JP2512771C - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a thermoplastic shrinkable film, especially a very high oxygen barrier.
A) a thermoplastic shrinkable film that imparts properties. More particularly, the invention relates to thermoplastic co-extruded, oriented, shrinkable films that provide very high oxygen barrier properties. Ethylene-vinyl alcohol copolymer (EVOH) is well known as a suitable oxygen barrier resin for use in multilayer films. It is also recognized that a vinylidene chloride copolymer commonly known as Saran exhibits oxygen barrier properties in a multilayer film. However, the properties of these barrier materials are such that their effect as an oxygen barrier is affected by the humidity of the environment in which the film is used, ie, the barrier properties of these barrier materials are moisture sensitive. The humidity dependency when evaluating the gas barrier properties of EVOH is described in T.W. Iwanami and Y. Hirai (H
irai) 's article "Ethylene / vinyl alcohol resin (Eth
ylene Vinyl Alcohol Resins for Gas-Barrier Material). This paper discusses that as the humidity increases, the oxygen barrier properties of EVOH deteriorate. Vinylidene chloride copolymer (Saran) typically shows the opposite behavior. That is, its oxygen barrier properties improve somewhat with increasing humidity. The combination of EVOH and Saran in a coextruded multilayer film is therefore desirable. This overall reduces the effect of humidity changes on the oxygen barrier properties of the film. A further problem of using EVOH with or without a saran layer in a multilayer structure is the problem of cracking associated with EVOH. In the past, the problem of cracking has been somewhat solved by mixing EVOH with nylon. Reduced. In this case, nylon also contributes to ease of orientation of the film containing the EVOH resin. However, such processing advantages are achieved at the expense of a higher oxygen permeation rate of EVOH / nylon compared to EVOH alone. Another problem associated with unmixed EVOH is the difficulty in orienting EVOH coextruded from a hydrothermal system when EVOH is the inner layer. EVOH
Has a significantly higher orientation temperature range than Saran, and results in inconsistencies in the orientation temperature range when both materials are used in a single multilayer film. Although the Saran material orients relatively easily after passing through the hydrothermal system, the inner layer of EVOH does not respond as well, making orientation difficult. This is especially true in the blow-bubble technology of orientation techniques well known in the art for producing biaxially oriented films which are useful in many shrinkable film applications. A further problem with the "inside" EVOH, namely the EV forming the inner layer of the multilayer structure
The problem with OH is that once wetting occurs, it is difficult to remove water from the layer. Of course, the difficulty of drying this inner EVOH is that due to the poor barrier performance at high relative humidity of EVOH,
This is to cause a loss corresponding to the oxygen barrier property. Past solutions to the problem of orienting EVOH from hot water have been to convert ethylene to EV
It was to use a relatively high mol% in the OH copolymer. Typically 32-38
An EVOH resin having mole percent ethylene, especially the higher proportion of this range, was used and made the EVOH closer to the orientation properties of the ethylene-vinyl acetate copolymer, and thus more easily oriented. Although EVOH resins with a high ethylene content solve the problem of orienting the EVOH-containing film from hot water to some extent, there is the disadvantage of reduced barrier properties.
In general, the higher the ethylene content in EVOH, the lower the oxygen barrier properties of the resin in films using this resin. This time EVOH is used, for example, in exposed layers in multilayer films having at least one further polyolefin layer and / or Saran layer (multilayer films are used in practice).
It has been discovered that the coextruded film can be co-extruded ( sometimes as the outermost layer or outer layer) and that the coextruded film can be quenched in a cold water bath, passed through a hot water system, and then oriented. EVOH wets and softens with hot water during hot water passage of the coextruded film. This wetting and softening effect significantly reduces the orientation temperature range of the EVOH, makes it more compatible with the saran layer of the structure, if present, and in each case significantly reduces the orientation temperature range of the EVOH. It is unnecessary for small amounts of nylon for processing purposes. Such a decrease in the EVOH orientation temperature range results in better efficiency in processing as compared to hot oil or hot air orientation systems. EVOH is obviously wet during the alignment process, but the exposure of its multilayer film
The location as a layer allows a relatively quick drying of the layer and substantially restores its oxygen barrier properties. A further advantage is that by using this method, EVO with low mole% ethylene
H-resin can be used and therefore high barrier EVOH resin can be used. For the purpose of extrusion, it is preferred to use a relatively high melt index EVOH resin as the exposed layer . A melt index of at least 15 g / 10 min (ASTMD-1238), more preferably at least 20 g / 10 min, is suitable. About 15g / 1
Extrusion becomes progressively more difficult with a melting index of 0 minutes or less. With a melt index of about 10 g / 10 minutes or less, coextrusion of a multilayer film having EVOH as the exposed layer is very difficult or impossible. It is an object of the present invention to provide a method of using a low ethylene content EVOH resin in a multilayer shrinkable film to obtain good oxygen properties of the low ethylene content resin. It is a further object of the present invention to provide a method for orienting a multilayer film having EVOH content at a relatively low temperature. It is another object of the present invention to provide an EVOH-containing multilayer oriented shrinkable film that can be dried relatively easily as compared to a structure in which EVOH contains EVOH. In one aspect of the present invention, a method of making an oxygen-barrier, shrinkable film comprises:
An ethylene-vinyl alcohol copolymer layer as an exposed layer and at least one polymer material bonded to the exposed layer and comprising a polyolefin or a chemically modified polyolefin and a polymer material selected from the group consisting of vinylidene chloride copolymer The multilayer film comprising the layers is coextruded and the coextruded film is quenched in a cold water bath and passed through hot water to soften and wet the ethylene-vinyl alcohol copolymer layer , and then by orienting comprises a Rukoto. In another aspect of the invention, the multilayer oriented film comprises an ethylene-vinyl alcohol copolymer layer as an exposed layer and a polyolefin or a chemically modified polyolefin bonded to and exposed to the exposed layer. Co-extruding a multilayer extrudate comprising at least one layer of a polymeric material selected from the group consisting of vinylidene chloride copolymer, and quenching the coextruded film in a cold water bath;
Pass through hot water to soften and moisten the ethylene-vinyl alcohol copolymer layer
, And then oriented . Of interest is U.S. Pat. No. 4,576,988 to Tanaka et al. Which discloses a melt molded material having a silicon-containing ethylene-vinyl alcohol copolymer coated with vinylidene chloride. Of further interest is UK Patent Application GB2014476A to Kuga et al., Which discloses a polyvinyl alcohol substrate coated on one or both sides with an aqueous dispersion of vinylidene chloride-vinyl chloride copolymer. Of further interest is Mollison UK Patent Application GB2121062A, which discloses a bag made from a film comprising a laminate of a base film and a sealant film. This base film is made of saponified ethylene
It may be a vinyl acetate film. A PVDC layer may be interposed between the base film and the sealing film. Of further interest is British Patent Application GB2106471A to Maruhashi et al., Which discloses a container comprising one or more layers of ethylene-vinyl alcohol copolymer coated with a layer of vinylidene chloride copolymer. It is. A single drawing is attached to this specification as a part of the present disclosure. FIG. 1 is a schematic sectional view of a multilayer film according to the present invention. Referring to FIG. 1, a schematic cross-sectional view of a multilayer film is shown. Exposed layer 1
0 comprises an ethylene-vinyl alcohol copolymer having a melt index of at least about 10 g / 10 min, more preferably at least about 15 g / 10 min, preferably at least about 20 g / 10 min. Optionally, nylon or a nylon copolymer can also be mixed with the EVOH. Due to the advantages afforded by the present invention, EVOH resins having a relatively low percentage of ethylene and thus having a higher oxygen barrier
It can be used for the exposed layer 10. Suitable ethylene contents range from 22 to 29 mol%. EVOH resins having 32-38 mol% can also be used, but will of course give relatively poor barrier properties. Layer 12 comprises a polyolefin or a modified polyolefin. If optional layers 14, 16, 18 and / or 20 are introduced into the multilayer film structure, layer 1
2 is preferably an anhydride modified or otherwise chemically modified polyolefin which promotes adhesion between layer 14 and exposed layer 10. These adhesives are based on the Plexar adhesive resin system from Norchem, DuPont.
pont) and commercially available from several companies, including the Admer modified resin from Mitsui. Layer 14 is preferably a barrier material, more preferably Saran. Both Saran with and without plasticizer are commercially available. Layer 16 preferably comprises a polyolefin or a copolymer of ethylene and a comonomer, such as vinyl acetate. Most preferably, layer 16 is a relatively high vinyl acetate EV
A content. Layer 18 comprises a polyolefin or a mixture of polyolefins, and more preferably comprises a mixture of polybutylene and polypropylene. Layer 20 (the innermost layer when the multilayer film is actually used)
The inner layer may include a polyolefin such as polypropylene. As shown, only a relatively thin exposed layer 10 is required to obtain the benefits of the present invention. The invention will be better understood with reference to the following examples, which are given by way of example only. Example 1 Six extruders were applied to extrude a six layer structure. The first extruder that provides the base orifice for the exposed layer was EVOH [Soarnol from Nippon Gohsei (Soa
rnol) ZL] 90% and copolyamide [Grillion CA6] 10%
Was fed. This EVOH had a melting index of 20 g / 10 min. A second extruder, which provided a base orifice for the layer adjacent to the exposed layer , was fed with a modified ethylene-vinyl acetate copolymer (CXA-E162 from DuPont). A third extruder, which provided the base orifice for the next layer, was fed Saran without plasticizer (PV864 from Solvay). This Saran was premixed with a small amount of processing aid. A fourth extruder, which provided the base orifice for the next layer, was fed with an ethylene-vinyl acetate copolymer [Alathon 3170 from DuPont]. A fifth extruder providing the base orifice for the next layer includes an ethylene-propylene copolymer containing about 3.8% by weight of ethylene [Eltex KS409 × 6206 from Soltex. ] 50% and polybutylene [
A 50% mixture of PB8640 from Shell] was fed. A sixth extruder, which provided the base orifice for the inner layer , was fed with an ethylene-propylene copolymer (Dypro from Cosden Chemical Co.). The various layers were coextruded as a tubular extrudate from a die orifice. The tape was then quenched in a cold water bath and sent to a hot water system. Contains EVOH
The multilayer film having the mixture layer as an exposed layer was passed through hot water. This process is EVO
The H layer was completely wetted and softened. The coextruded film was then biaxially oriented by the blow valve technique well known in the art. Example 2 A substantially similar oriented multilayer film as in Example 1 was prepared under the same conditions as in Example 1, except that an exposed layer of 100% EVOH (Soarnol ZL) was provided. Example 3 EVOH with a relatively low melting index (Eva Company of America (Eva
A multilayer film similar to that of Example 2 was prepared using EVAL EC-F101 from l Company of America. The resulting film has poor exposure tables due to viscosity mismatch between the relatively viscous EVOH and the rest of the film material.
Surface (EVOH). “Hot water” as used in the above examples is mainly water at or near the boiling point,
It is related to water near 0.2 to 100 ° C (180 to 212 ° F) . It has now been discovered that the use of an exposed layer of EVOH, while actually improving somewhat after the initial two or three weeks, imparts oxygen barrier properties to the film. This is shown in Table 1. Table 1 shows the drying and transmission of O ₂ in the wet state to the film of Example 1 and 2. Permeation readings at 100% relative humidity range from 1 day to 23 days of testing. The number in parentheses is the thickness in mils. Oxygen permeation was measured according to ASTM D-3985 at cm ³ , standard temperature and standard pressure (24 hours, m ² , pressure). Another advantage of using EVOH as the exposed layer of a multilayer film oriented from hot water is improved free shrinkage. This improvement is believed to be due to the softening and wetting of the EVOH by the hot water as the tubular film passes through the hot water bath. Table 2 compares the free shrinkage data for a film passed through hot water with that of the same film passed through hot oil. Examples 1 and 2 in Table 2 relate to the same materials as Example 1 in Table 1. Free shrinkage was measured according to ASTM D-2732-70 (reapproved in 1976). All values in Table 2 are average values obtained from measurements of four samples. C. L. Is the confidence limit, e.g., the reported average is 10, and 95% C.E. L.
Is 2, it means that 95 will have a value of 8-12 when 100 samples are measured. The average length direction represents the free contraction in that direction, and the average lateral direction represents the free contraction in that direction. Various modifications within the spirit and scope of the invention will become apparent to those skilled in the art upon reference to the above detailed description, and thus the above description and the presently preferred embodiments of the invention are set forth in the appended claims. It is to be understood that the particular embodiments shown are for illustrative purposes only. By way of example, a moistened EVOH layer as an exposed layer can be combined with one or more of a variety of polymeric materials to produce a coextruded film useful in different packaging applications. Further, while it is preferred to utilize an oriented film having substantial shrinkage properties for many applications, wetting a coextruded tape, i.e., a tape having an exposed layer of EVOH, in a hot water bath. Advantages can be obtained without subsequent orientation.

[Brief description of the drawings]   FIG. 1 is a schematic sectional view of a multilayer film according to the present invention.

Claims (1)

[Claims] 1. (A) Ethylene-vinyl alcohol copolymer layer as an exposure layer and its exposure
Coextruding a multilayer film comprising at least one layer made of a polymeric material selected from the group consisting of bonded and polyolefins or chemically modified polyolefins and vinylidene chloride copolymers in Deso, (b ) and rapidly cooling the coextruded film in a cold water bath (the films c) the quenching through in hot water of from 82.2 to 100 ° C., ethylene - softened vinyl alcohol copolymer layer and Shimeme et allowed, and (d) preparation of the oxygen barrier film for orienting the wet film, comprising the. 2 . The method of claim 1 wherein the ethylene-vinyl alcohol copolymer is mixed with a small proportion of the polyamide material prior to coextrusion. 3 . a) Exposed layer of ethylene-vinyl alcohol copolymer, second layer of polymer adhesive
Layers, a third layer of vinylidene chloride copolymer, a fourth layer of ethylene-vinyl acetate copolymer, a fifth layer of a mixture of ethylene-propylene copolymer and polybutylene, and a sixth layer of ethylene-propylene copolymer And b) passing the co-extruded film through hot water to soften and wet the ethylene-vinyl alcohol copolymer. the film. 4 . 4. The film of claim 3 wherein the wet film is oriented. 5 . The film of claim 3 wherein the ethylene-vinyl alcohol has a melt index of at least about 10 g / 10 minutes as measured by ASTM D1238. 6 . The film of claim 3 wherein the ethylene-vinyl alcohol has an ethylene content of about 22-38 mol%.