FR2463787A1 - Polymer article with areas of differing firmness - by pre-stiffening compsn. contg. crosslinkable cpd., followed by selected irradiation - Google Patents

Abstract

Polymer article with areas of differing firmness in the wall is prepd. by (a) uniformly mixing into the material 5-70 wt.% of a substance (I) which crosslinks or polymerises on irradiation with ionising radiation; (b) shaping the article; (c) pre-stiffening the article by gelation and/or crosslinking; and (d) exposing to ionising radiation those areas where increase in the firmness is required. Choice of the polymer is not limited. Process is simple. Appearance of the article is not altered in the irradiation stage. The prod. is esp. a folding bellows, partic. for air pipes in vehicle motors. The folds of the bellows can be given a greater hardness.

Description

 The present invention relates to a method for preparing pieces of polymeric materials having in wall regions of different mechanical strengths, in which process the material used shaping and then reinforcement.

 Such parts, to which the method described above has been applied, are described in Utility Model No. 77/16857 of the Federal Republic of Germany. In these parts, the regions of the wall which have different mechanical strengths are each prepared in. independent operating stages and then glued together. This process is labor intensive and can not be considered economically satisfactory.

 German Patent Application No. 1,920,029 describes a process for preparing such a piece of material in which, by inserting reinforcement elements into the otherwise homogeneous wall, In some regions, there are varying effects of reinforcement. This method can not be considered as satisfactory from the point of view of economics.

The Applicant has sought a simple and economical method for preparing shaped parts of polymeric materials which, without any particular requirement with regard to the choice of certain polymeric materials or relative to certain shaping techniques; a subsequent modification of the technical properties, and in particular of the hardness, in certain limited areas
Other objects and advantages of the invention will become apparent on reading the description below.

These aims and advantages have been achieved according to the invention by mixing with the polymer material used, in uniform distribution, from 5 to 70% by weight of a crosslinking or polymerizing substance when exposed to ionizing radiation, then forming the workpiece by shaping and subjecting it to a prior reinforcement by gelation and / or crosslinking, after which the workpiece is exposed to the action of ionizing radiation only in the regions in which an increase in mechanical strength is sought,
In order to limit, in particularly advantageous conditions, the regions in which a subsequent reinforcement is sought by the action of ionizing radiation with respect to the other regions, the latter will be protected, during the irradiation, by means of a mask of absorbent material.

 The process according to the invention can also be applied to the preparation of hollow bodies. However, in this case, taking into account that the radiation passing through the wall of the room can diffract, it has been advantageous, even when the radiation comes only from the outside, to cover the inner face of the wall. by a mask that represents the specular image of the mask placed on the outside. This is the only way to ensure that the subsequent reinforcement will be limited to unprotected and therefore well-defined regions.

 In a particular embodiment, 0.05 6% and preferably 0.1 to 2%, based on the total weight of the mixture, of an inhibitor, for example, are introduced into the polymer material used. a mixture of allyl phenols or a derivative of diphenylamine or a comparable anti-aging agent, preferably taken from the group of hydroquinone derivatives, quinoline or phenol or a mixture of such substances. This addition makes it possible to fix the reactive end groups of the substance which cross-links or polymerizes and to avoid undesirable continuation of the reinforcement, for example as a result of chemical aging processes.

However, the desired results are achieved only if the inhibitour is mixed uniformly, in the proportions indicated, with the substance which cross-links or polymerizes.

 The essential substances according to the invention which trigger the crosslinking or subsequent polymerization are low molecular weight substances bearing one or more double bonds, for example acrylates, methacrylates or allyl esters. These substances are introduced into the polymeric material at the uniform distribution necessary either for the preparation or in a subsequent mixture. Depending on the nature and quantity of the added crosslinkable substances and on the energy dose applied during the subsequent irradiation, one can act on the duretEdh material. The mutual adjustment can be realized in each particular case with the necessary precision by means of simple preliminary tests.

 The mask used to absorb the radiation may, in addition to the transparency in certain regions, also have different degrees of absorption, for example by corresponding variation of the thickness. The degree of subsequent reinforcement caused in certain regions of the material can then be varied and, apart from regular mechanical strength transitions, cause, for example, a succession of zones with different levels of mechanical strength.

 The process according to the invention can be applied to the subsequent partial reinforcement of pieces of material obtained by any known forming techniques, for example by compression, immersion or castings. The method is therefore suitable both for a subsequent partial reinforcement of pieces of materials with a very complicated external shape and for use in mass production. A particular advantage is that the pieces of material do not undergo any change in their external appearance during the treatment with ionizing radiation. Parts of materials prepared in exactly the same manner and with a very similar appearance can be given different strength properties.

 A field of application in which the advantages of the method according to the invention can be exploited in particularly favorable manner is the preparation of the bellows or "accorddons". The method according to the invention makes it possible to give the bellows, in the region of the outer arches and inner edges of the individual pleats and / or throughout the middle part a greater hardness and, consequently, a greater stability, which allows their use in the field of air ducts, stable pressure and vacuum of vehicle engines.

 The ionizing radiation used may be of different natures. In many cases, the use of high energy radiation, for example gamma or X radiation, is preferred because these radiations are capable of penetrating, without marked weakening under the action of any loadings> wall thickness even large pieces of material and, consequently, to modify them. On the other hand, in the case of the preparation of shaped parts with a small wall thickness, the electron beams will be preferred because they can be absorbed by a mask of relatively small thickness. The mask can therefore be manufactured more easily, which has advantages in practical manipulations.

 To achieve a balanced molecular structure over the entire thickness of the piece of material it is often sufficient to have a source of radiation on one side only of the piece of material. This results in great advantages with regard to simplification of the manufacturing operation, in particular in the manufacture of hollow parts.

 Taking into account the description given above, the process according to the invention can be considered as a two-stage process in which the first stage consists in mixing the polymer material used, for example a soft polyvinyl chloride, with a natural rubber. , a synthetic rubber or a polyurethane, # substances of low molecular weight crosslinkable under the action of ionizing radiation because they carry one or more double bonds, after which, if necessary by means of a shaping tool, one In its final form, the actual shaped object is prepared by immersion, casting, injection molding, compression or extrusion. In the second stage of operation, the piece of prefabricated material is exposed to ionizing radiation so as to cause the desired regions to cross-link. additional radio-chemical polymerization or polymerisation of the contained substances. This result is achieved, as mentioned above, using a mask.

 The following examples illustrate the invention without limiting its scope; in these examples, the indications of parts and percentages are by weight unless otherwise indicated.

Example 1
Preparation of a polyvinyl chloride bellows with a hard median part and a soft end part
First stage of operation
The cross-shaped bellows, having a wall thickness of 1.5 to 2 mm, is prepared in a manner known per se by immersion or by injection molding from a mixture of polyvinyl chloride containing crosslinkable additives under action of radiation.The polyvinyl chloride mixture has the following composition
Mixture I polyvinyl chloride 1) 100 parts plasticizer2) 40 parts trimethylolpropane trimethacrylate 3) 60 parts stabilizer4) 2 parts pigments 1 part inhibitors5) 1.5 part
1) Commercial polyvinyl chloride, eg, impervable type for the preparation of dip moldings or for the preparation of polyvinyl chloride granules suitable for the manufacture of injection molded parts.

2) Plasticizer suitable for the preparation of flexible polyvinyl chloride mixtures, for example dioctyl phthalate, dioctyl adipate, butyl phthalate and benzyl phthalate, dibutyl phthalate> dinonyl phthalate, didecyl phthalate, tricresyl phosphate, polymeric plasticizers , etc.,
(3) Trimethylpropane trimethacrylate can be replaced by other substances containing one or more double bonds and crosslinkable by ionizing radiation, for example acrylates, methacrylates, allyl esters, among others, or mixtures of such substances. ,
4) Usual commercial substances, eg organic compounds containing Ba, Cd, Zn, Pb, Ca, K, Sn, etc. or non-metallic organic stabilizers.

 5) Mixtures of aralkyl phenols or derivatives of diphenylamine or other suitable anti-aging agents (in particular derivatives of hydroquinone, quinoline or phenol).

 Observation: Small amounts of such inhibitors may be added to the mixture to prevent aging from further hardening of the soft segments as a result of crosslinking. The crosslinking under the action of radiation is not inhibited to an appreciable extent by these additives.

Second stage of operation
The prefabricated bellows is placed in the device shown in the single figure of the accompanying drawing. The ends 1 of the bellows, to where the hard middle segment should begin, are fitted into the sleeves 2 and 3 in 2 mm thick tees which cover the inner face and the outer face. The protective sleeves may, however, be made of a material other than iron preferably metal; it is then necessary to adapt the wall thicknesser to the degree of protection sought and the dose of radiation applied.

Around the axis of rotation of the bellows, at mutual angles of 120, three sources of radiation have been arranged, for reasons of simplicity only one is represented at 4 in the figure. The radiation sources are disposed at a distance of 150 mm from the surface of the bellows. This rotates at regular speed around its axis of rotation,
When the surface of the bellows is exposed to a 3 MeV electron beam, a molded part whose ends are soft is obtained with the device described above at a surface dose of approximately 40 & 60 kJ / kg. and the middle part lasts. The ends have a Shore A hardness according to German standard DIN 53.505 of about 63 while the middle part has a Shore A hardness of about 98 (Shore D hardness about 60).

Example 2
Preparation of a polyurethane plate with two zones of different hardnesses.

First stage of operation
The 4 mm thick plate, for example, is prepared from an adduct containing radiation-curable additives, itself prepared at 1200.degree.

The following mixture was used for this purpose:
Mixture It polycaprolactone 100 parts 4,4'-diphenylmethane diisocyanate 60 parts
After 10 minutes of reaction at 120 ° C., the following substances were added: 1,4-butanediol 13.6 parts pentaerythritol triacrylate 16 parts
The mixture was cast in a mold heated to 1200 C.

After a few minutes, the reaction between the hydroxy groups and the isocyanate groups of the components progressed sufficiently for the product to solidify. To complete the formation of urethane, another 48 h is heated, for example, to 100.degree.

 A plate having a Shore A hardness of about 88 is obtained.

Second stage of operation
The polyurethane plate is partially covered with a protective plate 2 mm thick. Unlike the case of the previous example, irradiation is applied to only one side of the room.

 After exposure to electron beams at a surface dose of 40 to 60 kJ / kg, the polyurethane plate comprises in the unprotected areas a hard zone, Shore A hardness of about 95, and in the protected areas a larger area. soft, Shore hardness about 88.

Example 3
Preparation of a synthetic rubber plate having two zones of different hardnesses.

First stage of operation
A mixture is used with the following composition
Mixture III NBR rubber (28% ACN) 100 parts ptte ZnO 907e 5 parts carbon black 40 parts stearic acid 1.5 part trimethylolpropane trimethacrylate 10 parts TMTD 2.5 parts
CBS 2.5 parts sulfur 0.4
After mixing the material with the kneader or on a rolling mill, a plate about 2 mm thick, having a Shore hardness of about 67, is prepared at a pressure of 180.degree. C. over a period of 15 minutes.

Second stage of operation
The plate is partially covered, as indicated in Example 2, with a protection plate and then exposed to radiation. Depending on the geometrical shape of the mask, the plate then comprises a soft zone, Shore A hardness about 67, and a harder zone, Shore A hardness about 76.

Observations on the examples above.

 The compositions given in the examples may vary within wide limits. The nature and the proportion of the base polymer used can be varied and a mixture of compatible polymers can be used. The nature of the double bond-containing and radically crosslinkable monomer can also be varied and used in a broad concentration range depending on the compatibility with the base polymers.

The following table gives an overview of these possible variations with reference to examples of mixtures of polyvinyl chloride at various levels of plasticizer (dioctyl phthalate) and with various additions of a photocrosslinkable monomer (trimethylolpropane trimethacrylate). For the tests, a polyvinyl chloride in microbeads of the type empAtable was used.
K 70. The mixtures were stabilized with one part of Ba-Cd stabilizer powder per 100 parts of the total polyvinyl chloride + plasticizer. The specimens (about 2 mm thick) were cast by casting whenever possible. The gelation was carried out in the oven at 18,000 Pandrt we duration of 20 minutes.

For some mixtures (polyvinyl chloride content greater than 65%), the viscosity was too much. strong for casting or it was not possible to obtain shepherd, It was then plasticized on a rolling mill and converted into plates of 2 mu compression of 15 minutes at 1700C.

The table below shows the variation of hardness values
Shore mixtures unirradiated and irradiated depending on the composition. For non-irradiated mixtures, values of Shore A hardness and, for irradiated mixtures, hardness values were indicated.
Shore D.

<Tb>

<SEP> Material <SEP> no <SEP> irradiated <SEP> Material <SEP> irradiated
<tb><SEP><SEP><SEP> Accelerator <SEP>
<tb><SEP> trons, <SEP> 3.25 <SEP> MV, <SEP> dose
<tb> Parts <SEP> superficial <SEP> 50 <SEP> kJ / ki <SEP>
<tb> chloride <SEP> of <SEP> polyvinyl <SEP> 40 <SEP> 60 <SEP> 75 <SEP> 85 <SEP> 95 <SEP> 40 <SEP> 60 <SEP> 75 <SEP> 85 <SEP > 95
<tb> phthalate <SEP> of <SEP> dioctylate <SEP> 60 <SEP> 40 <SEP> 25 <SEP> 15 <SEP> 5 <SEP> 60 <SEP> 40 <SEP> 25 <SEP> 15 <SEP > 5
<tb> parts <SEP><SEP> of <SEP> trimetha- <SEP><SEP> Hardness <SEP> Shore <SEP> A <SEP> Hardness <SEP> Shore <SEP> D
<tb> crypt <SEP> from <SEP> trimethylol- <SEP><SEP> DIN <SEP> 53 <SEP> 505 <SEP> DIN <SEP> 53 <SEP> 505
<tb> propane
<tb><SEP> o <SEP> 44 <SEP> 76 <SEP> 98 <SEP> 99 <SEP> 100 <SEP> i44 <SEP><SEP> 35 <SEP> 51 <SEP> 64 <SEP> 78
<tb><SEP> 20 <SEP> 34 <SEP> 61 <SEP> 82 <SEP> 95 <SEP> 99 <SEP> 29 <SEP> 46 <SEP> 63 <SEP> 73 <SEP> 82
<tb><SEP> 40 <SEP> 27 <SEP> 51 <SEP> 70 <SEP> 85 <SEP> 99 <SEP> 37 <SEP> 56 <SEP> 73 <SEP> 80 <SEP> 85
<tb><SEP> 60 <SEP> 22 <SEP> 42 <SEP> 58 <SEP> 70 <SEP> 83 <SEP> 45 <SEP> 63 <SEP> 78 <SEP> 83 <SEP> 86
<tb><SEP> 90 <SEP> 16 <SEP> 33 <SEP> 46 <SEP> 57 <SEP> 67 <SEP> 58 <SEP> 70 <SEP> 82 <SEP> 84 <SEP> 86
<tb> * Shore A
Of course, apart from the constituents mentioned in the examples above, the mixtures may also contain usual constituents such as fillers, pigments, accelerators, anti-aging agents, lubricants, etc.

Claims (3)

1. Process for the preparation of a piece of polymeric material having, in wall, regions with different mechanical strengths in which the material used for shaping and then for reinforcement is subjected, this process being characterized in that the material is mixed with the material uniformly, 5 -70 ~ / 0 by weight of a crosslinking substance or polymerizing on exposure to ionizing radiation, then the shaping material is subjected to prior reinforcement by gelling and / or crosslinking, after which the material to ionizing radiation only in areas where it is desired to increase the mechanical strength. 2. Method according to claim 1, characterized in that, during exposure to radiation, areas of the surface are protected in which no increase in mechanical strength is sought by means of a mask of material absorbent.  at. Process according to claim 2, characterized in that, in the case of application to a hollow body, with irradiation on one or more faces, the inner face is covered by a corresponding mask in mirror image to the outer mask. 4. Method according to any one of claims 1 to 3, characterized in that is further mixed with the poly mother material of 0.05 to 6X, preferably from 0.1 to 2%, relative to the weight of the mixture an inhibitor, for example a mixture of phenyl phenols or a derivative of diphenylamine or other anti-aging agent, preferably taken from the group formed by the derivatives of hydroquinone, quinoline or phenol or a mixture of these substances.