JP4372295B2 - Food packaging material for microwave oven heating - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
TECHNICAL FIELD The present invention relates to a food packaging material constituting a food packaging bag for heating a microwave oven, and more specifically, an air-impermeable sheet layer, a water-absorbing fiber sheet layer, and a moisture-permeable, air-permeable and waterproof melt-blown nonwoven fabric. The present invention relates to a food packaging material in which layers are laminated.
[0002]
[Prior art]
Conventionally, when food is cooked in a microwave oven at home, vinylidene chloride and polyethylene films have been used to prevent over-drying of the food, but these films themselves do not have moisture absorption or water absorption functions. For this reason, when cooking with a microwave oven, dew condensation occurs inside and the food flavor is impaired.
In addition, take-out foods such as hamburgers are packaged in an impermeable sheet so that the sauce and ketchup do not leak out. These impervious sheets include thin paper laminated with polyethylene film or polypropylene film, thin paper laminated with aluminum foil, and further laminated with polyethylene film or the like. Has been.
[0003]
In packaging materials processed into a bag shape, these impervious sheets alone, those with a water-absorbing sheet laminated on a part of the inside, and a part of the bag as a water vapor permeable layer during heating. The thing using a breathable waterproof film or a perforated film is used.
However, when a breathable waterproof film is used, although it is breathable, if the amount of water vapor generated is large, the breathability is insufficient and the effect is not recognized. Moreover, in the packaging material using a perforated film, the food inside is wetted by moisture condensed at a portion where there is no hole, and the flavor is impaired.
[0004]
The applicant of the present invention has proposed a food container for heating a microwave oven using a breathable waterproof sheet in Japanese Patent Laid-Open No. 3-200255, and a food packaging bag for heating a microwave oven in Japanese Patent Laid-Open No. 4-57768.
However, these inventions are merely a flat bonding of a melt-blown non-woven fabric and a pulp fiber sheet as a moisture-permeable waterproof sheet by means such as hot embossing, and both of them are not bonded. There is almost no space between them. Further, even if there is any operation for providing a space in this portion, no operation is performed.
Therefore, these food wrapping materials can prevent the melt-blown nonwoven fabric from exhibiting the moisture-permeable function when moisture exceeding the water absorption capacity of the pulp fiber sheet is generated from the food. That is, dew condensation occurs on the food side, and this moisture wets the food and impairs its flavor. Moreover, mainly on the lower side of the food, even when the pulp fiber sheet absorbs moisture near the limit of its water absorption capacity, water is pushed out through the melt-blown nonwoven fabric layer by the weight of the food, Similarly, it may wet food and impair its flavor.
[0005]
In order to improve this problem, the present applicant has proposed a food packaging material for heating a microwave oven having excellent water retention in Japanese Patent Application Laid-Open No. 11-94260. In this invention, after a melt-blown nonwoven fabric having a flat shape is produced, the nonwoven fabric is bonded to a water-absorbing layer in a separate manner in a separate process, and moisture is absorbed in the gathered space. . However, this invention has a problem that the process is complicated and it is difficult to increase the production speed. Further, since the irregularities are gathered, the gathers may fall down unless the winding tension is strictly controlled when winding the product, and the irregular structure may not be effective.
[0006]
[Problems to be solved by the invention]
In the food packaging material, the present invention is configured such that even if water exceeding the water absorption capacity of the water absorbent fiber sheet layer is generated, the water is absorbed and excessive water does not come into contact with the food again. An object of the present invention is to provide an improved food packaging material suitable for microwave heating without impairing the flavor of food.
[0007]
[Means for Solving the Problems]
The inventor of the present invention has arrived at the present invention as a result of intensive studies to overcome the above-mentioned problems. That is, the present invention relates to a food packaging material in which an air-permeable and waterproof sheet layer is an outer layer, a water-absorbent fiber sheet layer is an intermediate layer, and a moisture-permeable air-permeable and waterproof melt-blown nonwoven fabric layer is an inner layer. The meltblown nonwoven fabric layer has brushed projections on its surface that have a thickness of 2 mm or less and a thickness of 10% to 80% of the total thickness of the meltblown nonwoven fabric layer; A food packaging material for heating a microwave oven, wherein the raised protrusions are disposed in contact with the water-absorbent fiber sheet layer or are exposed on the inner surface.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
The food packaging material of the present invention has a laminated structure of a moisture permeable and waterproof melt-blown nonwoven fabric layer, a water absorbent fiber sheet layer on the outer side thereof, and an air-impermeable sheet on the outer side thereof, Further, as a melt-blown nonwoven fabric, there are raised protrusions on the surface, and the raised protrusions are arranged in contact with the water-absorbent fiber sheet layer or exposed on the inner surface. Vapor from the resulting food is absorbed by the water-absorbent fiber sheet layer of the intermediate layer without staying inside the packaging material, and the moisture that cannot be absorbed by the water-absorbent fiber sheet layer is melt-blown nonwoven fabric layer By holding in the space formed by the raised protrusions, there is an effect of preventing dew condensation on the inner side of the packaging material (on the surface of the melt-blown nonwoven fabric layer in contact with the food).
[0009]
In the structure in which the raised protrusions are arranged in contact with the water absorbent fiber sheet layer, the moisture that could not be absorbed by the water absorbent fiber sheet layer is held in the space of the raised protrusions and passed through the melt blown nonwoven fabric for packaging. Prevents returning to the inside of the material. Further, in the structure in which the raised protrusions are arranged so as to be exposed on the inner surface of the meltblown nonwoven fabric, even when moisture that could not be absorbed by the water absorbent fiber sheet layer is pushed back through the meltblown nonwoven fabric layer, Moisture is retained in the space of the raised protrusions, and re-contact between moisture and food can be prevented. The packaging material of the present invention can warm foods without damaging the flavor due to these actions.
[0010]
Hereinafter, the present invention will be described with reference to the drawings.
FIG. 1 is a cross-sectional view showing an example of the food packaging material of the present invention. The packaging material is composed of an innermost moisture-permeable and waterproof melt-blown nonwoven fabric layer 1, an intermediate water-absorbent fiber sheet layer 3, and an air-permeable and waterproof film layer 4. The packaging material of FIG. 1 has a structure in which a film layer 5 for cosmetics and printing is further added to the outside of the film layer 4, but the film layer 5 can be omitted and printing can be performed on the film layer 4.
The meltblown nonwoven fabric layer 1 has a large number of raised protrusions 2 on its surface. The packaging material of FIG. 1 has a structure in which the raised protrusions 2 are arranged so as to be exposed on the inner surface of the packaging material. The space formed by the raised protrusions retains excess moisture inside the packaging material, and even when there is moisture returning from the water absorbent fiber sheet, the moisture is retained in the space and the food comes into contact with moisture again. To prevent that.
[0011]
The raised protrusions are formed integrally with the meltblown nonwoven fabric, and a fiber bundle in which single fibers or a plurality of fibers are fused is raised on the nonwoven fabric surface in the form of brushed or looped or irregularly shaped entangled yarns. It is set. The thickness is preferably 2 mm or less and 10 to 80% with respect to the thickness of the entire meltblown nonwoven fabric layer. If the thickness is 2 mm or more, the surface of the packaged food may be damaged. The raised protrusions may be regularly arranged at regular intervals or irregularly formed by contraction or the like.
[0012]
The thickness of the raised protrusions is measured by the following method.
Take a 50 × photograph of the cross section of the nonwoven fabric with a microscope, remove the raised protrusions, draw a tangent line between the front and back of the web, and measure this distance. Such measurement is carried out at any five locations, and the average value of these measurements is defined as “web thickness”. On the other hand, the distance between the top surface of the raised protrusions and the web surface (back surface) on the opposite side is measured at any 10 points, and the average value is defined as the “overall nonwoven fabric thickness”.
The ratio of the raised protrusions of the melt-blown nonwoven fabric layer to the total thickness of the melt-blown nonwoven fabric layer is defined as the “raised protrusion ratio,” which is calculated by the following formula.
Brushed protrusion ratio (%) = (nonwoven fabric overall thickness−web thickness) / (nonwoven fabric overall thickness) × 100
[0013]
Further, the density of the raised protrusions is measured by the following method.
Take a 50 times photograph of the cross section parallel to the MD direction of the nonwoven fabric with a microscope, measure the tangent on the raised protrusion side of the web (fiber layer) and the distance from the apex of the raised protrusion at any 10 locations, Draw a parallel line of the tangent on the raised protrusion side of the web at an interval (height) of 1/3 of the average value. The number of raised protrusions protruding from this line per 1 cm is defined as “number of MD unit protrusions”. For the cross section parallel to the CD direction, the number of the raised protrusions measured in the same manner is defined as “number of CD unit protrusions”.
These products are defined as the density of the raised protrusions. In the present invention, it is desirable that the raised protrusions have a density of 3 pieces / cm ² or more. If the density is less than that, the intended effect cannot be obtained. The upper limit of the density is not particularly limited, but is preferably 50 / cm ² or less because of ease of production.
[0014]
The melt-blown nonwoven fabric layer having raised projections used in the present invention can be obtained by forming raised projections simultaneously with the production of the nonwoven fabric by the production method described later, or by partially raising the surface of the nonwoven fabric.
[0015]
The melt-blown nonwoven fabric layer used in this food packaging material does not contain additives or treatment agents from the viewpoint of food safety, is a breathable and waterproof material, and has heat resistance to microwave heating. In view of the above, a melt-blown nonwoven fabric mainly made of polypropylene is preferable. However, the raw material of the melt-blown nonwoven fabric is not limited to polypropylene, and any other resin such as polyethylene or nylon can be used as long as it satisfies the above conditions. Moreover, since this melt blown nonwoven fabric is joined and heat-bonded as an inner surface layer of a packaging material, it must also have heat sealability. If the heat sealability is insufficient, the sealed portion may be destroyed in microwave heating.
[0016]
The meltblown nonwoven fabric preferably has an average fiber diameter in the range of 5 to 30 μm, and more preferably in the range of 5 to 20 μm. The basis weight is 3 to 50 g / m ² , more preferably 10 to 30 g / m ² . If the basis weight of the melt-blown nonwoven fabric layer is less than 3 g / m ^2, it is difficult to obtain sufficient water resistance to block water from food, and conversely, if the basis weight exceeds 50 g / m ² , the vapor permeability is small. As a result, it becomes difficult to achieve the intended purpose, and it becomes uneconomical.
[0017]
The water-absorbing fiber sheet layer laminated with the melt-blown nonwoven fabric layer is such that water vapor generated from the heated food is separated from the food through the melt-blown nonwoven fabric layer, and the separated water vapor is on the outer side. It is a layer that absorbs and retains the generated water by cutting the passage through the film layer and cooling condensation. The water absorption of the water-absorbing fiber sheet layer can prevent the water vapor from condensing inside the melt-blown nonwoven fabric layer and re-contacting with food to impair the flavor of the food.
For that purpose, the water absorbent fiber sheet layer is preferably a nonwoven fabric of hydrophilic fibers, and natural pulp fibers are a preferred example. As a structure of the food packaging material of the present invention, a combination of a polypropylene melt-blown nonwoven fabric and a pulp sheet is particularly preferable in terms of processability, performance and cost.
[0018]
The basis weight of the pulp fiber sheet layer is preferably 5 to 50 g / m ² . If the basis weight is less than 5 g / m ² , a sufficient water absorption capacity cannot be obtained. Conversely, if the basis weight is more than 50 g / m ² , the entire sheet becomes too thick, and peeling within the layer easily occurs. In addition, the pulp fiber sheet layer is not limited to the use of 100% pulp fiber, and in order to further enhance the adhesive strength with the melt-blown nonwoven fabric layer, a heat fiber such as polyethylene fiber is used as long as the effect of the pulp fiber is not impaired. Nonwoven fabric or paper made of pulp fibers mixed with a small amount of fusible fibers can also be used. The nonwoven fabric composed of such fibers may be manufactured by either dry or wet methods.
[0019]
The melt-blown nonwoven fabric having raised protrusions used in the present invention is manufactured by a method in which melt-spun fibers are jet-spun with heated and pressurized gas, and the resulting fiber stream is collected on a collecting surface having an uneven surface. The When the fibers flow into the recesses of the collecting surface and solidify, raised protrusions are formed on one surface of the nonwoven fabric. The concavo-convex surface is constituted by a metal surface provided with a large number of protrusions having an arbitrary shape, or a wire mesh having an appropriate mesh.
The raised protrusions of the melt-blown nonwoven fabric layer in the present invention are preferably regular at regular intervals, but are not limited thereto, and may be distributed over the entire surface even if they are irregular.
[0020]
In order to form raised protrusions on the meltblown nonwoven fabric, it is important that the meltblown fiber stream reach the collection surface before the fibers solidify. Even if the fiber is solidified and collected on the collecting surface, the melt-blown nonwoven fabric does not have napped protrusions and becomes a nonwoven fabric having a flat surface. For this reason, when forming a melt-blown nonwoven fabric, the time to solidify is lengthened by increasing the fiber diameter by shortening the collection distance of the fiber stream or increasing the resin viscosity. There is a need. Specifically, the collection distance is preferably in the range of 5 to 40 cm, more preferably 10 to 25 cm. Moreover, since the fiber stream collected in this way needs to solidify immediately after that and to peel off from the collection surface with an unevenness | corrugation clearly, it may be necessary to cool a collection surface.
[0021]
As a means for laminating a melt-blown nonwoven fabric having raised protrusions on a water-absorbing fiber sheet, point bonding or line bonding is performed using an existing method such as hot embossing, pin sonic or hot melt method. When laminating, it is desirable not to crush the raised protrusions of the melt-blown nonwoven fabric as much as possible, and in order to maintain the breathability of the melt-blown nonwoven fabric, it is desirable that the adhesive area is small, so both fiber layers It is desirable to perform point bonding or line bonding instead of bonding with the adhesive.
[0022]
Further, in the thermal bonding step of the fiber layer, it is preferable that the heat-bonding portions are spaced as wide as possible and laminated with the raised projections of the melt-blown nonwoven fabric held in the widest possible range. For example, when laminating and bonding with hot embossing, that is, a combination of a metal handle roll and a flat roll, in order to laminate with the water-absorbent fiber sheet layer while holding the raised projections of the melt-blown nonwoven fabric, It is desirable that the thermocompression bonding portion has a distance of 10 mm or more between adjacent thermocompression bonding portions in at least one direction in the web plane direction.
The partial adhesion is preferably 1 to 50% of the entire fiber layer surface. Furthermore, it is preferable that the sheets are joined only by the surface layer that comes into contact as much as possible. In particular, in the case of the water absorbent fiber sheet layer, in order to give the layer a gas venting function, the water absorbent fiber sheet layer is bonded to the melt blown nonwoven fabric and the air-impermeable sheet layer laminated on both sides thereof. Is preferably adjusted so as to be bonded only on the surface of the water absorbent fiber sheet layer.
[0023]
Furthermore, the height of the thermocompression bonding portion needs to be about 80% or more of the total thickness of the sheets to be laminated. This is because if the height is low, the fibrous projections of the melt-blown nonwoven fabric are crushed even if the interval between the crimping portions is widened, and the interval between the food and the water absorbent fiber sheet cannot be maintained.
The above conditions are the same for Pinsonic anvil rolls.
Further, regarding the lamination with hot embossing, it is preferable to make the temperature of the embossing roll as low as possible. This is because if the embossing temperature is too high, the raised protrusions of the melt-blown nonwoven fabric are crushed during lamination.
[0024]
The air-impermeable and waterproof film layer 4 outside the water-absorbent fiber sheet layer is necessary for keeping food safe by shielding it from the outside while packaging and storing the food. It is a layer that prevents moisture absorbed in the water-absorbent fiber sheet layer from being diffused to the outside of the bag when heated in a range, and a single or laminated film such as polyethylene, polypropylene, or polyester is used. However, the material is not particularly limited.
[0025]
On the outside of the film layer, a sheet layer for cosmetics or printing may be used by sticking it by an extrusion laminating method or the like, if necessary. This sheet layer is made of paper or film, and is preferably used for displaying the contents of food products or for cosmetic purposes. Such a laminated form is easy in processing and economical, but is not necessarily limited thereto.
The packaging material of the present invention can be used as a packaging material for water-containing frozen foods or cooked foods, and is suitable for thawing heat treatment using a microwave oven.
[0026]
【Example】
EXAMPLES Hereinafter, although an Example demonstrates this invention in more detail, this invention is not limited by these Examples.
Example 1
Pulp paper having a basis weight of 15 g / m ² obtained by papermaking wood pulp was prepared.
Also, a melt flow rate of 60 g / 10 min of polypropylene was melt-extruded by an extruder and discharged from a nozzle at a spinning temperature of 285 ° C. and a single hole discharge rate of 0.5 g / min / hole, at a temperature of 285 ° C. and a pressure of 0 The fiber stream thinned by high-speed hot air of 4 kg / cm ^{2 was} collected on a roll on which a conveyor net placed at a position 20 cm away from the die was wound. The roll was cooled by passing water at 20 ° C.
As a result, a melt-blown nonwoven fabric having an average basis weight of 30 g / m ² and having raised protrusions at a density of 15 pieces / cm ² was obtained.
[0027]
The melt-blown nonwoven fabric layer and the pulp paper layer having the above-mentioned raised projections were introduced between the heat embossing roll and the flat roll engraved with the convex pattern of the connecting rhombus pattern by dotted lines, and laminated and adhered. Here, the melt blown nonwoven fabric was introduced so that the raised protrusions were on the embossing roll side. The height of the hot embossing roll protrusion was 2 mm, the temperature of the hot embossing roll was 110 ° C., and the temperature of the flat roll was 150 ° C. The embossing pressure was 35 kg / cm, and the treatment speed was 30 m / min.
Next, a waterproof sheet was extruded and laminated on the composite sheet material using polyethylene to obtain a packaging material having raised protrusions as shown in FIG. Using this packaging material, the packaging bag was made by heat-sealing so that the raised protrusions were inside the bag.
[0028]
Comparative Example 1
A packaging material was prepared using the same method as in Example 1 except that a melt-blown nonwoven fabric having a flat surface shape was used. The obtained bonded packaging material was extruded with a waterproof sheet using polyethylene in the same manner as in Example 1 to obtain a packaging material, and the melt-blown nonwoven fabric layer of this packaging material was inside the bag. A bag was made by heat sealing.
[0029]
Example 2
The same melt-blown nonwoven fabric and pulp paper as used in Example 1 were introduced into the embossing roll, and the raised protrusions were directed to the pulp layer side. After the waterproof sheet was laminated by the same method, a packaging bag was prepared.
[0030]
Example 3
A melt-blown nonwoven fabric having raised protrusions and pulp paper, using an embossed roll with a chain-line-arranged pattern, obtain a laminate in the same manner as in Example 1 except that the height of the convex part of the pattern is 2 mm. Further, after the waterproof sheet was laminated by the same method, a packaging bag was prepared.
[0031]
The cooked rice was frozen for 24 hours in the bags obtained in Examples 1 to 3, and heated in a microwave oven. On the other hand, the frozen rice was similarly heated using the bag obtained in Comparative Example 1.
As a result of eating these cooked rices, the cooked rice using the bags of Examples 1 to 3 had a fluffy texture that retained moderate moisture and had a good taste without excessive moisture adhering to the surface. On the other hand, the cooked rice using the bag of Comparative Example 1 was a sticky cooked rice with excessive moisture adhering to the surface and having a poor taste.
[0032]
【The invention's effect】
Providing food packaging materials suitable for microwave heating that prevent excessive moisture from re-contacting foods when foods and ingredients with high moisture content are heated in a microwave oven, and do not impair the flavor of the food. be able to.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view of an example of a food packaging material of the present invention.
[Explanation of symbols]
1: Melt-blown nonwoven fabric layer 2: Brushed protrusions 3: Water-absorbing fiber sheet layer,
4: Air-permeable and waterproof film layer

Claims (2)

A food packaging material in which an air-permeable and waterproof sheet layer is an outer layer, a water-absorbing fiber sheet layer is an intermediate layer, and a moisture-permeable air-permeable and waterproof melt-blown nonwoven fabric layer is an inner layer, The melt-blown nonwoven fabric layer has a raised protrusion on the surface thereof having a thickness of 2 mm or less and a thickness of 10% to 80% with respect to the total thickness of the melt-blown nonwoven fabric layer. A food packaging material for heating a microwave oven, wherein the food packaging material is disposed in contact with a water absorbent fiber sheet layer or exposed on an inner surface. The food packaging material for heating a microwave oven according to claim 1 , wherein the raised protrusions of the melt-blown nonwoven fabric layer are present at a density of 3 pieces / cm ² or more.

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