JP4893245B2 - Polyolefin foam film - Google Patents

Description

The present invention relates to a polyolefin-based foamed film having excellent infrared shielding performance, and more specifically, various packaging material components , such as ice cream and chocolate frozen desserts characterized by having both high infrared shielding performance and high surface strength. The present invention relates to a polyolefin-based foam film having excellent infrared shielding performance, which is useful when used as a packaging material or as an industrial application.

In general, an appropriate material / configuration is selected for the packaging material in consideration of properties such as concealment, barrier properties, aesthetics, and heat insulation properties in accordance with the purpose and application of the type of contents.
In particular, concealment is an important characteristic as a packaging material. As a measure for concealing the packaging film, (1) printing, (2) kneading and adding pigments and colorants, (3) use of foaming at the time of stretching by adding a foaming agent, etc. are known. Addition of a foaming agent can be said to be one of the mainstream methods for providing cushioning properties and heat insulating properties together. (For example, refer to the special literature 1 etc.).
Japanese Patent Application Laid-Open No. 55-126056

In the applications as described above, improvement of the surface strength is also very important. In recent years, polymer films have been used in place of paper as labels for product display in recent years. Advantages of paper include that it is resistant to water, has excellent design properties due to printing, etc. The point which can stick an adhesive substance, such as a tape, and can peel and re-stick, and the point which the attached label can re-peel are mentioned. This is an important advantage in the separation and recycling of garbage in recent countermeasures for environmental problems, and that it can be attached and peeled over and over depending on the application. For example, Patent Document 2 introduces a delayed label in which a polypropylene resin is used as a base material, printed on the front surface, and provided with an adhesive layer on the back surface.
Japanese Patent No. 3514819

On the other hand, it is widely known that shielding infrared rays is effective as a measure for improving heat insulation (see, for example, Patent Document 3).
JP, 2001-161178, A It is also known that infrared shielding performance is especially useful in various industrial uses (for example, refer to patent documents 4, 5 etc.). JP 2000-212480 A JP 2002-254866 A

  As mentioned above, as a packaging material / industrial material, in thermal insulation foam film, improvement of infrared shielding performance and surface strength is one of the most important characteristics. This design was difficult, and for example, it was not satisfactory enough for use as a label for product display.

  That is, in the foamed film described in Patent Document 1, the void strength generated by foaming causes the interlayer strength to be lower than that of the non-foamed film, so that the surface strength is lowered. Further, in order to shield infrared rays, it is generally necessary to add an expensive inorganic oxide or coating, and there is a problem that the manufacturing cost is too high for practical use as a packaging application.

  The present invention has been made paying attention to the above-described circumstances, and an object thereof is to provide a polyolefin-based foam film excellent in infrared shielding performance and surface strength.

The polyolefin-based foamed film of the present invention is a laminated polyolefin-based foamed film including a foamed layer (A), a surface layer (C) made of a propylene homopolymer, and an intermediate layer (B) provided therebetween, The thickness of each of the layer (A) and the intermediate layer (B) is 50 to 85% and 10 to 30% of the total film thickness, and the foamed layer (A) is 12% by weight or more of titanium dioxide having a particle diameter of 400 nm to 1500 nm. 30% to 70% by weight of a propylene α-olefin copolymer containing less than 24% by weight, the intermediate layer (B) containing no void-generating substance and having a cold xylene soluble content of 3% by weight or less A polyolefin-based foamed film characterized in that the average value of infrared light reflectance (% R) in the range of 700 nm to 2000 nm by a spectrophotometer is 70% or more. Lum.

  In this case, it is preferable that the filler having an infrared shielding effect added to the foam layer (A) is titanium dioxide.

  Furthermore, in this case, the content of the propylene α-olefin copolymer contained in the intermediate layer (B) and having a cold xylene soluble content of 3 wt% or less and a melt flow rate of 5 g / 10 min or less is included. It is suitable that it is 30 wt%-70 wt%.

  In this case, each layer structure of the foam layer (A), the intermediate layer (B), and the surface layer (C) is 50 to 85%, 10 to 30%, and 5 to 20% of the total film thickness. Is preferred.

  The polyolefin-based foamed film of the present invention has the advantage of being excellent in infrared shielding performance and surface strength.

Hereinafter, embodiments of the polyolefin-based foamed film of the present invention will be described.
The base polymer used in the foamed layer (A) of the polyolefin-based foamed film composed of three layers of the foamed layer (A), the intermediate layer (B) and the surface layer (C) in the present invention is a monomer unit mainly composed of propylene. In addition to propylene homopolymer, α-olefin copolymerizable with propylene, that is, a copolymer obtained by copolymerizing ethylene, butene, pentene, hexene, 4-methylpentene-1, etc. Can be used. In the copolymer, propylene is preferably a polymer having 90 mol% or more. The polypropylene resin preferably has a melt index (MI, JIS-K-7210; 230 ° C., 2.16 kg load) of 0.5 to 40 g / 10 minutes, particularly 1 to 15 g / 10 minutes. The melting point is generally 120 to 180 ° C, preferably 150 to 170 ° C.

As the foaming agent used in the foamed layer (A) of the polyolefin foam film of the present invention, inorganic fillers such as calcium carbonate and silica, and organic fillers such as polymethyl acrylate are preferable. Particularly preferred is calcium carbonate. Further, the blending amount of the foaming agent is preferably 8% by weight to 18% by weight, and particularly preferably 10% by weight to 15% by weight. When the foaming agent is less than 8% by weight, good foaming cannot be obtained, and it is difficult to reduce the specific gravity and concealment. When the foaming agent is more than 18% by weight, the void ratio is too high and the interlayer strength is deteriorated.
The particle size is preferably 1 μm to 10 μm, particularly preferably 1.5 μm to 5 μm. If it is 1 μm or less, voids are hardly generated, and if it is 10 μm or more, appearance defects due to aggregates occur. The particle size was measured with Microtrac HRA X-100.

In the foamed layer (A) of the polyolefin-based foamed film of the present invention, it is essential to blend inorganic fine particles having an infrared shielding effect. Examples of the inorganic fine particles include titanium dioxide and tungsten oxide. Titanium dioxide is particularly preferable from the viewpoint of cost.
As addition amount, 12 wt%-24 wt% are preferable, More preferably, they are 15 wt%-20 wt%. If it is less than 12 wt%, the infrared ray shielding effect is not exhibited, and if it is 24 wt% or more, the film-forming property is deteriorated. The particle size is preferably 400 nm to 1500 nm, particularly preferably 500 nm to 1000 nm. If it is 400 nm or less, it is difficult to exert the infrared ray blocking effect, and if it is 1500 nm or more, there is a problem such as generation of fluff due to aggregates. The particle size was measured with Microtrac HRA X-100.

Moreover, various surface treatments can be applied to the surface of these inorganic fine particles, and these can be used alone or in combination of two or more.
In addition, known stabilizers, antistatic agents, ultraviolet absorbers, processing aids, and plasticizers that are usually blended in polyolefin films can be blended as appropriate.

The polymer used for the intermediate layer (B) of the polyolefin-based foamed film of the present invention is a propylene α-olefin copolymer having a cold xylene soluble content of 3% by weight or less and a melt flow rate of 5 g / 10 minutes or less. It is necessary to contain one or more types of coalescence. By using this propylene α-olefin copolymer, the foamed layer (A) and the surface layer (C) are softer because the crystallinity is smaller than in the case of using a propylene homopolymer conventionally used. flexibly linked, surface strength you greatly improved.

Here, when the intermediate layer is formed only with a propylene α-olefin copolymer having a cold xylene soluble content exceeding 3% by weight, the intermediate layer has too little crystal component, so the intermediate layer has no waist, and the surface Decrease in strength and curl of film occur. Similarly, when the melt flow rate exceeds 5 g / 10 min, the intermediate layer loses its elasticity due to the short polymer chain in the intermediate layer, resulting in a decrease in surface strength and curling of the film.
The content of the propylene α-olefin copolymer having a cold xylene-soluble content of 3 wt% or less and a melt flow rate of 5 g / 10 min or less is preferably 30 wt% to 70 wt%. If it is 30 wt% or less, the flexibility of the resin is inferior and the surface strength cannot be improved. On the other hand, if it is 70 wt% or more, the sensation is lost, the film tends to tear, the film-forming property is poor, and since the crystal component is too small, the intermediate layer is not lumped and the surface strength is lowered. As a method for measuring cold xylene solubles, 1 g of a sample is completely dissolved in 100 ml of boiling xylene, then cooled to 20 ° C. and left for 4 hours. Thereafter, this was separated into a precipitate and a solution, and the filtrate was dried and dried at 70 ° C. under reduced pressure. The weight was measured to determine the weight percent, and this was taken as the cold xylene soluble content.

  As long as the effects of the present invention are not impaired, the polyolefin foam film intermediate layer (B) of the present invention may be blended with inorganic or organic fine particles as a means for improving concealability, productivity and the like. Is possible. Examples of inorganic fine particles include silicon dioxide, titanium dioxide, zeolite, etc. These shapes are not limited to spherical, elliptical, conical, indeterminate and types, and their particle size is also intended for film use and use. The desired compound can be used and blended according to the method. However, a substance that generates voids at the interface with the base resin by stretching cannot be blended.

Base polymer used in the surface layer (C) is to use a homopolymer of up propylene. The polypropylene resin preferably has a melt index (MI, JIS-K-7210; 230 ° C., 2.16 kg load) of 0.5 to 40 g / 10 minutes, particularly 1 to 15 g / 10 minutes. The melting point is generally 100 to 180 ° C, preferably 110 to 170 ° C. Further, it is necessary that the surface layer (C) is not substantially foamed. When the surface layer is foamed, the surface strength is weakened by the voids.

The film thickness at this time varies depending on the application and usage method, but the polypropylene-based foam film as a packaging film is generally about 10 to 200 μm, and more preferably 20 to 200 in terms of mechanical strength and handling. It is about 150 μm.
Moreover, it is preferable that each layer structure of a foamed layer (A), an intermediate | middle layer (B), and a surface layer (C) is 50 to 85%, 10 to 30%, and 5 to 20% of the whole film thickness. In this case, when the thickness of the foam layer (A) is thin, foaming is insufficient and the specific gravity cannot be lowered. On the other hand, when the thickness is thick, the void ratio increases and the surface strength is reduced. Further, if the thickness of the intermediate layer (B) is thin, the surface strength is lowered, and if the thickness is thick, foaming is insufficient and the specific gravity cannot be lowered. When the thickness of the surface layer (C) is thin, the sealing strength is lowered. On the other hand, when the thickness is thick, foaming is insufficient and the specific gravity cannot be lowered.

In addition, the method for forming a laminated polyolefin-based foam film characterized by providing an intermediate layer (B) between the foam layer (A) and the surface layer (C) in the resin composition of the present invention is a normal extrusion method. A raw film can be formed by a machine, for example, a T-die method, and can be appropriately stretched at a desired temperature and magnification. For example, it is not different from the film forming conditions in the case of a general polyolefin, and a resin composition obtained by melting and extruding at an extrusion temperature of 150 to 300 ° C. is stretched to a sheet solidified by a cooling roll of 10 to 100 ° C. It is obtained by applying.
However, it is essential for the film of the present invention to laminate three types of resin layers, and the laminating method is that the foamed layer (A), the intermediate layer (B), and the surface layer (C) are respectively separated from different extruders. Melting and kneading, laminating in a T die, and extruding is a preferred embodiment.
In the stretching step, the film can be stretched at an area magnification of about 8 to 50 times, preferably about 10 to 40 times. Further, the stretching method is not limited to uniaxial stretching or biaxial stretching. In the case of biaxial stretching, it can be carried out by simultaneous biaxial stretching method, sequential biaxial stretching method, inflation method or the like. Axial stretching is common.

  It is essential that the polyolefin-based foamed film of the present invention has the following composition by the above method. That is, it is a laminated polyolefin-based foam film comprising a foam layer (A), a surface layer (C), and an intermediate layer (B) provided therebetween, characterized in that a filler is added to the foam layer (A). The infrared light reflectance (% R) in the range of 700 nm to 2000 nm measured by a spectrophotometer is 70% or more, and the infrared shielding effect added to the foam layer (A) is A polyolefin-based foamed film characterized in that the filler has titanium dioxide, the content of cold xylene soluble in the intermediate layer (B) is 3% by weight or less, and the melt flow rate is 5 g / 10 min. The following propylene α-olefin copolymer content is 30 wt% to 70 wt%, and each layer structure of the foam layer (A), the intermediate layer (B), and the surface layer (C) is a film. 50% to 85% of the total thickness, 10-30%, is characterized in that 5 to 20%.

Next, contents and effects of the present invention will be described with reference to examples, but the present invention is not limited to the following examples without departing from the gist thereof. In addition, the measuring method of the characteristic value in this specification is as follows.
(Infrared shielding rate)
Measure reflectance (% R) at 700 nm to 2000 nm with a spectrophotometer. The average value was calculated.

(Thermal insulation test)
A test film was placed on the top of a polystyrene foam box with a built-in thermometer, irradiated with an infrared lamp from above, and the increase in internal temperature was confirmed over time. The distance between the lamp and the sample was 8 cm, and the distance between the top of the box and the detection end of the internal thermometer was 13 cm. The initial temperature was 23 ° C., and the rising temperature 20 minutes after lamp irradiation was measured.

(Surface strength)
Cellotape (registered trademark) (18 mm width made by Nichiban) is attached to the film sample, and then peeled off rapidly to visually check the presence / absence of delamination or cohesive failure. The peeling angle was carried out in the direction of about 150 ° while keeping the test sample flat.
Class 5 ... The whole was peeled off or cohesively broken.
Class 4: Mostly peeled off or cohesively broken.
Class 3 ... about half peeled or coherently destroyed.
Class 2 ... Most do not peel or cohesive failure.
Class 1 ... No peeling or cohesive failure.

(specific gravity)
The sample is cut into a size of 280 mm × 400 mm, and the weight is measured with an analytical balance. Then, the thickness is measured using a dial gauge. These results are calculated by applying the following formula.
Apparent specific gravity (g / cm ³ ) = weight (g) / (area (cm ² ) × thickness (μm))

(Cold xylene solubles)
After 1 g of sample is completely dissolved in 100 ml of boiling xylene, the temperature is lowered to 20 ° C. and left for 4 hours. Thereafter, this was separated into a precipitate and a solution, and the filtrate was dried and dried at 70 ° C. under reduced pressure. The weight was measured and the weight percentage was obtained to obtain a cold xylene soluble content.

(Melt flow rate: MFR)
It measured based on the polypropylene test method (230 degreeC, 21.18N) shown by JISK6758.

(Particle size measurement)
Measured with Microtrac HRA X-100.

Example 1
From one extruder, a polypropylene homopolymer (MFR = 2.5 g / 10 min, cold xylene soluble content 3.3 wt%) 60 parts by weight as a foam layer (A), a calcium carbonate-containing masterbatch (polypropylene (MFR = 2.5 g / 10 min, cold xylene soluble content 3.3% by weight) 40%, calcium carbonate (Bihoku Flour Chemical Industry PO150B-10) 60% by weight, titanium dioxide masterbatch having infrared shielding effect (large Nippon Ink Chemical Co., Ltd. L-11124M: Titanium content 60wt%, average particle size 1000nm) After mixing 20 parts by weight, melt extrusion at a resin temperature of 250 ° C and polypropylene as a middle layer (B) by the other extruder 20 parts by weight of polymer (MFR = 2.5 g / 10 min, cold xylene soluble content 3.3% by weight), polypropylene homopolymer (MFR = 7.0 g / 10 min, cold xylene soluble content 3.6 wt%) 30 parts by weight, propylene-ethylene-butene copolymer (MFR = 3 g / 10 min, ethylene component 2.5%, butene component) (7%, 1.6% by weight of cold xylene solubles) 50 parts by weight were melt extruded at a resin temperature of 260 ° C., and the polypropylene homopolymer (MFR = 2.5 g / 10 min, cold xylene soluble content 3.3 wt%) 30 parts by weight, polypropylene homopolymer (MFR = 7.0 g / 10 min, cold xylene soluble content 3.6 wt%) 70 parts by weight Are melt-extruded at a resin temperature of 260 ° C., and a foam layer (A), an intermediate layer (B), and a surface layer (C) are laminated in this order in a T-die, and cooled and solidified with a cooling roll at 80 ° C. An unstretched sheet was obtained. Subsequently, the metal roll heated to 120 ° C. was stretched 4.5 times in the vertical direction using the difference in peripheral speed, and further introduced into a tenter stretching machine, and stretched 9.5 times in the horizontal direction. A three-layer film having a foam layer of 28 μm, an intermediate layer of 10 μm, and a surface layer of 2 μm in total of 40 μm was obtained.
This film was a film that achieved both infrared shielding performance and high surface strength of the surface layer. Table 1 shows the characteristic values of the film.

(Comparative Example 1)
In Example 1, the polyolefin-based foaming was carried out in the same manner as in Example 1 except that the titanium dioxide master batch of the foam layer (A) was Dainippon Ink & Chemicals, Inc. L-11145M (titanium content 60 wt%, average particle size 200 nm). I got a film. This film was inferior in the infrared shielding performance as compared with the film of Example 1. Table 1 shows the characteristic values of the film.

(Comparative Example 2)
In Example 1, the blending composition of the intermediate layer (B) is 20 parts by weight of a calcium carbonate-containing masterbatch, polypropylene homopolymer (MFR = 7.0 g / 10 min, cold xylene soluble content 3.6 wt%) 30 Except for 50 parts by weight, propylene-ethylene-butene copolymer (MFR = 3 g / 10 min, ethylene component 2.5%, butene component 7%, cold xylene soluble content 1.6% by weight) A polyolefin foam film was obtained in the same manner as in Example 1. Compared with the film of Example 1, this film had the same infrared shielding performance, but the surface layer had a weak surface strength. Table 2 shows the characteristic values of the film.

(Comparative Examples 3 and 4)
A polyolefin-based foamed film was obtained in the same manner as in Example 1, except that the type of propylene α-olefin copolymer blended in the intermediate layer (B) was changed as shown in Table 2. Compared with the film of Example 1, this film had the same infrared shielding performance, but not only the surface strength was weak, but also there was no lumbar feeling, it was easy to tear, and the curl was severe. It became bad. Tables 2 and 3 show the characteristic values of the film.

(Comparative Example 5)
In Example 1, a three-layer film having a total of 40 μm in total of a foam layer of 35 μm, an intermediate layer of 3 μm, and a surface layer of 2 μm was obtained. As shown in Table 3, the present film had the same infrared shielding performance but a film with a weak surface strength of the surface layer.

  The results are shown in Table 1, Table 2, and Table 3.

  The polyolefin-based foamed film having good infrared shielding performance of the present invention is a film suitable for packaging materials and industrial applications that achieve both improved infrared shielding performance and improved surface strength.

Claims (1)

A laminated polyolefin-based foam film comprising a foam layer (A), a surface layer (C) composed of a propylene homopolymer, and an intermediate layer (B) provided therebetween, wherein the foam layer (A) and the intermediate layer (B ) Is 50 to 85% and 10 to 30% of the total film thickness, and the foamed layer (A) contains titanium dioxide having a particle size of 400 nm to 1500 nm in an amount of 12% by weight or more and less than 24% by weight. (B) is characterized in that it contains 30% to 70% by weight of a propylene α-olefin copolymer containing no void-generating substance and having a cold xylene soluble content of 3% by weight or less. A polyolefin-based foamed film, wherein an average value of infrared light reflectance (% R) in a range of 700 nm to 2000 nm is 70% or more.