JPH02139220A - White polyolefin film and manufacture thereof - Google Patents

Abstract

PURPOSE:To improve the hiding power, the surface gloss and the printability of the film by a method wherein the longitudinal strength and the sum of the Young's moduli in longitudinal and lateral directions of polyolefin film, the optical density and gloss of which are specified, are specified. CONSTITUTION:Of the polyolefin film, of which the optical density is 0.1 or more and the glossiness is 40% or more, its longitudinal strength is made to be 8kg/mm<2> or higher and the sum of its Young's moduli in longitudinal and lateral directions is made to be 250kg/mm<2> or more. Resin, which is prepared by adding 5-50 pts.wt. of methylpentene polymer, the extraction residue of n-heptane of which is 40% or more, to 100 pts.wt. of polypropylene, the isotactic index of which is 80% or more and the intrinsic viscosity of which is 1.2-3.5dl/g, is formed by fusing into the form of sheet or tube and, after that, micro- stretched in the elastic limit at 120 deg.C or lower and further stretched at least uniaxially within the range of 120-170 deg.C.

Description

Detailed Description of the Invention [Industrial Field of Application] The present invention is a polyolefin film that is white and opaque, has a paper-like luster, luster, and pearlescent luster, and has various printability, dimensional stability, and water resistance (moisture resistance). ), relates to a white polyolefin film suitable for packaging and decoration of printing paper, various labels, confectionery, snacks, etc. that requires chemical resistance, and a method for producing the same.

[Prior Art] It is well known that in order to obtain 1 q of white film, a large amount of white inorganic particles are added to a thermoplastic resin and then stretched in the -axis or biaxial direction (Japanese Patent Publication No. 46-40794). Publication, JP-A-50-90644, etc.). This film is white,
The reason why the film becomes opaque is that peeling occurs at the interface between the resin and inorganic particles during film stretching, creating minute voids inside the film and minute cracks on the surface, which prevents light from passing through the film surface and inside. This is because they are scattered.

In addition, a technique is known in which polypropylene or propylene copolymer is blended with methyl pentyl polymer and biaxially stretched (Japanese Patent Laid-Open No. 52-58773.52-5
8774 etc.).

(Problems to be Solved by the Invention) In order to obtain a white film, a film to which a large amount of non-containing particles have been added may suffer from surface cracks caused by surface cracks when undergoing secondary processing such as printing, punching, automatic packaging, etc. There are disadvantages in that the loose particles significantly deteriorate the printing finish, and since many internal voids are generated, the mechanical strength is poor and the efficiency of secondary processing is significantly reduced.

In addition, films made by blending polypropylene with methyl pentyl polymer and stretching using conventional uniaxial and biaxial stretching methods have a rough surface and tearability, but are paper-like, white, and have high hiding properties. 2. A film with high mechanical strength cannot be obtained.

As a result of extensive research into white polyolefin films, the present invention has revealed that they are white, have excellent hiding properties, have a pearl-like luster,
Various printing papers with high mechanical strength.

It is an object of the present invention to provide a white polyolefin film suitable for various labels, packaging and decoration of confectionery and snacks, and a method for producing the same.

[Means for Solving the Problems] The present invention provides an optical density (OD> of 0.1 or more and a gloss level of 4).
0% or more, the film has a strength in the longitudinal direction of 8 Krj/mTl or more, and a sum of Young's moduli in the longitudinal direction and the width direction of 250 Kfl/mTd or more. Furthermore, in order to obtain the white polyolefin film, the isotactic index (II
>80% or more and an intrinsic viscosity of 1.2 to 3.5 dl/a, to 100 parts by weight of polypropylene with an n-heptane extraction residue of 40% or more, 5 to 50
After melt-molding the resin containing ffi into a sheet or tube at a temperature of 120°C or less within the elastic limit, it is further stretched at least uniaxially at a temperature of 120°C to 170'C. It relates to a method for producing a white polyolefin film, which is characterized by stretching the film.

In the present invention, the optical density (OD) of the film is 0.1
It is preferably 0.3 or more. Optical density (OD>
If it is less than 0.1, the whiteness and concealment properties will be poor, and the printed characters and pictures will be visible from the back side, resulting in poor practicality.

Moreover, the glossiness is 40% or more, preferably 50% or more. If the gloss level is less than 40%, the surface of the film will be very rough and the ink will bleed when printed, making it difficult to obtain clear letters and pictures. It spoils the noble luster.

Furthermore, the strength of the film of the present invention in the longitudinal direction is 8Kg/mT.
d or more, preferably 10 Kg/rrlyy1 or more.

If the strength in the longitudinal direction is less than 8 Ky/mrd, the film may undergo dimensional deformation or tear during printing, resulting in a significant decrease in the efficiency of secondary processing.

Also, the sum of Young's modulus in the longitudinal direction and width direction of the film is 2
To 50! J/mTl1 or more, preferably 300 Kg/
mm or more. If the Young's modulus is less than 250 and 7mTl1, the edges of the film will sag during printing, misalignment of print will occur between the center and the edges, and the processing and handling properties will be poor in label applications, and the film will not be used for packaging. If it is, the shape retention property is poor and the content protection property is poor.

Note that the density of the film of the present invention is 0.7 g/ff1 or more,
Preferably, it is 0.8 g/a+f or more.

This is because if the density is less than 0.7 g/crj, the volume of voids in the film is large, and productivity, mechanical strength, etc. are often poor.

In addition, the thickness of the film of the present invention is 5% in terms of printing suitability, handling processing such as labels, and secondary processing properties such as automatic packaging.
~100 μm, preferably 10 to 60 μm. If it is thinner than the above range, it will lack hiding power, strength, shape retention, etc., and if it is thicker, it will be unfavorable in terms of processability, handling, etc.

The polyolefin as used in the present invention is a mixture of a polypropylene homopolymer or copolymer and a methyl pentyl polymer or copolymer.

Polypropylene and methylpentene can be used depending on the purpose. Homopolymers are preferable when heat resistance and mechanical properties are important, while copolymers are preferable when softness and flexibility are important.

If it is a copolymer, it is a random or block copolymer with other α-olefins, and as a copolymer, it is preferably 10 mol% or less. When further blending other resins, the blending ratio is 1
It is preferable that it is Qwt% or less.

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

The isotactic index (hereinafter abbreviated as II) of the polypropylene or copolymer must be 80% or more, and if heat resistance and solvent resistance are required, II is preferably 90% or more. .

In addition, the intrinsic viscosity of the polypropylene [η is 1°2 dl/
g to 3.5 dl/a, preferably 1.5 dl/a to 2.2 dl/a. When [η] is smaller than the above range, castability and stretchability are particularly deteriorated, and when it is larger, not only melt extrudability is deteriorated, but also film formation becomes difficult.

Next, the methyl pentyl polymer blended into the polypropylene or copolymer is a methyl pentene homopolymer or copolymer, and is a polymer of 4 methyl 1 pentene alone or a random copolymer with other α-olefins. The content of 4-methyl-1-pentene monomer units is 80 mol% or more. It is necessary that the n-heptane extraction residue of the polymer is 40% or more,
Preferably it is 50% or more. If the n-heptane extraction residue is less than 40%, the optical density (OD) will be 0.1 or less, and whiteness and hiding properties will not be achieved. Furthermore, when the melting point (Tm) of the polymer is 2°0 to 240°C and the crystallization temperature (TmC) is 180 to 220°C, the optical density (OD
) is 0.1 or more, and the whiteness and hiding properties are good. In addition, in terms of dispersibility, the Ml of the polymer is 2 to 2.
00 g/10 minutes, preferably 10 to 100 g/1 minute, is preferable because the gloss becomes high. The amount of the methyl pentyl polymer added is preferably in the range of 5 to 50 parts by weight, preferably 10 to 40 parts by weight, based on 100 parts by weight of the polypropylene. Optical density (OD) below 5 parts by weight
If the amount exceeds 50 parts by weight, dispersibility becomes poor and stretching becomes unstable, excessive voids are formed inside the film, resulting in poor mechanical properties.

Further, crystal nucleating agents, antioxidants, heat stabilizers, lubricants, antistatic agents, etc. may be added to the film of the present invention within a range that does not impair the purpose.

Next, the mixed resin is supplied to an extruder heated to 260°C to 310°C, melt-molded into a sheet or tube, and then slightly stretched within the elastic limit at a temperature of 120°C or lower. After that, further heat to 120℃~17
It is necessary to stretch at least uniaxially at a temperature of 0°C. By stretching only by the known stenter-type sequential or simultaneous two-wheel stretching method or tube-type simultaneous two-wheel stretching method, a white, highly opaque film with an optical density (OD) of 0°1 or more, which is the object of the present invention, cannot be obtained. This is because there is no

Slight stretching within the elastic limit means 3t r at the stretching temperature.
Ess-strain refers to the stretching of an in-curve to the yield point stress.

The effective reason for slight stretching within the elastic limit is to increase the size of the seabird structure in the mixed sheet of polypropylene and methyl pentyl polymer, which are basically incompatible resins, and to generate microvoids at the interface between the two. By increasing the diffused reflection at the interface due to the difference in refractive index between the two, whiteness and concealment properties are achieved.

In the stretching after slight stretching within the elastic limit, in the case of -axial stretching, the stretching temperature is 120°C to 170°C, and the stretching ratio is the areal ratio by a stretching method using a peripheral speed difference between rolls or a stenter type stretching method. Film formability becomes good in it being 3 to 10 times, preferably 4 to 8 times.

In the case of two-wheel stretching, two-wheel stretching is carried out by a stenter type sequential or simultaneous two-wheel stretching method, or a tube type simultaneous biaxial stretching method. In the case of simultaneous biaxial stretching, the stretching temperature is 145
It is preferable that the temperature range is from 165° C. to 165° C. because the film forming property is good.
The stretching ratio is 10 to 50 times, preferably 20 to 4
If it is 0 times, the film forming stability will be good and the gloss will be high.

In the case of sequential two-wheel stretching, it is stretched 3 to 7 times in the longitudinal direction at a stretching temperature of 120 to 150°C, and then 1
It is stretched 5 to 15 times in the width direction at a stretching temperature of 50 to 170°C.

The film stretched in the above manner has a 160 to 17
Heat treated at 5° C. for several seconds. At this time, if the heat treatment is carried out while allowing a few percent of relaxation, dimensional stability will be improved. Furthermore, if necessary, a surface activation treatment such as N2. C
If the surface tension is increased by corona discharge treatment or plasma treatment under various gases such as O2, the adhesion of printing ink or adhesion to vapor-deposited metal will be improved.

Further, a resin easily adhesive to the surface of the film of the present invention, such as an ethylene-propylene random copolymer.

Ethylene/ethyl acrylate copolymer, ethylene/
A resin such as a vinyl acetate copolymer or an ionomer may be laminated on both sides or one side in-line or offline.

The white polyolefin film obtained by the above method is not only suitable for various printing papers, various labels, wrapping and decoration of confectionery and snacks, but also has good properties as a base film for adhesive tapes.

[Effects of the Invention] The white polyolefin film of the present invention has the following excellent points.

(1) It is white, has excellent hiding properties, has a high gloss on the film surface and has excellent printability, and has the mechanical strength, dimensional stability, and solvent resistance necessary for secondary processing steps.

(2) Since it contains virtually no inorganic filler, internal voids are small and it has excellent moisture resistance, which is necessary for packaging confectionery and the like.

(3) Excellent film formability and cost efficiency.

[Measurement method] Next, the measurement method and terminology of each characteristic value in the present invention will be summarized below.

(1) Intrinsic viscosity ([η]) Completely dissolve 0.1 g of sample in 100 d of tetralin at 135°C, measure this solution with a viscometer in a constant temperature bath at 135°C, and calculate the intrinsic viscosity from the specific viscosity S according to the following formula. seek.

The unit is dl/l;l.

[η]=S10.1X (1+0.22xS) (2)
Isotactic index (I l) or n
- Vacuum dry the heptane extraction residue sample at 130°C for 2 hours. From now on weight W
(Take a sample of #Ig>, put it in a Soxhlet extractor, and extract with boiling l1n-heptane for 12 hours.

Next, take out this sample and wash it thoroughly with acetone.
After vacuum drying at 130°C for 6 hours, the weight w-<ms>
is measured and calculated using the following formula.

II (%) = W'/Wx100 (3) Breaking strength Conforms to JIS K-6782.

(4) Young's modulus Conforms to ASTM D-882-75b.

(5) Melting temperature (Tm)/melt crystallization temperature (TIIIC
) Sample 5η was measured using a scanning calorimeter DSC-II model (Perki
r) manufactured by Elmer Co., Ltd., and measured from room temperature under a nitrogen stream at a heating rate of 20° C./min, and the endothermic peak temperature accompanying melting is defined as the melting temperature Tm.

Similarly, after keeping the sample at 280°C for 5 minutes, the temperature was lowered to room temperature at a cooling rate of 20°C/min.
Let it be mc.

(6) Melt flow index (Ml) ASTM
-D-1238, measured at 260°C and 5Ks.

The unit is g/10 minutes.

(7) Optical density (OD) Measurement is performed using a Macbeth densitometer model TD504.

When the transmitted density is D, the amount of incident light is Io, and the amount of transmitted light is I, it is defined as D=-1op (I/Io).

(8) Glossiness According to JIS-Z8741 (60"-60"').

(9) Hiding ability of a hiding film indicates opacity, and AS
Bayesian measured according to TM-Dl 003-52 method is 9
0% or more was rated as ◯, 89-80% was rated as △, and 80% or less was rated as ×.

(10) The surface of the printable film is subjected to corona discharge treatment, and the treated surface is coated with commercially available cellophane printing ink Cellocolor STr White.
(manufactured by Toyo Ink Manufacturing ■) using Coating Bar #5, dried in an oven at 80℃ for 1 minute, and then heated at 25℃.
It was left under 50% RH for 24 hours.

a. Sellotape peel test
, width 24#l111) was attached and strongly peeled off, and the ink peeled area was evaluated in the following five grades.

Ink peeling area O% 2nd judgment 5 Ink peeling area less than 10% 2nd judgment 4 Ink peeling area 1
0% or more and less than 25%: Judgment 3 Ink peeled area 25% or more and less than 50% 2 Judgment 2 Ink peeled area 50% or more
: Judgment 1b, printing processing test When 1000 m of film was gravure printed, the presence or absence of troubles such as ink bleeding, misalignment of print, and wrinkles of the film was evaluated.

01) Punching test The film was subjected to a label punching test at a speed of 100 sheets/minute, and the number of defects such as punching defects, wrinkles, and kinks was evaluated.

Density Conforms to JIS-6758.

[Example] Hereinafter, the present invention will be explained based on examples.

Example 1 A polypropylene homopolymer with [η] of 1.85d110 and II=97% (“Mitsui Noblen” FO-850 manufactured by Mitsui Toatsu Chemicals) and a methylpentene homopolymer (manufactured by Mitsui Petrochemicals) "TPX" MX-019
, n-heptane extraction residue=95%, MI=1009/1
0 minutes) After mixing 12 parts by weight with a Henschel mixer, 30 parts by weight
Pellets were prepared by melt extrusion at 280° C. using a mφ twin-screw extruder. The pellets were fed into a 35 Mφ single screw extruder, extruded into a sheet using a T-die at a resin temperature of 290°C, solidified on a cooling drum kept at 60°C, and made into a sheet with a thickness of 80°C.
A polyolefin composition sheet having a temperature of 1 m at 0°C was obtained. The sheet was slightly stretched in the longitudinal direction at 110°C with a roll-type longitudinal stretching machine at a magnification of 1.15 times within the elastic limit, and further stretched in the longitudinal direction by 1.15 times.
Stretched 4.5 times at 5°C (multiple, then passed through a stenter and stretched 8 times in the transverse direction at 160°C, heat treated at 165°C while allowing 5% relaxation, biaxially oriented with a thickness of 20 μm) A polyolefin film was obtained (see Table 1).

When the optical properties of the film were investigated, the optical density (OD
) is 0.3, the glossiness is 89% on the drum surface and 88% on the non-drum surface, and the baize is 97%, indicating that it is white and has excellent hiding properties.

Further, when the mechanical properties of the film were examined, the strength in the longitudinal direction was 12 Kg/mTd, and the sum of the Young's modulus in the longitudinal direction and the width direction was 520 Kg/mm.

Furthermore, it can be seen that the film has excellent printability. (See Table 2).

Comparative Example 1 A polyolefin composition sheet obtained in the same manner as in Example 1 was stretched 5 times in the machine direction at 135° C. by a conventional sequential biaxial stretching method, and then stretched 8 times in the transverse direction at 160° C. using a stenter. A biaxially oriented polyolefin film with a thickness of 20 μm was
It's q. The film has an optical density (OD) of 0.08,
The haze was 68%, which was poor in whiteness and concealment. (First,
(See Table 2) Example 2 100 parts by weight of polypropylene homopolymer with [η] of 2.25 dl/g and II = 97% (“Mitsui No7ren” JS-1429 manufactured by Mitsui Toatsu Chemical Co., Ltd.) and methylpentene copolymer. (Mitsui Petrochemical ■TPX”RT-18,
n-heptane extraction residue = 74%, MI = 269/10 minutes) After mixing 18 folds, extrusion and solidification were performed in the same manner as in Example 1 to obtain a polyolefin composition sheet with a thickness of 600 μm. The sheet was slightly stretched in the machine direction at 100'C using a roll type longitudinal stretching machine at a magnification of 1.20 times within the elastic limit, and then stretched to 5 times both length and width at 165°C using a stenter type simultaneous stretching machine. This was simultaneously stretched to obtain a film with a thickness of 20 μm. (1st
(see table).

The optical density (OD) of the film was 0.2, the gloss was 75% on the drum side and 72% on the non-drum side, and the haze was 92%, indicating excellent whiteness and hiding properties.

Further, the strength in the longitudinal direction was 1QKg/mrtt, and the sum of the Young's modulus in the longitudinal direction and the width direction was 350Kg/mm.

(See Table 2).

Comparative Example 2 Polypropylene homopolymer (FO-850>100 parts by weight and methylpentene homopolymer (MX-019>6)
An attempt was made to form a film using 0 parts by weight of the composition in the same manner as in Example 1, but the film forming properties were extremely unstable, so the slight stretching temperature was changed to 130 parts by weight.
℃, the longitudinal stretching temperature was 140°C, and the transverse stretching temperature was 172°C to obtain a film with a thickness of 22 μm. (See Table 1). The film has many internal voids and has an optical density (OD) of 0.2.
However, the gloss level is low at 37%, and the longitudinal strength is 6.
9/mrd, the sum of the Young's modulus in the longitudinal direction and the width direction is 23
It was as small as 0'j/mrd, and the edge of the film sagged during printing, causing misalignment of the print. (See Table 2).

Comparative Example 3 Polypropylene homopolymer (JS-1429>100
Example 1 A composition containing 25 parts by weight of interstitial part and calcium carbonate
A film with a thickness of 30 μm was obtained in the same manner as above. (See Table 1) Although the film has a high optical yA degree (OD) and haze, and is excellent in whiteness and hiding properties, it is found that the glossiness and mechanical properties are poor because of the large void volume. (Second
(see table).

Claims (2)

[Claims] (1) Optical density (OD) is 0.1 or more, gloss is 40%
A white polyolefin film as described above, characterized in that the strength in the longitudinal direction of the film is 8 Kg/m_m^2 or more, and the sum of the Young's modulus in the longitudinal direction and the width direction is 250 Kg/m_m^2 or more. film. (2) Isotactic index (II) is 80%
As described above, a sheet of resin is prepared by adding 5 to 50 parts by weight of methyl pentyl polymer having an n-heptane extraction residue of 40% or more to 100 parts by weight of polypropylene having an intrinsic viscosity of 1.2 to 3.5 dl/g. A white polyolefin film, which is melt-formed into a shape or a tube, subjected to slight stretching within the elastic limit at a temperature of 120°C or lower, and further stretched at least uniaxially at a temperature of 120°C to 170°C. Production method.