JPH05302014A - Heat stabilizer for poly@(3754/24)oxymethylene) - Google Patents

Abstract

PURPOSE:To obtain a heat stabilizer which, when added to poly(oxymethylene), imparts excellent thermal stability to the polymer, can greatly reduce void generation during film formation from the polymer, and makes the polymer suitable for precision molding, particularly for use as a film material. CONSTITUTION:The title stabilizer is a mixture of a polyamide and a novolak resin in a weight ratio of 1:0.1 to 1:10.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a heat stabilizer suitable for precision molding of polyoxymethylene, especially for films.

[0002]

2. Description of the Related Art Polyoxymethylene resin is polymerized or copolymerized from formaldehyde or its cyclic oligomer trioxane, or a comonomer such as trioxane and a cyclic ether, the end of which is stabilized, and an antioxidant and other A heat stabilizer is added to prevent decomposition.

As the antioxidant, a hindered phenol compound is used, and as the other heat stabilizer, a compound such as polyamide, urea derivative, amidine compound, hydroxide of alkali or alkaline earth metal, organic or inorganic acid salt is used. Are known. Among them, polyamide is effective and widely used. Polyamide reacts with formaldehyde, which is a decomposition product of polyoxymethylene, and functions as an extremely excellent heat stabilizer by capturing this. But,
Since polyamide is poorly compatible with polyoxymethylene, it is phase-separated in polyoxymethylene and exists as fine particles. Therefore, in precision molding applications, it is often the case that these particles are not intentionally added for the reason that these particles are deposited on the surface of the molded product and deteriorate the surface property. Further, JP-A-61-25
When used for a polyoxymethylene film as disclosed in JP 2135, JP 61-286115 and JP 62-13318, it has a low affinity with polyoxymethylene and therefore is stretched around polyamide particles. Voids were generated, which not only markedly deteriorated the quality of the film surface and the like, but also caused the breakage of the film during stretching.

[0004]

SUMMARY OF THE INVENTION The present invention overcomes the problems of polyamide and provides a heat stabilizer for polyoxymethylene which is suitable for precision molding, especially for film.

[0005]

Means for Solving the Problems As a result of intensive studies to improve the compatibility between polyamide and polyoxymethylene, the present inventors have mixed a polyamide with a novolac resin, and changed the mixture into polyoxymethylene. The inventors have found that the above problems can be overcome by adding and mixing, and have completed the present invention.

That is, the present invention is a heat stabilizer for polyoxymethylene, which is a mixture of polyamide and novolac, and the weight ratio of polyamide: novolak is 1: 0.1 to 1:10. The present invention will be described in detail below. It is already known that novolac type phenolic resin is compatible with polyoxymethylene (Polymer Thesis Collection, 14
8, 7, 443 (1991)). A mixture of synthetic linear polyamide and novolac has also been widely used as an adhesive for metals since ancient times. The present inventors have noticed that novolak has a high compatibility with both polyoxymethylene and polyamide, and made a mixture of polyamide and novolac, and added this to polyoxymethylene. It has been found that they are extremely effectively finely dispersed without significantly impairing the function as an agent. Furthermore, when this was biaxially stretched into a film,
It was also found that the voids around the polyamide observed in the ordinary polyamide-added system are significantly reduced, the breakage of the film due to the voids during stretching is significantly reduced, and a high-quality film can be obtained.

In the mixture of the present invention, the ratio of polyamide to novolac is 1: 0.1 to 1:10 by weight of polyamide: novolac. If the amount of novolak is less than this ratio, the sufficient compatibilizing effect of the present invention cannot be provided. Further, if the amount of novolak is more than this range, the function of the polyamide as a heat stabilizer may be impaired, and in some cases, the amount of novolak in polyoxymethylene may become excessive and the thermal decomposition of polyoxymethylene by novolak may occur. It is not preferable because it may be accelerated.
A more preferable range is a ratio of polyamide to novolak of 1 :.
It is 0.5 to 1: 5.

When this mixture is added to and mixed with polyoxymethylene, the amount of the mixture added is 10% by weight of polyoxymethylene.
The amount of polyamide in this blend was 0.0
It is added to and mixed with polyoxymethylene so as to be in the range of 5 to 5 parts by weight. At this time, the function of the polyamide as a heat stabilizer acts more effectively. More preferably, it is 0.1 to 3 parts by weight with respect to 100 parts by weight of polyoxymethylene.

In the present invention, the method of mixing the polyamide and the novolac is not particularly limited. For example, it can be manufactured using a single-screw and twin-screw extruder or a conventional mixer such as "Banbury" or "Blavender". Also,
It can also be produced by dissolving a polyamide in a suitable solvent such as dimethylformamide or dimethylacetamide, and then adding novolak into the solution, mixing and then removing the solvent.

Various additives such as hindered phenolic antioxidants are usually used in combination with polyoxymethylene, but the present invention may contain these various additives. Further, in the system to which the mixture of the polyamide of the present invention and novolac is added, it is possible to further add novolak alone for the purpose of improving the kneading property of this mixture to polyoxymethylene or for other purposes. Also in this case, if the amount of addition of the novolac is large, the thermal decomposition of polyoxymethylene may be accelerated by the novolac, so the amount of addition must be adjusted as necessary. That is, the total amount of novolak including the amount of novolac in the mixture is preferably 30 parts by weight or less, more preferably 15 parts by weight or less, based on 100 parts by weight of polyoxymethylene.

The polyoxymethylene of the present invention is a polyoxymethylene polymer in which the main part of the main chain is substantially composed of repeating units of oxymethylene groups. For example, a polyoxymethylene homopolymer obtained by polymerizing formaldehyde or a cyclic oligomer of formaldehyde, such as trioxane or tetraoxane, whose main chain consists mostly of oxymethylene chains, but is not There is a polyoxymethylene copolymer obtained by adding 0.1 to 15 mol% of a cyclic ether having at least two adjacent carbon atoms to trioxane and polymerizing. Further, the copolymer includes, for example, a copolymer obtained by copolymerizing at least one polyfunctionally reactive compound copolymerizable with trioxane and at least one monofunctionally reactive compound copolymerizable with trioxane. Copolymers, specifically, for example, copolymers obtained by copolymerizing trioxane, 1,4-butanediol diglycidyl ether and ethylene oxide are also included. This copolymer forms a polymer whose molecular chain is not linear but branched or networked. The present invention is applicable to the above homopolymers, copolymers, and also a mixture obtained by mixing the homopolymer and the copolymer in an appropriate ratio. Further, the main part of the main chain is substantially oxynated, such as an acetalized product of polyoxymethylene, a reaction product with isocyanate, or a copolymer obtained by copolymerizing a small amount of a third component (for example, an alkyl group such as stearyl group). The present invention can be applied to any polyoxymethylene polymer composed of repeating units of methylene groups.

The novolac type phenolic resin of the present invention is a substantially linear and thermoplastic phenol-formaldehyde resin, and formaldehyde such as phenol, m-cresol, p-cresol, resorcinol or naphthol can be produced by a known method. It can be produced by reacting such a phenolic compound or a mixture thereof. Novolak is a thermoplastic phenol-formaldehyde resin, which can be converted into a thermosetting resin by further reacting with formaldehyde in the presence of an acidic catalyst. Various products of novolak are commercially available for applications such as epoxy curing agents and adhesives. For example, those consisting of a phenol component substituted with a long-chain alkyl group, and the like, novolaks suitable for the present invention are substituted with such a long-chain (having more than 3 carbon atoms) alkyl group. It is preferable not to include a phenol component, and it is preferable that the phenolic component is phenol or cresol. The softening point is as wide as 80 to 150 ° C. depending on the grade, but a relatively high softening point is preferable in the present invention. The average number of phenol nuclei is generally 5 to 7, but it usually includes low molecular weight compounds such as dinuclears. In the present invention, it is preferable that the number of low molecular weight substances such as binuclear substances is small. In addition, novolac usually contains a few percent of unreacted phenolic compound, but this may impair the thermal stability of polyoxymethylene, so it is preferable to remove it as much as possible, preferably these residual phenolic compounds. Is 1% or less.
Further, if ionic components such as metal ions are contained, the thermal stability of polyoxymethylene may be impaired, so it is preferable to remove these ionic components as much as possible.

The polyamide used in the present invention is a linear polymer having a main chain formed by repeating acid amide bonds and having a number average molecular weight of 1,000 to 50,000.
Isophthalic acid or Isophthalic acid substituted with an alkyl group having 5 carbon atoms or a halogen atom, or 3 to 10 such as malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, aceraic acid, and sepacic acid It can be produced by subjecting a dicarboxylic acid having the following carbon atom to condensation polymerization. Alternatively, it can be produced by ring-opening polymerization of a lactam having 3 to 12 carbon atoms such as ε-caprolactam, ε-laurolactam and the like. Specifically, nylon 3, nylon 6, nylon 66, nylon 610, nylon 612, nylon 1
1, nylon 12 and the like are generally known.

[0014]

EXAMPLES Next, the present invention will be described in more detail by way of examples.

[0015]

Example 1 30 g of polyamide (nylon 12) and phenol type novolac resin (Dainippon Ink and Chemicals, Inc.)
30 g of TD-2090P manufactured by TD-2090P) was thoroughly crushed and stirred in advance, and then 190 ° C., 50 rp using “Blavender”.
Melt kneading was performed for 10 minutes at m to obtain a yellow transparent mixture. 1 part by weight of this mixture and 0.2 part by weight of a hindered phenolic heat stabilizer (Irganox 1010 manufactured by Ciba-Geigy Co., Ltd.) together with 100 parts by weight of polyoxymethylene homopolymer containing no additive. After mixing, the mixture was melt-kneaded with a 25 mm extruder to form pellets. Next, the pellets were pressed at 190 ° C. to form a 500 μm sheet, which was pressed with a 50 ton press at a pressing temperature of 150 ° C. and the magnification in each axial direction was 2 ×.
2 press rolled. Next, this rolled product was biaxially stretched at a stretching temperature of 175 ° C. with a magnification of 3 × 3 in each axial direction using a batch simultaneous biaxial stretching machine to obtain a film having a thickness of 15 μm. The obtained film was transparent, and voids due to stretching were not observed around the polyamide by observation with an optical microscope. Further, the amount of thermal decomposition of the pellets was measured by a thermogravimetric measuring device in order to evaluate the thermal stability of the polymer. It had thermal stability.

[0016]

Comparative Example 1 0.2 part by weight of the hindered phenolic heat stabilizer of Example 1 and 0.5 part by weight of polyamide were pelletized in the same manner as in Example 1 together with 100 parts by weight of polyoxymethylene homopolymer. .. Then, a biaxially stretched film was obtained by the same method as in Example 1. The film had a slight whiteness, and voids having a diameter of about 10 to 30 μ were observed around the polyamide under the optical microscope on the entire surface of the film.
When the sample pellets were left in nitrogen at 250 ° C. for 30 minutes, the weight residual ratio was 99.2%.

[0017]

Comparative Example 2 0.2 parts by weight of the hindered phenolic heat stabilizer of Example 1 and 100 parts by weight of polyoxymethylene homopolymer were pelletized in the same manner as in Example 1. Next, a film was formed in the same manner as in Example 1. The film was transparent and no voids were observed under an optical microscope, but it was confirmed that the pellets in nitrogen were measured by thermogravimetry.
The weight residual ratio after 30 minutes at 50 ° C. was 89.6%.

[0018]

Example 2 Using the polyamide and novolac of Example 1, the weight ratios of polyamide and novolac were 1: 0.05, 1: 0.1, 1: 1, and 1: respectively in the same manner as in Example 1.
A mixture of 5, 1:10 and 1:15 was obtained. Next, to 100 parts by weight of the polyoxymethylene homopolymer of Example 1, the respective admixtures were added so that the amount of polyamide in each admixture was 0.5 parts by weight. 0.2 parts by weight of a phenolic heat stabilizer was added and mixed, and each mixture was melt-kneaded by the same 25 mm extruder to obtain 6 types of pellet-shaped samples. Next, each pellet was processed into a film by the same method as in Example 1.

For each film, the occurrence of voids was observed with an optical microscope. The results are shown in Table 1, in which voids are markedly generated, are marked with x, when some voids are found, are marked with Δ, and when no voids are found, are marked with ◯. Further, thermogravimetric measurements were performed on the above 7 types of pellets, and the weight residual ratio after 30 minutes at 250 ° C. in nitrogen is also shown in Table 1.

The above results show that the heat stabilizer of the present invention greatly suppresses the generation of voids in the film without significantly impairing the excellent heat stabilizing effect of the polyamide.

[0021]

[Table 1]

[0022]

INDUSTRIAL APPLICABILITY The heat stabilizer of the present invention, when added to polyoxymethylene, has an excellent heat stabilizing effect without significantly impairing the excellent heat stabilizing effect of conventional polyamides, and further, it has an excellent heat stabilizing effect. Due to its high affinity with, the occurrence of voids in the film can be greatly reduced. Further, even in precision molding applications, it is extremely useful from an industrial standpoint such that the deterioration of the surface quality of a molded product can be suppressed by improving the affinity and dispersibility with polyoxymethylene.

Claims (1)

[Claims] 1. A heat stabilizer for polyoxymethylene, which is a mixture of a polyamide and a novolac resin, and has a weight ratio of polyamide: novolak of 1: 0.1 to 1:10.