JP4591261B2 - Heat-sealable polyolefin foam film - Google Patents

Description

  The present invention relates to a polyolefin-based foam film imparted with heat-sealability. More specifically, when used as various packaging materials in order to achieve both high concealability, slipperiness and heat-seal strength, it has particularly excellent bag-making processability. The present invention relates to a heat-sealable polyolefin foam film.

  In general, an appropriate material and configuration of a packaging material is selected in consideration of properties such as concealment, barrier properties, and aesthetics according to the purpose and use of the type of contents.

  One of the important characteristics as such a packaging material is heat sealability. Current heat-sealable films include: (1) Laminated films in which various stretched films (polypropylene, polyester, polyamide, etc.) are used as a base material and heat-sealable sealant films (non-stretched polypropylene, polyethylene, etc.) are laminated. (2) Laminated films obtained by co-extrusion and stretching of a sealant resin and polypropylene or the like are the mainstream. As such a film, a polyolefin-based low temperature sealing film comprising two or three layers of A / B, A / B / A, or A / B / C is disclosed (for example, see Patent Document 1). .

  Another important characteristic as a packaging material is concealment. Measures for concealing the packaging film include (1) printing, (2) kneading and adding pigments and colorants, and (3) using foaming during stretching by adding a foaming agent. The formation of voids by adding a foam nucleating agent can be said to be one of the mainstream methods that can also provide heat insulation.

In addition, in providing concealability by foaming at the time of stretching, it is already known that a special appearance such as pearl tone or matte tone can be formed by keeping the resin in an incompatible state. As described above, foaming of the film by adding a foaming agent is useful as a means for achieving concealing properties, cushioning properties, heat insulation properties, special appearance and weight reduction of the packaging film. As such a film, a biaxially stretched polypropylene film having pearly luster characterized by containing polypropylene, a copolymer based on polypropylene, and an inorganic filler is disclosed (for example, (See Patent Document 2).
Japanese Patent Laid-Open No. 7-24980 Japanese Patent No. 3281410

  In the case of the foamed film having the heat sealing property described in Patent Document 1 or Patent Document 2, further improvement in slipperiness is required. The reason is that the antiblocking agent added for imparting slipperiness is buried in the seal layer, and its function cannot be fully expressed. In this case, defects such as poor flow in the line during bag making, or difficulty in opening the bag and entry of contents when the contents are inserted after bag making occur. Moreover, when an anti-blocking agent having a large particle size is added, it may become an obstacle during heat sealing and reduce the heat sealing property. From the above, it is difficult to impart the slipperiness of the seal layer because the balance must be determined.

  Moreover, volume reduction of packaging materials is useful from the consideration of the environment, and is demanded by end consumers. That is, it is useful to reduce the volume during disposal and to reduce the amount of CO2 generated during incineration.

  The present invention has been made paying attention to the circumstances as described above, and its purpose is to achieve both high slipperiness and heat seal strength, and particularly excellent bag making when used as various packaging materials. An object of the present invention is to provide a heat-sealable polyolefin foam film having processability.

Heat-sealable polyolefin foamed film of the present invention, two layers of at least the sealing layer and the foam layer a containing unrivaled Toshiru polyolefin-based foamed films, different anti-blocking agent to be added to the sealing layer of an average particle size of one side Is a combination of 5 to 8 μm cubic calcium carbonate and spherical PMMA cross-linked beads having an average particle size of 0.5 to 10 μm , and the dynamic friction coefficient between the seal layers is 0.50 or less , and heat Sealing at a sealing temperature of 130 ° C., a sealing pressure of 10 N / cm ² , a sealing strength of 5.0 N / 15 mm or more at a sealing time of 1 second, a heat sealing temperature of 90 ° C., a sealing pressure of 10 N / cm ² and a sealing time of 1 second The strength is 3.0 N / 15 mm or more .
At this time, when it is used as various packaging materials in order to achieve both high concealability, slipperiness and heat seal strength, it has particularly excellent bag-making processability.

  In this case, it is preferable that the antiblocking agent added to the sealing layer (B) of the film is cubic calcium carbonate.

Hereinafter, embodiments of the heat-sealable polyolefin foam film of the present invention will be described.
The base polymer used for the foam layer (A) of the heat-sealable polyolefin-based foam film composed of the foam layer (A) and the seal layer (B) in the present invention contains propylene as a main monomer unit, In addition to a propylene homopolymer, an α-olefin copolymerizable with propylene, that is, a copolymer obtained by copolymerizing ethylene, butene, pentene, hexene, 4-methyl-1-pentene, or the like can be used. . In the copolymer, propylene is preferably a polymer having 90 mol% or more. The polypropylene resin preferably has a melt flow rate (MFR, 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 foam nucleating agent used for the foam layer (A) of the heat-sealable polyolefin-based foam film, calcium carbonate is preferable. Further, the blending amount of the foam nucleating agent is preferably 14% by weight or less, and particularly preferably 8% by weight to 12% by weight. If the foam nucleating agent is less than 8% by weight, good foaming cannot be obtained, and concealing is insufficient. If the foaming nucleating agent is more than 14% by weight, the void ratio is too high, resulting in deterioration of interlayer strength and film forming property. .
The term “foaming” as used herein means that an incompatible resin or inorganic or organic fine particles are blended into a polyolefin resin, and the film is stretched after film formation, so that a fine particle is formed at the interface between the polyolefin resin and the incompatible resin or fine particles. A void may be generated, and the degree of the void is generally expressed by a void ratio.
In the present invention, a preferable void ratio is 25% to 35%.
The average particle diameter of the inorganic filler or organic filler that is the foaming agent to be added is preferably 1 μm to 5 μm.

In the foamed layer (A) of the heat-sealable polyolefin-based foam film, as long as the effects of the present invention and the heat-sealability are not impaired, as a means for improving the concealability, slipperiness, productivity, etc., inorganic or organic It is also possible to mix these fine particles. Examples of inorganic fine particles include silicon dioxide, titanium dioxide, talc, kaolin, mica, zeolite, etc. These shapes are not limited to spherical, elliptical, conical, indeterminate and types, and their particle size In addition, a desired material can be used and blended depending on the purpose and usage of the film.
The average particle size of the inorganic or organic fine particles to be added is preferably 0.1 to 0.3 μm, and the content is preferably 0.5 to 18% by weight. The fine particles preferably do not form voids. Titanium dioxide is particularly preferable.
The particle size of these particles is determined by the measuring method described in the catalog of the particle manufacturer.
As organic particles, cross-linked particles such as acrylic, methyl acrylate, styrene-butadiene can be used, and various shapes and sizes can be used in the same manner as inorganic fine particles. . In addition, various surface treatments can be applied to the surface of these inorganic or organic 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.

  As a polymer used for the sealing layer (B) of the heat-sealable polyolefin-based foam film, polypropylene and α-olefin having a melting point lower than that of isotactic polypropylene, that is, ethylene, butene, pentene, hexene, 4 -It is preferable to use a copolymer obtained by copolymerizing methyl-1-pentene or the like, or a terpolymer. These copolymers and terpolymers are not necessarily one type, and two or more types may be mixed depending on the application and purpose. In this case, if the melting point of the copolymer or terpolymer used is equal to or higher than that of polypropylene, an increase in sealing start temperature, a decrease in sealing strength, and the like occur, and good sealing performance cannot be achieved.

  As a polymer used for the sealing layer (B) of the heat-sealable polyolefin-based foamed film, an atactic polypropylene resin may be used. In this case as well as the above copolymer and terpolymer, if the melting point is equal to or higher than that of isotactic polypropylene, an increase in the sealing start temperature, a decrease in the sealing strength, etc. occur, and good sealing performance cannot be achieved. .

It is essential to add an antiblocking agent that achieves both good slipperiness and heat seal strength to the seal layer (B) of the heat sealable polyolefin-based foamed film. Specifically, by adding a combination of cubic calcium carbonate having a different average particle diameter and spherical PMMA cross-linked beads, it is surprisingly possible to impart very good slipperiness without deteriorating the heat sealability. Although the cause is under analysis and is not clearly understood, it is considered that the corners of the cube are exposed on the surface without being buried in the sealing layer resin in the case of cubic calcium carbonate.
Cubic calcium carbonate here means light calcium carbonate consisting of 5 to 8 μm per side , and a commercially available product can be purchased.
The average particle diameter of the spherical PMMA cross-linked beads to be added is preferably 0.5 to 10 μm.

In addition, inorganic or organic fine particles can be blended in the sealing layer (B) as a means for improving the concealability, productivity, etc., as long as the effects of the present invention are not impaired. Examples of inorganic fine particles include silicon dioxide, titanium dioxide, zeolite, and the like, and these shapes are not limited to spherical, elliptical, conical, and irregular shapes, and their particle diameters are also used and used for films. The desired compound can be used and blended according to the method.
The average particle size of the inorganic or organic fine particles to be added is preferably 0.1 to 0.3 μm, and the content is preferably 0.5 to 10% by weight. The fine particles preferably do not form voids. Titanium dioxide is particularly preferable.

  The film thickness at this time varies depending on the application and usage method, but a polypropylene-based foam film as a packaging film is generally about 10 to 200 μm, and more preferably 20 to 150 μm in terms of mechanical strength and handling. Degree. In recent years, volume reduction of packaging materials has been promoted due to environmental considerations. Moreover, as a layer structure of a foaming layer (A) seal layer (B), 3 to 15% of the whole film thickness and 97 to 85% are preferable. In this case, when the thickness of the foamed 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 interlayer strength is lowered. On the other hand, when the thickness of the seal layer (B) is thin, the seal strength is lowered. On the other hand, when the thickness is thick, foaming is insufficient and the specific gravity cannot be lowered.

In the heat-sealable polyolefin-based foam film, an intermediate layer or the like can be provided as necessary. We can improve heat seal strength and interlayer strength by providing an intermediate layer made of foam layer resin and seal layer resin that is not substantially foamed between the foam layer and the seal layer.
The polymer used in the intermediate layer (C) of the heat-sealable polyolefin foamed film, a resin forming the sealing layer (B), it is preferable to contain at least one polyolefin-based resins.
Here, the at least one polyolefin resin means a polypropylene resin containing the same copolymer component as the polyolefin resin forming the seal layer (B).

  As a polymer used for the intermediate layer (C) of the heat-sealable polyolefin-based foam film, polypropylene and α-olefin having a melting point lower than that of isotactic polypropylene, that is, ethylene, butene, pentene, hexene, 4 -It is preferable to use a copolymer obtained by copolymerizing methyl-1-pentene or the like, or a terpolymer.

The intermediate layer (C), the resin forming the sealing layer (B), it contains at least one kind of polyolefin-based resins, it is possible to obtain a high bond strength.
Here, the at least one polyolefin resin means a polypropylene resin containing the same copolymer component as the polyolefin resin forming the seal layer (B).
Moreover, it is preferable that it is not substantially foamed. When the intermediate layer is foamed, the interlayer strength is lowered, and the favorable sealing property mentioned as one of the objects of the present invention cannot be achieved.

  If the intermediate layer (C) of the heat-sealable polyolefin-based foamed film is within the range not impairing the effects of the present invention, inorganic or organic fine particles are used as means for improving the concealing property, slipping property, productivity, etc. It is also possible to mix. Examples of inorganic fine particles include silicon dioxide, titanium dioxide, zeolite, and the like, and these shapes are not limited to spherical, elliptical, conical, and irregular shapes, and their particle diameters are also used and used for films. The desired compound can be used and blended according to the method.

Heat-sealable polyolefin foamed film of the present invention, the sealing faces heat sealing temperature 130 ° C., sealing pressure 10 N / cm ^2, seal strength at the sealing time 1 second is to be on 5.0 N / 15 m m or less Is preferred. If the sealing strength is on 5.0 N / 15 m m or more, sufficient strength can be obtained even when the packing some heavy.
Further, heat sealing temperature 90 ° C., sealing pressure 10 N / cm ^2, it is preferable that the seal strength at the sealing time 1 second is on 3.0 N / 15 m m or less.

  The film of the present invention preferably has a dynamic friction coefficient between the sealing layers of 0.50 or less. The dynamic friction coefficient between the seal layers is important in the filling process of the bag-made product. If the friction coefficient exceeds 0.5, there is a high possibility that problems such as poor opening of the bag and poor filling of the contents will occur. Further, it is more preferable that the dynamic friction coefficient between the seal layers is 0.40 or less.

In addition, the method of forming the heat-sealable polyolefin foam film composed of the foam layer (A) and the seal layer (B) in the present invention is, for example, melt extrusion at an extrusion temperature of 150 to 300 ° C. such as a T-die method. The obtained resin composition is obtained by stretching a sheet obtained by solidifying with a cooling roll of 10 to 100 ° C.
However, it is essential for the film of the present invention to laminate at least two types of resin layers, and the lamination method is to melt and knead the foam layer (A) and the seal layer (B) from separate extruders, respectively. Extruding after laminating in a T-die is a preferred embodiment.
In the stretching step, the film can be stretched by 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.

  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.

(Total light transmittance)
The total light transmittance was measured according to JIS K7105.

(Thickness and apparent 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 fitting into the following equation (1).
Apparent specific gravity (g / cm ³ ) = weight (g) / (area (cm ² ) × thickness (μm)) (1)

(Slippery)
The sliding property between the sealing layers (B) was evaluated according to JIS K-7125. The slip piece mass was 1500 g.

(Heat seal strength)
The seal strength was measured according to JIS Z1707. The specific procedure is briefly described below. Adhere the seal layer surfaces of the sample together with a heat sealer. The adhesive sample was measured for T-peel strength using a tensile strength tester (manufactured by Toyo Keiki Co., Ltd .: trade name Tensilon UTM). The sealing pressure at this time is 10 N / cm ² , the sealing time is 1 second, the sealing temperature is 130 ° C., the tensile speed is 200 mm / min, and the specimen width is 15 mm. The unit is N / 15 mm.

(Calcium carbonate average particle size)
Measured with Microtrac HRA X-100.

(Void content)
Calculated by the following formula.
Cavity content (volume%) = 100 × (1−true specific volume / apparent specific volume)
However,
True specific volume = x1 / d1 + x2 / d2 + x3 / d3 + ... + xi / di
Apparent specific volume = 1 / Apparent specific gravity of film In the above formula, xi represents the weight fraction of the I component, and di represents the true specific gravity of the i component.

Example 1
The present example is a foamed film having a two-layer three-layer structure of sealing layer (B) / foaming layer (A) / sealing layer (B), and the sealing layer (B) is extruded from the same extruder. , The same resin composition divided by the adapter before dicing.
Specifically, 70 parts by weight of a polypropylene homopolymer (“FS2011DG3” MFR = 2.5 g / 10 min, manufactured by Sumitomo Chemical) as a foam layer (A) from one extruder, a calcium carbonate-containing masterbatch (25% polypropylene, calcium carbonate) (Bihoku Flour Industry “PO-150B-10” average particle size 2.3 μm, specific surface area 19000 cm ² / g) 50%, polystyrene (“Denkastyrol 525-52N” 25% manufactured by Denki Kagaku) 25) Part by weight, 10 parts by weight of titanium dioxide masterbatch (Dainippon Ink "L-11145M" polypropylene 40%, titanium dioxide 60%) are mixed, melt extruded at a resin temperature of 250 ° C, and sealed by the other extruder As the layer (B), a propylene-butene copolymer (“FSX89E3” M manufactured by Sumitomo Chemical Co., Ltd.) R = 9 g / 10 min, butene component 18%) 70 parts by weight, propylene-ethylene-butene copolymer (Sumitomo Chemical "FSX66E8" MFR = 3 g / 10 min, ethylene component 2%, butene component 5%) 30 wt. As an anti-blocking agent, calcium carbonate cubic particles (“CUBE50KAS” average particle diameter 5 μm manufactured by Maruo Calcium) 3750 ppm, calcium carbonate cubic particles (“CUBE80KAS” manufactured by Maruo Calcium average particle diameter 8 μm) 8250 ppm, PMMA cross-linked beads (Sumitomo Chemical average) (750 μm particle size) 750 ppm was added, melt extruded at a resin temperature of 260 ° C., a foam layer (A) and a seal layer (B) were laminated in a T-die, and cooled and solidified with a 50 ° C. cooling roll. An unstretched sheet was obtained.
Subsequently, the metal roll heated to 130 ° C. was stretched 4.5 times in the vertical direction using the difference in peripheral speed, and further introduced into a tenter stretching machine to perform 9.0 times stretching in the horizontal direction. Above, it wound up with the film winder and obtained the film. The final film thickness is 22 μm. The layer structure of the foam layer (A) and the seal layer (B) was seal layer (B) / foam layer (A) / seal layer (B) = 2 μm / 18 μm / 2 μm.
This film was a film with good concealability and slipperiness and a sealing property. The characteristic values are shown in Table 1.

(Example 2)
In Example 1, the sealing layer (B) was made of propylene-butene copolymer (Sumitomo Chemical "FSX89E3" MFR = 9 g / 10 min, butene component 18%) 30 parts by weight, propylene-ethylene-butene copolymer ( A heat-sealable polyolefin foam film was obtained in exactly the same manner except that 70 parts by weight of “FSX66E8” MFR = 3 g / 10 min, ethylene component 2%, butene component 5%) manufactured by Sumitomo Chemical was used. The characteristic values are shown in Table 1.

(Example 3)
In Example 1, the layer constitution is as follows: seal layer (B) / intermediate layer (C) / foamed layer (A) / surface layer (D), intermediate layer (C), surface layer (D) 20 parts by weight (manufactured by Sumitomo Chemical “FS2011DG3” MFR = 2.5 g / 10 min), 30 parts by weight of a polypropylene homopolymer (“FS7053G3” MFR = 7.0 g / 10 min by Sumitomo Chemical), propylene-ethylene-butene 50 parts by weight of a copolymer (“FSX66E8” manufactured by Sumitomo Chemical Co., Ltd., MFR = 3 g / 10 minutes, ethylene component 2.5%, butene component 7%) was melt extruded from a third extruder at a resin temperature of 260 ° C., A heat-sealable polyolefin-based foamed film was obtained in exactly the same manner except that they were laminated in a T-die. This film was a film having improved sealing strength as compared with the film of Example 1. The characteristic values are shown in Table 2.

(Comparative Example 1)
In Example 1, a heat-sealable polyolefin-based foamed film was obtained in exactly the same manner except that 12750 ppm of PMMA crosslinked beads (Sumitomo Chemical average particle size 1.8 μm) were added as an antiblocking agent to the seal layer (B). . This film was inferior to the film of Example 1 in terms of slipperiness. The characteristic values are shown in Table 3.

(Comparative Example 2)
Heat sealability is exactly the same except that 12000 ppm of calcium carbonate (average particle size of 10 μm) and 750 ppm of PMMA crosslinked beads (average particle size of 1.8 μm manufactured by Sumitomo Chemical) are added as an antiblocking agent to the seal layer (B). A polyolefin foam film was obtained. This film was inferior to the film of Example 1 in terms of slipperiness and heat sealability. The characteristic values are shown in Table 3.

  The heat-sealable polyolefin-based foam film of the present invention is capable of achieving both high concealability, heat-seal strength and slipperiness, and is suitable for packaging materials having excellent processability when used as packaging materials. It is a good film.

Claims (1)

A heat-sealable polyolefin-based foam film comprising at least two layers of a seal layer and a foam layer, wherein the antiblocking agent added to the seal layer is cubic calcium carbonate having a mean particle diameter of 5 to 8 μm and an average particle It consists of a combination of spherical PMMA cross-linked beads having a diameter of 0.5 to 10 μm, the dynamic friction coefficient between the seal layers is 0.50 or less , a heat seal temperature of 130 ° C., a seal pressure of 10 N / cm ² , a seal The seal strength in 1 second time is 5.0 N / 15 mm or more, the heat seal temperature is 90 ° C., the seal pressure is 10 N / cm ² , and the seal strength in 1 second seal time is 3.0 N / 15 mm or more. Heat-sealable polyolefin foam film.