JPS6044139B2 - insulating packaging material - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a heat insulating packaging material having an oxidized silver luster and sealing properties, and more specifically to a packaging material having a coated body with a subdued matte luster and a print that is easily visible even when viewed from an angle. Of course, there are also packaging materials that have insulation properties such as heat retention and cold retention.

As is well known, among packaging materials, plastic films are mainly transparent packaging materials, but it is a fact that the commercial meaning of packaging has become increasingly diverse in recent years.

Among these, paper-like and pearl-like plastic packaging materials are commercially available in small quantities as translucent or opaque materials. The present invention provides packaging materials that require cold insulation and heat retention, broadly including covering materials, protective materials, sealing material labels, etc., and these materials.

Conventionally, void-containing films have been commercially available, but they do not have heat-sealing or adhesive properties when used alone, and can be combined with other films, paper, etc., coated with other films, or coated with other materials. It is used by pasting laminated materials.

However, even if the interface between the cavity-containing film and the other laminated materials mentioned above is well bonded, the cavity-containing layer near the adhesive interface is easily torn, and when it is made into a bag, it has the disadvantage that it is easily torn at the woven edge. However, it has the disadvantage that it can be damaged by repeated external forces during transportation, exhibition, and other operations, resulting in loss of its protective function. Also,
The surface gloss is a characteristic of void-containing films, which have a matte appearance, but the gloss is non-uniform. In addition, when layering other materials on the cavity-containing film, many steps are required to diversify the functions, such as applying adhesive and laminating between materials, which is not only uneconomical but also It also has the disadvantage that residual solvents such as adhesives used during lamination are difficult to remove. Various methods have been proposed for obtaining void-containing films. For example, a method of uniaxially stretching an unstretched polypropylene film by creating a temperature difference on both sides of the film (Japanese Patent Publication No. 41
-4338 Publication), but the film obtained by this method not only has lower mechanical strength than ordinary transparent stretched polypropylene film, but also has no heat sealability.
It also had the disadvantage of poor heat-insulating properties and very poor operability since it was stretched under special conditions. Furthermore, it is known to produce paper-like films from polyethylene, ethylene/vinyl copolymers, and inorganic materials (UK Patent No. 109005).
No. 9), it is recognized that even when an unstretched film is biaxially stretched, the occurrence of cavities is extremely small (
Table 1 of the same British patent).

According to the findings of the present inventors, when biaxially stretching such a polymer composition in order to generate a large number of cavities by stretching, it is possible to maintain a uniform thickness without causing film breakage. It is difficult to stretch with good productivity;
This method has the same problems as when attempting to biaxially stretch polypropylene mixed with an inorganic substance. The present invention was achieved as a result of repeated research to improve these points. That is,
A base layer A consisting of a mixture of a stretched film-forming polymer and an inorganic filler or an organic polymer incompatible with the polymer, and polymers 5 to 5 containing an α-olefin component having 4 or more carbon atoms on at least one side thereof. obtained by stretching in at least one direction a laminated film consisting of a surface layer B layer formed from a polymer mixture containing 95% (by weight) and 95% to 5% (by weight) of polypropylene or ethylene polymer. A laminated stretched film consisting of a base layer A and a surface layer B having a cavity content of 10 to 85%, which has a gloss level measured from the surface layer B side of less than 40%, has an oxidized silver luster, and has sealability. The invention relates to a heat insulating packaging material. The cavity-containing layer, that is, the base layer A of the present invention, is a polyolefin polymer such as polyethylene, polypropylene, polybutene-1, a copolymer or mixture thereof, a polyester polymer, which may be exemplified by polyethylene terephthalate, polybutylene terephthalate, etc. Copolymerized polyesters having aliphatic, aromatic, and alicyclic diol residues that can be copolymerized with these, or mixed polymers thereof, nylon 6, nylon 9, nylon 11, nylon 6,6, nylon 6, 10, polyamide polymers, copolymers, or mixed polymers thereof, which can be exemplified by nylon 10,1 sowing, polystyrene polymers, copolymerized styrene polymers containing these as the main component, polycarbonates, etc. Examples include stretched film-forming polymers such as condensation polymers.

A cavity-containing layer is formed by mixing these polymers with an inorganic filler or an organic polymer that is incompatible with the polymer and stretching the mixture. Inorganic substances used in the present invention include calcium carbonate, calcium oxide, silica, titanium oxide, alumina,
Examples include aluminum sulfate, and calcium carbonate is particularly preferred. The particle size of the inorganic substance is preferably 0.1 to 15 microns, particularly 0.5 to 10 microns. The particle size of the inorganic substance is 0.1
If it is less than μ, cavities will be difficult to form from the surface of the base film to the inside. Furthermore, if the particle size exceeds 15 μm, the stretchability of the film will deteriorate. Preferably, this inorganic substance is present in the mixture in an amount of 2 to 5% by volume, particularly 5 to 8% by volume. When the amount added is less than 2% by weight, hardly any cavities are generated in the base film, and the cavity content tends to be small. On the other hand, if the amount exceeds 5...F amount %, the stretchability becomes significantly poor. In addition, the incompatible polymer has an SP value (solubility index) of 0.
Mainly using 5 or more, preferably 2 or more different polymers,
In addition, a polymer having a slightly different SP value is used to supplementally impart cavity-forming properties. For example, cavities can be formed by mixing polypropylene and polystyrene, polypropylene and polyamide, polyester and polypropylene, polyester and polyamide, and the like. Of course, the combination is not limited to these, but thermal insulation properties can be obtained by the multi-layer laminated cavity layer by stretching. It is necessary that the void content is 10 to 85%. If the void content is 10% or less, it is a film that is unusual in that it is not a transparent film to the naked eye, and does not have enough voids to exhibit heat insulating properties, and if it is 85% or more, it has excellent heat insulating properties, The necessary strength as a packaging material, especially somewhere within the hollow layer, delamination,
In addition, the film cannot be used for purposes such as the present invention because the film forming properties tend to deteriorate. Surprisingly, it was discovered that the void content and thermal conductivity of the film, that is, the insulating effects such as heat retention and cold retention, were significantly improved in the a-film obtained by the method of the present invention. It is common sense that the presence of cavities will improve insulation. However, the present invention showed far better characteristics than the common knowledge. The reason for this is probably that the surface layer is a layer with few cavities, and the base layer has cavities formed by stretching.Especially when the surface layer is formed on both sides of the base layer, cavities are secret, and single cavities are The vacuum state is more easily maintained due to the surface coating than the containing film,
Moreover, it is thought that this is because when the temperature of the film returns to room temperature after the stretching is completed, the surface layer acts as a layer that further prevents the flow of air. As an example of this, ice cream was packaged using a 40 μm thick film with a void content of 60% and compared with the present invention. When the single film was taken out of the refrigerator and left at room temperature for one hour, the ice cream became soft and began to melt, but the sealed packaged product of the present invention was okay even after about eight times. This phenomenon is caused not only by the degree of sealing of the packaging, but also by
It is surprising that the thermal conductivity is extremely low. The film of the present invention exhibits thermal insulation properties that are about 1 to 1 times higher than transparent packaging materials. Any existing method for mixing inorganic substances can be used, but it is possible to mix powdered polymers or moisten granular polymers with liquid additives, then add inorganic substances, and mix with a mixing device. is the preferred method. From the standpoint of film formation, it is preferable to extrude the mixture to obtain a uniformly mixed strand-like product, and then cut this into fine particles to obtain inorganic mixed pellets. Surface layer B
The α-olefin monomer-containing polymer used for formation has 4 or more carbon atoms and is usually a single or copolymer of 10 or less α-olefins, or one or two of the olefins and ethylene or propylene. It is a copolymer with

The content of the α-olefin monomer-containing polymer having 4 or more carbon atoms in the polymer forming the surface layer B is 5 to 95% (by weight), and the α-olefin monomer having 4 or more carbon atoms in the polymer The proportion of the olefinic monomer is 5 to 100%.
If the content of the polymer is less than 5 (by weight), the low-temperature heat-sealability of the layer decreases, and the cavity-containing layer of the base layer A tends to become transparent due to the heat of the heat-sealed portion, and moreover, the sealing performance decreases. be lost. Furthermore, if it exceeds 95% (by weight), the gloss tends to fluctuate depending on the stretching conditions, making it difficult to maintain a stable matte tone, and also reducing the ability of hot blades to separate from the automatic packaging machine, poor sliding on the heating heater surface, and reduced automatic cutting performance. There are other inconveniences. The reason for using a polymer containing an α-olefin monomer having 4 or more carbon atoms is for low-temperature heat sealability, gloss adjustment, and sealability. The polypropylene or ethylene polymer used to form the surface layer B is 95% to 90% of the constituent polymers of the surface layer B. 5
(weight)%.

The polypropylene used in the present invention is a propylene homopolymer or a propylene ethylene copolymer in which 9% or more of the heel weight is propylene. In addition, the ethylene polymer is an ethylene homopolymer or a polymer in which w weight % or more is ethylene.
It is an ethylene-propylene copolymer. By mixing one or more of these polymers with an α-olefin-containing polymer having 4 or more and 10 or less carbon atoms to form a surface layer, a packaging material with an oxidized silver-like luster can be obtained. Sealing performance as used in the present invention refers to the property of the heat-sealing surface having a high degree of airtightness.It does not simply refer to good low-temperature heat-sealing properties or strong heat-sealing strength, but also to the fact that there are gaps caused by wrinkles on the sealing surface. This is a complicated characteristic because adhesiveness is lost due to the adhesive surface tending to separate due to the elasticity of the film until the sealing surface cools down after sealing.

Further, if one of the polymer mixtures is a poly(propylene) or ethylene polymer, it is optimal for producing an oxidized silver-like luster. The melt index (MI) of the polypropylene or ethylene polymer used in the present invention is 0.5 to 80.
y/10 minutes, preferably 1.0 to 20 y/1 powder. M
If I is less than 0.5, there is an advantage that the gloss becomes dull, but the surface becomes rough, and if it is more than MI3O, the appearance is preferable, but the seal strength and the impact resistance of the seal part are reduced, making the bag easier to tear. . Ethylene polymer has a density of 0.912
~0.970y1cr1 can generally be used. ”
Polypropylene has an isotactic index of 85 (weight)
% or more, preferably 90 (weight) % or more. Now,
The packaging material of the present invention can be produced by separately melt-extruding the base layer A and the surface layer B, then combining them in the molten state and co-extruding them, or by obtaining the base layer film A and then laminating the surface layer B by extrusion. It can be produced by a method of obtaining a film, a method of separately melt-extruding base layer A and base layer B, and then heat-bonding them.

Among these methods, the preferred method is to obtain an unstretched composite film by coextrusion and then stretch it at least uniaxially, or to stretch the base layer A in one direction after melt extrusion, and then melt-extrude and laminate the surface layer B so that the composite film is stretched in the same direction. Method of stretching in the right angle direction,
Alternatively, a common method is to melt-extrude laminate the surface layer B on the unstretched base film A and then stretch it at least uniaxially. The above describes the basic method, and it can be easily inferred that it can be obtained by modifying these or adding additional techniques.The gist of the present invention is that after laminating A and B, at least one The object of the present invention is to provide a packaging material which has a strong interlayer bond obtained by stretching in the direction. A method has also been proposed in which polypropylene or an ethylene-propylene copolymer containing a small amount of ethylene is laminated on a hollow-containing film, and then stretched. The strong sealing performance plays an important role in preventing the deterioration of airtightness due to destruction of the seal edge. For stretching, uniaxial stretching using a roll, horizontal uniaxial stretching using a tenter, sequential biaxial stretching using a combination of these, or simultaneous biaxial stretching in the vertical and horizontal directions can be used, and it can be obtained by either the T-die method or the tubular method. . As for the stretching conditions, a stretching temperature of about 75 to 170°C is commonly used, preferably 90 to 160°C, and the area magnification of the base layer A is 8 times or more, preferably 10 to 5 times. It is stretched to After stretching, it is heat-set or heat-treated at a temperature below the melting point of the base layer A for 4 to 6 days, and then subjected to tension or relaxation heat-setting. The present invention is characterized in that the unstretched molten composite or either one of them is melted, or that the surface layer B is melted or almost softened and fluidized by the subsequent stretching, and then the main heat treatment or heat setting is performed. Therefore, the surface layer B melts or softens and flows even below the melting point of the base layer A, and the polymer film of the surface layer B flows into the surface cavity layer of the base layer A, penetrates, or chemically bonds to form an interface between the base layer A and the surface layer B. A major feature is that the change in layers occurs in a somewhat unclear manner. By stretching, the base film produces many flat microcavities running in layers parallel to the film surface, and the base film is biaxially oriented. The amount of cavities formed tends to increase as the stretching ratio increases, and as the stretching temperature decreases. This film may also be subjected to surface activation treatment such as corona discharge treatment and flame treatment.

In the production of the film of the present invention, small amounts of additives such as stabilizers, antistatic agents, dyes, and pigments may be mixed with the polymer. The film thus obtained has a base layer containing a large number of microscopic cavities, a total light transmittance of 70% or less, a cavity content of 10 to 85%, good dimensional stability, and heat insulation properties. The surface layer B is uniaxially or biaxially stretched, and the entire film has a uniform oxidized silver luster.
It has a glossiness of less than 40% as measured by No. 5, and has not only heat-sealing properties at low temperatures but also sealing properties.

The bonding force between the base layer A and the surface layer B was extremely strong, exhibiting properties not previously available. When bags were actually filled with items to be packaged and their practical strengths were compared, it was found that the present invention was significantly superior. It goes without saying that the packaging material of the present invention can be further laminated with other films, papers, fibrous webs, etc. by known methods.

As described above, the packaging material of the present invention has excellent functions, so
It can be used in many ways such as various food packaging, cosmetic packaging, portable hand warmer bags, vapor deposition materials, book covers, insulation materials, embossing materials, adhesive tapes, and labels. However, particularly preferred uses include the feature of the present invention, which provides a calm image due to the oxidized silver luster on the exterior, as well as prevention of deterioration and contamination of the packaged items due to the sealing properties, and heat retention effect due to the ease of identification, or the use of frozen desserts, frozen foods, etc. It is effective when used as a cooling effect. The present invention will be explained below with reference to Examples.

The measurement methods for the measurement items in the examples are as follows.

(1) Glossiness Measured according to JIS-Z874, incident angle 4
5 degrees (2) Total light transmittance Measured according to JIS-K67l4 (3) Heat shrinkage rate Shrinkage rate when left in heated air at 120°C for 5 minutes.

(4) Cavity content The apparent density d of the film was measured and calculated using the following formula.

(In the formula, ρ, is the support polymer, ρ2 is the incompatible polymer, ρ3 is the density of the inorganic substance, M1 is the support polymer, M2 is the incompatible polymer, and M3 is the mixing ratio of the inorganic substance. show.)(
5) Heat-sealability After heat-sealing with a heat-inclined heat sealer manufactured by Toyo Seiki Co., Ltd., the strength was measured using a tensile tester at a tensile speed of 20-1 m1n.

) (6) Airtightness The airtightness of the part sealed by an automatic packaging machine at 160° C. and 80 pieces/min was judged based on the amount of water leakage.

After packaging the box-shaped exterior body, it was taken out, 50 cc of tap water was poured into it, and the amount of leakage per minute was measured.

Example 1 Isotactic polypropylene powder with a melting index of 3y/1, calcium carbonate with an average particle size of 1.2μ, and a melting index of 0
．． A mixture of 87f/10min polystyrene in a weight ratio of 40:20:40 was melt-extruded to form strands, which were then shredded into small particles to obtain pellets.

The mixture was melted at 240°C (base layer A). On the other hand, isotactic polypropylene (MI
=2.2y/10n11n) and isotactic polybutene-1 were mixed at a weight ratio of 50:50 and melt-extruded (surface layer B). Both are introduced into the co-extrusion die and B/A
A cooled unstretched sheet having a total thickness of 1400 μm was obtained. Subsequently, this carbon number was stretched 5 times in the longitudinal direction using rolls heated to 125°C and having different circumferential speeds.
Next, send it into a tenter at 140°C and heat it horizontally for 7
The film was stretched twice to obtain a film with a thickness of 40 μm.

Furthermore, this film was heat-treated for a specific number of seconds in a hot air oven at 145°C held with a tenter clip, and the base layer A had a cavity content of 50%, and the surface layer B had a 3μ diameter on one side.
A layered composite film was obtained. One side of the obtained film was subjected to corona discharge treatment to give a wet tension of 37 dyne/Cm. Comparative Example 1 A composition mixed at the same proportion as the base layer A of Example 1 was adjusted to have a thickness of 40 μm as a single layer, and was sequentially biaxially stretched in the same manner.

Example 2 Base layer A is made of polypropylene and high density polyethylene (ρ=0
．． Calcium carbonate (average particle size: 2.0 μm) was mixed with a mixed polymer of 955q1d) at a weight ratio of 80:20 at various mixing ratios to form film layers with different cavity contents.

The surface layer B is made of a 50:50 mixture of isotactic polypropylene and ethylene butene-1 (60/4 nominal ratio) copolymer, and the unstretched sheet of the base layer A is uniaxially stretched in the longitudinal direction. Layer B was then formed by melt-extrusion lamination on both sides, and then uniaxially stretched in the transverse direction to obtain a three-layer laminated film. The resulting film has a total thickness of 100μ
A surface layer B having a thickness of 5 μm on one side was formed on both surface layers. Base layer A
The cavity content is as shown in Table 1, and the properties of the obtained film are also as shown in Table 1. Comparative Example 2 An isocyanate adhesive was applied to the film of Comparative Example 1, and unstretched PP film (thickness 20 μm) was dry laminated on both sides.

Example 3 Polyethylene terephthalate with an intrinsic viscosity of 0.8 dfly and isotactic polypropylene (with an intrinsic viscosity of 1.9
C1′-Yl (measured with 35°C tetralin solution)
The base layer A is mixed at a weight ratio of 20:20, and the surface layer is a composition containing polypropylene and ethylene-butene-1 (60/4 weight ratio) copolymer mixed at a weight ratio of 70:30, and is melted in a separate extruder. It was extruded and coextruded into three layers of B/A/B.

The obtained unstretched film was stretched 4 times in the longitudinal direction at 120°C.
Stretched 8.5 times in the transverse direction at 148°C, then stretched at 155°C
It was heat-set for 108'. The cavity content of base layer A is 63%
It was hot.

Table-2 Glossiness 12% Light transmittance 18% Heat shrinkage
2.1% (120℃ x 5 minutes) cavity content
Tin% heat sealability 1
30 C220y1C77! 150℃89
0〃Sealability B Stretchability
Good In order to examine the heat retaining properties of the film of the present invention, hot water at about 70° C. was sealed and packaged, and the temperature drop was examined.

For comparison, a polypropylene biaxially stretched film was dry laminated with polypropylene, and hot water was similarly filled in the film. As a result, when the hot water temperature was measured after 30 minutes, the product of the present invention had a temperature of 47C and the comparative example had a temperature of 3rC, indicating excellent heat retention.

Claims (1)

[Claims] 1 Base layer A consisting of a mixture of a stretched film-forming polymer and an inorganic filler or an organic polymer incompatible with the polymer, and a polymer 5 containing an α-olefin component having 4 or more carbon atoms on at least one side thereof. The void content obtained by stretching in at least one direction a laminated film consisting of ~95% (by weight) and a surface layer B formed of a polymer mixture of 95% to 5% (by weight) of polypropylene or ethylene polymer. 10-85
% of the base layer A and the surface layer B, the film is characterized by having a gloss level measured from the surface layer B side of less than 40%, having an oxidized silver luster, and having sealing properties. insulation packaging material.