JPH02311539A - Porous polypropylene film - Google Patents

Abstract

PURPOSE:To provide a porous polypropylene film having a high optical density and excellent shielding property, printability, etc., by mixing a crystalline polypropylene containing a beta-crystal nucleator with an incompatible thermoplastic resin of specified properties in a specified mixing ratio, melt-molding the mixture and orienting the obtained film. CONSTITUTION:50 to 85wt.% crystalline polypropylene containing a beta-crystal nucleator (e.g. gamma-quinacridone) is mixed with 50 to 15wt.% thermoplastic resin being incompatible with polypropylene and having a melting crystallization temperature >=140 deg.C and a weight-average mol.wt. to number-average mol.wt. ratio <=6 (e.g. poly-4-methylpentene-1). The mixed resin is melt-extruded into a sheet with an extruder, solidified by cooling and oriented. In this way, a porous polypropylene film of a density of 0.4 to 0.8g/cm<3> and an optical density >=0.3 is obtained. This film can be desirably used as various printing papers, labels, etc.

Description

Detailed Description of the Invention [Industrial Application Field] The present invention relates to a porous and opaque polypropylene film, which has particularly excellent whiteness, hiding properties, and printability, and is suitable for dust-free paper. , relates to a porous polypropylene film suitable for use in thermal transfer paper and waterproof paper.

[Conventional technology] Conventionally, the method for manufacturing porous films is to add an incompatible resin to polypropylene, form a sheet, then slightly deform it at low temperature to create cracks, and then biaxially stretch it. A method for obtaining a porous film has been proposed. (Japanese Patent Publication Nos. 53-990 and 55-41900) [Problems to be Solved by the Invention] However, the present inventors have found that this method has the following problems. In other words, (1) when an incompatible resin is added to polypropylene (hereinafter abbreviated as PP), the two are incompatible even in the molten state, so when normally extruded, the incompatible domains move in the flow direction. The film obtained by stretching, orienting, and cooling (hereinafter referred to as cast film) is prone to longitudinal cracking, making it difficult to continue stretching, and even if stretching is possible, the pores are continuous in the thickness direction. They can only do things that are inferior to their gender.

■ The process of micro-stretching at low temperatures is extremely unstable and tends to cause breakage and necking stretching.

In order to solve these problems, the present inventors proposed in Japanese Patent Application Laid-Open No. 199742/1983 that they solved the problem (2) by generating β crystals in PP and made it porous by ordinary biaxial stretching. Although the technology has been proposed, there are still insufficient points regarding problem (1).

An object of the present invention is to provide a porous polypropylene film that reduces the stretching phenomenon of the blend phase during extrusion (vertical cracking of cast film), has excellent film formability, and has excellent uniformity.

[Means for Solving the Problems] The present invention has been developed as a result of studies on the incompatible resin added to polypropylene, and in particular, the molecular weight distribution (M w
/Mn) plays an important role in imparting good porosity, and the above problem was solved.

That is, crystalline polypropylene 5 containing a β-crystal nucleating agent
0 to 85% by weight, and 15 to 50% by weight of a thermoplastic resin that is incompatible with polypropylene, has a melt crystallization temperature of 140°C or higher, and a Mw/Mn of 6 or lower, and has a density of 0.
4-0. The present invention relates to a porous polypropylene film having an optical density of 8 g/cm3 and an optical density of 0.3 or more.

In the present invention, the crystalline polypropylene is allowed to contain α-olefin (ethylene, butene, hexene, etc.) comonomers other than one teropylene monomer unit, but the porosity is improved if the content is 5% by weight or less of the PP. preferred above.

In addition, the intrinsic viscosity ([η]) of the PP resin is 1°2 d
l/g or more, preferably 1.4 to 2.3 dl/g, as this provides good film formability and good physical properties such as mechanical properties.

Furthermore, in order to achieve good opacity, the isotactic index (II), which is a measure of stereoregularity, is 93.
% or more, preferably 96% or more.

Examples of β-crystal nucleating agents added to PP include alkali or alkaline earth metal salts of carboxylic acids such as sodium benzoate, calcium 2-hydroxystearate, and magnesium succinate, and di- or triesters of di- and tribasic carboxylic acids. preferred are aromatic sulfonic acid compounds such as sodium benzenesulfonate, phthalocyanines such as phthalocyanine blue, quinacridones, and quinacridonequinones, with quinacridones and quinacridonequinones being particularly preferred.

The amount of such β-crystal nucleating agent added is 1 in the above PP.
The content is preferably from 1×10−9 to 1X10−2% by weight, more preferably from 1
-5% by weight is preferable because the formation of β-crystals is good and there are no problems such as coloring caused by additives.

In addition, as a method of adding the β-crystal nucleating agent, PP
Examples include a method in which master pellets are prepared and added by melt-blending the nucleating agent, and a method in which the nucleating agent is added at the time of melt-blending PP and a thermoplastic resin incompatible with polypropylene. A particularly preferred method for adding a β-crystal nucleating agent is a method in which the β-crystal nucleating agent is added to the polymerization catalyst during polymerization of PP (Japanese Patent Publication No. 63-378.0
No. 4, Japanese Patent Publication No. 63-37826) is preferred because of its excellent uniformity.

The melt crystallization temperature of the thermoplastic resin that is incompatible with polypropylene (hereinafter referred to as incompatible resin) must be 140°C or higher, preferably 150°C to 230°C.
It is. If the melt crystallization temperature is lower than 140°C, it becomes difficult to obtain a uniform porous film.

Specific examples of the incompatible resin include poly-4 methyl pentene 1, poly 3-methyl butene 1, polyethylene terephthalate, polybutylene terephthalate, polyamide, etc. Among these, poly-4 methyl pentene 1 (
PMP (hereinafter abbreviated as PMP) is preferable because it has excellent dispersibility with PP and chemical stability. Particularly, PMP having a melting point of 230° C. or higher and a melt crystallization temperature of 190° C. or higher is preferred in order to improve the porosity. Furthermore, as a more preferable range, the melting point is 235°C or higher,
Alternatively, the melt crystallization temperature is 195°C or higher, even more preferably 200°C or higher. The poly(4-methylpentene-1) resin, which usually has nuclear properties, has a polymer composition of 90 mol% or more, preferably 95 mol% or more of 4-methyl-1-pentene. Also, the P
The melt flow index of the MP resin is 5 g/10 minutes or more, more preferably 20 g/10 minutes or more, particularly preferably 60 g from the viewpoint of dispersibility when blending with PP.
/10 minutes or more is preferable.

Next, Mw/Mn of the incompatible resin needs to be 6 or less, preferably 2-5.

When M w /M n is larger than 6, when the blended resin with PP is melt-extruded, the incompatible resin phase is likely to be cooled and solidified while being stretched in the extrusion direction. Even if such a cast film is stretched, only a non-uniform film with low porosity and low pore density can be obtained. That is, in the present invention, by using an incompatible resin with M w / M n of 6 or less, the dispersed form of the incompatible resin phase is difficult to stretch, has good stretchability, has a high porosity, and has a small pore size. It was discovered that a film with high uniformity can be obtained.

In the porous polypropylene film of the present invention, the blending ratio of the above-mentioned incompatible resin is 15 to 50% by weight.
preferably 25 to 40% by weight
It is. When the blend ratio is less than 15% by weight, the pores formed in the film are not continuous and become independent pores. On the other hand, if the blend ratio exceeds 50% by weight, it will be easy to break during film formation, making it difficult to obtain a uniform film.

As for the thermal properties of the blend resin having the above resin composition, it is preferable that at least three melt crystallization peaks are observed using a differential scanning calorimeter (DSC). Here, at least 2 of these peaks
One is related to PP crystallization, and one is 105
The peak at ~117°C mainly due to α-type crystals (Tmcα
), and the other one is preferably a peak (Tmcβ) resulting from β-type crystals at 120 to 140°C. Especially Tm
If cβ is not observed, the porosity is often poor.

Next, it is necessary that the optical density of the porous polypropylene film of the present invention is 0.3 or more, preferably 0.3 or more.
It is 4 or more. If the optical density is less than 0.3, for example, characters printed on the front surface are likely to be seen through from the back surface, which often causes problems on the surface.

Further, the density of the polypropylene film of the present invention is 0.4
It is necessary to be 0.8 g/cm3, preferably 0.5 to 0.7 g/cm3. Density is 0.4g
If the density is less than 0.8 g/cm3, the mechanical properties will be poor and practical problems will often occur, while if the density exceeds 0.8 g/cm3, the cushioning properties will be poor and the printing performance will deteriorate.

In addition, in order to provide good mechanical properties and printability, the cross-sectional pore diameter observed from a cross section parallel to the maximum strength direction of the film of the present invention is 0.1 to 100 μm, preferably 1 to 30 μm.
It is good if it is m.

In the present invention, at least some of these pores are continuous with each other, so that oil-based ink can be impregnated from at least one side, and the ink-impregnable layer is 20% or more of the total thickness. is preferable, and more preferably 40% or more, since printability is improved. .

Further, at this time, it is preferable that the nitrogen permeability measured from the ink-impregnable surface is 3000 cc/(m2・hr・latm) or more because printing performance is good.
It is preferable that it is at least c/ (m2 ・hr*1 atm).

In order to improve printability, it is preferable to add polar groups to the surface of the film of the present invention by corona discharge treatment, low-temperature plasma treatment, etc. in order to improve ink wettability and adhesion. The base species are nitrogen (N) and oxygen (
0) etc.

Among these, it is preferable that at least nitrogen is introduced into the surface layer, and the ratio of surface nitrogen atoms/surface carbon atoms (N/C
) is preferably in the range of 0.01 to 0.3, since both slipperiness and printability can be achieved, and in particular, it is preferably in the range of 0.03 to 0.2.

Further, the total thickness of the film of the present invention is usually in the range of 5 to 500 μm, and is selected depending on the purpose.

Next, a method for producing the film of the present invention will be described.

First, it is preferable to add a β-crystal nucleating agent to the crystalline PP used in the present invention before blending it with the incompatible resin. When a β-crystal nucleating agent is added at the time of resin blending, there is a high probability that it will be dispersed at the interface between the resins, reducing the probability of forming eight products and making it difficult to form uniform pores. Therefore, the above-mentioned polymerization poetry addition method, which allows the β-crystal nucleating agent to be most uniformly dispersed in PP, is superior.

Next, the temperature when cooling and solidifying the cast film obtained by melt-extruding a blend resin consisting of PP containing a β-crystal nucleating agent and an incompatible resin was set to 90 to 140°C.
Furthermore, it is preferable to set it as 95-135 degreeC. In order to control the thickness of the ink-impregnable layer, it is sufficient to control the cooling temperature on the front and back sides of the film, and in particular, the surface where the cooling temperature is preferably held at 100° C. or higher becomes the ink-impregnable layer.

Here, if the cooling temperature is less than 90°C, the flow orientation of the incompatible resin phase during extrusion will remain in the cast film to a large extent, making subsequent stretching difficult, or even if stretching is possible, voids may be formed. This results in poor pore continuity. On the other hand, if the cooling temperature exceeds 140°C, the flatness of the cast film will be poor, and large spherulites will likely occur in the cast film, resulting in breakage during stretching or unevenness of the pores formed. decreases.

In compositions that do not contain a β-crystal nucleating agent, when such high-temperature casting is performed, partial crystallization of the polypropylene matrix is difficult to proceed, resulting in poor flatness of the cast film and coarse spheres. Crystals form, making subsequent stretching difficult.

In order to obtain more stable hiding properties, it is preferable that the β-crystal fraction contained in the PP crystals in the cast film as described above be 5 to 80% and 10 to 60%.

In the subsequent stretching step, the film can be made porous by either the -axial stretching method or the biaxial stretching method, but the biaxial stretching method is particularly preferred as a method for obtaining the film of the present invention because it provides an excellent balance of mechanical properties.

The stretching conditions are preferably in the temperature range of 120 to 165° C. and in the area magnification of 2 to 50 times, preferably 3 to 40 times, since both porosity and mechanical properties are good.

Furthermore, after stretching, while allowing relaxation of 20% or less at least in the final stretching direction, (the stretching temperature -
It is preferable to perform the heat treatment in a temperature range of 30° C. to (the stretching temperature + 10° C.) because the dimensional stability improves.

The film thus obtained is porous, and most of the β crystals in the film are transformed into α crystals during the stretching process. Normally, the β crystal fraction in the final film is
Less than 10%, preferably less than 5%.

In addition, a known heat stabilizer or antioxidant may be added to the film of the present invention for the purpose of imparting stability during melt molding or oxidative deterioration resistance. Depending on the purpose, additives such as organic or inorganic slip agents, antistatic agents, and antifogging agents may be added or coated.

In particular, it is important to impart antistatic properties to improve printability, and specific antistatic agents include fatty acid amides, alkylolamides, monoglycerides, cationic and/or nonionic surfactants. It is best to knead it into a film or coat it in advance.

Furthermore, in order to improve adhesion, ink adhesion, and metal deposition, the film of the present invention may be subjected to corona discharge treatment in an air atmosphere, inert gas atmosphere, etc., low-temperature plasma treatment, flame treatment, or sandblasting treatment. A known treatment can be performed.

Further, the film of the present invention can be used after being subjected to embossing, extrusion lamination, lamination with other resin films, paper, fabric, etc., depending on the purpose.

[Effects and Applications of the Invention] The porous polypropylene film of the present invention has the following effects and applications.

(1) Because it has a high optical density and excellent hiding properties, as well as cushioning properties and ink absorption properties, it can be printed uniformly and is excellent for various printing papers, various labels, packaging for confectionery and snacks, and decoration.

■ Since no inorganic filler is required, it has excellent chemical stability against various solvents, acids and alkalis, and can be used as separators for filters, batteries, etc.

(3) When poly-4-methylpentene 1 is used as the incompatible resin, not only does it hardly contain modified polymer components such as oligomers, but it also has excellent heat resistance, whiteness, and hygiene.

[Property Evaluation Method and Effect Evaluation Method 1 Next, the characteristics measurement method and effect evaluation method related to the present invention will be summarized.

(1) Optical density (OD) Measured using a densitometer model TD504 manufactured by Macbeth.

The amount of incident light is I. , if the amount of transmitted light is ■, then OD= l
Defined as Ogto (I/Io).

■Intrinsic viscosity ([η]) According to ASTM-D-1601, 0.1g of sample was
It is completely dissolved in 100 ml of tetralin at 135°C, and this solution is measured with a viscometer in a constant temperature bath at 135°C, and the specific viscosity S is determined according to the following formula.

[η] =S/ (0,LX (1+0.22xS))
(3) Vacuum dry the isotactic index (II) sample at 130°C for 2 hours. From now on, the weight W (m
Take a sample of g), put it in a Soxhlet extractor, and boil it.
- Extract with hebutane for 12 hours.

Next, take out this sample, wash it thoroughly with acetone, and then
Vacuum drying at 130°C for 6 hours, then weight W' (
mg) is measured and calculated using the following formula.

II (%) = (W' / W) x 100 (A) density Calculate by film weight/apparent volume.

That is, a film sample is accurately cut into a 10 cm x 10 cm square, 10 sheets are stacked, the thickness d (cm) is measured with a micrometer, and the thickness d (cm) is determined from the sample weight W (g) using the following formula.

Density (g/cm3) = W/ (dxloo) (5) M
Weight average molecular weight (M
w) and number average molecular weight (Mn) and the ratio is Mw/
Let it be Mn.

The conditions are as follows. ” ■Apparatus: GPC-150C (WATER3) ■Column: 5bodex KF-80M (Showa Denko) ■Solvent: 0-dichlorobenzene (0.1%
Ionol addition, 135℃) ■Sample concentration: 0.2 (wt/vat)% ■Flow
Speed: 1 ml/min (1) Molecular weight calibration: Monodisperse polystyrene (6) melt flow index according to ASTM-D-1238.

PP: 2'30℃, 2,160g PMP: 260℃, 5.000g (Measurement conditions are based on Monthly 5K6760) ω Melting point (Tm), melt crystallization temperature (Tmc) Differential scanning calorimeter (D S C2 type, The melting point (T m ) is defined as the melting endothermic peak temperature associated with melting of the crystal when 5 mg of the sample is heated from room temperature at a heating rate of 20° C./min. Next, the temperature was raised to the melting holding temperature of 280°C, held for 5 minutes, and then cooled at a cooling rate of 20°C/min. ).

(8) β-crystal fraction (K) In the melting peak caused by melting of PP during the above-mentioned DSC melting point measurement, the melting peak area due to α-crystal (
Sα) [peak area near 165°C and melting peak area (Sβ) caused by β crystal [peak near 152°C] are determined and calculated using the following formula.

K=Sβ/(Sα+Sβ)xloo (%) Here, the neighborhood refers to a temperature range of about 5°C.

(9) Cross-sectional pore diameter (A) A sample cross-section is cut out along the direction of maximum intensity, and the cross-section is observed using a scanning electron microscope (SEM). At this time,
Adjust so that there are 200±50 micropores in the observation field,
The diameter At of each pore is determined by the following formula from the area Si of the micropores recognized as existing on the surface of the warp, and this average value is taken as the cross-sectional pore diameter.

In addition, if there is a fibril-like substance (single or plural) inside the pore, this fibril-like substance is excluded from the measurement.
Structures (fibrils, etc.) of 0.01 μm or less were also excluded.

Ai=2x(St/π)1″ (g) Ink-impregnable layer fraction The sample film was immersed in a magic ink bath diluted with ethyl alcohol for 24 hours, then dried, and the cross section of the film was observed and colored with ink. Thickness up to the part where
tl) and the total thickness (t2) are measured and calculated using the following formula.

Ink-impregnable layer fraction (%) = tl/12X100 α1) A nitrogen permeability sample film was attached to a measurement cell (manufactured by Sarlorius, filter holder SM 165 08 B type, effective permeation area 1.3X10-3 m2). , 2 atmospheres of nitrogen gas was supplied with the end of the high-pressure side (ink-impregnable side) sealed with OIJ rank, and the amount of nitrogen passing through the film was measured using a precision membrane flowmeter 5F manufactured by Estek Co., Ltd.
Measured using 1100.

The ambient temperature was 25°C, and the measurement results were cc/(
m2 ・hr*latm).

(12) After the printability sample film was subjected to corona discharge treatment in nitrogen gas, one side was lined with a 30 μm polyester film “Lumirror” (manufactured by Toshiku Co., Ltd.), and a serial dot printer (manufactured by NEC) was used. The claim range of the present application was printed out using PC-PR201V), and the printability was evaluated.

At this time, the printability was ranked as follows.

Rank A: Printing is clear and ink does not bleed even if rubbed immediately after printing.

Rankro: Printing is almost clear, but if you rub it immediately after printing, the writing will smudge.

Rank C: Cannot print clearly.

Here, if it is rank A, it can be used without any problem.

On the other hand, in the case of rank B, it is thought that there is a possibility that it can be used by changing the type of printer used or the type of ink.

(To) Surface nitrogen atom/surface carbon atom number ratio (N'/C)
The integrated intensity A caused by carbon (C) is on the sample surface and the integrated intensity AN caused by nitrogen (N) is measured by the following method, and are determined by N/C''AN/X/AC.

Here, X is the relative sensitivity of the nitrogen atom to the carbon atom, 1
．． It is 7.

■Equipment: Shimadzu X-ray photoelectron spectrometer ESCA7
50 ■Excitation X-ray: α to Mg- (1253,6eV) ■Output 6kV-30mA ■Measurement vacuum: l, 0XIO-5Pa ■Energy correction: C1s main peak binding energy to 284.6
Measurement Temperature: Room temperature [Example] Next, the present invention will be explained in detail using Examples.

The resins used in the experiment are as shown in Table 1, and the PP resins include two types of resins obtained with a γ-quinacridone addition polymerization catalyst system, type A and type B (each with [η] of 2).
．． 0 dl/g, 1.7 dl/g, and γ-quinacridone content of 5 ppm) and a PP resin obtained using a normal catalyst system (type C1 [η] = 1.9 dl/g).

In Table 1, the melting points of PP at 162°C and 163°C correspond to the α-crystal, and the melting points at 151°C and 152°C correspond to the β-crystal.

Further, regarding the melt crystallization temperatures, 106° C. and 108° C. correspond to α crystal, and 130° C. and 132° C. correspond to β crystal 1.

In addition, as resins that are incompatible with PP, there are two types of PMP resins (
Type X1 Type Y) and high density polyethylene (HD
PE) was used.

Examples 1 to 4 γ-quinacridone-containing PP pellets and type X PMP pellets were mixed at the blend ratio shown in Table 2, and a 40 mm
The mixture was melt-blended at 28,000 in an extruder with φL/D=30, and melt-blended into a sheet from a coat hanger die.

The sheet was cooled and solidified at the casting temperature shown in Table 2.

Here, the β component fraction of each sheet was in the range of 45 to 65% as shown in Table 2, and the melt crystallization temperature had three peak temperatures.

Then, the sheet was prepared in Example 1. 2. 4 was first stretched in the longitudinal direction with a stretching roll heated to a predetermined temperature, then introduced into a stenter and stretched in the width direction at 160°C, and immediately allowed to relax 5% in the width direction at 163°C. It was heat treated for seconds and rolled up.

In Example 3, the film was stretched 5 times in the longitudinal direction between stretching rolls at 140°C, then heat-treated at 150°C between heat treatment rolls to allow 5% relaxation in the longitudinal direction, and then wound up.

In all experiments, castability and stretchability were good.

Next, Table 3 shows the results of evaluating the film thus obtained.
All of them had optical densities exceeding 0°3 and had excellent hiding properties. In addition, the nitrogen permeability observed from the ink-impregnable surface was 5000cc/(m
2.hr.1 atm) or more. As a result,
It also has excellent printability, with letters printed using a serial dot printer without any smearing, and even when rubbed immediately after printing, no smudging occurred.

Comparative Example 1 A film was formed in the same manner as in Example 1 except that the PMP resin was changed to Type Y. The film thus obtained did not have continuous pores and did not pass through even when alcohol was dropped.

It was also ranked inferior in the printing test, ranking B.

Comparative Example 2 Extrusion casting was carried out in the same manner as in Example 1 except that high-density polyethylene was used as the incompatible resin. The cast film contained β crystals at a high rate of 55%. When the cast film was tried to be stretched at the same stretching temperature as in Example 1, the stretching rolls became sticky, so the stretching temperature was lowered by 5° C. in each case.

The film obtained by straining has a low optical density of 0.1.
Furthermore, alcohol does not pass through and no continuous through-holes are formed. As a result, the printability test results showed that the printed characters were smeared and were ranked inferior to C.

Comparative Example 3 A film was formed in the same manner as in Example 1 except that Type C to which no β-crystal nucleating agent was added was used as the PP resin. When this resin was tried to be cast on a cooling drum at 100° C., it sagged from the drum, perhaps because crystallization did not proceed, and the resulting film had poor flatness. In the cast film, β crystals were formed in a small amount of 5%.

Note that the melt crystallization peaks of the resin composition were at 107°C and 2°C.
Only two peaks at 11°C were observed.

When an attempt was then made to stretch the cast film, although longitudinal stretching was possible, the film broke during transverse stretching and a film could not be obtained.

Claims (3)

[Claims] (1) Crystalline polypropylene containing β crystal nucleating agent 50~
85% by weight, and 15 to 50% by weight of a thermoplastic resin that is incompatible with polypropylene, has a melt crystallization temperature of 140°C or higher, and a Mw/Mn of 6 or less, and has a density of 0.4 to 50% by weight.
A porous polypropylene film having an optical density of 0.8 g/cm^3 and an optical density of 0.3 or more. (2) The porous polypropylene film according to claim 1, wherein the porous polypropylene film can be impregnated with an oil-based ink from at least one side, and the ink-impregnable layer accounts for 20% or more of the total thickness. (3) Nitrogen permeability measured from the ink-impregnable surface is 3
The porous polypropylene film according to claim 2, wherein the porous polypropylene film has a porous polypropylene film of at least 000 cc/(m^2·hr·1 atm). (A) The thermoplastic resin is poly-4-methylpentene 1 having a melt crystallization temperature of 190°C or higher and a melting point of 230°C or higher. Porous polypropylene film.