Polypropylene laminated film

A polypropylene laminated film containing a crystalline polypropylene layer and, laminated on at least one side of the layer of the crystalline polypropylene, a layer of a copolymer of propylene and at least one .alpha.-olefin of from 4 to 10 carbon atoms having a specific composition, melt flow rate and molecular weight distribution in which the .alpha.-olefin content in the cold xylene soluble portion of the random copolymer is less than 1.7 times the .alpha.-olefin content in the copolymer and the random copolymer satisfies the mathematical expression, EQU B.ltoreq.1.05A-10, wherein A is a weight percentage of the content of said at least one .alpha.-olefin having from 4 to 10 carbon atoms in the random copolymer and B is a weight percentage of the cold xylene soluble portion in the random copolymer, is superior in low temperature heat sealability and hot tack property and moreover has a good transparency, blocking resistance and printability, wherein the random copolymer is obtained by gas phase polymerization substantially in the absence of a liquid medium, and using a catalyst system comprising (i) a solid catalyst component containing magnesium, titanium and a halogen as essential constituents, (ii) an organoaluminum compound and (iii) an electron donative compound.

The present invention relates to a polypropylene laminated film which has a 
good low-temperature heat sealability and hot tack property and moreover 
has a good transparency, blocking resistance and printability; and a 
process for producing the same. 
Biaxially oriented crystalline polypropylene film (abbreviated as BOPP) has 
been widely used as a packaging film by virtue of its good stiffness, 
transparency and moisture impermeability. However, BOPP itself is 
unsatisfactory in heat sealability. Therefore, there have hitherto been 
widely used laminated films obtained by laminating a resin having a good 
heat sealability (hereinafter heat sealing resin) on one or both surfaces 
of a BOPP or by co-extruding such a resin with a BOPP. 
Of the properties required for the heat sealing resin, low-temperature heat 
sealability has been considered to be most important, and lowering the 
heat sealing temperature of the heat sealing resin has hitherto been of 
greatest concern in the art. This is because lowering the heat sealing 
temperature of the heat sealing resin permits speedup of the process of 
making bags of laminated film and improves the productivity. It is 
needless to say that such properties as transparency and blocking 
resistance of the sealing resin are also important. 
In recent years, however, diversification of package types, diversification 
of articles to be packaged and attending diversification of packaging 
machines have been rapidly advancing. In the circumstances, the hot tack 
property, which has previously been not regarded as so important property 
of the heat sealing resin, has come to be of great concern as well as 
low-temperature heat sealability. 
Various resins have hitherto been proposed as the heat sealing resin for 
BOPP. A widely known propylene-based heat sealing resin is a 
propylene-ethylene copolymer copolymerized with about 5% by weight of 
ethylene. This copolymer is superior in transparency and blocking 
resistance but is quite unsatisfactory in low-temperature heat 
sealability. Increasing the ethylene content of the propylene-ethylene 
copolymer for improving the low temperature heat sealability of the 
copolymer can improve the low-temperature heat sealability to a certain 
extent, but causes great deterioration of transparency and blocking 
resistance. Another widely known copolymer is propylene-butene-1 copolymer 
obtained by copolymerization of propylene and butene-1. For example, 
JP-A-50-128781 and JP-A-55-17542 disclose a propylene-butene-1 copolymer 
prepared by polymerization in an inert solvent (by the so-called slurry 
polymerization) and free from components soluble in the inert solvent. 
They teach that the copolymer has a good transparency and blocking 
resistance and fairly good low-temperature heat sealability. JP-A-56-22307 
discloses a propylene-butene-1 copolymer having a specific sequence 
distribution prepared by polymerization in the absence of a liquid diluent 
using a catalyst system comprising a solid compound based on titanium 
trichloride and an organo-metallic compound. This copolymer, however, is 
unsatisfactory in low-temperature heat sealability and poor in blocking 
resistance, and further undergoes deterioration of transparency with the 
passage of time. 
JP-A-60-166455 discloses a propylene-butene-1 copolymer obtained by gas 
phase polymerization substantially in the absence of a liquid medium, 
which copolymer is reported to show good results in all of the low 
temperature heat sealability, transparency and blocking resistance. 
According to the tracing experiment by the present inventors, however, the 
copolymer is unsatisfactory in the hot tack property. 
Propylene-ethylene-butene-1 terpolymers obtained by copolymerizing 
propylene with ethylene and butene-1 are also well known as a heat sealing 
resin. For example, JP-A-54-26891 describes a process for producing olefin 
copolymers wherein propylene, 0.1-4% by weight of ethylene and 1-30% by 
weight of an .alpha.-olefin having 4-8 carbon atoms, respectively relative 
to propylene, are fed to the polymerization system. JP-A-53-26882 
describes a propylene terpolymer which is characterized by having an 
ethylene content of 0.5-1.9% by weight and a butene-1 content of 0.5-4.9% 
by weight and having a substantially statistic comonomer distribution and 
a process for producing the terpolymer. JP-A-55-115416 describes that a 
soft or semirigid copolymer with low crystallinity can be obtained by 
copolymerizing propylene with 0.2-9% by mole of ethylene and 0.2-9% by 
mole of a linear .alpha.-olefin having 4 or more carbon atoms, 
respectively relative to propylene. However, none of these terpolymers are 
satisfactory in both of the low-temperature heat sealability and hot tack 
property and show a good transparency and blocking resistance. 
The object of the present invention is to provide a polypropylene laminated 
film which has a good low-temperature heat sealability, hot tack property, 
transparency and blocking resistance. 
The present inventors have made extensive study to attain the aforesaid 
object. As the result, it has been formed out that a polypropylene 
laminated film, on which a random copolymer of propylene with at least one 
.alpha.-olefin having from 4 to 10 carbon atoms which is obtained by a 
specific catalyst system and polymerization process and has a specific 
comonomer composition and molecular weight distribution, a specific cold 
xylene soluble and a specific cold xylene soluble composition is laminated 
as a heat sealing resin, has all of the aforesaid desirable properties. 
The present invention has been accomplished on the basis of the above 
finding. 
According to the present invention, there are provided a polypropylene 
laminated film which comprises a layer of a crystalline polypropylene and 
a layer of a random copolymer of propylene and at least one .alpha.-olefin 
having from 4 to 10 carbon atoms formed on at least one side of the layer 
of the crystalline polypropylene, wherein the random copolymer is obtained 
by gas phase polymerization substantially in the absence of a liquid 
medium, and using a catalyst system comprising (i) a solid catalyst 
component containing magnesium, titanium and a halogen as essential 
constituents, (ii) an organoaluminum compound and (iii) an electron 
donative compound, 
the random copolymer having the following properties: 
(1) the content of said at least one .alpha.-olefin having from 4 to 10 
carbon atoms in the random copolymer falls within the range of from 15 to 
30 percents by weight, 
(2) the melt flow rate of the random copolymer is not more than 20 g/10 
minutes when determined at 230.degree. C. under a load of 2.16 kg, 
(3) the molecular weight distribution, Mw/Mn, of the random copolymer is 
not more than 4.5, wherein Mw is weight average molecular weight of the 
random copolymer and Mn is number average molecular weight of the random 
copolymer, 
(4) the random copolymer satisfies the mathematical expression, 
EQU B.ltoreq.1.05A-10, 
wherein A is a weight percentage of the content of said at least one 
.alpha.-olefin having from 4 to 10 carbon atoms in the random copolymer 
and B is a weight percentage based on a ratio of the weight of the cold 
xylene soluble portion of the random copolymer to the weight of the random 
copolymer, and 
(5) the content based on percentage by weight of said at least one 
.alpha.-olefin having from 4 to 10 carbon atoms in the cold xylene soluble 
portion of the copolymer is less than 1.7 times the content based on 
percentage by weight of said at least one .alpha.-olefin having from 4 to 
10 carbon atoms in the random copolymer; and 
a process for producing a polypropylene laminated film which comprises the 
steps of: 
(a) copolymerizing propylene and at least one .alpha.-olefin having from 4 
to 10 carbon atoms by gas phase polymerization substantially in the 
absence of a liquid medium, and using a catalyst system comprising (i) a 
solid catalyst component containing magnesium, titanium and a halogen as 
essential constituents, (ii) an organoaluminum compound and (iii) an 
electron donative compound, to obtain a random copolymer having the 
following properties: 
(1) the content of said at least one .alpha.-olefin having from 4 to 10 
carbon atoms in the random copolymer falls within the range of from 15 to 
30 percents by weight, 
(2) the melt flow rate of the random copolymer is not more than 20 g/10 
minutes when determined at 230.degree. C. under a load of 2.16 kg, 
(3) the molecular weight distribution, Mw/Mn, of the random copolymer is 
not more than 4.5, wherein Mw is a weight average molecular weight of the 
random copolymer and Mn is a number average molecular weight of the random 
copolymer, 
(4) the random copolymer satisfies the mathematical expression, 
EQU B.ltoreq.1.05A-10, 
wherein A is a weight percentage of the content of said at least one 
.alpha.-olefin having from 4 to 10 carbon atoms in the random copolymer 
and B is a weight percentage based on a ratio of the weight of the cold 
xylene soluble portion of the random copolymer to the weight of the random 
copolymer, and 
(5) the content of said at least one .alpha.-olefin having from 4 to 10 
carbon atoms in the cold xylene soluble portion of the copolymer is less 
than 1.7 times the content, based on percentage by weight of said at least 
one .alpha.-olefin having 4 or more carbon atoms in the random copolymer; 
and 
(b) making polypropylene laminated film comprising a layer of a crystalline 
polypropylene and a layer of the random copolymer obtained in step (a) 
formed on at least one side of the layer of the crystalline polypropylene. 
The first outstanding feature of the laminated film obtained according to 
the present invention is that it is superior both in low-temperature heat 
sealability and in hot tack property. The second outstanding feature is 
that it has, in addition to good low-temperature heat sealability and hot 
tack property, good transparency, good blocking resistance and further 
good printability. 
The random copolymers of propylene and at least one .alpha.-olefin having 
from 4 to 10 carbon atoms used as the heat sealing resin in the present 
invention is produced by the so-called gas phase polymerization. Slurry 
polymerization, a conventional polymerization method in which 
polymerization is carried out in an inert hydrocarbon, is not suitable for 
preparing the random copolymer which meets the objects of the present 
invention, because a large amount of the produced polymer dissolved in the 
inert hydrocarbon solvent notably disturbs the progress of the 
polymerization. Moreover, it is economically disadvantageous for its low 
polymer yield. 
The gas phase polymerization may be conducted with a conventional fluid bed 
reactor, fluid bed reactor equipped with a stirrer, and the like. It is 
essential to carry out the polymerization under such temperature/pressure 
conditions that prevent the liquefaction of the monomer gases and the 
agglomeration of the polymer particles in the reactor. Particularly 
preferred polymerization conditions are: a temperature range of 
50.degree.-95.degree. C. and a pressure range of 2-30 kg/cm.sup.2 (gauge 
pressure, hereinafter abbreviated as G). A molecular weight controlling 
agent, such as hydrogen, is preferably added for the purpose of 
controlling the melt flowability of the polymer obtained. The gas phase 
polymerization may be conducted by any of batch polymerization, continuous 
polymerization, and the combination of the two. The monomers and the 
molecular weight controlling agent consumed in the course of the 
polymerization may be fed to the reactor either continuously or 
intermittently. The random copolymer used in the present invention may be 
washed after the gas phase polymerization with an alcohol, hydrocarbon 
solvent, or the like to remove the catalyst residue or to remove low 
molecular weight polymer. 
The catalyst system employed for producing the random copolymer used as the 
heat sealing resin in the present invention is a catalyst for 
stereo-selective polymerization of .alpha.-olefins known to the art. It is 
a catalyst system comprising (A) a solid catalyst component containing 
magnesium, titanium and a halogen as essential constituents, (B) an 
organoaluminum compound and (C) an electron donative compound. 
The solid catalyst component (A) contains titanium, magnesium and a halogen 
as essential constituents. It may generally be obtained by reducing a 
titanium compound with an organomagnesium compound to obtain a solid 
product, treating the solid product with an ester compound to obtain an 
ester-treated component, and treating the ester-treated component with 
titanium tetrachloride. 
The titanium compound used is represented by the formula, Ti(OR).sub.b 
X.sub.4-b, wherein R is a hydrocarbon group having 1-20 carbon atoms, X is 
a halogen atom and b is a number satisfying the inequality, 0&lt;b.ltoreq.4. 
Specific examples of R are alkyl groups such as methyl, ethyl, propyl, 
isopropyl, butyl, isobutyl, amyl, isoamyl, hexyl, heptyl, octyl, decyl, 
dodecyl, etc.; aryl groups such as phenyl, cresyl, xylyl, naphthyl, etc.; 
cycloalkyl groups such as cyclohexyl, cyclopentyl, etc.; allyl groups such 
as propenyl, etc.; and aralkyl groups such as benzyl, etc. 
The magnesium component used may be any type of organomagnesium compounds 
containing at least one magnesium-carbon bond in the molecule. 
Particularly preferred are Grignard compounds represented by the formula, 
RMgX, wherein R is a hydrocarbon group having 1-20 carbon atoms and X is a 
halogen, and magnesium compounds represented by the formula, RR.sup.1 Mg, 
wherein R and R.sup.1 may be the same or different and are a hydrocarbon 
group having 1-20 carbon atoms, respectively. 
Specific examples of the Grignard compound are methylmagnesium chloride, 
ethylmagnesium chloride, ethylmagnesium bromide, ethylmagnesium iodide, 
propylmagnesium chloride, propylmagnesium bromide, butylmagnesium 
chloride, butylmagnesium bromide, sec-butylmagnesium chloride, 
sec-butylmagnesium bromide, tert-butylmagnesium chloride, 
tert-butylmagnesium bromide, amylmagnesium chloride, isoamylmagnesium 
chloride, phenylmagnesium chloride, phenylmagnesium bromide, etc. Specific 
examples of the magnesium compound represented by the formula, RR.sup.1 
Mg, are diethylmagnesium, dipropylmagnesium, diisopropylmagnesium, 
dibutylmagnesium, di-sec-butylmagnesium, di-tert-butylmagnesium, 
butyl-sec-butylmagnesium, diamylmagnesium, diphenylmagnesium, etc. 
The organoaluminum compound (B) used in combination with the solid catalyst 
component (A) has at least one aluminum-carbon bond in the molecule. 
Specific examples of such organoaluminum compounds are trialkylaluminums, 
such as triethylaluminum, triisobutylaluminum, trihexylaluminum, etc.; 
dialkylaluminum halides, such as diethylaluminum halides, 
diisobutylaluminum halides, etc.; mixtures of trialkylaluminums and 
dialkylaluminum halides; and alkylalumoxanes, such as 
tetraethyldialumoxane, tetrabutyldialumoxane, etc. 
Among these organoaluminum compounds, trialkylaluminums, mixtures of 
trialkylaluminums and dialkylaluminum halides, and alkylalumoxanes are 
preferred, and triethylaluminum, triisobutylaluminum, the mixture of 
triethylaluminum and diethylaluminum chloride, and tetraethyldialumoxane 
are particularly preferred. 
The amount of the organoaluminum compound used may be selected from as wide 
a range as 1-1,000 moles, but preferably a range of 5-600 moles, per mole 
of titanium atoms in the solid catalyst component. 
The electron donative compound used is preferably a silicon compound (C) 
represented by the formula, R.sub.1 R.sub.2 Si(OR.sub.3).sub.2, 
exemplified below. 
##STR1## 
In the polymerization, the respective components of the catalyst system is 
used such that the molar ratio of the Al atom in the component (B) to the 
Ti atom in the component (A) falls within the range of from 1:1 to 
1,000:1, preferably 5:1 to 600:1, and the molar ratio of the component (C) 
to the Al atom in the component (B) falls within the range of from 0.02:1 
to 500:1, preferably 0.05:1 to 10:1. The polymerization is conducted by 
supplying propylene, at least one .alpha.-olefin and a molecular weight 
regulator (e.g. hydrogen) substantially in the absence of a solvent at a 
polymerization temperature of 20.degree.-150.degree. C., preferably 
50.degree.-95.degree. C. and a polymerization pressure of atmospheric 
pressure to 40 kg/cm.sup.2 G, preferably 2-30 kg/cm.sup.2 G. 
The random copolymer of propylene and at least one .alpha.-olefin having 
from 4 to 10 carbon atoms used as the heat sealing resin in the present 
invention contains a specific amount of said at least one .alpha.-olefin 
having from 4 to 10 carbon atoms. The .alpha.-olefin having from 4 to 10 
carbon atoms includes a linear monoolefin such as butene-1, pentene-1, 
hexene-1, heptene-1, octene-1, decene-1, and the like, branched monoolefin 
such as 3-methylbutene-1, 3-methylpentene-1, 4-methylpentene-1, and the 
like. The content of said at least one .alpha.-olefin having from 4 to 10 
carbon atoms in the random copolymer falls within the range of from 15 to 
30% by weight, preferably 18 to 25% by weight. When the .alpha.-olefin 
content is less then 15% by weight, the effect of the copolymer in 
improving the low-temperature heat sealability and hot tack property of 
the laminated film is insufficient. To the contrary, when the 
.alpha.-olefin content is more than 30% by weight, the production of the 
random copolymer is unstabilized due to the deterioration of powder 
properties of the random copolymer during the gas phase polymerization. 
The random copolymer of propylene and at least one .alpha.-olefin having 
from 4 to 10 carbon atoms used as the heat sealing resin in the present 
invention has a melt flow rate (hereinafter MFR) at 230.degree. C. of 
preferably 20 g/10 min. or less, more preferably 3-15 g/10 min. 
The MFR is a parameter which indicates the average molecular weight of a 
polymer. The larger the value of MFR of a polymer, the lower the average 
molecular weight of the polymer. When the MFR of the random copolymer is 
higher than 20 g/10 min., the effect of the copolymer in improving the hot 
tack property of the laminated film is sometimes insufficient. When the 
MFR of the random copolymer is excessively low, the effect of the 
copolymer in improving the low-temperature heat sealability of the 
laminated film is sometimes insufficient, and/or such problems as 
insufficient flowability of the copolymer sometimes occur in film 
formation. 
The random copolymer of propylene and at least one .alpha.-olefin having 
from 4 to 10 carbon atoms used as the heat sealing resin in the present 
invention has a ratio of the weight average molecular weight to the number 
average molecular weight (Mw/Mn) of 4.5 or less, preferably 4.0 or less as 
determined by gel permeation chromatography (GPC). The Mw/Mn is a value 
which indicates the molecular weight distribution of a polymer. The 
smaller the value of Mw/Mn of a polymer, the narrower the molecular weight 
distribution of the polymer. Though the influence of the molecular weight 
distribution of a polymer on the heat seal properties, e.g., 
low-temperature heat sealability, hot tack property, etc., is not yet 
clear, it is considered that the low molecular weight component contained 
in a large amount in a polymer having a wide molecular weight distribution 
influences the heat seal properties in some way. 
The .alpha.-olefin content and cold xylene soluble portion (CXS) of the 
random copolymer of propylene and at least one an .alpha.-olefin having 
from 4 to 10 carbon atoms used as the heat sealing resin in the present 
invention satisfy the following mathematical expression: 
EQU B.ltoreq.1.05A-10, 
wherein A is the .alpha.-olefin content (% by weight) in the random 
copolymer and B is the cold xylene soluble portion (CXS, % by weight) in 
the random copolymer. When the cold xylene soluble portion and the content 
of at least one .alpha.-olefin having from 4 to 10 carbon atoms in the 
random copolymer do not satisfy the above mathematical expression, the 
effect of improving the hot tack property of the resulting laminated film 
by the random copolymer is insufficient, and the blocking resistance and 
printability of the laminated film are sometimes damaged. 
The content, based on percentage by weight of the .alpha.-olefin having 
from 4 to 10 carbon atoms in the cold xylene soluble portion of the random 
copolymer of propylene and at least one .alpha.-olefin having from 4 to 10 
carbon atoms used as the heat sealing resin in the present invention is 
less than 1.7 times the content, based on percentage by weight of the 
.alpha.-olefin having from 4 to 10 carbon atoms in the random copolymer. 
When the .alpha.-olefin content in the cold xylene soluble portion of the 
random copolymer is not less than 1.7 times the .alpha.-olefin content in 
the random copolymer, the effect of improving the hot tack property of the 
resulting laminated film is insufficient, and the printability of the 
laminated film is sometimes unsatisfactory. 
Aftertreatment such as washing is not necessary for the random copolymer 
used as the heat sealing resin in the present invention obtained by gas 
phase polymerization; however, the random copolymer may be washed. 
The copolymer used as the heat sealing resin in the present invention may 
be blended within the limits of about 20% by weight with rubber-like 
ethylene-.alpha.-olefin copolymers, butene-1 polymers including those of 
copolymer type, and the like, and may also be blended with a small amount 
of other polymeric substances. 
Further, the copolymer may be incorporated with conventional additives, 
e.g., antistatic agents, antiblocking agents, lubricants, stabilizers, 
etc. 
The polypropylene laminated film of the present invention can be obtained 
by laminating the aforesaid heat sealing resin on one side or on the both 
sides (one side and the opposite side) of crystalline polypropylene base 
film by conventional methods. Thus, the laminated film of the present 
invention can be obtained, for example, by (i) adhering a crystalline 
propylene film and a previously formed sheet of the heat sealing resin 
with an adhesive by passing them between pressure rollers, (ii) coating 
the heat sealing resin in the form of solution or dispersion in a solvent, 
such as toluene, etc., on a crystalline propylene base film to effect 
lamination, (iii) melt-extrusion coating the heat sealing resin on a 
crystalline propylene base film to effect lamination, or (iv) extruding 
the heat sealing resin and the crystalline propylene base polymer through 
separate extruders and then bonding them in or at the outlet of a common 
die while the two are still in a molten state. 
The laminated film of the present invention is preferably uniaxially or 
biaxially stretched after the heat sealing resin has been laminated. Such 
polypropylene stretched laminated film may be produced by conventional 
methods. Such conventional methods include (i) preparing an unstretched 
laminated sheet by the so-called coextrusion, wherein the two kinds of 
sheets are combined in an extrusion die for forming the laminated sheet or 
in the neighborhood of its outlet while the two are still in a molten 
state, and biaxially stretching the laminated sheet, (ii) 
extrusion-laminating a heat sealing resin on a crystalline polypropylene 
base sheet, and biaxially stretching the laminated sheet, and (iii) 
uniaxially stretching a polypropylene base sheet in a heated condition in 
the machine direction (MD) through a group of rolls including a metallic 
roll, extrusion-laminating a heat sealing resin on the uniaxially 
stretched sheet, and stretching the extrusion-laminated sheet in the 
transversal direction (TD). 
The laminated films are stretched in the MD in the temperature range of 
usually 120.degree. to 160.degree. C., preferably 130.degree. to 
150.degree. C. 
A magnification of the stretching in the MD falls within the range of 
usually from 3 to 8 times, preferably 4 to 6 times. A temperature of the 
stretching in the TD falls within the range of usually from 145.degree. to 
165.degree. C., preferably 150.degree. to 160.degree. C. A magnification 
of the stretching in the TD falls within the range of usually from 4 to 10 
times, preferably 5 to 9 times. 
In the laminated film after stretching, the base layer of polypropylene 
usually has a thickness of from 10 .mu.m to 100 .mu.m, and the layer of 
the random copolymer has a thickness of from 0.1 .mu.m to 10 .mu.m. 
The polypropylene laminated film can be produced at low cost, and the thus 
produced film is superior in both low-temperature heat sealability and hot 
tack property, has a good transparency and blocking resistance and further 
a good printability. Thus, the film is of great practical value. 
The present invention is described in more detail below with reference to 
Examples, which, however, in no way limit the present invention. The 
values of the respective items shown in Examples and Comparative Examples 
were determined in the following manner. 
(1) .alpha.-Olefin (butene-1) content (% by weight) 
This was determined by IR spectrometry from the following equation. 
Butene-1 content (% by weight)=1.208 K', wherein K' is absorbance at 767 
cm.sup.-1. 
(2) Weight average molecular weight/number average molecular weight 
(molecular weight distribution, Mw/Mn) 
This was determined by gel permeation chromatography (GPC) under the 
following conditions. The calibration curve was prepared by using standard 
polystyrenes. 
Apparatus: Type 150 CV, mfd. by Millipore Waters Co., Ltd. 
Column: Shodex M/S 80 
Measuring temperature: 145.degree. C. 
Solvent: o-Dichlorobenzene 
Sample concentration: 5 mg/8 ml 
When determination was made under the above conditions with Standard 
Reference Material 706 (a polystyrene having Mw/Mn of 2.1) of NBS 
(National Bureau of Standards), a value of molecular weight distribution 
(Mw/Mn) of 2.1 was obtained. 
(3) Melt flow rate (MFR) (g/10 min.) 
This was determined at 230.degree. C. under a load of 2.16 kg according to 
JIS K 7210, condition 14. 
(4) Low temperature heat sealability (heat sealable temperature) 
(.degree.C.) 
Two sheets of film were placed one upon the other so that the random 
copolymer-carrying surfaces face each other, and heat-sealed by pressing 
them with a heat sealer (mfd. by Toyo Seiki Seisaku-sho, Ltd.) heated to a 
predetermined temperature under a load of 2 kg/cm.sup.2 G for 2 seconds. 
After standing overnight, the sealed sheets were peeled at 23.degree. C. 
at a peeling rate of 200 mm/min. and a peeling angle of 180.degree.. The 
temperature of the sealer at which the peeling resistance force reached 
300 g/25 mm was taken as the heat sealing temperature. 
(5) Hot tack property (g/25 mm) 
Two sheets of laminated film were placed one upon the other so that the 
random copolymer-carrying surfaces face each other. The thus overlapped 
sheets were cut into 3 inches (76.2 mm) in width and 150 mm in length. 
Then, a plate load spring was bent by hand into U-shape, and an inner edge 
of one of the overlapped sheets was adhered to one of the outer edges of 
the bent plate load spring, and an inner edge of the other overlapped 
sheet was adhered to the other outer edge of the bent plate load spring. 
Then, the other end parts of the two sheets were heat-sealed by pressing 
with a heat sealer (mfd. by Tester Sangyo Co., Ltd.) and heated to a 
predetermined temperature under a load of 2 kg/cm.sup.2 G for 2 seconds. 
Then, a peeling force was applied to the heat sealed part by releasing the 
hand which was holding the load spring immediately before raising a heat 
seal bar. After removing the sample from the load spring, a length of a 
peeled part was measured. Hot tack strength was determined as a spring 
load at which the peeled length of the sealed part showed 1/8 inch (3.2 
mm), with variation of the spring load within the range of from 53 g to 
295 g.

REFERENTIAL EXAMPLE 
(a) Synthesis of organomagnesium compound 
A 1-l flask equipped with a stirrer, reflux cooler, dropping funnel and 
thermometer was flushed with argon, and then 32.0 g of magnesium flakes 
for Grignard reagent was placed therein. In the dropping funnel were 
placed 120 g of butyl chloride and 500 ml of dibutyl ether. About 30 ml of 
the resulting mixture was added dropwise to the magnesium in the flask to 
initiate a reaction. After initiation of the reaction, the dropwise 
addition was further continued at 50.degree. C. for 4 hours. After 
completion of the addition, the reaction was continued at 60.degree. C. 
for further 1 hour. Thereafter the reaction liquid was cooled to room 
temperature, and the solid was removed by filtration. 
The concentration of butylmagnesium chloride in dibutyl ether was 
determined by hydrolyzing the chloride with a 1-N sulfuric acid, followed 
by back titration with a 1-N aqueous sodium hydroxide solution using 
phenolphthalein as an indicator. The concentration was found to be 2.1 
mol/l. 
(b) Synthesis of solid product 
A 500-ml flask equipped with a stirrer and dropping funnel was flushed with 
argon, and then 240 ml of hexane, 5.4 g (15.8 mmoles) of 
tetrabutoxytitanium and 61.4 g (295 mmoles) of tetraethoxysilane were 
placed therein to form a uniform solution. Then, 150 ml of the 
organomagnesium compound synthesized in (a) above was gradually added by 
drops from the dropping funnel in the course of 4 hours while keeping the 
temperature in the flask at 5.degree. C. After completion of the addition, 
the reaction mixture was further stirred at room temperature for 1 hours, 
and then separated into solid and liquid. The solid was repeatedly washed 
3 times with 240 ml of hexane, and dried under reduced pressure to obtain 
45.0 g of a brown solid product. The solid product contained 1.7% by 
weight of titanium atoms, 33.8% by weight of ethoxy groups and 2.9% by 
weight of butoxy groups. 
The solid product showed no obvious peak at all in its wide angle X-ray 
diffraction pattern obtained by using the Cu-Ka line and thus was of an 
amophous structure. 
(c) Synthesis of ester-treated solid 
A 100-ml flask was flushed with argon. Then, 6.5 g of the solid product 
synthesized in (b) above, 16.2 ml of toluene and 4.3 ml (16 mmoles) of 
diisobutyl phthalate were placed in the flask and allowed to react at 
95.degree. C. for 1 hour. 
(d) Synthesis of solid catalyst (activation treatment) 
After completion of the washing in (c) above, 16.2 ml of toluene, 0.36 ml 
(1.3 mmoles) of diisobutyl phthalate, 2.2 ml (13 mmoles) of dibutyl ether 
and 38.0 ml (346 mmoles) of titanium tetrachloride were added into the 
flask, and the resulting mixture was allowed to react at 95.degree. C. for 
3 hours. After completion of the reaction, the solid was separated from 
liquid at 95.degree. C. and washed two times with 33 ml of toluene at the 
same temperature. The aforesaid treatment with a mixture of diisobutyl 
phthalate, butyl ether and titanium tetrachloride was repeated once more 
under the same conditions. Then the treated solid was washed 3 times with 
33 ml of hexane to obtain 5.0 g of an ocherous solid catalyst. 
The solid catalyst contained 2.1% by weight of titanium atoms, 19.9% by 
weight of magnesium atoms and 12.7% by weight of phthalic ester. 
EXAMPLE 1 
(a) Catalyst component 
In a 250-l reactor equipped with a stirrer was placed 150 l of thoroughly 
purified hexane and the atmosphere in the system was thoroughly replaced 
with nitrogen. Then 3.2 moles of triethylaluminum (hereinafter abbreviated 
as TEA), 0.32 mole of cyclohexylethyldimethoxysilane (hereinafter 
abbreviated as CHEDMS) and 51.8 g, in terms of titanium atoms, of the 
solid catalyst obtained in the Referential Example described above were 
added to the system. Then 2.8 kg of propylene was continuously added over 
a period of 2 hours while keeping the temperature of the system at 
25.degree. C. 
(b) Polymerization 
Gas phase polymerization was carried out in a polymerization vessel having 
an inner volume of 1,000 l at a polymerization temperature of 65.degree. 
C. and a polymerization pressure of 12.5 kg/cm.sup.2 G by continuously 
feeding propylene and butene-1, feeding the catalyst component prepared in 
(a) above so that the average residence time might be 6 hours, 
simultaneously supplying 39 mmoles/hour of TEA and 2.8 mmoles/hour of 
CHEDMS and the H.sub.2 concentration might be 0.21% and the butene-1 
concentration might be 22% in the polymerization vessel. 
The copolymer thus obtained had a butene-1 content of 21.7% by weight 
(Table 1). 
To 100 parts by weight of the copolymer were added 0.15 part by weight of 
calcium stearate, 0.1 part by weight of Sumilizer BHT and 0.05 part by 
weight of Irganox 1010 and mixed in a Henschel mixer. The resulting 
mixture was melt-extruded to obtain pellets. 
(c) Lamination and stretching 
The copolymer pellets obtained above were pressed into a sheet of 100 .mu.m 
thickness. The thus obtained sheet was melt-bonded by means of pressing 
with a propylene homopolymer sheet (MFR=2.5) of 500 .mu.m thickness which 
had been formed beforehand by pressing, to obtain a laminated sheet. A 90 
mm.times.90 mm specimen was cut out from the laminated sheet obtained 
above and processed into a biaxially oriented film having a thickness of 
24.mu. under the following conditions. 
Stretching machine: a bench type biaxial stretching machine mfd. by Toyo 
Seiki 
Temperature: 150.degree. C. 
Preheating time: 3 minutes 
Draw ratio: 5.times.5 times 
Stretching rate: 5 m/minute 
The properties of the laminated stretched film thus obtained are shown in 
Table 2. The laminated stretched film was superior in both low-temperature 
heat sealability and hot tack property and also had good transparency, 
blocking resistance and printability. 
EXAMPLE 2 
The same polymerization procedure as in Example 1 was repeated except for 
changing the H.sub.2 concentration in the polymerization vessel into 1.1%, 
to obtain a copolymer. The copolymer had a MFR of 14 g/10 min. and 
butene-1 content of 21.8% by weight (Table 1). 
The copolymer was subjected to pelletizing, lamination and stretching under 
respectively the same conditions as in Example 1. The properties of the 
laminated stretched film thus obtained are shown in Table 2. The film 
showed a good low-temperature heat sealability and hot tack property. 
EXAMPLES 3 AND 4 
Copolymers were obtained under the same polymerization conditions as in 
Example 1 except for changing the H.sub.2 concentration and the butene-1 
concentration in the polymerization vessel into 0.36% and 23%, 
respectively (Example 3), and changing the H.sub.2 concentration and the 
butene-1 concentration into 0.25% and 25%, respectively (Example 4). The 
resulting copolymers had a butene-1 content of 22.7% by weight and 24.9% 
by weight, respectively (Table 1). 
The copolymers were subjected to pelletizing, lamination and stretching, 
respectively, under the same conditions as in Example 1. The properties of 
the laminated stretched films thus obtained are shown in Table 2. Both of 
the films showed a good low-temperature heat sealability and hot tack 
property. 
COMATIVE EXAMPLES 1 AND 2 
A propylene-butene-1 copolymer was obtained according to the method 
described in Example 1 of U.S. Pat. No. 4,675,247 except for changing the 
H.sub.2 concentration and the butene-1 concentration in the polymerization 
vessel into 1.5% and 25%, respectively (Comparative Example 1), and 
changing the H.sub.2 concentration and the butene-1 concentration into 
1.6% and 28%, respectively (Comparative Example 2) (Table 1). 
The copolymer was subjected to pelletizing, lamination and stretching under 
the same conditions as in Example 1 of the present specification. The 
properties of the laminated stretched film thus obtained are shown in 
Table 2. The laminated stretched film showed good low-temperature heat 
sealability but showed unsatisfactory hot tack property. 
COMATIVED EXAMPLE 3 
A copolymer was obtained under the same polymerization conditions as in 
Example 1 except for changing the H.sub.2 concentration and the butene-1 
concentration in the polymerization vessel into 3.2% and 21.5%, 
respectively. The copolymer thus obtained had a MFR of 28 g/10 min. and 
butene-1 content of 20.6% by weight (Table 1). 
The copolymer was subjected to pelletizing, lamination and stretching under 
the same conditions as in Example 1. The properties of the laminated 
stretched film thus obtained are shown in Table 2. 
The laminated stretched film showed a good low-temperature heat 
sealability, but showed unsatisfactory hot tack property. 
COMATIVE EXAMPLE 4 
A copolymer was obtained under the same polymerization conditions as in 
Example 1 except for changing the H.sub.2 concentration and the butene-1 
concentration in the polymerization vessel into 0.25% and 12%, 
respectively (Table 1). The resulting copolymer had a butene-1 content of 
12.0% by weight. 
The copolymer was subjected to pelletizing, lamination and stretching under 
the same conditions as in Example 1. The properties of the laminated 
stretched film thus obtained are shown in Table 2. 
The laminated stretched film was unsatisfactory in both low-temperature 
heat sealability and hot tack property. 
TABLE 1 
__________________________________________________________________________ 
Butene-1 CXS Butene-1 
content (A) MFR content (B) 
content (C) in CXS 
(wt %) Mw/Mn 
(g/10 min.) 
(wt %) 
(wt %) C/A 
__________________________________________________________________________ 
Example 1 
21.7 3.1 7.3 6.7 35.0 1.61 
Example 2 
21.8 3.0 14.0 9.1 34.2 1.58 
Example 3 
22.7 3.4 8.0 9.6 34.3 1.51 
Example 4 
24.9 3.1 6.8 14.0 36.8 1.48 
Comparative 
22.7 4.7 7.3 15.7 40.6 1.79 
Example 1 
Comparative 
24.6 5.7 8.3 18.2 42.1 1.71 
Example 2 
Comparative 
20.6 28.0 7.1 34.0 1.65 
Example 3 
Comparative 
12.0 8.0 1.2 20.3 1.69 
Example 4 
__________________________________________________________________________ 
TABLE 2 
__________________________________________________________________________ 
Heat 
sealable Hot tack strength (g/3 inches) 
temp. 70.degree. C. 
80 90 100 
110 
120 
130 
140 
150 
160 
__________________________________________________________________________ 
Example 1 
93 53&gt; 
295&lt; 
295&lt; 
295&lt; 
295&lt; 
240 
134 
90 
84 
Example 2 
94 53&gt; 
295&lt; 
295&lt; 
295&lt; 
295&lt; 
295&lt; 
233 
124 
89 
Example 3 
93 53&gt; 
295&lt; 
295&lt; 
295&lt; 
295&lt; 
295&lt; 
235 
130 
99 
Example 4 
87 53&gt; 
259 
295&lt; 
295&lt; 
295&lt; 
295&lt; 
274 
236 
172 
99 
Comparative 
80 85 132 
255 
295&lt; 
280 
241 
205 
171 
96 
63 
Example 1 
Comparative 
79 115 236 
254 
227 
156 
177 
190 
152 
116 
65 
Example 2 
Comparative 
102 53&gt; 
70 
290 
295&lt; 
280 
250 
175 
95 
Example 3 
Comparative 
129 53&gt; 
53&gt; 
80 
295&lt; 
260 
174 
110 
Example 4 
__________________________________________________________________________ 
The wider the temperature range within which the hot tack strength is 
satisfactory high, the better hot tack property. As shown in Table 2, the 
films in all of Examples 1 to 4 show a hot tack strength of 285 g/3 inches 
or more within the temperature range of 90.degree. to 120.degree. C., 
which were better results than comparative examples. 
According to the present invention, a polypropylene laminated film can be 
provided which is superior in low temperature heat sealability and hot 
tack property and moreover has a good transparency, blocking resistance 
and printability.