JP5151017B2 - Laminated polypropylene film - Google Patents

Description

  The present invention relates to a laminated polypropylene film, and has excellent printability in various printing methods such as gravure printing, flexographic printing, thermal transfer method, and ink jet method, and also has flexibility, cushioning properties, heat insulation properties and the like. The present invention relates to a laminated polypropylene film having linear cutability and hand cutting properties suitable for packaging materials, adhesive tapes, printing papers and the like.

  Many proposals have been made for a technique in which a porous resin layer in which a large number of pores are provided in polypropylene and a resin base material that does not contain pores or has a small amount of pores as a laminated structure as printing paper ( Patent Documents 1 to 3).

  However, in any technique, it is necessary to add a large amount of void forming additives such as fillers to the polypropylene in order to form a porous layer. There is a problem in that productivity is hindered due to an increase in properties and a phenomenon in which polymer degradation products and particle agglomerates accumulate on the tip of the die (so-called “eyes”).

On the other hand, a method has been proposed in which a β-crystal nucleating agent or the like is added to a polypropylene resin to produce a β-crystal richly and cause a crystal transformation from a β-crystal to an α-crystal during stretching (Patent Document 4,). 5). This technology utilizes the melting point and density difference (α crystal: crystal density 0.936 g / cm ³ , β crystal: crystal density 0.922 g / cm ³ ) between α crystal and β crystal, which is a typical crystal system of polypropylene. Thus, holes are formed. However, since the density difference between the α crystal and the β crystal is not so large, in order to increase the porosity to 30% or more, it is necessary to generate a large amount of β crystal in the unstretched sheet as a precursor. It is necessary to cast at a high temperature when forming an unstretched sheet. Further, as a stretching condition, a significant constraint is that pores are not efficiently formed unless stretching is performed at a relatively low temperature of about 130 ° C. or less. That is, for example, an ordinary polypropylene resin layer containing no β crystal nucleating agent (referred to as “Layer A”) and a resin layer that generates a large amount of β crystals (referred to as “Layer B”) are laminated in the same die. When trying to obtain a composite film by co-extrusion, the layer A forms a strong spherulite structure of α-crystal due to the restriction of high-temperature casting, resulting in problems such as fracture at low-temperature stretching. As described above, in the die co-extrusion method, there is a problem that a stable production of a multilayer composite film of a porous layer and a base polypropylene layer by a β crystal method is extremely restricted.

  On the other hand, as a proposal for a laminated polypropylene film, a polypropylene film having a laminated structure of a uniaxially oriented polypropylene layer having a linear cut property and a biaxially oriented polypropylene layer and an improved technique thereof have been disclosed (Patent Document 6). ~ 9).

  In this technology, a non-oriented polypropylene resin layer (B) is basically laminated on a uniaxially oriented polypropylene resin layer (A), and the laminate is stretched in a direction perpendicular to the orientation direction of the layer (A). Thus, the biaxially oriented polypropylene layer (A) and the uniaxially oriented polypropylene layer (B) are laminated without any other resin composition such as an adhesive or an anchor coat layer, and the uniaxially oriented layer (B ) To form a film that can be cut linearly in the orientation direction. Of course, another polypropylene resin (C) can be interposed in order to further strengthen the adhesion between the layer (A) and the layer (B) (Patent Document 9).

The present inventors have proposed the present invention as a result of pursuing the possibility that at least one of the polypropylene layers can be made a porous layer by using such a lamination technique.
JP-A-63-315293 (Claim 1) JP-A-2-070479 (Claims) Japanese Patent Laid-Open No. 5-078512 (Claim 1) JP-A-6-100720 International Publication No. 02/066233 Pamphlet Japanese Utility Model Publication No. 49-57567 Japanese Patent Laid-Open No. 51-19080 JP-A-57-259593 JP 2000-25173 A

The present invention is formed by laminating a uniaxially oriented polypropylene resin layer containing no voids or a small amount of voids and a porous polypropylene layer, and has a new texture such as cushioning and flexibility, printability, heat insulation The present invention proposes a laminated polypropylene that has the properties of straight cut and hand cut.

In view of the above problems, the present invention proposes a laminated polypropylene film having the following characteristics as means for solving the problems.
(1) In a laminated polypropylene film composed of a porous polypropylene layer (A) having at least continuous pores and a uniaxially oriented polypropylene layer (B), the lamination ratio of the layer (A) and the layer (B) is 20: 3. Laminated polypropylene film characterized in that it is 0 to 20: 5 (2) The β crystal generation efficiency of the resin constituting the layer (A) is 50% or more. Item (1) or (2), wherein the polypropylene film (3) layer (A) has a resin having a melt flow index of 2 to 50 g / 10 min and an isotactic index of 94% or more. (4) The resin layer (C) is interposed between the polypropylene layer (A) and the polypropylene layer (B), and the melting point of the resin layer is 130 to 158. The laminated polypropylene film according to (1) to (3), characterized in that the optical density is 0.5 or more, wherein (1) to (4) Laminated polypropylene film (6) The laminated polypropylene film according to any one of items (1) to (5), wherein the layer (A) has a porosity of 35 to 70%.

Since the present invention laminated polypropylene film is formed by laminating a porous polypropylene layer having continuous pores and a uniaxially oriented polypropylene layer,
-Excellent print receptivity for various types of printing methods and at the same time linear cut ability.
-Cushioning and concealment can be controlled widely by controlling the lamination ratio according to the application.
-Since the porous layer is backed by a uniaxially oriented layer, the strength is particularly high in the uniaxially oriented direction and the handling property is excellent.

For this reason, it can be applied to a wide range of uses such as packaging materials, adhesive tapes, and print receiving paper.

  In the present invention, in a laminated polypropylene film in which at least a porous polypropylene layer (A) and a uniaxially oriented polypropylene layer (B) are laminated, the lamination ratio of the layer (A) and the layer (B) is 20:50. The basic configuration is that it is ˜20: 5.

  The porous polypropylene layer (A) has a large number of pores in the layer using a polypropylene resin as a matrix. The pore size of the pores is, in particular, good concealability and whiteness, and the major axis of the pores observed from the film cross section is 0.1 to 20 μm, more preferably 0.2 to 10 μm. preferable. It is necessary that some or all of the many holes formed in the layer are continuous with each other. This is for improving the fixability and impregnation properties of printing ink and the like, and when it is completely independent holes, sufficient printability cannot be ensured. Whether the pores of the layer are continuous pores can be evaluated by impregnating the pores when a liquid having affinity for polypropylene resin such as fluid paraffin is adhered to the film surface. . That is, when it is not impregnated at all, it can be regarded as an independent hole, and when it is impregnated within a few seconds to a few minutes, it can be said that it has excellent continuous porosity. In the present invention, the impregnation property is preferably 0.05 to 10 seconds / μm.

  The layer (A) preferably contains substantially no organic and / or inorganic filler. This is because, as described above, the filler hinders productivity due to the formation of eyes and the like, and at the same time, surface defects such as fish eyes caused by poor dispersion are likely to occur and the quality is lowered. Here, “substantially does not contain” means that no filler is added for the purpose of forming pores. That is, it may be preferable to add an organic and / or inorganic filler to the polypropylene resin in order to improve a small amount of inorganic components and slipperiness as a chlorine scavenger for neutralizing chlorine caused by the catalyst. In the range of the amount of filler added for these purposes, it is regarded as “substantially free”. Usually, the total amount of fillers added for the purpose of neutralizing chlorine or imparting slipperiness is 10 to 10,000 ppm, and the concentration not substantially contained can be regarded as 10,000 ppm or less.

  Thus, in order to form the (A) layer containing substantially no filler and containing many pores, a method utilizing the crystal modification of polypropylene is preferable. In other words, a lot of β crystals are formed in the precursor film, and when the film is heated and stretched, a β → α crystal transition occurs, and a void is formed by utilizing the melting point difference, density difference, and stretching behavior difference. To do. From this viewpoint, the β crystal generation efficiency of the polypropylene resin constituting the layer (A) is preferably 50% or more, and more preferably 60% or more.

  Since the α crystal is stable as a crystal form of polypropylene, it is difficult to generate a sufficient β crystal amount by an ordinary cooling process only by optimizing the resin characteristics of polypropylene, and even if it is generated, it remains in the range of several percent. Therefore, in order to increase the β crystal generation efficiency, it is preferable to add a crystal nucleating agent that selectively generates β crystals. Various compounds have been proposed as β crystal nucleating agents for a long time, and examples thereof include carboxylic acid salts such as potassium 12-hydroxystearate, magnesium benzoate and magnesium phthalate, quinacridone pigments, etc. The amide compound represented by the formula is preferable because there is no problem of coloring and the like and the production efficiency of β crystals is high.

R2-NHCO-R1-CONH-R3 (1)
In particular,
(1) N, N′-diphenylhexanediamide, N, N′-dicyclohexylterephthalamide, N, N′-dicyclohexyl-2,6-naphthalenedicarboxamide,
(2) N, N′-dicyclohexynecarbonyl-p-phenylenediamine, N, N′-dibenzoyl-1,5-diaminonaphthalene, N, N′-dibenzoyl-1,4-diaminocyclohexane and N, N '-Dicyclohexanecarbonyl-1,4-diaminocyclohexane
(3) At least one selected from the group consisting of N-cyclohexyl-4- (N-cyclohexanecarbonylamino) benzamide and N-phenyl-5- (N-benzoylamino) pentanamide and / or a mixture of two or more thereof. Preferably there is.

  In the present invention, it is preferable to contain 0.01 to 2% of such a β crystal nucleating agent in the layer polypropylene resin from the viewpoint of efficiently generating β crystals, more preferably 0.05. ~ 0.5 wt%.

  Polypropylene resins that are easy to produce β crystals and improve porosity are exemplified by polypropylene homopolymers, random copolymers, block copolymers, etc., among which polypropylene homopolymers and block copolymers are preferred. . As the polypropylene homopolymer, higher crystallinity is preferable because the β crystal generation efficiency is higher, and the isotactic index is preferably 94% or more, more preferably 96% or more. The melt flow index also affects the production efficiency, but in view of mechanical characteristics, the melt flow index of the resin is preferably 2 to 50 g / 10 minutes, more preferably 5 to 30 g / 10 minutes. An example of the block copolymer is an ethylene propylene block copolymer. Similarly, the melt flow index is preferably 2 to 50 g / 10 minutes and 5 to 30 g / 10 minutes. Of course, other resins may be added to the resin as long as they do not contradict this purpose. Specifically, polyolefins such as polyethylene, polybutene 1, and poly-4-methylpentene 1, polyethylene terephthalate, polybutylene terephthalate, etc. Examples thereof include thermoplastic resins such as polyesters, polyamides, and fluorine resins.

  Thus, by adding a β crystal nucleating agent and melt-extruding a polypropylene resin, and cooling and solidifying at around 120 ° C. of the crystallization temperature at which β crystals are efficiently formed, the β crystal ratio is more preferably 50% or more. A porous film having a large number of pores in the film can be obtained by forming a precursor film of 60% or more, and stretching by heating.

  Next, the uniaxially oriented polypropylene layer (B) constituting the film of the present invention will be described.

  The layer (B) is a support layer for the layer (A) and a layer that imparts linear cutting properties, and needs to be uniaxially oriented. This is because polymer films tend to tear in the direction of molecular chain orientation, but unoriented or biaxially oriented films do not define the direction of tearing, and it is necessary to make them uniaxially oriented in order to develop a linear cut. Because. About uniaxial orientation, as described in “Make Film” (Polymer Processing One Point Kyoritsu Shuppan Co., Ltd. 1993, P24, P79), etc., confirm from molecular orientation by X-ray diffraction etc. Can do. However, in the present invention, pores may be formed in the layer (B). In this case, observation by the X-ray method may be difficult. You may judge from the ratio of a major axis to a minor axis. That is, when the ratio (RTD / RMD) of the axial length (RMD) in the longitudinal direction and the axial length (RTD) in the width direction of the void observed from the film film surface is 3 or more, it is regarded as uniaxial orientation.

  As the characteristics of the polypropylene resin constituting the layer (B), the melt flow index is preferably 2 to 80 g / 10 minutes, more preferably 4 to 50 g / 10 minutes, and particularly preferably 6 to 5 for improving the linear cut property. 30 g / 10 minutes.

  The resin may contain an organic and / or inorganic filler. Specifically, the organic particles include silicone particles, crosslinked polymethylmethacrylate particles, and crosslinked polystyrene particles, and the inorganic particles include calcium carbonate, titanium oxide, aluminum oxide, talc, and silicon oxide. An average particle size of 0.1 to 5 μm is preferable because the dispersibility becomes good. From the viewpoint of dispersibility, a surface treatment agent such as a surfactant is added to the surface of the particle and / or the polypropylene resin. It is possible.

  Furthermore, it is also possible to add a β crystal nucleating agent to the resin layer, and the addition amount and composition may be the same as or different from those of the layer (A).

  In addition, a known antistatic agent for imparting antistatic performance and slipping property, and an organic and / or inorganic lubricant can be added to the resin layer.

  The film of the present invention is a film in which the above-mentioned layer (A) and layer (B) are laminated, and the adhesion between both layers is obtained by extrusion laminating the layer (B) to the layer (A). However, it is not obtained through a so-called adhesive such as a hot-melt adhesive or an anchor coat agent, and is specifically obtained as follows.

  That is, after the resin layer (A) melt-extruded into a sheet is cooled and solidified on a chill roll, the resin layer (A) is stretched 3 to 7 times in the longitudinal direction by a roll stretching device, and then guided to the extrusion laminating device to be on the layer (A). The resin layer (B) is melt-extruded into a sheet to obtain a laminate composed of layer (A) / layer (B). At this time, the layer (A) is oriented in the longitudinal direction, and the layer (B) is in a non-oriented state. Next, both ends of the laminate are held with clips and guided to a hot air oven, and stretched 5 to 10 times in the width direction. As a result, the layer (A) is biaxially stretched, the layer (B) becomes a uniaxially oriented film in the width direction, and a laminated film in which both layers are firmly bonded can be obtained. According to such a process, the lamination ratio of the layer (A) and the layer (B) needs to be in the range of 20:50 to 20:10, and preferably 20:45 to 20:15. Range. If the layer (A) is too thin, lamination becomes difficult due to dimensional change or melting of the layer (A) when the precursor molten resin forming the layer (B) is laminated. Further, if the layer (B) is too thin, it is possible to provide a resin layer (C) between the layer (A) and the layer (B) in order to improve the adhesiveness of both layers. The melting point of the resin layer is preferably 130 to 158 ° C, more preferably 140 to 155 ° C. Examples of such a polypropylene resin include random polypropylene obtained by copolymerizing α-olefin such as ethylene, 1-butene, 4-methyl-1-pentene, and 1-hexene, and a polypropylene homopolymer having an isotactic index of 60 to 90%. Is exemplified.

As a method of providing the resin layer (C),
(A) Method: Sheet molding with layer (C) laminated on at least one side of layer (A) (b) Method: Sheet molding with layer (C) laminated on at least one side of layer (B) Method (c) Method: A method of performing both (a) and (b) is exemplified, but the method (a) is advantageous in terms of cost as well as providing sufficient adhesive force.

  Since the film of the present invention has a laminated structure, the structure of the layer (B) can be changed according to the purpose of use. Specifically, there are two cases: a transparent polypropylene layer selection case and a white polypropylene layer selection case, but the latter white polypropylene is particularly important when concealment is important for printing purposes. It is preferred to select the layer. In order to do this, the layer (B) is preferably a white polypropylene layer by adding an inorganic and / or organic filler or the like, particularly selected from titanium oxide, aluminum oxide and calcium carbonate. It is preferable to add 5 to 30% by weight of at least one filler. The particle size of the filler is 0.1 to 2 μm. In this case, the film of the present invention preferably has an optical density of 0.5 or more, more preferably 0.7 or more, which is a concealing index. preferable.

The total thickness of the film of the present invention should be set according to the application and is not particularly limited. However, the range of 20 to 100 μm is usually preferable because it is easy to use.

Measuring method of characteristic value The characteristic value of the present invention was measured by the following method.

(1) Isotacticity (%)
The resin used in the present invention is extracted with n-heptane at a temperature of 60 ° C. or lower for 2 hours to remove the additive to polypropylene. Thereafter, it is vacuum dried at 130 ° C. for 2 hours. A sample of weight W (mg) is taken from this, placed in a Soxhlet extractor and extracted with boiling n-heptane for 12 hours. Next, this sample was taken out and thoroughly washed with acetone, then vacuum-dried at 130 ° C. for 6 hours, and then cooled to room temperature. The weight W ′ (mg) was measured, and the following formula was obtained.

Isotacticity = (W '/ W) x 100 (%)
(2) Melt flow index (MFI: g / 10 min)
The measurement was performed under the conditions of 230 ° C. and 2.16 kg according to ASTM-D-1238.

(3) β crystal formation efficiency, melting point peak temperature (° C.) and crystal melting heat (J / g)
A Seiko Instruments thermal analyzer RDC220 type was charged with 5 mg of sample enclosed in an aluminum pan, heated at a rate of 320 ° C./min, held at 260 ° C. for 5 min, and then brought to room temperature at 20 ° C./10 min. Cooling. Subsequently, the peak temperature of the crystal melting endotherm observed when the temperature was raised at 20 ° C./10 minutes was determined. Moreover, the amount of heat of crystal melting was calculated from the area of the endothermic peak using a built-in program of the company's thermal analysis system SSC5200. The β crystal production efficiency (Efβ) is calculated as follows.

Ef = Aβ / (Aα + Aβ) × 100 (%)
Aα: Peak area resulting from melting of α crystal (melting peak 158 to 168 ° C.)
Aβ: Peak area resulting from melting of β crystal (melting peak 140 to 154 ° C.)


(4) Thickness (μm) and thickness ratio of resin layer A film cross section is cut out with a microtome, and the film cross section is observed with a scanning electron microscope to determine the thickness.
Device: JEM-1200EX manufactured by JEOL Ltd.
Observation magnification: 1000 times Accelerated electrons: 100 kV
When it is difficult to separate the resin layer, the layer can be divided by a dyeing method as necessary.
(5) Orientation state of each layer The orientation state of each layer (whether it is uniaxial orientation or biaxial orientation) is confirmed by peeling and separating each layer and confirming by X-ray diffraction pattern. (For example, a reference document “Creating a Polymer Processing One Point 2 Film”, Chapter 9, Section E (1993, published by Kyoritsu Shuppansha)).
(6) Optical density Using a Macbeth densitometer TR-927 (manufactured by Macbeth), an absolute density (density) is measured using an orthochromatic (white filter) filter by a transmission method. The number of samples was 5, and the average value was the optical density.

(7) A porosity film of 10 cm square is cut out and conditioned for 24 hours in a temperature-controlled room (23 ° C., relative humidity 60%), and then the weight (W1 (g)) is measured. Next, the sheet is taken out after being immersed in fluid paraffin for 8 hours, and the surface fluid paraffin is removed by Kimwipe and the weight (W2 (g)) is measured.

    The porosity (P) is determined by the following equation from the thickness (Tp (μm)) of the porous layer obtained in the above item (4). The measurement is performed at n = 10 and an average value is adopted.

P = (W2-W1) / (Tp × 10−2) / ρ × 100 (%)
Where ρ is the density of flowing paraffin at 23 ° C

(8) Straight line cut property The film is cut into A4 size strips. At this time, the long side direction cut direction of the strip is set. An incision having a width of 20 mm and a depth of 10 mm was made at the center of one short side of the strip, and evaluation was performed as follows when tearing the strip from the notch.

  In addition, the angle which takes out this notch was 30 degree | times with respect to this long side, and evaluated by n = 3.

It is possible to tear the strip cleanly within the range of the cutting width 20 mm ± 5 mm: ○
The cutting width fluctuates by more than ± 5 mm, but the strip can be torn: △
Incision breaks in the middle and strips cannot be torn: ×

(9) Printability A film sample was laminated on a public postcard using an adhesive, and printed with an ink jet printer manufactured by Seiko Epson Corporation. For each sample, 10 sheets were printed under the following conditions, immediately after printing, a 1 kg load was applied, and after 10 minutes, the printed surface and non-printed surface of each postcard were confirmed. Judged.

A. Printing conditions: Change point size to 8, 10, 12, 16, 24 and print alphabet (A to Z) B. Comparative sample: Seiko Epson standard inkjet receiving paper Evaluation criteria :
Printability (compared to standard product) X Equivalent: 5, Inferior: 3, Remarkably inferior: 1
Receptivity (transfer on opposite side) Y No transfer: 5, Some transfer: 3 Transfer: 1
D. Evaluation points were calculated by the formula 2 × X + Y and evaluated as follows.

13 or more: ○, 12-8: Δ, 7 or less: ×

1.
・ Raw material preparation Resin layer (A)
As shown in Table 1, polypropylene resin 1 (melt flow index = 8, isotactic index = 97%) and polypropylene resin 2 (melt flow index = 1 g / 10 min) manufactured by Sumitomo Chemical Co., Ltd. are used as polypropylene resins. As a β crystal nucleating agent, 0.1 wt% and 0.2 wt% of NU-100 manufactured by Shin Nippon Rika Co., Ltd. were added, and the mixture was melt-kneaded with a twin-screw extruder and pelletized. Moreover, the thing which does not add a nucleating agent was melt-kneaded with the same extruder, and was pelletized.

Resin layer (B)
As a polypropylene resin, Sun Allomer polypropylene resin 3 (melt flow index = 15 g / 10 min) was prepared. In addition, a resin prepared by adding 10% by weight of calcium carbonate (average particle size 1 μm) to the resin was also prepared. See Table 1.

Resin layer (C)
A polypropylene resin 4 (ethylene 4% copolymerized random polypropylene) manufactured by Sumitomo Chemical Co., Ltd. was prepared as a polypropylene resin. See Table 1.

2. Film-forming method Film-forming method 1
From a T die having two extruders (extruder A and extruder B) and a joining device capable of laminating the resin extruded from these into a sheet of two layers (A) single layer (= from both extruders) The same polymer was extruded) or a molten sheet of the (A) / (C) layer was extruded and cooled and solidified on a cooling drum. At this time, the cooling drum was maintained at 120 ° C. by circulating a heat medium. Next, the sheet was led to a 25 ° C. water bath and cooled, then led to a roll type preheating device and sufficiently preheated, and then stretched 4.5 times in the longitudinal direction.

Thereafter, the resin layer (B) was melt-extruded from the extruder C by the extrusion laminator, and the (A) layer and the extruded resin layer (B) were laminated between a cooling drum and a nip roll at 25 ° C. and cooled and solidified. Thus, a laminated film composed of the uniaxially stretched layer (A) and the non-oriented resin layer (B) was obtained.
Next, the both ends of the laminated film are held with clips, guided to a hot air oven, stretched 9 times in the transverse direction at 135 ° C., further heat-fixed at 155 ° C., and then cooled to 140 ° C. and 10% in the width direction. I took a relax.
The stretched film thus obtained is trimmed at the clip gripping portions at both ends, and then subjected to corona discharge treatment on the surface of the uniaxially stretched layer (B) so that the surface wetting tension is 40 mN / m, and then wound into a roll. It was.

Film formation method 2
A molten sheet of (A) / (B) layer is obtained from a T-die having two extruders (extruder A and extruder B) and a confluence apparatus capable of laminating the resin extruded from these into a two-layer sheet. The mixture was cooled and solidified on an extrusion and cooling drum. At this time, the cooling drum was maintained at 120 ° C. by circulating a heat medium. Next, the sheet was led to a 25 ° C. water bath and cooled, then led to a roll type preheating device and sufficiently preheated, and then stretched 4.5 times in the longitudinal direction. Next, the both ends of the laminated film are held with clips, guided to a hot air oven, stretched 9 times in the transverse direction at 135 ° C., further heat-fixed at 155 ° C., and then cooled to 140 ° C. and 10% in the width direction. I took a relax.
The stretched film thus obtained is trimmed at the clip gripping portions at both ends, and then subjected to corona discharge treatment on the surface of the uniaxially stretched layer (B) so that the surface wetting tension is 40 mN / m, and then wound into a roll. It was.

Example 1
Extruded sheet made of resin A-1 by supplying resin A-1 (β crystal nucleating agent 0.2 wt%) as resin layer (A) to both extruder A and extruder B by the film forming method 1 Formed. Next, the sheet was uniaxially stretched in the longitudinal direction at 120 ° C., and then resin B-1 was melt-extruded as a resin layer (B), laminated on the resin layer (A), and transversely stretched and wound up.

The thickness of the laminated film thus obtained was 35 μm, the lamination ratio of layer (A) and layer (B) was 20:15, and the porosity of layer (A) was 55%. In addition to being excellent in straight line cutability, the print test with an ink jet printer was good in printability and free from problems such as post-transfer.

Example 2
Extruded sheet made of resin A-1 by supplying resin A-1 (β crystal nucleating agent 0.2 wt%) as resin layer (A) to both extruder A and extruder B by the film forming method 1 Formed. Next, the sheet was uniaxially stretched at 115 ° C. in the longitudinal direction, and then resin B-1 as a resin layer (B) was melt-extruded, laminated to the resin layer (A), laterally stretched and wound up.

The thickness of the laminated film thus obtained was 50 μm, the lamination ratio of layer (A) to layer (B) was 20:30, and the porosity of layer (A) was 50%. In addition to being excellent in straight line cutability, the print test with an ink jet printer was good in printability and free from problems such as post-transfer.

Example 3
Extruded sheet made of resin A-1 by supplying resin A-2 (β crystal nucleating agent 0.1 wt%) as resin layer (A) to both extruder A and extruder B by film forming method 1 Formed. Subsequently, the sheet was uniaxially stretched, and then resin B-1 was melt-extruded and laminated on the resin layer (A) as a resin layer (B), and the sheet was stretched and wound up. In this case, the uniaxial stretching temperature was 115 ° C.

The thickness of the laminated film thus obtained was 35 μm, the lamination ratio of layer (A) and layer (B) was 20:15, and the porosity of layer (A) was 50%. The linear cut property was good and the printability was also good.
Example 4
Extruded sheet made of resin A-1 by supplying resin A-1 (β crystal nucleating agent 0.2 wt%) as resin layer (A) to both extruder A and extruder B by the film forming method 1 Formed. Next, the sheet was uniaxially stretched at 115 ° C. in the longitudinal direction, and then resin B-2 (calcium carbonate 10% by weight) as a resin layer (B) was laminated on the melt-extruded resin layer (A) and transversely stretched and wound up.

The thickness of the laminated film thus obtained was 50 μm, the lamination ratio of layers (A) and (B) was 20:30, and the porosity of layer (A) was 60%. Further, the optical density of the film was 0.8, which was excellent in hiding properties. In addition to excellent straight-line cutability, the printing test with an ink jet printer was good, and there were no problems such as post-transfer.
Example 5
According to the film forming method 1, resin A-1 (β crystal nucleating agent 0.2% by weight) is supplied to the extruder A and resin C (ethylene propylene random copolymer) is supplied to the extruder B as the resin layer (A). An extruded sheet made of Resin A-1 / Resin C was formed. Subsequently, the sheet was uniaxially stretched at 115 ° C., and then resin B-2 was melt-extruded as a resin layer (B), laminated on the resin layer C side, stretched laterally, and wound up.

The thickness of the laminated film thus obtained was 40 μm, and the layers (A), (C), and (B) were 18 μm, 2 μm, and 20 μm, respectively. The optical density of the film was 0.75, and it was excellent in linear cut property, and the printing test with an ink jet printer was good, and there were no problems such as post-transfer.

Example 6
According to the film forming method 1, resin A-4 (melt flow index = 1 g / 10 min, β crystal nucleating agent 0.2 wt%) is supplied to both the extruder A and the extruder B as the resin layer (A). An extruded sheet made of Resin A-1 was formed. Next, the sheet was uniaxially stretched, and then the resin B-1 was melt-extruded and laminated on the resin layer (A) as a resin layer (B), and then laterally stretched and wound up. In this case, the uniaxial stretching temperature was 115 ° C.

The thickness of the laminated film thus obtained was 40 μm, the lamination ratio of layer (A) and layer (B) was 20:20, and the porosity of layer (A) was 40%. The straight-line cut property was good, and although the post-transfer was seen in a print test with an inkjet printer, the print property was excellent.
Comparative Example 1
According to film forming method 1, resin A-3 (β crystal nucleating agent 0% by weight) is supplied to both extruder A and extruder B as a resin layer (A) to form an extruded sheet made of resin A-1. did. Next, the sheet was uniaxially stretched, and then the resin B-1 was melt-extruded and laminated on the resin layer (A) as a resin layer (B), and then laterally stretched and wound up. In this case, the uniaxial stretching temperature was 120 ° C.

The thickness of the laminated film thus obtained was 35 μm, the lamination ratio of layer (A) and layer (B) was 15:20, and the porosity of layer (A) was%. Although the linear cut property was developed, there was a problem in printability.
Comparative Example 2
By the film forming method 2, the resin A-1 was supplied to the extruder A and the resin B-1 was supplied to the extruder as the resin layer (A) to form an extruded sheet made of the resin A-1 / resin B-1. Next, the sheet was uniaxially stretched. However, since fracture occurred at 115 ° C., it was necessary to increase the stretching temperature to 145 ° C. in order to stabilize the sheet. Next, the film was gripped and stretched in the transverse direction in an oven. The obtained film was hazy, but the layer (A) had a low porosity and was difficult to measure. There was also a problem with printability.
Comparative Example 3
A laminated film was obtained in the same manner as in Example 1 except that the composition ratio of the layer thickness was changed to 30: 5 μm (20: 3), but there was a problem with the linear cut property.

Multilayer polypropylene film comprising the porous layer obtained in Example 1 and a transparent uniaxially oriented polypropylene layer A multilayer polypropylene film comprising the porous layer obtained in Example 4 and a white uniaxially oriented polypropylene layer A multilayer polypropylene film in which a third polypropylene layer is provided between the porous layer obtained in Example 5 and a white uniaxially oriented polypropylene layer.

Explanation of symbols

1: Porous polypropylene layer (A)
2: Uniaxially oriented polypropylene layer (B) (transparent)
2 ': Uniaxially oriented polypropylene layer (B) (white)
3: Third polypropylene layer (C)
4: Laminated polypropylene film

Since the porous layer of the film of the present invention forms continuous pores, it has liquid impregnation properties.
Therefore, it can be applied as a drug film by impregnating various chemicals. Specifically, it may be impregnated with a fragrance or a deodorant and used as an odor improving film in a room or in a vehicle, or impregnated with a rust inhibitor and used as a slip sheet such as a metal plate. In this case, if the drug impregnated in the form of a roll of drug film loses its function due to sublimation or reaction, etc., a new part is pulled out from the roll one after another, and it is especially used for cutting unnecessary parts. Combined with sexual functions, it can be used as an easy-to-use drug film.

  Also used for packaging materials such as frozen foods and confectionery, etc. that make use of heat insulation, labels for beverage cans, surface protection films or anti-vibration materials that make use of cushioning properties, anti-counterfeiting labels that make use of the easy cleavage of porous layers, etc. Is possible.

Claims (6)

In a laminated polypropylene film comprising a porous polypropylene layer (A) having at least continuous pores and a uniaxially oriented polypropylene layer (B), the lamination ratio of the layer (A) and the layer (B) is 20: 30 to 20 A laminated polypropylene film characterized by being: 5. The laminated polypropylene film according to claim 1, wherein the β-crystal production efficiency of the resin constituting the layer (A) is 50% or more. The laminated polypropylene film according to claim 1 or 2, wherein the resin constituting the layer (A) has a melt flow index of 2 to 50 g / 10 min and an isotactic index of 94% or more. The resin layer (C) is interposed between the polypropylene layer (A) and the polypropylene layer (B), and the melting point of the resin layer (C) is 130 to 158 ° C. A laminated polypropylene film according to any one of the above. The laminated polypropylene film according to any one of claims 1 to 4, wherein the optical density is 0.5 or more. The layered polypropylene film according to any one of claims 1 to 5, wherein the layer (A) has a porosity of 35 to 70%.