FR2782666A1 - Surface treatment of partly-polymerized polyurethane mixture, occurs inside cylindrical, rotary casting- and coating mold into which e.g. elastomer powder is introduced, vastly enhancing subsequent bonding with other objects - Google Patents

Abstract

During polymerization, a powdered adhesive agent is applied to the surface of the mixture. An Independent claim is included for the object produced. Preferred features: A cylindrical mold (2) is used for rotary casting. The powder is applied to the internal cast surface (1a) in excess, covering all of the mixture surface, forming a superficial layer (5) as a result of rotation. Application takes place at a set temperature following initiation of the polymerization reaction, the delay being about 20%-50% of the total polymerization time, especially 1/3 of its duration.

Description

METHOD FOR SURFACE TREATMENT OF A RESIN PART

  THERMOSETTING AND PART THUS OBTAINED

  The present invention relates to a surface treatment of a part made of thermosetting resin, in particular polyurethane, in order to improve the adhesion properties of said part with any type of support. It also relates to the part in thermosetting resin, the surface of which has been thus treated and which exhibits these properties.

improved adhesion.

  It is more and more frequent to associate materials of different natures to form sets, often called composites. This association is made using an adhesive which makes it possible to assemble the two materials and to give their interface sufficient mechanical strength. This joining technique, by adhesion, is not suitable for all materials, some of which may have a surface condition which is not suitable for the use of an adhesive. According to the applicant, this is in particular the case of a thermosetting polyurethane elastomer marketed by the company BAYER.

under the name VULKOLLAN.

  The aim set by the applicant is to propose a method of surface treatment of a part in thermosetting resin, in particular but not exclusively of polyurethane elastomer, which

  improves the adhesion properties of said part with any support.

  This object is perfectly achieved by the process of the invention which uses a part made of thermosetting resin which is obtained, in known manner, by mixing a prepolymer and a crosslinking agent, by pouring said mixture into a mold and leaving

  developing the crosslinking reaction for a determined time T.

  Characteristically according to the invention, an agent is applied to the surface of the mixture, during the crosslinking reaction.

adhesion powder.

  The term “adhesion pulverulent agent” denotes a compound, in the form of a powder, on the one hand whose surface state is capable of promoting good adhesion and on the other hand which is compatible

with the pre-polymer.

  As a pulverulent adhesive agent, it may be rubber, natural or synthetic powder, silica powder or

silicone powder.

  According to a preferred embodiment, the mold in which the mixture is poured is a rotary cylindrical mold and an excess quantity of pulverulent adhesion agent is introduced onto the surface of the mixture, inside the mold. so that it spreads over the entire surface of the mixture during crosslinking a surface layer of powdery adhesion agent due to the rotation of the cylindrical mold. Preferably the application to the surface of the mixture of the pulverulent adhesion agent takes place after a predetermined time t after the

  start of the crosslinking reaction.

  In the case of a polyurethane thermosetting resin, for which the prepolymer is a mixture of polyol and of di-isocyanate, and in the case of rubber powder as a pulverulent adhesion agent, the predetermined time t is about 1/3 of the time

  of the crosslinking reaction.

  In general, it can be taken into account that this predetermined duration t must be between 20 and 50% of the time

  total of the crosslinking reaction.

  The molded part obtained by the aforementioned method has very good adhesion properties on the treated face, that is to say that on which the pulverulent adhesion agent has been applied, during the crosslinking reaction. There is no risk of delamination between the surface layer formed by the pulverulent adhesion agent and the thermosetting resin, insofar as bonding forces have developed between this agent and the resin during the reaction of crosslinking. It is moreover remarkable that the surface treatment can have other repercussions than the improvement of the adhesion properties, due to the surface transformation of its surface state. There is of course an aesthetic aspect, the treatment modifying the visual appearance of the treated surface. This treatment can also confer properties

  non-slip on the surface of the part thus treated.

  The present invention will be better understood on reading the

  description of a preferred embodiment of a part molded in

  thermosetting resin, having a modified surface state in accordance with the invention, illustrated by the appended drawing in which the single figure is a schematic sectional representation of a mold

  rotary cylinder in which the method of the invention is implemented.

  In the field of thermosetting resins, certain polyurethane elastomers exhibit very high mechanical performance, in particular the polyurethane elastomer marketed by the company BAYER under the name VULKOLLAN has a shore A hardness of between 63 and 98, resistance to traction from 150 to 380 kg / cm and exceptional behavior with regard to resistance to bending, compression, tearing, impact and abrasion. However, this material has a drawback insofar as it is very difficult to bond to another support using an adhesive. The treatment method of the invention aims to overcome this drawback, in particular for this polyurethane elastomer but more generally to modify the surface condition of any molded part.

in thermosetting resin.

  Typically, according to the general concept of this

  invention is applied to the surface of the mixture consisting of the pre-

  polymer and of the crosslinking agent, while the crosslinking reaction is taking place, a powdery adhesion agent, this agent possibly being in particular a rubber powder, a silica powder

or a silicone powder.

  In the example illustrated, we started with a prepolymer consisting of a mixture of polyol and di-isocyanate, in the presence of a crosslinking agent, for example a peroxide. This mixture 1 is introduced into a cylindrical mold 2, driven in rotation. This cylindrical mold has for example a diameter of the order of one meter and a rotation speed of the order of lOOt / min. The mixture introduced into the mold is, due to the rotation, plated on the inner surface 3 of said mold. When the crosslinking reaction is complete, the molded part obtained can be

  cut into angular portions to form resin plates.

  The crosslinking reaction takes place over a determined duration T,

  which depends on the type of components used (constituents of the pre-

  polymer and crosslinking agent) and operating conditions.

  According to the characteristic of the invention, a certain quantity of a powdery adhesion agent 4 is introduced inside the mold 2 while the mixture 1 is already in the mold 2 in rotation. This agent 4, in the powder state, is introduced into the lower part of the mold 2. Due to the rotation of the mold 2, the agent 4 conforms like a flange, also turning on itself, in the same sense that the mold 2, according to the arrow F. Thus there is a continuous contact between the internal face of the mixture 1 and the pulverulent agent 4. A surface layer of pulverulent agent is created on said internal face, the layer surface in which the prepolymer, during crosslinking, at least partially coats the particles of adhesion agent 4. During the crosslinking, chemical bonds develop between the thermosetting resin proper and the adhesion so that the surface layer 5 of agent 4 remains anchored in the face 1a and

  thus constitutes the new external face of the part thus treated.

  Of course, given the excess use of powdery agent 4, it is necessary to remove the excess powdery agent, not included in

  the resin, for example by brushing.

  The moment of introduction of the pulverulent agent into the mold is an important parameter for obtaining the desired effect. If the introduction occurs too early, the pulverulent agent can penetrate too deeply inside the mixture 1 and form inclusions in the finished part, capable of altering the mechanical properties of the part. If the introduction takes place too late, during the crosslinking reaction, there may be no bonding between the mixture and the pulverulent agent so that the treated side is not obtained under the desired conditions. . Preferably, it has been retained that the introduction of the pulverulent agent must take place at a predetermined time t which must be of the order of 20 to 50% and preferably approximately 1/3, of the total time T

of the crosslinking reaction.

  i 5 The treated face of the molded part thus produced makes it possible to obtain assembly, by adhesion, of said part with any other type

  support in very good hanging conditions.

  This face, by the pulverulent presentation of the agent which constitutes it, has a visually different appearance from the other parts of the part. It also has intrinsic properties, due to the adhesion agent. With particular regard to rubber powder, this

  treated side gives the piece non-slip properties.

Claims (7)

  1. Method for surface treatment of a part in thermosetting resin, which is obtained by mixing a prepolymer and a crosslinking agent, by pouring the mixture into a mold and allowing the crosslinking reaction to develop for a time T determined, characterized in that a pulverulent adhesion agent is applied to the surface of the mixture, during the crosslinking reaction 2. Method according to claim 1 characterized in that the pulverulent adhesion agent is natural rubber powder   or synthetic, silica powder or silicone powder.   3. Method according to one of claims 1 or 2 characterized in that   the mold in which the mixture (1) is poured being a rotary cylindrical mold (2), is introduced on the surface (la) of the mixture (1), inside the mold (2), / an excess quantity of pulverulent adhesion agent (4) so that a surface layer (5) of agent is distributed over the entire surface of the mixture during crosslinking   adhesion pulverulent due to the rotation of the cylindrical mold (2).   4. Method according to one of claims 1 to 3 characterized in that   the application to the surface (la) of the mixture (1) of the pulverulent adhesion agent (4) takes place after a predetermined time t after   start of the crosslinking reaction.   5. Method according to claim 4 characterized in that the predetermined duration t is between 20 and 50% of the total time of the crosslinking reaction.   6. Method according to claim 5 characterized in that as regards   a polyurethane thermosetting resin, for which the pre-   polymer is a mixture of polyol and di-isocyanate, and in the case of rubber powder as a pulverulent adhesion agent, the predetermined time t is approximately 1/3 of the total duration of the reaction of crosslinking.   7. Molded part of thermosetting resin, at least one face of which comprises a surface layer (5) comprising particles of a membership agent.