GB1582186A

GB1582186A - Heat sealable multilayer film

Info

Publication number: GB1582186A
Application number: GB33334/77A
Authority: GB
Original assignee: Toray Industries Inc
Current assignee: Toray Industries Inc
Priority date: 1976-08-10
Filing date: 1977-08-09
Publication date: 1980-12-31
Also published as: DE2735547A1; JPS5321688A; BE857623A; JPS5618386B2; FR2361225B1; FR2361225A1

Description

(54) HEAT SEALABLE MULTILAYER FILM (71) We, TORAY INDUSTRIES, INC., a body corporate organized according to the laws of Japan, of 2, Nihonbashi-Muromachi, 2-Chome, Chuo-Ku, Tokyo, Japan, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed to be particularly described in and by the following statement:- This invention relates to a heat sealable film suitable for packaging a variety of products by automatic packaging machines.

Packaging techniques have progressed from simple manual packaging to methods using bag-making machines, where bags are made in the machine and then filled with products manually. More recently, there have been introduced automatic packaging machines, so called form-and-fill type machines, designed to work automatically and continuously according to the following process. A variety of products and a continuous web of packaging film are fed at the same time, and, then, the film is formed to the desired shape, into which the desired quantity of product is supplied and then the free edges of the package are heat-sealed together.

For automatic packaging applications, films are required to have good quality because of the automatic operation and high packaging speed. It is found in practice that a film suitable for manual packaging and bag-making machines is not always suitable for automatic packaging machines. In particular, the higher the packaging speed, the greater the number of rejected packages. The rejection ratio increases when automatic packaging machines are used, and film quality needs to be higher for automatic packaging machines.

Film quality may, in practice, only be evaluated by the percentage of rejected packages. When the percentage of rejected packages is more than l.0V,, the film is generally regarded as unsuitable for automatic packaging machines. Commercially, for example, a film is not suitable for industrial packaging use if more than 100 packages are rejected in 10,000 packages, and nowadays, in packaging applications, it is desirable to reduce the percentage of rejected packages to below 0.5, preferably to below 0.1% It is not possible to define the suitability of a film for automatic packaging machines in terms of common physical properties, because the suitability consists of a combination of many physical properties, which is why film suitability is evaluated only by the percentage of rejected packages in a real packaging run. (In the case of packaging by manual operation or bag-making machines, the problem is not so complicated because some common physical properties can represent the suitability for packaging). The following film properties, at least, are considered to be relevant to film suitablity for automatic packaging machines: friction coefficient, hot stick, thermal shrinkage, modulus, stiffness, creasing tendency, curl tendency, heat sealability, plasticity, tearability, formability, melt viscosity, thickness uniformity, degree of sag, electrostatic charge, scratch resistance and crystallisation characteristics, etc. Few of these properties are independent of each other, i.e., most of the properties listed above are closely related to at least some of the others.For example, modulus is one of the component factors of stiffness but is not equal to stiffness itself. Of these properties, there are some that can not be quantitatively expressed.

Some of the properties listed above, and their importance to the use of a film in automatic packaging machines, will be discussed in more detail below.

The film running property in automatic packaging machines depends on the friction coefficient between the film and machine. A film having a high friction coefficient creases too easily, whereas a film having a low friction coefficient causes telescoping too easily. To obtain suitable operability on automatic packaging machines, the dynamic friction coefficient of the film should advantageously range from 0.1 to 1.0, preferably from 0.2 to 0.8. "Hot stick" is the adhesion between the film and the heat sealing plate, which is usually heated to 100--200"C. A low degree of hot stick is necessary for good automatic packaging.

The degree of hot stick can be evaluated by measuring the dynamic friction coefficient between the film and a chromium-coated ferroplate heated to 700 C.

For suitable operability on automatic packaging machines, the dynamic friction coefficient measured by this method should advantageously be below 2.0, preferably below 1.2.

Thermal shrinkage relates to the extent that a film shrinks under heat. When the film shrinks too much, the outside appearance of packages are not acceptable because of many creases and protrusive parts. Thermal shrinkage of film is estimated by the percentage of (original length-shrunk length/original length), after exposing the film to 1200C for 15 minutes. To obtain suitable operability on automatic packaging machines, the percentage of thermal shrinkage is desirably below 8%, preferably below 5% in every direction. Modulus is a measure of the hardness of a film and is one of the component factors of stiffness. Modulus greatly affects film supply and running characteristics on automatic packaging machines.

To obtain suitable operability, a high modulus is desirable. Tensile modulus is commonly used to represent general moduli. To obtain suitable operability on automatic packaging machines, the sum of two tensile moduli, measured in longitudinal and lateral directions, is desirably about 400 kg/mm2, preferably above 450 kg/mm2. Stiffness demonstrates the rigidity of the film and is very difficult to be quantitatively expressed because of too many component factors.

But practically, high stiffness film (crisp film) is easy to handle on automatic packaging machines. The creasing tendency is also difficult to be quantitatively expressed, but easily creasing film has not only poor operability on automatic packaging machines but also undesirable outside appearance of packages. Curl tendency is the phenomenon of rolling up of film edges. Readily curling film is hard to handle on automatic packaging machines.

The degree of curl is estimated by measuring the rolling up height of film edges (the distance between the highest point and the plane) after the film is held in the atmosphere of 80"C for 5 minutes. To obtain suitable operability on automatic packaging machines, the rolling up height is advantageously below 15 mm, preferably below 10 mm.

Heat sealability is the property of bonding films by heat and is therefore necessary for sealing packages. Heat sealability is expressed quantitatively both by heat seal strength and heat sealable temperature range. For automatic packaging machines, heat seal strength is desirably above 50 g/cm, preferably above 100 g/cm.

The heat sealable temperature range is defined as the temperature range between T, and2, where T, is a temperature below which heat seal strength is less than 50 g/cm, and T2 is a temperature above which finished packages show an ugly appearance because of a considerable heat shrinkage of the film. To obtain suitable operability on automatic packaging machines, especially at high speed, the heat sealable temperature range is desirable to be as wide as 30"C, preferably more than 40"C. Plasticity of the film is related to local stretch of the film caused by the film tension in the packaging machines. If local stretch occurs, automatic packaging does not go smoothly.

Too high a tearability results in tearing when the film is cut on automatic packaging machines. A film difficult to be cut is not suitable for automatic packaging machines because of difficulty in making separate packages.

Formability is a property which enables the film package to keep a good shape after being formed. If the products are packaged with a film having a poor formability, the external appearance of the packages is so uneven that it is hard to obtain packages with good appearance.

Melt viscosity and crystallisation characteristics are related to "bottom seal rupture" of the packages on vertical automatic packaging machines. When products are introduced into the package with the bottom sealed, it is essential to avoid rupture of the bottom sealed part by the weight of incoming products. This rupture of the bottom sealed part is called "bottom seal rupture". In order to avoid "bottom seal rupture", it is desirable that melt viscosity of heat sealed part is high and greatly dependent on temperature, and that the polymer of the heat sealed part is readily crystallisable from the melt. Thickness uniformity is directly related to operability on automatic packaging machines. Films having poor thickness uniformity give poor operability and poor appearance of the packages.To obtain suitable operability on automatic packaging machines, the deviation from thickness uniformity over total film width is desirably below 15%, preferably below 10%, where thickness uniformity is measured by (maximum thickness-minimum thickness)/average thickness 100 ().

The degree of sag is an important factor for operability on automatic packaging machines. Films with considerable sag are not suitable for automatic packaging machines because sag causes many creases and folds on the packages.

To obtain suitable operability on automatic packaging machines, the degree of sag, sag length from horizontal plane, is desired to be below 10 mm, preferably below 5 mm.

Electrostatic chargeability is an important factor for supplying automatic packaging machines with films. Films carrying a lot of static charge cling to various parts of the machine so much that they are difficult to introduce into automatic packaging machines.

The tendency to carry static charge may be estimated by measuring surface resistivity. In order to obtain suitable operability on automatic packaging machines, the surface resistivity is desirably below 10'4 ohm/cm, preferably below 1012 ohm/cm.

Scratch resistance is related to the rigidity of the film surface. Films having poor scratch resistance pick up flaws on their surface so easily that the appearance of packages becomes poor. Therefore, good scratch resistance is one of the important properties of the film for automatic packaging machines.

Some of the film properties mentioned above cannot be numerically expressed. In such cases, three rank grading system will be used in the following description. Three ranks, A, B and C, are qualitatively defined as follows.

A. Satisfactory level for automatic packaging.

B. Acceptable level for automatic packaging.

C. Unacceptable level for automatic packaging.

This ranking was measured by inspection of packages resulting from actual automatic packaging runs.

The present invention provides a laminate comprising a first layer of biaxially oriented isotactic polypropylene or a biaxially oriented copolymer containing at least 50 mole percent propylene units having on at least one surface thereof a second layer comprising a blend comprising (A) isotactic polypropylene or a copolymer of propylene and (B) tactic polybutene-(l) or a copolymer of butene-(l).

The film of this invention, which is suitable for automatic packaging machines, is a laminated film comprising a biaxially oriented film of isotactic polypropylene or a copolymer containing at least 50 mole percent propylene units (PP for short, the PP, when biaxially oriented, being designated PP--BO), laminated, at least on one surface, with a polymer blend of (A) isotactic polypropylene or a copolymer of propylene (PP for short) and (B) tactic polybutene-(l) or a copolymer of utene- (1) (PB for short).

The film of the invention is illustrated in Figure 1 and Figure 2 of the accompanying drawings. These figures show the cross sections of the present films, having a layer 1 of PP-BO and a layer, or layers, 2 of PP-PB blend.

The laminated films of the present invention are suitable for automatic packaging machines and, therefore, the rate of rejected packages may be small.

Neither layer of the laminate film of the present invention, i.e., PP-BO layer and PP-B blend layer, is alone suitable for automatic packaging machines. Good packages are not obtained when PP-BO is used, because PP-BO is unsatisfactory in such properties as friction coefficient, hot stick, thermal shrinkage, creasing tendency, heat sealability and crystallisation characteristics.

The single films comprising blends of PP and PB, which are disclosed in Japan Patent No. 34-2245 and Japan Kokai No. 50-14741 where good heat-sealability is demonstrated, are not suitable for automatic packaging machines because they are unsatisfactory in such properties as thermal shrinkage, modulus, stiffness, creasing tendency, plasticity and formability. Accordingly, neither layer in the present laminated films is separately suitable for automatic packaging machines, while laminates surprisingly are suitable for use in automatic packaging machines. It should be noted that thermal shrinkage and creasing tendency, which are poor in each film separately, are significantly improved by laminating them together.

In the present invention, PP includes isotactic polypropylene and, when extracted with boiling n-heptane, the residue advantageously ranges between 70 and 99 weight %, preferably between 90 and 98 weight %. The Melt Flow Index, measured in accordance with ASTM D1238-57T at 2300C, is advantageously 0. 130 g/10 minutes, preferably 0.5-10 g/10 minutes, PP as used in this specification also includes a copolymer, the main component of which is propylene units, namely, copolymers containing more than 50 mole % propylene units, e.g., propyleneethylene copolymers, propylene-butene-l copolymers and propylene - styrene copolymers, are regarded as PP in this invention. Both random and block copolymers are suitable.PP especially suitable for the present PP-BO layer is a propylene homopolymer or propylene ethylene random copolymer containing 0.1-1.5 weight /n of ethylene and has a Melt Flow Index of 0.5-4.0 g/10 minutes.

PP-BO containing a small amount of PB is particularly suitable for automatic packaging machines. Incorporation of a small amount of PB (0.1-10%, preferably 0.5-5%, based on the weight of PP--BO) into PP-BO improves such properties of the final laminated films as thickness uniformity, degree of sag, friction coefficient, creasing tendency and curl tendency. Therefore, film operability on automatic packaging machines is considerably improved. PP-BO in the present invention may contain any of the additives conventionally employed in the manufacture of thermoplastic films.Thus, such additives as anti-static agents, stabilizers, plasticizers, ultra-violet absorbers, lubricants, inorganic fillers, clarifying agents, nucleating agents, waxes, polyterpenes, polyethylene, polystyrene and styrene-oligomers may be incorporated into PP-BO layer.

The PP suitable for blending with the PB of the heat sealable layer(s) of the invention is advantageously a propylene homopolymer or propylene-ethylene copolymer, preferably a random copolymer with an ethylene content of 1-3.5 weight %, or propylene-butene-l copolymer with butene-l content 2-20 weight %, and has a Melt Flow Index of 0.5-30 g/10 minutes, preferably 1--20 g/10 minutes.

The blending component, PB, is tactic polybutene-l and may be produced by the method disclosed in United States Patent Specification No. 3,362,940, although the invention is not limited to PB produced by this production method. PB suitable for the present invention advantageously has a Melt Flow Index of 0.420 g/10 minutes, preferably 1.010 g/10 minutes, and has more than 70 weight /n residue when extracted with diethyl ether. PB used in the invention includes, as well as homo-polybutene-l, copolymers of butene-l and alpha-olefines, e.g. ethylene, propylene, butene-2, pentene, hexene and octene.Particularly, butene-l copolymerised with 0.1-10 weight /n of long-chain (4-12 carbon atoms) alphaolefines (for example, hexene-l or octene-l) or block-copolymerised with 0.1-10 weight % of ethylene or propylene or blended with 1--15 weight /n polyethylene is suitable for the present invention because of good processability and operability on automatic packaging machines.

Blending of PP and PB to provide the second layer of the invention is not restricted to any particular method, but a homogeneous blend of polymers may be obtained by mixing molten polymers at high shear stress. Pellets, powder, or flakes, of both PP and PB may be admixed together by any suitable means and subsequently homogeneously mixed up by the extruders or banbury mixers.

The blend ratio of PP to PB for the heat sealable laminating layer(s) of the invention advantageously ranges from 80/20 to 20/80 based on total weight 100. It has been found that these blends have previously unknown behaviour, which is believed to be unique. For example, blends of PP and PB described above, with melting point of 160 and 1200C respectively, show another new melting point near 80"C. Figure 3 of the accompanying drawings depicts characteristic curves of polymers measured by Differential Scanning Calorimeter (DSC), where curve A shows a melting point near 1600C for PP and curve B shows a melting point near 1200C for PB.But curve C for 5-50 blend of PP and PB shows a new melting point near 80"C besides the original melting points for PP and PB. This fact suggests that a new crystal structure, with a melting point near 800 C, is created by blending PB with PP. This phenomenon is previously unknown. One hypothesis is that blending PB with PP promotes the formation of eutectic or mixed crystals. The degree of crystal formation increases with the degree of tacticity of PB. Also, the crystal formation takes place most easily when PB is a copolymer containing ethylene, propylene or long chain alpha-olefine as hereinbefore described, or when PB is blended with polyethylene as mentioned above. The formation of this crystal is most clearly observed when the blend ratio of PB to PP is between 80/20 and 20/80, and is most prominent when the blend contains equal amounts of PB and PP.

It seems that the amount of crystal formation is closely related to operability on automatic packaging machines and, therefore, films with a large amount of crystal formation are particularly suitable for automatic packaging machines. It is likely that the new crystal formation has an effect on improvement of film operability on automatic packaging machines, although the invention is not to be regarded as limited by theoretical considerations. Namely, this crystal formation likely improves (in a practical sense) such properties as friction coefficient, hot stick, thermal shrinkage, creasing tendency, curl tendency, heat sealability, melt viscosity, scratch resistance and crystallisation characteristics. To obtain suitable operability on automatic packaging machines, the blend ratio of PP and PB should advantageously range from 80/20 to 20/80, preferably from 70/30 to 30/70.Any additives, such for example as described in the case of PP-BO, may be incorporated into the blends of PP and PB. The thickness of the heat sealable layer(s) may range from 0.1 to 10,um depending on the thickness of substrate PP BO. The preferred range is from 2 to 8 ssm in the case of a laminate having a second layer on one surface only and from 0.5 to 2 ssm in the case of a laminate having a second layer on both surfaces of the first layer. To obtain optimum operability on automatic packaging machines, it is preferred for the second layer(s) not to be molecularly oriented, i.e., a non-oriented state is preferred for the blend layer(s).

But for some limited applications or practical uses, it is acceptable for the blend layer(s) to be uniaxially or biaxially oriented.

Preferable manufacturing method of the laminated films of the present invention is a direct laminating process as described hereafter. Since substrate and heat sealable layer may be directly laminated by means of direct laminating process without any adhesive agents of anchor coating agents, not only film properties are improved such as adhesive strength between laminated layers, odour, transparency, thickness uniformity, sag, thermal shrinkage and formability, but also manufacturing cost decreases in comparison with other laminating processes because the final laminated films may be made in a simple continuous line. One example of direct laminating processes is that two or three molten polymer streams are joined in the extruder or die to make a laminated structure followed by uniaxial or biaxial stretching.Another example is that a molten layer of PP-PB blend is extruded directly on one or both surfaces of a preformed non-oriented or uniaxially oriented PP layer to make laminated film followed by uniaxial or biaxial stretching.

Any process including combination of these processes may be acceptable. If desired, one or both surfaces of the laminated film formed by those processes may be activated by conventional surface treatments, such as corona discharge treatment (in air or inert gas), chemical treatment with chromic acid mixture or plasma treatment. These treatments are more effective in an atmosphere at high temperature.

The laminated films of the present invention are suitable for use in automatic packaging machines, such as over wrapping machines, vertical packaging machines and horizontal packaging machines, and, in a real packaging run, the percentage of rejected packages is usually below 0.1%, much superior to that of conventional films in similar conditions of use.

The following Examples illustrate the invention.

Example 1 Pellets of PP (having a percentage of extraction residue in boiling n-heptane of 96 weight % and Melt Flow Index of 2.0 g/10 minutes) were extruded through a die at 280"C and the molten polymer cast onto a cooling drum at 300C to form a cast sheet about 1.5 mm thick. The sheet was stretched 5 times its original length at 1450C in the longitudinal direction to form a uniaxially stretched sheet. A 50/50 blend of PP and PB was extrusion-laminated at 2700C on to one surface of the uniaxially stretched sheet. PB was a butene-l copolymer containing 2.0 weight /n hexene-l and the Melt Flow Index was 2.0 g/10 minutes. PP was a propylene copolymer containing 2t.5 weight /n ethylene with a Melt Flow Index of 10 g/10 minutes.Then, the laminated sheet was conveyed into a tenter oven to be transversely stretched 8.5 times at 1550C and then heat set at 1600C for 6 seconds with 5% widthwise relaxation followed by cooling and winding. The laminated film had a thickness of about 40,um, the substrate PP-BO having a thickness of 35 fllm and the heat sealing layer of PP/PB blend having a thickness of 5 ssm. The properties of this laminated film are summarised in Table 1.

Sweets were automatically packaged with this laminated film on a Kawashima Seisakusho vertical packaging machine Model No. KBF-l0. Automatic packaging ran smoothly at the rate of 60 packages/minute. After I hour automatic packaging run, the percentage of rejected sweets packages was about 0.08.

TABLE 1 Machine Transverse Properties Units direction direction Test Methods Tensile strength kg/mm2 14.2 28.0 ASTM-D638 Tensile elongation % 150 65 ASTM-D638 Tensile modulus kg/mm2 190 360 ASTM-D638 Thermal shrinkage % 4.5 0.6 120"C 15 minutes Haze % 3.0 ASTM-D1003-52 Friction coefficient - 0.42 ASTM-D1894-63 Blocking propensity g/12 cm2 200 40"C 60% RH Heatseal strength g/cm 530 sealed at 1200C Heat sealable temperature range "C 90155 Curl tendency mm 2.5 Scratch resistance A Creasing tendency A Plasticity A A Tearability A Formability A Thickness uniformity % 4.2 Degree of sag mm 1.0 Melt viscosity A Example 2 The procedure of Example 1 was repeated except that 0.5 weight % of antistatic agent (glycerine monostearate), 0. 1 weight % lubricant (stearic acid amide) and 0.08 weight % fumed silica, based on the weight of PP--BO, were incorporated into PP--BO. After corona discharge treatment on the PP-BO surface, the laminated film was aged for 3 days at room temperature. This aging not only achieved good antistatic property but also stabilized the crystalline transition in the PP/PB blend layer. "Cookies-in-tray" were automatically packaged with this film on a horizontal packaging machine Model New Wrapper No.W308 (Omori Kikai), at a rate of 200 packages/minute. Packaging results were good and the percentage of rejected packages was 0.05%, a significantly low value.

Example 3 The procedure of Example 1 was repeated except that the thicknesses of the substrate PP-BO and the laminated PP/PB blend layer were 20 ,um and 3 ,um respectively. Seasoned sea weed was automatically packaged with this film on an Ajitsuke-Nori packaging machine (Towa Seiki) at a rate of 100 lines/minute, which corresponded to 600 packages/minute because each line contained six packages.

The film ran very well on the machine and none of the packages was rejected.

Example 4 The following two polymers were used.

(a) PP The percentage of extraction residue in boiling n-heptane was 97 weight % and the Melt Flow Index was 2.2 g/10 minutes. The polymer was propylene-ethylene random copolymer containing ethylene of 0.8 weight %. As stabilisers, 0.05 weight%, Irganox 1010 (Geigy Inc.) (Yoshitomi Seiyaku) 0.1 weight %, BHT swanox, and 0.1% by weight calcium stearate were incorporated into the polymer.

0.6 % by weight glycerine monostearate (antistatic agent) and 0.15 % by weight as lubricant stearic acid amide were incorporated. 1.0 weight % PB was incorporated into the polymer; the composition of PB was the same as used in b) below.

(b) 45/55 PP/PB blend PP: PP was propylene-ethylene random copolymer containing ethylene of 3 weight % and the Melt Flow Index was 8.0 g/10 minutes. The same stabilisers as used in (a) above, 4% of microcrystalline wax and 0.05 of finely powdered zeolite were incorporated into PP.

PP: PB was a butene - 1 - octene - I copolymer containing 2 weight % octene- 1. The same stabilisers as described in (a) were incorporated. A mixture of pellets of 45 weight % of PP and 55 weight % of PB was blended and fed into the pelletizing extruder at 2300C to mix and melt the blend to form pellets.

Each of materials of (a) and (b) was fed into two extruders respectively and then molten polymer (a) was extruded at 2600C and polymer (b) at 2400 C. Two molten polymer streams joined in the tube just before the die in such a manner that the extruded laminated sheet consisted of a single core layer of PP sandwiched by two heat sealable layers. The co-extruded three-layered sheet was stretched 4.8 times its original length at 1500C in the longitudinal direction and then, stretched 9 times at 1600C in the transverse direction and then heat set at 1600C for 5 seconds with 5% widthwise relaxation followed by corona discharge treatment on both surfaces and winding.The three-layered laminated film thus obtained has 20 ym thickness (core layer) and 3 4m (heat sealing blend layers). The properties of this laminated film are shown in Table 2.

Cigarette packets were overwrapped with this film at a rate of 150 packets/minute, using a W-7 overwrapping machine (Tokyo Jidokikai).

The film was smoothly introduced into the automatic overwrapping machine and had good tearability and formability without any hot stick trouble. The operability of this film on automatic overwrapping machines was obviously very good because the percentage of rejected packages was as low as 0.02 /".

TABLE 2 Machine Transverse Properties Units direction direction Test Methods Tensile strength kg/mm2 14.0 26.5 ASTM-D638 Tensile elongation % 155 70 ASTM-D638 Tensile modulus kg/mm2 180 350 ASTM-D638 Thermal shrinkage % 4.2 0.2 1200C 15 minutes Haze % 1.8 ASTM-D1003-52 Friction coefficient - 0.38 ASTM-D1894-63 Blocking propensity g/12 cm2 less than 100 40"C 60 /n RH Heatseal strength g/cm 180 sealed at 1300C Heat sealable temperature range "C 100155 Curl tendency mm 2.0 Electrostatic charge ohm/cm 2x 10" Scratch resistance - A Hot stick - 0.8 Creasing tendency A A Plasticity - A Tearability - A Formability - A Thickness uniformity /" 3.5 Degree of sag mm 0.8 In order to compare operability of this film with that of conventional films, the results of the various packaging tests are given in the following Comparative Examples.

Comparative Example 1 Commercially available PP-BO film (40 Mm thick) was tested on automatic packaging machine in the same conditions as those of Example 1, with completely poor results. The percentage of rejected packages was 100%, showing that plain PP-BO was not suitable for automatic packaging machines.

Comparative Example 2 A plain film 40 m thick was made from 50/50 PP/PB blend (the same blend as that of Example 1). The preparation method was described in Japan Kokai No. 5014741. This film was tested on automatic packaging machine in the same conditions as those of Example 1, with very poor results. The percentage of rejected packages was 100%.

Comparative Example 3 A three layered film (22 ,um thick) was prepared by the method of United States Patent No. 3,671,383. This film had a PP-BO core layer laminated on both sides with propylene ethylene copolymer layer. This film was tested on an automatic packaging machine in the same conditions as those of Example 4. The film was not so good for automatic overwrapping machine because percentage of rejected packages was as high as 15%.

Comparative Example 4 A three layered film with 22 m thick was prepared by the method described in Japan Kokai 50-128781. This film had a core layer of PP-BO laminated on both sides with propylene - butene - 1 copolymer layers. The film was tested on an automatic packaging machine in the same conditions as those of Example 4. The film ran fairly well and the percentage of rejected packages was 0.3 /". This percentage is not too bad but still worse than 0.02 /" shown in Example 4 in this invention.

Example 5 (including comparative Samples) The procedure of Example 1 was repeated except that blend ratio of PP and PB was varied. The films obtained were tested on automatic packaging machine.

The results are shown in Table 3.

TABLE 3 Sample Blend ratio of PP Percentage of rejected No. and PB (by weight) packages ( /n) PP PB 0 0 100 1.20 2 10 90 0.85 3 20 80 0.22 4 30 70 0.12 5 50 50 0.08 6 70 30 0.09 7 80 20 0.20 8 90 10 0.55 9 100 0 0.85 From these results, it is clear that advantageous blend ratios of PP/PB for the blend layer(s) are from 80/20 to 20/80, preferably from 70/30 to 30/70 by weight.

Figures 1 and 2 depict a cross section of laminated film of the invention, where 1 is a biaxially oriented polypropylene layer and 2 is polypropylene-polybutene-l heat sealable layer(s).

Figure 3 shows crystal melting peaks measured by differential scanning calorimeter, where A is for polypropylene, B is for polybutene-l and C is for 50/50 PP/PB blend.

WHAT WE CLAIM IS: 1. A laminate comprising a first layer of biaxially oriented isotactic polypropylene or a biaxially oriented copolymer containing at least 50 mole per cent propylene units having on at least one surface thereof a second layer comprising a blend comprising (A) isotactic polypropylene or a copolymer of propylene and (B) tactic polybutene-(l) or a copolymer of butene-(l).

2. A laminate as claimed in claim I, wherein the first layer comprises isotactic polypropylene having a residue on extraction with boiling n-heptane between 70 and 99% by weight.

3. A laminate as claimed in claim 2, wherein the residue is between 90 and 98% by weight.

4. A laminate as claimed in claim 2 or claim 3, wherein the melt flow index of the isotactic polypropylene of the first layer is between 0.1 and 30 g/10 minutes.

5. A laminate as claimed in claim 4, wherein the melt flow index is between 0.5 and 4.0 g/10 minutes.

6. A laminate as claimed in claim 1, wherein the first layer comprises a copolymer of propylene with ethylene, butene-l or styrene.

7. A laminate as claimed in claim 6, wherein the copolymer has the properties specified in any one of claims 2 to 5.

8. A laminate as claimed in claim 1, wherein the first layer comprises polypropylene or a random copolymer of ethylene and propylene containing 0.1 to 1.50/, by weight ethylene, the polymer having a melt flow index of 0.5 to 4 g/10 minutes.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **.

film was not so good for automatic overwrapping machine because percentage of rejected packages was as high as 15%.

Comparative Example 4 A three layered film with 22 m thick was prepared by the method described in Japan Kokai 50-128781. This film had a core layer of PP-BO laminated on both sides with propylene - butene - 1 copolymer layers. The film was tested on an automatic packaging machine in the same conditions as those of Example 4. The film ran fairly well and the percentage of rejected packages was 0.3 /". This percentage is not too bad but still worse than 0.02 /" shown in Example 4 in this invention.

Example 5 (including comparative Samples) The procedure of Example 1 was repeated except that blend ratio of PP and PB was varied. The films obtained were tested on automatic packaging machine.

The results are shown in Table 3.

TABLE 3 Sample Blend ratio of PP Percentage of rejected No. and PB (by weight) packages ( /n) PP PB 0 0 100 1.20

2 10 90 0.85

3 20 80 0.22

4 30 70 0.12

5 50 50 0.08

6 70 30 0.09

7 80 20 0.20

8 90 10 0.55

9 100 0 0.85 From these results, it is clear that advantageous blend ratios of PP/PB for the blend layer(s) are from 80/20 to 20/80, preferably from 70/30 to 30/70 by weight.

Figures 1 and 2 depict a cross section of laminated film of the invention, where 1 is a biaxially oriented polypropylene layer and 2 is polypropylene-polybutene-l heat sealable layer(s).

Figure 3 shows crystal melting peaks measured by differential scanning calorimeter, where A is for polypropylene, B is for polybutene-l and C is for 50/50 PP/PB blend.

WHAT WE CLAIM IS: 1. A laminate comprising a first layer of biaxially oriented isotactic polypropylene or a biaxially oriented copolymer containing at least 50 mole per cent propylene units having on at least one surface thereof a second layer comprising a blend comprising (A) isotactic polypropylene or a copolymer of propylene and (B) tactic polybutene-(l) or a copolymer of butene-(l).
2. A laminate as claimed in claim I, wherein the first layer comprises isotactic polypropylene having a residue on extraction with boiling n-heptane between 70 and 99% by weight.
3. A laminate as claimed in claim 2, wherein the residue is between 90 and 98% by weight.
4. A laminate as claimed in claim 2 or claim 3, wherein the melt flow index of the isotactic polypropylene of the first layer is between 0.1 and 30 g/10 minutes.
5. A laminate as claimed in claim 4, wherein the melt flow index is between 0.5 and 4.0 g/10 minutes.
6. A laminate as claimed in claim 1, wherein the first layer comprises a copolymer of propylene with ethylene, butene-l or styrene.
7. A laminate as claimed in claim 6, wherein the copolymer has the properties specified in any one of claims 2 to 5.
8. A laminate as claimed in claim 1, wherein the first layer comprises polypropylene or a random copolymer of ethylene and propylene containing 0.1 to 1.50/, by weight ethylene, the polymer having a melt flow index of 0.5 to 4 g/10 minutes.
9. A laminate as claimed in claim 1, wherein the first layer comprises a

copolymer of propylene with 0.1 to 10% by weight of butene-l.
10. A laminate as claimed in claim 9, wherein the copolymer comprises 0.5 to 5% by weight of butene-l.
11. A laminate as claimed in any one of claims I to 10, wherein the second layer comprises as component B a copolymer of butene- I with ethylene, propylene, butene-2, pentene, hexene or octene.
12. A laminate as claimed in any one of claims 1 to 10, wherein component B of the second layer comprises a copolymer of butene- I with 0.1 to 10% by weight of an alpha-olefine with from 4 to 12 carbon atoms or a block copolymer of butene-l with 0.1 to 10% by weight of ethylene or propylene or a blend of polybutene-l with from 1 to 15 /n by weight of polyethylene.
13. A laminate as claimed in any one of claims 1 to 12, wherein component A of the second layer is a propylene-ethylene copolymer.
14. A laminate as claimed in claim 13, wherein the copolymer is a random copolymer containing from 1 to 3.5 /n by weight of ethylene.
15. A laminate as claimed in any one of claims 1 to 12, wherein component A of the second layer is a propylene-butene-l copolymer.
16. A laminate as claimed in claim 15, wherein the copolymer contains 2 to 20% by weight of butene-l.
17. A laminate as claimed in any one of claims 13 to 16, wherein component A has a melt flow index of 0.5 to 30 g/l0 minutes.
18. A laminate as claimed in claim 17, wherein the melt flow index is 1 to 20 g/10 minutes.
19. A laminate as claimed in any one of claims 1 to 18, wherein the ratio of component A to component B in the second layer is from 80/20 to 20/80 by weight.
20. A laminate as claimed in claim 19, wherein the ratio of component A to component B is 70/30 to 30/70 by weight.
21. A laminate as claimed in claim 19, wherein the ratio of component A to component B is 50/50 by weight.
22. A laminate as claimed in any one of claims 19 to 21, wherein the blend of the second layer has a crystalline melting point of about 80"C in addition to the melting points of component A and component B.
23. A laminate as claimed in any one of claims I to 22, wherein the thickness of the second layer is from 0.1 to 10 ,um.
24. A laminate as claimed in any one of claims 1 to 22, which comprises a laminate carrying the second layer on only one surface of the first layer and wherein the thickness of the second layer is from 2 to 8,us.
25. A laminate as claimed in any one of claims 1 to 22, wherein the laminate comprises a first layer having a second layer on each surface and wherein the thickness of each second layer is from 0.5 to 2 Mm.
26. A laminate as claimed in any one of claims 1 to 25, wherein the or each second layer is not molecularly oriented.
27. A laminate as claimed in claim 1, substantially as described in any one of the Examples herein.
28. A method of wrapping which employs a film laminate as claimed in any one of claims 1 to 27.