the microwave, the package does not have the internal dew condensation seen in conventional food packages of this type, has no moistened bread surface, and has a dry feel. At the beginning, the taste was good.

[0040]

As described above, in the food packaging material of the present invention, the packaging material itself has a moisture absorbing / absorbing function and prevents dew condensation, so that the food can be directly heated in a microwave without impairing the flavor of the food. In addition, since the heat seal strength is high, the processing speed is excellent, the heat seal part of the package does not peel off and is not damaged, and even when configured as a packaging bag such as a vertical pillow, its characteristics can be exhibited more. is there.

[Brief description of the drawings]

FIG. 1 shows a cross-sectional view of a food packaging material of the present invention.

FIG. 2 (a) is a perspective view showing an example of a food packaging bag in which food packaging materials are thermally bonded, in which food is inserted and an upper end portion is not sealed. (B) is a perspective view showing a state before the open end of the packaging bag is bent and placed in a microwave oven.

FIG. 3 is a cross-sectional view of the packaging bag of FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Melt blown nonwoven fabric layer 2 Water-absorbing pulp fiber sheet layer 3 Impermeable waterproof film layer 4 Cosmetic or printing outer layer 5 Food

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) B65D 81/34 B32B 27/12 B32B 27/32

Claims (1)

(57) [Claims] 1. A food packaging material comprising an air-impermeable sheet layer as an outer layer, a water-absorbing pulp fiber sheet layer as an intermediate layer, and a melt-blown nonwoven layer having a moisture-permeating and waterproofing function as an inner layer. Melt blown nonwoven layer
A microwave oven characterized by being made of an ethylene-polypropylene random copolymer resin or a mixed resin of a polypropylene resin and an ethylene resin having an ethylene content of 2 to 10% in all resins. For food packaging.