JPH0243629B2 - SATSUKINKANONANETSUKASOSEIFUIRUMU - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention generally relates to heat-shrinkable, relatively gas-impermeable thermoplastic packaging films that can themselves be heat-sealed to form bags, sachets, cases, or other containers. be. The invention particularly relates to food bags in which products are kept at elevated temperatures for extended periods of time.

HJ Brax is a heat-shrinkable thermoplastic multilayer packaging film that has had considerable commercial success for producing bags with low gas permeability.
U.S. Patent issued June 26, 1973 to et al.
3741253. One preferred film in the Bracks et al. patent consists of stretching a first or substrate layer of ethylene-vinyl acetate copolymer in an unstretched tubular form and moving it through an electron beam during a series of passes to form the copolymer. It can be produced by cross-linking molecules of The film is then expanded but not substantially stretched and passed through a tubular coating die where it receives a second layer of vinylidene chloride copolymer. This bilayer tube is then passed through another tubular die where it receives a coating of ethylene-vinyl acetate copolymer. The tube, which now has three layers of polymer layer walls, is cooled, folded, and sent into a hot water bath where it is sufficiently softened to expand in the bubbles, which are then separated into two spaced layers. The air is condensed between a pair of pinch rollers. The expansion thins the tube, like stretching it into a film, and as the bubble exits into the hot water bath, it rapidly cools in the air and begins to orient. After the air bubbles are broken, the film is then rolled up into a flat seamless tubular film which is then used to make bags such as: (1) heat sealing the width of the flat tube crosswise and sealing the tube; end-seal bags, which are typically manufactured by cutting to produce the bottom of the bag, and (2) lateral seals forming the sides and one end of the tube forming the bottom to facilitate manufacturing the bag from the tube. A side-sealed bag that can be used.

In the manufacture of such bags by compressing the flattened tubular wall together with a heated sealing rod, the residence time of the sealing rod should be as short as possible, but it does not allow the inner surface layer of the tube to form on itself. It must be sufficient to melt and bond into a smooth, continuous, strong seal. The importance of a strong and reliable seal will be easily understood when describing the use and function of the bag. This type of bag mainly contains raw meat and processed meat, and the bag is vacuumed.
A wide variety of products are prepared by combining and sealing it with a metal clip around the combined mouth of the bag, and then immersing the bag in a hot water bath at the same temperature at which the film was stretch oriented. Used for packaging raw and processed meat. Until now, this temperature has typically been between 160° and 205°.
Hot water immersion is one of the fastest and most economical means of applying sufficient heat to the film to uniformly shrink the film. however,
One of the objects of the invention is to allow the bag to retain its original appearance at high temperatures for the time normally required for shrinkage, thereby extending the time so that the product within the bag can be sterilized. be.

The problem with manufacturing side-sealed bags on some commercially available machines is that at high speeds the seals do not have time to "assemble" and the tension when transporting the tube can cause the seals to pull apart. It is a matter of being lost. For example, when a side seal bag is manufactured from a flattened tube, a lateral double seal with a perforated wire therebetween is manufactured over the tube. A double seal consists of two parallel spaced apart seals, and a series or row of holes is cut between and parallel to the two seals. One longitudinal side of the flattened tube is trimmed before or after applying the double seal to form the top or mouth of the bag. The distance between the rows of holes is the overall width of the bag.

Intermittent motion is necessary as the bag is moved back and forth on the sealing platform because of the time required to stop the tube while performing a lateral seal.
To move the bag from the sealing stand, the bag is passed around the reciprocating rollers and a tube is opened for the next bag, such as when using a side-sealing bag machine from Gloucester Engineering Company, Gloucester, Mass. Can be pulled. At high bag production speeds, if the side seals are not strong, the force to rapidly accelerate the lead bag from a complete stop and advance the next bag to the sealing platform will cause the newly manufactured side seals to be compressed while they are still warm. will be pulled apart. A prior method is to simply reduce the machine speed and bag production rate to allow the seal to cool. However, one object of the present invention is to
The objective is to provide a film with a strong seal at high bag production speeds.

In addition to end and side sealed bags, other containers such as sachets and cases can also be made from thermoplastics. Sachets can be made by placing the product between two separate sheets of film and then wrapping the sheets together, generally heat sealing around the product. The casing is manufactured from sheets of seamless tube by sealing or closing one end of the tube in a combined closure or by overlapping or heat-sealing the opposite ends of the sheets together. The assembled closure can then be used to close one end of the tube. A satisfactory and commonly used closure means is a metal clip. After filling the casing, the open end is usually closed with a clip. It is therefore an object of the present invention to provide such a film from which pouches and casings may be made which will withstand sterilization temperatures.

Another object of the present invention is to provide a film that has excellent high temperature seal strength and yields a bag that has gas permeability at least about the same as prior art films. Many food products require sterilization if they are to be hermetically packaged. Sterilization is necessary to kill harmful bacteria that grow in the absence of air. In some countries, health laws and regulations require that food products be kept at least 93 degrees Celsius in vacuum-sealed closed bags for certain products.
(200〓) temperature for 3 minutes. In other countries, the requirement is to keep food at a temperature of 82°C (180°).
Keep it for 30 minutes. It is therefore a further object of the present invention to provide a bag which retains its original seal for an extended period of time at temperatures up to the boiling point of water.

Yet another object is to provide the high temperature strength of propylene polymers and the hot water shrinkage performance of ethylene polymers in a single film. Propylene homopolymers and copolymers tend to have high melting points in excess of 300°, while ethylene polymers and copolymers have melting points near and below the boiling point of water, typically 220°
It tends to melt below.

The above objects are achieved by the present invention, which are summarized in the following sections.

(a) a formulation in which one component of the formulation is selected from the group consisting of propylene homopolymers and copolymers and the other component of the formulation is selected from the group consisting of butene-1 homopolymers and copolymers; (b) a second layer consisting of a polymer selected from the group consisting of ethylene homopolymers and copolymers; (c) a vinylidene chloride copolymer and a hydrolyzed (d) a third or low gas permeable layer comprising a polymer selected from the group consisting of ethylene-vinyl acetate copolymers; and (d) selected from the group of formulations as specified for the first layer. A multilayer, heat-shrinkable, thermoplastic packaging film that produces a heat-seal with improved sealing strength at elevated temperatures, comprising a fourth or outer surface layer consisting of the formulation, solves the above problems and solves the present invention. It has surprisingly been discovered that the object of the invention can be achieved.

In another aspect, the present invention also encompasses the above-described multilayer film in which a second layer of ethylene polymer or copolymer is crosslinked.

In yet another aspect, the invention provides (a) (1) propylene homopolymers and copolymers; and (2)
a first polymer layer comprising a formulation selected from the group consisting of butene-1 homopolymers and copolymers; and a second polymer layer comprising a polymer selected from the group consisting of ethylene homopolymers and copolymers. (b) irradiating the coextruded layers with an irradiation level of at least 2 MR, resulting in a heat seal having improved seal strength at elevated temperatures; A method of manufacturing a packaging film is also provided.

The following patents are listed and 37C.FR1.97 and
1.98 is briefly explained. Reference should be made to each patent itself for a better appreciation of the disclosure therein.

(1) U.S. Patent No. 17, 1970, issued to OA Freshhour et al.
No. 3,496,061 discloses a stacked pair of multiple layers of two polyolefin materials. In particular, bilayer films whose layers are blends of polyisobutylene and ethylene-butene copolymer, blends of polypropylene and ethylene-propylene copolymer, and blends of ethylene-butene copolymer, polyisobutene, and low density polyethylene are used. Disclosed.

(2) AJ Foglia on January 11, 1972
Another issued U.S. Patent No. 3,634,553 describes high isotactic content ethylene/butene-
A heat-shrinkable film having 10-90% of a high isotactic polypropylene resin blended with a polypropylene copolymer is disclosed.

(3) U.S. patent issued to JJ Graboski on October 2, 1979
4169910 has a strong seal and is ethylene-
A film suitable for garbage bags is disclosed that includes an outer layer that can be a vinyl acetate copolymer and a core layer that is a blend of polybutylene and polypropylene.

(4) U.S. patent issued to Stanley Lustig et al. on June 10, 1980
4207363 is a blend of propylene-ethylene copolymer, (butene-1)-ethylene and thermoplastic elastomer with up to 6% ethylene in the first outer layer and 12-24% vinyl acetate in the first core layer. the second core layer is a polyvinylidene chloride copolymer and the second outer layer has 10-14% vinyl acetate. A multilayer film primarily for packaging pieces of meat is disclosed, such as one made of ethylene vinyl acetate copolymer.

Five to six criteria are met by the film of the present invention. The film can shrink at hot water temperatures (160° to 205°), can withstand high temperatures for long periods of time to sterilize food packaged in the film, and can be sealed to produce bags at commercially acceptable rates. It was hoped that it would be possible. It has been discovered that the combination of layers in the multilayer film of the present invention meets all of these criteria. A particularly surprising feature is that the first layer, consisting of a blend of propylene-ethylene copolymer and polybutylene or (butene-1)-ethylene copolymer, is not visibly degraded or irradiated with electrons as described below. It is important not to impair its sealing properties when The first and second layers are extruded together and irradiated to cross-link the material of the second layer. Usually non-crosslinked polymers, such as propylene-ethylene copolymer (butene-1)-ethylene copolymer or polybutylene,
would have been expected to deteriorate given the dosing criteria used, but no appreciable changes in properties were detected as described above.

Perhaps the most important feature of the invention is the ability of the heat seal in the preferred film bag to withstand sterilization temperatures. For example, filling products such as processed ham,
When evacuated and hermetically closed, the seal of the side-seal bag made with the film of the preferred embodiment is 93
Sterilization for 5 minutes at ℃ (200〓) and 82℃ (180〓)
It was able to withstand sterilization for 30 minutes.

The above-mentioned closures are used for manufacturing containers, such as bags, as described above.

A preferred embodiment of the present invention can be made by a process similar to that described in connection with the Bracks et al. patent cited above, but in which the substrate is coextruded in two layers rather than in one layer. In other words, in the first stage of manufacturing a suitable film, two extruders provide one tubular coextrusion die, where the inner layer or first layer is
It is a 50-50 weight blend of propylene-ethylene copolymer with 4 weight percent ethylene and (butene-1)-ethylene copolymer with about 0.65 weight percent ethylene. In this regard, the outer or second layer is an ethylene-vinyl acetate copolymer having a vinyl acetate content of 6% and a melt flow rate of about 2.
The second layer is about twice as thick as the first layer and about 10
mils thick, while the first layer will be about 5 mils thick. This co-extruded tube has a diameter of approximately 4 1/2 inches. After cooling it is flattened and it can be used as a substrate to which another film layer is bonded, or it is led into a shielded irradiation chamber where it is passed under the beam of an electron accelerator to form a within a range, preferably about
Receive an irradiation dose of 3MR. Dosage is 10MR
Although it is possible to go up to or even higher, higher doses do not necessarily improve properties. Irradiation with electrons to cross-link molecules in polymeric materials is well known in the art. As mentioned above, it has surprisingly been found that the material of the first layer can be irradiated without visible deterioration. The irradiated film can be a substrate to which another layer is bonded, or it can be heated and stretch oriented to form a two-layer heat-shrink packaging film.

The tube is then flattened, but not stretched, and the flattened tube is then passed through a coating die where the tube is coated with a vinylidene chloride and vinyl chloride copolymer coating, making it relatively gas permeable. Apply the third layer. A preferred copolymer is a lightly plasticized copolymer of vinylidene chloride and vinyl chloride, which is a mixture of 10% suspension polymerized and 90% emulsion polymerized copolymers. The emulsion polymerized copolymer consists of about 70% vinylidene chloride and about 30% vinyl chloride, and the suspension polymerized copolymer consists of about 80% vinylidene chloride and 20% vinyl chloride. . In preferred embodiments, the vinylidene chloride copolymer layer has a thickness within the range of 3.5 mils to 4.0 mils.

After receiving the vinylidene chloride copolymer layer, the coated tube is fed into another coating die where it is coated with a fourth layer of about 6 mils of the same formulation used for the first layer. Now take the last layer. Of course, this layer and the third layer are not irradiated.

A preferred structure in this regard has the following layer arrangement: PEC = propylene-ethylene copolymer: Lexene Polymers Company, BEC = (butene-1)-ethylene copolymer: Shell Chemical Company, EVA = ethylene vinyl acetate copolymer: DuPont Chemical Company. Alathon” trademark, VDC-VC=vinylidene chloride-vinyl chloride copolymer from Dow Chemical Company.

After applying the final layer, the film is then cooled again and folded, after which it is fed into a hot water tank with about 190 ml of water, where it is passed through pinch rolls, softened by hot water, and It is expanded in a bubble and stretched to a point where the thickness is about 2 mils. Suitable thicknesses may range from 1.0 to 4.0 mils. This will be the final thickness of the multilayer film in the preferred embodiment. As the bubble leaves the hot water tank, it cools rapidly in the air, then collapses and rolls up into a flat tube. It is from this tube at this final thickness that the bag is manufactured as described above. This film has a low gas permeation rate like the preferred film described in the Blax et al. patent cited above. The important properties are summarized in the table below.

Table A Enzyme permeation rate: 30-40c.c./m2/mil/24 hours/atmospheric pressure Shrinkage temperature range: 80℃ ( ^176〓 ) ~ 96℃ (205〓) Shrinkage tension: 85℃ (185〓) Machine direction (Vertical): 245 lbs/ ⁱⁿ² Lateral: 225 lbs/ ⁱⁿ² Optical Haze, % 9 Total Transmission, % 91 Side-sealed bags from the flattened tube of the preferred embodiment Growcester Side-sealed Bag Making Machine It was possible to manufacture the bag at twice the speed of the unirradiated bag above. If the film is unirradiated, the seals tend to pull apart when attempting to increase production speed.
Also, these bags, when filled with a product such as ham, evacuated and hermetically closed, can be sealed for 5 minutes at 93°C (200°) or 30° at 82°C (180°).
It also meets the sterilization conditions of being kept for minutes.

The resin or base polymer material fed into the extruder to produce the films of the invention can be purchased from a number of suppliers, and these include, for example
Modern Plastics Encyclopadia1980~1981, 815
can be found by reviewing commercial publications such as those entitled "Resins and Molding Compounds" on pages 826-826. Previous editions of the Encyclopadie should also be considered.

The blend of propylene homopolymer or copolymer and butene-1 polymer or copolymer for the first layer, which is also the sealing surface layer, is resistant to extreme heat at high temperatures when sealed to itself to produce the bag. provides a layer that provides a strong seal. In order to properly adhere the first layer to the second layer, i.e. the shrink volume, the two layers are extruded together, thereby melt bonding the two layers. It is believed that the second layer modulates or initiates shrinkage of the film, and the first and second layers shrink affiliatively with each other. A second layer that is orientable at low temperatures, ie below the boiling point of water, will therefore shrink at relatively low temperatures. The first layer of propylene polymer is 212〓 (100℃)
It has a much higher shrinkage temperature, but when incorporated with butene-1 polymer it produces a composite which also shrinks below 212° (100°C) when properly oriented. Thus, the coextruded combination of first and second layers will exhibit shrinkage properties similar to those of ethylene-vinyl acetate copolymer when placed in a hot water bath. This, ie, that films with a significant proportion of propylene polymer will shrink below the boiling point of water, is another surprising feature of the invention. Although the first layer is necessary for its seal strength and high temperature strength, the relatively high shrinkage temperature of the propylene polymer alone is undesirable and can be overcome by the combination of the first layer formulation and by the second layer. Ru.

A 50-50 (by weight) blend ratio for the first layer polymer is preferred, but the blend can vary from 90:10 (propylene:butene) to 40:60 depending on the particular polymer used. For example, propylene polymers that are readily used and form the preferred propylene component of the first layer include propylene homopolymers and 3.0% to 4.0%
%, but the ethylene content may range from 1 to 6% or more. The properties of the propylene-ethylene copolymer can be varied somewhat by the proportion of ethylene, and this changes the ratio of the formulation. 60% butene-1 component
If it begins to exceed , the optical properties tend to be adversely affected. The butene-1 component can consist of isotactic polybutene-1 or (butene-1)-ethylene copolymers with up to 6% ethylene.

In the second or shrink layer, the vinyl acetate content may be in the range of 3% to 12% and the melt flow rate is in the range of 0.5 to 10.0, the vinyl acetate content of the ethylene-vinyl acetate copolymer The orientation temperature decreases as . Polyethylene can be used as it is also cross-linked, but ethylene-
Vinyl acetate copolymers are preferred. Although end-sealed bags can easily be produced without irradiation of this layer, this layer should be irradiated to produce side-sealed bags at high speed.

For the third layer, which is relatively gas permeable, hydrolyzed ethylene-vinyl acetate copolymer or vinylidene chloride copolymer may be used instead of vinylidene chloride copolymer to effectively reduce gas permeation.
Acrylate copolymers can be used. When using vinylidene chloride copolymers it is generally undesirable to irradiate the third layer due to its tendency to deteriorate and discolor. However, irradiation does not adversely affect the hydrolyzed ethylene-vinyl acetate copolymer. The main gas involved is oxygen, and the permeation is considered to be low, i.e. the permeation rate is
The material is relatively gas permeable when below 70 c.c./m ² /mil thickness/24 hours/atmosphere. The multilayer film of the present invention has a transmittance below this value as shown in Table A above.

In the fourth layer, the same formulation as in the first layer is preferred, but other formulations selected from the same polymers can also be selected. As mentioned above, the third and fourth layers are not irradiated.

In another embodiment, which is particularly suitable for manufacturing bags when the first and second layers are not irradiated, the polymers of the second and third layers remain the same and for the first and fourth layers 50: Use 50 formulations again. However, it is preferred that the thicknesses of the layers before stretching are approximately as follows: first layer: 9-11 mils; second layer: 2-3 mils; third layer: 3-4 mils; Fourth layer, 3-6 mil. When stretched, the final thickness will be about 2 mils. End-sealed bags and side-sealed bags made from this film meet the above sterilization conditions. Also, using the thicknesses listed immediately above, films and bags that meet sterilization conditions will contain a 70:30 ratio of propylene-ethylene copolymer (butene-ethylene copolymer) to
1) - Manufactured using first and fourth layers consisting of ethylene copolymer.

Claims (1)

Claims: 1. (a) one component of the formulation is selected from the group consisting of propylene homopolymers and copolymers and the other component of the formulation consists of butene-1 homopolymers and copolymers; (b) a second layer consisting of a polymer selected from the group consisting of ethylene homopolymers and copolymers; (c) vinylidene chloride; and (d) a formulation as specified for the first layer. a fourth or outer surface layer consisting of said formulation selected from the group of products, wherein said multilayer, heat-shrinkable, thermoplastic packaging film produces a heat seal with improved sealing strength at elevated temperatures. . 2 The formulation for the first and fourth layers is 1.5% to 4.0%
90-40% by weight of propylene-ethylene copolymer with ethylene and butene-1 homopolymer or
Contains up to 6.0% ethylene (butene-1)
- A film according to claim 1, comprising a blend of 10 to 60% by weight of ethylene copolymer. 3. The second layer consists of an ethylene-vinyl acetate copolymer with a vinyl acetate content of 3 to 12% by weight,
A film according to claim 1. 4. The film according to claim 1, wherein the second layer is made of polyethylene. 5. Claim 3, wherein the second layer comprises an ethylene-vinyl acetate copolymer and the first and second layers are irradiated to an irradiation level of at least 2MR.
Film mentioned in section. 6 Approximately 6% by weight of ethylene-vinyl acetate copolymer
4. The film of claim 3, wherein the copolymer is cross-linked to an irradiation level in the range of 2 to 6 MR. 7 the film is stretch oriented and 1.0
7. The film of claim 6 having a thickness in the range of -4.0 mils.