JPS5811147A - Bastericidal thermoplastic film and vessel made of said 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 generally relates to a heat-shrinkable, relatively gas-impermeable thermoplastic packaging film that can itself be heat-sealed to produce 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.

A heat-shrinkable thermoplastic multilayer packaging film that has had considerable commercial success for producing bags with low gas permeability has been described by H. J. Bray et al.
U.S. Patent No. 3.741., issued June 26, 973.
It is written in 253. A preferred film in the Bracks et al. patent consists of stretching a first or substrate layer of ethylene 6-vinyl acetate copolymer in an unstretched tubular form and moving it through an electron beam during a series of passes. It can be produced by cross-linking copolymer molecules. 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. Cooling the tube, which now has three polymer layer walls,
It is folded and sent to a hot water bath where the tube is sufficiently softened to expand in bubbles which are condensed between a pair of spaced pinch rollers. The expansion thins the tube, as if it were stretched into a film, and as the bubble leaves 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 and sealing the tube crosswise; 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 is mainly used to put raw meat and processed meat into the bag, vacuum the bag, put it together, put a metal clip around the gathered mouth of the bag to seal it, and then put the bag in hot water. It is used to package a wide variety of raw and processed meats by immersion in a bath at the same temperature at which the film was stretched and oriented. This temperature has heretofore been typically carried out between 160° and below 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 present invention is to allow the bag to retain its original form 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. For example, when a side-seal bag is manufactured from a flattened tube, a lateral double seal with a perforated wire in between is manufactured over the tube. The seal consists of two parallel spaced apart seals, and between the two seals a series or row of holes is cut parallel to them. One side 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 platform, the bag is passed through the station of reciprocating rollers for the next bag, such as with the side-seal bag machine of Gloucester Engineering Company, Crowcester, Massachusetts. You can pull the tube. Side-10- At high bag production speeds, if the side seals are not strong, the force to rapidly accelerate the first bag from a complete stop and advance the next bag into the sealing platform will cause the newly manufactured side seals to overwhelm them. will be pulled apart while it is still warm. A prior method is to simply reduce the machine speed and bag production rate to allow the seal to cool. However, one objective of the present invention 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 produced by manufacturing the tube from a sheet by sealing or closing one end of the limb from a seamless tube in a combined closure or by overlapping or heat sealing the opposite ends of the sheets together. A bundled closure can be produced by using it 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 lip. It is therefore an object of the present invention to provide such a film from which pouches and casings may be made that 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, for certain products, health laws and regulations require food products to be placed in vacuum-sealed closed bags at least 93°C (20°C).
0) for 3 minutes. In other countries the condition is to keep the food product at a temperature of 82°C (180T) for 30 minutes. It is therefore a further object of the present invention to provide a bag which maintains the original seal at temperatures up to the boiling point of water for extended periods of time.

Yet another objective 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 are 3
They tend to have high melting points in excess of 00''F, while ethylene polymers and copolymers tend to melt near and below the boiling point of water, generally below 220T.

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

13- a) 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 a third or low gas permeable layer consisting of a polymer selected from the group consisting of ethylene-vinyl acetate copolymers; and d) said formulation selected from the group of formulations as specified for the first layer. The above problems could be solved by a multilayer, heat-shrinkable, thermoplastic packaging film that produces a heat seal with improved sealing strength at elevated temperatures, consisting of a fourth or outer surface layer consisting of It has surprisingly been discovered that the objects of the invention can be achieved by:

In another aspect, the present invention also encompasses a multilayer film as described above 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;
2) a first polymer layer consisting of a formulation selected from the group consisting of butene-1 homopolymers and copolymers and a second polymer layer consisting of a formulation selected from the group consisting of ethylene homopolymers and copolymers. a) coextruding polymer layers; b) irradiating the coextruded layers with an irradiation level of at least 2 MH; producing a heat seal with improved seal strength at elevated temperatures; A method of making a plastic packaging film is also provided.

The following patents are listed and 37 C, F, R.

1.97 and 1698. Reference should be made to each patent itself for a better appreciation of the disclosure therein.

1) 0 on February 17, 1970. A. Freshore (Fr
U.S. Pat. In particular, the layers are made of polyisobutylene and ethylene.
Blends of butene copolymers, polypropylene and ethylene
Bilayer films are disclosed that are blends of propylene copolymers and blends of ethylene-butene copolymers with polyisobutyne and low density polyethylene.

2) On January 11, 1972, A. J. Foglia (F.
U.S. Patent No. 3.654°555 issued to
has a high isotactic content of ethylene from 10 to 90
A heat-shrinkable film having 10-90% high isotactic polypropylene resin blended with a butene-1 copolymer is disclosed.

5) On October 2, 1979, J. J. Grabosky (
U.S. Patent No. 4 issued to
No. 169.910 discloses a film suitable for garbage bags having a strong seal and comprising an outer layer which can be an ethylene-vinyl acetate copolymer and a core layer which is a blend of polybutylene and polypropylene. ing.

4) On June 10, 1980, Stanley Lusteig (
U.S. Pat. The first core layer comprises an extrudable adhesive which can be an ethylene-vinyl acetate-17-copolymer having 12 to 24 units of vinyl acetate, and the second core layer comprises a polyvinylidene chloride copolymer. and
It also discloses a multilayer film primarily for packaging pieces of meat, in which the second outer layer consists of an ethylene-vinyl acetate copolymer having 10 to 14 inches of vinyl acetate.

Five to six criteria are met by the film of the invention. The film can be shrunk at hydrothermal temperatures (160° to below 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 wanted. 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 -18- as described below. It should not lose its sealing properties when irradiated with electrons. The first and second layers are extruded together and irradiated to crosslink the materials of the second layer. Typically, non-crosslinked polymers, such as propylene-ethylene copolymers, (butene-1)-ethylene copolymers or polybutylene, would be expected to degrade at the dosage standards used, but as discussed above, No appreciable changes in properties were detected.

Perhaps the most important feature of the invention is the ability of the heat seal in the preferred film bag to withstand sterilization temperatures. When filled with a product, such as a processed ham, evacuated and hermetically closed, the seal of the side-seal bag made with the film of the preferred embodiment is sterilized for 5 minutes at 96°C (200″F) and 82°C. It was able to withstand 30 minutes of sterilization at °C (180?).

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

A preferred embodiment of the invention can be made by a method similar to that described in connection with the Brax et al. patent cited above, but in which the substrates are extruded together in two layers rather than in one layer. In other words, in the first stage of manufacturing the preferred film, two extruders provide one tubular coextrusion die, where the inner or first layer is propylene-propylene with 6-4% by weight of ethylene.
A 50-50 weight blend of ethylene copolymer 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;
The first layer, on the other hand, will be about 5 mils thick. This co-extruded tube has a diameter of approximately 4% 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 and exposed to 2
An irradiation dose in the range of ~6 Megaland, preferably about 3 MR is received. Dosages can be increased up to the IOMR or even higher, but higher doses do not necessarily improve properties. Irradiation with additional 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-shrinkable packaging film.

The tube is then flattened, but not stretched, and then passed through a coating die where the tube is coated with a copolymer of vinylidene chloride and vinyl chloride, thereby making it relatively smooth. Apply a gas permeable layer or third layer. A preferred copolymer is a lightly plasticized copolymer of vinylidene chloride and vinyl chloride, which
It is a mixture of 0% 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 a preferred embodiment, 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 or final layer of approximately 6 mils of the same formulation used for the first layer. layer 22-. Of course, this layer and the third layer are not irradiated.

A preferred structure in this regard has the following layer arrangement: PEC=
7'Robireso ethylene copolymer: Lexene Borimers Company, BEC = (Budeso 1)-ethylene copolymer Niziel Chemical Company, EVA = ethylene vinyl acetate copolymer: “Alathon” from DuPont Chemical Company "Trademark, VDC-VC=vinylidene chloride-vinyl chloride copolymer from The Dow Chemical Company.

After applying the final layer, the film is then cooled again and folded, after which it is approximately 190? of water into a hot water tank where it passes through pinch rolls and
It is softened with hot water and expanded in bubbles and stretched to a point where it is about 2 mils thick. A suitable thickness would be in the range of 1.0 to 4.0 mils. This will be the final thickness of the multilayer film of 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 Brax et al. patent cited above. The important properties are summarized in the table below.

Table A Enzyme permeation rate = 30-4 ocr = /rt/mil/2
4 hours/pressure contraction temperature range 2 80℃ (176T) ~ 9
6°C (205 bottom) Shrinkage tension = 85°C (185”F) Machine direction (longitudinal): 245 Bond/inch 2 Lateral direction =
225 Bonds/inch 2 Optical Haze, CH 9 Total Transmission, CH 91 From the flattened tube of the preferred embodiment, side-sealed bags were produced on a Gloucester side-sealed bag making machine at twice the speed of unirradiated bags. It could be manufactured with. If the film is unirradiated, the seals tend to pull apart when attempting to increase manufacturing speed.

These bags can also be filled with products such as ham,
When evacuated and hermetically closed, the sealed area will reach a temperature of 93°C (2
It also meets the sterilization conditions of being kept at 82°C (180T) for 5 minutes or at 82°C (180T) for 30 minutes.

The resin or base polymer material fed into the extruder 25 to produce the films of the invention can be purchased from a number of suppliers, and these include, for example, Modern
Plastics Encyclopadia 198
0 A+1981, pages 815-826, entitled "Resins and Molding Compounds".
Previous versions of opadie should also be considered.

The first layer phase, which is also the sealing surface layer, is a blend of propylene homopolymer or copolymer and butene-1 polymer or copolymer, which when sealed to itself to produce the bag, has high temperature resistance. A layer that provides a strong seal. In order to properly adhere the first layer to the second or shrink layer, 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 that the second and second layers shrink affiliatively with each other.
− Do. A second layer that is orientable at low temperatures, ie below the boiling point of water, will therefore shrink at relatively low temperatures.

First layer propylene polymer G; t2121F (10oC
), but when blended with butene-1 polymers produces a composite that also shrinks below 212"F (100C) when properly oriented. The coextruded combination of and second layer will exhibit shrinkage properties similar to those of the ethylene-vinyl acetate copolymer when placed in a hot water bath.

This, i.e. that a film with a significant proportion of propylene polymer will shrink below the boiling point of water;
are other surprising features 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.

For the first layer polymer, a 5O-50 (by weight) blending ratio is preferred, but the blend may vary depending on the specific polymer used.
:10 (propylene:butene) to 4°:60. For example, propylene polymers that are readily used and form the preferred propylene component of the first layer include propylene homopolymers and propylene-ethylene copolymers having an ethylene content within the range of 3.0% to 4.0%. Although it is a polymer, 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. If the butene-1 content begins to exceed 60%, optical properties tend to be adversely affected. Butene-1 component is isotactic polybutene-1
or (butene-1)-ethylene copolymers with up to 6% ethylene.

In the second layer or shrinkage layer, the vinyl acetate content is 3% ~
12% and the melt flow rate is α5~1
0.0, and as the vinyl acetate content of the ethylene-vinyl acetate copolymer increases, the orientation temperature decreases. Ethylene-vinyl acetate copolymers are preferred, although polyethylene can also be used because of its cross-linking properties.

Although end-sealed bags can be easily manufactured 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 is substituted for the 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 29-ethylene-vinyl acetate copolymer.

The main gas involved is oxygen, and the permeation is considered to be low, i.e. the permeation rate is 70CL/rrf/
The material is relatively gas permeable when it is below mil thickness/24 hours/atmospheric pressure. The multilayer film of the present invention is
K has a transmittance lower than this value as shown.

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 fourth and fourth layers 50: 50 formulations are used again. However, it is preferred that the thickness of the layers before stretching is approximately as follows: First layer: 9
~11 mil; 30- Second layer: 2-6 mil; Third layer = 3-4 mil, and 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 requirements.

Also, using the thicknesses listed immediately above, films and bags that meet sterilization conditions can be made of a 70:30 ratio of propylene-ethylene copolymer to (Pudeso 1)-ethylene copolymer. - and a fourth layer.

Patent applicant W.R. Brace &
Company 1's1- 2571

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; A first or surface sealing layer comprising said formulation selected from the group. b) a second layer consisting of a polymer selected from the group consisting of ethylene homopolymers and copolymers; C) selected from the group consisting of vinylidene chloride copolymers and hydrolyzed ethylene-vinyl acetate copolymers. and d) a fourth or outer surface layer consisting of a formulation selected from the group of formulations as specified for the first layer. A multilayer, heat-shrinkable, thermoplastic packaging film that produces a heat seal at elevated temperatures with improved seal strength. 2. Propylene-ethylene copolymer 90 in which the formulation for the third and fourth layers has 1.5% to 4.0% ethylene.
Claim 1 consisting of a blend of ~40% by weight and 10-60% by weight of a butene-1 homopolymer or a (butene-1)-ethylene copolymer with up to 6.0% by weight of ethylene. The film mentioned. 5. The film according to claim 1, wherein the second layer is made of an ethylene-vinyl acetate copolymer having a vinyl acetate content of 3 to 12% by weight. 4. The film according to claim 1, wherein the second layer is made of polyethylene. 5. The film of 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 2 MR. 6. The ethylene-vinyl acetate copolymer contains about 6 parts by weight of vinyl acetate, and the copolymer contains 2 to 6 MH
4. A film according to claim 3, wherein the film is cross-linked to correspond to an irradiation level within the range of . l the film is stretch oriented and has a 1,0 to 4
．． Claim 6 having a thickness in the range of 0 mils.
The film described in section. aa) (1) Propylene homopolymers and copolymers and (
2) a first polymer layer consisting of a formulation selected from the group consisting of butene-1 homopolymers and copolymers and a second polymer layer consisting of a formulation selected from the group consisting of ethylene copolymers and copolymers. a) coextruding polymer layers; b) irradiating the coextruded layers with an irradiance level of at least 2 MR; A method for producing a plastic packaging film. 9. The method of claim 8, comprising the step of stretching to orient the multilayer film. 10. The method of claim 8, including the step of bonding at least one additional polymer layer to the second layer after irradiation is complete. 11. The first layer consists of a blend of 90-40% by weight of propylene-ethylene copolymer and 10-60% by weight of (butene-1)-ethylene copolymer or butene-1 homopolymer, and 9. The method of claim 8, wherein the second layer comprises an ethylene-vinyl acetate copolymer. 12. extruding and coating on the second layer a third layer of a polymer selected from the group consisting of vinylidene chloride copolymer and hydrolyzed ethylene-vinyl acetate copolymer; The method according to claim 10. 13. The method of claim 12, comprising the step of coating the third layer with a fourth layer consisting of a formulation selected from the group consisting of formulations specified for the first layer. 14. A container formed by heat sealing together selected surface portions of the film of claim 1. 15. A container formed by heat sealing together selected surface portions of the film of claim 7. 16. two opposite edges 5 of the sheet of film;
A case made from the film of claim 7 by heat sealing the portions together to form a tube and bringing together and closing one end of the limb tube.