Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Patent
1996-10-15
1999-08-10
Nutter, Nathan M.
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C08L 7700, C08J 518
Patent
active
059360445
DESCRIPTION:
BRIEF SUMMARY
DESCRIPTION
The present invention relates to films based on polyamide and on polymers containing polyamide blocks and polyether blocks.
Prior art JP 04-314 741 describes films consisting of a mixture of (i) polyamide 6 and (ii) of polyetheresteramide. The polyetheresteramide is a block polymer obtained by the condensation of polyoxytetramethylene glycol and of polyamide blocks with carboxylic acid ends. The polyamide blocks originate from polycaprolactam (PA-6) or from polydodecalactam (PA-12). The quantity of polyetheresteramide is between 0.5 and 9% by weight of the mixture.
The property of this film is that it resists folding at 0.degree. C. according to method 101c of the standard MIL-B-131 F. The number of holes produced in the course of 1000 foldings is measured.
If the quantity of polyetheresteramide is too small the perforation is considerable; if the quantity of polyetheresteramide is too great, the transparency and the mechanical properties of the film are reduced.
In this prior art the polyetheresteramide is such that the proportions by weight of the polyamide blocks and the polyether blocks are in the ratio 45/55 to 30/70.
It is useful that the polyamide films which are employed in the foodstuffs industry should have a good resistance to folding, especially at low temperature for the packaging of deep-frozen products. However, it is indispensable that the films for packaging the products which are deep-frozen (or to be deep-frozen) should resist the perforation due to the projecting parts or to the sharp edges of these products. It is also useful that, during the transport and the handling of the deep-frozen product, the said projecting parts and sharp edges should not cause the film to be perforated.
This property is also sought after for the packaging of sterilized medical equipment. In fact, perforation of the film would cause an entry of air and hence a contamination. The Applicant found that the most representative test of this resistance was the impact strength, according to ISO Standard 7765-1 (Method B), the impact being that of a punch falling from a certain height onto the film.
The Applicant has found films based on (i) polyamide consisting essentially of polyamide-6 or of polyamide-6,6 and (ii) on a polymer containing polyamide blocks and polyether blocks, the polyamide blocks consisting essentially of polyamide-6 or of polyamide-6,6, the polyether blocks consisting essentially of polytetramethylene glycol, the polyamide/polyether ratio by weight of (ii) being higher than or equal to 50/50.
The main advantage of these films is that they have an impact strength according to ISO 7765-1 (Method 3) which is superior to that of the same polyamide film.
The prior art JP 04-314 741 referred to above has described closely related compositions; however, they do not have a sufficient impact strength.
U.S. Pat. No. 4 970 274 describes moulding materials and films of polyamide-6 containing polymers with polyamide blocks and polyether blocks. However, the combination of they polyamide-6 blocks with the polytetramethylene glycol (PTMG) blocks is neither mentioned nor exemplified. The Applicant has found that this combination provides particular results, namely an impact strength while retaining the tensile strength and the tearing resistance of a polyamide-6 (PA-6) or polyamide-6,6 (PA-6,6) film. The films of the invention have a structure of a polyamide matrix in which nodules of polymers containing polyamide blocks and polyether blocks are dispersed.
These nodules are smaller than 0.3 .mu.m.
Prior art U.S. Pat No. 4 970 274 shows that the polyamide compositions have been made more supple but with a loss in the mechanical properties such as, for example, the tensile strength, whereas in the present invention the impact strength has been improved without loss of the other properties.
Another advantage of the invention is that the polyamide and the polymer containing polyamide blocks and polyether blocks mix very easily, for example in the extruder which feeds the machine for producing the film.
REFERENCES:
patent: 4970274 (1990-11-01), Chacko et al.
patent: 5239004 (1993-08-01), Pyke et al.
Alex Patrick
Melot Denis
Elf Atochem S.A.
Nutter Nathan M.
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