JPS61154826A - Manufacture of heat-sealing, heat-shrinkable and biaxial oriented polyester film - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a heat shrinking film, a heat sealing film, a biaxially oriented polyester film, and a method for producing the same.

According to the present invention, the relative viscosity (at 1% concentration 1 faoc in 60/40 tetrachloroethane/phenol) is at least 1.80 and the substantially balanced potential shrinkage is about 31-47% at 100t:' , and the average contraction force is approximately 1.000 p a i (
70Kr/cyA) or less, a melting point of about 215C or more, and a haze of about 5% or less, a heat-sealable, heat-shrinkable, modified polyethylene terephthalate film as defined herein; A biaxially oriented polyester film is provided.

Preferred films of the invention overlap around articles, are easily heat-sealable to themselves, and are
Capable of rapidly shrinking at shrink tunnel temperatures of 0-475F (104-246C) to form a skin-like contact with the article while retaining seal integrity, the film's clarity is particularly remarkable and the film maintains its luster and luster. The film was found to have high usable shrinkage (up to about 40%), retains its properties, does not sag upon aging, and provides commercial value for most products.

This film is tough, durable and strong and can withstand rough handling. This film exhibits tear resistance. This film has a deflection at one time as low as -80'F (-62r:>sr), and aooy(x5oC
) It carries its strength in the above. This film has excellent mechanical properties and is an excellent barrier against moisture.

The wide range of usable shrink tunnel temperatures means that thermal excursions or accidental line blockages can reduce the
There are fewer problems caused by burn-through.

During shrinkage, the excess film caused by the irregular shape is pulled evenly, forming [doσ-ears]
) J is pulled in an orderly manner. The film accommodates uneven surfaces and protrusions, and can even accommodate sharp objects.

Although such films can be used with products of virtually any size and shape, they are particularly suitable for products that undergo burn-through in processing or that have unusual shapes.

FIG. 1d is a schematic diagram of an apparatus for producing a biaxially stretched film of the present invention. The apparatus includes an extruder for casting a molten web of polymeric material onto a quench roll to form a film, a means for stripping the formed film from the quench roll, and a slow nip roll and a fast nip roll. and a machine direction aging means with a radiant heater located therebetween, and a tenter for aging the film in the transverse direction.

Figures 2, 3, and 4 are graphs showing the improvement in heat seal strength obtained by using a film of a polymer with a relative viscosity of 1.80 or higher; It is shown that there is not only improved reliability, but also improved reliability as expressed by improved number of seals, stress-flex resistance or durability. Stress-Flex is “A New 5tress Frew Te5ter”
”, Modern Packing, March 1961, p. 123.

The method for producing the heat-sealable, heat-shrinkable, biaxially oriented polyester film of the present invention involves the following steps:
forming a polymer consisting of monomer units selected from a glycol and/or a second acid, and casting a molten web of the polymer onto a cooled quench surface to cool it below its glass transition temperature. This film is peeled off from the quenched surface, and the film is first rolled in a nip roll timer in a weaving direction of approximately 2.5 to
3.6 times, and then the film was stretched in a tenter in the transverse direction by about 2.9 times.
It consists of extending the time by ~4.0 times.

The film of the present invention is a modified polyethylene terephthalate film containing primarily repeating ethylene terephthalate single carrier units of the formula and other single conductor positions selected from other ester-forming components. Thus, up to about 25 mole percent of the copolymer may contain diethylene glycol, propane-1,3-diol, polyethylene glycol, or polypropylene glycol, and/or azelaic acid, inphthalic acid,
Bibenzoic acid, naphthalene 1,4- or 2,6-dicarboxylic acid, adipic acid, sebacic acid, decane-1,10
- composed of single monomer positions such as dicarboxylic acids, the most preferred being diethylene glycol and azelaic acid. According to the preferred polycondensation method of the present invention, they can be prepared by copolymerization at elevated temperatures, for example 220-300C, to increase the reaction rate. Additionally, this reaction is usually carried out in the presence of a suitable catalyst and under reduced pressure to facilitate removal of the ethylene glycol produced during the condensation.

Polyethylene terephthalate films are widely used in packaging. Automatic packaging equipment
It is difficult to form films that exhibit adequate shrinkage where the shrinkage force does not exceed the seal strength. Conventional methods of forming such films have resulted in films with poor optical properties and other drawbacks such as narrow heat shrinkage temperature ranges. If the heat shrinkage temperature range is narrow, the film will be 1!1! requires elaborate and expensive equipment. All of these properties are satisfied by the preferred films of the present invention.

By forming the film from a polymer having a relative viscosity of at least 1.80, average seal strengths as low as 1000 g/in (400 g/cs+) can be achieved; such seal strengths are 2° It is rarely less than 800 g/am. Since the seal strength is this great, it is necessary to split the seal and shrink the film in a shrink tube to apply it to the article. can be brought into contact.

This ability to maintain seal integrity during the shrinkage operation is further enhanced by (1) a substantially balanced shrinkage potential, i.e., a difference in shrinkage between the machine direction and the transverse direction of 10% (preferably 5%);
%) and (2) low contraction force; IJII shrinking the film around the article in the shrink tunnel places unusual, often non-uniform forces on the seal that tend to destroy the effectiveness of the seal. Required relative viscosity, substantially balanced 100
Potential shrinkage of approximately 31-47% at °C and 100 °C
Approximately 1,000 psi (70 kg/am2
) by applying a low contraction force of at least 1
A seal with a strength of 400 g/cwt will withstand the rigors of the shrink package manufacturing process.

Balanced latent shrinkage is important in removing uneven wrinkles, and this is important when removing radial wrinkles that originate from the corners of angular articles located and packaged on cardboard. A certain desired relative viscosity can be obtained by known methods, such as those described in US Pat.
Cd US time lfFMS3-187. -0'/5 and obtaining a balanced potential contraction is R1
ehards, US Pat. No. 2,928,132. The contractile force is mainly due to the spread ratio, the spread l! It is a function of temperature and relaxation.

The melting point of the film of the present invention should be about 215-230C, and should be at least about 215C to prevent sticking and minimize bar 7 through, and form the desired average shrinkage. It should not exceed substantially 230C to prevent distortion during shrinkage and preserve the optical properties of the package.

Inflection of a substantially pure polyethylene terephthalate polymer to lower its melting point is described in Hull, US Pat. No. 3,554,976, the disclosure of which is incorporated herein by reference. Figures 2 and 4 of this US patent show the decrease in melting point of polyethylene terephthalate as a function of molten and weight percent of dihydroxyethyl azelate loaded, respectively. In practice, this additive is introduced on the basis of the treated layer of polymer.

WeLdatron L-8eα1 is a film with a relative viscosity of less than 1.80.
When forming a heat seal using a hot wire sealer such as
1,0002/inch (400r/Q'16
) was found to be smaller than the minimum mean of When the relative viscosity is 1.80 or more, the reliability of bonding is excellent.

Further shown in Figure 1, the strength of a heat seal generally increases with increasing relative viscosity of the film's polymer, while seals of films of lower viscosity sometimes exhibit higher strength and vice versa. Seals with high viscosity JW films exhibit unexpected weakness, but statistically the higher the viscosity, the higher the percentage of satisfactory seals (preferably) (>goot/ wet).

Additionally, tackiness appears to be a determinant of seal durability, ie, how well heat-sealed and shrink-wrapped packages withstand use and handling. The stress-flex test of FIG. 4 shows that the fracture resistance of the heat seal increases as the viscosity increases above about 1.80.

Another common drawback of shrink films is that they tend to form a pattern of optical distortion due to shrinkage. This distortion manifests as thick ridges with sharp, well-defined boundaries of high birefringence on the package. This drawback is believed to be caused by the non-uniform application of the shrink force on a partially constrained film. Attempts to eliminate this drawback by adjusting the variables of stiffness, spread ratio, drawing temperature, slip, and heat set have been
Successful only when contraction was too low. however,
Unexpectedly, films of low melting point polymers do not exhibit this drawback. This drawback is not present in the preferred films of the invention, which have melting points below 230C, but the melting point must be above 215C to prevent the film from becoming sticky or rubbery during processing.

Shrink packages are typically formed by heating within a shrink tunnel that supplies forced hot air. By changing the pupil closure and processing speed, the heating temperature of the film can be changed. When this temperature is below the film's full shrinkage temperature, the package is loose and wrinkles are present. On the other hand, if the temperature that the film is exposed to is too high, the heat seal will break and
and the film will not tear or form small holes @ Therefore, the film of the present invention has as wide a practical shrinkage temperature range (FETE) as possible and can easily stay between the upper and lower limits of operation. It is desirable to do so.

PS'l' wide enough for reliable control
To obtain R, the film of the present invention must have an average balanced latent shrinkage at 100C of 31-47% (above this range, seal distortion and /'
! or tearing occurs).

゛And the shrinkage tunnel temperature of this film is about 200 ~
350'p (93-177C).

The overall properties of the package are: heat seal retention during shrinkage;
Depends on it. The extent of seal failure is a function of contraction force.

Although this failure is normal at contraction forces of 1,300 pgi (92 to 9/d).

It was found to be rare at 825-1,000 psi (58-70~/6It).

Regarding optical properties, maximum cloudy fishing is 5, minimum transparency is approximately 7
Minimum gloss 15 at 2 and 20U and 30C
0 and 115 are desirable but not essential in the final film. The ASTM tests used are listed below.

Generally, the polymers used to make the films of this invention can be prepared in the desired proportions by any conventional method capable of producing homogeneous compositions. The resulting polymer can be extruded from the melt into flat or tubular films by conventional methods known in the art. In order to obtain the desired heat shrink properties, the film is stretched and oriented in mutually perpendicular directions ζ. The stretching temperature for this film will vary based on the particular polymer used to make the film. After stretching, heat setting and relaxation, the film is cooled under tension while maintaining the sheet in a substantially expanded dimension. The equipment used for this stretching is of the type commonly used in the art, such as those manufactured by Goldman and W.
Allenfes, US Pat. No. 3,141,912, the disclosure of which is incorporated herein by reference.

Other equipment that can be used (with minor modifications) to stretch films is shown in US Pat. No. 2,823,421 to Carlett. As seen in this patent, essentially two
Such films are stretched in the machine direction and then in the transverse direction in an apparatus consisting of two parts, a stretching zone in the machine or machine direction and a stretching zone in the transverse direction. The longitudinal stretching zone consists of horizontal rolls arranged in parallel alignment in different vertical and horizontal planes. 10th-
One roll is a "slow roll" that is actively driven, the next roll is a closely spaced idler roll that is not actively driven, and the next roll is a "fast roll" that is actively driven. Actual stretching is performed at a distance between rolls including the idler roll.

The lateral section of the IEI' device is essentially divided into four sections, all of which consist of a tenter with a series of tenter clips on each side of the film. As the film exits the machine direction stretching zone, it is directed between parallel rows of tenter clips, which grip the edges of the machine direction stretched film and direct the film outward in a direction. Stretch towards. After stretching, the film is lightly heat set and relaxed. The thickened edges of the film formed during this mechanical operation provide an excellent and unique gripping means for the tenter clip. These spoiled beads or beads are then cut from the film and sent to a collection area.

Referring to FIG. 1, there is shown an apparatus 10 for carrying out the method of the present invention, which dispenses a web W of film, such as the improved polyethylene terephthalate film of the present invention, and imparts desired physical properties to the film. to give a certain characteristic.

The web W of material to be drawn by the device 10 is supplied from a source 11
a first set of nip rolls 13 and 14 and non-contact heating means 15;
passing through the expansion means 12 and then a second in the form of a tenter furnace 17;
It goes to the rolling means 16 and from there to the winding roll 18.

Source 11 may be any suitable source, such as a web of amorphous film or a feed roll tear as the film exits a polyethylene terephthalate processing line. Regarding polyethylene terephthalate film, the polymer is melt-extruded from a slit orifice of a hopper 22 and cast onto a rotating quenching drum 23 which is internally cooled and maintained at about 30C to form a substantially non-polymerized polyethylene terephthalate film. Produces a crystalline, self-supporting film. . Electrostatic pinning means 24 may be used if desired to accelerate the quenching process.

Next, the web W is stripped off from the drum, and passed on the stripper roll 25 for 4 m, and then passed on the tension separation roll 26.
and then the first drawing zone or means 12
The film is then sent to the machine, where it is first stretched in the machine direction and uniaxially oriented. From this first stretching means 12, the web W passes between tenter oven preheating rolls 27 to a second stretching means in zone 16, where the film is further heated by a tenter oven heater 28 and a second It is stretched in the horizontal direction and is biaxially oriented. To control shrinkage, the web W is 65
After being lightly heat set at ~100C and slightly relaxed (up to 5%), it is wound onto a take-up roll 18.

The first (7) nip rolls 13 (so-called "slow rolls") consist of an upper nip roll and a lower nip roll, driven by suitable means (not shown) at a first speed, and a second set of nip rolls. 14 (so-called "fast roll") consists of an upper nip roll and a lower nip roll, and is driven at a second speed faster than the first speed,
A stretching force is thereby applied to the web W. Slow roll 13 is heated.

Heating means 15 in the form of indirect or non-contact separate heating means such as electric radiant heaters spaced above and below the web W
When the web W passes through, the web is heated to a drawing temperature somewhat higher than its glass transition temperature W. By heating the web, the web becomes more ductile and deformable or time resistant, with substantially all the stretching occurring after the knife heating, i.e. in the short distance between the heating means 15 and the set of fast nip rolls 14. . With this reduced distance, the web W can be effectively stretched and oriented. The web W is stretched by slow nip roll set 13 and fast nip roll set 14.
The degree of longitudinal stretching f is determined by the difference in nominal speed of such rolls by methods known in the art.

The web W is approximately 60 to 8 by contact with the slow roll 13.
It is heated to a temperature of 0C, and further heated to a drawing temperature of about 65 to 85'C by an indirect, instant heating means 15. Stretching occurs primarily over a short distance between the indirect heating means 15 and the fast rolls 14.

The film .' is first stretched in the longitudinal direction by the first stretching means at a stretching ratio of 2.5 to 3.6 times.

A time delay device (P
can be found in U.S. Patent Application No. 110,683 to Eet et al.

After the film is uniaxially stabilized under these critical conditions by a 71.11$L heating means, the film is heated to approximately 50-80C by a tenter preheating roll 27 and then passed through the tenter 17. The film is fJ5 in tenter 17.
When heated to 0-85C, 2.
Biaxial orientation is achieved by elongation at a smoking ratio of 9 to 4.0 times.

Preferably, step 1 is to heat the double-rolled film to 65-100C in a re-rolling tenter and simultaneously relax the film to 5.0% of its rolled width.

12.4% of the ethylene glycol component was replaced with diethylene glycol, and 1.16% of the dihydroxyethyl terephthalate component was added during the polymerization of 500 ppm of the dihydroxyethyl terephthalate component with the dihydrogen glycol component. Polyethylene terephthalate containing phosphonates was prepared as described in Owens et al. U.S. Pat.
, 223, 757, the edges of the film were electrostatically fixed while being cast from a slot die onto a quenching drum that had been cooled to 19C with a fluid circulating inside the drum. This modified poly(ethylene terephthalate) has four crystal points with two
It was 29C.

Speed 123 feet/min (35 m 7 min) and angle approx. 2
The formed substantially amorphous film was stripped from the quench drum after it was brought into contact with the drum surface at 70° and the 1' island was below the glass transition temperature of the straight rhinoceros. The film was immediately fed into the nip rolls of a machine direction nip roll timer with a slow nip roll and a fast nip roll spaced apart.

This film was slow nip rolled to 72C.

It is then further heated to 74C by a radiant heater in the free distance between the slow nip roll and the fast nip roll to approximately 500,000% to 3.4 times the original length at the free distance of 2 inches (5 (jab)). The processed film was then passed over a preheated roll held at 72C and sent to a tenter, where it was stretched 3.4 times in the transverse direction at 74C at a speed of 4,000%/min. At the completion of this rolling, the film was heat set in the extension of an instant tenter at about 81-82C and under 2% relaxation.

The properties of the heat sealability, heat shrinkability, and biaxially processed film thus formed are summarized in the table below.

Nominal thickness gauge) Tensile strength (vertical) Tensile strength (horizontal) Fracture groan (vertical) Fracture groan (horizontal) Modulus (vertical) Modulus (horizontal) Transparency 20' Gloss Slip angle Relative viscosity table 0.5 mil (13 microns) 34.500psi (2400Kg10+35.20
0ps i (2430Ky/cA) 107% 124chi 417.000p&7 (29,400Kg/cw mouth 44
3.000 ps i (31,200 positions/cJ)80.
4 2.8% 35° 1.85 Melting point Ty (glass transition temperature) Shrinkage temperature (in 100 tons of water) Vertical horizontal contraction force (vertical) Shrinkage force (horizontal) Practical contraction temperature node (average seal strength) (vertical) (horizontal) *Results are based on the test described below 29C 8r 36.5 39.0 947 p si (67Kg/cd) 849ps
i (63Kf/cJ) 100F, (55C,) 2510F/inch (104 (1/biased) 2335f/inch (93!M'/positive)
ASTM D882 horizontal average) Stiffness modulus (vertical ASTM Dssz and horizontal average) Moan (vertical and horizontal ASTM D882 average) Tear strength (vertical and horizontal average) M V T RA S T Af E 96 Operation E Oxygen Transparency JASTM D143
4 Coefficient of friction (F/L/M vs. ASTM D1
894 film) Transparency ASTM-17
46-6psi (h/y) 30
,000 (2120)'I)8 j (Kq/m)
soo, ooo (3520)%
100t
15f / 100 square inches (t / 645c4) inch / 24 hours CC / 100 square inches / 24 hours / atmospheric pressure 9 (
c c/645crl/24 hours/atmospheric pressure) 0.4 7 T
79.0 Embodiments of the invention are as follows.

(1) Relative viscosity (at 30C at 1% salinity in 60/40 tetrachloroethane/phenol) of at least 1
．． 80 and a substantially balanced potential contraction of 1ooC
It is about 31-47% in , and the average contraction force is 100C
A modified polyethylene terephthalate film as defined herein having a temperature of about 1,000 psi (70Kr/c) or less, a melting point of about 215C or more, and a haze of less than 5%. Heat-sealable, heat-shrinkable, biaxially processed polyester film 0 (2) The film shall be heat-sealed to itself to have an average seal strength of at least 1,000 f/in
0? /rn) The film according to item 1 above, which is capable of forming a seal.

(3) The film has an average seal strength of at least 2,00 1/in.
800r/I'm)
Film by term.

(4) The film according to item 1 above, having a melting point of up to 230C.

(5) The film overlaps the article and can be heat-sealed to itself, and further
F (A film made of any one of the above items 1 to 4, which is capable of shrinking at a tunnel temperature of 140 to 246 tl, forming a skin-like contact with an article to form a shrink package, and at the same time maintaining seal bonding properties.

(6) A film according to item 5 above that can be used for shrink tunnel temperatures of 250-350F (104-177C) while retaining seal bonding properties.

[Brief explanation of the drawing]

, -pJ1 is a schematic diagram of an apparatus for manufacturing the biaxially stretched film of the present invention. Figures 2, 3 and 4 are graphs showing the improvement in heat seal strength obtained by using a film of a polymer having a relative viscosity of 1.80 or higher. 10... Rolling device 11... Supply source 12... First stretching means 16... Second stretching means 18... Winding roll W,... Web FIG, 1

Claims (1)

Claims: Up to 25 mole % modified with monomer units selected from at least one ester-forming component and a relative viscosity of at least 1.80 (1% in 60/40 tetrachloroethane/phenol) concentration at 30°C), 30%
A polyester film having a latent shrinkage at 100°C greater than 5% and a haze of less than 5%, the polyester film mainly comprising ethylene terephthalate monomer units of the formula ▲ mathematical formula, chemical formula, table, etc. ▼ other esters. A modified polyethylene terephthalate film comprising together with other monomer units selected from the forming components, up to 25 mol% of the copolymer comprising diethylene glycol, propane-1,3-diol, polyethylene glycol or polypropylene glycol and/or or azelaic acid, isophthalic acid, bibenzoic acid, naphthalene-1,4-
or is made from monomer units of 2,6-dicarboxylic acid, adipic acid, sebacic acid or decane-1,10-dicarboxylic acid, and the polyester film has a melting point of 215-230°C, 31-47°C. % shrinkage potential at 100°C, provided that the difference in shrinkage between the machine direction and the transverse direction is not greater than 10%, an average shrinkage force at 100°C of not more than 70 kg/cm^2 and at least 400
A heat-sealing property characterized by having an average sealing strength when heat-sealed to itself of g/cm;
A process for producing a heat-shrinkable, biaxially oriented polyester film having a relative viscosity (at 30°C at 1% concentration in 60/40 tetrachloroethane/phenol) of at least 1.80 and a melting point of 215-230°C, and diethylene glycol, propane-1,3-diol, polyethylene glycol, polypropylene glycol and/or azelaic acid, isophthalic acid, bibenzoic acid, naphthalene-1,4- or 2,6-dicarboxylic acid, adipic acid, sebacic acid or decane- Casting a molten web from modified polyethylene terephthalate comprising ethylene terephthalate monomer units with up to 25 mole percent of monomer units made from 1,10-dicarboxylic acid, and lowering the molten web below its glass transition temperature. A film is formed by cooling and the film is passed in the machine direction 2.
Stretched 5 to 3.6 times, then 2.9 to 4.0 times in the transverse direction
A method consisting of stretching to double.