JPH0493233A - Improvement of permanent compressive strain of polyvinyl chloride-based resin molded article - Google Patents

Abstract

PURPOSE:To make it possible to hold excellent permanent compressive strain under the condition that excellences in moldability, weatherability and production cost are preserved by a method wherein the non-rigid polyvinyl chloride resin molded article concerned is heat-treated in the specified temperature range for the specified period of time. CONSTITUTION:Molded article, which is made of non-rigid polyvinyl chloride-based resin composition consisting of polyvinyl chloride-based resin and plasticizer, is heat- treated at the temperature of 80-120 deg.C for the period of time of not less than 3min and less than 20min so as to improve the permanent compressive strain of the polyvinyl chloride-based resin molded item. The addition of rubber-like material to the polyvinyl chloride-based resin composition may be allowed. As the rubber-like material, acrylonitrile-butadiene copolymer (NBR), chloroprene rubber, acrylic rubber or the like is exampled and partially crosslinked NBR is preferable from the view point of improving effect of permanent compressive strain and of age resistance. The rubber- like material can add as much as possible unless the characteristics of polyvinyl chloride-based resin are lost and its loadings normally is within the range of 20-200 pts.wt. to 100 pts.wt. of the polyvinyl chloride-based resin.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for improving compression set by short-time heat treatment of a molded article made of a soft vinyl chloride resin composition.

[Prior Art] Vinyl chloride resin is a typical general-purpose synthetic resin that is inexpensive and has well-balanced physical properties, and is used for a variety of purposes, from hard to soft.

In particular, by adding a plasticizer to this, a texture similar to that of rubber can be obtained, and sulfur and organic II! E crosslinked with oxide
Compared to PDM, NBR, and chloroprene rubber, it is superior in terms of moldability, weather resistance, cost, etc., and is widely used. However, this type of soft vinyl chloride resin molded products are inferior in compression set, which is one of the most important characteristics of rubber and creep characteristics at high temperatures, so they are used in fields such as packing, gas furnaces, sealing materials, etc. It cannot be used as a substitute for rubber.

One way to improve compression set is to increase the degree of polymerization of vinyl chloride resin, but the average degree of polymerization is 30[]
The compression set of polyvinyl chloride resin molded products with a polymerization degree of O~4000 is 55~60%, which is significantly higher than the 20~40% of vulcanized rubber.Currently, the production of vinyl chloride resin with a higher degree of polymerization requires polymerization. A molded product has been proposed in which polyvinyl chloride can be obtained by adding a polyfunctional compound and crosslinking it during polymerization, which has various technical and engineering limitations. , has not arrived,
In addition, recently vinyl chloride resin and rubbers (e.g.
Polymer blends with NBR, chlorinated PvC acrylic rubber, polyurethane rubber, etc.) have been studied, and it has become possible to obtain molded products with compression set close to that of rubber. However, even in this case, it is 100 to 2
Since as much as 0.00% by weight of rubber must be added (Japanese Patent Application Laid-Open No. 63-30551), the inherent advantages of vinyl chloride resin, such as low cost, excellent processability and weather resistance, tend to be lost.

Furthermore, JP-A No. 61-211021 discloses a method of heat-treating a molded article at a temperature of 40 to 120"C for 20 minutes or more in order to reduce the compression set.
Such long-term treatment has the disadvantage that productivity is poor and the industrial value is halved.

[Problems to be Solved by the Invention] The present inventor has made extensive efforts to study the possibility of obtaining a molded product with excellent compression set while retaining the advantages of soft vinyl chloride resin molding itself. The inventors have now completed the present invention by discovering that compression set can be improved by heat-treating a soft vinyl chloride resin molded article at a specific temperature range for a period shorter than 20 minutes.

That is, an object of the present invention is to provide a method for improving the compression set of a vinyl chloride resin molded article.

[Means for solving the problem] Accordingly, the present invention provides a molded article obtained from a soft vinyl chloride resin composition comprising a vinyl chloride resin and a plasticizer.
The present invention relates to a method for improving the compression set of a vinyl chloride resin molded article, which comprises heat-treating at a temperature of 0 to 120° C. for 3 minutes or more but less than 20 minutes.

To explain the present invention in detail, the vinyl chloride resin used as a raw material for the soft vinyl chloride resin composition in the present invention includes vinyl chloride homopolymers, vinyl acetate, acrylic esters, methacrylic esters, Any copolymer of vinyl chloride and a copolymerizable monomer such as vinylidene chloride or maleic esters can be used, and these can be used in general chlorination polymerization such as suspension polymerization, emulsion polymerization, fine suspension polymerization, and bulk polymerization. Manufactured by vinyl polymerization method. The average degree of polymerization of the vinyl chloride resin is preferably 1,800 or more. and,
In order to impart flexibility to these resins, a plasticizer is added to form a vinyl chloride resin composition, which is then made into a molded article.

The plasticizer that is a component of the vinyl chloride resin composition is not particularly limited as long as it is commonly used for vinyl chloride resins, such as di-2-ethylhexyl phthalate, di-n-octyl phthalate, dibutyl phthalate, etc. Examples include phthalic acid esters, fatty acid esters such as dioctyl adipate and dioctyl sebacate, trimellitic acid esters, and polyester plasticizers.

The amount of plasticizer to be blended can be selected as appropriate depending on the quality and purpose of the final product, but in consideration of processing and moldability, it is usually desirable to range from 20 to 150 parts by weight per 100 parts by weight of the vinyl chloride resin.

A rubber substance may be added to the vinyl chloride resin composition, which improves the initial compression set and does not adversely affect the improvement of the compression set of the vinyl chloride resin. As the rubber substance, acrylonitrile-butadiene copolymer (N
BR), ethylene vinyl acetate copolymer, chlorinated polyethylene, thermoplastic polyurethane, thermoplastic polyester,
Examples include chloroprene rubber, acrylic rubber, etc., and partially crosslinked NBR, which is widely available on the market, is preferred from the viewpoint of improving compression set and aging resistance.

The amount of rubber substance to be added can be within a range that does not lose the properties of the vinyl chloride resin, and usually the amount of rubber substance added is within the range of 1 to 1
The range is from 20 to 200 parts by weight per 00 parts by weight.

Vinyl chloride resin compositions generally contain additives such as heat stabilizers, ultraviolet absorbers, antioxidants, lubricants, flame retardants, antistatic agents, fillers, and colorants, which are generally added to vinyl chloride resins as necessary. Additives for resins such as additives may be added.

The composition is prepared by uniformly mixing the above-mentioned components using a mixer such as a ribbon blender, kneader-1 crusher, super mixer, Banbury mixer, etc., and then injection molding, extrusion molding, compression molding, or rotary molding. It is considered to be a molded product by paste processing such as slush molding.

The method of the present invention provides excellent compression set by heat-treating the above-mentioned soft vinyl chloride resin molded product at 80 to 120°C, preferably 100°C for 3 minutes to less than 20 minutes, preferably 5 to 15 minutes. It is possible to obtain a molded article having the following properties.

〔Example〕

Next, the method of the present invention will be explained in more detail with reference to Examples, but the present invention is not limited to the following Examples unless the gist thereof is exceeded.

Example (1) Preparation of soft vinyl chloride resin composition The compounded composition (weight ratio) shown in Table 1 was kneaded in a Banbury mixer at a discharge temperature of 160°C, formed into a sheet with a sheeting roll, and then passed through a pelletizer. Pellets were prepared using the resin composition, and the pellets were used as a soft vinyl chloride resin composition.

Table (2) Manufacture of molded products Using a 40rn single screw extruder equipped with a full-flight screw with L/D = 22 and a compression ratio of 3.0, similar shapes 3 made of the above-mentioned soft vinyl chloride resin composition A profiled extrusion molded product (colander) of seeds was manufactured.

Molding setting conditions Niji cylinder temperature (from hopper side) C145°C, Cz155°C C,165"c, C,175"C Die temperature 175°C Screw rotation speed 20 rpm Molded product shape (see Fig. 1) Fig. 1 is The numbers in Figure 0, which is a longitudinal cross-sectional view of a profile extrusion molded product, indicate the dimensions of each part of the molded product.
Shown in the table.

Table 2 Note that from the composition of Formulation 1, the above three molded products were added to the composition of Formulation 2.
From the composition, only the shape of molded article 2 was molded and used as a material for compression set measurement.

(3) Measurement of compression set: After heating the molded product in a hot air dryer and hot water bath set at temperatures of 80°C, 1100°C, and 120°C for a predetermined time, it was left in a constant temperature room at 23°C overnight. Then, compression set was measured.

Compression set is determined by setting the compression ratio of the molded product to 50% at the rib height (parts marked ■ and ■ in Figure 1), and applying it at 80℃ for
The molded product was left for 8 hours, and then left in a constant temperature room at 23"C for a day and a night. In order to improve measurement accuracy, the molded product was shaped into the shape shown in Figure 1.
It was cut into thick pieces and the dimensions were measured using a projection magnifier. The lip heights before and after the test were measured, and the ratio of the difference between them and 50% of the lip height before the test was defined as the compression set value (percentage).

For reference, the compression set was measured in the same manner as in the examples after being left at room temperature for a predetermined period of time.

The results for the composition of Formulation 1 are shown in Tables 3 and 4, and the results for the composition of Formulation 2 are shown in Table 5.

Table [Effects of the Invention] According to the method of the present invention, heat treatment is performed after molding, so
It can be used with any molding method for vinyl chloride resins, does not require any means to improve compression set such as compounding rubber materials or crosslinking, and is no different from general soft vinyl chloride resins in terms of formulation. Therefore, the weather resistance, processability, and cost inherent to vinyl chloride resins are not compromised.Furthermore, the heat treatment after molding can be done from 80°C to 120°C.
Because of the temperature range, no special heating equipment is required, there is no need to worry about burning or decomposition of the molded product, and the heating time is short, from 3 minutes to less than 20 minutes, so the process line may need to be changed slightly. There is no need to reduce production speed.

In this way, it is possible to obtain a vinyl chloride resin molded article that retains the characteristics of vinyl chloride resin and has improved compression set.

[Brief explanation of the drawing]

FIG. 1 is a longitudinal cross-sectional view of a profile extrusion molded product for measuring compression set. In the figure,

Claims (2)

[Claims] (1) A vinyl chloride resin molded article obtained by heat-treating a molded article obtained from a soft vinyl chloride resin composition at a temperature range of 80°C to 1200°C for 3 minutes or more but less than 20 minutes. How to improve compression set (2) The soft vinyl chloride resin composition contains 20 to 200 parts by weight of partially crosslinked NBR per 100 parts by weight of the vinyl chloride resin.
The method according to claim 1 containing